Download The Gulf of St. Lawrence Marine Ecosystem: An Overview of its

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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
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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,
encompassing an area of 1 344 000 km2 with a mean annual discharge of 10 900 m3 s-1 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 twolayer 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
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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 socioeconomic 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).
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Coastal eutrophication. The eutrophication of coastal waters also represents a growing issue in
the EGSL ecosystem. This is particularly the case in the southern Gulf of St. Lawrence, where
nutrients from agricultural sources present a significant problem. In addition, the current
expansion of shellfish aquaculture in several areas of the EGSL ecosystem has increased organic
matter fluxes in coastal waters, thus contributing to eutrophication in areas where this activity is
more intense. The fjord structure of some estuaries in the EGSL ecosystem causes conditions of
low water circulation and slow replenishment of oxygen which makes them particularly also
sensitive to increased organic loading and ultimately oxygen depletion. This is particularly the
case in the St. Lawrence Estuary where hypoxia conditions have been observed and expanded in
deep waters since the 1930s, in conjunction with an increase in organic matter fluxes towards the
bottom. While part of the increase in hypoxia conditions is known to be related to changes in the
origin of deep waters in the Laurentian Channel, it is hypothesized that eutrophication in the
St. Lawrence River and Upper Estuary is also responsible for the observed changes in hypoxia
conditions over the past decades.
Chemical contamination. In addition to local inputs of contaminants, the St. Lawrence marine
ecosystem receives and accumulates large amounts of contaminants that are exported from
heavily urbanised and industrialised centres of the Great Lakes and St. Lawrence River, both
through atmospheric transport and freshwater outflow from the St. Lawrence. The vast majority
of contaminants transported towards the St. Lawrence Estuary accumulate in sediments of the
Laurentian Channel, where topography and circulation patterns favour the deposition of
suspended particles and their associated chemical contaminants. Although there is some evidence
of biological effects of chemical contaminants in marine resources of the EGSL ecosystem, there
is yet no documented impact of contaminants on marine populations except for the well-studied
St. Lawrence beluga population. However, there is concern about the impacts of contaminants in
the EGSL ecosystem as a result of the presence and increase of new and emerging contaminants,
the additive effects of multiple contaminants in marine resources, and their interactions with
other environmental stresses.
Freshwater runoff modulations. The huge watershed of the Great Lakes and St. Lawrence
system drains a surface area of 1,5 × 106 km2, and thus forms the main freshwater supply to the
Estuary and Gulf of St. Lawrence. Much of this supply flows into the EGSL ecosystem through
the St. Lawrence River, (mean annual flow of 9 868 m3 s–1 at Sorel, Quebec), the remaining
inputs originating from the Saguenay Fjord and other coastal rivers. However, the major
tributaries of this watershed are regulated using different works designed for hydroelectricity
generation, flooding control, and irrigation as well as for recreational or industrial use, including
the St. Lawrence River. The impacts of these water flow regulation works have been discussed
from a more or less theoretical. Other studies have also looked at empirical evidence of links
between recruitment patterns in some marine populations and interannual variations of
freshwater inputs, with more or less success. Nevertheless, this issue requires some scientific
attention because of the importance of freshwater inputs on estuarine processes and the scale of
changes in freshwater runoff in the EGSL ecosystem.
Disturbance. The issue of disturbance came to attention only recently in the EGSL ecosystem,
although some of the human activities with disturbance potential have been occurring for many
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years in the EGSL ecosystem, namely navigation (recreational and commercial) and seismic
exploration (geological surveys). The major source of disturbance in the Estuary and Gulf of
St. Lawrence Estuary relates to marine traffic, including whale–watching activities, ferries,
recreational boating, and shipping. Oil and gas development in the Estuary and Gulf of
St. Lawrence is still in the exploration stages, primarily involving seismic surveys, but it has the
potential to become a major activity in the future. Disturbance is of importance mostly for
marine mammals, although some fish and macroinvertebrate species may also be affected.
In order to develop a governance structure for the integrated management of human activities
that drive these pressures, the OAP initiative for the EGSL ecosystem included the definition of
conservation objectives (COs). These COs would identify those components (areas, species) of
importance for ecosystem integrity which roles and functions should not be compromised by
human activities. Based on the EBSAs and ESSs that were identified within the system, a total of
more than 80 COs were first developed for the EGSL ecosystem, 39 of which were of high
priority. The formulation of each CO clearly identifies the targeted component, its role/function
in the ecosystem, as well as the need to prevent human activities from compromising this
role/function.
The development of COs represents a first step towards the establishment of an integrated
management approach at the ecosystem level (ecosystem-based management) of human
activities within the EGSL ecosystem. In this regard, these objectives should be viewed as the
conservation requirements to maintain the integrity of the ecosystem, with the appropriate
indicators and reference points. For each of the COs, socio-economic objectives should be
developed for human activities of significant concern with regards to their impacts on the
targeted component, in order to ensure that they will be managed in an integrated manner.
However, such an approach requires significant communication and coordination efforts among
all stakeholders involved, including government organizations, private interests, and non
governmental organizations (NGOs). At present, legal and management responsibilities for
conservation and socio-economic development around the EGSL ecosystem are shared between
three levels of government (federal, provincial, and municipal), including several federal
departments and five Canadian provinces (Quebec, New Brunswick, Prince Edward Island, Nova
Scotia, Newfoundland & Labrador), each with differing responsibilities and/or different
structures to address common ones. Coordination and communication efforts among these
various instances represent a huge challenge and a strategic plan is currently under development
for the implementation of governance approaches in support of the integrated management of
human activities within the EGSL ecosystem.