May 23rd is World Fish Migration Day – a worldwide celebration of free-flowing rivers and the life they support. We have some very special fish here in Aotearoa, and this year we’re literally shining a spotlight on five species of galaxiid that move between freshwater and the sea during their lives.
So, so, much more than fritter-fare
The galaxiid species are collectively known as whitebait and they’re caught in their tens of thousands around the country as they migrate into and up rivers in the spring. And traditionally made into fritters. A touch of egg, salt, two minutes in the pan, white bread, squeeze of lemon, and you’re holding a Kiwi icon in your hand.
But as we’re about to find out, there’s a whole lot more to whitebait than that.
Before the 1960s many scientists thought whitebait was just one species – īnanga. But enter Bob McDowall, the ‘godfather’ of New Zealand freshwater ecology. In 1964, his research found several different species in the Awarua River in South Westland. Later that decade the five galaxiids we know today were described and reported in the scientific literature.
Here’s roughly what’s in a typical whitebait catch:
→ 85% īnanga (Galaxias maculatus)
→ 5–10% kōaro (Galaxias brevipinnis) and banded kōkopu (Galaxias fasciatus)
→ less than 1% giant kōkopu (Galaxias argenteus) and shortjaw kōkopu (Galaxias postvectis)
There are also likely to be smelt and possibly other species like eels present. (Fun fact: the name galaxiid comes from ‘galaxy’, after the starry pattern found on the skin of adult fish.)
Digging into the mystery
McDowall and his colleague Tony Eldon went on to publish a report called The Ecology of Whitebait Migrations in 1980. It’s become a bit of a classic.
This was the first time the whitebait fishery had been examined in such detail (173 pages of detail), including the numbers and mix of species present, timing of whitebait runs, water level and temperature, salinity, sediment, weather conditions and day length reported across several rivers.
One of the most helpful things in the report is a line drawing of the five species, and information about how to tell them apart.
McDowall rather delightfully notes:
The species also differ in stoutness…G. fasciatus, though the smallest whitebait, is also the stoutest, G. brevipinnis is intermediate in stoutness, and G. maculatus is generally the largest and most slender.
Time for an update
That guide was published 46 years ago and we thought it was time to put out an updated version – something our staff and whitebait fishers could use to find out which species were being caught when and where around the country.
We’re proud to be working with a contemporary expert, Professor Angus McIntosh. He’s a freshwater ecologist based at Te Whare Wānanga o Waitaha | University of Canterbury. Not only is he a freshwater researcher, he’s also a passionate and excellent photographer.
“We’re essentially updating the identification guide, trying to figure out who all the galaxiids are, given the subtleties of how they’re different. It’s very interesting and quite a mystery – but also a lot of fun,” Angus says.
The tech we have to hand now is a lot more powerful with digital photography, online databases like iNaturalist, affordable genetic analyses and AI species detection available.
“One of the main differences is that McDowall worked on preserved or frozen specimens under a microscope. Our goal is to produce something that could be used with a fish viewing box or a good quality photo. Obviously that’s a lot more challenging.”
While adult galaxiids look really different to each other as adults, they’re very similar as juveniles.
“We’re looking to identify them when they’re about 5 cm long and have been in the rivers for just 4–6 weeks – before they develop pigmentation.” (Pigmentation is an adaptation that makes them less visible in freshwater than translucent sea-going fish.)
Close-up photography reveals patterns and colours that could help identify different species. Photo: Angus McIntosh
Wriggly little fish just keep on swimming
Photographing tiny fish isn’t easy, but Angus has developed a few techniques that make it possible.
“I have a tank that I use, so I took this over to Hokitika and set it up in DOC’s garage. Suze Harris, DOC Freshwater Ranger, and I went out and caught a range of fish in streams and at the river mouth. We brought them back and put them into the tank to photograph, a few at a time.”
The challenges build because the fish need to be square on, with head and tail in focus. This orientation best shows the features needed for identification.
“When you’re working in macro, the depth of focus is very shallow, so there’s not much to work with. I’m also using flash with a soft box to reduce the shadows. And I have a big, black, blanket over the top of me to reduce the reflection in the glass of the tank.
“So I’m sitting there trying really hard to get a fish in focus and fire the flash at the right time, under a blanket and only looking through the viewfinder. It’s quite comical!
Identifying characteristics
Here are some of the stand-out features that generally help identify the species:
→ Bandeds have big eyes.
→ Giants have big mouths.
→ Shortjaws have an undershot jaw even as juveniles.
→ Kōaro have a snout-shaped head.
There are more subtle differences like how far the edge of the mouth extends under the eye, and the placement and angles of their fins.
Not only is this work replicating McDowall’s identification chart, it’s also showing up some quite new features.
“We’ve noticed that bandeds have colouration on their heads that nobody has ever identified before – iridescent blue with white spots. Kōaro can be quite golden when they’re young, and kind of sit up a bit. Īnanga have a small mouth but develop pigmentation quite early. We’ve also seen distinctive colour patterns like two lines under their bellies that might be characteristic.”
Zeroing in on a correct ID
Even with these detailed photos, it’s not easy to distinguish some of the species. It’s also hard to find some of the rarer species, like shortjaw that only make up a really small percentage of the fish.
“They’re the one in a hundred fish – so it’s going to take a few trips to the coast to get those done. The goal is to have photos of each species at four different life stages.
“We talk to our colleagues and try to agree the characteristics among ourselves. We can also use genetic analysis to confirm the identifications of particular fish we’ve photographed.”
Research for a sustainable fishery
In the foreword to McDowall’s report it says:
Maintenance of the unique whitebait fishery poses a series of unusual problems, but it is quite apparent that appropriate resource management cannot be achieved unless the fish themselves are better understood.
This premise is still true today – it’s the basis of our work to manage the whitebait fishery to ensure its sustainable and will be there for future generations.
“We’re trying to solve the same problems – the fish haven’t changed but we’ve got much better methods than they had.”
What has changed is the urgency of the task. Whitebait were once a plentiful resource but catches have declined, even from the 1980s, and all the species are now threatened or at-risk of extinction.
Whitebait are in trouble because of the loss of spawning habitat, water pollution, predation by invasive species and barriers like dams, culverts and floodgates that make it hard for them to swim between rivers and the sea.
“I hope my photos can support DOC in their important work to better understand and protect these amazing fish.”
Thanks Angus – you’re a star
Angus has generously shared his fish photos with us over the years. We are very grateful for the opportunity to use them – they show the beauty that would otherwise be missed. THANK YOU ANGUS!
“When life is a bit less busy and maybe when I retire, I really want to spend 5 years on the photography – there are so many things that people just don’t get to see.”
We’re definitely looking forward to that! (And we’ll let you know when the guide is done.)
Links
McDowall and Eldon report
How you can help whitebait: Whitebait
