A Comparative Study of Habitat Value for the Juvenile Blue Crab (Callinectes sapidus) Provided by Off-bottom Oyster Farming in the Northern Gulf of Mexico

Abstract

In the northern Gulf of Mexico (nGOM), the quality and quantity of nursery habitat available for juvenile utilization is the most critical limiting factor affecting local populations of the blue crab, Callinectes sapidus. Though submerged aquatic vegetation (SAV) and oyster reefs (both natural and artificial) have been more-commonly acknowledged of late for their provisioning of this valuable habitat, each has also suffered decline recently throughout many areas. However, the gear used in off-bottom oyster farming (i.e. the culture of oysters within mesh containers held above the seafloor; OBOF) holds potential to provide additional habitat that is valuable for juvenile blue crabs (JBCs), especially in areas lacking other types of suitable habitat. In order to make a qualitative assessment regarding the potential value of habitat that OBOF gear could provide for JBCs in the region, comparative field sampling and tethering experiments were performed to collect quantitative data from OBOF gear (specifically, the gear used in adjustable longline systems), along with bagged oyster shell, SAV, and unvegetated bottom habitats, during Summer and Fall 2013, at three spatially separated field sites within the coastal waters of Alabama and Louisiana. Following experimentation, an evaluation was made based on comparisons of average density, size, and percent survival data. Results showed that JBC densities, sizes, and survival rates were generally higher in the OBOF gear than in the other habitat types to which it was compared, though there appeared to be a functional change in its relative value over time. Consequently, OBOF gear seems to provide JBCs with valuable habitat which ranges by comparison from equivalent to significantly greater, depending on an exponentially based, size/density-dependent process, which resembles the Ricker function.