In lakes with largemouth bass populations, absence of an adult male bass can spell doom for a brood of young fish, according to new research.

If an adult male bass is caught by a fisherman in an area where there are a high number of brood predators, the male's absence opens a window for predators to feast of the young, University of Illinois researchers report.

"One of the main conclusions of the study was that in a lake where there are very few brood predators, when you angle a male away from his nest and then immediately release him, the chance of a negative impact is less, but if the nest is located in a part of a lake where there is a high density of brood predators, once the male is removed, predators get into the nest very quickly," said Jeff Stein a fisheries research scientist at University of Illinois. "On average, the time it took brood predators to begin eating bass young was less than five minutes in cases where the nest was located near schools of brood predators."

The practical takeaway from the research, Stein said, is that catch-and-release fishermen should let fish go back into the water as soon as possible after hooking them, particularly if the lake where they are fishing is known to have a high density of largemouth bass predators such as bluegill, pumpkinseed, or rock bass.

The researchers studied 70 largemouth bass nests across nine lakes in southeastern Ontario and southwestern Quebec, which were closed to publish fishing during the study period.

Female largemouth bass do not spend any time defending the brood nest, the responsibility lies only with the males.

When a male bass it taken from the water, it may take the fish up to 30 minutes to return to its nest once its been released back into the water.

"They're disoriented so they go to the bottom to sit and recover for a while and get their heart rate back to stasis," Stein said. "The fish is saying, 'Okay, I lived through whatever that was. Now where is my nest?' and by the time it actually gets back to the nest it has been gone from it 30 minutes."

Stein said this window of time where the adult bass is absent might not make a big difference in large lakes with fewer predators, but in a smaller body of water with a large concentration of largemouth bass predators, that 30 minutes could spell big trouble for the nest.

"We definitely know that the success rate of largemouth bass nests when parental care is interrupted is lower," Stein said. "During catch-and-release angling, the male may become so physically taxed that it doesn't continue parental care. The big question we're still looking at is how it affects the whole population."

Stein and his collaborators published their research in the journal Environmental Biology of Fishes.