Spawning monitoring – measuring to manage

Fish & Game staff throughout the country are busy conducting spawning surveys for trout and salmon to ensure there are sustainable fisheries for the future and to check up on stream and river health. 

Fish & Game New Zealand chief executive Corina Jordan said there were a range of ways to monitor spawning, from using fish traps to walking up a stream and counting. 

“Fish spawning monitoring tells us if a population is in trouble, if sites have moved and need protecting, and help us with planning work.” 

Spawning is when a female fish ‘digs’ holes in stream gravels by turning on their side and thrusting their tail. They lay eggs in the hole, and the male fish deposits milt onto the eggs to fertilise them. The female then ‘digs’ a new hole in front of the eggs, which covers the eggs in gravel. The excavations are called redds, which simply means nest. 

“Salmon and different species of trout spawn at different times, but often in the same waterways. There are also differences depending on where you are in the country, but generally, salmon spawn from March to June, brown trout from May and rainbow trout from June onwards. 

“So, while this work is continuing, we are already getting interesting findings. Our Nelson Marlborough team recently monitored brown trout redd density for a section of Motupiko River. Based on the survey, which found an uptick in spawning activity, they are making recommendations to avoid any instream works activity upstream of the main spawning zone from May to October (as designated within the Motueka Water Conservation Order). 

“We are also keeping an eye on salmon migrating from the sea to the headwaters of the main central South Island rivers to spawn as there’s been a decline in recent years." 

Jordan said spawning surveys were just one part of the work Fish & Game does to monitor and manage species and the work also allows the organisation to keep a close eye on the health of our precious waterways. 

“Fishing and hunting are ways of being part of nature and its cycle. So, part of our focus is ensuring our wild places stay wild. And more than that, we must ensure that the life that survives there thrives there.  

“Fish & Game’s journey has always been about protecting, restoring and rewilding Aotearoa New Zealand’s natural freshwater habitats and species. And that means safeguarding indigenous species and the management of valued introduced ones for the benefit of people and whenua.”  

 

Regional updates: 

Auckland-Waikato 

Auckland/Waikato staff conduct spawning surveys to ensure there is adequate habitat for fish to spawn. If Hydro Lakes have no natural spawning or limited spawning, survival and hatchery releases are necessary to maintain the fishery.  The spawning survey will be followed up with electrofishing in the spring to confirm juvenile survival. 

 

Hawke’s Bay 

Staff surveyed several Tukituki/ Waipawa tributaries; The Manganuku, Mangamate, Upokororo, Mangamauku, Tukipo, Makeretu as well as some spawning streams off the Ngaruroro. 

The rain has made it challenging, waiting for streams to drop and clear; only to have another dump of rain as target streams were almost clear enough. 

So far, we have been pleasantly surprised with the number and quality of the fish seen in both Ngaruroro and Tukituki system streams. 

We are all hoping for good reasonably settled weather free from major floods for the rest of the spawning season, with the occasional fresh to help our spawning stock travel upstream into the smaller quieter waters to spawn.  

Caption: A rainbow trout spotted during the survey (rainbow Jack2)

 

Eastern 

Eastern Region conduct a number of spawning surveys around the Rotorua lakes.  

A fish trap in the Ngongotaha stream monitors numbers and sizes of brown and rainbow trout throughout the year – except when high rainfall prevents it from operating. Brown trout brood fish are also collected for use at the hatchery. 

Lake Tarawera’s spawning tributary streams are also monitored. Tarawera is an important fishery in the Eastern Region with the lake providing rainbow trout brood fish to run the hatchery. The Te Wairoa stream is trapped daily between the beginning of April and the end of August. Walk-up spawning counts are also conducted in other key Tarawera streams and drift dives of the lake’s outlet are carried out four times over winter. 

Intensive anger creel surveys and walk-up spawning trout counts are also undertaken with Lake Waikaremoana and its tributaries on a 3-yearly basis. Trout are a key indicator species for ecosystem health and fluctuations in trout numbers or fish size may be indicative of changes occurring in the catchment. 

