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Bibliography of the Maurice Lamontagne Institute

Lyne MORISSETTE

MORISSETTE, L., M.O. HAMMILL, 2011. A preliminary evaluation of the impacts of Grey Seal, (Halichoerus grypus), predation on the 4T ecosystem and possible effects of their removal on Cod (Gadus morhua) recovery ; Évaluation préliminaire des impacts de la prédation par le phoque gris, (Halichoerus grypus), sur l'écosystème 4T et des effets possible d'un abattage sur le rétablissement des stocks de morue (Gadus morhua). DFO, Canadian Science Advisory Secretariat, Research Document ; MPO, Secrétariat canadien de consultation scientifique, Document de recherche, 2011/016, 31 p .

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In this research document, we use an Ecopath with Ecosim (EwE) model to examine the trophic role of grey seals in the southern Gulf of St. Lawrence ecosystem and assess their direct and indirect impacts on Atlantic cod populations and other species interconnected with them. We assumed different feeding scenarios for grey seals, and simulated to which extent reducing their population is likely to affect the recovery of Atlantic cod. 11 harvest scenarios were tested. Our results suggest that the removal of seals could help the recovery of cod in some circumstances, but additional work is needed to tune the model to better mimic the decline in the southern Gulf of St. Lawrence cod stock, to examine how long recovery might take, to examine a strategy where seals in areas of high overlap with cod could be targeted, examine the impacts of removals on other depleted stocks of hake, and skate and potential effects on other ecosystem components including other fisheries. Additional scenarios need to be examined to explore a more complete range of possible outcomes under different grey seal removal strategies.

MORISSETTE, L., M. CASTONGUAY, C. SAVENKOFF, D.P. SWAIN, D. CHABOT, H. BOURDAGES, M.O. HAMMILL, J. MARK HANSON, 2009. Contrasting changes between the northern and southern Gulf of St. Lawrence ecosystems associated with the collapse of groundfish stocks. Deep-Sea Res., Part II, Top. Stud. Oceanogr., 56(21-22): 2117-2131 .

In order to have a global view of ecosystem changes associated with the collapse of groundfish species in the Gulf of St.Lawrence during the early 1990s, Ecopath mass balance models were constructed in corporating uncertainty in the input data.These models covered two ecosystems (northern and southern Gulf of St.Lawrence; NAFO divisions 4RSand 4T), and two time periods (before the collapse, in the mid-1980s, and after it, in the mid 1990s). Our analyses revealed that the ecosystem structure shifted dramatically from one previously dominated by piscivorous groundfish and small-bodied forage species during the mid-1980s to one now dominated only by small-bodied pelagic species during the mid-1990s in both southern and northern Gulf.The species structure in the northern Gulf versus southern Gulf was different, which may explain why these two ecosystems did not recover the same way from the collapse in the early1990s. Productivity declined in the northern Gulf after the collapse but increased in the southern Gulf. The collapse of groundfish stocks resulted in declines in the mean trophic level of the landings in both the northern and the southern Gulf. Even though fishing mortality was then intentionally reduced, this part of the total mortality was taken up by predation.The temporal changes in the internal structure of both ecosystems are reflected in their overall emergent properties.©2009 Elsevier Ltd.

MORISSETTE, L., M. CASTONGUAY, C. SAVENKOFF, D.P. SWAIN, D. CHABOT, H. BOURDAGES, M.O. HAMMILL, J.M.HANSON, 2008. Contrasting changes between the northern and southern Gulf of St. Lawrence ecosystems associated with the collapse of groundfish stocks. Deep-Sea Res., Part II , Top. Stud. Oceanogr. [ARTICLE IN PRESS] .

In order to have a global view of ecosystem changes associated with the collapse of groundfish species in the Gulf of St. Lawrence during the early 1990s, Ecopath mass-balance models were constructed incorporating uncertainty in the input data. These models covered two ecosystems (northern and southern Gulf of St. Lawrence; NAFO divisions 4RS and 4T), and two time periods (before the collapse, in the mid-1980s, and after it, in the mid-1990s). Our analyses revealed that the ecosystem structure shifted dramatically from one previously dominated by piscivorous groundfish and small-bodied forage species during the mid-1980s to one now dominated only by small-bodied pelagic species during the mid-1990s in both southern and northern Gulf. The species structure in the northern Gulf versus southern Gulf was different, which may explain why these two ecosystems did not recover the same way from the collapse in the early 1990s. Productivity declined in the northern Gulf after the collapse but increased in the southern Gulf. The collapse of groundfish stocks resulted in declines in the mean trophic level of the landings in both the northern and the southern Gulf. Even though fishing mortality was then intentionally reduced, this part of the total mortality was taken up by predation. The temporal changes in the internal structure of both ecosystems are reflected in their overall emergent properties. ©2008 Elsevier Ltd.

