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Reproductive and natal homing of marine threespine sticklebacks (Gasterosteus aculeatus) Saimoto, Ron Shigeo 1993

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Reproductive and Natal HomingofMarine Threespine Sticklebacks (Gasterosteus aculeatus)byRON SHIGEO SAIMOTOB.Sc., The University of British Columbia, 1989A THESIS SUBMITTED IN PARTIAL FULFILLMENT OFTHE REQUIREMENTS FOR THE DEGREE OFMASTERS OF SCIENCEinTHE FACULTY OF GRADUATE STUDIES(Department of Zoology)We accept this thesis as conformingothereuiredTHE UNIVERS F B ITISH COLUMBIASeptember 1993© Ron Shigeo Saimoto, 1993In presenting this thesis in partial fulfilment of the requirements for an advanceddegree at the University of British Columbia, I agree that the Library shall make itfreely available for reference arid study. I further agree that permission for extensivecopying of this thesis for scholarly purposes may be granted by the head of mydepartment or by his or her representatives. It is understood that copying orpublication of this thesis for financial gain shall not be allowed without my writtenpermission.Department of ZooL.z yThe University of British ColumbiaVancouver, CanadaDate No1’. D [993DE.6 (2/88)UABSTRACTNatal and reproductive homing were investigated in marine and anadromouspopulations of threespine sticklebacks (Gasterosteus aculeatus). Three breeding sites within1 km2 of Pender Harbour, British Columbia, were examined. For the reproductive homingexperiment (displacement of adults from a breeding site), female sticklebacks from OysterLagoon, Salt Lagoon, and Paq Creek were marked and displaced (.15 - 1.0 km) to threerelease sites. These displaced females predominately returned to their original breeding sites,although there was some straying. The proportion of marked fish recaptured at their originalbreeding site ranged from 0.81 to 1.00. The anadromous population (Paq Creek) showed thestrongest tendency to return (0.99 - 1.00). Natal homing (return to birth site) was investigatedin the Oyster Lagoon population. Young of the year were marked on three different out-migrations (April 1991, August 1991, and April 1992): 0.85 %, 3.5% and 5.2 % respectively,were recaptured as adults during the 1992 breeding season at Oyster Lagoon. Relatively shortstays outside the lagoon (2 - 4 months), by juveniles that overwintered in Oyster Lagoon,resulted in strong natal homing and weak straying to adjacent breeding sites; however,straying to Salt Lagoon increased with longer stays outside the lagoon. This suggests aninverse relationship between the length of time spent out of the lagoon and the accuracy ofhoming. Straying to the anadromous breeding site (Paq Creek) remained low for all lengthsof stay in the sea (2 - 16 months). This maintained avoidance of Paq Creek suggests that themarine and anadromous populations may be genetically isolated. The level of strayingbetween Salt and Oyster lagoons probably is sufficient to prevent divergence between theseadjacent marine populations. Generally however, this study demonstrates both reproductiveand natal homing in threespine sticklebacks and, on a larger geographic scale, this natalillhoming may be sufficient to allow the evolution of inter-population heterogeneity amongmarine and anadromous populations.TABLE OF CONTENTSPage #ABSTRACT iiTABLE OF CONTENTS ivLIST OF TABLES viLIST OF FIGURES viiACKNOWLEDGEMENTS viiiGENERAL INTRODUCTION 1STUDY SITEPender Harbour 5Oyster Lagoon 7Salt Lagoon 7Paq Creek 8REPRODUCTWE HOMING EXPERIMENTIntroduction 10Materials and MethodsCollection for Mark and Release 11Marking Technique 11Controls 12Release Sites 12Release Procedure 13Monitoring of Returns 13Sampling at Oyster Lagoon 15Sampling at Salt Lagoon 15Sampling at Paq Creek 15Data Analysis 16Results 16ControlsEffects of Dye Injection 19Non-displacementRecaptures at Oyster Lagoon 19Recaptures at Salt Lagoon 20Recaptures at Paq Creek 20VREPRODUCTIVE HOMING EXPERIMENT (cont.)Monitoring of DisplacementsRecaptures at Oyster Lagoon 21Recaptures at Salt Lagoon 23Recaptures at Paq Creek 24Summary 24NATAL HOMING EXPERIMENTIntroduction 26Material and MethodsMark and Release 27Spine Clipping Control 27Monitoring of Returns 28Data Analysis 28Results . 29Effects of Spine Clipping 29Comparisons to Reproductive Homing 30Summary 32GENERAL DISCUSSION 35LITERATURE CITED 38APPENDICES 41viLIST OF TABLESTable 1. Recaptures (corrected for different numbers released) and “Proportions of homers”(the ratio of homers to combined strayers) at each breeding site.page 22Table 2. Number of marked Oyster Lagoon fish recaptured in Oyster Lagoon, Salt Lagoon,and Paq Creek during spring/summer 1992 (for detail see Appendices V, VI, and VII).Recaptures from release site “A” of the Reproductive Homing Experiment (seeReproductive Homing, page 14) are included as comparative ratios of recapture.page 30viiLIST OF FIGURESFigure 1. Map of Pender Harbour, British Columbia. Included are the 4 known breedingsites for marine or anadromous threespine sticklebacks; Paq Creek, Oyster Lagoon,Salt Lagoon, and Gerrans Bay.page6Figure 2. Release sites “A”, “B”, and “C” used for displacements during the reproductivehoming experiment.page 14Figure 3. Numbers of marked fish released at sites “A”, “B”, and “C” recaptured in OysterLagoon, Salt Lagoon, and Paq Creek. The numbers graphed are not corrected.page 17viiiAcknowledgementsThis project was conducted in coordination with Regina Saimoto’s work on the lifehistory of marine threespine stickleback. It was Regina’s useful preliminary evidence ofhoming that motivated me toward a more complete study of this interesting strategy. Alsospecial thanks to J.D. McPhail for financial support, his introduction to Gasterosteusaculeatus, and his editorial comments on my thesis. Max Blouw gave useful suggestions onmy initial proposal and field work. Cohn Brauner also gave useful comments on the finaldraft. The people in Pender Harbour were both friendly and helpful; in particular the Patons(Richard, Gail, Julie, Shannon, and Ginger), the Chathams (Roy-boy, Linda, and Boo-Boo),the Phillips (Ray, Doris, Glen and Sandra), Mild and Terry. And in the long tedious daysof marking and releasing fish, it was SUPER-DAVE Ghan, and my wife that made theincredible total numbers possible.1GENERAL INTRODUCTIONEarlier studies of the threespine stickleback (Gasrerosteus acuteatus) document theremarkable array of allopatric, parapatric, and sympatric forms that exist within this speciescomplex (Hagen 1967; McPhail 1969, 1984, 1992, 1993; Moodie & Reimchen 1976; McPhail& Hay 1983; Bentzen & McPhail 1984; Ridgeway & McPhail 1984; Reimchen et at. 1985,Blouw & Hagen 1990; Schluter & McPhail 1992; Reimchen 1992). This diversity isespecially evident in British Columbia, where research has focused on divergent stream andlake populations. Many of the morphological differences among freshwater populations, andbetween freshwater and anadromous populations, have a genetic basis and directly influenceforaging efficiency or defence from predators (McPhail 1969; Mooclie 1970; Wootton 1976;Reimchen 1983, 1988, 1990; Bentzen & McPhail 1984; Taylor & McPhail 1986).Consequently, they are viewed as adaptations to local selection regimes. Typically, there aredifferences among populations in lateral plates, spine lengths, pectoral fin shape, body shape,mouth width, gill raker number, gill raker lengths, and colouration. In addition, somepopulations show variability in life history traits such as age at maturity, breeding behaviours,mate choice, breeding site selection, and durations of breeding periods (e.g. McPhail & Hay1983; Bell 1984; Mon 1984; Saimoto 1993). Also, in B.C., allozyme surveys have revealedgenetic differences among freshwater populations, and between freshwater and anadromouspopulations (Withler & McPhail 1985). Since most of coastal B.C. was glaciated during thelast (Fraser) glaciation, most freshwater populations must be post-glacial colonists, and oneobvious source of colonists was the sea. Thus, the divergence between freshwater andanadromous, or marine, sticklebacks and the divergences among freshwater populations maybe relatively recent. The evolutionary processes involved in these rapid divergences areGENERAL INTRODUCTION 2poorly understood, but, if marine or anadromous sticklebacks are ancestral to freshwaterpopulations, then an examination of their biology is fundamental to understanding themechanisms that give rise to the diverse freshwater populations now found in coastal BritishColumbia.Generally, anadromous sticklebacks are thought to be the primary ancestor of residentstream and lake populations; however, this hypothesis overlooks the existence of purelymarine populations of G. aculeatus. Indeed it is possible that marine and estuarinepopulations, as well as anadromous populations, contributed to the post-glacial recolonizationof freshwaters along the B.C. coast (McPhail 1993). This introduces the added complexityof a heterogeneous origin of today’s freshwater populations and necessitates a closerexamination of both marine and anadromous populations. Questions that need answers are1) what is the genetic relationship between marine and anadromous sticklebacks, and 2) arethese forms genetically homogeneous, or do they exhibit deme structure?During the last glaciation, most freshwater populations in British Columbia probablywere destroyed or forced south into glacial refugia. On the west coast of North America, theprimary freshwater refugia of the last glaciation were in Washington, Oregon, California andAlaska (Bell 1976); however, there is growing evidence for central coast refuge that includednorthern Vancouver Island and Graham Island (McPhail 1993). Certainly some of themorphologically most extreme sticklebacks are found in these areas (Moodie & Reimchen1976; Lavin & McPhail 1993); however, because of their relatively small populations,freshwater residency, and low dispersal, freshwater populations that survived in