Nursery origin of yellowfin tuna in the Hawaiian Islands

Abstract

Stable isotopes of carbon (! 13 C) and oxygen (! 18 O) in otolith cores (first 2 mo of age) of young-of-the-year (YOY) yellowfin tuna Thunnus albacares were used as natural tracers to pre- dict 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 deter- mine whether ! 13 C and ! 18 O values of otolith cores (! 13 Cotolith and ! 18 Ootolith) were sufficiently dif- ferent 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 ! 13 Cotolith and ! 18 Ootolith 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 ! 18 Ootolith, while samples obtained from the Philippines were most depleted in both ! 13 Cotolith and ! 18 Ootolith relative to other regions. Inter-annual variability in otolith core chemistry was minor and only observed for individ- uals 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.