In May the Washington state Department of Fish and Wildlife announced that south Puget Sound is closed this season for all crab harvesting, including Dungeness and red rock crabs.
“A combination of trends in crab population over the last five years and some recent scientific papers and presentations about crab survival led to this decision,” said Robert Sizemore, Puget Sound shellfish manager for the WDFW. “Harvest reports from south Puget Sound have been dismal.”
WDFW and tribal co-managers agreed to close crab harvesting, aside from limited ceremonial and subsistence harvest for tribes, in Puget Sound south of the northern tip of Vashon Island. The closure will likely last for several years.
The Dungeness crab population is tracked through harvest reports and test harvesting conducted by the WDFW and the tribes. According to data from the WDFW, the Dungeness crab harvest in Marine Area 13 (south Puget Sound) has declined from a peak of 289,505 pounds in 2012 to 9,457 pounds in 2017, a drop of nearly 97 percent.
WDFW test fishing in Marine Area 13 in 2018 showed that there were no Dungeness crabs in the size range of 3.5 to 5.7 inches, indicating that several year-classes of Dungeness crab are missing.
Marine Area 11, from the Narrows Bridge to the north end of Vashon Island, showed a harvest decline of 87 percent from its peak in 2015.
Washington state has 13 marine areas stretching from the Pacific Coast, around the Strait of Juan de Fuca and into Puget Sound and Hood Canal. In contrast to the falling population in Marine Area 13 and southern Hood Canal, the number and size of crabs in other Washington marine areas, including the Strait of Juan de Fuca and San Juan Islands, have been relatively unchanged. The WDFW has not called for changes in crab harvests in those areas.
Sizemore said the cause of the decline is not well understood, but recent environmental shifts may provide a clue. He noted that south Puget Sound, with its many shallow embayments, is warmer than many other parts of Puget Sound. The number of tributaries and increased flow from snow melt lowers surface salinity and can cause stratification of marine waters. Low oxygen levels in south Hood Canal, particularly in 2013 and 2015, may have played a part there and in other locations.
These environmental factors could affect survival of larvae and foraging behavior of juveniles, Sizemore said. Ocean acidification does not appear to be a significant factor affecting survival at this time. “Overharvesting of a relic adult population could also be a contributing factor to low local reproductive potential,” he said.
Although all the harvest data are for Dungeness crab, fishing for red rock crab will also be prohibited. “When harvesting red rock crab, the traps used will also catch Dungeness crab in the area,” Sizemore said. “The act of repeatedly trapping and releasing Dungeness crab causes unavoidable mortality. Any additional Dungeness crab mortality, when the existing population abundance is critically low, can be a significant impediment to recovery.”
WDFW is also concerned about sequential depletion: If the Dungeness population is depleted, red rock crabs could become the next target species. At this time there is too little information regarding red rock crab numbers or life cycle to inform the basis for making a decision with the tribes on the appropriate fishery amounts in order to draft a harvest agreement. “When critical information is missing or incomplete, fishing presents a high risk, with a potential outcome of depleting red rock crab species in addition to causing harm to an extremely depressed Dungeness crab population,” Sizemore said.
Enforcement of the Dungeness crab fishing closure would be very difficult without full closure on red rock crab as well. “Having crab gear in the water (for a targeted red rock crab fishery) when Dungeness crab retention is not allowed creates an enormous burden in enforcing the closure,” Sizemore said.