The Stone Crab Fishery
Written by Kate Rose, Graduate Student in Fisheries and Aquatic Sciences, UF IFAS School of Forestry, Fisheries & Geomatic Sciences
There is perhaps no seafood as quintessential to the Florida experience as the Florida stone crab. This crab is nearly completely a Florida fishery, and over 95% of stone crabs harvested are consumed here in Florida. The process of getting this animal’s meat from maritime to meal, however, is about as whacky as the state that it’s named after. Stone crabs exhibit autotomy, which means they can drop their limbs as a method of escape and regrow them later. Fishing practices capitalize on this by allowing fishermen to take one or both claws, where most of the meat resides, from the animal (assuming they are of minimum size) and returning it—alive—to the water. Most animals, aquatic or terrestrial, aren’t designed to be consumed and live to tell the tail. Even fewer are designed to recover from the experience!
Because of their abilities, it’s tempting to think of the Florida stone crab population as a population that will never run out. But if you were dumbfounded at the fact that fishermen could take both of a crabs’ claws, and it would be just fine, you were rightly so. Fishing mortality studies show that only 40% of crabs that have both of their claws removed survive to regenerate another claw. The other 60% either perish from injuries directly associated with claw removal or indirect consequences of missing claws, like not being able to crush the shells of the snails and bivalves stone crabs normally feed on.
My research investigates the effects of trap fishing on crabs before they have their claws removed. I had a theory that if crabs are stuck with other angry crabs in a trap for long periods of time, it could affect their growth and survival after being fished. The time that a trap is in the water fishing is called its soak time, and it’s important for fisheries managers to understand how soak times contribute to the stone crab fishing mortality if they are to manage the population sustainably. Understanding this relationship has become particularly relevant recently to fisheries managers for three reasons:
- In search for higher catches, stone crab fishers have been observed setting their traps farther offshore and checking them less frequently to compensate for the increased time and fuel required to check traps.
- Trap reduction policies implemented with the goal of reducing fishing mortality are likely to shift fishing behavior, including soak times.
- Understanding the rate of fishing mortality has prompted managers to focus on the health of sub-legal crabs, whose claws are too small to be removed.
My first instinct was that if crabs were being held in traps for sometimes upwards of 30 days, that they might starve in traps. I am testing this hypothesis with a field study, conducted jointly by members of the Florida Wildlife Research Institute and myself, as well as a corresponding starvation study in the NCBS wet lab. I originally tried to conduct this starvation study at university facilities in Gainesville, but it turns out having access to seawater while housing 32 marine crustaceans is helpful! Using the lab’s capabilities to pump and filter seawater, I was able to create a flow-through system that kept the crabs comfortable in separate 10-gallon tanks that allowed me to control their diets. With the help of some undergraduate volunteers, I have been measuring a variety of nutritional and neurological indicators at the beginning, middle, and end of a 30-day starvation window.
The NCBS team has also been immensely gracious in helping me troubleshoot challenges I’ve encountered along the way. Stone crabs, even those that are starved, are very mischievous and as such, I’ve had to employ especially large airstones that the crabs can’t damage with their powerful claws and netting over the top of the tanks to prevent the little buggers from crawling out, or into other tanks. Recently, as the state becomes saturated with rainwater, I was even able to switch the water source in my system from surface seawater (which is subject to freshwater inputs from the Suwannee River) to water from a saltwater well to maintain a constant salinity. Despite all my poking and prodding, I think that the crabs are healthy and performing well. Results of this study will hopefully inform managers about the implications of soak time on sub-legal stone crab growth and survival, which could directly improve the management of this important Florida fishery.