Population Estimates of Four Kelp Forest Fishes and an Evaluation of Three in situ Assessment Techniques
Abstract:Population estimates of four kelp forest fishes were made using in situ mark-resighting techniques and modified Schnabel multiple censuses at three locations in Channel Islands National Park, California. A diver-controlled electrofishing apparatus was used to collect fish for tagging; resighting was accomplished by systematic diver surveys of 0.6-, 1.8-, and 7.1-ha study sites 1 h to 84 days after release. Population estimates calculated for these sites ranged from 1,475 to 1,525 ha−1 for California sheephead, Semicossyphus pulcher; 468 to 1,908 ha−1 for kelp bass, Paralabrax clathratus; 865 to 3,258 ha−1 for black perch, Embiotoca jacksoni; and 238 ha−1 for garibaldi, Hypsypops rubicundus. These densities are several times greater than previously reported for southern California kelp forests. We compared these densities, for accuracy and precision, with indices of three simultaneously conducted in situ assessment techniques that have been used to estimate relative abundance or density of kelp forest fishes: visual transects, color video-taped transects, and timed counts at baited stations. Although precise, these techniques inconsistently estimated fish abundance with mean accuracies of only 8% to 38% of the mark-resighting estimates. Of the three assessment techniques tested, visual transects provided the most accurate and precise density estimates. We advise caution in comparing relative abundance and density estimates derived from visual or video transect assessments, especially among sites. If the low accuracy we experienced with these assessment techniques is typical, previous reports may have seriously underestimated densities and thence the ecological influence of kelp forest fishes.
Document Type: Research Article
Publication date: May 1, 1989
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