Time series of the abundance of the post-larvae of the crabs Cancer magister and Cancer spp. on the southern Oregon coast and their cross-shelf transport

Using stationary zooplankton nets that fished the tidal current we measured the daily abundance of Cancer crab megalopae near the mouth of Coos Bay, Oregon, during the 1997 spring settlement season. During the spring of 1997, the coastal waters were dominated by a significant El Nino event. Sea surface temperatures (SST) were higher than normal, upwelling indices were an order of magnitude smaller than during the two previous springs, and upwelling favorable winds were weak. Daily catches of Cancer magister megalopae ranged from 0 to 78 with 61% of the total catch occurring during four pulses. Peak catches tended to occur every 13.6 d close to 13.8 d average period between spring tides. Significant cross correlations were found between the maximum daily tidal range and the catch of C magister megalopae; large catches tended to occur 4 to 7 d after the spring tide. Daily catches of Cancer oregonensis and Cancer productus ranged from 6 to 307 with catch significantly positively cross correlated to the maximum daily tidal range at a lag of -5 days suggesting that the largest catches tended to occur after the spring tides. We hypothesize that a tidally-generated phenomenon internal waves, transported Cancer megalopae shoreward and caused the observed variation in their abundance in Coos Bay.