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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