isolatedrefugia, probably did not contribute much to the post-glacial expansion of the species.Glaciation may not have effected the anadromous populations as drastically as itGENERAL INTRODUCTION 3effected freshwater populations. They simply may have shifted south to unglaciated streams.If so, whatever pre-glacial diversity that existed among anadromous populations probably waslost to inter-breeding during this shift. Alternatively, they may have fused with marinepopulations, or simply gone extinct. Some populations south of glaciation may havemaintained their distinctive genetic nature and their divergence from marine populations.This would have produced at least two potential post-glacial colonizers. Genetically differentanadromous populations may have dispersed up the coastline into newly forming streams andrivers as glaciers retreated. Once established in new streams, natal homing may also haveevolved in much the way it is thought to evolve in salmonids (i.e. on average, individuals thatreturn to the site where they were successfully reared are more successful reproductively thanindividuals that stray). Once natal homing evolves, local selection will fine tune thepopulation to local conditions and this should lead to inter-population divergence.Little attention has been paid to the potential effects of glaciation on marinepopulations of threespine sticklebacks. Marine breeding sites probably shifted in responseto fluctuations in sea level; however, if marine populations show natal homing they areunlikely to be genetically homogeneous. Study of the mechanisms of population isolationwill assist in defining the role of ancestry behind the existing diversity of threespinesticklebacks.Currently, there is no information on relationships among anadromous and marinepopulations. However, a recent life history study of a marine population along the B.C.coast, suggested natal homing. Saimoto (1993) found that many marked marine sticklebacksreturned to their place of birth, but adjacent breeding sites were not monitored for straying.The purpose of my study is to investigate both natal (return to place of birth) andGENERAL INTRODUCTION 4reproductive (return of displaced adults) homing by threespine sticklebacks. Three adjacentsites (Oyster Lagoon, Salt Lagoon, and Paq Creek) were studied. The two lagoons are marinesites and the creek is a freshwater site used by anadromous sticklebacks. The inclusion ofan anadromous breeding site may be questioned because of possible differences in salinitytolerance/preference in marine and anadromous populations; however, Soin et al. (1984) andmy own preliminary studies showed that both marine and anadromous sticidebacks can spawnin variable salinities (0 - 32 ppt). Thus, the inclusion of a site used by anadromoussticklebacks allows comparisons of the levels of homing in both marine and anadromouspopulations, and the degrees of straying between the two breeding habitats.5STUDY SITEPender HarbourFender Harbour (49° 32’ N; 124° 02’ W) is a small mainland inlet off MalaspinaStrait, British Columbia, Canada (Fig. 1). The harbour reaches approximately 4 km inlandand two narrow channels link it to the strait. Three small creeks drain into the harbour, butestuarine habitats are limited by daiiy inflow of high salinity water from the strait. Tidelevels in the harbour fluctuate 1 - 4 m bi-daily and maintain a relatively stable marine salinity(28 - 32 ppt). Pender Harbour supports a diverse community made up of marine plant,invertebrate and fish species.Through early spring into late summer, migrating adult sticklebacks enter PenderHarbour from the strait and select breeding sites. There are three lagoons in the harbour, ofwhich two (Oyster and Salt lagoons) are threespine stickleback breeding sites. The thirdlagoon is a small, shallow tidal pool that lacks the physical characteristics typical of moststickleback breeding sites: protective cover, nest material, temperature stability, and foodavailability. This site is not used by sticklebacks. Of the three creeks that drain into FenderHarbour, only Faq Creek appears to support an anadromous population. A fourth breedingsite (Gerrans Bay) lies approximately 1 km west of the three study sites, but was not includedbecause it has a short, delayed breeding season, low stickleback density, and less definedboundaries from the open harbour. Oyster Lagoon, Salt Lagoon, and Faq Creek constitutemy study sites.Faq Creek, Salt Lagoon, and Oyster Lagoon were chosen primarily because of theirdiscrete, confined breeding sites (Fig. 1). The areas between these 3 sites were examined toconfirm their complete isolation (i.e. no breeding sticklebacks in the intervening areas). Therelatively small area containing these three isolated breeding sites (< 1 km2) permitsSTUDY SITE 6Figure 1. Map of Pender Harbour, British Columbia. Included are the four known breedingsites for marine or anadromous threespine sticklebacks; Paq Creek, Oyster Lagoon, SaltLagoon, and Gerrans Bay.PenderHarbourMalaspinaStraitSTUDY SITE 7evaluation of population dispersal.Oyster LagoonOyster Lagoon is a small, shallow lagoon. Salinity ranges from 20 ppt in winter to32 ppt in summer, with rainfall often forming a thin freshwater layer on the surface. Thesurface area of the lagoon is 1.8 ha and the maximum depth is 3 m. The lagoon is connectedto the harbour at 4.0 m tides, and tidal in-flow occurs at tide levels greater than 4.2 m (thehighest tide of each day fluctuates from 4.0 - 4.9 m). This limited in-flow allows terrestrialgrass to expand to the low tide level of the lagoon and provides protective cover foroverwintering young and early nesting adults. At the peak of the 1992 breeding season, halfof the lagoon bottom was covered with thick beds of eel grass (Zostera sp.) and thickfilamentous algal mats. This aquatic vegetation provided seasonal protective cover from birdsand perhaps nest protection against attacks by other sticklebacks.The majority of young that hatched in 1991, left the lagoon that same summer;however, many young also overwintered in the lagoon and did not migrate out until the startof the adult in-migration the following breeding season. In 1992, sticklebacks began enteringOyster Lagoon in late February. The first young of 1992 were observed in late April, anda few males were still nesting in September. The peak of the breeding season was in Juneand July, and the rapid decrease of nesting males in August appeared to coincide with highwater temperatures (>26 °C) on sunny days prior to flooding (for details see Saimoto, 1993).Salt LagoonSalt Lagoon differs from Oyster Lagoon, in that it is slightly larger (surface area = 4ha) and deeper at low tide (max. depth 6 m). The salinity remains more stable (25 - 32 ppt)because of greater daily flushing at lower tide levels (>3.0 m). This lagoon’s shoreline alsoSTUDY SITE 8differs from Oyster Lagoon. The bi-daily tidal fluctuations of 1 - 2 m prevents terrestrialgrassy shorelines from remaining in contact with the water. This lack of shoreline cover maybe what prevents overwintering of young in Salt Lagoon. The two main entrance channelsare also wider, and not as long as the one entrance into Oyster Lagoon. In 1992, thebreeding season at Salt Lagoon was delayed by 1 - 2 months in comparison to OysterLagoon. Perhaps, the delay is because of a slower rise in temperature due to the morefrequent and longer periods of flooding, larger area, and greater depth in Salt Lagoon.Apparently, this active tidal flooding also results in more frequent in- and out-migrations ofsticklebacks throughout the entire breeding season. Another recognizable, and possiblyinfluential difference between Salt and Oyster lagoons was the higher density of predators(great blue herons, mergansers, kingfishers and cutthroat trouts) at Salt Lagoon.Paq CreekPaq Creek is obviously different from the lagoons. The creek is less than 5 m widewith a mean depth of 30 - 50 cm, and only the short, lower stretch (< 100 m) with one small(15 m x 15 m), shallow (< 1 m) pool is suitable for breeding. This stretch of creek is lowgradient and is partially clogged and slowed by sedges (Carex and Scirpus sp.) and cattails(Typha larifolia). Up-steam migration is blocked by a culvert with an approximately 60 cmdrop to the lower stream. At its mouth, the creek spreads Out over gravel and is too shallowto allow in-migration until high tides (> 4.0 m) create access to the first, deepest pool.Although this lowest pool is slightly brackish water for short periods after flooding, salinitytests show the nesting areas to be either always, or predominantly in fresh water. In 1992,in-migration to Paq Creek started earlier and ended earlier (mid July) than at Oyster Lagoon.Other differences between Paq Creek and the lagoons were the presence of predatory crayfishSTUDY SiTE 9in the creek and the rarity of the isopod gill parasite (Rocinella angustara) that is commonlyfound in both Oyster and Salt lagoons. Most importantly, the Paq Creek population isanadromous, and thus provides an opportunity for the evaluation of inter-change betweenmarine and anadromous populations of threespine sticklebacks.10REPRODUCTIVE HOMING EXPERIMENTIntroductionIn this study, reproductive homing is defined as the propensity of adults to return toa breeding site after they are displaced from that site. Several authors (Hagen 1967; Kynard1978; Paepke 1983) have suggested that sticidebacks home, but there is little quantitativeevidence to support this suggestion. The primary purpose of my reproductive homingexperiment was to determine if both marine and anadromous populations of threespinesticidebacks choose specific breeding sites. The experiment involved displacement of markedsticklebacks from three different initial breeding sites (Oyster Lagoon, Salt Lagoon, and PaqCreek) and release at three locations in Pender Harbour (release sites “A”, “B”, and “C”;Fig.2, page 14). Returns were then monitored at the three breeding sites for the remainder of thebreeding season (14 weeks). If the fish disproportionately return to their initial breeding site,this indicates that they distinguish among breeding sites and have a preference for the sitethey first chose.The migratory nature of these populations prevents accurate estimates of populationsize, and this increases the difficulty of monitoring and comparing total numbers ofindividuals in each population that home or stray. Consequently, the experiment uses relativenumbers of marked individuals from the three displaced populations recaptured at their initialbreeding sites as an indication of the strength of the propensity to home. This experimentalso gives an estimate of the ratio of homers to strayers for each population. This estimateis important because only the out-migrating young from the Oyster Lagoon population weremarked to test natal homing (return to place of birth). For the Oyster Lagoon population, theratio of “reproductive homers to reproductive strayers” is comparable to recapture ratios oft’natal homers to natal strayers” (Natal Homing Exp., page 26).REPRODUCTIVE HOMING 11Materials and MethodsCollection for Mark and ReleaseThe experiment began when the in-migration of fish to the three breeding sitesproduced enough fish for a Consistent number of releases over 10 days (May 13th -22, 1992).Capture at Oyster Lagoon was by a funnel fence and a large plexiglass minnow trap (100 cmx 90 cm x 60 cm) set in the entrance channel. Salt Lagoon and Paq Creek fish were capturedwith 20 minnow traps (7 mm mesh) set in the lagoon near its entrance channels and 20minnow traps set in the lower pool of Paq Creek. To avoid the complications of samplingterritorial males, only females were used in the experiment. Fish for mark and release weresorted at the location of capture and males were released; sex was identified by visualrecognition of sexual colouration of males (red throat and/or blue eyes), head size (maleshave longer heads, and larger mouths), and sexual maturity of females (gravid condition).Each day’s collections were stored in 80 litre tanks with no more than 100 fish/tank.Fish from different breeding sites were held in separate tanks. All holding tanks containedwater collected from outside the harbour and were maintained at constant salinity (28 ppt)and temperature (8 - 10 °C). Fish used for mark and release were collected two days beforerelease and a portable air compressor was used to aerate water every 2-4 hours in the 24holding tanks. Fish were marked the day after collection and held overnight to monitormortality due to stress, dye injection, or anesthesia. At loading for transport to release sites,sex was re-checked, and the exact numbers of different individuals were recorded.Marking TechniqueThree different acrylic dyes (red, orange, and pink) were used to differentiate betweenthe three populations. These concentrated dyes were diluted 1:1 with mammalian Ringer’sREPRODUCTIVE HOMING 12solution, and manually injected using 28 gauge needles. Tricainmethansulfonate (MS 222)in sea water was used to anesthetize fish before injections and rapid aeration of 2 litrecontainers assisted recovery. For an additional distinction between the three release sites, thedyes were injected under different lateral plates in each population. Fish were injected underanterior plates on the right side for release site “A”, under posterior plates on the right sidefor release site “B”, and under anterior plates on the left side for release site “C”.ControlsAn additional acrylic dye (blue) was used for control releases during the three daysfollowing the completion of the displacement releases (May 30th June 1st)• This involvedmark and release, but no displacement, of the three populations at their initial breeding sites.For these controls, Oyster Lagoon fish were injected under the right anterior plates, SaltLagoon fish were dye injected under the right posterior plates, and Paq Creek fish weremarked under the left anterior plates. This control was used to estimate the effects ofdisplacement and the efficiency of trapping at the three breeding sites, and it also allowed arough estimation of the time females stay on a ‘breeding site.The effects on survival of different colour dyes and different locations of injectionwere monitored for seven days’ after marking. Separate tanks with ten female fish for eachof the four different colour dyes and three different places of injection were monitored. Thisrepresented three replicates of tests for mortalities due to different coloured dyes, and fourreplicates of tests for mortalities due to different locations of injection.Release SitesThe displacement experiment included three release sites (“A”, “B”, and “C”). Releasesite “A” was within 150 m of the entrance to Oyster Lagoon; release site “B” was positionedREPRODUCTIVE HOMING 13between the entrances to Salt Lagoon and Paq Creek (approximately 150 m from bothbreeding sites); while release site “C” was a control release site at an equal distance (500 m)from site “A” as site “B” but in the opposite shoreline direction (Fig. 2). Site “C” wasincluded to test the effects of the relative positioning of sites “A” and “B”, since there is anarrow, shallow pass between sites “A” and “B” but no constriction between Sites “A” and“C” (Fig. 2).Release ProcedureDuring afternoon high tides, the three populations were released concurrently on tenconsecutive days (May 13th - 22nd, 1992). Individuals from the three populations werereleased at the same site but, to help avoid inter-population schooling, the releases of differentpopulations were separated by 5 minute intervals. For both Oyster Lagoon and Salt Lagoonpopulations, I attempted to include 100 females each day at each site. Since fewer fish wereavailable from Paq Creek, approximately 50 females were released each day at each site(Appendix I).Monitoring of ReturnsSampling for reproductive homers and strayers was done at the Oyster Lagoon, SaltLagoon, and Paq Creek breeding sites. The goal was to recapture at least 100 marked fishfrom each population. This would allow reasonable comparisons of recaptures of homers tostrayers. Because of geographic differences between release sites, and habitat differences anddifferential access among breeding sites, different (most efficient) methods of trapping wereused at each site. Initially, recaptures were preserved in 10 % formalin, but later, newrecaptures were recorded, re-marked with different spine clips, and re-released. Re-recapturesof fish with both dye marks and clipped spines were recorded separately and were not>4cd (1 (I) CD I-I Cr2 CD CD C) CDREPRODUCWE HOMING 15included in total recapture Counts.Sampling at Oyster LagoonA funnel fence with a large plexiglass minnow trap (100 cm x 90 cm x 60 cm) setin the entrance channel was used to collect fish during, and after, marking in Oyster Lagoon.The trap was emptied daily and fish were sexed, counted and checked for dye markings(Appendix II). This trap was used rather than setting minnow traps because it caught ahigher proportion of new in-migrating fish, and allowed for less time consuming collectionand sorting. The mark for re-release after recapture was the clipping of both the first dorsaland right pelvic spines.Sampling at Salt LagoonDuring the 10 days of marking, and for the following two weeks, 20 standard meshminnow traps were set in Salt Lagoon near the entrance channels. The traps were checkedeach day for marked fish. Later, to increase the sample sizes of collections, 20 additionalminnow traps were distributed along the lagoon shoreline. Daily sampling continued to theend of June and then was reduced to alternate days until completion of this experiment(Appendix ifi). The fish were sexed, counted and released, except for a small number ofrecaptures that were preserved. Re-released recaptures were marked with the spine clips ofboth right and left pelvic spines.Sampling at Paq CreekTwenty minnow traps were used for all collections at Paq Creek. All fish were sexed,counted, and checked for dye markings (Appendix IV). Recaptures were preserved until>100 fish had been obtained from each of the 3 release sites. Recaptures were then re-markedby spine clip of the first dorsal spine and re-released. Paq Creek was sampled daily fromREPRODUCTIVE HOMING 16May 14th to June 7th, and then less frequently because of efficient trapping and an early endto the breeding season (Appendix IV).Data AnalysisAnalysis required accounting for different numbers of fish that were marked anddisplaced from different sites and to different release sites. Since the numbers of fishreleased from each site were different, the number of recaptures were corrected as follows:Corrected Values = (51 1/# released) x # of recaptures,where 511 is the lowest number of a particular population released from any site. Thus, thesecorrected values (CV) provide a conservative, relative comparison of recaptures of displacedfish from each breeding site. Log likelihood ratio analysis (G test) was used to test for equalreturns of all populations. Yates correction (G test) was used for the more specificcomparisons of two populations.ResultsReturns to the breeding sites were monitored through the entire 1992 breeding season.After displacement, most sticklebacks returned to their initial breeding site within four weeks;however, small numbers continued to return throughout the entire breeding season(Appendices II,uI,IV). The data (Fig. 3) show a marked tendancy for displaced sticklebacksto return to their initial breeding sites. This implies that both marine and anadromoussticklebacks can distinguish among breeding sites and, once they have chosen a site, theyshow a strong preference for this initial site. The following sections present a detailedanalysis of these recaptures and compares the numbers of homers and strayers relative to bothrelease sites and breeding sites.REPRODUCTIVE HOMING 17Figure 3. Numbers of marked fish released at sites “A”, “B”, and “C” recaptured in OysterLagoon, Salt Lagoon