Abundance, Sex and Size Distribution of European Green Crabs, Carcinus maenas (Linnaeus, 1785), at Natural and Aquacultured Oyster Areas in Great Bay Estuary, NH

Abstract

Great Bay Estuary (GBE) is a complex estuarine system at the convergence of seven rivers, ocean and land. The GBE ecosystem supports typical estuarine species but, like many estuaries, has been a target of both invasive and range-expanding species. The goal of this study was to compare abundance, sex and size distribution of green crabs between oyster farm sites and non-farmed sites within GBE in 2021 and 2022. Overall catch was higher in 2021 compared to 2022. The highest population of green crabs was estimated to be in the farm area around Cedar Point, and natural/restoration area near Moody Point had the smallest European green crab population. In both years, the majority of green crabs captured (98%) were adult males, and few were juveniles captured. At the last sampling date of 2021 and 2022, most crabs were large (68 ± 0.5 mm and 63 ± 2 mm carapace width, respectively). Shellfish growers, restoration and management teams could use these data in mitigation strategies to sustain industries and enhance GBE health. This information is important for oyster restoration initiatives and oyster growers as they may want to: consider putting traps around their restoration reefs and farms to help reduce green crab infestation/predation in their growing areas; make decisions regarding best management practices and optimal growing locations when applying for permits; and work with management teams with gear improvement, such as floating gear, to reduce green crab intrusion into cages. High-priority locations for trapping should be areas such as oyster farms, oyster reefs and restoration sites.