Relocation of seals can and must stop

The TCT opposes the euthanasia or relocation of seals that are claimed to be a problem for fish farms. This is because of the unacceptable animal welfare impacts and because there are practical alternatives.

The State Government recently announced it would stop relocation of seals from fish farms to the north-west coast but it has allowed relocations to continue. This policy stopped criticism of seal relocations from north-west based commercial and recreational fishers. The north-west electorate of Braddon is expected to be a key battleground in the state election and the government has addressed this political risk. 

But the government has allowed seal relocations to continue, maintaining this inhumane, costly and avoidable practice. Continuing relocations just gives the industry an excuse to delay implementing more effective solutions that do not harm seals.  Solutions have been available to the industry for decades and the government should be taking the lead by banning relocation of seals and requiring fish farms to use effective fish pen systems and farm practices.

Seals can be a problem around fish farms. They can bite through nets to access fish and can haul-out on to the fish farm structures, which can be very unnerving for workers. But the instances of fish farm workers actually being harmed by seals are very rare. All these problems can be solved and the best solution is to keep seals from being able to access fish. There are a range of fish pen systems that, if properly utilised and maintained, can keep seals and fish separated. These will never be perfect but existing systems are sufficiently effective to remove the need for relocations.

Fish farm nets can develop holes and seals can even bite holes in them, so even the best technology must be regularly checked and maintained.  Nets must be kept taut to ensure seals cannot push against them and catch fish inside the pens. Great care must also be taken by fish farm workers when moving fish to avoid accidental release which will attract seals to fish farms. Dead fish must be regularly cleaned from the bottom of pens. In the long term, if fish are made much less accessible the next generation of seals will probably grow up with less awareness that fish farms are a source of food. 

A typical Tasmanian fish cage is the polar circle type (shown in the below picture). A circular plastic tube, or two or more concentric tubes, float on the water and support a hanging net bag, held open by weights or mooring lines. This holds the fish as well as surface infrastructure such as feeders. The float tubes are low and in the past, seals would have no trouble getting over the top and in with the fish. Open top cages also allow seabirds to take fish food, or even fish if it is a big bird.  

A very early development in fish cage design was the introduction of the predator net. This is basically a second net that encloses the net holding the fish, and reduces access by seals and other underwater predators. Predator nets can be effective but need to be carefully designed and tensioned to ensure that there is an adequate gap between the nets to stop seals simply pushing the outer predator net up against the inner net and accessing fish. A problem with predator nets is that they complicate the cleaning that is needed to keep the cage nets free of seaweeds and other biofouling organisms to maintain water flow through the cage and adequate oxygen for the fish.

Predator nets have become a normal part of Tasmanian fish farming, as have beefed-up bird nets that are now strong enough to discourage most seals. 

Problems remain because it is hard to get enough separation between a traditional predator net and the inner net to stop every determined seal. The standard design bird nets do not always stop seals that may weigh several hundred kilograms. The standard floating ring structure of fish cages also acts as a convenient place for seals to get out of the water and rest, which is a natural part of seal behaviour.

Something as simple as an electric fence or a relatively lightweight fence around the cage can stop seals getting in over the top of the floats and into the fish enclosure or hauling out onto the cage to rest. This design has been used on South Australian tuna farms and salmon farms in Washington State. 

System cages are a farm design that uses a series of floating pontoons and walkways to create a rigid cage system that is very resistant to hungry seals. This design is quite common in other countries. A farm in the Tamar Estuary currently uses system cages and by all accounts does not seem to have problems with seals. Unfortunately the rigid structure prevents system cages being used in places where they can be exposed to larger waves.

Tassal’s preferred approach is to use much more rigid nets in a single bag enclosure, doing away with the predator net altogether. The netting is also tougher, which makes it harder for seals to chew holes. The more rigid netting, along with a decent tensioning system, makes it much harder for seals to deform the netting to get close to the captive fish. There is still the need for regular inspections to ensure that holes are not developing.

Tassal’s technology seems to work well but Huon Aquaculture has an even better system. This is basically an improvement on the old predator net/inner net system. Huon Aquaculture’s new cages have a very big space between the inner and outer nets. Combined with proper tensioning, this completely eliminates the possibility that seals can get to the inner net and eat captive fish. A mechanical cleaner that crawls across the nets takes care of the problem of cleaning the dual nets, and a really strong fence around the surface structure stops seals from hauling out on the cages. This strong and effective surface barrier allows the use of a lighter bird net across the top to exclude seabirds.

Technologies exist that are very effective at keeping seals away from farmed fish. The real problem is that aquaculture companies have been reluctant to pay the additional costs associated with those technologies and successive Tasmanian Governments have been unwilling to regulate to ensure that appropriate cages are being used.

Article and photographs for Job Bryan, TCT's Marine Campaigner