Sustaining a thriving lobster fishery through science and community.
Lobster life begins when females extrude fertilized eggs that attach to the underside of the abdomen (spawning). Above, an ovigerous female is shown hatching her eggs. The brooding period time between spawning and hatching is estimated to be 9 to 11 months.
This photo shows the underside of an egg-bearing female. The developing embryos remain attached to the female for an estimated 9 11 months. Brooding females care for and protect their eggs.
The Lobster Conservancy works with eggers in three places: field, classroom, and at the Lobster Life Studies Center.
Mapping the Spawning and Hatching Grounds of the American Lobster: Sonar Tracking Project
In the field, we are mapping the spawning and hatching grounds of the American lobster in Muscongus Bay. We are testing a local brood stock hypothesis. The prevailing view is that larvae travel great distances to populate coastal waters. We think that local larval production is important, too and that eggs that hatch and seed inshore waters come from both local and distant production. Specifically, we are testing the hypothesis that smaller first and second time breeders remain local spawning and hatching in near shore locations, while larger females travel greater distances and are responsible for longer distance larval dispersal.
This project is funded by the Northeast Consortium and Davis Conservation Foundation.
To map the distribution of spawning and hatching females in Muscongus Bay we have recently launched the Sonar Tracking Project. We train fishermen to track sonar-tagged lobsters using a hydrophone. This allows us to determine the location of brooding females whether or not they are captured. Previous tagging projects aimed at tracking egg-bearing females have failed to follow the females for long periods of time. Because we are able to remotely sense the lobsters, we know where they are and where they are not and we can find them when they are inactive and find them in areas that are not being fished.
The Principle Investigators for this project are Diane Cowan (The Lobster Conservancy), Win Watson (University of New Hampshire*) and Andy Solow (Woods Hole Oceanographic Institution*); the research associate is Dan OGrady an Island Institute Fellow working with the Lobster Conservancy; and lobster trackers include me, Dan, twelve lobstermen from Friendship, two lobstermen from Monhegan and one Marine Patrol Officer.
Tag and release positions were recorded on a global positioning system.
Each sonar transmitter emits a unique series of beeps that can be heard by an underwater listening device called a hydrophone. Using a hydrophone, a lobster can be individually identified from a boat up to 800 meters away. The 12-month life of the sonar transmitter battery allows for sufficient time to follow females from spawning to hatching. Lobster boats were outfitted with hydrophones, and the captain and crew were trained to identify lobsters and record the necessary data. The lobstermen listen for the females and report on their current location.
The temperature data logger records the water temperature every hour for over a year. This information will be useful in determining the range of temperatures the female lobsters and their eggs were exposed to during the brooding period. Lobster eggs develop faster in warmer water. During the summer, shallow water is warmer than deep water, but in the winter the reverse is true. Some scientists believe lobsters, and especially egg-bearing females, move in response to temperature change. Brooding females are thought to move out to deep water for accelerated incubation time. The relatively large number of females tagged for this study should allow this hypothesis to be tested.
The red identification tag contains TLCs name and phone number and the lobsters identification number. This allows any lobsterman who hauls up a sonar-tagged lobster to call in and report its location, depth and condition.
This map shows the capture and release locations of the 191 females we tagged from Sep 5 Oct 10, 2002. Each female lobster being tracked is equipped with three objects:
The 191 eggers tagged ranged in size from 79 to 151 mm CL. Dotted red lines indicate minimum and maximum legal size, respectively. The smaller of these animals represent first time breeders weighing less than one pound and are approximately 7 11 years of age. The larger females in this study weigh up to approximately 10 pounds and are possibly 40 years old.
We are interested in how the females of different sizes contribute to replenishing the lobster supply.
103 of the original 191 females have been located at least twice. 33 three times; 13 four times; 9 five times; 2 six times; and one female has been heard on seven separate dates.
This map shows the travel trajectories of the forty five females who have moved > 1 km from their original capture location, we call them the movers. The net movement thus far has been away from the mainland. The females shown here have moved into deeper waters. Their paths seem to be along geological features forming channels between ledges. In Spring we will be able to determine whether these females make return migrations to near shore waters to hatch their eggs.
The first female we tagged has been detected on seven occasions. She is a large female measuring approximately 4 inches in carapace length. She weighs approximately 2.5 pounds. Female #0001 was heard near the same location 4 times between Sep 5 and Oct 15. Then she was heard about 4 miles away on Nov 4; a bit further away Nov 23; and further still on Nov 26. She was last heard at the boundary separating Friendship from Monhegan waters. We have equipped two Monhegan boats with hydrophones hoping to pick up the locations of females who have apparently migrated into those waters.
Fifty-eight of the tagged females who have been subsequently detected have not moved > 1 km from the original release site. These females would go undetected with traditional tagging methods. They seem to be hunkered down for the winter brooding their eggs where they spawned.
This project is ongoing. Updates will be added to this page as we map more locations.