Abundance, Distribution, and Life History Characteristics of Mantis Shrimp, Squilla Empusa, in Narragansett Bay, RI

The mantis shrimp, Squilla empusa are benthic, megafaunal burrowers and a predatory species. Its abundance is significantly correlated to sediment type. Mantis shrimp reside in self-excavated burrows and established different burrow shapes in the winter and summer seasons. In Rhode Island mantis shrimp have traditionally not been considered to have commercial value in the fishery. However recently, a new market for this species has emerged from local Asian restaurants in Boston and New York, and several fishermen in Rhode Island are periodically targeting the species in a directed fishery. Mantis shrimp fishery in Rhode Island occurs mainly in Mount Hope Bay.

Our study of mantis shrimp abundance and distribution was conducted in both the winter and summer seasons. In winter season the study was conducted based on video observation, while in summer season was based on trawl survey. In the winter season, we found that the density mantis shrimp based on burrows was 1.7/m² and 1.1 / m² using sequential and continuous data analysis methods, respectively. Across locations, using both data analysis methods of sequential and continuous, we found that mantis shrimp density across the locations was significantly different, whereas Mt. Hope Bay that dominated with sandy mud has the highest mantis density and Providence River that dominated with muddy has the lowest density. In the summer season, trawl survey predicted very low mantis density with average density across the location was 0.02/m².

With regard to life history characteristic, in our study, it was determined that mantis shrimp experience isometric growth with ln(W (gr)) = -11.129 + 3.00 ln(L (mm)). Females are slightly larger than males in mean length and length distribution, however the differences is not substantive to be considered in growth calculation. We found that there was seasonal growth in mantis shrimp and the annualized instantaneous growth coefficient (K) is about 0.4 and maximum length is about 202 mm. Mantis shrimp has  50 % probability of maturity at about 120 mm in their second year of life (age 1). We believe mantis shrimp spawn in late winter and early spring. Recruitment to the fishing gear starts in the late fall and early winter in the first year of life, but these small animals are discarded.  Mantis shrimp life span is estimated to be about 3 years, and only animals in their second and third years of their life are retained in the fishery.