Characterizing environmental and spatial variables associated with the incidental catch of olive ridley (Lepidochelys olivacea) in the Eastern Tropical Pacific purse‐seine fishery

Abstract

In the Eastern Tropical Pacific (ETP), a region of high fishing activity, olive ridley (Lepidochelis olivacea) and other sea turtles are accidentally caught in fishing nets with tuna and other animals. To date, the interaction between fishing activity, ocean conditions and sea turtle incidental catch in the ETP has been described and quantified, but the factors leading to the interaction of olive ridleys and fishing activity are not well understood. This information is essential for the development of future management strategies that avoid bycatch and incidental captures of sea turtles. We used Generalized additive models (GAM) to analyze the relationship between olive ridley incidental catch per unit effort (iCPUE) in the ETP purse‐seine fisheries and environmental conditions, geographic extent and fishing set type (associated with dolphins, floating objects or in free‐swimming tuna schools). Our results suggest that water temperature, set type and geographic location (latitude, longitude and distance to nesting beaches) are the most important predictor variables to describe the probability of a capture event, with the highest iCPUE observed in sets made over floating objects. With the environmental predictors used, sea surface temperatures (SST) of 26–30°C and chlorophyll‐a (chl‐a) concentrations <0.36 mg m−3 were associated with the highest probability of an incidental catch. Temporally, the highest probability of an incidental catch was observed in the second half of the year (June to December). Four regions were observed as high incidental catch hotspots: North and south of the equator between 0–10°N; 0–10°S and from 120 to 140°W; and along the Colombian coast and surrounding regions.

Biodiversity and Habitat Characteristics of the Bycatch Assemblages in Fish Aggregating Devices (FADs) and School Sets in the Eastern Pacific Ocean

“…Predictions are considered bias (underestimated/ overestimated) if test values are lower than 0.05 (Montero et al, 2016). Finally, the residuals were also plotted to obtain information about the fitting performance.…”

“…The major limitation of this study is the use of fisheries-dependent data, which is focused on catching tuna, not bycatch species. Thus, diversity patters could be partially biased by the nature of the data and fishery behavior (Montero et al, 2016). Although in the Atlantic and Indian Oceans the observer coverage is low (around 10% of coverage rate) (Lewison et al, 2004), which can compromise the analysis and results (Lennert-Cody, 2001), the high coverage of the eastern Pacific Ocean increase the representativeness of the estimates.…”

“…Although in the Atlantic and Indian Oceans the observer coverage is low (around 10% of coverage rate) (Lewison et al, 2004), which can compromise the analysis and results (Lennert-Cody, 2001), the high coverage of the eastern Pacific Ocean increase the representativeness of the estimates. IATTC observer programs in the eastern Pacific Ocean provide important information for evaluating spatial-temporal variability of fish assemblages and impacts of commercial fisheries on the most vulnerable species (Montero et al, 2016). In that sense, the IATTC purse-seine database covers a large area and period of years compared with the other Oceans, so the information about the species involved is of high quality and quantity; even considering the limitations mentioned above (Montero et al, 2016).…”

“…IATTC observer programs in the eastern Pacific Ocean provide important information for evaluating spatial-temporal variability of fish assemblages and impacts of commercial fisheries on the most vulnerable species (Montero et al, 2016). In that sense, the IATTC purse-seine database covers a large area and period of years compared with the other Oceans, so the information about the species involved is of high quality and quantity; even considering the limitations mentioned above (Montero et al, 2016). Anyway, the inclusion of fisheries independent data would considerable contributes to improve the conclusions of this study.…”

Biodiversity and environmental characteristics of the bycatch assemblages from the tropical tuna purse seine fisheries in the eastern Atlantic Ocean

“…Thus, determining which factors can explain the diversity of the bycatch communities in purse seine fishing is of primary importance for appropriate management of the exploited resources and also for the conservation of the most vulnerable species. Up to now, most of the studies analysing the environmental preferences of pelagic tropical species have been based on catch data and effort of tuna fishing fleets, especially longline CPUE (Catch Per Unit of Effort) data, but very rarely on purse seine fishing (López, ; Montero et al, ) using observer data. Thus, a better understanding of the interactions between pelagic species and their environment must be developed to ensure the correct implementation of an Ecosystem‐Based Fishery Management (EBFM) (Pikitch et al, ), before performing any conservation plan.…”