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. Lawrence"

by

Lyne Morissette

Mike O. Hammill

Claude Savenkoff

ABSTRACT

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@globetrotter.net.