and Paq Creek. The numbers graphed are not corrected.Displacements to Release Site “A” 18I I Release Site “B”Release Site “C”300 288 Recaptures268at250 Oyster LagoonC!)200150_______—VA I100500OYSTER SALT PAQ50Recaptures42at40— Salt Lagoon269653OYSTER SALT PAQ250 Recapturesat200 Faq Creek163150 12810050 ii2 01 0010OYSTER SALT FAQINITIAL BREEDING SITEREPRODUCTIVE HOMING 19ControlsEffects of Dye InjectionComparisons of mortalities due to injection indicated no significant differences amongeither colors or locations of injection. Mortality was low in all 12 control tanks: five deathsin the 120 marked fish after one week.Non-DisplacementRECAPTURES AT OYSTER LAGOONOver three days, 1 013 Oyster Lagoon females were caught, marked (blue, rightanterior lateral plate) and released back into the lagoon. The day after the total release (June2’), 10 minnow traps in Oyster Lagoon caught 376 female sticklebacks, of which 37 werenon-displaced recaptures. In addition, six reproductive homers from displacements wererecaptured and preserved. These reproductive homers were missed in my in-migrationmonitoring, and suggest that a significant number of reproductive homers may have by-pastthe in-migration funnel fence trap. Consequently, the numbers of recaptures at the OysterLagoon funnel fence are a conservative estimate of total returns. Further trapping in thelagoon showed a daily decline in the number of non-displaced recaptures. Following thisrelease, recaptures at the funnel fence showed a slow but steady in-migration of non-displacedfish for 3 - 4 weeks. This return suggests that many of the marked and non-displaced fishinitially may have left the lagoon but then returned after only a short absence.Non-displacement controls also were run at Salt Lagoon and Paq Creek. Over theentire breeding season only one Salt Lagoon, and no Paq Creek, non-displaced strayers wererecaptured at the Oyster Lagoon in-migration fence. This low straying indicates that once aninitial breeding site choice is made, it is maintained for the entire breeding season.REPRODUCTIVE HOMING 20RECAPTURES AT SALT LAGOONOver three days, 1 277 Salt Lagoon females were caught, marked (blue, right posteriorlateral plate) and released back into the lagoon. The day after the complete release (June 2j,minnow traps caught 607 females, of which two were non-displaced recaptures (releasçd) andone was a reproductive homer (preserved). On the next day (June 3rd), 570 females weresampled of which none were marked non-displaced individuals, and two were markeddisplaced homers (preserved). Again on June 4th, 431 females were sampled, three of whichwere marked non-displaced fish (released) and none were displaced homers. These resultsemphasize the difficulty of trapping in Salt Lagoon, and account for the low number ofrecaptures in the reproductive homing experiment from this lagoon. After 10 days (June 2’ -1 1th), the total recaptures consisted of 15 non-displaced controls (CV = 8) and 20reproductive homers from the three displacements (CV’s “A” = 6, “B” = 7, and “C” = 3).The four of these corrected values are not significantly different (G = 5.131, p > 0.10). Thissuggests that trapping difficulties rather than high dispersal after displacement caused the lownumbers of recaptures at Salt Lagoon.RECAPTURES AT PAQ CREEKOver two days, 401 Paq Creek females were caught, marked (blue, left anterior lateralplate) and released back into the creek. On the first day after releases (June l’, 156 femaleswere caught, 85 of which were non-displaced recaptures (released), and 18 were reproductivehomers (preserved). The next day’s sample (June 2”) consisted of 292 females, 35 of whichwere non-displaced recaptures (released) and 35 were reproductive homers (preserved). OnJune 3, 310 females were sampled, 20 of which were non-displaced recaptures (released),and 42 were reproductive homers (preserved). The recapture rates indicate trapping in PaqREPRODUCTIVE HOMING 21Creek is an efficient collecting technique, but the rapid decline in recaptures of the non-displaced fish suggest either a relatively rapid turnover of the creek’s spawners or thatmarked fish leave the system. Thus, the actual numbers of reproductive homers recapturedat Paq Creek represent conservative estimates of total returns.Monitoring of DisplacementsMonitoring returns to the three breeding sites suggest that more fish home than stray;regardless to which of the three release sites they were displaced. Corrected values ofrecaptures from the different populations and different release sites are summarized in Table1. This section presents detailed comparisons of results, with tests for differences betweendisplacements, and for differences in the proportions of homers or strayers.Recaptures in Oyster LagoonOf the fish originating in Oyster Lagoon, 26.1 % were recaptured at Oyster Lagoon(release sites : “A” = 27.8 %, “B” = 22.5 %, and “C” = 27.3 %). Strays from the otherdisplaced populations (Salt Lagoon and Paq Creek) represented only 1.3 % and 1.5 %,respectively, of their total numbers marked and released. For all three populations, releasesite “B” produces fewer returns to Oyster Lagoon than release sites “A” and “C”. For PaqCreek strayers there is a significant difference of returns from different release sites (“A” =14, “B” = 1, and “C” = 8; G = 13.508, p <0.005). Curiously, however, recaptures of OysterLagoon homers (CVs: “A” = 142, “B” = 115, and “C” = 140) and Salt Lagoon strayers toOyster Lagoon (CVs : “A” = 10, “B” = 2, and “C” = 7) were not significantly differentamong different release sites (G = 3.522, p > 0.10, and 0 = 5.946, p > 0.05). Despite thislack of statistical significance, the corrected values were in the direction of lower returnsfrom release site “B”. Perhaps, reproductive homing to Oyster Lagoon from release site “B”REPRODUCTIVE HOMING 22Displacement to RELEASE SITE “A”Initial Breeding Site: ProportionofOyster Lagoon Salt Lagoon Paq Creek HomersRecaptured at:Oyster Lagoon 142 10 14 0.86Salt Lagoon 5 21 0 0.81Paq Creek 1 0 128 0.99Displacement to RELEASE SITE “B”Initial Breeding Site: ProportionofOyster Lagoon Salt Lagoon Paq Creek HomersRecaptured at:Oyster Lagoon 115 2 1 0.97Salt Lagoon 3 29 3 0.83Paq Creek 0 0 232 1.00Displacement to RELEASE SITE “C”Initial Breeding Site: ProportionofOyster Lagoon Salt Lagoon Paq Creek HomersRecaptured atOyster Lagoon 140 7 8 0.90Salt Lagoon 3 19 0 0.86Paq Creek 1 1 163 0.99Table 1. Recaptures (corrected for different numbers released) and “Proportion ofhomers” (the ratio of homers to combined strayers) at each breeding site.REPRODUCTIVE HOMING 23was partially influenced by the narrow channel at Canoe Pass and easier access to an alternatebreeding site (eg. Salt Lagoon, Gerrans Bay, or Paq Creek).The few recaptures of strayers into Oyster Lagoon makes a statistical comparison ofthe propensity of marine and anadromous populations to stray difficult. There is no cleardifference between the number of recaptures of Salt Lagoon and Paq Creek strayers in OysterLagoon. This implies that straying rates of nearby anadromous and marine populations (ie.Salt Lagoon and Paq Creek) to this marine breeding site are not different. Still, thepredominance of homers over strayers from all three release sites clearly demonstratesreproductive homing by the Oyster Lagoon population.Recaptures in Salt LagoonOf the fish originating in Salt Lagoon, 4.5 % were recaptured in Salt Lagoon (releasesites : “A” = 4.1 %. “B” = 5.6 %, and “C” = 3.8 %). Strays from the other displacedpopulations (Oyster Lagoon and Paq Creek) represented only 0.7 % and 0.2 %, respectively,of their total numbers marked and released. Potentially, either Canoe Pass or proximity toOyster Lagoon could inhibit the return of Salt Lagoon homers from release sites “A” and “C”(CVs : “A” = 21, “B” = 29, and “C” = 19); however, the small numbers recaptured requiresthat such comparisons be treated with caution (G = 2.364, p > 0.25).For the same reason (small sample size), straying rates of the marine (Oyster Lagoon)and anadromous (Paq Creek) populations were difficult to compare. As in Oyster Lagoon,there are no obvious differences between the numbers of recaptures of Oyster Lagoon andPaq Creek fish in Salt Lagoon. Although the numbers are small, it is clear for all threerelease sites that more displaced Salt Lagoon fish return to Salt Lagoon than do strayers fromthe Oyster Lagoon and Paq Creek populations.REPRODUCTIVE HOMING 24Recaptures in Paq CreekOf the displaced fish originating in Paq Creek, 34.3 % were recaptured in Paq Creek(release site : “A” = 25.0 %, “B” = 45.5 %, and “C” = 31.9 %). Strays from the otherdisplaced populations (Oyster Lagoon and Salt Lagoon) represented only 0.1 % and 0.05 %,respectively, of their total numbers marked and released. Again, either Canoe Pass orproximity to Oyster Lagoon could inhibit returns to Paq Creek from release sites “A” and“C”. Comparison of homers from the different displacement sites (CVs : “A” = 128, “B” =232, and “C” 184) indicate a significant difference among sites (G = 30.56, p <0.001).Recaptures from release site “B” were higher than from release sites “A” and “C”. Releasesite “A” also produced fewer returns than release site “C”. This suggests that a release site’sproximity to an alternate breeding site may influence the number of fish that home.Despite the efficient recapture in Paq Creek, there were low numbers of strayersrecaptured (3 from Oyster Lagoon, 1 from. Salt Lagoon). Apparently straying to thisanadromous (freshwater) breeding site is lower than straying to lagoons.SummaryThe primary goal of this experiment was to examine reproductive homing bythreespine sticklebacks. Since the relationship between straying and gene flow is unknown,the actual number of strays is not critical for this study. The null hypothesis was that thenumber of recaptures for each population would be equal at each breeding site. This wouldindicate an equal distribution of returns regardless of initial breeding site. The nullhypothesis