Reference | Willis, Scott A., W.W. Falls, C.W. Dennis, D.E. Roberts, and P.G. Whitchurch. 1995. Assessment of season of release and size at release on recapture rates of hatchery-reared red drum. American Fisheries Society Symposium 15:354-365. |
Abstract | Stock enhancement is a management tool that may be used to augment depleted wild populations of fish. Red drum Sciaenops ocellatus was used as a test species to evaluate the efficacy of marine stock enhancement in Florida. Fingerlings were marked with either Coded Wire Tags or internal anchor tags. Three experiments were conducted to compare tag return rates from fingerlings released during different seasons and at different sizes, to develop guidelines for using internal anchor tags on larger fingerlings, and to assess the entry of hatchery-reared fish into the subadult population. In the red drum size-at-release experiment, approximately 60,000 fingerlings were graded equally into three size-classes: 60, 90 and 120 mm mean total length (TL). The experiment consisted of two phases: (1) using fingerlings produced during the natural fall spawning period (in season); and (2) using fingerlings produced approximately 6 months later (out of season) by photothermal manipulation of broodstock to induce spawning. Two sampling designs were used at the study site: seine sampling at randomly selected stations and at fixed stations. Red drum recaptures from the released group that had been produced in season totaled 821; there was only one return from the released group that had been produced out of season. In random-station sampling there was no significant difference in recapture rates between size-classes. In fixed-station sampling there was a significant positive correlation between recapture rate and increasing fish size at release. The correlation was already established by day six, and the rates of recapture for the three size-classes remained unchanged during 6 months of poststocking sampling; large fish were 3.7 times more likely to be recaptured than were small fish. In the second experiment, fingerlings were graded into two size-classes (157.1 and 201.7 mm mean TL), tagged with internal anchor tags, and released. Total returns for the two size-classes after 767 d were 52 (1.4%) and 189 (5.4%), respectively. Fish in the larger size-class were 3.9 times more likely to be returned than were smaller fish, and there was no significant difference between size-classes in either growth rate or net distance traveled postrelease. In the third experiment, we used trammel nets to sample throughout Volusia County to determine the rate of entry of hatchery-reared fish into the local stocks. A total of 2% of the 395 red drums caught during trammel-net sampling (218-828 mm TL) were hatchery reared. Recapture rates localized in the area where fish were released were higher (4.2%; N = 168). |
Tag | Coded Wire Tag (CWT) |
Objective | Evaluate stocking programs |