The following article about juvenile lobster research was prepared by researchers associated with the Bedford Institute of Oceanography.
Most people are used to seeing adult lobsters in fishermen‚Äôs catches, in a live tank at an aquarium or supermarket, or on their dinner plate.
But even lobster fishermen seldom see baby lobsters, those that are less than two to three centimetres long. Clearly, tiny lobsters are too small to eat, but finding and counting baby lobsters could be the key to insuring the long-term future of the lobster fishery.
In any given year, the number of young lobsters on the ocean floor is linked to the number of adult lobsters that will show up in fishermen‚Äôs catches in future years, and hence the health of the lobster fishery. But how do you even find baby lobsters, let alone get an idea of their numbers in the ocean?
Lobster biologists at the Bedford Institute of Oceanography are exploring two unusual methods for collecting baby lobsters, and the results to date are very promising.
Newly-settled lobsters (one to three months old when found by biologists), look exactly like an adult lobster, but are smaller than a quarter (scientifically speaking, when the body or carapace length is less than 13 mm long). Even older lobsters, from one to four years of age, are still able to easily fit into the palm of your hand. So traditional lobster traps can‚Äôt catch them at all.
The first method of collecting baby lobsters basically involves underwater vacuuming of the seafloor. It‚Äôs called suction sampling. Suction sampling is carried out by a team of scuba divers, who position a square plastic frame (a quadrat) over a small area of the ocean floor, then use an under-water vacuum to suck up everything inside the quadrat, including new, very small lobsters who might be hiding in the cobble. The vacuuming is done by using a large plastic tube that is held like a bazooka and an extra scuba tank that is connected to a fitting at the tube‚Äôs open end facing the seafloor while a mesh bag covering the upper end catches everything being sucked up. When the scuba tank valve is opened, air is rapidly forced through the tube, creating suction through to the end with the mesh bag. Everything larger than the 2mm openings in the mesh bag is caught and brought to the surface for examination. Suction sampling takes place each October in numerous locations in the Maritimes and in some northeastern states in the United States. Since 2005, divers from the Bedford Institute of Oceanography have conducted this work at several locations in Lobster Bay in southwest Nova Scotia.
The second method of collecting baby lobsters is by using passive collectors. Passive collectors are simply wire boxes filled with grapefruit-sized rocks that are lowered to the bottom of the ocean for periods of about three to four months and later brought back to the surface to recover the sea life that has settled within them.
The spaces between the rocks in the collectors are good habitat for baby lobsters and other young marine organisms, presumably because they make good hiding places from larger predators.
Since 2007, up to 400 collectors have been deployed each year at various locations around Nova Scotia in water depths of 3 to 42 meters, usually from June to October. The collectors weigh about 300 pounds each, so they‚Äôre deployed and recovered using a commercial fishing vessel.
The concentration (number per unit area) of newly-settled lobsters differs a great deal across the different regions. In 2011, for example, the greatest concentration of lobster babies were found in St. Mary‚Äôs Bay (2.9 per metre squared) and the fewest in Port LaTour (0) and Lobster Bay (0.2 per metred squared). More importantly, baby lobster abundance shows good and ‚Äúnot so good‚ÄĚ settlement years. Overall, 2011 had the lowest settlement in the most recent five years, while the years 2009, 2007 and 2005 had relatively good settlement. As the number of years of the monitoring increases, so does the ability to see patterns in settlement, including what factors might be behind these differences.Wind and temperature seem to be key variables, with certain winds and warm temperatures helping the young lobsters to stay in an area and survive to settle.
It appears both the collectors and suction sampling results are giving reliable indicators of the number of baby lobsters on the ocean floor, with good years showing up as good in both methods, and poor years doing the same.
One difference seen is that the collectors appear to under-represent the abundance of one-year-old lobsters (in the size range of 13 to 20 mm carapace length). This might be expected because these tiny lobsters are thought to be less mobile and shelter restricted than larger sizes. As such they might be less likely to enter collectors.
By predicting the health of future lobster populations, this research helps insure that the Atlantic Canadian lobster industry remains healthy and sustainable over the long term. And while the main focus of suction sampling and collectors is to find and count young lobsters, many other species of marine life are found with the lobsters providing information on the biological associations of young lobsters and indication of the biodiversity of Nova Scotia waters.