Photos attached

 

Nelson-Marlborough 

Motupiko River Brown trout spawning foot survey found 16 trout spawning egg nests (redds), and 150 adult brown trout were observed.  Another survey of a10 km stretch of the Tadmor-Motueka River found only two trout spawning egg nests (Redds), and 6 adult brown trout were observed within the surveyed section, possibly due to the lower river often running dry during drought years.  No migratory pods of fish were observed making their way further upstream up into the Tadmor headwaters, unlike observations within the Motupiko this year.   

  

Central South Island 

March – Sockeye salmon spawning surveys in the Mackenzie Basin / Waitaki Lakes. Both helicopter and ground surveys. 

March through July – sea-run Chinook salmon spawning surveys. The focus was on Rangitata / Rakitata Catchment, Ōpihi Catchment and Lower Waitaki River Catchment. helicopter and ground surveys. (note – brown trout spawning counts undertaken during sea-run salmon counts as a secondary focus) 

May to November - brown and rainbow trout spawning surveys, aerial and ground and focussed on enhanced spawning habitat projects at Lake Alexandrina, Aviemore spawning race (Lake Waitaki) and Upper Ōhau River controlled fishery.      

Caption: Senior Fish & Game Officer Hamish Stevens undertakes a sea-run salmon spawning survey at Ōhapi Creek, South Canterbury. 

 

Otago 

Otago Fish & Game has been monitoring its waterways during the 2024 winter for brown trout and salmon spawning. 

Upper lakes salmon spawning: This is to learn where our lake salmon are spawning. It is important as the upper lakes have important salmon fisheries and are also a large contributor to the Clutha/Mata-au sea-run fishery via migration down through the dams. Work is largely paid by Contact Energy, so consists of helicopter and foot surveys as well as the use of EDNA to help target efforts. 

Lower Clutha River/Mata-au salmon spawning: We are concentrating on traditional sea-run salmon spawning grounds. This gives us a picture of the salmon spawning run, which is at very low levels.  

Brown trout monitoring: Otago Fish & Game repeats monitoring in some sections of rivers semi-regularly to look at trends in the brown trout spawning run over time.  

Brown trout exploratory work: We are also looking at new areas to determine the extent of brown trout spawning in our region. This data is needed to support policy and planning work. It will contribute to our own regional spawning model and a planned nationwide project. This work is focussed on important fisheries, especially those that are under threat from changes to water and land use. 

Caption: Otago Fish & Game officer Ben Sowry conducting a brown trout spawning survey in Fraser River, Central Otago, in June 2024. Photo: Mason Court, Otago Fish & Game 

 

Southland 

Over the autumn and winter months, Southland Fish & Game conducts spawning surveys on several important fisheries. On the upper Waiau for example, we have been monitoring the spawning activity of rainbow trout. Because the flow of the upper Waiau is modified for hydropower generation, there is a risk that trout redds in shallow areas could become dewatered by flow manipulations. By monitoring the spawning activity and location of trout redds, we can provide this information to Meridian Energy, allowing them to consider it when managing flows for operational purposes. 

As part of our monitoring programme, we also conducted a salmon spawning survey on an important spawning stream in the Oreti River catchment. This year's count was lower than usual, but the count varies widely from year to year, likely reflecting sea feeding conditions. Although the sea run salmon population in Southland is small, monitoring the population remains important as these salmon are highly valued by anglers. 

In June, we assessed spawning brown trout in a tributary of Waituna Lagoon. Each year, we capture a sample of 100 adult brown trout to measure their length and assess the health of the fishery. Earlier this year, there was a significant algal bloom in Waituna Lagoon, raising concerns about its impact on the trout population. Fortunately, we observed good numbers of spawning trout, and the average measured length was 540mm, consistent with the long-term average.   
Caption: Ben Febery with a trout at Waituna Lagoon