Ecosystem Targets and Supporting Indicators
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The American lobster (Homarus americanus) lives in the cold waters of the Northeastern US and Canada, including Long Island Sound, and range offshore as far south as Virginia. In US waters three separate lobster stocks are recognized: the Gulf of Maine where they are very abundant, Georges Bank where populations are stable or increasing, and southern New England where abundance has dramatically declined in the last decade.
Lobsters are social, territorial crustaceans that live in a variety of different habitats, preferring areas that have a rocky or firm mud bottom they can burrow into. Studies have shown that inshore lobsters like those in the Sound have localized movements, while offshore lobsters seasonally migrate from as far as the edge of the continental shelf to inshore waters to spawn in late spring and summer.
Because most of the Sound’s lobster population does not migrate, the standardized catch of lobster from the CT DEEP Long Island Sound Trawl Survey is used to assess the relative abundance of the local stock. The trawl index is a more accurate representation of abundance than lobster landings because landings are influenced by how each fisherman sets their gear, how often they fish, and socio-economic factors such as market price.
The above graph shows the trend of lobster abundance in the fall (note that no data are available for 2010) and spring. The fall and spring indices for American lobster are on a steady decline. Both indices have remained below the time-series average since 2003, and in recent years are nearing or reaching zero. One of the factors implicated in the lobster population decline is increased summer water temperatures in Long Island Sound. American lobsters cannot maintain their metabolisms in waters above 20°C for long periods of time. The LISS climate change indicator, for example, shows that the Niantic Bay has experienced water temperatures greater than this threshold in the summer for the past 10 years. Additionally, some warm water species that prey on lobsters are becoming more abundant in the Sound, such as Black Sea Bass. Other species such as Smooth dogfish and striped bass that have high consumption rates on lobster, may be contributing to keeping lobster abundance to the current depressed level.