was rejected at all breeding sites. The predominance of homers among recapturesat each breeding site indicates the presence of reproductive homing in all three populationsREPRODUCTIVE HOMING 25used in this study. Clearly, sticklebacks show a strong propensity to return to an initialbreeding site even after displacements of up to 1 km. Some individuals did not return forup to three months after release, and this is comparable to the duration of natal migrationtimes (see Natal Homing, page 26). This prolonged delay in reproductive homing suggeststhat threespine sticklebacks can retain a “memory” of their breeding site for at least threemonths.There was some variation in proportion of homers at different breeding sites and thepropensity to home from different release sites. Proportions of homers ranged from 0.81 atSalt Lagoon from release site “A”, to 1.00 at Paq Creek from release site “B” (Table 1, page22). Possible influences on returns from different release sites involve variation ingeography, intensity of predation through different migratory routes, degree of disorientation,presence of alternative breeding Sites, and habitat identification. Apparently, these factors dosignificantly influence both homing success and straying; nevertheless, sticklebacks clearlyshow reproductive homing. The results from this experiment raise the possibility that theymay also show natal homing. If so, this could have profound effects on levels of gene flowand deme structure in marine and anadromous sticklebacks.26NATAL HOMING EXPERIMENTIntroductionThis section investigates natal homing in the Oyster Lagoon population of threespinesticklebacks (Gasterosteus aculeatus). Natal homing refers to the return of sexually matureadults from the ocean to their site of birth. There is no direct evidence for natal homing bythreespine sticklebacks; however, the evidence for reproductive homing given in thepreceding chapter suggests the possibility of natal homing. If natal homing occurs in thisspecies it could result in genetic differences among populations from different breeding sites.The following experiment attempts to determine whether natal homing occurs in marinesticklebacks and, if so, to estimate the precision of natal homing. The latter goal involvesestimating the amount of straying. Presumably, there is some relationship between theamount of straying and the probability that a population will diverge.Coincident with the reproductive homing experiment (Reproductive Homing, page 10),the Oyster Lagoon population was monitored for natal returns into the Oyster Lagoon, andstraying into the Salt Lagoon and Paq Creek breeding sites. In the 1992 breeding season, Imonitored returns of fish that were marked at 3 different times (April 1991, August 1991, andApril 1992) during their migration out of Oyster Lagoon. The April and August markingswere necessary because some young of the year leave in their first summer (summermigrators) while other individuals overwinter in the lagoon and leave the next spring(overwinterers). Apparently, overwintering at a breeding site before migration is not commonamong marine or anadromous populations (pers. obs.) and, even in Oyster Lagoon, most ofthe young leave the lagoon during the summer or early fall of their birth year. In OysterLagoon, these overwintering migrators allowed a partial replication of natal homing.NATAL HOMING 27Materials and MethodsMark and ReleaseAs they migrated out of Oyster Lagoon, young of the year were collected at theentrance channel to Oyster Lagoon. This was accomplished by partially blocking themigration channel with a large funnel fence (10 mm mesh) and trapping out-migrators with2 small plexiglass minnow traps (30 cm x 30 cm x 60 cm). Daily catches were marked withspine clips and released on the other side of the fence. Different spines were clipped atdifferent release times (April 1991, August 1991 and April 1992). April 1991 migrators wereclipped on the second dorsal spine and August 1991 migrators were clipped on the rightpelvic spine. These out-migrators (April 1991 and August 1991) ranged in length from 20 -35 mm. Out-migrators in April 1992 ranged in standard length from 25 mm to 35 mm andwere clipped on the first dorsal spine. During the out-migrations, 100 - 1500 fish werereleased per day but were divided into groups of 50 - 100 fish; small groups were used toreduce the likelihood of individuals migrating back into the lagoon.Spine Clipping ControlsThe effect of spine clipping on survival of juvenile sticklebacks was tested, and therecognition of spine clips after winter growth was evaluated. A grab sample (variable sizes)of 61 migrating young were taken from Oyster Lagoon on August 3l, 1991 and raised inthe laboratory over the 199 1/92 winter. All fish were measured and their left pelvic spinesclipped on September 14th They were fed Tubifex and Anemia and their survival monitoreduntil March 18th, 1992. At this time, several individuals of both sexes began showing signsof sexual maturation. Standard lengths at times of death and at the end of monitoring wererecorded.NATAL HOMING 28Monitoring of ReturnsReturns to Oyster Lagoon and the two nearest alternative breeding sites (Salt Lagoonand Paq Creek; Fig. 1, page 6) were monitored at the same time as the reproductive homingexperiment. There was an additional sampling earlier in the season (April and May;Appendices V, VI, and VII) that used the same trapping techniques (Monitoring of Returns,page 13). All recaptured fish were preserved. Occasionally there were fish with brokenspines, apparently due to bird predation, but these were easily identified and not included inrecapture data.Data AnalysisThe comparison of homers and strayers is complicated by several factors : the markingof only one population but the monitoring of three breeding sites, my inability to estimatepopulation sizes, and the use of different trapping techniques at each breeding site (seeMonitoring of Returns, page 13). Therefore, ratios of natal homers to natal strayers werecompared to ratios of returns by displaced adults from the reproductive homing experiment.For these comparisons, data from release site “A” (288 reproductive homers to 9 strayers atSalt Lagoon and 2 strayers at Paq Creek; reproductive homing, Fig. 3, page 17) were usedbecause “A” was in a similar location to where the young of the year were released for themonitor of natal homing. When increases of straying were suspected, log likelihood ratioanalysis of contingency tables were used to test for significant differences. These statisticalcomparisons tested whether natal homing was similar to reproductive homing. If necessary,tables were subdivided and William’s adjusted log likelihood ratio analysis (Gd test)independently compared proportions of natal strayers, to reproductive strayers for both SaltLagoon and Paq Creek. These comparisons allowed for better definitions of how, and toNATAL HOMING 29which sites, natal straying was different from the low levels of reproductive straying. Wherethe numbers of natal strayers were found to be significantly higher than reproductive strayers,log lilcelihooci with Yates correction (G test) also compared numbers of natal strayers to thereproductive homers of that site; corrected values (CV) were calculated to adjust numbersof natal strayers for relative comparisons to the reproductive homersCorrected Values = # natal strayers x (2881# natal homers),where 288 is the number of reproductive homers from release site “A”. No significantdifference between natal strayers and reproductive homers indirectly implied equal natalreturns to the two different breeding sites (i.e. natal homers equal natal strayers).ResultsReturns were monitored through the entire 1992 breeding season (March - August)at Oyster Lagoon, Salt Lagoon, and Paq Creek (Appendices V, VI, and VII). Clearly, fishborn in Oyster Lagoon show a strong tendency to return to Oyster Lagoon and exhibitrelatively low straying rates to Paq Creek (Table 2). Interestingly, straying to Salt Lagoonwas low for overwinterers, but higher for summer migrants. This suggests that there may bean inverse relationship between time since migration and the precision of homing.Effects of Spine ClippingAt marking, the mean standard length of the 61 control fish was 25.8 mm. Allrecorded deaths (35) occurred within two weeks of marking (32 after only one day) and felldisproportionately on smaller fish (mean standard length of those that died = 22.3 mm). Thelargest fish that died was 28 mm. Some fungus appeared on spines that were clipped tooshort, but no deaths occurred from October to March. This experiment shows that spineNATAL HOMING 30BREEDING SITES MONITOREDOyster Lagoon Salt Lagoon Paq CreekOyster Oyster Salt Oyster Paqhomers strayers homers strayers homersReproductive HomingfromRELEASE SITE “A”date # lengthreleased released of migrationMAY 1992 1009 0 - 3 months 288 9 32 2 128Natal HomingAPR 1992 10025 2 - 4 months 520 7 0AUG 1991 7476 5 - 11 months 260 59 11APR 1991 11000 8 - 16 months 94 11 0Table 2. Number of marked Oyster Lagoon fish recaptured in Oyster Lagoon, Salt Lagoon,and Paq Creek during spring/summer 1992 (for detail see Appendices V, VI, and VII).Recaptures from release site “A” of the Reproductive Homing Experiment (see ReproductiveHoming, page 14) are included as comparaive ratios of recapture.clipping has a fast and relatively large effect on small fish (S.L. <25 mm). The survivingfish increased in standard length (mean = 40.7 mm on March 18th) from September to March.Although these fish grew, the clipped pelvic spines were still easily recognized in March.Comparisons to Reproductive HomingOf the 10025 young of 1991 that were marked as they migrated out of Oyster Lagoonin April 1992 (overwinterers), 520 were recaptured 2 - 4 months later as they re-entered thelagoon. In addition, seven individuals were recaptured in Salt Lagoon but, despite efficienttrapping, no fish were recaptured in Paq Creek (Table 2). By comparison to