Estimating Effort in Tidally Influenced Shellfish Fisheries in Oregon Estuaries

Surveys monitoring recreational crab and clam fisheries in Oregon's estuaries provide catch and effort that can help guide management.  Popular species harvested include Dungeness crab (Cancer magister), red rock crab (Cancer productus), gaper (Tresus capax), butter (Saxidomus gigantea), cockle (Clinocardium nutallii), and native littleneck clams (Protothacha staminea).  Catch per unit effort (CPUE) is estimated from creel survey data using a relatively simple process of finding mean values over time and/or space.  In contrast, estimating effort parameters is more complex, needing models to extrapolate total fishery effort from point observations.  Taking advantage of the tidally influenced nature of estuarine crab and clam fisheries, we have developed two models to estimate fishery effort.  Clam harvesters need low tides to access the resource, and the magnitude of effort rises and falls with the tide.  Crab fishers are likewise influenced by the tide; the greatest amount of effort is during the slack current of high tide.  Instantaneous counts of crab buoys at high tide and clam diggers at low tide are expanded by the two models to estimate whole-day effort.  Days are categorized by type (weekend, weekday), and/or tide level, and effort estimates are expanded to create, weekly, monthly, and annual totals.  We will compare and contrast the development, effort units, and biases of these two models.