FEEDING FRUSTRATION

The report found that motivation for food seemed to be an important factor, with greater ‘leaps of progress’ occurring when seals had recently been fed less. Toward the end of training sessions, when animals were nearing satiation, they quickly became frustrated if they were unable to reach the target, and were more likely to give up.

The fact that seals took significant time and persuasion before they would interact with netting suggests that they are not inherently predisposed to try to take salmon by attacking fish farm nets.

This indicates that if the initial stimulus for interaction can be removed or reduced, it may be possible to prevent the positive reinforcement of predatory behaviour.

There was a clear preference for seals to use teeth and fore-flippers in combination to manipulate fish whenever possible. As access to the fish was made increasingly difficult, the effectiveness of this feeding behaviour was substantially reduced.

In cases where the fish were placed some distance away from the netting, it proved difficult or impossible for seals to simultaneously manipulate fish with their teeth and flippers. Feeding was far less effective when seals were only able to use their teeth. The fact that increasing the difficulty of accessing the fish led to seals rapidly losing interest in the task indicates that improved containment measures are likely to be an effective solution.

The scientists were able to highlight certain depredatory behavioural mechanisms, but the deep gashes and abdominal gouges (‘belly bites’) typically seen during investigations on fish farms were not replicated.

Combining this with observations from site visits of recently retrieved still live fish exhibiting these same wounds provides a strong indication that these injuries occur only when the fish are alive.

This leaves open the question of the exact mechanism of this type of attack given the difficulty seals had in manipulating or even reaching fish behind a flat net panel.

It would seem that this apparent conundrum can only be addressed by in situ underwater recording of seal depredation.