From Primary Predator to Picked-on Prey: Shark Fishery in the Pacific Ocean

by Hannah Tannenbaum

In 2001 sharks were first listed as endangered species, and since then several measures have been enacted towards their protection. However, the majority of shark fishing is an incidental byproduct of purse seine and long-line fisheries which operate outside of national Exclusive Economic Zones (EEZ). Therefore the effectiveness of international treaties banning shark finning is hard to discern. Another major difficulty in assessing the effectiveness of conservation is the paucity of data on shark population size and structure. Clarke et al. (2013) collected and analyzed onboard observer data on shark catches from 1995–2010 in order to evaluate the threat to sharks from commercial fishing, and determine changes in shark populations after finning bans were established. The authors analyzed data on blue, oceanic whitetip, silky, and mako sharks because of their tendency to appear as bycatch in the Pacific tuna fishing industry. Through the analysis of observer data, no clear trend of reduced catches was found consistently for any species, any area, for either type of fishery. The authors suggest that shark retention bans may have a greater impact on population size than finning bans, and that management and monitoring must be made more consistent in order to properly evaluate conservation.

The Western and Central Pacific Fisheries Commission (WCPFC) did not require catch data for sharks until 2011 and observer records are inconsistent and unrepresentative of the whole fishery. Furthermore, there are few data from Chinese, Japanese, and Korean fleets that fish in their own EEZs or in international waters. Clarke et al. therefore combined observer data when available with catch-rate analysis to produce standardization models to determine confidence intervals related to catch rate. The authors also used observer data for size-indicator analyses using size as a proxy for age to determine if sharks caught were sexually mature or immature.

Observations were organized into five categories for analysis: retained, finned, discarded, escaped, and unknown. Unknown was removed from analysis. Retained implies the whole shark is kept to be utilized in its entirety versus finned in which the body might be tossed back and just the fin retained. Although the ban on finning was established in 2007, a comparison of before and after finning rates was not appropriate as the various participatory members are currently phasing in the ban gradually.

The results indicated different population and catch rate trends for each of the different fisheries, longline and purse sein, as well as between species of shark. Trends also varied between geographic regions over time. Overall, the oceanic whitetip sharks and blue sharks were found to be in decline over time, despite international efforts to curb shark finning. The authors suggest that the technology is currently not available to completely avoid shark bycatch, and that oceanic whitetip, silky, and mako sharks are more likely to be retained than finned. This evidence clearly shows the undermining of the bans on shark finning, and the authors suggests the ban on finning actually diverts away from efforts to assess population status and conservation. Instead they suggest that in addition to bans on finning and/or retention, there should be additional mandatory monitoring aboard fishing vessels in order to effectively monitor populations with greater precision and accuracy.

Clarke, S.C., Harley, S.J., Hoyle, S.D., Rice, J.S., 2013. Population trends in Pacific Oceanic sharks and the utility of regulations on shark finning. Conservation Biology 27, 197-209. Full text at http://bit.ly/1rH98Hg

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