Spatial distribution of effort by artisanal fishers: Exploring economic factors affecting the lobster fisheries of the Corn Islands, Nicaragua

摘要

Spatial distribution of fishing effort is increasingly recognised as an important consideration for fisheries management, as it can affect trends in catch rates, and be incorporated into planning of spatial management tools like marine protected areas (MPAs). One hundred and ninety-eight household questionnaires provided a coarse indication of effort distribution of artisanal lobster fishers around the Corn Islands, and 32 semi-structured interviews with skippers were used to map individual fishing sites and describe the operating costs and revenues of typical dive and trap-fishing operations. Artisanal fisheries had ranges of up to 50km, and had moved significantly offshore within the previous 10 years. At the scale of a 5x5min latitude/longitude grid, trap fishing effort was highly aggregated (dispersion coefficient=3.5), while diving had a regular dispersion (d.c.=0.1). Descriptions of catch composition at each site showed a clear spatial pattern in the distribution of two locally recognised types of lobster, potentially indicating local stock structures. Economic information was summarised into balance sheets for typical fishers and suggested that fuel accounted for about 52 and 37% of the operating costs of dive and trap fishing captains, respectively. Qualitative questions highlighted trap theft, adoption of geographical positioning system (GPS) technology and fuel costs as major factors affecting spatial behaviour. The costs and benefits of using more distant grounds were examined by testing for relationships between stated typical catch rates and distance of 90 trap-fishing grounds and between fuel expenditure and catches in 291 daily records of the activities of 3 divers. Maximum catch rates stated by trap fishers were significantly higher at more distant sites and daily catches by divers had a positive relationship with fuel expenditure, which suggested that increasing fuel expenditure to target more distant sites would lead to higher gross revenue as well as higher net revenues, after considering variable operating costs. Thus, there appears to be an economic incentive to extend the range of the fishery. However, fishers may not perceive these positive trends in catch rate with distance due to catch variability, and costs other than fuel, which complicate the trade-off between catch and distance.