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Shark bycatch in the purse seine fishery

Posted by Mike Crispino
1 November 2012

In a recent blog post, the authors of a study on FADs & bycatch wrote that “After the sustainability of tuna stocks, the most pressing issue facing the commercial fishing industry is the management and mitigation of bycatch of non-target species.” Digging a bit deeper, the numbers show that  81-95% of bycatch is made of non-commercial tuna and bony fish, all considered to be fast growing with early sexual maturity and high fecundity.

Aside from small fish, two species of sharks are taken as bycatch in FAD fisheries – silky sharks (Carcharhinus falciformis, Carcharhinidae) and oceanic white tip sharks (C. longimanus, Carcharhinidae), with roughly 90% of the sharks captured being silky.

I thought it would be interesting to take the data from the study and illustrate how shark bycatch stacked up on two fronts – against shark bycatch in FAD-free fisheries and  from ocean region to ocean region. Take a look:

When you look at the infographic keep in mind that 73% of the world’s tuna comes from the Pacific, where there is marginal difference in the bycatch of sharks among FAD and FAD-free fisheries.

But as the study makes clear, although purse seine fishing on FADs is not responsible for the major fishing mortality of silky and oceanic white tip sharks, research efforts to limit their mortality in FAD fisheries is needed and improved RFMO measures should be put in place as more is learned.

 



2 Responses to “Shark bycatch in the purse seine fishery”

  1. Svein Fougner says:

    it would be interesting to see comparable numbers for catch of bigeye in purse seine sets with and without FADs in different ocean areas. Thanks.

  2. From our technical report 2011-03 (http://iss-foundation.org/resources/downloads/?did=147): “In
 general,
 FAD
 target
 catches
 are
 comprised
 of
 skipjack
 tuna
 (from
 57%
 to
 82%
 depending
 on
 ocean
 region
 ‐
 see
 Figure
 1),
 but
 also
 yellowfin
 and
 bigeye
 tuna.
 Combining 
all 
Oceans,
 the
 catches
 in
 FAD
 sets 
are 
75%
 SKJ, 
16% 
YFT, 
and 
9% 
BET.
 Sets
 on
 free‐swimming
 schools
 are
 often
 mono‐specific
 (but
 not
 always).
 Skipjack
 and
 yellowfin
 tuna
 represent
 the
 main
 catch
 on
 free‐swimming
 schools.
 There
 is
 more
 variability
 by
 ocean
 region
 in
 free
 school
 sets
 than
 in
 FAD
 sets
 (Figure
 2).
 For
 example,
 the
 catch
 of
 skipjack
 varies
 between
 19%
 and
 77%
 in
 free
 school
 sets.
 Combining
 all
 Oceans,
 the
catches
 in 
free 
school
 sets 
are 
63% 
SKJ, 
35%
 YFT, 
and 
2% 
BET.
”

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