Evidence of long-lasting memory of a free-ranging top marine predator, the bull shark Carcharhinus leucas

Abstract

Abstract Recent studies suggest sharks cognitive abilities are comparable to other vertebrates such as mammals and birds, but we still know relatively little about the long-term memory capacity of sharks. We took advantage of the COVID-19 anthropause to determine whether bull sharks conditioned at a provisioning ecotourism site in Fiji would remember the site after an 18-month hiatus in shark feeding activities. We hypothesized that if bull sharks remembered the food rewards associated with divers at the site, they would return to the reactivated site more rapidly than the original recruitment process that occurred when the site was first established in, 2015. We assumed that original recruitment to the newly established site represent a period of learning and conditioning, whereas a significantly faster recolonization of the site would imply memory recall of the original conditioning. We monitored bull shark abundance at the site for three years (1018 dives) from its original establishment in 2015 until all feeding and diving activities were ceased for 18 months in December, 2020. When shark feeding resumed, we documented bull sharks returning to the site over a three-week period (45 dives beginning June 22, 2022) and compared observed abundances with modelled predictions assuming no interruption to provisioning. Results revealed a rapid return to ‘business as usual’, suggesting that bull sharks still remembered the food reward conditioning despite an 18-month hiatus in provisioning. This supports the existence of long-lasting cognitive capacities in this species and highlights their relevance for managing activities that could disrupt their natural ecology.