Influence of climate variability and shark interactions on artisanal deep-water fisheries in Spain's largest marine reserve

Artisanal fisheries in the Canary Islands are an essential element of local livelihoods but face increasing challenges due to climate variability, access restrictions due incompatibility with other marine activities (i.e. wind farm and aquaculture), and resource depletion. Moreover, in recent years, fishers operating in the deep-water artisanal fishery of northern Lanzarote reported significant declines in catches, attributing up to 30% of losses to shark depredation on their captures while hoisting. We combined fisher surveys (n = 26), onboard monitoring trips (between 2022 and 2023), and time-series analyses of landings (2006-2023) to evaluate the magnitude of this stealing sharks interactions and their ecological context. Survey data indicated frequent shark encounters, mostly involving shortfin mako (Isurus oxyrinchus), thresher sharks (Alopias spp.), and hammerhead sharks (Sphyrna spp.). However, direct observations during 317 monitored fishing sets recorded only two possible shark-related losses, representing just 0.7% of total fishing effort. By contrast, wavelet analyses of landing series revealed strong correlations between the North Atlantic Oscillation (NAO) and catch variability, with 8-18 month lags. Periods of negative NAO (2014-2017) coincided with exceptional recruitment of deep-water fish species and subsequent record catches between 2018 and 2020, followed by sharp declines after 2021. Our findings suggest that catch losses by stealing sharks, although occasionally perceived as severe by fishers, exerts only a minor direct effect on catches. Instead, climate-driven fluctuations in recruitment and stock availability largely explain observed trends. These results underscore the importance of incorporating climate indices into fisheries assessments and management, while continuing to monitor shark-fishery interactions given their potential socioeconomic implications.