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Shrimp Trawl Bycatch report available


Steve Branstetter <[log in to unmask]>


[log in to unmask]


Fri, 15 Aug 1997 16:19:02 -0700





text/plain (1 lines)

Please excuse multiple receipt of the following posting; to reach a wide
audience this message is being posted to several pertinent mail lists.
Thank you for your patience. -- SB

The Gulf and South Atlantic Fisheries Development Foundation, Inc.
(Foundation) announces the availability of the following technical

Branstetter, S. 1997. Bycatch and it reduction in the Gulf of Mexico
and South Atlantic shrimp fisheries.

The executive summary of this report is included below.

(((We have been contacted by the owner of a specific web site who is
interested in making an electronic copy, including graphics, available
on his site. We will make that information available if and when the
process is completed.)))

Until then, this report (27 pages, 5 tables, 21 figures) is available
for five dollars ($5.00 US) to cover the cost of processing requests and
getting them mailed out. Payment must be in US funds; personal checks
are fine, but credit card orders cannot be handled. The Foundation also
recognizes that it may be difficult for international parties to obtain
payment in U.S. funds; if so, please contact our office.

Other documents concerning Foundation activites are also available
through the Foundation office. For a complete list of available
reports, please contact us.

Branstetter, S. 1997. Bycatch and it reduction in the Gulf of Mexico
and South Atlantic shrimp fisheries. Gulf and South Atlantic Fisheries
Development Foundation, Inc., Tampa, Florida.


Concerns over the magnitude and species composition of bycatch,
discards, and incidental finfish mortality associated with shrimp
trawling prompted a 1990 amendment to the Magnuson Fishery Conservation
and Management Act that mandated the development of a Bycatch Reduction
Research Program. As part of a multi-organizational response to this
mandate, the Gulf and South Atlantic Fisheries Development Foundation,
Inc. (Foundation) coordinated the development of a strategic planning
document - A Research Plan Addressing Finfish Bycatch in the Gulf of
Mexico and South Atlantic Shrimp Fisheries. The long- term goal of this
comprehensive four-year plan was to provide reliable information about
bycatch in the southeast U.S. shrimp trawl fishery. Subsequently, the
Foundation focused its programmatic contribution on four of the eight
high-priority objectives outlined in that Plan:

        update and expand bycatch estimates temporally and spatially ("catch

        identify, develop, and evaluate gear options for reducing bycatch
("BRD evaluations"),

        provide continued cooperative oversight of research plan
implementation, and develop an information transfer and education
program for commercial shrimp fishers and other parties affected by
finfish bycatch ("information transfer"), and

        develop and operate a standardized data management system for the
cooperative research program

In 1993, the Foundation began placing observers aboard voluntarily
participating commercial shrimp trawlers to collect fishery-dependent
data concerning shrimp trawl bycatch. From 1993-1996,
Foundation-contracted observers logged 2,320 days aboard trawlers,
collecting information on 3,162 shrimp trawl tows. According to NMFS
Galveston, the programmatic partners' pooled dataset consists of ~5700
tows, thus Foundation generated data comprises about 55% of the total.
Characterization sampling by Foundation observers included 403 days in
the Gulf of Mexico collecting data on 479 shrimp trawl tows, 34 days in
the South Atlantic producing data for 34 tows, and an additional 14
days were logged monitoring the catch of 20 tows in the rock shrimp
fishery operating off the Atlantic Florida coast. Greater effort was
expended evaluating the exclusion efficiency of various bycatch
reduction devices (BRDs) and turtle-excluder-devices (TEDs). Observers
logged 1426 days in the Gulf of Mexico collecting data on 1696 tows
examining BRDs, and 244 tows examining TEDs. In the South Atlantic,
observers spent 443 days evaluating 689 BRD tows.

According to two separate NMFS analyses, over 450 and 150 taxa have been
identified in trawls from the Gulf of Mexico and South Atlantic
respectively; the average catch was 27 kg (~60 lb.) of biomass per hour
of trawling. The bycatch to shrimp catch ratios generated by these data
were in stark contrast to an often quoted ratio of 10:1. For the Gulf
of Mexico, the bycatch to shrimp ratio was 5:1, and for the South
Atlantic it was 4:1. More importantly, the generalization of a 10:1
bycatch ratio has been often misquoted to represent the finfish to
shrimp ratio when in fact, in the Gulf of Mexico the finfish to shrimp
ratio was 4.2:1, and in the South Atlantic the ratio was 2.8:1.

