REGIONAL GROWTH PATTERNS OF JUVENILE ALBACORE (THUNNUS ALALUNGA) IN THE EASTERN NORTH PACIFIC
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abstract
Population structure of North Pacific albacore (Thunnus alalunga) may be more complex than the current single-stock hypothesis given the apparent regional differences in size-at-age and movement patterns in the eastern North Pacific. In this study, otolith-based techniques were used to analyze the age structure, daily growth rates and hatch dates of 126 albacore collected from two regions in the eastern North Pacific (northern: >40 N and southern: <40 N) in July through October of 2010 and 2011. Juvenile albacore collected from the southern region had significantly larger size-at-age than those collected from the northern region over a similar age range examined (423-1254 days). No significant regional difference in growth rates of juvenile albacore was detected over the ages examined, suggesting processes occurring in the first year and a half of life may have been driving regional size-at-age differences. Back-calculated hatch dates suggest protracted spawning for fish from both regions ranging from February to September with peak hatch dates between April and July (73% of all fish). Results from this two-year study suggest that juvenile albacore length-at-age estimates in the eastern North Pacific are region-specific and may need to be considered for future life history studies and stock assessments.
