Small-scale fisheries targeting sedentary-stocks (‘S-fisheries’) are spatially structured in that the distribution of both the resource and the fishing effects are patchy and persistently heterogeneous. This close relationship between the spatial distribution of the resource and the effort allocation provides an opportunity for the use of fishery data to map the distribution of the resource and fishing mortality. Since GPS (Global Positioning System) modules have become an accessible technology of remarkable precision, the combination of GPS loggers and logbook programs to compile catch data offer an effective, low-cost approach to monitor these fisheries, as a complement to more expensive fishery-independent surveys.
This project aimed to develop and test a monitoring methodology based on a combination of GPS and depth data-loggers, with voluntary logbooks, in an S-fishery: the hookah-diving shellfish fishery of the Gulf of San José (Península Valdés, Chubut province, northern Patagonia). A GPS-depth logger was installed in an artisanal fishing boat, and depth loggers were attached to each of the boat’s divers. GPS-depth loggers recorded date, hour, latitude, longitude, depth, speed and heading, among other variables, while divers’ depth loggers recorded depth profiles for each diver. A total of 30 fishing trips were monitored, and some additional variables including the timing of fishing events (e.g., traveling, searching and fishing), fishing depths, and catches, were recorded.
The spatial dynamics of the fishing process was studied through the analysis of the boat’s tracks. Data from the divers’ depth loggers were classified into the four most prominent activities carried out during a fishing trip: ‘traveling’ (to and from the coast to the fishing grounds), ‘searching’ (towing a diver at low speed in order to locate shellfish patches), ‘fishing’ (harvesting by divers, with the boat anchored to the bottom), and ‘moving’ (traveling from one part of the fishing zone to another). In addition to describing the spatial dynamics of the fishing process, information arising from the classification of fishing activities, along with logbook records, were used to calculate indices of local resource biomass based on catch per area fished. The large operational range of divers around the boat (in this fishery, divers are commonly supplied with air through 50-m long hoses) and the lack of positional information for divers negatively affected the accuracy of the estimates of the areas effectively harvested and the catch per area indices. Nevertheless, the spatial distribution of the resource could be reconstructed from geo-referenced information of catches, and catch per area indices were accurate enough to allow comparisons among fishing beds and over time.
This information is very useful for applying spatially explicit management, such as a system of permanently or temporary closed and open areas, rotation of fishing areas, etc. Finally, efforts to involve fishermen in data gathering have many rewards, beyond the value of the data collected: it is a worthy cause in any form of co-management as it assigns a central role to fishermen in the stock assessment process. ($7,330)