Salmon Farms Contaminate Wild Fish

Wild fish living off the coast of Norway near salmon farms are getting a free lunch – and more. The fish are eating food pellets meant for their penned neighbors – pellets that can be contaminated with chemicals known to end up in farmed fish.

Now, the wild fish harbor these chemicals too, according to recent study that compared contaminant levels in wild fish living near the pens with those that live farther away and do not eat the fish food pellets.

The researchers report that the wild fish living in areas adjacent to Norwegian salmon farms had twice the levels of certain pollutants than fish not living near the farms. Important differences were seen between the two fish species – salmon and saithe – studied. The results suggest that eating wild fish that live near salmon farms may also be a concern for human exposure to these contaminants.

Farmed-raised salmon are fed fish pellets that have higher concentrations of contaminants than wild salmon would have in their natural diets. Prior studies show this is true. This has raised concerns about the safety of eating farmed fish because of human exposure to these pollutants.

There are many health benefits associated with eating fish – especially salmon – due to their high levels of omega-3-fatty acids. These 'good' fats are purported to protect against some heart and blood pressure health risks.

Fish also carry such pollutants as mercury and persistent organic pollutants that have their own set of health effects. To reduce exposures, – especially for pregnant women and children – experts suggest limiting the number of fish meals and choosing to eat species with lower levels.

In this study, researchers collected two species of fish – Atlantic cod and saithe – next to the penned fish at three salmon farms and from control sites miles away from the salmon. They analyzed stomach contents and measured liver tissue for a number of chemicals, including organchlorines, flame retardants PBDE and HBCD, and the surfactant chemical known as PFOS. The wild fish neighbors were compared with the distant wild fish.

Almost half of the cod and the saithe living near the salmon farms had fish food pellets in their stomachs, indicating that these wild fish ate residual pellets that escaped the salmon pens. Pellets were not found in any of the control fish.

The cod living near the salmon farms had significantly higher concentrations of pesticides, such as DDT and chlordanes, the industrial contaminants PCBs, and the flame retardants PBDEs and hexabromocyclododecane (HBCD), than the control fish. The saithe had less than half the amounts of chemicals than the cod, yet they are known to eat higher amounts of the pellets. These differences are likely due to fish lifestyles and physiology.

In addition, fish living near the salmon farms had higher amounts of lipids in their liver compared to fish from the control sites. This is important because most of the contaminants that were studied accumulate in lipid-rich tissues.

Results from this study suggest that salmon feed is escaping from the salmon pens and is either directly ingested by wild fish living in these areas, or settling into the underlying sediment where it may be ingested by animals living there. These factors most likely contribute to contamination of wild fish in the areas close to the farms. Further studies are needed to determine if wild birds and marine mammals (such as seals and otters) are also at risk for higher chemical exposures from residing near salmon farms.