If you are a little fish, the biggest skill you need is to avoid bigger fish that might eat you. But if you were born and raised in a hatchery, you won't have had much of a chance to learn to avoid the big guys. When you get dumped out of the back of truck from the hatchery, your first experience of a big fish might be your last.
That's the fate of an awful lot of hatchery fish that we restock in our oceans and rivers. A few minutes in the wild blue yonder and gulp! Gone.
The Murray-Darling Basin Authority and the Queensland Department of Primary Industries and Fisheries are trying to do something about the predation of restocked native fish. It turns out fish can learn. They can learn from their own experiences and they can learn from the experiences of fish around them. It's not that unusual really - all animals need to react and adjust to their environment, but generally we haven't given fish much credit for their brainpower.
Fish school for schools of fish isn't new, but it isn't that common, either. The ABC's Catalyst program did a great segment on Dr. Culum Brown's efforts at Macquarie University which is really interesting. Now the MDBA/QDPIF is seeing if teaching Murray cod life skills will enhance their survival. Early results are looking good according to Dr. Michael Hutchison who talked about the ongoing experiments at a recent forum on the Northern Basin.
Apparently, exposing fingerling fish to predators back at the hatchery can significantly improve their ability to avoid those predators in the wild, once released. The predator is behind mesh screen that gives the fingerlings an opportunity to escape easily. They learn quicker if they see others avoid predators.
So after fingerling fish finishing school, these guys are released into the wild and survicve better that their untrained counterparts. But wait ther's more! Apparently little Murray Cod brains aren't big enough to cope with life lessons AND the transport to the river. So the lesson only sticks if the little guys have time to settle down after their ride to the river. The researchers are putting them in big "socks" in the river to let them acclimatise for an hour or so, and then they remember their life skills lessons.
It sounds quirky but work like this has practical outcomes that can be quickly applied.
Community groups that conduct carp fish-out days often use the money raised to restock the area with native fish. I've written before that the removal of carp from such days is generally very low (0.5 - 2.0% of the carp in the area). But introduction of native predators like Murray Cod might help "tip the balance" in favour of native fish. Obviously imporoving the survival of any restocked fish significantly improves the investment (as long as the training can be done for less than the value of fish saved).
Invasive Animals CRC PhD student at the University of Queensland, Katie Doyle, is trying to understand the predator-prey relationships in our river system. That's a hard project but well worthwhile if it helps us understand how to manage restocking and other aspects of fish management.