Natal origin of atlantic bluefin tuna (thunnus thynnus) from the gulf of st. lawrence using δ13c and δ18o in otoliths

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Title: Natal origin of atlantic bluefin tuna (thunnus thynnus) from the gulf of st. lawrence using δ13c and δ18o in otoliths
Author: Schloesser, Ryan Walter
Abstract: Increased knowledge of stock mixing and migration patterns of Atlantic bluefin tuna (Thunnus thynnus ) is required to appropriately manage and conserve declining populations . The nursery origin of giant bluefin tuna present in the Gulf of St . Lawrence was identified using stable carbon ( ?13C ) and oxygen ( ?18O ) isotopes in sagittal otoliths . Anthropogenic and natural processes are capable of impacting atmospheric and oceanic concentrations of ?13C and ?18O , affecting otolith concentrations . Therefore , inter -decadal variation of ?13C and ?18O in the otolith cores (corresponding to the first year of life ) of bluefin tuna was examined prior to stock predictions and temporal variability was detected in both isotope ratios . Significant changes in both ?13C and ?18O were recorded in the otolith cores of individuals with birthdates between 1947 and 2003 . Both ?13C and ?18O varied significantly as a function of year of birth , with ?13C decreasing and ?18O increasing over the time period investigated ( -2 .39 ?10 -2 and 5 .78 ?10 -3 per year , respectively ) . The rate of change in otolith ?13C was nearly identical to the reported rates of atmospheric ?13C depletion , recently attributed to the burning of fossil fuels (referred to as the Suess effect ) . Observed shifts in otolith ?18O were less pronounced and likely linked to changing physicochemical conditions (i .e . salinity ) in oceanic reservoirs over the time period investigated . The results show that otolith cores of bluefin tuna effectively track inter -decadal trends and record past oceanic ?13C and ?18O levels . After adjusting for inter -decadal trends , the isotopic composition of milled otolith cores of giants from three decades (1970s , 1980s , 2000s ) and three regions were compared to otolith ?13C and ?18O values of yearling bluefin tuna collected from eastern and western nurseries . Maximum likelihood estimates indicated that 99 % of bluefin tuna caught in the Gulf of St . Lawrence fishery originated from the western nursery , with no significant differences among the decades and regions examined . Results suggest that little to no mixing of eastern and western populations of adult bluefin tuna occurs in the Gulf of St . Lawrence , making it important for the management and conservation of the declining western population .
URI: http : / /hdl .handle .net /1969 .1 /ETD -TAMU -3265
Date: 2009-05-15

Citation

Natal origin of atlantic bluefin tuna (thunnus thynnus) from the gulf of st. lawrence using δ13c and δ18o in otoliths. Available electronically from http : / /hdl .handle .net /1969 .1 /ETD -TAMU -3265 .

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