2004 Inverse modelling of trophic flows through an entire ecosystem: the northern Gulf of St

• Main Authors: Claude Savenkoff, Martin Castonguay, Alain F. Vézina, Simon-pierre Despatie, Denis Chabot, Lyne Morissette, Mike O. Hammill
• Other Authors: The Pennsylvania State University CiteSeerX Archives
• Format: Text
• Language: English
• Subjects: Gadus morhua; Northwest Atlantic; Phoca groenlandica
• Online Access: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.514.7677; http://ccmtgc.mar.dfo-mpo.gc.ca/science/ocean/ecosystems/downloads/savenkoff04.pdf

Abstract: Mass-balance models using inverse methodology have been constructed for the northern Gulf of St. Law-rence ecosystem in the mid-1980s, before the groundfish collapse. The results highlight the effects of the major mortal-ity sources (fishing, predation, and other sources of mortality) on the fish and invertebrate communities. Main predators of fish were large cod (Gadus morhua) followed by redfish (Sebastes spp.), capelin (Mallotus villosus), and fisheries. Large cod were the most important predator of small cod, with cannibalism accounting for at least 44 % of the mortal-ity of small cod. The main predators of large cod were harp (Phoca groenlandica) and grey (Halichoerus grypus) seals. However, predation represented only 2 % of total mortality on large cod. Mortality other than predation domi-nated the mortality processes at 52 % of the total, while the fishery represented 46%. Tests were performed to identify possible sources of this unexplained mortality. The only way to significantly reduce unexplained mortality on large cod in the model was to increase landings of large cod above those reported. This suggests that fishing mortality was sub-stantially underestimated in the mid-1980s, just before the demise of a cod stock that historically was the second larg-est in the northwest Atlantic. Résumé: Des modèles d’équilibre de masse utilisant les méthodes inverses ont été construits pour représenter l’écosystème du nord du Golfe du Saint-Laurent dans le milieu des années 1980, avant l’effondrement des stocks de poissons de fond. Les résultats mettent en évidence les effets des principales causes de mortalité (pêche, prédation et