The commercial purse seine fishery is one of the most efficient and economically important fishing methods on the planet. Therefore, the sustainability of purse seining is of high importance but is put into question by studies suggesting that large proportions of slipped (i.e. released) catches can suffer from delayed mortality. Stressors during purse seine capture such as crowding, hypoxia or injury have been simulated in experiments proving detrimental effects on the fishes’ welfare. Even under current slipping regulations, stressors during are assumed to be severe, even prior to release, potentially leading to a high unaccounted fishing mortality.
This project represents one of the first attempts to directly observe the catch during commercial purse seining using a deployable monitoring system. The aims of this study were to develop a method of analysing the behaviour of fish caught from spherical videos and draw conclusions about the welfare of the catch. Schooling behaviour was used as an indicator for the animal’s wellbeing, showing a depolarised structure if welfare was compromised.
Schooling structure in these observations was mainly ordered, not indicating high levels of stress. In general, the extent of stressors seems to be dependent on the sizes of the targeted schools. Protocols for video treatment, analysis and data manipulation are provided in order to replicate the methodology for future samples.
