Issues in Shrimp Trawl Bycatch and BRDs
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The tropical penaeid shrimp species constitute a substantial portion of the
total world shrimp and prawn catch. Trawling which is the most dominant
benthic sea fishing, isprobably the least selective. This exercabate the
bycatch(catch incidentalto the target species catch) problem. The bycatch is
usually discarded. Thejuviniles of the target species is now deemed as
bycatch as they are alsodiscarded-a practice which threatens the maintenance
of biodervisity and
long term sustainability (FAO,1995).The bycatch problem in the first place
arises when different species with different sizes, body shapes and fleeing
behaviour occur on the same fishing ground. I reckon it's as old as the then
art of fishing itself. As most fisheries resources in the world are fully
exploited or overexploited, the large discarded quantity (estimated at 25
million toones) represent the most significant source available to increase
marine harvest levels. Introduction of better management regimes eg.
shifting exploitation patterns towards larger individuals by using size
selective fishing gears and techniques is another way to increase yields
from the sea.In the shrimp trawl fishery, the bycatch problem is even more
pronounced because of ususally the huge market price of shrimp as compared
to other species in the shrimp trawl catch. The tendency is to reserve the
preservation and storage space for shrimp therefore other species have to be
sent overboard if utilization programs are not in place. Shrimp is a low
volume high value species. For the internal rate of return (IRR)to remain
positive, long periods are spent at sea to obtain a substantial volume of
shrimp catch. The bycatch is therefore continiously discarded during the
fishing period.
In temperate countries, the distinct difference in size between shrimp and
fin fish species; the relatively few species and the passive behaviour of
shrimp enhances the development of gear and tecniques for catching one
species rather than another ie inter-specific selectivity. There is a large
number of different species on the same ground with shrimp in tropical
waters. Moreover, a size overlap between shrimp and fin fish have been
observed. This make inter-specific selectivity unattainable in warm waters.
In as much as a substantial proportion of global shrimp supplies originate
from the tropics, the bycatch problem is as acute. But ironically, most
studies on selectivity of shrimp trawls for bycatch reduction have been and
is being done in higher lattitudes. Selective gear and techniques used in
higher latitudes are not readily transferable to tropical waters as the
success of a selective gear depends on the application of design appropriate
to the fauna and fishing techniques used in a given fishery. Encouragement
and support in this area is urgently needed. A logical approach to fishing
gear selectivity in warm waters should focus on size selectivity. The
fishing mortality of the juvinile component of the stock would be alleviated
and growth over fishing brought undre control. Higher yields per recruit
will be obtained while sorting time reduced during fishing operations. As
size selectivity only ensures the exclusion of certain predetermined sizes
form the catch, the bycatch and discard problem is not completely overcome
by size selective gears. Bycatch utilisation progrms must be developed and
instituted to address this problem of waste admist hunger in the
tropics.
After years of experimenting with soft sorting devices(meshed net screen)
tangling, gilling and clogging problems coupled with illegal modification of
the flexible panels militated against their operational success as a
separator device. Moreover, size may not be the only factor in size
selectivity of shrimp. The many appendages of shrimp may make them prone to
becoming entangled in the net. The operational inadequacies of the nets
induced the testing of hard sorting devices; for example to exclude
turtles(TEDS)in the gulf of mexico shrimp fishery in the late 70's (Ogren et
al., 1977; Seidel, 1979; Siedel and Watson,1978 ; etc etc etc) which kicked
off the development of bycatch reduction devices(BRDs) throughout those
years and more recently, the development and introduction of a very
successful BRD, NORDM=D8RE grid( a rigid separator device for inter-specific
selectivity) used in separating shrimp from fish in the pandalus borealis
shrimp fishery (see Isaksen et al., 1992). A tropicalised multi-species
fishery versions of the nordm=F8re grid adapted for size selectivity (Top
grid) have been recently tested in tropical waters (Mahika, 1992; Isaksen
and Larsen, 1993 , Isaksen et al., 1995 ; Baio, 1996....analysis in
progress). Reported studies indicate the potential of top grid to replace
mesh size regulations in the tropics.
Although aquaculture accounted for 30% of the global marine supplies by
1992, an increase form less than 4% to 7% betwween 1984 and 1992,(FAO, 1995)
the future of the sector's sustainable contribution to shrimp supplies is
questionable. The concern of a host of authors is that rapid expansion of
intensive commercial shrimp farming in it's present form in coastal areas of
a given country can only be sustained for a couple of decades at most before
diseases associated with self pollution causes drastic decreases in
production. The capture of wild shrimp may remain to be the most economic
and environmentally sustainable method of shrimp production. This would be
true only if the resource is sustainingly utilized in harmony with the
environment and capture practices that are not harmful to the ecosystem,
resource or their quality are used. This embodies "Responsible Fishing".
This is what BRDs stand for. Let it be resposible fishing now and
forever.
Interested in multi-species BRDs for warm waters. Would appreciates
contributions ,leads, references etc.
Cheers,
Andrew.
IFM,UiB
HiB
N-5020
Bergen
Norway
Tel:4755584311(Dept) 4755276091(Home)
Fax:4755584450(Dept) 4755276030(Home)
E-mail:Andrew.Baio@ifm.uib.no
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Error of opinion maybe tolerated where resoning is left free to combat it.
(Thomas Jefferson,1743-1826).
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