Species-specific behaviour and environmental drivers of trap interactions in wild ornamental fishes

Abstract

The harvest of animals from the wild is a pervasive selective force, especially in fisheries, where harvesting often targets individuals with specific traits. While most research has focused on large-scale commercial or recreational fisheries, little attention has been paid to artisanal fisheries, particularly those targeting ornamental species. Furthermore, environmental factors such as temperature and oxygen levels influence the behaviour of fishes, such as boldness and sociability, but their role in the harvesting process remains poorly understood. Here, we used underwater video to examine how two ornamental Amazonian fishes, Hemigrammus sp. and Copella nattereri, interact with artisanal trap gear. We quantified the number of passes, inspections, entries and exits using latency to inspect and enter traps as proxies for boldness, and coefficients of dispersion (CDs) to assess sociability and group coordination. We found that the majority of fish that inspected traps did not enter them, and a given trap typically caught one species over the other. Overall, Copella were captured more frequently, but within individual trials there was no statistical difference in catch numbers between species. While both species inspected traps, Hemigrammus exhibited significantly more passes and a higher rate of inspection. Latency to inspect and enter traps did not differ between species but decreased with increasing temperature for both. Hemigrammus also displayed greater group coordination, with higher CD values across behaviours. Notably, temperature had opposing effects on coordination: for Hemigrammus, CD of inspections increased with temperature and CD of exits decreased, whereas for Copella, inspection CD decreased and exit CD increased. These findings reveal that different species interact with fishing gear in behaviourally distinct ways, influenced by environmental conditions. This highlights the potential for selective pressures to vary not only by species, but also with ecological context. Understanding such dynamics is critical for predicting how artisanal fisheries may shape behavioural traits in wild populations.