Dungeness Crab

Dungeness crab

Evaluation: Okay/Continue Monitoring

Issue Summary:
The Dungeness crab population in Oregon and Coos Bay appears to be stable, supporting what appears to be a sustainably managed commercial and recreational fishery; questions remain about potential effects of climate change.

Why do we care:
Dungeness crabs are important species for our area in terms of their commercial and recreational value, iconic cultural status, and as indicators of coastal ecosystem health.

Figure 1. Commercial Dungeness crab landings 1947-2011. Data: ODFW.

What’s Happening

Oregon Department of Fish and Wildlife’s (ODFW) commercial Dungeness crab landings data indicate that the Dungeness crab fishery has been healthy and robust for long time (Figure 1). The commercial Dungeness crab fishery takes 90-95% of adult male crabs over the legal size limit each year. This means commercial Dungeness crab landings data provide resource managers and scientists with a very reliable index of four year old adult Dungeness crab populations in the Coos and other estuaries (S. Groth and A. Shanks, pers. comm.). It should be noted that the trend evident in Figure 1 suggesting a steady overall increase in crab populations over the past 65 years does not take into account the increased effort exerted by coastal communities to catch Dungeness crab over that time (e.g., number of crab boats and crab pots). Figure 2 shows the increasing number of commercial crab pots and vessels engaged in crabbing in Oregon between 1948 and 2001. Adjusted for fishing effort, the actual population trend would likely indicate a Dungeness crab population that is remaining relatively stable over time, though some of the increase may be actual due to long-lived cyclical changes in North Pacific climate, the latest cycle of which happened to benefit crab populations (A. Shanks, pers. comm.).

Figure 2. Commercial Dungeness crab pot use and vessel activity: 1948-2001. Graph: ODFW.

The recreational Dungeness crab fishery is also apparently stable. ODFW conducts recreational crab harvest creel surveys each year (e.g., Figure 3). Coos is Oregon’s most popular clamming and crabbing estuary.
ODFW recreation Dungeness crab fishery report

With Oregon’s Dungeness crab fishery certified sustainable by the Marine Stewardship Council, one naturally wonders whether the fishery can remain robust should permanent climate-influenced changes take place in nearshore ocean conditions.
Research conducted locally by Shanks and Roegner (2007) linked the number of Dungeness crab megalopae settling in Coos Bay with the number of adult crabs caught in Coos Bay four years later (more megalopae = more adults).

Further, they determined that the number of Dungeness crab megalopae settling in Coos Bay is correlated with the timing of the spring transition, the time when low productivity wintertime ocean conditions off the Oregon coast shifts to high productivity summertime ocean conditions (productivity determined by north wind-driven upwelling in the summer and south wind-driven downwelling in the winter). Shanks and Roegner report that early spring transitions result in greater the numbers of megalopae settling, and four years later, more adult crabs available for harvest.

Figure 3. Recreational Dungeness crab catch per person in Coos Bay 2010-2011. Data: ODFW.

This raises the question about how the local effects of long term climate change, which may include changes to offshore wind patterns and ocean currents, will affect the timing of spring transition. There does not seem to be consensus among scientists about how local wind forcing other weather cycles may or may not shift in the future in response to climate-driven changes (OCCRI 2010).

Literature cited

Oregon Climate Change Research Institute (OCCRI). 2010. Oregon Climate Assessment Report. K.D. Dello and P.W. Mote (eds). College of Oceanic and Atmospheric Sciences, Oregon State University, Corvallis, OR.

Shanks A.L. and G. C. Roegner. 2007. Recruitment Limitation In Dungeness Crab Populations Is Driven By Variation In Atmospheric Forcing. Ecology. 88(7). pp. 1726–1737.