Comparing the activity of exploited and unexploited populations of a reef-dwelling seabream, Chrysoblephus laticeps, during an extreme upwelling and cold-spell event

Abstract

Along the south coast of South Africa, extreme upwelling events lead to rapid temperature declines and prolonged marine cold-spells, which have, on occasion, led to large-scale mortalities of coastal fishes. In a somewhat antagonistic process, fishing exploitation has been shown to target specific phenotypes, potentially selecting for higher physiological diversity within exploited populations, reducing resilience to adverse environmental conditions. This study investigated the effects of thermal stress and exploitation in two populations (exploited and unexploited) of the commercially and recreationally targeted red roman Chysoblephus laticeps (family Sparidae) during an intense upwelling and a marine cold-spell event, using acoustic telemetry data. The results show that the acceleration of tagged fish (a proxy for fish activity) during the upwelling event differed significantly between the two populations (p < 0.05), with fish in the unexploited population maintaining their activity, and fish in the exploited population exhibiting reduced activity. The activity of the fish was also significantly different between the populations during the marine cold-spell, with those in the exploited population exhibiting reduced activity over time compared with the unexploited population. These findings highlight the impact of thermal extremes on fish activity and suggest that exploitation may selectively remove individuals that are tolerant to these events, which might consequently reduce resilience of the fish population. Based on these findings, it is concluded that networks of marine protected areas can promote fish populations that are resilient to future climatic conditions.