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Bycatch in the Pacific Tuna Purse Seine Fishery

May 2011

There has been considerable recent media coverage, particularly in the United Kingdom, of concerns about bycatch issues related to catching tuna with purse seine nets for canned tuna products.

Much of this media coverage is misplaced, as the tuna purse seine fishery has only limited bycatch issues related to sharks and juvenile tuna.  The two Regional Fisheries Management Organizations (RFMOs) that oversee management of the tuna purse seine fishery in the Pacific Ocean – the Inter-American Tropical Tuna Commission (IATTC) and the Western and Central Pacific Tuna Commission (WCPTC) – have taken steps to address these concerns.  A further complication is that tuna caught by longlining involves much higher rates and numbers of bycatch than tuna purse seining, yet little of this tuna is used for canning purposes.  Most is sold as fresh fish or fresh/frozen fish.

Claims of bycatch of marine mammals and sea turtles in the tuna purse seine fishery are exaggerated, except in the case of vessels that deliberately chase and encircle schools of dolphins with purse seine nets, a practice which does not conform to Dolphin Safe international standards.  Mexico, Venezuela and Colombia are the major countries that still fish “on dolphin” and therefore have very high bycatch of dolphins – such tuna should be avoided.

RFMO Policies to Reduce Bycatch:

The two RFMOs, the IATTC and the WCPTC, have put in place a number of policies to avoid bycatch of sharks, sea turtles, and juvenile tuna.  Media accounts have not mentioned these specific steps to avoid bycatch.

In 2008, the WCPTC updated their regulation requiring avoidance of encircling sea turtles with nets to the extent practical and release of sea turtles alive from purse seine nets (Conservation and Management Measure 2008-03).  The IATTC also established a similar regulation in 2007 (Resolution C-07-03).

Similarly, the IATTC updated their regulation in 2005 requiring release of sharks alive from purse seine nets (RESOLUTION C-05-03).  The WCPTC updated their regulations for live release of sharks from purse seine nets in 2010 (Conservation and Management Measure 2010-071). It also prohibits finning of sharks and dumping of shark bodies overboard.

Both the IATTC and the WCPTC have also imposed closures on purse seining during different times of the year, in order to reduce the catch of juvenile tuna and maintain viable stocks of tuna.  Again, these closures have not been reported in the media stories about bycatch and canned tuna. 

Sea Turtle Catch in Purse Seine Nets is Minimal:

Most sea turtles that are caught in purse seine nets are released alive, as per the regulations established by the IATTC and the WCPTC.

In the IATTC’s latest Annual Report (2008) in Table 3 (pp 47-50) are listed bycatch species in tuna purse seine nets.  The sea turtle catch is minimal (these are turtles that either were dead or seriously injured, as opposed to turtles that were caught and successfully released).  According to this report (which is based on 100% observer coverage of all IATTC tuna purse seiners), deaths of sea turtles totaled: 19 in 2006; 24 in 2007; and 5 in 2008.

The WCPTC prepared a summary of all bycatch data from onboard observers since 1994 for purse seine vessels (since 1992 for longline vessels) in the Western and Central Pacific Ocean (Non-Target Species Interactions with the Tuna Fisheries of the Western and Central Pacific Ocean, WCPFC-SC6-2010/EB-IP-8, 2010).  The key quote is: “The number of reported interactions between marine mammals, seabirds and turtles are insufficient for more complex analyses.”  In other words, sea turtles and marine mammals are so rarely found in nets that they are insignificant in terms of population effects. 

To claim that the purse seine fishery harms sea turtle populations with these small numbers is unscientific and misleading in the extreme. 

Shark and Ray Bycatch in Tuna Purse Seine Vessels are High, but Lower than Longline and Other Fisheries:

The IATTC 2008 Annual Report includes catch of sharks on Table 3, which shows that considerable number (46,000 in 2008) can be caught each year, despite IATTC policy requiring release.  Better enforcement of restrictions is clearly needed.

The WCPTC has lower numbers of sharks and rays observed in purse seine nets.  2,400 metric tonnes of sharks were observed in purse seine nets from 1994 to 2009 (Non-Target Species Interactions with the Tuna Fisheries of the Western and Central Pacific Ocean, WCPFC-SC6-2010/EB-IP-8, 2010, Table 4).  This is with low observer coverage, so the number of actual sharks killed is quite a bit higher.  But catch of sharks by longline fleets are far higher (14,029 metric tonnes; see Table 3) than with purse seines.

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