Pacific Clam Species

Manila Clam

Photo: manila clam. Photo: Graham Gillespie. Manila clams (Venerupis philippinarum) were introduced in BC during the 1930s in oyster seed from Japan. They quickly spread throughout the Strait of Georgia and were accidentally introduced on the west coast of Vancouver Island. Manila clams that exist around Bella Bella are believed to have been carried into the area as pelagic larvae from Quatsino Sound.

Manila clams are found from the central coast of BC to California. They are found in the upper half of the intertidal zone in BC in mixed substrates of mud, sand and gravel. These clams live in shallow transitory burrows in the substrate. No significant subtidal populations of Manila clams have been found in BC.

Species Biology

Manila clams have separate sexes and are broadcast spawners, synchronously releasing gametes into the water column, where fertilization occurs. Maturation occurs between 20-25 mm in length, or approximately 1-3 years of age and spawning occurs from June to September in the Strait of Georgia. Temperatures of 12-13°C are required for gonadal development, and temperatures of 15°C are required for spawning.

Fecundity increases with size, with estimates ranging from 188,000 eggs/female at first maturity to 2,350,000 eggs/female at 40 mm TL (Total Length). Larvae are planktonic for 3 or 4 weeks before settling in suitable habitat. Adult populations are closed: once settled on one beach, these clams cannot move to another.

Although there may be some movement of Manilas on a beach, distinct growth rates on upper and lower portions of a beach indicate that these movements are relatively limited. Recruitment, the introduction of adults into a population, is highly variable due primarily to environmental conditions. Recruitment is sporadic in the Central Coast.

Interpretation and counts of annual rings on the shell surface are used to estimate age. Maximum size of 75 mm TL (Total Length) is achieved after 8-10 years, and maximum age in B.C. is 16 years. Age at recruitment to legal size (38 mm TL) varies from beach to beach and between areas on a single beach. Growth is greatly affected by tidal elevation and substrate characteristics, and growth can vary as much between different areas of the same beach as between different beaches. Under optimal conditions, Manila clams can reach legal size (38 mm total length) in approximately 3-4 years in the Georgia Strait, 4 years on the west coast of Vancouver Island, and 3-4.5 years in the Central Coast.

Manila clams are filter feeders, and thus can accumulate fecal contaminants (bacteria and viruses that can cause disease) which originate in fecal materials from human, wildlife or agricultural sources. Water quality in shellfish growing areas is monitored by Environment Canada, and beaches suffering elevated levels of fecal contamination are restricted from both commercial and recreational harvests.

Manila clams can also accumulate algal toxins, including those causing paralytic shellfish poisoning (PSP). The Canadian Food Inspection Agency (CFIA) uses mussel stations to monitor PSP levels, and areas showing increased levels of toxic algae are closed to harvest until algal blooms decline and toxin levels in shellstock samples are safe for human consumption.

Fishery

Photo: Four Manila clams. Photo: Graham Gillespie.Commercial clam landings since the 1950's were dominated by butter clams until a shift in market preference in the 1980's increased demand for steamer clams (Manila and native littleneck clams). The market shift was primarily driven by demand for Manila clams, which are an attractive clam that separates easily from the shell after cooking. Most Manila clams are sold as live product to restaurants in the States.

Clam harvesters fish during low tides, using rakes or scrapers to turn Manila clams out of the substrate and collect them by hand.Landings of Manila clams are primarily from the South Coast of British Columbia, because there are few Manila populations in the North Coast and water quality monitoring programs were discontinued in most northern areas in the 1960's.

Landings of Manila clams and mixed steamers (which are presumed to be primarily Manila clams) increased dramatically in the early 1980's, averaging 1,654 t between 1980 and 2000, as opposed to 189 t from 1951 to 1979. Manila clam landings decreased after 1988, primarily as a result of more restrictive management measures. In recent years, openings have been reduced in most areas to only a few days per year. Regardless of reduced opportunity, landings increased to 1,327 t in 1994, and have fluctuated between approximately 1,100 and 1,500 t since then. However, these statistics include depuration landings since 1994, representing the revival of operations on some beaches that had been lost to contamination, and landings from the Central Coast since 1992.

Licensed commercial clam diggers are required to designate one of six clam areas they wish to fish each year and then compete for available clams during short intense openings. In 1998, the intertidal clam fishery underwent licence limitations, resulting in a reduction from approximately 2,500 licensed diggers in 1988 to 1,160 eligible participants.

Several collaborative pilot projects that provide First Nations with communal commercial harvest opportunities on beaches fronting reserves are underway in the Strait of Georgia and on the west coast of Vancouver Island.

There are no limits on the number of recreational harvesters, but recreational harvests are assumed to be minor relative to commercial harvest levels. Since 1995, recreational fishers wishing to harvest clams are required to purchase a Tidal Water Sport Fishing Licence. Recreational and First Nations food, social and ceremonial harvests are open year-round, except for time and area closures due to fecal contamination or Paralytic Shellfish Poison (PSP).

