Seasonal catch, size, color, and assessment of trapping variables for the European green crab Carcinus maenas (Linnaeus, 1758) (Brachyura: Portunoidea: Carcinidae), a nonindigenous species in Massachusetts, USA

The population of the nonindigenous green crab Carcinus maenas (Linnaeus, 1758) in Salem Sound, Massachusetts, USA, was studied over a three-year period from July 2013 through June 2016 using baited traps deployed monthly at five sites. Seasonal catch per unit effort, sex, size, and color were determined and the role of habitat variables, including temperature, salinity, water depth, and substrate, were evaluated. Seasonal catch per unit effort was highest in the fall (October-December), followed by summer (July-September), spring (April-June) and winter (January-March). Few crabs were captured when water temperature dropped below 5 °C. Crabs captured at sites with very fine sand were larger than those captured on other sediment types. Females comprised 73% of the total catch of 7,822 crabs. Only 57 individuals exceeded 70 mm carapace width. Females were larger (mean = 51.7 mm) than males (mean = 48.8 mm). Green-phase crabs comprised 56.8% and red-phase crabs 43.2% of the catch. Green-phase crabs were significantly smaller (mean = 48.1 mm) than red-phase crabs (mean = 53.6 mm, P < 0.0001). Red-phase females were most common in the spring and green-phase in the fall, whereas red-phase males were most common in the spring and fall and green-phase in the summer. A yellow-phase category is proposed as a distinct intermediate between red and green phases. Merits of various types of traps and of bait were evaluated based on different trapping requirements and goals. This is the first investigation of multiple aspects of a population of C. maenas in Massachusetts. The findings should prove useful for researchers studying other populations of C. maenas, as well as for commercial crab fishers or others trapping green crabs for bait, or in efforts to reduce population numbers of this destructive invasive species.