Climate Change Suspected for Lobster Decline in Southern New England Stocks

In April, the Atlantic States Marine Fisheries Commission (ASMFC)— a multi-state governmental body charged with fisheries management and conservation duties for 15 states—released a fisheries management plan detailing the decline of Southern New England (SNE) lobster stocks and its likely climate change link.

The SNE lobster stock, ranging from Cape Cod, Massachusetts to Virginia, is critically depleted. According to the ASMFC fisheries management plan, the SNE stock hit its peak in the 1990s but has since seen a steady decline. During the same period of decline (since 1999), the region has experienced a widespread increase and duration in water temperatures above 20°C (68°F) throughout inshore waters.

Total lobster abundance as measured by the University of Maine Length Based Model for the 2009 assessement. The median (yellow) and 25th percentile (red) of the 1984‐2003 reference period are noted. © ASMFC

Anomalies from the mean number of days > 20°C [68°F] of the Woods Hole seasurface temperature, 1945 ‐ 2009. © ASMFC

According to the management plan, prolonged exposure to water temperature above 20°C (68°F) causes the following in lobsters:

• “Respiratory and immune system stress”
• “Increased incidence of shell disease, acidosis, and suppression of immune defenses”

Lobsters prefer cooler temperatures, causing migration to offshore deeper waters from inshore shallow waters. This shift may have implications for larva as their nursery grounds are traditionally inshore. Additionally, “[w]ater temperature has a pervasive effect on all of the major life history processes of American lobster including growth, maturity, spawning, egg maturation, and larval maturation.”

While it’s impossible to generate a direct correlation between the SNE lobster stock decline and warmer ocean temperatures, there is a strong link. According to the report, “the strong coincidence in the timing of the increase in water temperature with the timing of the decline in landings, spawning stock biomass, and recruitment, coupled with overwhelming experimental evidence of increased physiological stress, immunosupression, and increased rates of disease in lobster exposed to prolonged periods of temperatures ≥ 20 °C [68°F], strongly suggest that increasing water temperatures have played a primary role.”

In addition to climate change, increased predation may also be playing a role in the decline. According to the report, the abundance of mid-Atlantic predators (e.g. striped bass, dogfish, and scup) has increased over the past decade. Experts forecast that warmer northeast waters from climate change may allow the southern fish communities to expand northward, ultimately increasing lobster predators.   

The management plan concludes that the stress of warmer ocean temperatures and fishing (even though overfishing is not occurring in SNE) are too harsh for long-term survival of the SNE lobster fishery. The plan is recommending a 5 year moratorium on fishing in order allow the stock to rebuild and support a sustainable long‐term fishery.