Looking for the ‘wrong’ fish

Today we hear from Juliet, a Pest Fish Ranger who had the task of surveying pest fish populations around the South Island last summer. This work is an important part of protecting our native species.

Juliet Bruce, Pest Fish Ranger

Did you know there are 58 species of native freshwater fish in New Zealand?

Many of these species are not found anywhere else in the world – they are beautiful and unique! Our freshwater ecosystems, such as lakes and rivers, need these fish to be healthy.

Freshwater pests, including fish and plants, are some of the most pressing threats to our native freshwater fish, their habitats and food sources. One way that DOC protects native species is through surveys for populations of pest fish, which are koi carp, rudd, catfish and gambusia, and pest plants such as hornwort and lagarosiphon.

Ceratophyllum demersum : Rohan Wells | NIWA and Lagarosiphon major : Sjaan Charteris | DOC.

Pest fish team leader Vanessa Brough and her faithful, enthusiastic sidekick (that’s me) surveyed 28 Canterbury sites and 31 Otago sites. Public sites included local council or DOC sites, and private ones were often ponds and lakes on farms. Only public sites are featured in this story.

It would be fair to say that the daily routine was probably one of the strangest I’ll ever have! Many species of fish are most active at dusk, so by setting out the equipment in the afternoons and leaving it overnight, we aimed to increase the chances of catching a variety of species.

We would inflate the rubber boats and put on waders and life jackets, plus a GPS for marking the location of each piece of equipment. If the weather might turn, I’d take a rain jacket too.

We would set out the Gee minnow traps and fyke nets, before setting out the gill nets and watching them until about 10 pm, an hour after sunset. This prevented diving birds, such as scaup or shags, from becoming caught in the gill nets. About 5 am the next morning, we would bring in the gill nets before the birds wake up, and record any species caught. Then we brought in the Gee minnow traps and fyke nets, recording species caught in each trap or net.

We definitely went full-throttle in the name of conservation. As well as plenty of day trips within Canterbury, we had two trips of nine days to Dunedin, nine days in Alexandra, and a nine day trip combining Wanaka and Queenstown. Shorter trips included four days each in Cheviot, Timaru, and Oamaru.

The best part of the pest fish work wasn’t about looking for pest fish. By far the most memorable sites were those that had plenty of variety of native fish and plant species. It was quite exciting to know first-hand which species were living in a pond or lake, and approximately how large the populations were based on how many of each species we caught.

The nets and traps set at Lake Waihola, near Dunedin, caught a wide variety of native and introduced species, including bully, eel/tuna, inanga, yelloweye mullet, brown trout, and a flounder. Ross Creek Reservoir, Sullivans Dam and Cedar Farm Forest near Dunedin had populations of dozens of kōura. The longest were about 13 cm.

At Lake Taylor, we recorded eel/tuna, common bully, smelt, brown trout, and an unknown species of galaxiid, possibly Canterbury galaxias or kōaro.

Biosecurity was an important part of using the same equipment at different sites. Freshwater pest plants such as hornwort pose a serious threat to freshwater ecosystems. Using either diluted bleach or salt solutions and potentially a water blaster, we cleaned every piece of equipment that came into contact with water at a site, before using it at the next site. Cleaning and repairing equipment after each site ensures that pest species are not moved between sites.

Everyone can help to protect freshwater ecosystems

You can stop the spread of freshwater pests by:

• Check, clean and dry between waterways
• Do not move plants and fish between waterways
• Do not release plants and fish into waterways

There are high financial penalties for:

• Introducing any aquatic life into an area where they don’t already occur, without a permit.
• Releasing, spreading, selling, or breeding unwanted organisms. Gambusia and koi carp are unwanted organisms throughout Aotearoa/New Zealand.
• Possessing, controlling, rearing, raising, hatching or consigning noxious fish without authority. Koi carp and rudd are both noxious fish, except rudd is considered a sports fish within the Auckland/Waikato Fish and Game region.

One of my favourite things about this work is an entirely new sense of wonder. Despite a general interest in practical conservation, I knew relatively little about native fish. It’s as if a part of me was asleep, waiting to realise that these small, important creatures and humans are interconnected in so many beautiful ways.