University of Alaska Fairbanks
Sea Grant Marine Advisory Program
2221 E. Northern Lights Blvd. #110, Anchorage, Alaska 99508-4140
ABSTRACT In 1989, Alaska Senate Bill 514 revitalized the shellfish culture industry. As a result of the legislation, regulation changes were made that streamlined permit processing and added more security for use of state tidelands for aquaculture. The stabilizing effect of the new regulations has increased the number of aquatic farms from a handful in the mid-1980s to 72 at the end of 1992. The majority of Alaska aquatic farmers culture Pacific oysters Crassostrea gigas because spat are available, and the oysters grow very well on the abundant high quality phytoplankton. Cold, clean water retards sexual maturation which results in high quality half-shell oysters being marketable during the summer when oysters from other United States farms are in reproductive condition and unsuitable for consumption. Small quantities of blue mussels and scallops are cultured because spat are available from natural reproducing populations. Littleneck clams, urchins, and abalone are potential candidates for farming, but spat are not available and growth of these species is slow at northerly latitudes. Giant kelp, Macrocystis integrifolia, culture was investigated, but further research and development are needed. Young sporophytes are not available to stock the farms.
Alaska has strict shellfish transportation regulations to control interaction between cultured and wild species of shellfish and to prevent spread of diseases. As an example, import restrictions allow only spat of the Pacific oyster into the state. Oyster spat must also be less than 20 mm shell height to prevent importation of the parasite Mytilicola orientalis. Alaskas shellfish culture industry is severely hampered by the absence of a shellfish hatchery in the state. In addition to import restrictions, detailed review of shellfish transport and aquatic farm permit applications are major components of Alaskas shellfish transportation regulations. These strict regulations are a source of controversy between the shellfish culture industry and the Alaska Department of Fish and Game. Due in part to the conflict, the Alaska Department of Fish and Game is currently modifying the existing regulations. A shellfish transport policy based on larval drift patterns is proposed.
INTRODUCTION Alaskas shellfish aquaculture industry has a relatively long history beginning in 1910 with introduction of the Pacific oyster rassostrea gigas. The oysters were planted on beaches from Ketchikan to Homer, Alaska, but they grew best in southeastern Alaska where meat production reached a peak of 550 gallons in 1943 (Yancey 1966). The industry ended production in 1961. Shellfish culture started again in the late 1970s with the reintroduction of Pacific oyster spat into southeast Alaska. This time the renewed industry cultured oysters for raw consumption in the half-shell market. Restrained primarily by lack of capital and restrictive tidelands permit regulations, the industry was confined to a few farms in southeastern Alaska near the community of Wrangell.
In 1989, passage of Alaska Senate Bill 514 revitalized the shellfish culture industry. New regulations streamlined permit processing, agency coordination vastly improved, and changes in tidelands permit regulations added more stability to the industry. Improvements in permit processing increased the number of applications. By the end of 1992, 72 aquatic farms using 196 acres of tidelands were permitted to culture seaweed, clam, scallop, blue mussel, abalone, and sea urchin (Table 1).
The new industry is now more dispersed with aquatic farms located in five primary areas: Kodiak Island, Kenai Peninsula, Prince William Sound, Yakutat, and southeastern Alaska (Fig. 1). As a result of increased participation in shellfish aquaculture, sales of shellfish have increased substantially since 1989 (Fig. 2).
Shellfish aquaculture in Alaska is a challenging enterprise. To begin with, the state of Alaska does not have a shellfish hatchery and does not allow importation of any fish or shellfish into the state other than Pacific oyster spat that are less than 20 mm in length. Oyster spat are purchased from shellfish hatcheries in Oregon, Washington, and California that are approved by the Alaska Department of Fish and Game. These import restrictions require shellfish farms, culturing species other than Pacific oysters, to use only species native to Alaska. Seed stock for the farms culturing native species must currently be captured from wild populations.
High operation cost is another major problem faced by Alaska shellfish farmers. The expense of shipping equipment to the farms and product to market is a major problem. For instance, paralytic shellfish poison (PSP) toxin affects all bivalve shellfish cultured in Alaska, and all shellfish cultured in Alaska must pass the PSP test before the shellfish can be shipped to market. The PSP problem has not seriously harmed shellfish aquaculture, and over 10 years of extensive PSP monitoring of shellfish farms throughout Alaska have resulted in very few failed tests. However, PCP testing adds to the expense of getting the product to market and adds uncertainty to marketing. If toxicity is detected, the shellfish cannot be delivered to market.
