Inshore juvenile lobsters threatened by warming waters and migratory fish predators in southern New England

Abstract

The southern New England stock of the American lobster Homarus americanus has declined since its peak in the 1990s. While the decline of lobsters has been directly attributed to warming sea temperatures, indirect effects such as migratory fish species shifting north may also be important. Two sets of experiments and a survey of gut contents collected from wild-caught scup Stenotomus chrysops and black sea bass Centropristis striata during the summer were performed to assess thermal and predatory stressors on juvenile lobsters. A temperature experiment compared the growth and survival of young-of-year (YOY) and 1 yr old lobsters in ambient seawater and seawater warmed or cooled by 3°C. Two predation experiments compared the survival of juvenile lobsters in treatments with scup, black sea bass, and Asian shore crabs Hemigrapsus sanguineus. Increased water temperature did not increase mortality in juvenile lobsters, but it did tend to have a negative impact on growth and weight gain of YOY lobsters and weight gain of 1 yr old lobsters. In the predation experiments, fewer lobsters survived in mesocosms with black sea bass and scup than in the control treatment. Fish gut contents contained few lobsters, but black sea bass stomachs contained many juvenile cancer crabs, signifying that the fish prey in cobble habitat that is preferred by both juvenile cancer crabs and lobsters. While juvenile lobsters can survive current temperatures, they may face compounding challenges as warmer water slows their growth and leaves them more susceptible to predation by increasing numbers of migratory scup and black sea bass.