recaptures ofNATAL HOMING 31displaced adults (288 homers, 9 strayers to Salt Lagoon, and 2 strayers to Paq Creek), it isclear that natal straying by fish that overwintered in Oyster Lagoon, and thus spent relativelyshort time (2 - 4 months) out of the lagoon, return to the lagoon with the same fidelity asdisplaced adults.Of the 7 476 young of 1991 that were marked as they left Oyster Lagoon in August1991 (summer migrators), 260 were recaptured 7 to 12 months later as they re-entered thelagoon. In contrast to overwinterers, 59 summer migrators were recaptured in Salt Lagoonand 11 in Paq Creek (Table 2). Statistical comparison of this ratio of summer migratorreturns, to the returns of displaced adults, shows a significant difference (G = 47.88, p <0.001). In more detail, the proportion that strayed to Paq Creek (260: 11) was significantlydifferent from the proportion of displaced adults that strayed to the creek (288 : 0) (G =15.459, p <0.001) indicating more natal straying than reproductive straying; however, 11natal strayers (CV = 12) was considerably less than the 128 reproductive homers to PaqCreek which implies that fewer summer migrators returned to Paq Creek than to OysterLagoon. Also, the proportion of summer migrators that strayed to Salt Lagoon (260: 59)was compared to the proportion of displaced adults that strayed (288 : 6) and there was asignificant difference (G = 50.109, p <0.001). Interestingly, further comparison of the 59strayers (CV = 53) to the 32 Salt Lagoon homers (displaced adults), indicates that natalstraying by summer migrators was significantly higher than reproductive homing to SaltLagoon (G = 4.750, p <0.05); this implies that there were more Oyster Lagoon summermigrators returning to Salt Lagoon than to Oyster Lagoon.For Oyster Lagoon sticklebacks, the longer times spent out of the lagoon appear torange from 8 - 16 months. Of the 11 000 overwintering young of 1990 that were marked asNATAL HOMING 32they left Oyster Lagoon in April 1991, 94 were recaptured returning to Oyster Lagoon in thespring and summer of 1992 (8 -16 months after marking). In addition, 11 strayers to SaltLagoon, and none to Paq Creek were recaptured (Table 2). Comparison of this ratio of twoyear old returns, to returns of displaced adults found a significant difference (G = 9.124, p<0.025). Interestingly, with no recaptures of these overwinterers at Paq Creek, there is norecognizable difference between natal straying, and straying by displaced adults to Paq Creek.However, recaptures of these overwinterers were comparatively high at Salt Lagoon (11strayers; CV = 34); comparison of proportion of natal strayers (94 :11) to displaced OysterLagoon adults shows a significant difference (Gadj = 7.65, p <0.01). In fact, the number oftwo year old strayers to Salt Lagoon was not significantly different from the 32 displacedadults that homed to Salt Lagoon (G = 0.015, p > 0.90); this relative similarity implies thatthe Oyster Lagoon fish that overwintered, and left the lagoon for 8 - 16 months, returned insimilar numbers to both Oyster and Salt lagoons.These results suggest that the precision of homing in marine threespine sticklebacksis an inverse function of the length of time the fish are away from the breeding site.Interestingly, in the 1992 breeding season, no overwinterers from either year (April 1991 orApril 1992 markings) strayed to Paq Creek; however, summer migrators did stray to thecreek. Why there is this difference in propensity to stray to Paq Creek between summermigrators and overwinterers is still not resolved.SummaryMy study suggests that marine sticklebacks born in Oyster Lagoon return to thelagoon to breed as adults. The percent return is similar to that found in salmonids : 0.85 %NATAL HOMING 33to 5.2 % for Oyster Lagoon sticklebacks and 1 % to 20 % for salmonids (Groot & Margolis1992). The level of straying to nearby Paq Creek and Sail Lagoon is generally low butvariable. The level of straying seems to be related to season and lengths of time away fromthe lagoon. Also, this marine population strays less to Paq Creek (a freshwater breeding site)than to the Salt Lagoon. marine breeding site. Summer migrators stray more thanoverwintering fish, and the level of straying between the two marine populations probably issufficient to prevent divergence. Overwintering juveniles that spent only 2 to 4 monthsoutside of the lagoon, returned more successfully than summer migrators which were absentfor 7 to 12 months. Although they are not common in the lagoon, two year old fish had thelowest returns (0.85 % of those marked). The total returns of the summer migrators (3.5 %of those marked) is most representative of the role of natal homing at Oyster Lagoon.The low numbers of strayers to Paq Creek suggest little or no gene flow from marineto anaxiromous populations of sticklebacks. The salinity differences between freshwater andmarine breeding sites may contribute to the apparent ease with which Oyster Lagoon fishdistinguish between these sites. However, there may be isolation between marine andfreshwater breeding habitats without effective isolation among anadromous populations,although geographic distance may provide some reduction in inter-population gene flow.The results from Paq Creek indicate the possibility of genetic isolation between marine andanadromous populations, and this introduces the possibility of two sources of post-glacialcolonists to fresh water.The high number of Oyster Lagoon summer migrators recaptured at Salt Lagoon(August 1991 release) bring into question the strength of this population’s natal homing.Because more marked fish returned to Salt Lagoon than Oyster Lagoon, in reality, these twoNATAL HOMING 34marine breeding sites may be one site; however, the straying by overwinterers (April release)to Salt Lagoon was as low as reproductive straying and this suggests some degree of isolationbetween the two.The most important outcome from this experiment is the confirmation of natal homingby threespine sticklebacks. It is this knowledge that opens the way to more detailed studies.There is now a need to better measure the levels of gene flow between, and among,anadromous and marine populations.35GENERAL DISCUSSIONThis study examines the propensity of both marine and anadromous threespinesticklebacks (Gasterosteus aculeatus) to return to their place of birth to breed (natal homing),and of breeders to return to their breeding site if displaced (reproductive homing). All threepopulations (Oyster Lagoon, Salt Lagoon, and Paq Creek) exhibited strong reproductivehoming but only the Oyster Lagoon population was tested for natal homing. Young of theyear that were marked as they left the lagoon returned to the lagoon as mature adults.Overwinterers showed remarkable fidelity to Oyster Lagoon with only a relatively smallnumber of individuals returning to nearby Salt Lagoon and no strayers were recovered at theanadromous spawning site (Paq Creek). This level of homing with little or no straying toalternative breeding sites that are within a kilometer of Oyster Lagoon, suggests thepossibility that these populations are genetically isolated from one another. The level ofstraying between the two marine populations (Oyster and Salt lagoons) may be sufficient toprevent divergence but, for natal homing, the anadromous population (Paq Creek) appears tobe completely isolated. Consequently, given enough time and strong enough selection, themarine and anadromous populations could diverge. Clearly, information, especially onhoming and straying, is needed before the evolution of post-glacial diversity in this speciescan be understood.Orti et a!. (1992) suggests at least three ancestral clades (of northern, eastern andwestern Pacific origins) were involved in the post-glacial invasion of British Columbia. Theirsuggestion is based on mtDNA sequence analysis of the cytochrome B gene, and thedifferences among the three clades imply pre-glacial divergence. Much of the divergence infreshwater, however, clearly is post-glacial (Bell 1976; Withler & McPhail 1985). MostGENERAL DISCUSSION 36freshwater populations are thought to be derived from anadromous or marine populations, andthese founding populations generally are viewed as homogeneous (Bell 1976; Withler &McPhail 1985). The discovery of natal homing in threespine sticklebacks provides amechanism that could generate heterogeneity in marine sticklebacks, and between marine andanadromous populations. Certainly, divergence among marine populations of Gasterosteushas been demonstrated on the east coast of North America. The recently discovered whitestickleback is reproductively isolated from G. aculeatus and has distinctly different breedingcolouration, nest site selection, and parental care (Blouw & Hagen 1990). Since the diversityamong freshwater populations of Gasterosteus is greater on the west coast than on the eastcoast of North America, it is possible that there is more diversity among marine andanadromous populations in this area than has previously been supposed. For example,sexually mature sticklebacks occur at least 150 km offshore on the west coast (Quinn & Light1989), and would have to make prodigious migrations to reach shore in time to spawn.Perhaps there is some unique, pelagic stickleback out in the North Pacific. Also, there arehints in the literature of morphological and electrophoretic divergences among anadromouspopulations (Withier 1980), and if anadromous populations home as accurately as marinepopulations, they may have a deme structure comparable to anadromous salmonids.Sticklebacks could also be useful models for the study of mechanisms of homing inanadromous species. At present, nothing is known about the sensory mechanisms thatsticklebacks use to return to their place of birth, or whether this propensity is inherited.Certainly, there is evidence of a genetic component in the homing and migrations ofsalmonids (Brannon, 1972; Kelso et aL, 1981; Taylor, 1988). Salmonids have alsodemonstrated abilities such as sun compass, or celestial orientation, and experiments haveGENERAL DISCUSSION 37shown that both vision and olfaction play a role in natal homing (for examples see Quinn andDittman, 1992). The major advantage that sticklebacks have over salmonids for studyinghoming is their short life cycle (one year to maturity). Indeed, some marine sticklebacksreturn to their breeding site within two months. Also, the species is abundant and easy towork with.This study of homing was designed to investigate a possible mechanism thatcontributes to the evolution of post-glacial diversity among sticklebacks along the northwestcoast of North America. 