Natal origin of Atlantic bluefin tuna (Thunnus thynnus) from Canadian waters based on otolith δ¹³C and δ¹⁸O

Authors: Schloesser, Ryan W.; Neilson, John D.; Secor, David H.; Rooker, Jay R.

Source: Canadian Journal of Fisheries and Aquatic Sciences, Volume 67, Number 3, March 2010 , pp. 563-569(7)

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Abstract:

Increased knowledge of stock mixing and migration of Atlantic bluefin tuna (Thunnus thynnus) is required to properly manage and conserve declining populations. Here, we predicted the nursery origin of giant bluefin tuna (n = 224) present in samples from Canadian waters using stable δ¹³C and δ¹⁸O isotopes in otoliths. The isotopic composition of milled otolith cores (corresponding to the first year of life) of giant bluefin tuna from three decades (1970s, 1980s, 2000s) and three regions within or adjacent to the Gulf of St. Lawrence was compared with otolith δ¹³C and δ¹⁸O of yearling bluefin tuna collected from eastern (Mediterranean Sea - eastern Atlantic, n = 136) and western (western Atlantic, n = 103) nurseries. Maximum likelihood estimates indicated that greater than 99% of bluefin tuna in our Canadian samples originated from the western nursery. No significant differences in estimates of origin for bluefin tuna were detected among decades or among regions, suggesting little to no mixing of eastern and western populations in the Canadian samples examined. These findings justify the use of catch rates from the Gulf of St. Lawrence area as an index of abundance for the oldest members of the western population.

Il est nécessaire de mieux connaître le mélange des stocks et la migration des thons rouges (Thunnus thynnus) de l'Atlantique afin de mieux gérer et préserver ces populations en déclin. Nous avons déterminé la nourricerie d'origine de thons rouges géants (n = 224) provenant d'échantillons tirés des eaux canadiennes à l'aide des isotopes stables δ¹³C et δ¹⁸O dans les otolithes. La composition de cylindres centraux moulus d'otolithes (correspondant à la première année de vie) de thons rouges géants de trois décennies (les années 1970, 1980 et 2000) et de trois régions intérieures ou adjacentes du golfe Saint-Laurent a été comparée aux δ¹³C et δ¹⁸O des jeunes thons rouges de l'année récoltées dans les nourriceries orientales (Méditerranée - est de l'Atlantique, n = 136) et occidentales (ouest de l'Atlantique, n = 103). Les estimations de vraisemblance maximale indiquent que plus de 99 % des thons rouges dans les échantillons canadiens proviennent des nourriceries occidentales. Il n'y a pas de différence décelable dans les estimations d'origine des thons rouges entre les décennies ou entre les régions, ce qui laisse croire qu'il y a peu ou pas de mélange entre les populations orientales et occidentales dans les échantillons canadiens examinés. Ces constations justifient l'utilisation des taux de capture dans la région du golfe du Saint-Laurent comme indices d'abondance pour les membres les plus âgés de la population occidentale.

Document Type: Research article

Publication date: 2010-03-01

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Published continuously since 1901 (under various titles), this monthly journal is the primary publishing vehicle for the multidisciplinary field of aquatic sciences. It publishes perspectives (syntheses, critiques, and re-evaluations), discussions (comments and replies), articles, and rapid communications, relating to current research on cells, organisms, populations, ecosystems, or processes that affect aquatic systems. The journal seeks to amplify, modify, question, or redirect accumulated knowledge in the field of fisheries and aquatic science. Occasional supplements are dedicated to single topics or to proceedings of international symposia.
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