Eat or Be Eaten!
Crab predators include other crab species, halibut, dogfish, sculpins, octopus and sea otters. Cannibalism may occur, particularly on young crabs during the first weeks after settlement to the bottom, or on newly molted crabs. Salmon and other fin fish feed on crab larvae when they are available in the plankton. Newly settled crabs have the highest survival rates in shallow waters, including the intertidal zone, presumably to avoid predators. They also require cooler waters.
Crabs are carnivores and their diet can include shrimp, mussels, small crabs, clams and worms. Dungeness crabs are foragers. They scavenge along the sea floor for organisms that live partly or completely buried in the sand.
Commercial Fishing
Extensive commercial fisheries began before Glacier Bay National Monument, Alaska, was established in 1925. During the 1990s, fisheries around the world collapsed. People began to wonder if certain fisheries would continue indefinitely. A growing body of scientific information suggests that "no-take marine reserves" could enhance the long-term sustainability of many fisheries and marine biodiversity. But, most of the data comes from studies in tropical areas rather than in high latitude regions such as Glacier Bay. Between 1970 and 1995, the harvest of Dungeness crabs for Glacier Bay and Icy Strait has ranged from 76,000 to 658,000 pounds.
Recently, commercial fishermen have harvested a large proportion of the legal Dungeness crabs living in Southeast Alaska. A Dungeness crab that can be legally harvested is defined by size and gender; i.e., any female crab or male crab with a carapace of less than 165 mm must be thrown back. As a result there has been a decrease in the maximum size of males in the population. Crustacean fisheries, such as the Dungeness crab fishery of Southeast Alaska, that are experiencing major declines are usually closed temporarily because, otherwise, the fishery would collapse altogether. Such closures normally remain in effect only until there is evidence that the crustaceans are coming back.
After Glacier Bay was closed to commercial fishing, the number and size of legal-sized male Dungeness crabs increased dramatically at the experimental sites.
