The commercial fishery for American lobster 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 lobsters.
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.
This research was published in 2012 in the Journal of Shellfish Research. Read the entire paper here.