Massachusetts Aquaculture White Paper - Support Systems

Hatcheries can be and are used to some degree in Massachusetts to supplement production of fish and shellfish both in the natural environment and for use in aquaculture facilities. Relaying and depuration are two different approaches used in the state for cleansing contaminated shellfish. Neither are presently used for aquacultured shellfish although the possibility exists that they could be.

Hatcheries

There are several hatcheries in Massachusetts devoted to shellfish production. Although individual variations in diet or equipment may occur, the basic operations are similar.

In the typical hatchery, adult shellfish, selected for broodstock on the basis of desirable attributes such as rapid growth and disease resistance, are conditioned to spawn by being held in trays of circulating seawater at temperatures that stimulate the development of eggs and sperm. During the conditioning period, food in the form of microscopic unicellular algae is added to the seawater. The algal food may consist of several different species that are of proven nutritional value to bivalves and that are maintained in cultures in the hatchery facility.

After the conditioning process, which may last some weeks, the adults are induced to spawn, usually by exposing them to a rapid temperature increase and, if necessary, by adding a suspension of sperm to the holding trays. Eggs that are discharged are collected and thoroughly mixed with sperm to insure fertilization. The fertilized eggs are then transferred to tanks filled with seawater that has been filtered to remove possible predators. The temperature of the water in the larval containers is maintained between 25 - 30 degrees C. The larval density usually ranges from 1,000 to 10,000 per liter (approximately 4,000 - 40,000/gallon of water).

Although hatcheries may vary somewhat in their larval-rearing routine, it is the usual practice to change the water in the larval tanks several times each week. This is accomplished by draining the water from the tanks through fine mesh screens that retain the larvae. The tanks are then cleaned and refilled with warm, filtered seawater to which algal food has been added, and the larvae are returned to the tanks. The duration of the larval period in most hatcheries is between one and two weeks. These methods have been successfully applied to hard clam and oyster larvae in Massachusetts.

Many culturists do not go through the hatchery procedure for oyster seed production; in some areas culturists may rely completely on natural production. For example, on Long Island, NY, areas of natural bottom are dredged to remove oyster predators. Oyster shell is then spread on the bottom during the spawning period to collect seed. After a year of growing in the setting beds, the young oysters are moved to more favorable growing areas, where they grow to maturity. This rather traditional system has worked when conditions are favorable for natural reproduction and when disease and predation can be controlled. In many areas of New England, natural reproduction is too erratic or negligible to provide a reliable basis for culture, making hatchery production an economic necessity.

Aquaculture Research Corp. in Dennis is the state's only commercial shellfish hatchery and produces clam spat for virtually all of Massachusetts' producers.

The Martha's Vineyard Shellfish Group. Five towns on Martha's Vineyard have a cooperative aquaculture agreement for the operation of a non-profit shellfish hatchery which produces seed quahogs, scallops, and oyster spat for distribution to the five Vineyard towns, the Martha's Vineyard Shellfish Group (MVSG). The solar hatchery provides the towns with shellfish seed and uses joint resources for research into improving methods of shellfish propagation. The hatchery has developed its own, genetically-tagged scallops in order to track survival, interbreeding, and population distributions when introduced into the wild shellfish communities. The project also runs public education programs on shellfish enhancement and culture, as well as pollution-abatement programs. The MVSG relies upon support from the state, Dukes County, the towns of Edgartown, Tisbury, Chilmark, Oak Bluffs, and Aquinnah, private donations, and the expertise of the local shellfish constables, private aquaculturists, and research facilities at Woods Hole.

The Nantucket Research and Education Foundation is a pilot project for aquaculture training. The program is designed to expand the Town's economic base by enhancing wild shellfish populations through the grow-out of cultured seed and to train fishermen in hatchery techniques, water quality testing and monitoring, and shellfish aquaculture methods.

The Foundation supplies the Town with quahog seed, oyster spat, and eyed larvae and runs a training course in shellfish aquaculture, currently the only one in Massachusetts.

Shellfish Relaying

Massachusetts, along with most other states with shellfish resources, has vast shellfish beds that cannot be utilized because of contamination. As a result, the practice of relaying: moving contaminated shellfish from restricted areas to clean areas and allowing sufficient time for the shellfish to purge pathogens is monitored by the Massachusetts Division of Marine Fisheries. Shellfish are collected under DMF supervision and re-planted for at least one spawning season (June 15 - September 15). Relaying requirements vary from state to state but must be done according to National Shellfish Sanitation Program guidelines.

Relaying provides several benefits. It allows for the utilization of an otherwise unavailable resource; it works over (cultivates) existing natural beds, usually of benefit to the substrate; it further distributes a local gene pool and may provide some natural spawning enhancement. The most significant benefit may be the depletion of natural stock from polluted areas, which reduces the incentive for illegal harvests. Illegal harvests of contaminated shellfish pose a significant public health hazard.

