International Council for the Exploration of the Sea SHELLFISH
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T International Council for CM 19~/K:l The Exploration of the Sea Administrative Report SHELLFISH AND BENTHOS COMMITTEE • by J. E. Stewart 1976 MOLLUSCA AND BENTHOS BELGIUM (Reporting on Crustacea Only) Canada (J. E. STEWARTt Crassostrea virginica Oyster population assessments were carried out in Caraquet Bay, Prince Edward Island, and the Miramichi River estuary in New Brunswick to monitor changes in structure and standing crop, to forecast future conditions in the fishery, to recommend changes in exploitation procedures and to determine potential for the implementation of management procedures such as resource enhancement. Efforts to expand and re-habilitate Maritime oyster stocks included: - the cleaning, prior to spatfall, of approximately 24 hectares of oyster bottom in Caraquet Bay in order to improve recruitment and expand the population. Several small yet formerly productive oyster beds in Prince Edward Island were also cleaned and stocked with 22 metric tons of broodstock. - a co-operative resource enhancement operation with Prince Edward Island Fisheries resulted in a total of 7 hectares of new oyster ground being developed in the Dunk and Wilmot Rivers of Summerside Harbour. This was done by relaying 181 metric tons of oyster stock from overcrowded areas of the natural bed and planting them on good but presently unstocked areas of bottom. The effect is twofold: increased production acreage is being developed and oyster quality and hence price per unit is increased by the thinning. Placopecten magellanicus Research on this species in Newfoundland has been primarily on problems relating to its culture. Larval settlement and survival are being examined to further our understanding of resource enhancement possibilities. - 2 - A study is also underway to determine peak settlement times. When comp1eted, this study shou1d e1iminate the guesswork invo1ved in deciding the best time to set out co11ectors. New co11ecting materials and various modifications in ~ the design of co11ectors are also being examined. Growth characteristics of anima1s in suspended cu1ture as we11 as in bottom cu1ture are being investigated. Georges Bank Increased 1andings of 7,480 and 9,709 M.T. of shucked meat in 1975 and 1976 respective1y (compared with an average of 4,476 M.T. from 1970 to 1974) appear to ref1ect the beneficia1 impact of regulations on 1anded meat size (adductor musc1e), which were first introduced in 1972 and put into effect by the Canadian participants in June, 1973. The Canadian fishery at present accounts for approximately 85% of the 1andings from the bank. The regulation, which now specifies that no more than 5% of the samp1es taken from the 1anded catch must contain meats sma11er than a mean size (11.3 gm) equivalent to 40 meats/lb., has been progressive1y lowered annually together with a freeze in fleet size, is a beginning towards imp1ementation of ICNAF recommendations in 1972, namely that, on a yield/ recruit basis, a 34% increase in yie1d will resu1t from an increase in age at first capture from age 4 (rough1y 48 meats/1b) to age 5 (roughly 32 meats/1b). Bay of Fundy • Dec1ines in this fishery due to long-standing effects of overfishing since the 1930's have been documented in papers presented at ICES in previous years. Oscil1ations in fleet size in response to periodic fluctuations in scal10p abundance (whose timing appears to be related to long-term environmental fluctuations), have undoubtedly contributed to the wide amplitudes of annual catch fluctuations, and an attempt was made to stabilize the fishery in 1972 by introducing limited entry. A freeze in unused licenses has been introduced this year to implement recommendations for further cuts in overall effort. Chlamys islandicus Resource surveys of the distribution and abundance of this species were conducted a10ng the northwest slope of St. Pierre Bank, in the northeastern Gulf of St. Lawrence and off Nain in Labrador. None of the 1009 scallops tagged in the Gulf in 1975 were recaptured this year. A tagging programme has also been initiated on St. Pierre Bank. Il1ex illecebrosus Squid were p1entiful in inshore Newfoundland waters during 1976, and landings increased from 3202 metric tons in 1975 to 9869. Biological sampling of the commercial catch was continued and staff participated in a research cruise from Nova Scotia to Delaware by the Institut Scientifique et Technique des Peches Maritimes of St. Pierre &Miquelon. Studies into squid population biology will be continued in 1977. - 3 - Mya arenaria Assessments of soft-shell clam stocks in P.E.I. to determine their potential for hydraulic harvesting were carried out in cooperation with the P.E.I. Department of Fisheries. Approximately 15 estuaries were surveyed and stocks totalling 1,134 metric tons of market size clams were identified. Studies on the recruitment, meat quality, and growth pattern of these populations are continuing. In addition, a study was initiated in Fortune Bay, P.E.I. to assess the short- and long-term effects of