Intertidal clam fisheries have been closed in the north coast region since 1963. These closures are the result of concerns regarding water quality and paralytic shellfish poison (PSP), which, in the absence of monitoring programs, create potential human health risks. A pilot commercial communal fishery occurs near Bella Bella, with special water quality and product monitoring programs.

Area 7 Fishery

Exploratory surveys in the early 1980's first found Manila clams in the area around Bella Bella, and a pilot communal commercial fishery was established in Area 7 in 1992, with special water and product quality monitoring programs.

The eiltsuk Tribal Council administers 50 Aboriginal Commercial Licences for the Area 7 fishery. The fishery is co-managed by DFO and the Heiltsuk Fisheries Program. The Heiltsuk conduct annual assessment surveys on index beaches in each of the Subareas fished, and Subarea catch ceilings are developed pre-season to insure that fishing effort is not concentrated in a few Subareas close to Waglisla. Logbooks and a dockside validation program track landings in-season.

The Area 7 fishery is conducted in the winter, usually between November and April. Clams are harvested during low tides, using rakes or scrapers to turn Manila clams out of the substrate and collect them by hand. Clams are wet stored on beaches in designated areas, and delivered to Waglisla on pre-determined dates. The clams are purchased and transported to processing facilities in the South Coast.

The fishery was managed under a Total Allowable Catch (TAC) of 113.6 t until 1999, when the TAC was reduced to 68.2 t after a review of the fishery. Littleneck and butter clams, which had also been under 114.1 t TACs, were removed from the commercial fishery due to low interest from the diggers (mainly concerns regarding price) and to set these species aside for food, social and ceremonial use.

Littleneck Clam

Photo: Native Littleneck. Photo Rick Harbo.Littleneck clams (Protothaca staminea) are found from the Aleutian Islands to Baja California, though they are generally abundant only north of Oregon. These clams inhabit the mid to lower intertidal zone in British Columbia, in mixed substrates of gravel, sand and mud. Although occasionally recorded to 10 metres depth, there are no significant subtidal populations of littleneck clams in B.C.

Species Biology

Littleneck clams have separate sexes. They mature at between 22 and 35 mm in length, or approximately 2 to 3 years of age. In B.C., they spawn from April to October. Larvae are planktonic for 3 to 4 weeks before settling in suitable habitat. Adult populations, once settled on one beach, cannot move to another. Although there may be some movement of clams on a beach, distinct growth rates on upper and lower portions of a beach indicate that these movements are relatively limited.

Age is estimated from counts of annual rings on the shell surface. Maximum age in B.C. is 14 years. Growth varies considerably from beach to beach, and between tide levels on a given beach. Growth is rapid to five years of age, and then slows. Littleneck clams can reach legal size (38 mm) in the Strait of Georgia in 3 years. Maximum size (70 mm) is reached in 10 years.

Fishery

Clam harvesters fish during low tides, using rakes or scrapers to turn littleneck clams out of the substrate and collect them by hand.

Photo: Littlenecks in hand. Photo: Rick Harbo.Intertidal clam landings have been recorded since the turn of the century, and clams such as the native littleneck were important to First Nations people long before contact. The littleneck clam resource currently supports commercial, depuration and recreational harvests, and First Nations food and ceremonial requirements. These fisheries also exploit stocks of Manila clams (Venerupis philippinarum) and to a lesser extent, butter clams (Saxidomus gigantea).

Although Manila clams are the main commercial species in BC, littleneck clams are often harvested along with Manilas (see manila clam fishery), as they are also a recognized steamer clam. Since the market price for littleneck clams is lower than for manilas, this species is not always targeted by commercial diggers. However, a few specialty markets do exist for littleneck clams in the States.

Butter Clam

Photo: Butter clam. Photo Rick Harbo. Butter clams occur from the Aleutian Islands to northern California, and are common throughout British Columbia wherever suitable conditions occur. They live in a wide variety of soil types from pure sand to pure gravel, but the typical substrate is a porous mixture of sand, broken shell, and small gravel. They occur mainly in the lower third of the tidal zone, but are also found to a depth of 30 ft below the zero tidal level.

Species Biology

The butter clam, Saxidomus gigantea, was initially the targeted species of the intertidal clam fishery in British Columbia. It is a relatively large clam, attaining a length of 12 cm. The shells are heavy and solid, square to oval in shape. The external surface has prominent concentric striations and deep winter checks. Shells are yellow in colour in juveniles, changing to grey-white with age, but the colour is often affected by the type of substrate in which it lives. The internal surface is white and smooth, but not glossy. There is a strong prominent external hinge ligament and pronounced umbones.

Sexes of butter clams are separate and spawning takes place in late spring. Examination of gonad sections taken throughout the year show that spawning may occur as early as April and May, although spent gonads may be found at any time during the year.

Successful breeding is not a regular occurrence on British Columbian beaches. All age classes are not equally represented in the various populations and successful reproductive years are infrequent. There is evidence that some populations may fail to spawn in some years, and these irregular seedings result in fluctuations in adult populations.

Fishery

For information on the fishery for butter clam and other intertidal clams such as the butter, manila, varnish and razor clams please view the current Integrated Fisheries Management plan for Intertidal Clams or the clam publications page.

