Cull rings are required by law to be present in all wire traps in the U.S. blue crab fishery. Unlike the blue crab fishery in Florida, the Florida’s stone crab fishery does not require the installation of cull rings in plastic or wood stone crab traps. The addition of cull rings to wire traps reduces byatch, on-vessel cull time, and sublegal blue crab catch by 75-80% (Guillory and Hein 1998; Guillory et al. 2004; Rudershausen and Turano 2009; Rudershausen 65 and Hightower 2016). In the stone crab fishery, containment in traps causes an estimated 12.8% mortality in stone crabs, additionally, 23-100% mortality can be incurred by on board handling and exposure to fluctuating air and water temperatures while hauling traps (Simonson and Hochberg 1986; Kronstadt et al. 2017). Reducing entrapment of sublegal stone crabs can prevent exposure to the stress and mortality caused by containment and culling. Incorporating a cull ring into a stone crab trap is a simple and inexpensive management strategy that effectively releases sublegal crabs and bolsters the reproductive population of stone crabs while having a negligible effect on the catch and retention of legal stone crab claws.
Based on the data collected, a minimum cull ring size of 2 3/16 inches is recommended for use in all stone crab traps.
Reflex Action Mortality Predictor (RAMP)
Predicting mortality of species discarded from fishery operations is essential for developing accurate stock assessments and determining sustainable fishery practices. In the Florida stone crab fishery, only legal-size claws are harvested. Declawed crabs, intact egg bearing females, and sublegal crabs should all be discarded alive. This study used a technique known as the reflex action mortality predictor (RAMP) method, to determine the fate of crabs discarded from the fishery. This method used the severity of reflex impairment observed in an animal as an indicator to determine the likelihood of mortality. While the RAMP method has been successfully used in other species, this research project was the first successful attempt to adapt these methods to the Florida stone crab. The RAMP method can be a beneficial tool in assessing discard mortality rates of sublegal crabs as well as the sustainability of current handling and holding techniques in the stone crab fishery.
Eight reliable reflex behaviors were identified, then the crabs were exposed to a treatment of either physiological trauma (desiccation or exposure to air) or physical trauma (dropping from five different standard heights) or no trauma at all. These crabs were evaluated for loss or impairment of reflexes immediately before and after treatment and then surviving crabs were evaluated again after holding the crabs for observation over the course of 14 days. Crabs in all experimental treatments had relatively low reflex impairment scores before either treatment was performed. Of the crabs that died, the most mortality occurred within the first 9 days of the 14-day holding period and mortality of crabs increased with increasing reflex impairment or loss. Mortality reached 100% when 4 or more of the 8 reflexes were impaired for the physical treatments and when 5 or more of the 8 reflexes were impaired for the physiological treatments. In general, mortality occurred more quickly when more reflexes were impaired post treatment.
Accurate estimates of reproductive potential are a key component of any stock assessment. The objective of this research was to quantify the relationship between batch fecundity (number of eggs per clutch) and carapace width while accounting for several factors including differences in survey locations, temporal differences over the 2-year sampling period, and differences among individuals with missing claws. Egg-bearing stone crabs were collected from April 2013 through April 2015 with a total of 606 egg masses harvested in that time. After the egg clutches were processed, a subsample of 25 eggs per clutch were photographed under a microscope and measured using computer software to determine the average diameter of an egg per clutch. The eggs were then dried and the dry weight of an individual egg was calculated for each egg mass. The weight of the individual egg was then compared to the weight of the entire egg mass in order to calculate the number of eggs per each clutch (i.e. batch fecundity).
Modeling results revealed that fecundity significantly increased with an increase in carapace width (size) of the crab. Batch fecundity was lowest in spring and winter, when mean monthly temperatures were lower, and highest in July and August, when mean monthly temperatures were highest. This agreed with the general understanding of seasonal patterns in crustacean reproductive cycles. Additionally, batch fecundity was 39% lower for crabs with no claws, indicating that claw removal by the ﬁshery negatively affects reproductive output. This is significant when considering the overlap between the Florida stone crab season (October 15 through May 15) and season reproductive patterns of the stone crab, thus we hypothesize that the spatial differences in food quality, food quantity, and fishing effort may be important drivers of variability in stone crab fecundity.
The commercial stone crab fishery in Florida requires the return of all crabs to the water after removing the legal claw(s). These live crabs are then theoretically able to regenerate new claws and potentially re-enter the fishery at a later date. An in-situ study was conducted during the 2011-2012 fishing season to refine estimates of mortality that takes place after the declawed, live crab is released back into the water. This study found that 12.8% of crabs died when no claws were removed, when one claw was removed properly, 23-59% died, when two claws were removed properly 46-82% died. The study also found that the number of claws removed, how the claw was broken (i.e. clean break vs. a “bad break” where the diaphragm is damaged rather than intact), and the water temperature at time of release were all significant factors contributing to potential mortality. The data suggest that release mortality rates increase when the water temperatures are seasonally and/or regionally warmer (i.e. southern Florida year-round or northern Florida in the spring/summer months when the water is warmer).