The constraints under which shellfish aquaculture in Alaska operates are unique to the nation. Finding ways of dealing with the constraints and taking advantage of the promises are what will ultimately determine the success or failure of each shellfish aquaculture venture.
PACIFIC OYSTER CULTURE
Pacific oysters do not reproduce in the cold waters of Alaska. As a result, Alaskan oyster farmers must buy oyster spat from a shellfish hatchery. Unfortunately, Alaska does not have a shellfish hatchery; thus, farmers must buy spat from an out-of-state hatchery. This prolem places the farmers in a precarious position because spat are not always available, shipments can be delayed, and spat may not arrive at the farm at the optimum time to take advantage of abundant feed from natural plankton blooms. An example of the spat availability problem occurred in 1993 when only one oyster hatchery was certified to ship oyster spat to Alaska, and several shipments were delayed.
Nearly all oyster farming in Alaska employs suspended culture techniques. Oyster are cultured off the bottom in lantern net cages and suspended from some form of flotation, buoy, or raft. Suspended culture is labor intensive and is a costly form of culture.
Alaska is an outstanding place for Pacific oyster culture. The Pacific oyster, although native to warmer waters, is an attractive species for aquaculture in Alaska because it grows very well in cold water providing there is abundant, high quality plankton as a source of feed. Many estuaries in Alaska produce an amazing quantity of high quality plankton during bloom periods. This enables some farms to match growth achieved in the warmer waters of the Pacific Northwest (Fig. 3). Cold, clean water also reduces bacterial contamination, enables extended shelf-life, assures safety for the consumer, and retards sexual maturation making the Alaska oyster marketable during the summer when the supply of half shell oysters is low.
PACIFIC BLUE MUSSEL CULTURE
Native populations of Pacific blue mussels (Mytilus trossulus) live on many beaches in Alaska. Mussel farmers cannot buy spat from a shellfish hatchery but must capture spat from the wild population.
Mussel larvae generally set during the summer. Spat are ready for transfer to culture gear during the fall or spring following the set. The farmer removes spat from the gear and packs them into a net mesh tube called a mussel sock. The spat filled mussel sock is hung from a raft or buoy until the mussels reach market size. In Alaska, blue mussels grow from spat to a market size of 2 to 3 inches in about 1 year (Fig. 4).
A major constraint for culturing mussels is the labor required to culture, harvest, and process mussels for market. Mussel culture has promise because cultured mussels are fast growing and the meat high quality. Attaining an adequate production level to allow mechanization of some of the laborious tasks, providing a stable flow of product to the market, and developing a marketing strategy are some of the challenges facing mussel farmers.
SCALLOP CULTURE
The muscle from large scallops is in great demand and commands a high price. For these reasons, scallop culture is very attractive. Four scallop species have aquaculture potentil. Of these species, weathervane scallop Patinopecten caurinus attracts the most attention since it has a large, marketable size adductor muscle. Unfortunately, weathervane scallop spat are not available because shellfish hatchery technology is not able to produce spat efficiently.
Wild spat collection, applied with great success to capture spat of the Japanese scallop, Patinopecten yessoensis, has not proven successful for capturing spat of weathervane scallop. The growth rate for wild weathervane scallop is slow. Although the growth rate of farmed shellfish often exceeds that of their wild counterparts, the question of potential growth for cultured weathervane scallop needs study.
Culture of purple hinge rock scallop Crassadoma gigantea has promise because this species also has a large marketable size muscle. Spat can be hatchery produced, but since Alaska has no shellfish hatchery, this species is not currently feasible to culture. Collecting spat from wild populations has not been successful. Traditional shellfish culture gear cannot be employed to culture purple hinge rock scallops, since 1-inch-size scallops have the uncontrollable tendency to attach to a hard surface. The only way to remove scallop from the culture gear at harvest time is to cut them out and, in the process, destroy the gear.
Collecting scallop spat from wild populations has not been a total failure, because incidental captures of pink scallop Chlamys rubida and spiny scallop C. hastata spat have been very successful. Unfortunately, pink and spiny scallop do not grow large enough to produce a marketable size muscle (Fig. 5). Farms currently culturing these species hope to develop a whole scallop market. Although of very good quality and easy to culture, whole scallop can retain more PSP toxin than is accumulated in the scallop muscle alone. Whole scallops must also be kept alive for market but have a short shelf life out of water.
LITTLENECK CLAM
In Alaska, littleneck clam, Protothaca staminea, will be cultured on the bottom and mixed with the existing wild population of clams. Farming clams will cause the greatest potential for interaction with wild species, since the clam spat will be planted among the wild population. Culture of littleneck clams in Alaska has not started since spat are not available. Growth of littleneck clams is slow in the northern latitudes, requiring up to 6 years for a crop to reach market size of 35 to 50 mm in length (Fig. 6).
