Dear colleagues,
A new paper was recently published in the book "Ecosystem Ecology
Research Trends" (Editors J. Chen and C. Guo, ISBN: 97816041838):
"Interactions between marine mammals and fisheries: implications for
cod recovery"
by:
Claude Savenkoff
Lyne Morissette
Martin Castonguay
Douglas P. Swain
Mike O. Hammill
Denis Chabot
J. Mark Hanson
ABSTRACT:
Abundance of many Atlantic cod (Gadus morhua) and groundfish stocks
in the Northwest Atlantic declined to low levels in the early 1990s,
resulting in cessation of directed fishing for these stocks, thus
ending one of the largest and longest running commercial groundfish
fisheries in the world. The stocks of the northern (nGSL) and
southern Gulf of St. Lawrence (sGSL) were closed to directed cod
fishing from 1994 to 1996 for the nGSL and from 1993 to 1997 for the
sGSL, followed by the opening of a small directed fishery in the two
systems. In the northern Gulf of St. Lawrence, the ecosystem biomass
structure shifted dramatically from one dominated by demersal fish
predators (Atlantic cod Gadus morhua, redfish Sebastes spp.) and
small-bodied forage species (capelin Mallotus villosus, mackerel
Scomber scombrus, herring Clupea harengus, northern shrimp Pandalus
borealis) to one now dominated by only small-bodied forage species.
The decline of large predatory fishes has left only marine mammals as
top predators during the mid-1990s, and marine mammals and Greenland
halibut Reinhardtius hippoglossoides during the early 2000s. Large
changes also occurred in the biomass structure and ecosystem
functioning of the adjacent southern Gulf of St Lawrence (sGSL) but
they were not as dramatic. Although predatory fishes decreased
between the mid-1980s and mid-1990s, and prey consumption by seal
species increased considerably, large cod remained among the most
important single predators on fish in the sGSL. The changes in top-
predator abundance driven by human exploitation of selected species
resulted in a major perturbation of the structure and functioning of
both Gulf ecosystems and represent a case of fishery-induced regime
shift. Overfishing influenced community biomass structure directly
through preferential removal of larger-bodied fishes and indirectly
through predation release. Species interactions are central to
ecosystem considerations. In marine ecosystems, predation can be the
major ecological process affecting fish populations and piscivory is
often the largest source of fish removal, usually larger than fishing
mortality. In both northern and southern Gulf ecosystems, predation
mortality exceeded fishing mortality for most groups in recent years
because fishing mortality was intentionally reduced by fisheries
closures. Seals have benefited from reduced hunting (harvesting and
culling/bounties) since the 1970s. Consumption of fish by marine
mammals exceeded consumption by predatory fishes in the two
ecosystems in the recent time periods. Since the collapse of
groundfish stocks, commercial fisheries and seals have become
important predators on predatory fishes possibly slowing their
recovery. In recent years, consumption by seals shifted towards
species at lower trophic level (forage fishes and invertebrates),
which were also the main target of fisheries. Thus, commercial
fisheries and seals may have become important competitors of
predatory fishes for the same resource.
PDF is available upon request to Lyne Morissette:
[EMAIL PROTECTED]
Lyne Morissette, Ph.D.
Postdoctoral Fellow
Arizona State University
&
Fisheries Centre
University of British Columbia
Lenfest Ocean Program
http://www.lenfestocean.org/whales_fisheries.html
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