Recruitment Variation in the Dungeness Crab (Cancer magister) and the Prediction of the Commercial Catch

For 14 years (1997-2001, 2006-2014) daily abundance of Cancer magister megalopae was measured in Coos Bay, Oregon.  Before 2007, megalopae catch varied from 2,000 to 80,000/yr, but after catch has varied from 164,000 to 2.3 million/yr. The shift appears related to a shift to negative Pacific Decadal Oscillation (PDO). Annual catch is significantly negatively correlated to the day of the year of the spring transition and positively correlated to the amount of upwelling during the settlement season.  The size of the Oregon commercial catch is set by the number of returning megalopae; the relationship is parabolic.  At lower returns, the population is recruitment limited, but at higher returns it is recruitment regulated, density dependent effects predominate and set the population size. Commercial catches in Washington and Northern and Central California were also related to the number of megalopae returning to Coos Bay suggesting that the forces causing variation in larval success are coast wide. If high return rates are due to a PDO regime shift, then for years to decades the commercial catch may be set by density dependent effects following settlement and the huge numbers of returning megalopae may impact benthic community structure.