Heredity or traditional knowledge: Fishing tactics and dynamics of artisanal mangrove crab (Scylla serrata) fishery

Abstract

Globally, artisanal fisheries are challenged by the combined impacts of overfishing, ecosystem degradation, climate change and lack of management intervention. Little is known of how traditional knowledge/skills held by fishers influence ability to exploit marine resources and whether such information could be incorporated into management practices. Failure to understand fishers’ traditional knowledge/skills and behaviour may undermine the success of fisheries management measures. Use of traditional knowledge in exploitation of mangrove crabs (Scylla serrata) on local fishing grounds is assessed. The study used complementary approaches (field experiments and fisher-based surveys) to investigate fishing tactics employed by artisanal crab fishers. Also time series data from the ministry of fisheries was used to assess annual trends in production and value of the fishery. Fishers with calibrated GPS fished in different areas and catch per unit effort (CPUE), fishing time, distance and efficiency were assessed. Key informant and semi-structured interviews and direct observation were conducted among mud crab fishers to establish knowledge/skill requirement, fishing tactics and entry into the fishery. The results indicate that mud crab fishing is a male dominated activity. Fishing is done at spring low tide by foot fishers in burrows mainly with rare use of baited traps and lift nets at ankle height water along the intertidal mangrove front boundaries or channels. Fisher’s follow specific tracks that are strongly guarded by individual fishers. Fishing for adult crabs showed deeper and further movement in the mangrove forest unlike juvenile crab collection. Fisher’s in new areas collected few crabs due to low efficiency compared to well known areas. Entry into the fishery is minimal and skills are inherited from parents or grand parents with limited transfer being obtained from colleagues. The average size of marketable crabs has declined over the years while season and tide have remained major challenges for production and market determination in the fishery. Fisher-based surveys overestimated CPUE and sizes of smallest crabs caught while it underestimated fishing time and distance moved. A weak management system was observed with most fishers operating without a license and lacking a synchronized landing system. Inability of fishers to shift to new areas, “natural closures” and limited distance covered by foot fisher’s support site-specific management for the fishery.