2012. Ocean-based nurseries for cultured lobster (Homarus americanus Milne Edwards) postlarvae: initial field experiments off the coast of eastern Maine to examine effects of habitat and container type on growth and survival. Journal of Shellfish Research 31, 167-176.
The commercial fishery for American lobster Homarus americanus Milne Edwards in Maine has experienced the highest landings during the past 2 decades than at any time since the 1950s. However, there is no scientific consensus on why landings have increased nearly 250% from 1990 to 2010, and no one can predict how long landings can be expected to remain at current levels. This uncertainty has sparked a renewed interest in lobster stock enhancement using cultured individuals. Historically, lobster stock enhancement in North America has focused primarily on releasing early benthic phase (stage IV) animals. It is not cost-effective to feed and maintain animals in the laboratory or hatchery until they are larger (ca. stage X–XI), as is typical of enhancement efforts with cultured individuals of Homarus gammarus (L.) in Europe, even though survival to commercial size presumably would be greater. One difficulty with releasing early benthic phase animals is that they have the capacity to swim away from the release site, making tests to determine the efficacy of such programs logistically difficult and expensive. A low-cost, low-maintenance, ocean-based nursery grow-out system for stage IV H. americanus was tested in waters off eastern Maine using technology first developed and implemented successfully for cultured individuals of H. gammarus in Ireland. A single individual was added to a plastic soda bottle (ca. 350 mL) or Petri dish (440 mL) containing a series of small holes to allow continuous flow of seawater into and out of the units. Bottles (n = 630) and dishes (n = 420) were added to rigid nursery cages constructed of traditional vinyl-coated lobster trap wire and deployed in July 2002 ca. 2 m off the bottom in depths of 10 m, 15 m, and 25 m in and around Chandler Bay near Jonesport. After nearly 70 days, survival in the bottles varied from 20% at the deepwater site to 90% at the shallow-water site; however, after an additional 244–288 days, most bottles had filled with muddy sediments, and mortality rate was nearly 100%. Conversely, survival rates after 448 days in the dishes varied, on average, from 21.5–47.2% per cage originally deployed at the deepest and shallowest site, respectively. Growth rates in the dishes generally doubled during the 14-mo field trial from a carapace length of 4.2 mm to that of 8.9 mm. Results suggest that ocean nurseries can be used to rear cultured lobsters to larger sizes prior to release for stock enhancement purposes; however, these animals are too small to apply visible tags (i.e., streamer or T-bar tags) that fishermen could discern easily.
These are large Petri dishes (6-inches diameter x 1-inch deep) with holes that have been in the field during the fall/winter of 2002-2003. Each was initially “seeded” with a stage IV lobster. There are ten of them in two stacks (an upper and lower stack). Five top dishes are stacked underneath five bottom dishes with vinyl-coated trap wire separating the two groups of five dishes. The unit is held together with nylon cable ties. The entire unit of ten dishes was placed on one shelf in a nursery cage.
Above: This is a Petri dish that was part of a stack of 10 dishes in a nursery cage in waters off Jonesport, Maine for 448 days from July 31, 2002 to October 22, 2003. The lobster inside is alive; however, it grew very little over the experimental period, only doubling in size (see photo below).
Lobsters doubled in size from a mean of 4.2 mm (carapace length, CL) to 8.9 mm CL during the 448-day field experiment.
Survival in the Petri dishes varied from 22% to 47%, but survival success depended whether the dishes were the five on the top vs. bottom of the stack in each shelf. Dishes in the bottom stack tended to fill with sediments and lobster survival ranged from 14% to 29%. Lobsters in the top stack fared much better with survival ranging from 29% to 69%.
Beal, B.F. and G.C. Protopopescu
2012. Ocean-based nurseries for cultured lobster (Homarus americanus Milne Edwards) postlarvae: field experiments off the coast of eastern Maine to examine effects of flow and container size on growth and survival. Journal of Shellfish Research 31, 177-193.
