Dungeness Crab
Dungeness Crab
Background
Dungeness crabs prefer a sand or sand-mud substrate and are distributed in estuaries from the intertidal level to the deepest channels.
Fish Commission of Oregon tagging studies have shown that Dungeness crabs readily move between bays and the ocean and from bay to bay, but 57 to 84% of the crabs tagged in bays were recovered within 4 miles of the tagging site.
Mating occurs in the near shore ocean zone in the spring. The eggs hatch the following winter, and the larvae are free swimming for 3 to 5 months. Crab larvae occur in high abundance in the ocean and in the larger bays in late spring and early summer. Crab larvae are a significant prey item for a wide variety of predators. Larvae settle out as bottom-dwelling juveniles in the ocean and in coastal bays and tolerate lower salinity water than adult crabs. Growth is achieved by molting of the shell and a 6.25 inch male molts approximately 14 times in four years (Collier 1983). Male and female Dungeness crabs mature at age 2, although most males do not begin breeding until age 3. Molting probability decreases with age, and females do not molt after reaching approximately 6 inches in carapace width (Hankin 1985). At this size females are believed to become senescent, no longer producing viable egg masses.
The relative importance of rearing in estuaries versus the ocean is not fully understood, but there is evidence to show that growth and survival may be enhanced in estuarine habitats (Gunderson 1990). Eelgrass beds or shell and cobble substrates provide optimum habitat for juvenile crabs. The lower Coquille River channel near Bandon, the rocky habitat near the South jetty, and the Bandon marsh eelgrass beds are good examples of these types of rearing habitats. Little is known about the utilization of the Coquille River estuary by Dungeness crabs throughout their like history. The relatively small size of the marine and bay portions of the Coquille River estuary and the relatively large freshwater inputs may preclude large-scale benefits to the near shore ocean population of crabs. Adult crabs move freely between the ocean and the bay, with maximum numbers of adults and juveniles in the bay coinciding with salinity maximums in summer and early fall. As the fall rains commence and the salinity drops, crabs begin leaving the bay and by early winter the bay is virtually devoid of Dungeness crabs. Crabs of all ages begin moving back into the bay as freshwater inputs diminish in the spring, with the more freshwater-tolerant juveniles preceding the adults and distributing farther up the estuary. Dungeness crabs have been observed in the late summer as far upstream as the mouth of Bear creek at river mile 8.
The lower Coquille River estuary has supported a popular and productive recreational crab fishery for many years. A resource use study by the Fish Commission of Oregon (Gaumer 1973) showed that in 1971, Dungeness crabs made up 91% of the recreational boat fishing catch in the lower bay. Red rock crabs comprised less than 1% of the recreational catch. June through October was the months of highest catch. June through October was the months of highest catch. The same study showed shore based crab catch to be very minor, but with recent improvements in dock facilities the value of crab to this group of users had no doubt increased and value may not be completely measured simply in terms of numbers caught. The Port of Bandon fishing dock became instantly popular and is one of the most effective fish docks on the South Coast. It provides valuable shore angler access to a very productive portion of the Coquille River estuary. Commercial landings are negligible, with harvest occurring in 5 of the last 20 years and averaging less than 200 pounds per year. The bay crab fisheries are seasonal and depend on movement of legal –sized crabs from the ocean into the bay when salinity is relatively high. Less than 5% of Oregon’s total crab harvest comes from estuaries.
Fishery regulations for Dungeness crab allow for the taking of only mature males of 5.75 inches or greater (recreational) or 6.25 inches or greater (commercial). The recreational catch limit is 12 legal crabs per person, with fishing gear restricted to 3 pots or rings per person. Commercial bay crabbers are restricted to fishing on weekdays only (excluding holidays), from the day after Labor Day through December 31 of each year. Commercial gear is restricted to 15 crab rings per vessel (no pots). These regulations were designed to minimize conflicts between the two fisheries. (ODFW 1992)