SAVENKOFF, C., L. MORISSETTE, M. CASTONGUAY, D.P. SWAIN, M.O. HAMMILL, D. CHABOT, J.M. HANSON, 2008. Interactions between marine mammals and fisheries: implications for cod recovery FOR COD RECOVERY. Pages 107-151 in J. Chen & C. Guo (ed.). Ecosystem Ecology Research Trends. Nova Science Publishers .

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.©2008 Nova Science Publishers, Inc.

SAVENKOFF, C., M. CASTONGUAY, D. CHABOT, M. O. HAMMILL, H. BOURDAGES, L. MORISSETTE, 2007. Changes in the northern Gulf of St. Lawrence ecosystem estimated by inverse modelling : evidence of a fishery-induced regime shift?. Estuar. Coast. Shelf Sci., 73(3-4): 711-724 .

Mass-balance models have been constructed using inverse methodology for the northern Gulf of St. Lawrence for the mid-1980s, the mid-1990s, and the early 2000s to describe ecosystem structure, trophic group interactions, and the effects of fishing and predation on the ecosystem for each time period. Our analyses indicate that the ecosystem structure shifted dramatically from one previously dominated by demersal (cod, redfish) and small-bodied forage (e.g., capelin, mackerel, herring, shrimp) species to one now dominated by small-bodied forage species. Overfishing removed a functional group in the late 1980s, large piscivorous fish (primarily cod and redfish), which has not recovered 14 years after the cessation of heavy fishing. This has left only marine mammals as top predators during the mid-1990s, and marine mammals and small Greenland halibut during the early 2000s. Predation by marine mammals on fish increased from the mid-1980s to the early 2000s while predation by large fish on fish decreased. Capelin and shrimp, the main prey in each period, showed an increase in biomass over the three periods. A switch in the main predators of capelin from cod to marine mammals occurred, while Greenland halibut progressively replaced cod as shrimp predators. Overfishing influenced community structure directly through preferential removal of larger-bodied fishes and indirectly through predation release because larger-bodied fishes exerted top-down control upon other community species or competed with other species for the same prey. Our modelling estimates showed that a change in predation structure or flows at the top of the trophic system led to changes in predation at all lower trophic levels in the northern Gulf of St. Lawrence. These changes represent a case of fishery-induced regime shift. ©2007 Elsevier Ltd.

SAVENKOFF, C., D.P. SWAIN, J.M. HANSON, M. CASTONGUAY, M.O. HAMMILL, H. BOURDAGES, L. MORISSETTE, D. CHABOT, 2007. Effects of fishing and predation in a heavily exploited ecosystem : comparing periods before and after the collapse of groundfish in the southern Gulf of St. Lawrence (Canada). Ecol. Model., 204(1-2): 115-128 .

Mass-balance models, using inverse methodology, were applied to the southern Gulf of St. Lawrence for the mid-1980s and the mid-1990s to describe ecosystem structure, trophic group interactions, and the effects of fishing and predation on the ecosystem for periods preceding and following the collapse of groundfish stocks in this area. These models were used to determine how the ecosystem changed, and whether its structure and functioning were affected by the observed changes in key species between the two time periods. Our analyses indicate that the ecosystem structure shifted dramatically from one previously dominated by piscivorous groundfish and small-bodied forage species (e.g., capelin, herring, and shrimp) in similar proportions to one now dominated by small-bodied forage species. Overfishing removed a functional group, large-bodied demersal predators that has not been replaced 12 years after the cessation of heavy fishing, and left marine mammals such as seals and cetacea as top predators of many species (especially fishes) during the mid-1990s. Predation by marine mammals on fish increased from the mid-1980s to the mid-1990s while predation by large fish on fish decreased. A change in the prey of seals from juvenile cod to capelin occurred between the models for the mid-1980s and the mid-1990s consistent with observed shifts in the abundance of the two prey species between the two time periods. These major changes were accompanied by a decrease in total catches and a transition in landings from long-lived and piscivorous groundfish toward planktivorous pelagic fish and invertebrates. ©2007 Elsevier B.V.

MORISSETTE, L., M.O. HAMMILL, C. SAVENKOFF, 2006. The trophic role of marine mammals in the northern Gulf of St. Lawrence. Mar. Mamm. Sci., 22(1): 74-103 .

The trophic role of apex predators was evaluated in the northern Gulf of St. Lawrence ecosystem. An Ecopath model was developed for the period 1985-1987 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 (Pagophilus groenlandicus), 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.7copy; 2006 Society for Marine Mammalogy.

SAVENKOFF, C., M. CASTONGUAY, R. METHOT, D. CHABOT, M.O. HAMMILL, 2005. Input data and parameter estimates for ecosystem models of the northern Gulf of St. Lawrence (2000-2002). Can. Tech. Rep. Fish. Aquat. Sci., 2588, 96 p .

