L'importance des estuaires
Les estuaires sont des endroits où les poissons, les oiseaux et les
animaux de toutes sortes se réunissent pour se nourrir, trouver refuge,
croître jusqu'à l'âge adulte, et organiser leurs migrations.
Les estuaires sont des endroits uniques, fortement affectés par les
marées, où la terre, la rivière et la mer se fusionnent en un complexe
naturel dynamique. Même si au Canada Atlantique nous ne voyons pas de
forêts tropicales et peu de récifs coralliens, nous vivons parmi et à
côté de myriades d'estuaires qui soutiennent historiquement une
abondante vie sauvage.
coastal communities, the local "estuary" is called by any
number of names -- bay, sound, lagoon, inlet, river mouth, salt marsh.
include: Alewife, American eel, American sand lance, American
shad, Atlantic herring, Atlantic tomcod, Blueback herring, Cunner,
Longhorn sculpin, Mummichog, Ocean pout, Pollock, Rainbow smelt,
Rock gunnel, Silver hake, Spiny dogfish, White hake and Winter
Shellfish include: Blue mussel, Green crab, Green sea urchin, Northern shrimp, Sea scallop, Sevenspine bay shrimp and
Softshell clam (NOAA, 1994).
Habitat Lost: Taking the Pulse
of Estuaries in the Canadian Gulf of Maine
The Importance of
Harvey, J., D. Coon and J. Abouchar
"Habitat Lost: Taking the pulse of estuaries
in the Canadian Gulf of Maine." Fredericton:
Conservation Council of New Brunswick Inc.
the Atlantic coast, estuaries are among the most important coastal
features, both ecologically and with respect to human settlement and use
(Environment Canada, 1987). Estuaries are semi enclosed bodies of water
formed when fresh water from rivers and coastal streams flows into and
mixes with salt water of the ocean. The fresh water is slowed from
streaming into the open ocean by either surrounding mainland,
peninsulas, barrier islands, or fringing salt marshes. This mixing of
fresh and salt water creates a transition zone between land and sea
known as an estuary. These are places where fish, birds and animals of
all sorts congregate to feed, find refuge, grow to adulthood, and stage
migrations. Estuaries are unique places, strongly affected by tidal
action, where land and river and sea merge into a dynamic natural
Western Head, Musquash
MPA Campaign website, CCNB)
Most definitions of estuaries do not reflect the uniqueness of these
waters as habitats. They fail to convey the dynamic nature of the
physical processes operating in estuaries, or to explain the roles that
these processes play in shaping the character of aquatic and terrestrial
life in and around estuaries (Lippson et al, 1979). Many commercially
and recreationally important species depend on estuaries. However, since
commercial and recreational fishing occurs predominantly offshore or in
rivers, the vital life history and energetic connections with estuaries
have largely been disregarded.
(photo: South African
Coastal Information Centre)
Estuary Productivity and Function
Estuaries rank along with tropical rainforests and coral reefs as the
world's most productive ecosystems, more productive than both the rivers
and the ocean that influence them from either side. While we in Atlantic
Canada see no rainforest and few coral reefs, we live amidst and beside
myriad and diverse estuaries that support our historically abundant
In an estuary, nutrient-rich river
waters combine with warmer,
infused shallow coastal waters and the upwelling of nutrient-rich deep
ocean waters to generate primary productivity. The mixing of lighter
fresh water and heavier salt water trap and circulate nutrients such
that they are often retained and recycled by benthic (bottom dwelling)
organisms to create a self-enriching system.
Estuaries can generate year-round primary production from macrophytes
(seaweeds, sea grasses and marsh grasses), benthic microphytes (mud
algae) and phytoplankton. Estuaries are also the beneficiaries of energy
subsidies through the tidal transport of food and nutrients and removal
This vast primary productivity is the cornerstone of the estuarine
food chain, providing food for large populations of shellfish such as
clams, mussels, oysters or quahogs (Environment Canada, 1987). In some
estuaries, where productivity exceeds what can be used within the
estuary, the action of regular tidal flushing moves nutrients and
organic materials to adjacent coastal waters thereby increasing their
In areas of extremely high tides such as the Bay of Fundy, this
export of nutrients to adjacent waters does not seem to occur. Instead,
the estuaries themselves use up everything they produce, making them
incredibly efficient in their production of marine life. The primary
source of nutrients in the Bay of Fundy proper are the upwellings that
occur at the mouth of the Bay. These are such prolific nutrient
generators that they export nutrients out of the Bay and into the larger
Gulf of Maine.
