Application of Survey Techniques to the Dolphin, Coryphaena hippurus, Fishery of North Carolina

Abstract

North Carolinaˈs dolphin fishery was surveyed in 1961 and 1962 to evaluate its importance to the offshore sport-fishing industry, and to develop suitable and reliable techniques for sampling a marine sport-fishery. As a prelude to the investigation, characteristics of the prominent offshore charter-boat fishery are described. Duration of the sport-fishing season, species captured, fishing methods, and economical aspects of the fishery are discussed. In 1961, catch-forms, personal enumerations, and interviews with dockmasters were used to estimate the catch of party boats, private boats, and transient charter boats. Catch by these boats was approximately 3,150 fish. The activity of resident offshore charter boats operating from the principal North Carolina ports was sampled by use of log books. Complete catch records were returned from 20% of the 90 resident boats that habitually frequented offshore waters. Ports were stratified for statistical treatment into five areas on the basis of proximity and similarity of fishing grounds. Monthly estimates of fishing pressure and catch were calculated for each area. Catch by resident charter boats was estimated to be about 35,050 fish, or 92% of the total catch. Ninety-nine percent of this catch occurred during June through September. Merits of the offshore boat-day as a unit of fishing effort, and the inefficiencies inherent in the log-book survey are discussed. In 1962, the catch of party boats, private boats, and transient charter boats was estimated to be 3,000 fish. Resident offshore charter boats were again stratified into the five areas described in the 1961 survey. A complete enumeration of fishing activity was obtained at Hatteras, North Carolina (Area IV). At Areas I, II, III, and V, log books were distributed to captains who kept reliable records of fishing effort and success. The remaining boats were surveyed by a stratified random-sampling design. Secondary stratification divided the fishing season into four 1-month intervals, thereby producing a total of 16 strata. The original frame consisted of 9,028 total boat-days that were sampled to estimate fishing pressure and success by proportionally allocated postcards. In each stratum, total boat-days were divided into the following categories: offshore boat-days, bad-weather boat-days, and inshore or no-charter boat-days. Dolphin catch and its variance was determined for each stratum. Catch by resident charter boats was estimated to be 68,007 fish (96% of total catch). Ninety-five percent confidence limits were 59,790 and 76,220 fish. Fishing pressure was approximately double that of 1961; catch per unit of effort remained essentially constant, resulting in a two-fold increase in catch. Seasonal catch of a typical resident charter boat was about 700 fish. Inclement weather curtailed offshore activity during approximately 10% of the fishing season. Rate of postcard return was 39% (882 of 2,240 postcards originally distributed). Rate of return did not decrease as the fishing season progressed and did not appear to be a function of fishing effort.