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Tuna be, or not tuna be : using catch data to observe the ecological impacts of commercial tuna fisheries in the Pacific Ocean at varying spatial scales

University of British Columbia

Tuna are arguably the world’s most valuable, versatile, yet vulnerable fishes. With current landings over 4 million tonnes annually, all species of tuna from all three major ocean basins are caught, traded, and consumed at various intensities around the globe. Understanding the implications of such an extensive industry is paramount to protecting the long-term health and sustainability of both the tuna fisheries as well as the ecosystems in which they operate. Given that the Pacific Ocean accounts for roughly two-thirds of the global commercial tuna catch, this thesis assesses the trends and ecological impacts of commercial tuna fishing at both the artisanal and industrial scale in this ocean. To observe the importance of tuna fisheries at a local scale, a case study of the Galápagos Islands is presented. In this context, it was observed that over-fishing and the subsequent depletion of large, low fecund serranids has resulted in a high level of ‘fishing down’ within the near-shore ecosystem. Consequently, as fishers are forced to expand to regions off-shore, tuna and coastal scombrids are becoming increasingly targeted. With regard to industrial fishing, tuna vessels (especially distant-water longliners) are known to generate a substantial amount of associated bycatch and discards. The second component of this thesis quantified the amount of bycatch (retained and discarded) generated by Pacific tuna fishing fleets from 1950 to 2010. Unreported retained bycatch amounted to 1.4 million t; the total discarded catch associated with tuna fishing was 3.6 million t of target species and 7.9 million t of non-target species; sharks were the most commonly discarded species. These totals represent about 14% of the reported landings during this time. Lastly, an analysis of the applicability of the ‘Catch-MSY’ method developed by Martell and Froese (2012) in the context of large pelagic fishes is presented. It was observed that this method produces MSY estimates highly correlated to those produced by complete stock assessments. Collectively, the results of this thesis suggest that the tools to adequately manage tuna exist; however, proper data collection is rare, and the implementation of adequate sustainable fishing measures by fisheries managers is still wanting.

Text

2014-08-21

Attribution-NonCommercial-NoDerivs 2.5 Canada

http://hdl.handle.net/2429/50110

Zoology

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/2.5/ca/