Historically, stock enhancement programs for American lobster, Homarus americanus, have a common theme: production and release of large numbers of stage IV or stage V individuals. However, these animals are difficult to mark, highly mobile when released on the bottom, susceptible to a wide array of predators, and their claws have yet to develop bilateral asymmetry. Many of these attributes make it difficult to test the efficacy of hatch-and-release efforts. It is possible to hold postlarval lobsters individually in the laboratory or hatchery and provide food regularly for several months to release older, larger individuals (as with enhancement efforts in Europe with Homarus gammarus). However, the costs to do so compared with the value of commercial-size animals makes this practice cost prohibitive. Attempts to reduce costs of rearing early postlarvae to larger sizes in ocean-based nursery cages in eastern Maine for periods of longer than 1 y have resulted in variable survival (in general, <50%) and slow growth (doubling in carapace length (CL) from 4.2–8.9 mm). A series of field trials (2004 to 2010) examined methods to improve survival rates and enhance growth with the goal of producing animals large enough to apply a physical tag that can be seen easily by fishers and scientists interested in testing directly the efficacy of enhancement efforts. The effect of flow rates into and out of various types of containers (350 mL and 440 mL) holding individual, cultured stage IV lobsters was examined experimentally during a 309-day period from August 2004 to July 2005 in off-bottom, ocean-based nursery cages deployed in shallow (12 m) water near Great Wass Island, Beals, ME. Mean survival rate varied directly with flow as animals in containers with the greatest exchange of seawater demonstrated survival rates of ca. 90% compared with ca. 30% in containers allowing lower flow rates. Sediment deposition in the low-flow rate containers tended to be high, and was associated with significantly lower mean lobster survival. In a separate field trial in shallow water from August 2009 to October 2010 (419 days), lobster growth in submerged wooden trays was assessed using 5 different container sizes that ranged from 0.02–0.26m2 (ca. 1.5–21 L). Growth was best described by a sigmoidal function, with a strong linear component over container sizes between 0.02 m2 and 0.13m2 (ca. 1.5–10 L), and no significant difference observed in mean CL of lobsters in the largest 2 container sizes. Final mean CL and mass (23.9 ± 1.4 mm and 10.7 ± 2.1 g, respectively, ±95% CI) of animals in the two largest containers was 57.4% and 349% greater, respectively, than animals in the smallest containers. Rearing cultured individuals of H. americanus to large sizes in ocean based nursery cages may provide managers of stock enhancement programs with a more viable assessment tool than those used traditionally.
The experiments conducted after 2004 focused on the effects of flow rates on lobster survival.
Above, a 3 1/2-inch hole was cut in both the top and bottom of a 6-inch diameter Petri dish, and pieces of nylon window screening were used to cover the holes so that a stage IV lobster would be retained within the dish. Screening was affixed to the polycarbonate Petri dish with PVC cement. Flow rates within dishes with the large hole and window screening were approximately five times greater than rates associated with Petri dishes with 50 holes (1/8th inch) drilled in them. Experiments were carried out to examine effects of flow rate on lobster survival.
Left, a nursery cage is prepared with three different containers – Petri dishes with 50 holes, Petri dishes with a large hole in both the top and bottom portion (as above), and plastic soda bottles (350 mL) with either twenty-five or fifty holes. Nine dishes or bottles occur on each of the eight shelves. The topmost shelf, 5th shelf, and the bottommost shelf contain Petri dishes with the large hole covered with window screening. Bottles with 25 holes occur on the second shelf. Bottles with 50 holes occur on shelves four and six, and Petri dishes with 50 holes were placed on the third and seventh shelf. Each bottle and Petri dish contained one stage IV lobster. A total of 13 cages similar to this one were deployed near Middle Ram Island, Beals, Maine on August 26, 2004 and 12 cages were retrieved on July 1, 2005 (309 days later).
Although fouling over the 309-day experimental period was intense (see the juvenile blue mussels, jingle shells, and barnacles), overall survival varied significantly among the treatments with 30% in the bottles (regardless whether they had 25 or 50 holes), 75% in the Petri dishes with fifty holes, and 91% in the dishes with the large hole covered by window screening.
Unfortunately, lobster growth was not as impressive as lobster survival. Animals doubled in size (as in previous experiments) leading us to wonder whether growth was related to the size of the container that lobsters were held within. To test the hypothesis that lobster growth is related to the size of its container, we conducted several field experiments.
The first experiment used lantern nets and two sizes of containers: white, 1-gallon containers with window screen tops and bottoms (levels 2-7) and 6-inch diameter Petri dishes with large holes covered with window screening (as above) in the topmost and bottommost levels (1 & 8). The trial was conducted over a 474-day period from August 2, 2006 to November 19, 2007 in Mud Hole Cove on the eastern side of Great Wass Island in the town of Beals.
Above center: The lobsters on the left came from the white, 1-gallon containers while the lobsters on the right came from the Petri dishes. On average, lobsters were 33% larger in the 1-gallon containers (average carapace length = 13.3 mm) than in the Petri dishes (average carapace length = 10.0 mm), and this difference was statistically significant.
To get a better idea of whether lobster growth truly was related to container size, we constructed wooden trays, and then created 10 partitions within each tray (2 replicates of each of five partition sizes). The smallest area is similar in size to the 6-inch x 1-inch Petri dish, with a volume of about 440 mL, and the largest area has a volume of approximately 20 L. One lobster was added to each compartment, and then the trays were situated in the middle of the water column in Mud Hole Cove from August 12, 2009 to October 5, 2010 (419 days).
