Appendix E. Modeling commercial harvest losses.
Green crab impacts on commercial shellfish landings were estimated based on the linear damage function described under “Impacts on Shellfish Populations” together with relative density ranges of green crabs and data on current and historic landings of the species. The shellfish damage function generates an estimate of the percent of shellfish lost in a particular area based on green crab CPUE. For most species and states, commercial shellfish landings are a combination of shellfish collected in the wild and aquaculture harvest. Because clam farmers generally protect their bivalves using anti-predator devices such as bags or nets, aquaculture losses from green crab predation are likely to be lower than wild harvest losses. Beal and Kraus (2002) and Beal (2006) found anti-predator devices reduced predation losses by between 13 and 55 percent. The harvest due to green crab predation was calculated using the following formula:
F = Total annual foregone harvest
A = Actual wild harvest
B = Actual aquaculture harvest
X = Percentage of potential harvest lost to green crab predation (damage function output)
Y = Percentage of losses prevented by anti-predator devices.
Beal, B. F., and M. G. Kraus. 2002. Interactive effects of initial size, stocking density, and type of predator deterrent netting on survival and growth of cultured juveniles of the soft-shell clam, Mya arenaria L., in eastern Maine. Aquaculture 208:81–111.
Beal, B. F. 2006. Relative importance of predation and intraspecific competition in regulating growth and survival of juveniles of the soft-shell clam, Mya arenaria L., at several spatial scales. Journal of Experimental Marine Biology and Ecology 336:1–17.