Tench

(Tinca tinca)

Progressive Control Pest

Tench are olive-green fish whose colour varies from dark to light green. They have a single small barbel at each corner of the mouth. The fins tend to be thick and fleshy and the body is covered in small scales. Their most distinctive characteristic is their bright orange eyes. A native of Europe, they were introduced to New Zealand in 1867. Although imported as a sports fish, they are generally not recognised in New Zealand as quality sporting fish but can grow up to 4 kg and are valued by European anglers. Part of a group described as coarse fish, they have been present near Oamaru for many years. They are most common in the Auckland area but have also been found during recent surveys in isolated locations in Northland, Bay of Plenty, Wellington, Tasman-Nelson, Marlborough, and Canterbury.

Reasons for the Strategy

An example of a Tench fish.

Tench generally live in still or slow-flowing waters and are able to tolerate high levels of turbidity. They are carnivorous, feeding on insect larvae, crustaceans and molluscs. They are prolific breeders and a large female may produce hundreds of thousands of small eggs. They are considered to pose a significant threat to native aquatic fauna in the Tasman- Nelson region and are associated with reductions in water clarity. An active campaign has been conducted by the Department of Conservation in recent times against illegal releases of tench.

Sports fish are defined in the Conservation Act 1987 and the Freshwater Fisheries Regulations 1983. Schedule 1 of the Regulations lists tench as sports fish. However, Fish and Game NZ has responsibility for management of the sports fish resource for the recreational interests of anglers and the recent arrival of tench in the Tasman-Nelson region was not authorised by Fish and Game NZ. It has developed policies that may allow a limited population of tench to be established in an appropriate area as a sports fish.

They are assessed at “2” on the infestation curve. At present, they have a very limited distribution in the region, having been recorded in a number of small ponds. The low incidence, extensive areas of habitat, and the potential for it to cause significant adverse effects mean the benefits of progressive control far outweigh the cost.

Objective

To reduce the distribution and density of Tench in the Tasman-Nelson region during the term of the Strategy, except for any area that is legally sanctioned by the director- General of Conservation and the Nelson-Marlborough Council of Fish and Game NZ, and granted an exemption by the Management Agency.

Alternative Measures

The alternative of doing nothing or relying on voluntary control will not achieve the objective of reducing the distribution and density of Tench and will result in significant additional costs to the community with respect to lost natural values and the increased cost of control in the future.

Strategy Rule for Tench

The occupier shall report any suspected sightings of Tench and allow access to the Management Agency, the Department of Conservation or their agents, to destroy all adult and juvenile forms of Tench in waterbodies on land that they occupy, except for legally sanctioned areas. A breach of Strategy Rule 5.x.5 is an offence under Section 5.4.5 of the Biosecurity Act 1993.

Biosecurity Act Requirement

No person shall knowingly sell, propagate, breed, release or commercially display Tench under Sections 52 and 53 of the Act.

Note: The unauthorised release of Tench without the approval of the Director-General of Conservation and Fish and Game NZ is also an offence under the Conservation Act.