We used citizen science to improve understanding of population trends and behavior in the American horseshoe crab (Limulus polyphemus) along the entire coast of Florida. First, we used 18 years of public sightings data, beginning in 2002, on horseshoe crab mating to determine which spawning locations were used most. Then, a subset of those locations was more rigorously surveyed through the Florida Horseshoe Crab Watch program. Florida Horseshoe Crab Watch, implemented in 2015 by a collaboration between the Florida Fish and Wildlife Conservation Commission (FWC),
In the Western Atlantic and Gulf of Mexico (GOM), the blue crab Callinectes sapidus fishery is managed at a regional scale, and its assessment does not consider the population structure of the species. To understand connectivity of the blue crab population, we simulated larval dispersal using a biophysical model driven by high-resolution ocean currents and including early life-history traits of the species. Simulations were conducted during 2015 and 2016, and larvae were released from locations along Florida's GOM and Atlantic coasts. A high degree of local larval retention was observed in Florida's GOM waters, mainly during summer when weak southeastern winds tend to yield a shoreward net flow. Results demonstrated clear evidence of connectivity between the Gulf coast of Florida population and those of Mississippi, Alabama, and Louisiana, suggesting that the blue crab populations in the GOM are intermixed and the hypothesized boundary (in Florida) of 2 stocks needs further consideration. Outputs of the model also indicated connectivity between the blue crab populations of Florida's Gulf coast and the South Atlantic Bight (SAB). Larval trajectories showed inter-annual variability driven by the interaction of winds, Loop Current (LC) intrusions in the northern GOM, LC eddies and their cyclonic counterparts, and the Mississippi River plume. The latter provides a conduit for larval transport from the GOM to the SAB. These findings provide evidence of the physical oceanographic processes that sustain the homogenous genetic population structure for blue crabs between SAB and GOM populations, highlighting the need for collaborative management in US waters.
The present study aimed to investigate the life history traits of blue crabs Callinectes sapidus found in four estuarine systems-two on the Gulf coast of Florida (St. Andrews Bay and Suwannee Sound) and two on the Atlantic coast (St. Johns and Halifax rivers). Females in St. Andrews Bay, Suwannee Sound, the St. Johns River, and the Halifax River reached maturity at a carapace width (measured from lateral spine tip to lateral spine tip) of 116.5, 121.9, 129.5, and 123.7 mm, respectively. At both Gulf coast locations, year-round spawning was not observed; peak spawning occurred in early to late spring, and in St. Andrews Bay there was an additional fall spawning event. On the Atlantic coast, spawning females were collected almost year round, with the greatest abundance in winter through spring and an additional peak in late summer. Potential fecundity on both coasts was directly correlated with body size and was greatest at the beginning of each reproductive season. Egg diameter from crabs on both coasts was independent of female size and was influenced by month, with the largest egg diameters observed in the earlier months of the year. Overall, there was an inverse relationship between potential fecundity and egg diameter. Mean potential fecundity for females sampled in St. Andrews Bay, the Halifax River, and the St. Johns River was 1.8, 2.1, and 2.2 million eggs, respectively. This demonstrates that seasonality is important for blue crab reproductive output and for the timing of juvenile and fishery recruitment.
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