Fecundity, oocyte atresia, and gametogenic staging accuracy of Atlantic sea scallops at varying population densities

Marine protected areas and other spatial management strategies are common tools in fisheries management. One benefit of spatial management is larval export from closed areas. Larval export relies on reproductive output of resident spawning adults, which can vary with population density. Atlantic sea scallops Placopecten magellanicus support a valuable US fishery that utilizes spatial management strategies to increase yield- and biomass-per-recruit. Two high-density recruitment events were leveraged to assess scallop fecundity across a range of population densities and shell heights in narrow geographic areas. Female gonad samples were collected quarterly from May 2018 to January 2020, and quantitative histology was used to estimate individual fecundity, area-based fecundity, proportion of oocytes undergoing atresia, and accuracy of gametogenic staging at sea. Fecundity increased with shell height, from 1.5 million eggs at 73 mm to 105 million eggs at 162 mm. Area-based fecundity plateaued above 5 scallops m -2 , at a mean of 35 million eggs m -2 . Oocyte atresia was observed in all gametogenic stages. In mature scallops, the mean proportion of oocytes undergoing atresia varied from 55% at 73 mm to 40% at 162 mm. Gametogenic staging accuracy varied with gametogenic stage, study area, and proportion of oocytes undergoing atresia. Our estimates of fecundity are 57-89% lower than previous estimates using the difference in gonad weight after spawning. On average, 47% of oocytes in mature sea scallops were atretic, representing substantial losses to fecundity. Our results provide updated estimates of sea scallop fecundity and elucidate an important component of larval export in spatial management strategies.