Does aquaculture impact wild fish quality?

The belief that fish farms have an adverse impact on the quality of wild fish caught in their vicinity is largely misplaced, according to a recent study.

Picture illustration: sockeye salmon kenai fish wild red. peakpx

“Relatively little research on how fish farming affects wild fish has been carried out. Some fishermen and fish buyers find that their experience is not the same as findings from research. We are not comfortable with this disagreement, and want to understand what it is that makes the perception of quality so different from what has been documented,” says Nofima’s Bjørn-Steinar Sæther.

Bjørn-Steinar Sæther © Nofima

The recently completed project was a collaboration between Nofima, the Norwegian Institute for Nature Research (NINA), the Norwegian Institute of Marine Research, and the University of Alicante, and was financed by the Norwegian Seafood Research Fund (FHF). It started as a result of inquiries from fishermen and fish landing facilities, with respect to the poor quality of wild fish that had eaten salmon fodder near farming facilities. The first mention of such effects came from Ryfylke, and over recent years there have been reports of similar situations along several parts of the coast.

“For fisheries and aquaculture to be able to live side by side, it is important to acquire knowledge about issues when disagreements arise. There is increasing competition about the use of coastal space, and we ought to have as a goal that prioritising of how it is used is based on knowledge,” says Sæther.

The project has carried out an extensive literature review of research worldwide, and has summarised this. In addition, scientists carried out field studies where they looked more closely at individual conditions. Initially they investigated the quality of saithe that are caught near fish farms, and compared this with saithe in areas without fish farming facilities.

“The saithe that had eaten fish farm fodder had somewhat softer and more fissured muscle than other saithe, but it was still within the good quality category. Such a change in quality, however, is usual for fish that have good access to food; for example cod, when it preys on capelin,” says Sæther.

The biggest difference scientists found had to do with “pellet saithe” – wild fish that had entered and been trapped in salmon pens – which were shown to spoil more rapidly than other fish.

“We have found some answers; still, there is more that we wonder about. How could it be that there is such a big gap between our results and what fishermen actually experience? We would like to cooperate with them to understand why we experience the fish so differently,” Sæther continues.

Second generation

But what of the offspring of wild fish that eat salmon fodder? Will the parent’s diet affect the next generation of wild fish? A common component of wild fish diet is marine oil, but a large proportion of plant oils is used in salmon fodder. The project group wishes to determine whether the wild fish roe could be adversely affected.

The scientists caught saithe and cod, held them captive, alive in cages, and gave them salmon fodder over two spawning seasons.

The cod roe and fry were then followed. Both the fish and the roe had an increased content of vegetable fatty acids, but scientists found no essential negative effects on the quality of the roe or fry, which developed normally.

The literature review of the effects shows that aquaculture can affect the biology of a number of marine organisms. But the effects can vary among different species, life stages and other ecological factors.

“Different interest groups may experience the effects differently; both in a positive and negative direction, depending on the perspective of the various groups,” says Sæther.

“For those making decisions about how the coastal environment will be used, it will be a balancing act between the ecosystem and various stakeholder concerns.  It is important that those who consider this take the entirety of ecological and social concerns into account,” he concludes.

Known impacts of marine net pen farms

• Nutrients in the sea: emissions of nutrients from aquaculture facilities along the Norwegian coast are relatively small in relation to natural sources. In general, there is little risk for significant global and regional over-fertilization, perhaps with the exception of local effects in places where there is especially poor water exchange/circulation, or where there is intensive fish farming.

• Benthic conditions: Current conditions and depth below the facility determine if the seabed is affected by the descending salmon fodder and faeces. If conditions are shallow with little current under the facility, or if it is located furthest inland in a fjord, the seabed under the facility will be affected more than if conditions are deeper with more current, often in outer fjord areas. It is considered very unlikely that the seabed will be permanently affected in open coastal areas and large, deep fjords, but there may nonetheless be a significant overall local impact in areas with a lot of fish farming.

• Wild fish quality: fishermen and fish landing facilities have experienced that wild fish that have fed on salmon fodder outside the cages are of poor quality and cannot be traded. Research shows a small average quality difference between wild fish that has fed on salmon fodder and other wild fish, but that the quality is clearly reduced in some individual fish.

• Impact on wild fish offspring: Wild fish that have more access to food can also produce more roe; but there is a question as to whether fodder ingredients might be unfortunate for the offspring. Experiments where wild fish are fed salmon fodder showed natural development in the next generation.

• Fewer fish for fjord fishermen? Since fishing nearer than a hundred metres from an aquaculture facility is not allowed in Norway, it is thought that access to wild fish is limited in fish farming areas, but it may also be that the amount of wild fish will increase. The figures available are not good enough to draw a conclusion about this. If large-scale fishing is organised for wild fish that are attracted to aquaculture facilities, there should be a plan to avoid over-fishing the local area.

• Wild fish behaviour: wild fish that feed on fodder that falls out of the cages can help to reduce the environmental impact on the seabed below. Simultaneously, it cannot be ruled out that wild fish outside the cages may help spread pathogenic bacteria or viruses among the facilities, or to wild populations.  Wild fish outside cages may also feed on escaped farmed fish, and there is some speculation that predators may bite holes in the cages and thus cause escape, but this has not been documented.

• Sexual maturation and spawning conditions: wild fish that feed on salmon fodder achieve better growth and fitness, which can lead to earlier sexual maturation. It is possible that early sexual maturation may affect spawning time and journeys to spawning grounds, but this has not been investigated.

• Behaviour of wild fish on spawning journeys: wild fish are attracted to the access to food, and there is a worry that journeys to spawn will be delayed because journeying wild fish will stop to eat outside fish farm cages. But it is also claimed that wild fish avoid fjords with fish farms. It is very difficult to carry out controlled investigations of changes in the behaviour of wild populations. Investigations must be made of the behaviour and distribution of fish in the area before, during and after the establishment of a fish farm. So far, such surveys have not been conducted.