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Elements in otoliths of
Atlantic bluefin tuna have been used to delineate yearlings (age-1) from
eastern and western Atlantic nurseries (Rooker et al. 2003); however,
classification success for several year-classes has been moderate and
classification functions show strong year to year variability. The
utility of an alternative chemical marker in otoliths, carbon and oxygen
stable isotopes, have been used recently to discriminate bluefin tuna from
natal regions. The discriminatory power of stable isotopes (d13C,
d18O)
in otoliths of yearlings (age-1) was high, with over 90% of individuals
classified correctly (based on cross-validated classification) to eastern
and western nurseries (Figure 1). In contrast to trace element analyses,
year to year variation in stable isotope signatures was minimal over five
year classes (1999-2003) of yearlings. Thus, these stable isotopes and in
particular d18O
can be used to reliably predict nursery origin of Atlantic bluefin tuna.
In an initial application, we compared otolith core material
(corresponding to the first year of life) of large school, medium, and
giant category bluefin tuna to reference samples of yearling signatures to
determine their origin. A large fraction of the Atlantic bluefin tuna
collected in the western Atlantic fishery originated from nurseries in the
east. Alternatively, medium and giant category bluefin tuna from the
Mediterranean were largely of eastern origin. Thus, initial evidence
suggests that the western fishery received high subsidy from the
Mediterranean population. |
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for more information:
Rooker JR, Secor DH (2003) Stock structure
and mixing of Atlantic bluefin tuna: evidence from stable
d13C
and
d18O
isotoopes in otoliths. Col Vol Sci Pap ICCAT 56(3):115-1120.
PDF
Rooker JR, Secor
DH, Zdanowicz VS, de Metrio G, Relini LO (2003) Identification of
Atlantic bluefin tuna (Thunnus thynnus) stocks from putative
nurseries using otolith chemistry. Fish Oceanogr 12(1):1-10.
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