Injury in trapped Dungeness crabs (Cancer magister)

Abstract

Barber J. S., and Cobb, J. S. 2007. Injury in trapped Dungeness crabs (Cancer magister). – ICES Journal of Marine Science, 64: 464–472. Although traps are the most effective fishing equipment used to capture crabs they can also result in indirect damage to target species. We examined the effect of trap-soak time, crab density, and the legal to sublegal size ratio on injury rates to male Dungeness crabs, Cancer magister. Our field results show that injuries increase significantly with increased trap-soak time, and as a consequence of different size ratios (crabs in traps with a greater ratio of sublegal crabs had more injuries). The injury rate was independent of density. In a laboratory experiment, injured crabs were as capable as intact crabs of obtaining, defending, and consuming food. However, studies on other crab species indicate that injury reduces growth, delays reproduction, decreases mating success, and increases mortality. If the costs of injury are similar for Dungeness crabs, this could diminish the rate of recruitment into the fishery.

Qualitative observations of Dungeness crabs,Cancer magister, in and around traps: evidence of resource guarding and clustering

“…Alcock 1993). This observation is further supported by the fact that injuries to trapped Dungeness crabs are independent of size (Barber and Cobb 2007). However, it is also feasible that interactions did occur between sublegal and legal crabs and they were not documented due to the nature of the time-interval recording.…”

“…If this type of behavioural modification occurs with trapped Dungeness crabs, no relationship would be expected between injuries and trap soak time. However, Barber and Cobb (2007) found a positive relationship between injuries and soak time, while a long-term field study of Dungeness crab found an inverse relationship between limb loss and catch rate (Thomas Shirley, S. James Taggart and Jennifer Mondragon unpublished data). This suggests that injury and limb loss may be related to activities other than agonistic interaction, so clustering could still serve to reduce the number of agonistic interactions in traps.…”

“…Each day the trap was hauled we measured and tagged crabs following methods detailed in Barber and Cobb (2007). During this time, we attempted to place unique markers on the carapace of the trapped crabs to allow for the identification of individuals in the films.…”

“…This project was developed as part of a larger study that investigated causes of injury in trapped Dungeness crabs (Barber 2004;Barber and Cobb 2007). Although ethograms have been successfully used to produce quantitative studies involving behaviour and the management of a fishery (e.g.…”

The Biology, Ecology and Fishery of the Dungeness crab, Cancer magister

“…Additionally, having pots with doors that open on the top of the pot may not allow trapped crabs to escape even after the clasp breaks since the lids are often held closed by encrusting organisms. Crabs in pots (and more specifically small crabs) have an increased probability of being injured as soak time (the time the pot is in the water) increases (Barber and Cobb, 2007). However, preventing crabs from utilizing their pinchers did not decrease in pot mortality, suggesting that cannibalism within pots is not common (Shirley and Shirley, 1988).…”