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Stone Crab Season Upon Us

Stone crabs are feisty, fearsome predators, even cannibalistic! Two commercial species of stone crab coexist in the state of Florida, the Florida stone crab (Menippe mercenaria) and the Gulf stone crab (Menippe adina). These two crabs are managed as a single fishery in the state. The Florida stone crab (our crab) occurs in the eastern portion of the Gulf of Mexico and extends from North Carolina throughout peninsular Florida and the Caribbean. The Gulf stone crab occurs principally in the northern and western Gulf of Mexico.

The Florida stone crab inhabits mixed seagrass-hard bottom habitat. Adult crabs dig burrows under the seagrasses or excavate holes in emerged rocks on the seafloor. The Gulf stone crab also occupies those habitats, but prefers muddier bottoms and oyster reefs. Both species feed primarily on mollusks, including scallops, clams, conchs, and oysters, which they crush with their powerful claws. Predators that feed on stone crabs include octopus and humans.

Stone crab fun fact: Stone crabs are usually right handed; the large crusher claw can exert over 14,000 pounds per square inch of force!

Age estimates suggest male stone crabs can live up to seven or eight years and females can live up to eight or nine years. In a fished population, however, it is unlikely they will reach their maximum age. Males typically grow larger than females and their growth rate is more variable.

Stone crabs become sexually mature around two years of age and females, on average, reach maturity at a smaller size than males. Mating occurs after a molt; so, when a female crab is ready to molt, the male crab takes her into his burrow and stays with her. After she molts, her exoskeleton is soft, at which time he mates with her. After mating, male and female crabs go their separate ways. Mating typically occurs in the fall (September through November), which corresponds to peak molting times in females. Males usually molt during winter months.

Females store sperm received during mating in special sacs, and use it to fertilize their egg mass, known as a sponge. They can hold the sperm for up to a year, or until the next time they molt. A single female may produce four to six sponges during a single mating season. The size of the egg mass is proportional to the size of the female, so each sponge may contain anywhere from 160,000 to 1,000,000 eggs.

Stone crab spawning occurs May through September and is influenced by temperature and light intensity. Because of warmer average temperatures and longer periods of daylight in the southern portion of its range, some females can spawn year round in the Florida Keys and south Florida.

Spawned eggs hatch as larvae two weeks after being deposited under the female’s abdomen. Hatched larvae are planktonic (free floating) and go through six stages while suspended in open water. After about a month, they settle to the sea floor as juvenile crabs.

The stone crab fishery is unique in that only the claws are harvested and the crab is returned to the water, where during the next molt, a new claw will be regenerated. Regeneration is a defense mechanism that allows a crab to “drop” a claw or leg that has been grasped by a predator or wounded in a fight. It takes about 24 months for a regenerated claw to reach harvestable size.

The stone crab fishery did not become an important fishery for south Florida until the 1960s, but since then fishing pressure and demand has increased tremendously making it one of the most important in the region. Today, the stone crab supports one of the top five commercial fisheries in the state of Florida and is valued at approximately $23 million.

In Florida, stone crab season run from October 15th to May 15th. The minimum size of claws must be 2 ¾ inches, and for recreational harvesters, the bag limit is 1 gallon of claws per person or 2 gallons per vessel, whichever is less. For additional information on stone crab regulation, readers should visit: http://myfwc.com/fishing/saltwater/recreational/stone-crabs/.

The harvesting of egg-bearing females is illegal for both the recreational and commercial sectors in Florida. All crabs should be checked for the presence of a sponge prior to declawing. If a sponge is detected, the crab must be placed back in the water immediately and unharmed. Extended periods of time out of the water can damage the delicate eggs and cause a female to drop the sponge. Once dropped from stress or damage, the sponge and eggs contained in that spawn are lost.

Stone Crab

A stone crab after removal of it’s claw and showing a clean break. Stone crabs have a much better chance of survival if the diaphragm at the body/claw joint is intact. The diaphragm functions as a seal to close the wound and stop the bleeding. Photo: FWC

When harvesting claws, it is important to break the claw right. A stone crab can re-grow either of its claws only if the joint that linked the claw to the body is left intact. A bad break will result in cracking of the crab shell, causing loss of blood and an increased probability of death.

One claw or two? A 2015 declawing study reported 63 percent of the crabs declawed by double amputation died from the trauma while 41 percent of crabs with a single amputation died. The odds of dying increased with increasing temperature, and rose to >90% when temperatures were above 77 degrees. Wounding associated with improper declawing increased mortality of crabs by 73-85%.

References:

Bert, T.M., J. Tilmant, J. Dodrill, and G.E. Davis. 1986. Aspects of the Population Dynamics and Biology of the Stone Crab (Menippe mercenaria) in Everglades and Biscayne National Parks as Determined by Trapping. South Florida Research Center Report SFRC-86/04. National Park Service, Everglades National Park, Homestead, Florida, USA. 77 pp.

Duermit, E., P.R. Kingsley-Smith & D.H. Wilber. 2015. The Consequences of Claw Removal on Stone Crabs Menippe spp. and the Ecological and Fishery Implications, North American Journal of Fisheries Management, 35:5, 895-905.

FWC. 2017. http://myfwc.com/fishing/saltwater/recreational/stone-crabs/

FWC. 2011. 2011 Stone Crab Stock Assessment: Executive Summary, http://myfwc.com/research/saltwater/crustaceans/stone-crabs/stock-assessments/

Gandy, R., C. Crowley, D. Chagaris, and C. Crawford. 2015. The effect of temperature on release mortality of declawed Menippe mercenaria in the Florida stone crab fishery, Bull Mar Sci. 92(0):000–000.

Gerhart SD, Bert TM. 2008. Life-history aspects of stone crabs (genus Menippe): size at maturity, growth, and age. J Crustac Biol. 28(2):252–261.

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