Estimating gill-net selectivity for Labeo umbratus (Pisces: Cyprinidae), and an evaluation of using fyke-nets as a non-destructive sampling gear in small reservoirs
Department of Ichthyology and Fisheries Science, Rhodes University, P.O. Box 94, Grahamstown, 6139, South Africa
Estimates of gill-net selectivity for the cyprinid fish, Labeo umbratus, were compared using two conventional and two new estimation methods. All four methods provided similar estimates. The SELECT method was shown to be the simplest and most robust statistically. The Sechin model was found to be appropriate for the smaller mesh sizes. Being based on fish morphology, the Sechin model is not suggested for estimating the gill-net selectivity when fish are likely to get tangled. Although the direct fyke-net method appeared to adequately estimate gill-net selectivity, large sample sizes are required to obtain an accurate estimate of the population structure. This method is, therefore, considered appropriate for high-density populations and may have application for species that are likely to get tangled. The length-structured selectivity model was the most complicated mathematically. While it accurately described the gear selection process it required additional estimates of age and growth. © 2006 Elsevier B.V. All rights reserved.
cyprinid; fish; gillnet; growth rate; population structure; statistical analysis; Cyprinidae; Cypriniformes; Labeo umbratus; Pisces