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Life history of marine threespine stickleback in Oyster Lagoon, British Columbia Saimoto, Regina Karin


Marine populations of three spine sticklebacks (Gasterosteus aculeatus) are possible ancestors of the many of the divergent freshwater populations of this species found along the glaciated coast of British Columbia. Until this study, the life history and reproductive behaviours of marine population along the Pacific coast of North America were unknown. Data was collected from September 1990 to August 1992 at Oyster Lagoon, Pender Harbour, British Columbia. Morphology, migration and growth, reproduction, and nesting success were examined for this purely marine population. Morphology analysis of 11 characters on 80 males and 80 females from Oyster Lagoon indicate that this marine population is similar to many populations of three spine sticklebacks, and is intermediate to the most extreme morphological states reported in the literature. The Oyster Lagoon population is sexually dimorphic in post orbital length, mouth width, first dorsal spine length, and anal fin ray number. The population is also polymorphic for lateral plates. The morphology of 35 low and partially plated fish was compared to 160 high plated fish. Low and partially plated fish have fewer and shorter gill rakers than high plated fish, and females of this group have wider mouths than high plated females. Morphologically, the low and partially plated fish are more similar to stream resident sticklebacks than are their high plated counterparts. Migration and growth data for Oyster Lagoon fish indicate sexual maturity at one year, and that the population is iteroparous. There are two well defined peaks of out-migrations of young for this population. Some young migrate in the summer of their birth (summer migrators), while other young overwinter in the lagoon (overwinterers) and migrate out the following spring. Summer migrators return as mature adults early next spring, whereas most overwinterers do not return to the lagoon to breed until mid-summer. The prolonged breeding season of this population lasts from March/April to September. Reproductive behaviours of both sexes are similar to those reported for other populations; however, the characteristic Zig Zag dance is absent from this population. Cannibalism is high in Oyster Lagoon, and all three types of diversionary displays (nest defence behaviours) were observed. Female fecundity and egg morphology is more similar to anadromous populations than to freshwater populations. Oyster Lagoon males tend to prefer to nest under rocks, in shallow areas near the shoreline. Nests under rock were less likely to be abandoned before the end of courtship, and contained more eggs at the end of courtship, than nests in open areas. After the end of courtship there was no significant difference between the two nesting microhabitats in the probability of nest survival. In summary, the Oyster Lagoon marine population is similar to other, mainly freshwater, populations of the species. This life history study supports the notion of postglacial marine ancestry for freshwater populations on this coast. When compared, the better studied east coast marine populations, there are some differences. The question of relationship between anadromous and marine sticklebacks is discussed, but not resolved.

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