While every species has unique needs that must be served by its habitat,
there are a number of general habitat types in Gulf of Maine estuaries
which define the ecology of each estuary. These classes of habitat are:
fresh/brackish marsh and water; dunes and vegetated beach ridges; sand
flats; salt marsh and salt ponds; mudflats; oyster and mussel bars;
rockweed (found on bedrock); beaches (sand, gravel, cobble and boulder);
sea bottom (mud, sand, gravel, cobble, boulder or bedrock); shallows
(ledges, bars, reefs, shallow bays); seaweed beds (i.e. kelp) and
eelgrass beds. All these different types of estuary habitat support
vigorous marine food chains and attract a vast array of fish, marine
mammals and birds. Some of the more familiar types of intertidal
(between the low and high water marks) habitats in Bay of Fundy
estuaries include rocky shores, mudflats and salt marshes.
is the combination of physical features and living organisms that
provide food, nesting and resting areas, and shelter for fish and
Estuaries and Fish
Estuaries provide a nursery for the larval forms of some marine fish
species, and provide shelter and food for many young and adult fish and
shellfish. These in turn provide food for other levels of the food chain
including shore birds, waterfowl, larger fish and marine mammals. Many
seafood species such as lobster, herring, menhaden, gaspereau, crab,
oyster and clam rely on the rich food supply of estuaries during some
part of their life cycle (Environment Canada, 1987).
Many species of fish live their whole lives in northern estuaries;
others migrate short distances into or out of estuaries; still others
migrate from offshore and from estuaries into fresh water to breed.
Non-migratory estuarine fish are mostly small fish that rarely venture
into the open coast but usually range far up the estuary into brackish
and even fresh water. These include: tomcod; white perch; smooth
flounder; mummichog; silverside; pipefish; sticklebacks (three-spined,
four-spined and nine-spined); and winter flounder. Migrant fish that
pass through estuaries on spawning runs include: smelt; Atlantic salmon;
sea sturgeon; sea lamprey; gaspereaux (alewife and blueback herring);
shad; striped bass; brook trout; and American eel.
In marine areas of the lower estuary, common bottom dwellers include
lobsters, oysters, crabs, mussels, clams, scallops, flounder, hake and
cod. Cod and flounder spawn in marine waters just outside estuary
boundaries (Maine Coastal Program, 1991). Striped bass spawn in fresh or
brackish waters; males feed predominantly near the waters where they
were hatched and females return to the waters where they were born to
spawn (U.S. Department of the Interior, 1993).
In the US, the National Oceanic and Atmospheric Administration (NOAA
1994) compiled information on the distribution and abundance of fishes
and invertebrates in North Atlantic estuaries, with Passamaquoddy Bay in
New Brunswick (Quoddy Region) the most northerly study area. Of 13
shellfish and 45 finfish studied, seven shellfish and 18 finfish are
categorized as abundant or highly abundant during at least one life
history stage in Passamaquoddy Bay.1
Five of the fishes are abundant in Passamaquoddy Bay during all five
life stages - adult, spawning adult, juvenile, larvae, eggs. Of these
five, Atlantic tomcod, mummichog and winter flounder are abundant in the
fresh tidal or mixing zone of Passamaquoddy Bay (encompassing the St.
Croix river and estuary) during at least part of the year.
(photo: MRRI | NOAA CSC)
According to research done in the US, estuaries are essential to the
fishing industry, providing spawning, nursery and feeding grounds for
60-90 percent of the fish species of commercial interest along the
northern coast. Each acre of Atlantic coast estuaries is estimated to
produce up to 125 pounds of commercial fish. Approximately 87 percent of
the dollar value of US finfish harvests are species whose life cycles
depend on coastal habitats. The combined commercial and recreational
catch of these species contributes over $30 billion US annually to the
economy of the United States (US Environmental Protection Agency, 1992).
While relatively little research has examined the importance of
Atlantic Canadian estuaries specifically, we can assume that they make
comparable contributions to commercial and recreational fisheries in the
Maritimes. Berrill and Berrill (1981) report that well-mixed estuaries
are particularly valuable as feeding grounds for young fish because
phytoplankton and zooplankton populations remain dense throughout the
summer months. Because of the tidal action in Fundy and adjacent
estuaries, they are indeed very well mixed.
Berrill, M. and D. Berrill (1981). A Sierra Club
Naturalist's Guide: The North Atlantic Coast. San Francisco: Sierra
Environment Canada (1987). A profile of important
estuaries in Atlantic Canada. Environmental Quality Division,
Conservation and Protection, Atlantic Region. Dartmouth, NS.
Lippson, A. J. et al. (1979). Environmental atlas of
the Potomac Estuary.
NOAA (National Oceanic and Atmospheric Administration)
(1994). Distribution and abundance of fishes and invertebrates in North
Atlantic estuaries. US Dept. of Commerce, Maryland.
US EPA (Environmental Protection Agency) (1992). Protecting
coastal and wetland resources: A guide for local governments. US EPA
Office of Water; Office of Wetlands, Oceans and Watersheds; Office of
Policy, Planning and Evaluation.