1 ICES CM 2008/J:18 The Gulf of St. Lawrence Marine Ecosystem: An Overview of its Structure and Dynamics, Human Pressures, and Governance Approaches Michel Gilbert Fisheries and Oceans Canada Maurice Lamontagne Institute 850, Route de la Mer Mont-Joli, Quebec Canada G5H 3Z4 Tel.: (418) 775-0604 Fax: (418) 775-0546 E-mail: [email protected] Réjean Dufour Fisheries and Oceans Canada Maurice Lamontagne Institute 850, Route de la Mer Mont-Joli, Quebec Canada G5H 3Z4 Tel.: (418) 775-0623 Fax: (418) 775-0740 E-mail: [email protected] The Estuary and Gulf of St. Lawrence (EGSL) represents one of the largest and most productive estuarine/marine ecosystems in Canada and in the world. However, the EGSL ecosystem is affected by a wide variety of human activities that pose significant threats to its integrity and the sustainable use of its resources. These include fisheries, navigation, mariculture activities, coastal development, recreational use (including marine mammal observation), climate change, and several land–based activities that occur along the EGSL shores and in coastal and upstream rivers and tributaries, including industrial and municipal activities, agriculture, and river damming (for water level control and hydropower). In 2005, the Government of Canada initiated the Oceans Action Plan (OAP) in order to implement an ecosystem-based management approach for five Large Ocean Management Areas (LOMAs), including the Estuary and Gulf of St. Lawrence. This presentation provides an overview of the EGSL ecosystem structure and functioning, as well as its human pressures, through a summary of the scientific tools that were developed within this initiative. As well, a brief description of governance approaches currently being developed in the area to implement these tools is also provided. The EGSL ecosystem is a large semi–enclosed sea that opens to the Atlantic Ocean through the Cabot Strait and the Strait of Belle Isle. Its most prominent feature is a long and continuous trough, the Laurentian Channel, which is over 300 m in depth and extends some 1250 km from 2 the continental shelf upstream to the mouth of the Saguenay Fjord, with two other channels branching off towards the Strait of Belle Isle and into Jacques Cartier Strait, north of Anticosti Island. In addition, the St. Lawrence River has the fourteenth largest drainage basin in the world, 2 3 -1 encompassing an area of 1 344 000 km with a mean annual discharge of 10 900 m s at Québec City. The Saguenay River and several coastal rivers along the shores of the Estuary and Gulf also contribute to significant freshwater inputs into the system, which represent more than half of the freshwater inputs runoff the entire Atlantic Coast of North America. The EGSL ecosystem is also strongly influenced by the presence of seasonal ice cover that initially forms in December in the Estuary and northern Gulf and extends towards the southern Gulf and Cabot Strait until late February-early March. The Estuary area near the mouth of the Saguenay Fjord remains ice–free most of the winter, because of strong upwelling and mixing processes that occur at the head of the Laurentian Channel. These features greatly influence the circulation, mixing and characteristics of water masses within the EGSL ecosystem. Over deep channel areas, the water column is strongly stratified, with three distinct layers (the surface layer, the cold intermediate layer (CIL) and the deeper water layer) except in winter when the surface layer merges with the CIL, resulting in a two- layer vertical structure. The presence of the CIL throughout the EGSL ecosystem originates from the intrusion of the Labrador Current through the Strait of Belle-Isle and local cooling within the Gulf during winter. Nutrients, essentially nitrate availability, are identified as the primary driver of the spring phytoplankton blooms over the entire EGSL ecosystem as well as for sporadic and/or season– long production events at specific sites. The important mechanisms that bring nutrients to the surface layers, where they become accessible for the primary producers, occur at different time scales and differ in the various regions of the St. Lawrence. In addition to the typical seasonal replenishment (from mixing processes) and depletion (production) of nutrients in surface waters, several important physical mechanisms are governing nutrient replenishment in surface waters and ultimately productivity in the EGSL ecosystem. These include tidal mixing, upwelling at the head of deep channels, wind–induced coastal upwelling, buoyancy–driven gyres and eddies, and the intrusion of Labrador waters through the Strait of Belle Isle. In 2006, an initiative was conducted to identify ecologically and biologically significant areas (EBSAs) that are associated with particular physical features in the EGSL ecosystem. The identification and characterization of EBSAs followed an analytical approach in which significant areas were mapped for particular physical processes as well as for seven biological components/compartments of the ecosystem (phytoplankton, zooplankton, meroplankton, benthic invertebrates, pelagic fish, demersal fish and marine mammals), based on criteria of uniqueness, aggregation, and fitness consequence. The areas identified for each biological component were then layered together to extract those that were most significant for several components. A total of ten EBSAs were identified, covering ca. 30 % of the surface of the EGSL, nine of which were associated with particular oceanographic features that may be responsible at least in part for their high level of significance. A second initiative was also initiated to identify species and community properties of ecological significance at the ecosystem level in the Estuary and Gulf of St. Lawrence. This initiative was 3 conducted through consultations among DFO scientists using three selection criteria (highly influential predators, forage species, structure-providing species). More than 70 species or group of species were reported as ecologically significant at the ecosystem level using these criteria, 32 of which were considered to be highly significant. Other species were also identified on the basis of the need to control their expansion and/or increased abundance (invasive and harmful/toxic species), for example the green crab and toxic algae. In contrast with EBSAs, the ecologically significant species (ESSs) that were identified in the EGSL ecosystem on the basis of their importance as highly influential predators are considered to be those species that exert a strong top-down control of biological productivity in the system. In the EGSL ecosystem, numerous human activities are occurring either within the system or around its drainage basin, including the Great Lakes. Several of these activities are generating pressures that are affecting the structure and dynamics of EBSAs and/or ESSs, with possible implications for ecosystem integrity. Fisheries. Commercial fisheries, including ground fish, pelagic and shellfish fisheries, marine plant and seal harvesting, target more than 50 species within the Estuary and Gulf of St. Lawrence. Moratoria placed on Atlantic salmon, Atlantic cod and redfish stocks during the early 1990s resulted in increased effort on a number of previously underutilized but potentially more valuable species, including snow crab, shrimp and lobster. Previous fishing practices (mainly bottom trawling) have been cited as contributing to the loss of marine habitat and depletion of a number of fish stocks. Climate change. The current and long-term effects of climate change on the structure and dynamics of the EGSL ecosystem are difficult to assess because of the large variability that naturally occurs in the system. However, recent evidence of long-term changes has started to emerge and provide some insight into physical and biological impacts of climate change. The most important change that occurred in recent decades relates to oxygen concentrations in deep waters of the EGSL ecosystem. It has been shown that the dissolved oxygen content of bottom waters in the Lower St. Lawrence Estuary was twice as high in the 1930s than in the 1990s. Between one half and two–thirds of the observed oxygen decline in the Lower St. Lawrence Estuary has been attributed to recent changes in the currents entering the Gulf from the Atlantic Ocean through the Laurentian Channel, as a result of climate change. The remainder of the oxygen decrease could be related to eutrophication (see below). Invasive species. The issue of invasive species has grown quite significantly in the EGSL ecosystem with the recent appearance of some species that are known to have caused huge environmental and socio-economic impacts elsewhere in the world. These species include the green crab ( Carcinus maenas ), the oyster thief ( Codium fragile ), the chinese mitten crab (Erocheir sinensis ), and several species of tunicates. At present, there are 21 species that can be stated with certainty to be invasive in the southern Gulf and eight more in the northern Gulf. However, most of the observed effects of these introductions are currently limited to socio- economic impacts (aquaculture), but evidence is growing that some of the introduced species in the EGSL ecosystem could cause significant impacts on the ecosystem, either through changes in biodiversity or loss of ecologically significant and valued species (including those already endangered or at risk). 4 Coastal eutrophication. The eutrophication