WONDERING why some fish would engulf his lure, while others would resolutely ignore all offerings, US angler Michael Louison decided to put his scientific skills to the test.
A PhD candidate in sports fish research Mr Louison wanted to know the answer to the perennial question that is front of mind for all fishers, not least the growing fleet of inland Aussie anglers.
“I find the question of what makes a fish hit a lure to be really interesting,” he said.
“I’ve done a lot of fishing and wondered why in some cases I can pitch a lure near a fish and get an immediate strike, while in other cases the fish ignores it or swims off.”
Mr Louison works for the Illinois Natural History Survey, one of the US’s premier natural history institutions, with a staff of more than 200 scientists.
We wanted to know if certain behavioural or physiological traits were key in leading a fish to be more likely to attack a lure
With a team of researchers assembled, Mr Louison set up a practical study in fish behaviour. Fortuitously, the institute had bred two populations of largemouth bass since the 1970s; one was descended from fish that readily took a bait, the other came from a population that was reluctant to bite.
Largemouth bass are not present in Australia, but their aggressive, lure-striking behaviour and fondness for holing up in snags under sunken trees and other hidey-holes is similar to our favourite freshwater sports fish such as Murray cod, golden perch and Australian bass.
The researchers designed a trial to assess boldness of the fish, and their response to stress. The results are published in the respected Journal of Experimental Biology.
“We know in all sorts of animals that physiology drives many decisions and we wanted to know if certain behavioural or physiological traits were key in leading a fish to be more likely to attack a lure,” Mr Louison said.
Louison and his scientific fishing mates isolated the fish populations in a pond and went to ‘work’ in the summer, angling for bass for a couple of hours a day for one week. Fish caught were returned to water.
The results were surprising.
“We had expected that our ‘high vulnerability line’ would actually be more likely to be caught,” Mr Louison said.
It turned out the line of fish that were vulnerable to capture in the ‘70s were just as hard to catch as the population which was bred from the population which was difficult to catch.
But fish capture was not the only metric measured in the experiment. The researchers tested susceptibility to stress, by holding the fish out of water for three minutes and then recording the levels of the stress hormone cortisol in a fish’s blood.
The characteristic that appeared most strongly linked to a fish’s ability to avoid capture was its response to stress.
Mr Louison said the most stress-sensitive fish may be shyer and less prepared to risk striking at a lure, which would help them avoid being caught.
“Fish that showed a more pronounced rise in cortisol levels after an air exposure were less likely to be caught”, he said.
That means you are more likely to catch, and potentially keep, a fish that is susceptible to capture and effectively narrowing the gene pool down to those frustratingly snooty beggars that won’t take a lure for love or money.
“We can definitely expect to see selection favouring fish that are harder to catch.”
So when we plunder fish stocks from a river, we make a rod for our own backs, so to speak. And if we are removing numbers of fish from stocked dams, we’d better hope fisheries staff who restock population can supply the stress-less variety. That is, if we want to have tight lines next time we visit.
The most recent official recreational fishing survey estimated there are 3.4 million anglers in Australia. Each year, they contributing nearly $2 billion to the economy, much of it ending up in local fishing shops and regional towns.