Relaying is not cheap; careful oversight, testing, and monitoring is required. However, in Massachusetts, it has generally been found that the retail value of relayed shellfish, coupled with the unmet production demands, offsets the costs of relaying.

In Massachusetts relaying has been restricted to municipal propagation and enhancement programs and is generally not regarded as aquaculture. The use of moderately contaminated areas as nurseries and a source of seed for aquaculture has been under consideration for some time, but contaminated shellfish are considered to be a public resource. The relaying of moderately contaminated shellfish from other states has been allowed in the past, but is not presently common. In these circumstances stock must be held for at least 30 days before harvest.

Depuration Facilities

Depuration is the term applied to the purification of shellfish, harvested from moderately contaminated areas, under controlled conditions. The process generally involves holding the shellfish in tanks of flowing seawater for periods of forty-eight to seventy-two hours. The seawater used is sterilized by ultraviolet light. Shellfish harvested from moderately contaminated areas normally purge themselves of bacterial contaminants within forty-eight hours, but may be held for up to 72 hrs. in some circumstances, after which a decline in quality and shelf life may occur.

Philosophic and practical conflicts surround depuration activities. Like relaying (removing shellfish from moderately contaminated areas and re-planting them in clean substrate), depuration provides the means for utilizing an otherwise unavailable resource. It also represents a way of assuring consumers of a clean and safe product. Depuration is practiced globally: England, France, Spain, and Australia have successfully used it for years with a variety of species. Massachusetts has practiced depuration techniques for over sixty years.

Depuration has been resisted on several fronts. Commercial fishermen fear a loss of economic control over the product. Scientists have retained certain reservations about the process. It has been discovered in soft clams that, if harvested from severely polluted areas; i.e. fecal coliform counts in excess of 88 per 1000 ml, a percentage of the shellfish will fail to purge themselves within the forty-eight to seventy-two hour period. It has also been found that some shellfish, particularly if damaged during harvest, may not siphon during the depuration period at all. Finally, even if the shellfish can be purged of most of the bacteria contained in their gut, they may not be able to release viruses in their tissues. Others argue that depuration discourages solving the pollution problems which lead to shellfish bed closures. However, given that population models project that by the year 2000 half of the nation's population will be living within the coastal zone, the challenges toward coastal pollution abatement will continue to grow irrespective of practices such as depuration.

Although several eastern states have authorized the operation of depuration facilities by private sector entities (i.e. Virginia and Maine) Massachusetts has no private depuration capacity. The Department of Fisheries, Wildlife, and Environmental Law Enforcement, Division of Marine Fisheries, operates a shellfish depuration facility for soft shelled clams at Plum Island, in Newburyport.

The Massachusetts Plum Island facility is the only depuration operation in the Massachusetts/Rhode Island/New Hampshire area. Only clams harvested from moderately contaminated areas, i.e. with fecal coliform counts ranging between 14 and 88 per 100 ml, are accepted for processing. Any clams brought to the plant by fishermen and found to have fecal coliform concentrations in excess of 1600 per 100 grams of meat prior to treatment are not considered acceptable and are confiscated. This is because many clams having such high initial bacteria counts may fail to purify within the prescribed time period. Clams qualifying for treatment are held in seawater sterilized by ultraviolet light for 24 hours and are again analyzed. Those with fecal coliform concentrations no greater than 500/100 gram sample after the initial 24 hour period may be released for market without further testing after an additional 24 hours of purification. If the initial 24 hour test indicates concentrations higher than 500/100 grams, additional samples from this group are analyzed again after 24 hours. By the end of the total 48 hour treatment, the counts must be less than 230/100 grams. If they are not, the shellfish are retained for further sampling or confiscation. The ultimate objective is to meet the National Shellfish Sanitation Program standard of median concentrations of 50 fecal coliforms/100 grams within a 48 hour period, with no more than 10% of the samples exceeding 130/100 grams.

The Plum Island facility operates year-round and currently processes approximately 50,000 bushels of clams during the year. During its sixty year history, there has been no record of any illness that could be attributed to clams processed at the facility. Shellfish which are depurated at the Plum Island facility are tagged as safe for consumption so as to "certify" their cleanliness for marketing purposes.

Depuration has not proven to be successful in purging shellfish of heavy metals. Although scientific literature suggests that metal depuration is possible, the mechanics of that process have not been adequately addressed. Metal depuration rates vary widely, showing diverse ranges for the same metal within different bivalve species and for different metals within the same species. Laboratory studies have demonstrated that depuration of quahogs of heavy metals was insignificant.

Depuration is not presently used by aquaculturists in Massachusetts but could be under different scenarios. For example, if a shellfish grow-out area became contaminated prior to harvest, an aquaculturist could feasibly bring his harvest to a depuration plant or relay them for cleansing rather than dumping them. Despite warranted concerns, depuration should be evaluated as a potential option while still adequately addressing the public health questions because it makes available to the public natural resources which would otherwise be unutilized.

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Published: September 1995