The pioneering use of microchip technology has the potential to reveal the closely held secrets of an elusive native fish, including its mysterious sex life.
Threatened-Nationally Vulnerable shortjaw kōkopu are found only in Aotearoa. As juveniles, they are one of six species known as whitebait.
Over the past year, DOC Ranger Suze Harris has inserted 12.5 mm-long PIT (passive integrated transponder) tags under the skin of 41 shortjaws living in a tributary of Kaniere River, Hokitika.
The inserted PIT tags allow her to track individual fish via a detector blue-toothed to her phone.
"We need to know the females' spawning time so we can track down nesting sites. This helps us target conservation efforts such as trapping – since rats eat shortjaw kōkopu eggs. We can also make recommendations under the Resource Management Act on the timing of activities, like earthworks, that sometimes occur along stream margins."
Suze also says although the West Coast remains a shortjaw stronghold, with enviable populations compared to the rest of the country, some streams with previously strong populations are being claimed by other whitebait species – and the shortjaws have either significantly decreased or gone altogether.
"The usual freshwater monitoring methods, like electric fishing, don't work well on shortjaws. Their preference for deep rocky pools and their flitty behaviour makes them hard to survey.
"PIT tagging the fish means I don't have to keep recapturing them. Instead, when I'm monitoring in the field, my phone might ping, I'll look at a summary of the fish on my phone and think, 'oh, that's Charlie Brown, who is male – I'll leave him alone because I'm looking for females at the moment'."
Shortjaw reproduction occurs in late autumn, with males producing milt (sperm) and raring to go earlier than females.
"Males dominate the Hokitika site. We still haven't managed to tag a female – they're so elusive. But tagging males helps because their presence indicates the right conditions for spawning, meaning females are likely to show up soon.
Suze was granted animal ethics approval to tag up to 50 shortjaws. She tagged a total of 41 in February 2024 and 2025. Of those, 39 are giving signals from live fish.
New Zealand's native species, like shortjaw kōkopu, are unique and special, with 88 per cent of our fishes found nowhere else in the world. DOC freshwater rangers throughout the country are identifying populations of shortjaw kōkopu so DOC can work with iwi, hāpu, councils, landowners and community groups to protect them.
Background information
Shortjaw kōkopu are a migratory galaxiid species (named for their skin which looks like a galaxy of stars). Their largest populations are in Northland, Taranaki, Wairarapa, Tasman, Marlborough and the West Coast.
PIT tags are the same technology used to microchip dogs and cats, with a variety of sizes as appropriate for the animal.
As the fish being tagged are adults, and it is the juvenile fish which are eaten as part of the whitebait catch, there is no chance of a PIT tag being eaten by a human.
