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Arctic Surf Clam (Mactromeris polynyma)

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Species overview

Physical description

Arctic surf clam with bar scale. Refer to physical description.
Arctic Surf clam (Mactromeris polynyma). Photo credit: Dale Roddick

Arctic Surf clam, also known as Stimpson’s Surfclam, is a large bivalve that grows up to 160 millimetres (mm) in length. It has a triangular whitish gray shell with concentric rings. The outermost layer of the shell, called the periostracum, is shiny tan to dark brown. It has a white shell inside and the foot muscle is generally purple but can be yellowish.

Distribution

Arctic Surf clam is found in coastal waters off both the northern North Pacific and the northwestern Atlantic oceans. Populations large enough to sustain commercial fisheries are found:

Life cycle

Arctic Surf clam can live to be more than 60 years old. Arctic Surf clam is a broadcast spawner, meaning it releases gametes into the water column. Each individual will have only male or female reproductive organs. They reach reproductive maturity between 5 and 8 years old and spawn mainly in summer or fall. Larval development and growth are temperature dependent. After a larval stage of 1 to 3 weeks, juveniles settle on inshore or offshore sandy banks with medium to large grain sediments and water temperatures less than 15˚C. Growth rates for Arctic Surf clam decrease after approximately a 50 mm shell length. The size and age at 50% maturity is 45.2 mm shell length and 8.3 years old on Banquereau Bank. The size and age at 50% maturity is 39.9 mm shell length and 5.3 years old on Grand Bank.

Fishery history

Maritimes
Map of Banquereau Bank and Grand Bank fishing areas (solid lines) from licence conditions.
Banquereau Bank and Grand Bank fishing areas (solid lines) from licence conditions.

Commercial quantities of Arctic Surf clam were found on Banquereau Bank during surveys conducted on the Scotian Shelf from 1980 to 1983. In 1987, a 3-year Offshore Clam Enterprise Allocation Program was developed with industry consensus to support a regulated fishery. During this time, the fishery was exploratory, but later grew into an established commercial fishery. Total Allowable Catches (TACs) and EAs were set for each of the 3 years of the program with 3 companies participating. The TAC in 1987 was set at 30,000 tonnes (t). The TAC remained at that level until it was reduced to 24,000 t in 2002. In 2018, following an assessment, the TAC was further reduced to 20,943 t.

Exploratory fishing on Grand Bank in 1987 and 1988 led to the expansion of the fishery to this area in 1989. Four exploratory licences were issued for 1 year for the Grand Bank with a TAC of 20,000 t. The TAC remained at that level until the 2010 Grand Bank assessment when the TAC was adjusted to 14,756 t.

Quebec
Map of management areas for the Arctic surf clam fishery in Quebec.
Management areas for the Arctic Surf clam fishery in Quebec.

In Quebec, the inshore fishery is managed through 10 fishing areas: 8 on the North Shore and 2 on the Magdalen Islands, with an area-wise Total Allowable Catch (TAC).The first exploratory fisheries in the northern Gulf took place in 1990 in the Magdalen Islands and in 1991 on the North Shore. Subsequently, other exploratory fisheries took place on the North Shore, on the shores of the Lower St. Lawrence, and on the north shore of the Gaspé Peninsula. These exploratory fisheries located several spawning beds. From that time onward, the fishery began to develop more abundantly on the North Shore and in the Magdalen Islands. The first landings were recorded in 1993. In Quebec, the Arctic Surf clam fishery is complementary to other fisheries that are pursued by harvesters during the year.

Ecosystem context

The offshore Arctic Surf clam fishery uses bottom contact gear that disturbs the seabed. This has a large immediate impact on the substrate and benthic organisms because dredges liquefy sediment down to a minimum of 20 cm. Dredges remove many large organisms and cause sedimentation and displacement of organisms next to the dredging track. The long term impacts of hydraulic clam dredges on the habitat and benthic community of fished areas was studied over a 10-year period at a site of 65 to 70 m depth on Banquereau Bank. The largest impacts were observed to be the removal of non-target clams and bivalves from the area. Given the sedentary nature of clams and their slow growth rate, these impacts may be considered to be long-term in nature.

Sonar imaging of the ocean floor detected some of the track locations 10 years after dredging, suggesting that changes to the sediment structure caused by hydraulic dredges can persist. This occurred at deep sites, suggesting that water depth likely influences track persistence. Shallower areas are more actively impacted by waves and currents. Hydraulic clam dredge fisheries occur on fairly mobile, well sorted sand, which may help mitigate the overall impact.

Although clam dredges have a large immediate impact on the bottom, the impact of the fishery is usually ranked lower than other bottom contact gear because it has a relatively small footprint. Climate change and various environmental phenomena such as storm surges, shoreline erosion, and reduced ice cover could negatively affect Arctic Surf clam populations. With warming temperatures, a bathymetric shift in the distribution of Arctic Surf clams during a period of unusually warm water is possible. A latitudinal shift is also likely to occur, where depth (e.g., Laurentian Channel) and substrate (e.g., Grand Bank) do not limit suitable habitat. In addition to changes in latitude and depth of species related to bottom temperature, we would also expect changes in growth rate, tissue weight, and mortality rates with climate change.

Science advice and research

Science advice and research for Arctic Surf clam

Sources

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