Spawning patterns of blue crabs in Florida

blue crabs in bucketThe blue crab, Callinectes sapidus, is an ecologically and economically important component of ecosystems along the Atlantic and Gulf of Mexico coasts of the United States. A well-established fishery exists from Texas to Florida and from Florida to New Jersey. The Fish and Wildlife Conservation Commission (FWC) achieves management of this valuable stock in Florida through the routine collection, analysis, and application of data in stock assessments.

After the completion of state and regional stock assessments in 2011, two needs were identified for blue crab research – a detailed understanding of blue crab spawning stock dynamics, as well as of population connectivity through dispersal models. Researchers believe that having this information will increase the resolution of the Fish and Wildlife Research Institute’s (FWRI) 2018 blue crab stock assessment for Florida coastal waters and aid future regional assessments for blue crabs in the Gulf of Mexico. To gain this understanding, researchers are in the early phase of a project to learn about the connectivity of spawning and recruitment of blue crabs within Florida waters and between Florida and neighboring states.

researcher measuring blue crab on boat
Image courtesy of
Jimmy Hull

In 2013, FWRI researchers began a spawning stock population survey to learn more about the poorly understood spawning patterns of adult blue crabs in Florida. Researchers selected four study locations – two on the west coast (Cedar Key and Panama City) and two on the east coast (Melbourne and Jacksonville). At these study locations, four stations, each consisting of five commercial blue crab traps, are arranged from the mid to lower estuary. For two years, researchers focus on one coast and visit the traps once a week, where they note the number of crabs collected and their reproductive condition, and measure the physical water conditions including temperature, salinity, pH, and dissolved oxygen. Other trap lines in sight of the study location are noted, as a proxy for local fishing pressure. Weekly, a subsample of female blue crabs are collected from each station and taken to the laboratory for histological processing of ovaries to determine reproductive stage. Also taken to the laboratory are crabs that possess a newly formed sponge (egg mass). From these crabs, researchers can determine the number of eggs in the sponge, which helps researchers determine the potential fertility of the crab.

Once work on the population survey has completed in 2017, staff will process and analyze all the samples that have been collected during the past four years. Using these results, combined with past blue crab research, scientists will turn their attention to another missing piece of blue crab research data – larval dispersal across Florida waters. Researchers hope to address this lack of data through the creation of a larval dispersal model, which will tell researchers where larvae are being spawned, and where they go. This model will also provide insight into blue crab stocks in Florida, and help to address questions as to whether there are just two distinct stocks (Gulf and Atlantic) or have environmental barriers prevented larvae from mixing beyond a certain point, thus creating sub-stocks.

Work on this project is still in the early stages. The first two years of this project have concentrated on collecting samples from the west coast and researchers are currently analyzing these samples. Sample collection is underway on the east coast and will continue through 2017. Once all samples have been processed and the resulting data sets analyzed, work will begin on the larval dispersal model. While findings are still years away, scientists are already developing a much more refined understanding of the spawning patterns of female blue crabs in Florida. These early findings offer much promise for future results, and in turn the continued successful management of this important Florida resident.