Patterns and Processes Underlying Spatiotemporal Variation in Bay Scallop (Argopecten irradians concentricus) Density and Size Structure within Three North Carolina Sounds

ABSTRACT Populations of bay scallops (Argopecten irradians concentricus) in North Carolina (NC) declined precipitously following harmful algal blooms in the late 1980s and have struggled to recover. Following these harmful algal blooms, there was an increase in the frequency and magnitude of hurricanes and tropical cyclones in the 1990s, and a >30% loss of seagrass between 2006 and 2020 that further impacted the bay scallop populations. The last assessment of scallop density and distribution in multiple sounds in NC was performed in response to a 1987 red tide event. In the present study, 510 visual surveys of bay scallop densities and sizes in seagrass beds in southern Core Sound, Back Sound, and Bogue Sound, NC were conducted from May–November 2022. The mean scallop densities were 0.54/m2 in Core Sound, 0.26/m2 in Back Sound, and 0.19/m2 in Bogue Sound. Using the healthy population density limits of bay scallops from Florida and New York to Massachusetts, a healthy density threshold of >1.0 spawning adult scallops/m2 for NC was estimated. There was a positive relationship between seagrass density and scallop density, and as seagrass density decreased in the fall, scallop density also decreased. Bay scallops increased in size from May to August. In the fall there was a decline in the mean size as new recruits were added and a die-off of the adults occurred. Water quality appeared suitable to support healthy scallop populations at all sounds, consistent with previous observations in this system and others. The temporal scale of water quality sampling was not adequate to record short-term freshets that may have impacted scallop density. The information from this study can update the status of the bay scallop population in NC sounds, as well as inform management for the purpose of sustainable harvest or restoration.