Age and Growth of Canadian East Coast Pollock: Comparison of Results from Otolith Examination and Mark–Recapture Studies

Abstract

Pollock Pollachius virens were marked and released at relatively young ages in Canadian Maritime waters during 1979–1984. Substantial (n = 694) recaptures provided a unique opportunity for validation of age determinations made from examination of otoliths. Comparisons of mean lengths at age (age as determined from otolith examination) and the lengths at the assumed age (age at release, plus years at liberty) of recaptured fish indicated no significant differences. However, some (n = 211) of the recaptured tagged fish were also returned with the corresponding otoliths for each individual, and age determinations were completed. Thus, individual comparisons of otolith-derived ages and assumed ages were possible for those fish. Such comparisons revealed a tendency for the ages derived from otolith examination to exceed the assumed age by a year. Though these findings indicate a potential bias in age determinations during the 1980s, results from stock assessments indicate that strong and weak cohorts were tracked well during that period. Using fish assumed to be age 1 upon release (based on previous studies of growth during the larval and juvenile phases of pollock life history), we compared the increments of growth observed between fish released and recaptured in the eastern and western portions of the management unit. Fish released in the western area grew at a significantly faster rate than those released in the east.