General ecological concerns aside, bycatch reduction has a more
pragmatic consequence for fishery management: alleviation of incidental
mortality on heavily fished finfish stocks. For example, juveniles of a
common Gulf of Mexico species (red snapper, Lutjanus campechanus) and a
common South Atlantic species (weakfish, Cynoscion regalis) have been
particularly identified as fishes impacted by shrimp trawling. Similar
impacts are hypothesized for two other species (king mackerel,
Scomboromorus cavalla, and Spanish mackerel, S. maculatus) which occur
in both the Gulf of Mexico and the South Atlantic. This juvenile
mortality is thought to effect recruitment to the fishable stocks, thus
restricting allocations for directed recreational and commercial fishing
efforts. The initial goal of the Bycatch Program was to reduce
incidental mortality on these species, and others, by 50%.

To address this goal, the Foundation evaluated the exclusion efficiency
of various bycatch reduction devices (BRDs) and turtle-excluder-devices
(TEDs). Two general types of BRDs were tested: fisheyes (cone-shaped
metal frames inserted into the codend webbing to provide an escape
hole), and expanded mesh (large square- hung mesh located in the front
of the codend usually encircling a funnel). Three different hard-grid
TEDs were tested either against each other or against a "naked" net (net
without a TED). Two soft TEDs were compared against naked nets and
against each other, and one was compared against a hard TED.

Fish exclusion and shrimp retention were very dependent upon the
placement and configuration of the BRD. A total of 12 different fisheye
configurations were tested; some configurations were represented by
minimal sample sizes and no analyses were conducted on the data. For
the Gulf of Mexico, we found that only one configuration - a 5" X 12"
placed 30 meshes back from the start of the codend - successfully met
mortality reduction goals for red snapper by eliminating 38% of the
individuals per net-hour; however there was a 6% shrimp loss associated
with this gear. Other fisheye configurations reduced the number of red
snapper by 20-25%, but none met the minimum 50% mortality reduction
criterion. Four configurations of expanded mesh were extensively
tested; three of these provided good fish exclusion, including red
snapper (10-25%), without an associated shrimp loss, but only one
configuration met the red snapper mortality reduction criterion. Other
limited testing occurred for four other BRD concepts; none of these
gears met the combined goals of shrimp retention and fish exclusion, but
two of them warrant further evaluations. For the South Atlantic, none
of the fisheye or expanded mesh configurations met the weakfish
reduction goals during Foundation tests; however when combined with
other researcher's data, the 5" X 12" fisheye at 30 meshes and the 3-bar
expanded mesh BRD did exclude 40% or more of the weakfish taken per
net-hour with less than a 5% difference in shrimp catch.

Most TED testing was against naked (no TED) nets in the offshore (> 15
fm) northwest Gulf of Mexico; other tests, comparing one TED to another,
were conducted over a wider area. Results of these tests indicated
hard-grid TEDs (Anthony Weedless, Georgia-grid, Super-Shooter, Seymore)
did not contribute substantially to the reduction of finfish catch; this
does not mean that they do not contribute to the mechanical exclusion of
large fishes, but that they did not tend to reduce the catch of smaller
fishes. Two soft TEDs (Morrison, Andrews 5") did have substantial
(40-60%) total finfish exclusion capabilities; the Andrews TED excluded
>70% of the red snapper, and the Morrison excluded ~25% of this species. TEDs have been mandated for several years now, and finfish mortality reductions attributable to soft TED use should be incorporated in the stock assessments for "key" species such as red snapper and weakfish, dependent upon the percent of the trawlers that have used soft TEDs over that time period.

Summary - The southeastern shrimp fishery may, in certain areas and at
certain times, have an unwanted bycatch far exceeding the targeted
shrimp catch. In recent years there has been a contribution to bycatch
reduction by the industry through their use of TEDs, and bycatch can be
further reduced through the use of BRDs. It is imperative, however,
that this contribution does not also induce an economic hardship through
a concurrent loss of shrimp from the catch. Otherwise, any benefits
stemming from enhancement of finfish stocks would be negated by the
additional burden on the shrimp industry. If this can be accomplished,
in the long-run, reduction of finfish bycatch in the shrimp fishery is
ecologically and economically beneficial to the southeast US fishing
industry, and thus to the general public and the nation.

Steve Branstetter, Ph.D., Program Director
Gulf & S. Atl. Fish. Develop. Fndn.
Ste. 997, Lincoln Cntr., 5401 W. Kennedy
Tampa, FL 33609
Phone 813-286-8390 FAX 813-286-8261
email: [log in to unmask]

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