OTHER SPECIES
Abalone is a seafood commanding a very high price, but culture of the Alaska pinto abalone Haliotis kamtschatkana is not currently feasible because no spat are available. Abalone grow slowly and are expensive to feed. A serious potential abalone farmer should consider including seaweed culture as part of the farm operation to assure a constant food supply. Sea urchin Strongylocentrotus sp. culture has generated some interet in recent years because the wild fishery is plagued by the inconsistency of gonad quality. This causes wide fluctuations in market price. Culturing urchins may help to eliminate this problem but has not been explored in Alaska to date.
INTERACTION OF CULTURED SHELLFISH WITH WILD SPECIES
Even though shellfish production of the current industry is small and has a negligible effect on the wild shellfish populations, the number of farms and production is expected to increase. Shellfish farmers and the Alaska Department of Fish and Game are currently developing a comprehensive shellfish transportation policy. Conflicts concerning transportation issues are increasing. Alaska is also a special place because our marine systems are often in pristine condition and highly productive in their natural state. For shellfish aquaculture to be compatible with the current and future uses of state marine ecosystems, the potential problem of wild and cultured species interaction must be addressed.
Shellfish farmers are very apprehensive about the potential implications of the developing shellfish transport policy. The farmers feel that to some degree they must have the ability to move shellfish between selected locations. The question is how far and where should shellfish be allowed to be transported within the state of Alaska.
The state of Alaska has several regulatory controls that can effectivelylimit the impact cultured species have on wild shellfish populations. These controls are in the form of an import ban on exotic species that also applies to native species that are located outside the state. Essentially, the regulation prohibits any aquaculture species to be transported across the state boundary into Alaska with the exception of Pacific oysters. Before importation into the state, the oyster spat must come from a certified disease free source, and spat must be less than 20 mm in shell size to prevent importation of the parasite Mytilicola orientalis. The aquatic farm permit application process also screens applications to determine the impact cultured species will have on the local marine ecology and existing uses of the uplands and marine resources. The aquatic farm permit review process is extensive and may require more than a year to complete (Fig. 7). The third controlling mechanism is the shellfish transport permit. This permit provides the Alaska Department of Fish and Game with the most potent tool to control shellfish transportation by enabling department-wide scrutiny to identify and respond to the potential effects of shellfish transport on wild shellfish populations. A shellfish transport permit is required for any individual to transport or hold shellfish. The permit application must be approved by the Alaska Department of Fish and Game pathology section, district and regional fisheries managers, mariculture coordinator, the genetics section, and director of the department. All permit applications must be signed by the commissioner of Fish and Game (Fig. 8). This review process takes approximately 45 days and can be a very complex and controversial process.
The shellfish transport permit review done by the Alaska Department of Fish and Game must assure authorities that the shellfish are disease free, not genetically harmful to the existing wild populations of the same species, and that the intensity of culture will not significantly effect biodiversity of the marine life in the area. Currently, permit review is done on case-by-case basis. Shellfish farmers view this as too arbitrary and restrictive.
A major part of the current problem with shellfish transport regulations is that a comprehensive shellfish transport policy has not been developed and decisions concerning shellfish transportation are made cautiously. Adequate information about the genetic impacts of aquaculture on wild species is not available to formulate a policy, and the industry is very concerned about the potential for a very restrictive policy being developed. In addition, the state legislature has passed funding to construct a shellfish hatchery. Operation of this facility will require developing broodstock. With no clear policy about shellfish transport or how many regional broodstocks must be developed, future operation of the new shellfish hatchery is not clear. If transportation of shellfish is very restrictive, how realistic will it be for a shellfish hatchery to manage numerous broodstocks, one to supply each region of the state.
Current thinking about shellfish transport within the industry and the Alaska Department of Fish and Game is directed toward developing an initial policy based on shellfish larval drift patterns. Shellfish transportation then can occur within the normal drift pattern of the shellfish of concern.
A policy based on drift patterns of larva requires information about ocean currents, estimates of shellfish reproduction location and timing, measurements of shellfish larva development time, and an understanding of metamorphosis and spat setting. Unfortunately, ocean current data is incomplete and complex, and larva development data is estimated only from laboratory research. Even with these limitations, however, a rough larval drift pattern can be developed.