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Mass-balance models were used to reconstruct trophic flows through the whole northern Gulf of St. Lawrence ecosystem (NAFO divisions 4Rs) for the 2000-2002 period. The whole-system model of the northern Gulf of St. Lawrence is divided into 31 functional groups or compartments from phytoplankton and detritus to marine mammals and seabirds, including harvested species of pelagic, demersal, and benthic domains. We present here details of the input data (biomass, production, consumption, export, and diet composition) for each compartment used for modelling. The parameter estimates from inverse modelling are also shown for comparisons. The successful development of ecosystem models will provide powerful new tools to evaluate the impact of human and environmental factors on marine ecosystems

SAVENKOFF, C., M. CASTONGUAY, A.F. VÉZINA, S.-P. DESPATIE, D. CHABOT, L. MORISSETTE, M.O. HAMMILL, 2004. Inverse modelling of trophic flows through an entire ecosystem: the northern Gulf of St. Lawrence in the mid-1980s. Can. J. Fish. Aquat. Sci., 61: 2194-2214 .

Mass-balance models using inverse methodology have been constructed for the northern Gulf of St. Lawrence ecosystem in the mid-1980s, before the groundfish collapse. The results highlight the effects of the major mortality 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 (Sebastesspp.), capelin (Mallotus villosus), and fisheries. Large cod were the most important predator of small cod, with cannibalism accounting for at least 44 % of the mortality 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 dominated 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 substantially underestimated in the mid-1980s, just before the demise of a cod stock that historically was the second largest in the northwest Atlantic.©2004 NRC Canada

SAVENKOFF, C., H. BOURDAGES, M. CASTONGUAY, L. MORISSETTE, D. CHABOT, M. HAMMILL, 2004. Input data and parameter estimates for ecosystem models of the northern Gulf of St. Lawrence (mid-1990s). Can. Tech. Rep. Fish. Aquat. Sci., 2531, 93 p .

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In the present study, we use Ecopath and inverse methods to reconstruct trophic flows through the whole northern Gulf of St. Lawrence ecosystem (NAFO zones 4RS) for the mid-1990s period, prior to the groundfish stock collapse. This was a period of relatively constant biomass for the major species. The whole-system model of the northern Gulf of St. Lawrence is divided into 32 functional groups or compartments from phytoplankton and detritus to marine mammals and seabirds, including harvested species of pelagic, demersal, and benthic domains. We present here details of the input data (biomass, production, consumption, export, and diet composition) for each compartment used for modelling. the successful development of ecosystem models proposed by the Comparative Dynamics of Exploited Ecosystems in the Northwest Atlantic (CDEENA) program will provide powerful new tools to evaluate the impact of human and environmental factors on a variety of Atlantic shelf ecosystems.

SAVENKOFF, C., H. BOURDAGES, D.P. SWAIN, S.-P. DESPATIE, J.M. HANSON, R. MÉTHOT, L. MORISSETTE, M.O. HAMMILL, 2004. Input data and parameter estimates for ecosystem models of the southern Gulf of St. Lawrence (mid-1980s and 1990s). Can. Tech. Rep. Fish. Aquat. Sci., 2529, 105 p .

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In the present study, we use Ecopath and inverse methods to reconstruct trophic flows through the whole northern Gulf of St. Lawrence ecosystem (NAFO zones 4RS) for the mid-1990s period, prior to the groundfish stock collapse. This was a period of relatively constant biomass for the major species. The whole-system model of the northern Gulf of St. Lawrence is divided into 32 functional groups or compartments from phytoplankton and detritus to marine mammals and seabirds, including harvested species of pelagic, demersal, and benthic domains. We present here details of the input data (biomass, production, consumption, export, and diet composition) for each compartment used for modelling. the successful development of ecosystem models proposed by the Comparative Dynamics of Exploited Ecosystems in the Northwest Atlantic (CDEENA) program will provide powerful new tools to evaluate the impact of human and environmental factors on a variety of Atlantic shelf ecosystems.

MORISSETTE, L., S.-P. DESPATIE, C. SAVENKOFF, M.O. HAMMIL, H. BOURDAGES, D. CHABOT, 2003. Data gathering and input parameters to construct ecosystem models for the nothern Gulf of St. Lawrence (mid-1980s). Can. Tech. Rep. Fish. Aquat. Sci., 2497, 94 p .

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In the present study, we use Ecopath and inverse methods to reconstruct trophic flows through the whole northern Gulf of St. Lawrence ecosystem (NAFO zones 4RS) for the middle 1980s period, prior to the groundfish stock collapses. This was a period of relatively constant biomass for the major species. The whole-system model of the northern Gulf of St. Lawrence is divided into 32 functional groups or compartments from phytoplankton and detritus to marine mammals and seabirds, including harvested species of pelagic, demersal, and benthic domains. We present here details of the input data (biomass, production, consumption, export and diet composition) for each compartment used for modelling. The successful development of Northwest Atlantic (CDEENA) program will provide powerful new tools to evaluate the impact of human and environmental factors on a variety of Atlantic shelf ecosystems.