Exploitation rates of two benthic resources across management regimes in central Chile: Evidence of illegal fishing in artisanal fisheries operating in open access areas

Abstract

There is an urgent need to quantify the impacts of artisanal fisheries and define management practices that allow for the recovery and conservation of exploited stocks. The extent of illegal catch is particularly critical as a driver of overexploitation in artisanal fisheries. However, the lack of data at proper spatial scales limits the evaluation of illegal fishing and effectiveness of management practices. We used a catch curve analysis to estimate total instantaneous mortality as a proxy of fishing pressure in the artisanal benthic fishery in central Chile. We compared the patterns of total mortality in fishing grounds under the well-studied territorial use rights for fisheries system (TURF) immersed in a landscape of open access areas (OAA; no access restriction), and from these patterns determined the extent of illegal fishing in open access areas focusing on the two most frequently extracted resources: locos (Concholepas concholepas) and keyhole limpets (Fissurella spp.). The beauty of this seascape is the presence of the no-take (NT) area of Las Cruces as control (no fishing), allowing us to estimate natural mortality. Loco exploitation is banned in OAAs. However, loco mortality in OAAs was 92% higher than in the NT, and 42% higher than in TURFs. Keyhole limpet mortality was similar between TURFs and the NT, but doubled in OAAs. We also found strong differences in mortality among fishing grounds with the same level of protection (i.e. TURFs), and over time. Our results highlight (a) the high level of illegal fishing that may occur in artisanal fisheries under traditional management regimes, and (b) that TURFs can be effective to reduce fishing mortality. However, large variability among TURFs suggests the need for a deeper understanding of the drivers of success of TURFs.

Fig 1. Map of the study area showing the no-take area of Las Cruces and different management areas where samples were collected.

In the three sites (Algarrobo, Las Cruces and Quintay) traditional open access fishing grounds were also sampled.

Fig 2. Regional trends in total instantaneous mortality (Z) in the three studied management regimes.

(A) Loco (Concholepas concholepas). (B) Keyhole limpets (Fissurella spp.). NT: no-take area of Las Cruces; MA: Management Area; OAA: Open Access Areas. Error bars represent the 95% confidence intervals for the estimates of Z. Note the different scales in the y-axis between panels A and B.

Fig 3. Local patterns of total instantaneous mortality (Z) in the two management regimes (MA and OAA) at the two study sites (Algarrobo and Quintay).

(A) Loco (Concholepas concholepas). (B) Keyhole limpets (Fissurella spp.). Light-grey bars show Z for the different Management Areas (MA) within each site (A, B, C); dark-grey bars show Z estimates for the group of MAs of each site (data pooled for all MAs located within each site); black bars show Z in Open Access Areas (OAA). Error bars represent the 95% confidence intervals for the estimates of Z. Note the different scales in the y-axis between panels A and B.

Fig 4. Historical trends in total instantaneous mortality (Z) over a 14-year period, at five management areas located in two sites of central Chile: Algarrobo and Quintay.

(A) Loco (Concholepas concholepas). (B) Keyhole limpets (Fissurella spp.). Grey bars represent the average total instantaneous mortality (across sites). Letters A, B or C after the name of a site indicate individual Management Areas. Note the different scales in the y-axis between panels A and B.