Amazingly, lobsters grew nearly perfectly with the size of their container. The animals on the left are approximately two-inches long (tip of claw to end of telson), and were growing in the smallest compartments. The animals on the left are nearly five-inches long, and were growing in the two largest size compartments. There was no difference in growth of animals held in the fourth largest and largest size compartments.
Beal, B.F., Chapman, S.R.
2001. Methods for mass rearing stages I-IV larvae of the American lobster, Homarus americanus H. Milne Edwards, 1837, in static systems. Journal of Shellfish Research 20(3), 337-346.
We conducted a series of five laboratory experiments (7-18 days in duration) to test the interactive effects of stocking density, aeration rates, and food types on survival of American lobster (Homarus americanus) larvae through their first three planktonic stages (I-III) to the postlarval stage (IV). Experimental units and culture protocols were designed to replicate a 1:100 scaled-down version of equipment used in association with a fishermen-sponsored, stock enhancement lobster hatchery located in Cutler, Maine. The first four trials revealed that extremely high rates of aeration (ca. 240 mL air sec super(-1)) were necessary to distribute larvae and food sufficiently to reduce cannibalistic encounters; however, the best survival from stage I-IV (at stocking densities of 7-26 L super(-1) fed ad libitum with enriched Artemia) was only 24%. The final experiment (stocking density = 20 L super(-1)) yielded a mean survival rate ( plus or minus 95% CI) of 75.8 plus or minus 10.2% (range = 62.7% to 90.7%; n = 6). One important difference between the last and first four experiments was how stage I larvae were managed prior to their culture. In the first four trials, unfed larvae were collected from a relatively small (46 cm x 30 cm x 20 cm), screened capture basket located near the discharge pipe of a broodstock holding tank at the hatchery where they may have resided for > 12 hr. Larvae used in the final laboratory experiment were collected directly from the broodstock tank within 30 min after being liberated from the mother’s swimmerets. Larvae, at relatively high densities within the screened box, likely had many more cannibalistic encounters prior to their culture than those collected directly from the broodstock tank and, therefore, suffered high rates of mortality during the first four laboratory trials. Mass rearing methods for larval American lobsters developed in conjunction with these laboratory experiments were used successfully by staff at the Cutler Marine Hatchery from 1988 to 1992.
The three most important aspects of rearing mass quantities of lobster larvae are: 1) obtaining stage I larvae immediately after they have been released from the female (any residence time in a small container, especially without food, is deadly for the recently hatched stage I larvae); 2) bubbling the seawater in the rearing container so vigorously that the water appears to be boiling (this is necessary to keep animals away from each other during the culture period of up to 16 days); and 3) overfeeding with live, enriched Artemia (brine shrimp).
Beal, B.F., Chapman, S.R., Irvine, C., Bayer, R.C.
1998. Lobster (Homarus americanus) culture in Maine: A community-based, fishermen-sponsored, public stock enhancement program. Gendron, L (ed.). Proceedings of a Workshop on Lobster Stock Enhancement held in the Magdalen Islands (Quebec) from October 29 to 31, 1997. pp. 47-54. [Can. Ind. Rep. Fish. Aquat. Sci./Rapp. Can. Ind. Sci. Halieut. Aquat.]. no. 244.
In 1985, Maine’s lobster fishermen spoke with a unified voice as their Lobstermen’s Association (MLA) voted to ask the Maine State Legislature to allow a portion of their annual license fees to be placed into a fund created specifically for stock enhancement through hatchery production of juvenile American lobster (Homarus americanus). The Legislature approved MLA’s request and, because the Maine Department of Marine Resources (DMR) administers the license fees, gave the DMR the responsibility of creating a fair mechanism to disburse those funds. The eastern Maine fishing village of Cutler was awarded the grant money, and 400 citizens organized themselves into a Hatchery Committee. The funds allowed the Cutler Marine Hatchery to become an entity specifically for the production of juvenile lobsters for stock enhancement. Funding of this fishermen-sponsored community-based public stock enhancement program ended in 1992 and there have been no funds for lobster hatcheries in Maine since that time. The Cutler Marine Hatchery produced an average of 175,000 stage 4 and 5 animals each year from 1986 to 1991 for release to the wild for stock enhancement purposes.
This hatchery did not have the capability of holding thousands of lobsters in separate containers to reach a size where they could be tagged effectively and without injury. Consequently the hatchery became interested in developing a strain of genetically blue lobsters to use them as markers for this and other hatch-and-release programs. Results suggest that cultured blue lobsters have no significant behavioral differences in attempting to escape predation compared with normal colored individual, and that behavior across a variety of different substrates was also similar.