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Board Can. 26: 3183 - 3208.1984. Ecology and evolution of sympathc sticklebacks (Gasterosteus):morphological and genetic evidence for a species pair in Enos Lake, British Columbia.Can. J. Zoology, 62: 1402 -1408.1992. Ecology and evolution of sympatric sticklebacks (Gasterosteus):evidence for a species pair in Paxton Lake, Texada Island, British Columbia. Can.J. Zoology, 70: 361 -369.391993. Speciation and the evolution of reproductive isolation in thesticklebacks (Gasterosteus) of southwestern British Columbia. in “The EvolutionaiyBiology of Threespine Stickleback.” Ed. S. Foster and M.A. Bell. Oxford UniversityPress, Oxford.McPhail, J.D. and D.E. Hay. 1983. Differences in male courtship in freshwater and marinesticklebacks (Gasterosreus aculeatus). Can. J. Zool. 61 : 292 - 297.McPhail, J.D. and C.C. Lindsey. 1970. Freshwater fishes of northwestern Canada andAlaska. Bull. Fish. Res. Board Can., 173 : 1 - 373.Moodie, G.E.E. 1970. Predation as a mechanism in the evolution of an unusual populationof sticklebacks in the Queen Charlotte Islands, Canada (Pisces: Gasterosteidae). Ph.D. Thesis, Dept. of Zoology, University of Alberta.Moodie, G.E.E. and T.E. Reimchen. 1976a. Phenetic variation and habitat differences inGasterosteus populations of the Queen Charlotte Islands. Syst. Zool., 25 : 49 - 61.1976b. Glacial refugia, endemism, and sticklebackpopulations of the Queen Charlotte Islands, British Columbia. The Canadian Field-Naturalist, 90 : 471 - 474.Mori, S. 1984. Reproductive behaviour of the landlocked threespine stickleback,Gasterosteu.s aculeatus miccrocephalus, in Japan. Behaviour, 93: 21 -35.Ortf, G., M.A. Bell, T.E. Reimchen and A. Meyer. 1992. Global survey of mitochondrialDNA sequences in the threespine stickleback : evidence for recent colonizations.Evolution, in press.Paepke, H.-J. 1983. “Die stichlinge : Gasterosteidae.” A. Ziemsen Verlag, DDR WittenbergLutherstadt.Quinn, T.P. and A.H. Dittman. 1992. Chapter 4 : Fishes, in “Animal Homing”. Ed. F.Papi. Chapman and Hall, London.Quinn, T.P. and J.T. Light. 1989. Occurrence of threespine sticklebacks (Gasterosteusaculeatus) in the open North Pacific Ocean: migration or drift? Can. 3. Zoology, 672850 -2852.- Reimchen, T.E. 1980. Spine deficiency and polymorphism in a population of Gasterosteusaculearus: an adaptation to predation. Can. 3. Zoology, 58: 1232 - 1244.1983. Structural relationships between spines and lateral plates in threespinestickleback (Gasterosteus aculeatus). Evolution, 37: 931 -946.1988. Inefficient predators and prey injuries in a population of giantstickleback. Can. J. Zoology, 66: 2036 - 2044.401990. Size-structured mortality in a threespine stickleback (Gasterosteusaculeatus) - cutthroat trout (Oncorhynchus clarki) community. Can. 3. Fish. Aquat.Sci. 47: 1194- 1205.1992. Injuries on stickleback from attacks by a toothed predator(Oncorhynchus) and implications for the evolution of lateral plates. Evolution, 46 (4):1224 - 1230.Reimchen, T.E., E.M. Stinson, and J.S. Nelson. 1985. Multivariate differentiation ofparapathc and allopatric populations of threespine stickleback in Sangan Riverwatershed. Queen Charlotte Islands. Can. 3. Zool. 63: 2944 -2951.Ridgeway, M.S. and J.D. McPhail. 1984. Ecology and evolution of sympathc sticklebacks(Gasterosteus): mate choice and reproductive isolation in the Enos Lake species pair.Can. 3. Zoology, 62: 1813 - 1818.Saimoto, R.K. 1993. Life history of the marine threespine stickleback in Oyster Lagoon,British Columbia. M. Sc. thesis, University of British Columbia, Vancouver, B.C.Schiuter, D. and 3.D. McPhail. 1992. Ecological character displacement and speciation insticklebacks. Amer. Naturalist, 140 (1): 85 - 108.Soin, S.G., O.P. Danil’chenko and A.S. Khandal’. 1984. Combined effect of salinity andtriethyl stannic chloride on the development of the marine forms of threespinestickleback, Gasterosteus aculeatus (Gasterosteidae). J. Ichthyology, 24 (4) : 26 - 34.Taylor, E.B. 1988. Adaptive variation in rheotactic and agonistic behaviour in newly-emerged fry of chinook salmon (Oncorhynchus tshawytscha) from ocean- and stream-type populations. Can. 3. Fish. Aquat. Sci., 45 : 237 - 243.Taylor, E.B. and J.D. McPhail. 1986. Prolonged and burst swimming in anadromous andfreshwater threespine stickleback, Gasterosteus aculeazus. Canadian Journal ofZoology, 64 : 416 - 420.Withier, R.E. 1980. Genetic relationships among threespine sticklebacks, Gasterosteusaculeatus. M.Sc. thesis, University of British Columbia, Vancouver, B.C.Withier, R.E. and J.D. McPhail. 1985. Genetic variability in freshwater and anadromoussticklebacks (Gasterosteus aculeatus) of southern British Columbia. Canadian Journalof Zoology, 63 : 528 - 533.Wootton, R.J. 1976. “The Biology of the Sticklebacks.” Academic Press, London.APPENDICES 41Appendix I. Numbers of female sticklebacks that were collected at Oyster Lagoon, SaltLagoon, and Paq Creek breeding sites for displacements to release sites “A”, “B”, and “C”.Fish were dye injected under anterior lateral plates on the right side for release site “A”,under posterior right lateral plates for release site “B”, and under left anterior lateral platesfor release site “C”. Fish with different initial breeding site choices were marked withdifferent colour dyes : orange for Oyster Lagoon (Appendix Ia), pink for Salt Lagoon(Appendix Ib), and red for Paq Creek (Appendix Ic).APPENDICES 42Appendix Ia. Numbers of female sticklebacks from the Oyster Lagoon that were marked andreleased for the Reproductive Homing Experiment.# OF FISH RELEASED TOTAL #DATE at RELEASE SITES of FISHDISPLACED“A” “B” “C”1MAY 13th 84 88 87 2592 MAY 14th 85 85 100 2703 MAY 15th 100 96 86 2824 MAY 16th 95 90 96 2815 MAY 17th 95 96 94 2856 MAY 18th 120 108 110 3387 MAY 19th 93 87 94 2748 MAY 20th 120 120 110 3509 MAY 21st 110 116 100 32610 MAY 22nd 105 101 104 310TOTAL NUMBERS 1009 987 981 2987RELEASEDAPPENDICES 43Appendix lb. Numbers of female sticklebacks from Salt Lagoon that were marked andreleased for the Reproductive Homing Experiment.# OF FISH RELEASED TOTAL #DATE at RELEASE SITES of FISHDISPLACED4H II1 MAY 13th 80 79 71 2302 MAY 14th 76 65 28 1693 MAY 15th 78 71 70 2194 MAY 16th 49 48 32 1295 MAY 17th 40 51 38 1296 MAY 18th 91 83 77 2517 MAY 19th 84 82 91 2578 MAY 20th 109 109 111 3299 MAY 21st 95 94 95 28410 MAY 22nd 79 79 77 235TOTAL NUMBERS 781 750 690 2221RELEASEDAPPENDICES 44Appendix Ic. Numbers of female sticklebacks from Paq Creek that were marked andreleased for the Reproductive Homing Experiment.# OF FISH RELEASED TOTAL #DATE at RELEASE SITES of FISHDISPLACED,,•L.,,1 MAY 13th 55 50 60 1652 MAY14th 44 50 31 1253 MAY 15th 88 98 96 2724 MAY 16th 35 36 40 1115 MAY17th 44 42 35 1216 MAY 18th 40 40 45 1257 MAY 19th 42 43 44 1298 MAY 20th 42 45 44 1319 MAY 21st 56 57 58 17110 MAY 22nd 65 69 58 192TOTAL NUMBERS 511 530 511 1552RELEASEDAPPENDICES 45Appendix II. Summary of recaptures in Oyster Lagoon for the Reproductive HomingExperiment from May to August, 1992. For daily record of returns, see Appendices Ha — Hf.HOMERS STRAYERSOYSTER LAGOON SALT LAGOON PAQ CREEKPOPULATION POPULATION POPULATIONFROM FROM FROMRELEASE SITES RELEASE SITES RELEASE SITESA B C A B C A BJCMay 14 - 31 133 52 138 13 0 7 11 0__] 7June 1 - 15 121 125 87 1 2 0 2 0__J__1June 16 - 30 17 26 22 2 1 0 0 0__j_0July 1 - 15 15 16 17 0 0 2 1 0 0July 16 - 31 2 1 4 0 0 0 0 1 0Aug.l-15 0_} 2 0 0 0 0 0_J_o 0TOTALRECAPTURES 288 222 268 16 3 9 14 1 8APPENDICES 46Appendix Ha. Daily record of recaptures in Oyster Lagoon for the Reproductive HomingExperiment from May 14th- 3 1st, 1992.HOMERS STRAYERSSAMPLE OYSTER LAGOON SALT LAGOON PAQ CREEKSIZE POPULATION POPULATION POPULATIONof FROM FROM FROMFemales RELEASE SITES RELEASE SITES RELEASE SITESMAY A B C A B C A B C14 234 5 0 4 0 0 1 0 0 015 643 20 2 19 5 0 0 1 0 016 90 7 1 7 1 0 0 1 0 017 387 11 4 12 1 0 2 2 0 118 444 25 4 25 1 0 1 0 0 019 285 3 4 8 0 0 0 0 0 320 388 11 3 10 2 0 2 3 0 121 406 15 2 17 1 0 1 1 0 122 73 5 7 12 1 0 0 1 0 123 28 3 0 2 0 0 0 1 0 024 97 6 1 4 0 0 0 0 0 025 91 3 6 4 0 0 0 1 0 026 102 3 0 7 0 0 0 0 0 027 45 1 0 1 0 0 0 0 0 028 39 1 2 1 0 0 0 0 0 029 77 3 2 1 0 0 0 0 0 030 22 0 0 2 0 0 0 0 0 031 397 12 14 6 1 0 0 0 0 0TOTALRECAPTURES 133 52 138 13 0 7 11 0 7MAY14-31APPENDICES 47Appendix Hb. Daily record of recaptures in Oyster Lagoon for the Reproductive HomingExperiment from June 1st - 15th, 1992.HOMERS STRAYERSSAMPLE OYSTER LAGOON SALT LAGOON PAQ CREEKSIZE POPULATION POPULATION POPULATIONof FROM FROM FROMFemales RELEASE SITES RELEASE SITES RELEASE SITESJUNE A B C A B C A B C1 443 19 12 7 0 0 0 0 0 02 779 11 18 13 0 1 0 0 0 03 1219 20 23 14 0 0 0 0 0 14 992 15 24 14 0 0 0 0 0 05 922 19 10 7 0 0 0 2 0 06 726 12 7 5 1 0 0 0 0 07 119 1 3 3 0 0 0 0 0 08 42 1 0 0 0 0 0 0 0 09 91 0 0 2 0 0 0 0 0 010 73 3 1 0 0 0 0 0 0 011 184 3 3 2 0 0 0 0 0 012 419 4 5 6 0 0 0 0 0 013 714 2 8 3 0 0 0 0 0 014 744 3 5 7 0 1 0 0 0 015 696 8 6 4 0 0 0 0 0 0TOTALRECAPTURES 121 125 87 1 2 0 2 0 1JUNE 1 - 15APPENDICES 48Appendix He. Daily record of recaptures in Oyster Lagoon for the Reproductive HomingExperiment from June 16th - 3 1st, 1992.HOMERS STRAYERSSAMPLE OYSTER LAGOON SALT LAGOON PAQ CREEKSIZE POPULATION POPULATION POPULATIONof FROM FROM FROMFemales RELEASE SITES RELEASE SITES RELEASE SITESJUNE A B C A B C A B C16 1037 3 7 6 1 1 0 0 0 017 860 1 4 3 0 0 0 0 0 018 