Hook Size Selectivity in the Handline Fisheries of Shimoni, South Coast Kenya

Abstract

Handline fisheries employ hooks of different sizes and therefore select fish according to species and size which can influence the composition of fish stocks in any given fishery. The aim of this study was to assess the selectivity of the hooks used by artisanal fishers in Shimoni, specifically to identify the fish species captured by handline fishers, determine the size frequency distribution of the species and evaluate the impact of handline hooks on fish stocks. This study was conducted from January to June, 2016 using hook sizes No. 16, 15, 10, 9 and 8 from Mpunguti, Waga, Nyuli and Mundini study sites. Selectivity was determined using Holt’s 1963 model. A total of 966 fish belonging to 65 species in 23 families were caught during the study period. Snubnose emperor (Lethrinus borbonicus), pink ear emperor (Lethrinus lentjan), spotcheek emperor (Lethrinus rubrioperculatus), dory snapper (Lutjanus fulviflamma) and green jobfish (Aprion virescens) dominated the catch. The abundance of fish captured decreased with increase in hook size but CPUE increased with increase in hook size with the larger hook size No. 8 having the highest CPUE. However, the smaller hook sizes No. 16, 15 and 10 recorded high species diversity while the larger hook sizes No. 9 and 8 recorded low species diversity. Higher species diversity was recorded for the calmer NEM season compared to the rougher SEM season. Fish caught from Mpunguti and Nyuli had high diversity while those captured at Mundini and Waga had low diversity. Hook size mainly had an effect on the length of fish caught (p = 0.12). Also, fishing site had effect on the length of fish captured (p < 0.05). The interaction of season and hook size; fishing site versus hook size had no effect on the length of fish captured (p = 0.884 and p = 0.057) respectively. Also, the interaction of season, sampling site and hook size had no effect on the length of fish captured (p = 0.195). All the hooks selected mature L. borbonicus, hook size No. 8 selected immature L. lentjan, hook sizes No. 9 and 10 selected mature L. lentjan and L. rubrioperculatus, hook size No. 15 selected immature L. lentjan, L. rubrioperculatus and A. virescens except for L. fulviflamma specimens while hook size No. 16 selected immature A. vi virescens and L. rubrioperculatus fish. The fish species caught by hook size No. 16 were highly similar to those caught by hook size 15 while fish species caught by hook size No. 8 were similar to those caught by hook size 9. However, fish species captured by hook size No. 10 were different from those caught by the other hook sizes. Hook size No. 8 was recommended for handline fishery as it gave high CPUE and had narrow selection ranges to allow for sustainable exploitation of the fishery. Future studies will need to consider, effects of bait type and size, mouth size of fish and duration of fishing.