[MARMAM] More on marine mammals vs fisheries interactions

Lyne Morissette lyne.morissette at globetrotter.net
Wed Aug 6 03:50:39 PDT 2008

Dear colleagues,

After my message posted last week, I received many requests and  
comments on our 'marine mammals vs fisheries' work. In line with  
that, I would thus want to recommend you this earlier paper on the  
same topic:

"The trophic role of marine mammals in the Northern Gulf of St.  


Lyne Morissette
Mike O. Hammill
Claude Savenkoff

This paper is available in Marine Mammal Science 22(1): 74-103  
(January 2006).

The trophic role of apex predators was evaluated in the northern Gulf  
of St. Lawrence ecosystem. An Ecopath model was developed for the  
1985-1987 period prior to the collapse of commercially exploited  
demersal fish stocks in this area. Marine mammal trophic levels were  
estimated by the model at 4.1 for cetaceans, 4.4 for harp seals  
(Phoca groenlandica), 4.7 for hooded seals (Cystophora cristata), 4.5  
for gray seals (Halichoerus grypus), and 4.3 for harbor seals (Phoca  
vitulina). Harp seals were the third most important predator on  
vertebrate prey following large Atlantic cod (Gadus morhua) and  
redfish (Sebastes spp.). Different seal species preyed on different  
levels of the food chain. Harp seals preyed on most trophic groups,  
whereas larger seals, such as gray seals and hooded seals, mainly  
consumed higher trophic levels. The model suggested that apex  
predators had a negative effect on their dominant prey, the higher  
trophic level fish, but an indirect positive feedback on the prey of  
their preferred prey, mainly American plaice (Hippoglossoides  
platessoides), flounders, skates, and benthic invertebrates. Our  
results suggest that both marine mammals and fisheries had an impact  
on the trophic structure.

Keywords: Ecosystem model, predation, harp seal, gray seal, harbor  
seal, hooded seal, cetaceans, predation, Gulf of St. Lawrence, food web.

PDF is also available upon request at: lyne.morissette at globetrotter.net.

Lyne Morissette, Ph.D.

Postdoctoral Fellow
Arizona State University
email: lyne.morissette at asu.edu
Fisheries Centre
University of British Columbia
e-mail: l.morissette at fisheries.ubc.ca

Lenfest Ocean Program

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