SEA SURFACE CURRENT INFORMATION
The northeastern Pacific is dominated by the Alaska current that flows northward along the coast of southeastern Alaska, then turns in a counterclockwise direction west along the south-central region passing Kodiak Island, then along the Aleutian chain (Fig. 9). The velocity of the Alaska current varies between 8.6 and 12.9 km/day with the higher velocities occurring on the outside of the current and closer to the Alaska shoreline. Current velocities along the Alaska stream, which flows from the Kenai Peninsula southwest past Kodiak Island and into the Aleutians, run between 21.6 and 43.2 km/day (Favorite 1970).
In southeastern Alaska, the average surface current velocity along the western shore is approximately 15.12 km/day (Ingraham et al. 1976). Sea surface current direction and velocity through the islands of southeastern Alaska, commonly called the inside waters, is more complex, caused by the irregularity of the shoreline, influence of tidal currents, and forces added from freshwater runoff. Studies by Martin (1969), Washburne (1989), and Crean (1967) show a complex surface current flow picture for the inside waters south of Sumner Strait (Fig. 10). The surface current in this vicinity flows north and east during ebb tide and south and west during flood tides. The general trend of surface current is directed southeast, out of Clarence Strait, then flowing north along the west coast of Prince of Wales Island. North of Sumner Straits, the currents are dominated by a northerly flow pattern. Currents flow both east and west across the southern tip of Kuiu Island, but the westerly flow dominates. Chatham Strait has both a northand south current, but the north current dominates. For channels nearest the mainland, the surface current is predominantly directed north. Velocities in the inside water vary from 0 to 8.1 km/hr. The average current velocity is approximately 2.8 km/hr.
Sea surface currents within Prince William Sound flow west as demonstrated by deposition of oil from the Exxon Valdez oil spill which fouled the beaches of the Kenai Peninsula, Cook Inlet, and Kodiak Island (Fig. 11). The average velocity of the surface current in this vicinity is estimated to be over 12 km/day. The surface currents that enter into Cook Inlet flow into the inlet along the northern shore of the Kenai Peninsula, change direction at the northern extreme of the inlet, and then flow southwest reaching Kodiak Island and the Aleutian chain (Fig. 12). Current velocities within Cook Inlet range from 1.8 to 5.6 kms/hr (Rosenburg et al. 1967). Around Kodiak Island, the prevailing surface current flows southeast toward the Aleutian chain (Fig. 13).
SHELLFISH LARVAL DEVELOPMENT
Shellfish larval development is most dependent on water temperature (Strathmann 1987). In Alaska, bivalve larvae begin to appear in significant numbers during May and June (Coyle and Paul 1990, Overseas Fisheries Cooperation Foundation of Japan et al. 1989). Of the Alaska bivalve species, the Pacific blue mussel and spiny scallop are most widely dispersed, and larval development data is available to estimate the length of their drifting planktonic phase.
Sea surface temperature data from June through September indicates a warming trend during the summer and sudden cooling in September. The surface water temperature for the inside waters of southeastern Alaska are found in Table 2, while Fig. 14 and Table 3 show the locations and surface temperatures for the Alaska current. This data was used to estimate larval growth for inside waters in southeastern Alaska and the Alaska current.
Pacific blue mussel development was estimated using growth rate data reported by Widdows (1991) (Table 4). Within the ocean surface temperature ranges found in Alaska, the rate of larval growth was assumed to have a linear relationship with temperature causing settling to occur within 24 to 56 days. Hodgson and Bourne (1988) estimated spiny scallop larva setting times based on temperature. From their conclusions, estimates of larva development were calculated assuming a linear relationship between larval growth and temperature (Table 5). Settling occurs between 31 and 50 days after spawning.
A point of caution is due at this point. The larval development data obtained from most research is done under laboratory conditions where temperatures and nutrition of the larva are controlled. The growth rates calculated from laboratory studies can only be an estimate of natural growth rates. Bivalve larva also have the ability to extend their larval life if environmental conditions at the setting site are not suitable or if food deficiency slows the growth rate. Spiny scallop larvae, for example, can extend their larval life phase by 95 days before evidence of deterioration occurs (Hodgson and Bourne 1988). Widdows (1991) reported that blue mussel larva can extend their larval life by up to 3 months. One factor common to both studies, however, is that mortality of larvae is increased substantially during an extended larval growth period.
Combining the effect of sea surfacetemperature on development, the length of larval life of blue mussels and spiny scallop, and the direction and velocity of surface currents, a pattern of larval drift was estimated. These estimated larval drift patterns and setting location will be discussed by region.
