Migratory fish, resting and growing in the fresh waters. These secretive creatures have tales to tell of the journey they’ve taken to get there…
Check out the Migratory Fish UrbanNature panel at George Street
Some species of fish are diadromous, that is, they undergo one or multiple migrations between fresh and salt water during their lifetime. Migrations, though energetically expensive, may allow species to exploit seasonally favourable conditions for growth and/or reproduction.
Despite their importance, human actions can sometimes get in the way of these natural behaviours. As such, attempts are often made to remedy this. Structures such as fish ladders can be built to provide routes for migratory fish around obstacles.
In certain Dunedin rivers and lakes, you can see examples of migratory species. The tuna (eel) is a native example. We have two main species of eel in New Zealand, the shortfinned (anguilla australis) and the longfinned (anguilla dieffenbachii), both of which can be found in Dunedin.
Despite what you may think, eels don't spend all their time lurking in the shadows of your favourite swimming hole. In fact, they undertake a remarkable migratory journey spanning hundreds of kilometres over the course of their lifetime.
Tuna are born in the ocean, small larvae that drift with the currents from their spawning ground to land masses. They enter fresh water ways from July to November, making their way upstream. Young eels will stop at nothing to reach their destination, wriggling up waterfalls and dams, sometimes up to 20 metres tall!
Upon arrival, tuna may reside in rivers and lakes for many years (up to 80 in the longfin), growing and gathering energy reserves. Just before it's time for them to make their way back to the ocean, they go through a process of maturation called "silvering", through which they develop physical and behavioural traits necessary for their upcoming migration.
Other migratory species in New Zealand include the introduced chinook salmon, oncoryhnchus tshawytscha (which migrate in the opposite pattern to eels – birth in freshwater and growth at sea), and certain native galaxiid species.
All of these migratory fish go to great lengths to complete their life-cycles. They are vulnerable to disruption via human activities and hence often able to be assisted by small acts of human ingenuity.