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Age and growth of the mosshead sculpin Clinocottus globiceps Girard with an assessment of its role in production of tidepool fishes Mgaya, Yunus Daud


Age and growth of Clinocottus globiceps Girard were investigated with the aid of otoliths taken from fish obtained from tidepools at Helby Island, British Columbia during the period May 1988 to June 1989. Length-frequency analysis was used to verify otolithic ageing. Data from fish collected between 1980 and 1987 were also included in this study. Growth rate was estimated using a back-calculation formula and a Gompertz growth curve. Instantaneous growth rates were determined. Results indicated that the C. globiceps population was composed of individuals from less than one year of age to 5 years of age. Growth was faster for younger age groups (about 17 mm per year) and declined at older age groups (about 9 mm per year). Growth was described by a Gompertz model and the following equation was obtained: Lt = 26.7mm * exp{1.58(l - exp[-0.30t])}. Instantaneous growth rates were highest for the 0+ age class. The highest levels of instantaneous growth rates occurred during the spring and early summer, the period that water temperatures reach a maximum and food is most abundant. The lowest instantaneous growth rates occurred during the fall and winter months. The age —length relationship for C. globiceps is presented. The length—weight relationship of the species is described. No differences in growth between sexes as revealed by length — weight relationship were observed, thus the following expression described the length — weight relationship for C. globiceps population at Helby Island: W = 1.5913 * 10⁻⁵ L[sup 3-1552]. Overall tidepool production with regards to C. globiceps was assessed by direct comparison with production of sympatric Oligocottus maculosus Girard, an abundant tidepool cottid. Production was estimated by both the instantaneous growth rate and size-frequency methods. Annual production as computed by the instantaneous growth rate method was 6.9 and 11.0 g/m²/year for C. globiceps and O. maculosus respectively. Young- age groups (between 1+ and 2 +) contributed 33 and 65% of production for C. globiceps and O. maculosus respectively. Estimates made by the size-frequency method were higher and it was suggested that these estimates may be more accurate, since the method is not affected by nonsynchronous cohort development. Production was analyzed by zones on the intertidal area and the results reflected the distribution pattern of the two species, i.e., higher production was observed at the upper intertidal pools for O. maculosus and at the lower pools for C. globiceps. The relationships between the physical characteristics of the tidepools and production of the two species are given. None of the physical variables examined were significant predictors of production.

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