[MARMAM] New publication: interactions between marine mammals and cod fishery

Lyne Morissette lyne.morissette at globetrotter.net
Thu Jul 31 06:06:27 PDT 2008


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:  
lyne.morissette at globetrotter.net


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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