[MARMAM] new paper on bycatch and California sea lions

Manuela Gonzalez Suarez manuela.gonzalez at asu.edu
Fri Jul 18 07:15:47 PDT 2008

Dear colleagues,

A new paper on estimating fishing and bycatch rates for California sea lions
was recently published in Conservation Biology.

You can send PDF requests to: jared.underwood at asu.edu

Jared G. Underwood, Claudia J. Hernandez-Camacho, David Aurioles-Gamboa, and
Leah R, Gerber (2008). Estimating sustainable bycatch rates for California
sea lion populations in the Gulf of California. Conservation biology, 22

*Abstract: *Commercial and subsistence fisheries pressure is increasing in
the Gulf of California, Mexico. One consequence often associated with high
levels of fishing pressure is an increase in bycatch of marine mammals and
birds. Fisheries bycatch has contributed to declines in several pinniped
species and may be affecting the California sea lion (Zalophus californianus)
population in the Gulf of California. We used data on fisheries and sea lion
entanglement in gill nets to estimate current fishing pressure and fishing
rates under which viable sea lion populations could be sustained at 11
breeding sites in the Gulf of California. We used 3 models to estimate
sustainable bycatch rates: a simple population-growth model, a demographic
model, and an estimate of the potential biological removal. All models were
based on life history and census data collected for sea lions in the Gulf of
California. We estimated the current level of fishing pressure and the
acceptable level of fishing required to maintain viable sea lion populations
as the number of fishing days (1 fisher/boat setting and retrieving 1 day's
worth of nets) per year. Estimates of current fishing pressure ranged from
101 (0–405) fishing days around the Los Machos breeding site to 1887
(842–3140) around the Los Islotes rookery. To maintain viable sea lion
populations at each site, the current level of fishing permissible could be
augmented at some sites and should be reduced at other sites. For example,
the area around San Esteban could support up to 1428 (935–2337) additional
fishing days, whereas fishing around Lobos should be reduced by at least 165
days (107–268). Our results provide conservation practitioners with
site-specific guidelines for maintaining sustainable sea lion populations
and provide a method to estimate fishing pressure and sustainable bycatch
rates that could be used for other marine mammals and birds.

* *

*Keywords: *bycatch, California sea lion, fisheries, gill-net entanglement,
Gulf of California, population viability, Zalophus californianus


"I have never let my schooling interfere with my education"
Mark Twain
Manuela Gonzalez
SOLS Biology Graduate Program
P.O Box 874601 ASU Tempe, AZ 85287-4601
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