Cetaceans, seals and birds become entangled in anti-predator nets, which surround fish farms. The exact figures relating to cetacean entanglement are not available, but the information that is available suggests that a significant number of cetaceans are dying as a result of entanglement in anti-predator nets each year.
Seal scrammers are acoustic devices, which are used to deter seals from taking fish from the sea cages. The intensity of the sound emitted causes pain and suffering to the seals. They do, however, become habituated to the sound and therefore the deterrent effect of the scrammers is significantly reduced. The evidence suggests that these devices have adverse effects upon cetaceans. Research in a number of countries has shown that cetacean populations have left and not returned to areas where scrammers were used.
Significant numbers of seals are shot in order to prevent them taking fish from the sea cages. There is also evidence that cetaceans and birds are also shot. Many are not killed initially, but die after days or even weeks of horrendous suffering. There are no available figures for the numbers of cetaceans and birds shot each year. However, there are approximate figures for the number seals– 3,500 each year.
Evidence suggests that the pollution from sea cage fish farms is destroying the marine environment, and causing harm to cetacean populations. Research in a number of countries indicates that cetaceans, inhabiting areas in close proximity to sea cage fish farms, have higher incidences of skin disease, and higher levels of toxic burden. The research also suggests that the mortality rate of first – born calves is significantly higher.