Blue crab spawning and larval dispersal in Florida
The blue crab fishery is one of the most valuable fisheries in the state Florida and has remained a vital part of fishing culture for decades. Florida’s coastline exceeds 8,000 miles and has diverse and unique systems on both coasts that provide critical habitat for blue crabs. For the past 15 years, annual blue crab landings have declined on both coasts which highlights why further research is needed to manage the Florida stock. Prior to the spawning and recruitment study conducted by the Fish and Wildlife Research Institute (FWRI) from 2014-2018, little was known about size at maturity, fecundity potential, and spatial and temporal differences in the blue crab stock throughout the state. The objective of this research was to evaluate spatial and temporal differences in the blue crab spawning stock structure in four locations: St. Andrews Bay, Suwannee Sound, the Halifax River, and the St. Johns River. Data collected in this study provided information for use in future stock assessments.
Progression of internal egg development (orange egg seen under shell), to newly deposited orange eggs under the females’ apron, and finally the mature gray/brown eggs that are ready to be released as larvae.
Size at maturity for female blue crabs was assessed by apron shape (immature females have triangular aprons while mature females have broad rounded aprons) and was determined to be highly variable among the four locations. Overall, St. Andrews Bay crabs achieved the smallest size at maturity, while crabs collected from the St. Johns River had the largest size at maturity. The size of a mature female blue crab directly relates to how many eggs she releases, larger females produce more eggs than smaller females. Collectively, this study determined that female fecundity was highly variable among the four locations and estimates ranged from 47,000 to 5.4 million eggs in a single egg mass. This research also found that the Atlantic coast populations produced spawning females throughout the year whereas the Gulf Coast population spawn primarily from spring to fall. Additionally, the largest eggs (diameter), were observed in the earlier months of the year. Data collected from this research was used to inform a larval dispersal model, which was created in partnership with researchers from Florida Atlantic University and the University of Miami (RSMAS).This model also incorporated larval behavior and physical ocean trails to simulate how blue crab larvae is distributed throughout Florida and neighboring states. The model demonstrated clear evidence for high retention in the Gulf of Mexico during the summer months but also connectivity to the neighboring Gulf states such as Alabama, Mississippi, Louisiana, and the South Atlantic Bight. Additionally, the model verified Florida Gulf Coast connectivity to the South Atlantic Bight from Panama City and Tampa Bay. This research highlights how connected Florida’s blue crab population is among its own estuaries and the connectivity to other Gulf of Mexico and Atlantic stocks.