527 3 2 1 0 0 0 0 0 019 1330 6 7 3 1 0 0 0 0 020 769 2 1 3 0 0 0 0 0 021 629 0 2 2 0 0 0 0 0 022 125 0 0 0 0 0 0 0 0 023 50 1 1 0 0 0 0 0 0 024 32 0 0 0 0 0 0 0 0 025 17 0 0 0 0 0 0 0 0 026 20 0 0 1 0 0 0 0 0 027 31 0 0 1 0 0 0 0 0 028 340 0 1 1 0 0 0 0 0 029 764 1 0 0 0 0 0 0 0 030 768 0 1 1 0 0 0 0 0 0TOTALRECAPTURES 17 26 22 2 1 0 0 0 0JUNE 16 - 30APPENDICES 49Appendix lid. Daily record of recaptures in Oyster Lagoon for the Reproductive HomingExperiment from July 1st - 15th, 1992.HOMERS STRAYERSSAMPLE OYSTER LAGOON SALT LAGOON PAQ CREEKSIZE POPULATION POPULATION POPULATIONof FROM FROM FROMFemales RELEASE SITES RELEASE SITES RELEASE SITESJULY A B C A B C A B C1 533 0 1 1 0 0 0 0 0 02 784 2 3 0 0 0 1 0 0 03 385 0 3 0 0 0 0 0 0 04 736 3 1 4 0 0 0 0 0 05 1223 1 0 1 0 0 0 0 0 06 105 1 0 1 0 0 0 1 0 07 388 0 1 1 0 0 0 0 0 08 69 0 1 0 0 0 0 0 0 09 218 0 0 0 0 0 0 0 0 010 142 1 1 0 0 0 0 0 0 011 87 1 1 2 0 0 0 0 0 012 1052 0 2 1 0 0 0 0 0 013 798 0 1 3 0 0 0 0 0 014 595 3 0 2 0 0 0 0 0 015 1204 2 1 1 0 0 1 0 0 0TOTALRECAPTURES 15 16 17 0 0 2 1 0 0JULY1-15APPENDICES 50Appendix He. Daily record of recaptures in Oyster Lagoon for the Reproductive HomingExperiment from July 16th - 31st, 1992.HOMERS STRAYERSSAMPLE OYSTER LAGOON SALT LAGOON PAQ CREEKSIZE POPULATION POPULATION POPULATIONof FROM FROM FROMFemales RELEASE SITES RELEASE SITES RELEASE SITESJULY A B C A B C A B C16 865 0 0 1 0 0 0 0 0 017 1201 0 0 1 0 0 0 0 0 018 1194 1 0 1 0 0 0 0 0 019 873 0 1 0 0 0 0 0 0 020 568 0 0 0 0 0 0 0 0 021 578 0 0 0 0 0 0 0 0 022 87 0 0 1 0 0 0 0 0 023 100 0 0 0 0 0 0 0 0 024 140 0 0 0 0 0 0 0 1 025 45 0 0 0 0 0 0 0 0 026 - - - - - - - - - -27 - - - - - - - - - -28 397 0 0 0 0 0 0 0 0 029 1564 1 0 0 0 0 0 0 0 030 528 0 0 0 0 0 0 0 0 031 942 0 0 0 0 0 0 0 0 0TOTALRECAPTURES 2 1 4 0 0 0 0 1 0JULY 16 - 31APPENDICES 51Appendix hf. Daily record of recaptures in Oyster Lagoon for the Reproductive HomingExperiment from August 1st - 15th, 1992.HOMERS STRAYERSSAMPLE OYSTER LAGOON SALT LAGOON PAQ CREEKSIZE POPULATION POPULATION POPULATIONof FROM FROM FROMFemales RELEASE SITES RELEASE SITES RELEASE SITESAUG. A B C A B C A B C1 666 0 0 0 0 0 0 0 0 02 764 0 0 0 0 0 0 0 0 03 288 0 1 0 0 0 0 0 0 04 612 0 0 0 0 0 0 0 0 05 578 0 0 0 0 0 0 0 0 06 245 0 1 0 0 0 0 0 0 07 498 0 0 0 0 0 0 0 0 08 - - - - - - - - - -9 83 0 0 0 0 0 0 0 0 010 431 0 0 0 0 0 0 0 0 011 306 0 0 0 0 0 0 0 0 012 154 0 0 0 0 0 0 0 0 013 1077 0 0 0 0 0 0 0 0 014 1641 0 0 0 0 0 0 0 0 015 608 0 0 0 0 0 0 0 0 0TOTALRECAPTURES 0 2 0 0 0 0 0 0 0AUG.1-15APPENDICES 52Appendix Ill. Summary of recaptures in Salt Lagoon for the Reproductive Homing Experimentfrom May - August, 1992. For daily record of returns, see Appendices ifia- ifie.HOMERS STRAYERSSALT LAGOON OYSTER PAQ CREEKPOPULATION POPULATION POPULATIONFROM FROM FROMRELEASE SITES RELEASE SITES RELEASE SITESA B jc AJB jc AjB CMayl4-31 6 [9] 6 4J4 3 O]2 0Junel-15 iolio 3 1 2 0 oJi o]June 16 - 30 8 11 1 10 1 0 1 f__0 0 0July 6 7 5 3 0 0 0 0 0August 2 5 2 0 0 1 0 0__J_0_1TOTALRECAPTURES 32 42 26 9 6 5 0 3 0APPENDICES 53Appendix ha. Record of recaptures in Salt Lagoon for the Reproductive Homing Experimentfrom May 14th - 31st, 1992.HOMERS STRAYERSSAMPLE SALT LAGOON OYSTER PAQ CREEKSIZE POPULATION POPULATION POPULATIONof FROM FROM FROMFemales RELEASE SITES RELEASE SITES RELEASE SITESMAY A B C A B C A B C14 210 0 0 4 0 0 0 0 0 015 130 0 0 0 0 0 0 0 0 016 129 0 0 0 0 1 0 0 1 017 251 0 0 0 0 0 0 0 0 018 257 0 1 0 0 0 0 0 0 019 329 0 0 0 0 0 0 0 0 020 284 1 0 0 0 0 0 0 0 021 235 2 0 1 0 1 1 0 0 022 295 1 0 1 0 0 1 0 0 023 324 0 1 0 0 0 0 0 0 024 498 0 2 0 0 1 0 0 0 025 565 2 1 1 1 0 1 0 0 026 519 0 2 0 0 0 0 0 0 027 368 0 1 1 3 0 0 0 0 028 231 0 1 0 0 1 0 0 0 029 310 0 0 1 0 0 0 0 1 030 275 0 0 1 0 0 0 0 0 031 360 0 0 0 0 0 0 0 0 0TOTALRECAPTURES 6 9 6 4 4 3 0 2 0MAY 14-31APPENDICES 54Appendix ilIb. Record of recaptures in Salt Lagoon for the Reproductive Homing Experimentfrom June 1st - 15th, 1992.HOMERS STRAYERSSAMPLE SALT LAGOON OYSTER PAQ CREEKSIZE POPULATION POPULATION POPULATIONof FROM FROM FROMFemales RELEASE SITES RELEASE SITES RELEASE SITESJUNE A B C A B C A B C1 382 1 0 0 1 0 0 0 0 02 610 0 1 0 0 0 0 0 0 03 572 1 1 0 0 0 0 0 0 04 435 0 0 0 0 1 0 0 0 05 504 0 0 1 0 0 0 0 0 06 595 2 1 0 0 0 0 0 0 07 830 2 4 0 1 0 0 0 0 08 724 1 1 0 0 0 0 0 1 09 747 1 0 1 0 0 0 0 0 010 596 0 0 1 0 0 0 0 0 011 577 1 1 0 1 0 0 0 0 012 422 0 1 0 0 0 0 0 0 013 289 1 0 0 1 0 0 0 0 014 470 0 0 1 0 0 0 0 0 015 394 0 0 0 0 0 0 0 0 0TOTALRECAPTURES 10 10 3 1 2 0 0 1 0JUNE 1 - 15APPENDICES 55Appendix Illc. Record of recaptures in Salt Lagoon for the Reproductive Homing Experimentfrom June 16th - 31st, 1992.HOMERS STRAYERSSAMPLE SALT LAGOON OYSTER PAQ CREEKSIZE POPULATION POPULATION POPULATIONof FROM FROM FROMFemales RELEASE SITES RELEASE SITES RELEASE SITESJUNE A B C A B C A B C16 579 0 1 0 0 0 0 0 0 017 744 0 2 1 0 0 0 0 0 018 975 0 0 0 0 0 0 0 0 019 905 1 0 0 0 0 0 0 0 020 891 0 1 2 0 0 1 0 0 021 1026 1 2 0 1 0 0 0 0 022 1251 1 1 0 0 0 0 0 0 023 - - - - - - - - - -24 806 1 0 4 0 0 0 0 0 025 726 1 1 0 0 0 0 0 0 026 1011 2 1 0 0 0 0 0 0 027 701 1 2 1 0 0 0 0 0 028 765 0 0 1 0 0 0 0 0 029 - - - - - - - - - -30 338 0 0 1 0 0 0 0 0 0TOTALRECAPTURES 8 11 10 1 0 1 0 0 0JUNE 16 - 30APPENDICES 56Appendix HId. Record of recaptures in Salt Lagoon for the Reproductive Homing Experimentduring July, 1992.HOMERS STRAYERSSAMPLE SALT LAGOON OYSTER PAQ CREEKSIZE POPULATION POPULATION POPULATIONof FROM FROM FROMFemales RELEASE SITES RELEASE SITES RELEASE SITESJULY A B C A B C A B C2 533 1 0 1 0 0 0 0 0 04 784 1 0 0 0 0 0 0 0 06 385 0 1 0 0 0 0 0 0 08 736 1 2 1 0 0 0 0 0 010 1223 0 2 1 0 0 0 0 0 012 105 2 0 1 1 0 O 0 0 014 388 0 1 0 1 0 0 0 0 016 69 0 0 0 0 0 0 0 0 018 218 0 1 0 0 0 0 0 0 020 142 1 0 0 1 0 0 0 0 022 87 0 0 0 0 0 0 0 0 024 1052 0 0 0 0 0 0 0 0 026 798 0 0 0 0 0 0 0 0 028 595 0 0 0 0 0 0 0 0 030 1204 0 0 1 0 0 0 0 0 0TOTALRECAPTURES 6 7 5 3 0 0 0 0 0JULY1-30APPENDICES 57Appendix Ille. Record of recaptures in Salt Lagoon for the Reproductive Homing Experimentduring August, 1992.HOMERS STRAYERSSAMPLE SALT LAGOON OYSTER PAQ CREEKSIZE POPULATION POPULATION POPULATIONof FROM FROM FROMFemales RELEASE SITES RELEASE SITES RELEASE SiTESAUG. A B C A B C A B C1 492 0 1 0 0 0 0 0 0 03 424 0 2 1 0 0 0 0 0 05 500 0 0 0 0 0 0 0 0 07 - - - - - - - - - -9 571 0 2 0 0 0 1 0 0 011 605 0 0 0 0 0 0 0 0 013 468 1 0 0 0 0 0 0 0 015 544 0 0 1 0 0 0 0 0 017 387 1 0 0 0 0 0 0 0 0TOTALRECAPTURES 2 5 2 0 0 1 0 0 0AUG.1-15o o o n CD CD (DC) c- CD ‘0 rn CD :I. CD.,.‘-‘-‘-4‘-4I-.4-.Ic>Ut):•t-C0\cCl)I--.UtUto-tt’.00t’.)nru————t..)-Ut()Cl)I-’Q”ooo’)CCCCCL.)>—————floCCCCC::•aZ======CCCCCCC>Cl,————CCCC———---..CcccUI00APPENDICES 59Appendix IVa. Record of recaptures in Paq Creek for the Reproductive Homing Experimentfrom May 14th- 3 1st, 1992.HOMERS STRAYERSSAMPLE PAQ CREEK OYSTER LAGOON SALT LAGOONSIZE POPULATION POPULATION POPULATIONof FROM FROM FROMFemales RELEASE SITES RELEASE SITES RELEASE SITESMAY A B C A B C A B C14 139 0 4 0 0 0 0 0 0 015 116 2 4 0 0 0 0 0 0 016 105 2 18 1 0 0 0 0 0 017 121 3 7 2 0 0 0 0 0 018 226 3 9 4 0 0 0 0 0 019 205 2 5 3 0 0 0 0 0 020 180 3 5 5 1 0 0 0 0 021 147 2 6 3 0 0 0 0 0 022 115 0 8 4 0 0 0 0 0 023 120 7 5 4 0 0 0 0 0 024 197 6 7 4 0 0 0 0 0 025 360 3 11 5 0 0 0 0 0 026 231 2 8 4 0 0 0 0 0 027 302 6 5 5 0 0 0 0 0 028 219 0 3 2 0 0 0 0 0 029 195 8 3 3 0 0 0 0 0 030 123 1 4 2 0 0 0 0 0 031 167 5j14 5 1 0 0 0 0 0TOTALRECAPTURES 55 126 56 2 0 0 0 0 0MAY14-31APPENDICES 60Appendix 1Vb. Record of recaptures in Paq Creek for the Reproductive Homing Experimentduring June and July, 1992.HOMERS STRAYERSSAMPLE PAQ CREEK OYSTER LAGOON SALT LAGOONSIZE POPULATION POPULATION POPULATIONof FROM FROM FROMFemales RELEASE SITES RELEASE SITES RELEASE SITESJUNE A B C A B C A B C1 259 2 5 11 0 0 0 0 0 02 362 6 18 11 0 0 0 0 0 03 372 10 13 19 0 0 0 0 0 04 414 11 11 11 0 0 0 0 0 05 321 7 9 8 0 0 0 0 0 06 226 6 6 5 0 0 0 0 0 07 181 5 6 5 0 0 1 0 0 019 289 10 11 10 0 0 0 0 0 120 279 9 15 16 0 0 0 0 0 0JULY15 190 4 5 4 0 0 0 0 0 016 137 1 3 2 0 0 0 0 0 029 50 1 1 0 0 0 0 0 0 030 61 0 1 1 0 0 0 0 0 0TOTALRECAPTURES 72 104 103 0 0 1 0 0 1MAY14-31APPENDICES 61Appendix IVc. Record of recaptures in Paq Creek for the Reproductive Homing Experimentduring August, 1992.HOMERS STRAYERSSAMPLE PAQ CREEK OYSTER LAGOON SALT LAGOONSIZE POPULATION POPULATION POPULATIONof FROM FROM FROMFemales RELEASE SITES RELEASE SITES RELEASE SITESAUG. A B C A B C A B C2 44 0 1 3 0 0 0 0 0 03 39 0 0 0 0 0 0 0 0 05 45 0 1 1 0 0 0 0 0 07 25 0 1 0 0 0 0 0 0 09 23 0 0 0 0 0 0 0 0 011 24 0 0 0 0 0 0 0 0 013 23 1 0 0 0 0 0 0 0 0TOTALRECAPTURES 1 3 4 0 0 0 0 0 0AUGUSTAPPENDICES 62Appendix V. Number of Oyster Lagoon fish recaptured at Oyster Lagoon (natal homers) duringspring/summer 1992.RECAPTURED # OFOYSTER LAGOON NATAL HOMERSreleased inSAMPLE APR. 1991 AUG. 1991 APR. 1992SIZE (1 1000) (7476) (10025)*MARCH, 1992 1 822 1 9 -APRIL, 1992 11 323 11 114 -MAY, 1992 13 638 9 79 0JUNE, 1992 23 419 34 47 61JULY, 1992 21 852 35 10 319AUGUST, 1992 10 679 4 1 140TOTAL # 82 733 94 260 520NOTE: = Total number of fish marked and released at given dates.APPENDICES 63Appendix VI. Number of Oyster Lagoon fish recaptured at Salt Lagoon (natal strayers) duringspring/summer 1992.RECAPTURED # OFOYSTER LAGOON NATAL STRAYERSreleased inAPR. 1991 AUG. 1991 APR. 1992SAMPLE (11000) (7476)* (10025)*SIZEAPRIL 12th, 1992 40 0 0 0MAY, 1992 26 889 2 19 0JUNE, 1992 57 353 5 25 0JULY, 1992 30 950 3 14 5AUGUST, 1992 8 429 1 1 2TOTAL 123 661 11 59 7NOTE: () = Total number of fish marked and released at given dates.APPENDICES 64Appendix VII. Number of Oyster Lagoon fish recaptured at Paq Creek (natal strayers) duringspring/summer 1992.RECAPTURED # OFOYSTER LAGOON NATAL STRAYERSreleased inSAMPLE APR. 1991 AUG. 1991 APR. 1992SIZE (11000)* (7476)* (10025)*APRIL 27-28, 1992 481 1 2 0MAY, 1992 9 884 0 6 0JUNE, 1992 4 984 0 2 0JULY, 1992 634 0 1 0AUGUST, 1992 268 0 0 0TOTAL 16221 1 11 0NOTE: ()* = Total number of fish marked and released at given dates.

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