Predation of fish

All the fish species that inhabit the Wye and Usk are subject to predation, whether as a juvenile or adult. Otters, herons and kingfishers, for example, have existed in the Wye and Usk catchments for millennia, in addition to the well-known fish predators such as pike and trout.

This predation has always taken place. However, the impacts are more significant when the population of a prey fish species is already depleted. Such impacts may be even more adverse if a new predator species arrives on the scene.

Avian predation

Thirty years ago, there were no goosanders on the Wye. According to the 1999 MAFF survey, up to 98% of the salmon parr produced on the Upper Wye are eaten by goosanders. Additionally, cormorants (a sea bird) are seen in large groups, each eating 2-3kg of fish each per day.

Cormorants and goosanders have a significant effect on coarse species too. Sections of the Wye that were well known for large shoals of dace and bleak are now devoid of them. Large numbers of goosanders are also regularly seen on the Usk too, where the trout population takes the brunt of the extra predation.

More recently, there has been an increase in otter numbers in the Wye and Usk. Welcome by most, this has resulted in quite significant mortalities of unspawned salmon, especially where they are held up at falls. The effects of these natural predators would not be so marked on a salmon stock at former high levels. However, they are likely to impact significantly when stocks are low and trying to recover, as on the Wye and Usk today.

Mitigating the effects predation

Licences to control avian predation are issued by statutory authorities every year but the numbers involved are, by and large, insignificant. Unfortunately, the health of the population of the prey species is not taken into account when deciding the yearly quotas.

There are also powerful pressure groups lobbying against the control of avian predators. It is worth noting, however, that such organisations have few objections when it comes to controlling species that predate on bird species whose populations are threatened.

Instead, the Foundation has developed techniques within its habitat restoration programme that give fish species more refuge from predators.

Read more about the Foundation’s work to mitigate the effects of predation on fish species whose stocks are low.