Hidden demographic impacts of fishing and environmental drivers of fecundity in a sea turtle population

Abstract

Fisheries bycatch is a critical threat to sea turtle populations worldwide, particularly because turtles are vulnerable to multiple gear types. The Canary Current is an intensely fished region, yet there has been no demographic assessment integrating bycatch and population management information of the globally significant Cabo Verde loggerhead turtle (Caretta caretta) population. Using Boa Vista island (Eastern Cabo Verde) subpopulation data from capture–recapture and nest monitoring (2013–2019), we evaluated population viability and estimated regional bycatch rates (2016–2020) in longline, trawl, purse‐seine, and artisanal fisheries. We further evaluated current nesting trends in the context of bycatch estimates, existing hatchery conservation measures, and environmental (net primary productivity) variability in turtle foraging grounds. We projected that current bycatch mortality rates would lead to the near extinction of the Boa Vista subpopulation. Bycatch reduction in longline fisheries and all fisheries combined would increase finite population growth rate by 1.76% and 1.95%, respectively. Hatchery conservation increased hatchling production and reduced extinction risk, but alone it could not achieve population growth. Short‐term increases in nest counts (2013–2021), putatively driven by temporary increases in net primary productivity, may be masking ongoing long‐term population declines. When fecundity was linked to net primary productivity, our hindcast models simultaneously predicted these opposing long‐term and short‐term trends. Consequently, our results showed conservation management must diversify from land‐based management. The masking effect we found has broad‐reaching implications for monitoring sea turtle populations worldwide, demonstrating the importance of directly estimating adult survival and that nest counts might inadequately reflect underlying population trends.

Diet of loggerhead turtles in the Gulf of Manfredonia, South Adriatic Sea: evidence of winter feeding and anthropogenic impacts

“…If turtles were attracted to trawling discards, this would likely increase bycatch rates. This would have important conservation implications for both the juvenile turtles, which represent most of the population (Casale et al 2012b), and the larger turtles, which have high reproductive value (Roast et al 2023), ultimately affecting the Greek rookery from which most of these turtles originate (Tolve et al 2018). The high bycatch reported during winter is of ecological interest, since Lazar et al (2011) assumed that turtles do not feed in winter, at least in the cold waters of the north Adriatic, although direct evidence is still lacking.…”

Ensemble modelling to predict the distribution of vulnerable marine ecosystems indicator taxa on data‐limited seamounts of Cabo Verde (NW Africa)

“…Indeed, available image data showed pristine and diverse CWC gardens on Cadamosto Seamount(Orejas et al, 2022;Vinha et al, 2022) and exceptional sponge and crinoid fields and scleractinian coral reefs on Nola Seamount(Hansteen et al, 2014). In addition, three of the seamounts considered in our study -Boavista, Cabo Verde and Nola -are currently included in designated ecologically and biologically significant areas (EBSAs) (UNEP/CBD/COP/DEC/ XII/22, 2014), where significant fishing activity occurs(Martins et al, 2022;Roast et al, 2023). Priority should, therefore, be given to collecting new data in global under-sampled deep-sea regions, involving local researchers and communities.ACK N OWLED G EM ENTSWe are thankful to Herculano Dinis and Jacob González-Solís for sharing knowledge on the marine biodiversity and conservation of theseamounts of Cabo Verde.…”