LARVAL DRIFT IN SOUTHEASTERN ALASKA
In southeastern Alaska, the effect of water temperature indicates that Pacific blue mussel larva can drift, during their normal development period, 30 days during the month of June (Table 6). Estimated current velocities during the larval development period can disperse bivalve larva throughout much of southeast Alaska and, in the Alaska current, larvae can drift the entire distance from Dixon Entrance to Cape Spencer. For the inside waters, however, tidal influences can cause bivalve larvae to drift back and forth for extended periods. This is particularly true for the region south of Sumner Strait (Table 7). The southeastern Alaska region appears to be separated from Prince William Sound since mussel larva, even when starting a northerly drift at Cape Spencer, must have an extended larval period to reach Cordova in Prince William Sound.
Larvae dispersal and setting is similar for spiny scallop larvae. Scallop larva drifting for 31 days in a northerly direction along the coast of southeastern Alaska have ample time to be widely dispersed. Setting will occur between 31 and 50 days at summer water temperatures which means that scallop larvae starting their drift at Dixon Entrance can set throughout much of southeastern Alaska. Larvae starting their drift at Cape Spencer, like blue mussel, will reach settle size before arriving at Prince William Sound (Table 8).
LARVAL DRIFT IN SOUTH-CENTRAL ALASKA
Blue mussel and spiny scallop larvae drifting out of Prince William Sound can reach much of the Kenai Peninsula, Kachemak Bay, Kodiak Island, and portions of the Aleutian chain within normal larval development times (Table 9). Table 10 presents a summary of settling sites for the blue mussel and spiny scallop larva and indicates several important features.
Bivalve larvae in the outside waters of southeastern Alaska will most often drift north, and the long section of coastline between Cape Spencer and Prince William Sound effectively separates southeastern larvae from south-central larvae when their development time is normal and the setting environment is suitable. For south-central Alaska, with the predominant currents flowing west, the eastern stock of bivalves impacts more on the western stocks and the influence may extend from Prince William Sound to the Aleutian chain. Western stocks of bivalves do not influence more eastern stocks, except for possible short distance transport influnced by tides and freshwater runoff. For reproducing bivalve species, a shellfish transport policy based on larval drift appears to have some merit.
OTHER SHELLFISH TRANSPORT ISSUES
While considering shellfish transportation, the potential for spread of disease also must be considered. This issue is not addressed in this paper. Obviously, shellfish farmers and the Alaska Department of Fish and Game want to prevent importation or spread of disease. This issue needs to be addressed independently of larval drift arguments.
It is important to keep in mind what else affects the survival of bivalve larva to adult age, other than larval drift. Blue mussel populations have been found to be genetically similar for broad regions, particularly the younger age classes (McDonald and Koehn 1988 and McDonald et al. 1991), but selective pressure caused by environmental conditions can significantly change the genetic characteristic of the adult population from that of the origin spat set (McDonald and Siebenallar 1989). Generalizing the assumption that selective pressure will sort out shellfish transportation mistakes can also be dangerous since scallop, for example, have been shown to have less selective pressure and a number of subpopulation genotypes can coexist in the same area (Beaumont 1982, Kijima et al. 1984, Krase 1989).
RESEARCH NEEDS
A comprehensive shellfish transportation policy needs further research to establish regulations using sound information. Genetic studies need to be conducted on several important bivalve species including the Pacific blue mussel, littleneck clam, and scallop. Studies that can determine the extent of selective pressures will be useful to refine guidelines for reviewing shellfish transport permit applications and to estimate the prospects for success of culturing or transplanting a bivalve species from one location to another. Reciprocal transplants and studies comparing spat and adult population genetic characteristics should be conducted to estimate the effects of natural selection. In southeastern Alaska, research needs to be conducted to determine if there are populations of bivalveS isolated by counter surface current flows. Other laboratory techniques used to define shellfish transportation policy are only estimates of natural phenomena and should be treated as such.
CONCLUSIONS
1. The use of larval drift for evaluation of shellfish transport permit pplication appears to have merit.
2. Drift of larva from a single location can spread over a wide area, and in the Gulf of Alaska the drift is predominantly north for southeastern and west for south-central Alaska.
3. A larval drift policy must also account for localized shift in currents as occurs in southeastern Alaska which may cause mixing of populations of shellfish in more than one direction of current flow.
4. The south-central region, with current flow from east to west, causes extensive dispersion of eastern population of bivalve toward the western region ranging from Prince William Sound to the Aleutian chain.
5. Transporting shellfish over a long distance with significant environmental differences can result in high mortalities and is not an effective way to manage an aquaculture operation.
6. Environmental similarities, particularly temperature and salinity, are important to consider when transporting shellfish if the transplant is to be successful.
7. Extensive research is necessary for eventual development of a comprehensive shellfish transport policy.
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