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Estimating Recreational Clam and Oyster Harvest in Puget Sound (Bivalve Regions 1, 5, 6, 7 and 8)

Category: Fish/Shellfish Research and Management - Management and Conservation

Date Published: May 2007

Number of Pages: 187

Publication Number: FPT 07-07

Author(s): Are Strom and Alex Bradbury


The Washington Department of Fish & Wildlife (WDFW) has estimated recreational harvest of clams and oysters on Puget Sound public beaches since about 1970. The first systematic aerial surveys of sport harvesters occurred in 1969, and “ingress surveys” that recorded effort patterns throughout the course of a day began the following year. These early effort and harvest estimates involved a variety of survey methods, and tended to focus on a few of the most popular public shellfishing beaches.

More formal methods of estimating Puget Sound recreational clam and oyster harvest began following the 1994 Federal District Court order United States v. Washington (No. 9213, Subproceeding 89-3, Judge Edward Rafeedie), which reaffirmed the rights of treaty tribes to 50% of the harvestable surplus of shellfish. A method for estimating the recreational clam and oyster harvest was detailed in a 1997 appendix to the Bivalve Management Agreement (BMA) that described general management principles for state and tribal clam and oyster fisheries on public tidelands. The appendix remained an incomplete draft, however, and the BMA itself expired December 31, 2002. Revised harvest estimation methods for many areas of Puget Sound were described in appendices to the regional Bivalve Plans beginning in 2003 (Bradbury and Strom 2003).

Currently, annual estimates of the recreational catch of clams and oysters on public beaches are required by regional state-tribal Bivalve Plans. Under terms of these regional Plans, WDFW estimates recreational effort and catch on all actively managed public beaches, and total effort is reported on many passively managed beaches. (The distinction between active and passive management is described in all regional Bivalve Plans and the Glossary in this report). Besides meeting the requirements of federally mandated shellfish management plans, estimates of recreational effort and harvest are used to help recommend seasons and other regulations for the recreational fishery. Harvest estimates are generated annually for Manila clams, native littleneck clams, butter clams, cockles, horse clams, geoducks, eastern softshell clams, and Pacific oysters.

Harvest estimates are generated from two primary field activities: (1) aerial surveys, which are conducted from fixed-wing aircraft to estimate total effort (total harvester-days), and (2) creel surveys, which are conducted on selected beaches to determine catch per unit effort (CPUE, or pounds caught per harvester-day) by species. Additional sampling activities that have been conducted to refine harvest estimates include low tide counts, egress surveys, plus-tide surveys, and winter-harvest surveys.

In this report, we describe the methods currently used by WDFW to assess the recreational harvest of clams and oysters in Bivalve Regions 1 (Strait of Juan de Fuca), 5 (Admiralty Inlet), 6 (Central Puget Sound), 7 (South Puget Sound), and 8 (Hood Canal). All eight Bivalve Regions are shown in Figure 1. In Part I, we present the current harvest estimation methods contained in the appendices to all regional Bivalve Plans listed above. In Parts II through VI, we present data analyses that were used to design and justify the current harvest estimation methods. These include analyses of the flight route, the stratification of effort, the effort expansion factor, CPUE estimation, and the estimation of effort on “plus tides.”