|Document Type:||Contract Report|
|Title:||Abundance and size-class structure of Dungeness crabs in or near frequently dredged areas in the Columbia River estuary: Final report|
|Author/Editor:||George T. McCabe, Robert J. McConnell|
|Publisher:||National Marine Fisheries Service|
|Contracting Agency:||U.S. Army Corps of Engineers. Portland, Oregon|
In October 1985, the National Marine Fisheries Service (NMFS) completed a 2-year study of Dungeness crabs, Cancer magister in the Columbia River estuary. Objectives of the study were to determine estuarine distribution, relative abundance, size-class structure, and location and timing of movements of Dungeness crabs across the Columbia River bar. This study demonstrated that crab densities fluctuate annually in the estuary. For example, densities on the bar in the spring and summer of 1984 were less than 115 crabs/ha, whereas during the same period in 1985, densities exceeded 1,800 crabs/ha.
Because of the large annual fluctuations in crab densities at some frequently dredged estuarine areas, the U.S. Army Corps of Engineers requested that NMFS continue to sample at some of the established stations. The objectives of the extended study were to describe the abundance and size-class structure of Dungeness crabs in or near frequently dredged areas in the Columbia River estuary. This final report is a summation and analysis of data collected from November 1983 through September 1988 at sites in or near frequently dredged areas in the Columbia River estuary.
Sampling on the bar and the three stations upstream from the bar (Stations 3, 6, and 10) clearly showed that densities of Dungeness crabs fluctuate temporally and spatially in the Columbia River estuary. High densities of crabs on the bar during the spring and summer are extremely dependent on the immigration of early instar crabs or megalops larvae into the estuary. Although densities fluctuate annually, seasonal patterns have been identified at some sites. This information about the Columbia River estuary has and will continue to aid resource managers in making decisions about dredging schedules and methods to minimize impacts on Dungeness crabs.
This report does not constitute NMFS's formal comment under the Fish and Wildlife Coordination Act or the National Environmental Policy Act.