Determination of Gillnet and Hook Selectivity for Caranx heberi Captured off Kanyakumari Coast of India
The larger carangids are most important fishery in the coast of Kanyakumari, Tamil Nadu. They are caught by large meshed gillnets and hooks in these region. However, there is no selectivity studies conducted on this fishery especially in this coast. The selectivity nature of every gear is important for managing the fishery as well as for conservation of resources. Large meshed gillnets having mesh sizes of 13.5 cm, 14 cm, 14.5 cm and 15 cm and Hooks No.5,6,7 and 8 were chosen for determining the selectivity and fishing power of the gears to capture the larger carangid Caranx heberi of Kanyakumari coast of India. The catch data were analysed using the software GILLNET (Generalized Including Log-Linear N Estimation Technique) comprised of the methodology of SELECT (Share Each Length Class Total) by fitting various uni-normal models viz., normal scale, normal location, log-normal, gamma and bi-normal model. Models were tested using various selectivity parameters like Model Deviance, Dispersion Parameter and residual plots. Bi-normal model was found appropriate for gillnet catch data while normal location for hook catch data despite over dispersion was common in both the fits. The mesh size of 13.5 cm and hook No.5 and 6 were found as optimum size for capturing larger carangid C. heberi. Comparison of the selective effects of different gears is complex particularly between selective gears. Further, the mean size of fish caught from one gear to another gear varies due to various biological factors such as availability, abundance, age, sex, and size, or environmental factors such as fishing ground, depth, etc. Selection curves of gillnets and hooks of the present study are assumed as bell shaped multi-normal and uni-normal in nature respectively. In this study, hook selectivity data fit appropriately with uni-normal model despite it is complex in nature in general. It is also opined that fit may depend on models applied though it is normally influenced by biological behavior and capturing methods. This study revealed that gillnet yielded obvious size selection range than hooks in capturing larger carangid, C. heberi of the study area.
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