Razor Clam

Species Biology

Photo: Razor shells. Photo Rick Harbo.Razor clams (Siliqua patula) are found on surfswept sandy beaches from Pismo Beach, California to the Aleutian Islands in Alaska. There are two major stocks in British Columbia: the largest occurring at North Beach near Massett in Haida Gwaii and smaller populations at Long Beach and other west coast of Vancouver Island beaches. Razor clams are found from the mid-intertidal beach region to subtidal depths of 20 m.

Razor clams are molluscs, having a long siphon, a prominent muscular foot and brittle elongated valves. They can use their foot to burrow at rates exceeding 20 cm per minute and are found up to 25 cm in the sand. Adults left on the surface of the beach will quickly re-burrow. Adult razor clams reach shell lengths up to 160 mm and ages of 18 years. Time of spawning varies with location, but generally occurs from April to September, occurring later at northern latitudes. Age and size of sexual maturity varies with latitude, but most clams are sexually mature at 2 to 4 years of age and 100 mm in length.

Fishery

The management plan for razor clams has been jointly developed by the Council of the Haida Nation (CHN) and Fisheries and Oceans Canada. This managment plan applies to the commercial, recreational and Haida non-commercial fisheries. In 2004, the CHN will continue to designate Haida Participants in the commercial fishery who will commercially fish razor clams under a Communal Licence issued to the CHN under the Razor Clam Sub-agreement. Fisheries and Oceans Canada will continue to license individual commercial fishers (Licensees). Entry into this fishery was limited in 1995.

Historically most commercially harvested razor clams were used as bait in the crab fishery. In recent years, however, there has been a growing demand for razor clams as a food product. This demand along with recent clam abundances resulted in historic high landings. The fishery experienced a record catch in 2000 (since 1941) and then three years of above average catches. Recent recruitment has been at a more normal level and catch ceilings have been adjusted to reflect the available stock.

When harvesting razor clams (Siliqua patula) for sale, each participant must be in possession of a non-transferable designation card from the CHN and each Licensee must be in possession of a current year Area A clam "Z-2" licence from Fisheries and Oceans Canada. Identification and designation cards or licences must be carried at all times when harvesting clams and must be produced upon request of a CHN Fisheries Guardian, Fisheries and Oceans Canada Fishery Officer, or Fisheries and Oceans Canada Fishery Guardian.

Recreational harvesters are required to hold a valid British Columbia Tidal Waters Sport Fishing Licence to harvest razor clams. The recreational harvest of razor clams is restricted to a daily limit of 75 clams and a possession limit of 150 clams. There is no size limit for razor clams harvested recreationally.

Varnish Clam

Photo: Varnish clams. Photo Graham Gillespie.This recently introduced Japanese species has been reported in increasing numbers since the early 1990's. The varnish clam (Nuttallia obscurata) has been reported form beaches in Puget Sound, Sooke and as far north as Manson's Landing on Cortes Island. Sightings have been recorded in 1997 from Barkley Sound on the West Coast of Vancouver Island. A huge increase in varnish clams at Savary Island has been noted between clam surveys undertaken in 1995 and 1998 (G. Gillespie, pers comm).

Species Biology

Varnish clams are capable of filter-feeding, selectively removing food particles from the water column. They also utilize pedal feeding, collecting organic detritus from the sediment using the foot.

Photo: Open Varnish clam. Photo Graham GillespieLittle is known about age and growth of varnish clams, but there is evidence that they may grow at rates similar to Manila clams, Venerupis philippinarum, achieving 38 mm in length in about four years. Size and age at maturity are not known but is currently being investigated.

Anecdotal and survey information indicate that varnish clams have established fairly large populations on most beaches in Georgia Strait in a relatively short time (< 10 yr).

Varnish clams are typically found associated with manila, littleneck (Protothaca staminea), softshell (Mya arenaria), and macoma clams. They are host to pea crabs, Pinnixia faba, sometimes with relatively high infestation rates. These crabs are found in other intertidal clams, but generally mature only in horse clams, Tresus capax.

Varnish clams are preyed on by moonsnails (Euspira lewisi), crabs, gulls, crows (Corvus caurinus) and oystercatchers (Haematopus bachmani).

Fishery

Following resolution of public health concerns regarding risks associated with Paralytic Shellfish Poisoning (PSP) and coliform contamination by the Canadian Food Inspection Agency (CFIA), varnish clams were harvested on a small scale under experimental licence. The purpose of the project was to collect biological data and test marketability. Studies included the documentation of harvesting techniques and processing methods, and experiments to examine competition between varnish and Manila clams.

Limited information gathered by the CFIA indicate that varnish clams accumulate and depurate PSP toxins at rates similar to Manila clams and Pacific oysters (Crassostrea gigas).

Limited landings of varnish clams were also harvested during an experimental opening in the wild commercial clam fishery in 2001 during which the retention of varnish clams was permitted.

The market name "Savoury Clam" has been registered with the CFIA for the purpose of an international marketing study. Results of the market study show interest from both Canadian and U.S. restaurant markets.

Varnish clams are fished recreationally, but effort, landings or relative importance in the recreational fishery is not known.