Nursery origin of yellowfin tuna in the Hawaiian Islands

Stable isotopes of carbon (δ13C) and oxygen (δ18O) in otolith cores (first 2 mo of age) of young-of-the-year (YOY) yellowfin tuna Thunnus albacares were used as natural tracers to predict the nursery origin of sub-adults (age-1) collected from the Hawaiian Islands. YOY fish were first collected from nurseries throughout the western and central Pacific Ocean (WCPO) to determine whether δ13C and δ18O values of otolith cores (δCotolith and δOotolith) were sufficiently different to discriminate individuals from different nurseries used during the YOY period. Nurseries examined included both nearshore Hawaiian Islands and offshore Hawaiian Islands (Cross Seamount), and 4 locations in the equatorial Pacific Ocean: Line Islands, Marshall Islands, Solomon Islands, and Philippines. Significant differences existed in δCotolith and δOotolith among YOY yellowfin tuna from different nurseries for each year of the 2 yr study period (2008−2009). Individuals from the nearshore Hawaiian Islands were most enriched in δOotolith, while samples obtained from the Philippines were most depleted in both δCotolith and δOotolith relative to other regions. Inter-annual variability in otolith core chemistry was minor and only observed for individuals collected from the Philippines. Overall classification success from quadratic discriminant function analysis of YOY yellowfin tuna to their respective nursery of collection was 63 and 87% for 2008 and 2009, respectively. Mixed-stock analysis indicated 91% of the sub-adult yellowfin tuna collected from the nearshore Hawaiian Islands originated from this same nursery. In addition, sub-adults from the offshore location within the Hawaiian Islands appear to originate from the nearshore Hawaiian Islands, highlighting the importance of local production and retention of yellowfin tuna to the standing stock and domestic fisheries of Hawaii.