Comparing and Combining Effort and Catch Estimates from Aerial–Access Designs as Applied to a Large-Scale Angler Survey in the Delaware River JON H. VøLSTAD* Versar, Inc., 9200 Rumsey Road, Columbia, Maryland 21045-1936, USA KENNETH H. POLLOCK Department of Zoology, North Carolina State University, Raleigh, North Carolina 27695-7617, USA WILLIAM A. RICHKUS Versar, Inc., 9200 Rumsey Road, Columbia, Maryland 21045-1936, USA Abstract.—We used probability-based aerial access surveys to estimate effort, catch, and harvest of American shad Alosa sapidissima and striped bass Morone saxatilis by recreational anglers in the Delaware River and upper estuary in 2002. Sampling of anglers at access points and flights over the river were conducted weekly from mid-March through October. Daily flight times were randomly selected; probabilities were proportional to the observed distribution of daily angler effort in a prior aerial access survey (random count). Additional experimental flights were scheduled to occur at the time of day with expected peak effort (maximum count). Effort estimates derived from these maximum counts were more precise than estimates derived from the random flights, but the maximum-count observations caused bias except when the daily count expansions were based on effort distributions from the concurrent access survey. The aerial and access surveys produced similar estimates of boat angler effort and little evidence of bias, but shore anglers were undercounted in the aerial survey. We maximized the precision and minimized bias in total effort estimates by combining the estimates of boat angler effort and shore angler access. An estimated sevenfold increase in the access survey sampling effort (at nearly five times the cost) would be required to achieve the same precision in the total effort estimate produced by the aerial–access survey. Effective stratification and the use of efficient model-based estimators helped us to achieve the target precision of 20% in relative standard error (RSE) for estimated recreational catch of American shad (mean ¼ 26,885 fish; RSE ¼ 16%) and striped bass (mean ¼ 47,671 fish; RSE ¼ 15%). A single access survey during the American shad run would have required a 10-fold increase in sampling effort to achieve the same precision in estimated catch at six times the cost of the complemented surveys. Precise and accurate estimates of catch and harvest from surveys are needed to effectively manage sport fish populations in large river systems (e.g., Matlock 1991; ASMFC 1999). A variety of survey techniques may be used to collect data for these estimates. Such techniques include counting anglers from airplanes or boats or interviewing anglers along the shoreline as they complete their fishing trips (roving–access survey) or while they are actively fishing (roving–roving survey) (Pollock et al. 1994; Lockwood 2000). However, few data are available to determine which technique or combination of techniques is optimal in terms of precision per unit of survey cost. We conducted aerial observations to count anglers (fishing effort), and we used survey clerks to collect catch, harvest, and trip-length data during interviews with anglers at access sites as they completed their fishing trips. This type of complemented survey is referred to as an aerial–access angler survey (Pollock et al. 1994; Lockwood 2000). The data were used to determine the most efficient combination of the two techniques for estimating fishing variables associated with recreation- al angling of American shad Alosa sapidissima and striped bass Morone saxatilis in the Delaware River and estuary during 2002. The survey was probability based and was designed to achieve precise estimates of angler effort, catch (the total number of fish caught, including the ones released), and harvest (the number of fish kept). The study was conducted on behalf of the Delaware River Basin Fish and Wildlife Management Cooperative (the Cooperative), which includes the states of Delaware, New Jersey, Pennsylvania, and New York, as well as the U.S. Fish and Wildlife Service and National Marine Fisheries Service. The * Corresponding author: jvolstad@versar.com Received August 27, 2004; accepted January 23, 2006 Published online August 28, 2006 727 North American Journal of Fisheries Management 26:727–741, 2006 Ó Copyright by the American Fisheries Society 2006 DOI: 10.1577/M04-146.1 [Article]