hydraulic harvesting on soft~shell clams and their habitat. Effects on the stocks themselves (growth, recruitment, condition, etc.), on the benthic fauna and on the substrate are being monitored. Analysis of the initial data is underway but the study will require four to five years for completion. This study will contribute greatly to the development of a sound management policy for clam stocks. Spisula solidissima An assessment was made of available information on surf clam stocks in the southwestern Gulf of St. Lawrence in response to industry enquiries. The review revealed few biologically sound surveys and suggested the need for • systematic surveys to determine the level and value of these stocks. Mytilus edulis Mussels are being analyzed for their polychlorinated biphenyl, hexachlorobenzene, myrex, Hg, Pb, Cd, Zn, Cu, As and Se content. Chondrus crispus Chondrus crispus is harvested in large quantities in the Maritime provinces by either handraking (southwestern Nova Scotia) or dragraking (Gulf of St. Lawrence). The mean standing crop in the commercially important beds in southwestern Nova Scotia and western Prince Edward Island per 0.25 m2 was 109 9 and 26.3 9 respectively. A study on the ecological impact of the traditional harvesting techniques was undertaken. The handrakes removed approximately 26% immature Chondrus crispus plants while the percentage in the harvest of the dragrakes was 58%. The percentage of the handraked harvest attached to holdfasts was • 5% whereas that of the dragraked harvest was 33%. Similar studies were carried out in western Prince Edward Island on two different versions of the dragrake. It was shown that the basket dragrake was significantly more damaging to the C. crispus population. - 4 - Lobsters (Homarus americanus). occupy the f. crispus beds in western Prince Edward Island and it has been shown that their incidental harvest along with f. crispus varies with season and location. Mean lobster capture per hour ranges from between 1 and 30, and the percent injured. from a subjective inspection only. ranges up to 25%. Studies on the growth of f. crispus were undertaken in both the above mentioned areas in the latter part of 1975. Growth appears to be slow; plants 15 months old have a maximum length of only 4 cm and have developed 3 dichotomies. However, between November and February growth appears to have been exponential. Shellfish growth, Productivity A program to develop indices of production potential of Maritime inlets was begun during the summer of 1974. Initial trials have concentrated on the development of holding systems which would be suitable for a variety of species. In the initial experiment three bivalves (mussels. Mytilus edulis; soft-shell clams, Mya arenaria; and razor clams, Ensis directus) were placed near Luke Island in St. Margaret's Bay. Trays of cylindrical containers successfully maintained the two clam species over two winters and virtually eliminated the mortalities due to predator pressure evident on nearby beaches. The soft-shell clams attained a mean shell length of 40 mm in two seasons. The razor clam experiments were less successful since these mobile molluscs were capable of escaping from the containers. Mussels were successfully held in suspended culture on ropes for two years although drift ice and storms resulted in the need for constant maintenance to the support system. Also, the relatively unprotected mussels suffered some losses from starfish. Despite these problems, the mussels grew to more than a minimum commercial size within two growing seasons. Production indices for different environments cannot be based on growth and mortality measurement for indicator species unless it can be assured that differences due to inherent physiological (genetic?) influences among the stock specimens can be distinguished from those due to environmental effects. Earlier work with mussels in Bedford Basin and St. Margaret's Bay gave assurance of major bay-to-bay differences in production parameters but gave indications as well that there were different growth "strains" within the • single stock used. Accordingly, experiments were be gun in 1976 to more critically examine these anomalies. - 5 - Benthic, community Dynamics Measurements of organic carbon, nitrogen and total organic matter in surface sediments in Bedford Basin are maximum in locations where changes in steep bottom gradients occur. High concentrations at the base of steep slopes suggest that accumulation could be due to downslope trans~ort caused by erosion from currents which meet the bottom at these depths. Profiles of organic content indicate that vertical gradients occur in'sediment from depositional areas in deep water. Cores from regions of slope gradient change contain approximately equal amounts of organic matter throughout the upper 10 cm. Physical mixing of sediment through current-induced water . movement and animal burrowing could homogenize sediments in areas where accumulations occur. Man-made organic compounds (DDT and its metabolites) occur in benthic invertebrates, demersal fish and sediments taken from St. Margaret's Bay, Nova Scotia.