Biodiversity Effects
Community Changes
The artificial structures, fish wastes and uneaten food present at marine salmon farms all have the potential to affect local seabed communities and ecosystems.
One potentially positive effect is an increase in local biodiversity, through the variety of marine life attracted to farm structures. Wild fish aggregate around artificial structures like salmon farms, and fish in the vicinity of fish farms may feed on waste feed, thereby attracting larger fish.
Salmon farming also results in changes to communities and habitats directly below the farm. Particularly, they can reduce the abundance of species that are relatively intolerant of the enriched conditions which can develop below salmon farms. Other enrichment-tolerant species, like worms, can increase in abundance.
Both central and local government and the New Zealand aquaculture industry are clear that salmon farms, and other aquaculture, should only be sited in environmentally appropriate locations.
As a result, salmon farms are generally not approved if they are proposed over reefs or complex habitats with a high diversity or abundance of species, and consequently applicants generally avoid such sites.
As part of the assessment for a new aquaculture site, the likely effects on general biodiversity as well as likely effects on fisheries – particularly important spawning or nursery habitats – are taken into account by decision makers.
Diseased and Escaped Fish
Overseas studies highlight the risks of escaped fish altering the genetic structure of wild fish populations and transmitting disease from farmed stocks to the wild populations. These both appear to be relatively minor issues for New Zealand at present.
New Zealand has few serious salmon diseases present, so disease is not a significant issue.
As king salmon is not native to New Zealand, genetic effects from farm escapees will not impact indigenous marine biodiversity.
At present the effects of escapee salmon are likely to be minimal, given the small scale of the industry and the limited salmon numbers in wild populations within existing grow-out regions.
Marine mammals
New Zealand is home to several species of dolphins, whales, and seals. The welfare of these species is carefully considered when assessing marine farm applications.
New Zealand fur seals can be a problem around salmon farms, leading farmers to use predator exclusion nets around most sea-cages.
In approximately 25 years of sea-cage salmon farming in New Zealand there have been five entanglements of marine mammals in predator nets (2 seals, 3 dolphins). Subsequent management responses by the industry (e.g.changes to net design, development of protocols for net changing) mean that entanglement is unlikely to be a significant ongoing issue.
Exclusion of marine mammals from critical habitat by finfish farms is highly unlikely at present in New Zealand, given the small scale of the industry. Risks from future development could be minimised by appropriate site selection.
Marine mammals are protected by a number of regulations and closed or restricted areas around New Zealand’s coasts. It is an offence under the Marine Mammals Protection Act to intentionally take or harass any marine mammals in New Zealand waters, whether alive or dead, without a permit from the Department of Conservation.
Seabirds
New Zealand is home to a variety of seabird species, some unique only to New Zealand. Under the new legislation governing aquaculture since the beginning of 2005, effects of aquaculture activities on seabirds are considered by regional councils when they assess effects of a proposed Aquaculture Management Area (AMA).
Marine farming is avoided in areas of particular importance for seabird feeding or breeding, especially for threatened seabird species.
Potential effects on seabirds relate mainly to habitat modification, entanglement in structures and habitat exclusion. Salmon farms may also provide roosts for seabirds.
