By Guest Author 26/12/2016

Phil Jellyman is jet boating up the Waimakariri River in Canterbury – not because it’s a fun thing to do but in search of salmon.

The NIWA freshwater fish ecologist is planning to implant acoustic tags on the fish to find out whether irrigation schemes are affecting their migration to spawning grounds up river.

Along the river he will install about 25 receivers that will gather information transmitted from the tags on the salmon’s whereabouts.

The Waimakariri has a reputation as one of New Zealand’s top salmon fishing rivers, and at 151 km long is one of the largest in North Canterbury. Irrigation schemes allow farmers to extract water from the river for most of spring and summer but recent schemes are targeting floodwaters for harvesting, however little is known about how that could affect the movement of salmon.

“We want to know what sized flood is prompting their movements up the river and how their upstream migration to spawning grounds is affected when water is taken from the river,” says Dr Jellyman

Salmon typically migrate when the water is dirty after the peak of a flood, probably because the dirtier floodwater gives them more cover, is slightly cooler and taps into some innate instinct they have, so the aim is to find out how much the flow harvesting by irrigation schemes could potentially delaying the upstream movements of these fish.

“The salmon are coming in from mid-December onwards to get to their spawning grounds from April onwards. The upstream movement of salmon is happening at the same time that irrigation intake is at its peak.”

The aim is to tag about 10 fish a month from January on – but Dr Jellyman admits it’s a high risk project that relies on them being able to net the fish in the first place. The Waimakariri is a braided river that also changes frequently which makes locating the fish a more difficult task.

The Waimakariri River. Wikimedia / Greg O'Beirne.
The Waimakariri River. Wikimedia / Greg O’Beirne.

“We’ll be trying it in mid-January. Salmon are a good species to target as they are large and will not be affected by the size of the tag we implant…and we know roughly when they’ll arrive and where they want to get to in the catchment. We need to surgically implant the tags which are about 3 cm long by 2 cm wide, so that adds an extra degree of difficulty.”

NIWA will be partnering with North Canterbury Fish & Game and aims to ensure salmon anglers understand the project is important for the long-term sustainability of the fishery.

Summer is for scientific fieldwork. This article is from the NIWA Summer Series, sharing the stories of scientists heading into the wild blue yonder.

Featured image credit: Dave Allen.