UNIV. OF ILLINOIS RESEARCH REVEALS NEW SECRET FOR AGRI-MARKETERS WHO LIKE TO
FISH
Apr. 15, 2009

Source: University of Illinois news release

In an experiment spanning over 20 years, researchers at the University of
Illinois have found that vulnerability to being caught by anglers is a
heritable trait in largemouth bass.

The study began in 1975 with the resident population of bass in Ridge Lake,
an experimental study lake in Fox Ridge State Park in Charleston. The
fishing was controlled. For example, anglers had to reserve times, and every
fish that was caught was put into a live well on the boat. The fish were
measured and tagged to keep track of how many times each fish had been
caught. All fish were then released.

“We kept track over four years of all of the angling that went on, and we
have a total record " there were thousands of captures,” said David
Philipp (AFS member, ’78), ecology and conservation researcher at U of I.
“Many fish were caught more than once. One fish was caught three times in
the first two days, and another was caught 16 times in one year.”

After four years, the pond was drained, and more than 1,700 fish were
collected. “Interestingly, about 200 of those fish had never been caught,
even though they had been in the lake the entire four years,” Philipp said.

Males and females from the group that had never been caught were designated
Low Vulnerability (LV) parents. To produce a line of LV offspring, these
parents were allowed to spawn with each other in university research ponds.
Similarly, males and females that had been caught four or more times in the
study were designated High Vulnerability (HV) parents that were spawned in
different ponds to produce a line of HV offspring. The two lines were then
marked and raised in common ponds until they were big enough to be fished.

“Controlled fishing experiments clearly showed that the HV offspring were
more vulnerable to angling than the LV offspring,” said Philipp.
This selection process was repeated for several generations over the course
of the 20 year experiment.

“As we had predicted, vulnerability was a heritable trait,” he said. Philipp
went on to explain that with each generation, the difference between lines
in angling vulnerability grew even larger.

“Most of the selection is occurring on the LV fish " that is, for the most
part, the process is making that line of fish less vulnerable to angling. We
actually saw only a small increase in angling vulnerability in the HV line,”
Philipp said.

Male bass are the sole caregiver for the offspring. Females lay eggs and
leave. The male guards the nest against brood predators for about three to
four days before the eggs hatch and another eight to 10 days after they
hatch, before they become free-swimming. Even after the baby bass start to
swim, the dads stay with them for another three weeks while they feed and
grow, protecting them from predators.

Philipp explained that the experiment sped up what’s actually happening in
nature. “In the wild, the more vulnerable fish are being preferentially
harvested, and as a result the bass population is being directionally
selected to become less vulnerable. We selected over three generations, but
in the wild the selection is occurring in every generation.

“We’ve known for 50 years that commercial fishing exerts selection on wild
populations,” he said. “We take the biggest fish, and that has changed life
histories and growth patterns in many populations of commercially harvested
species. Because there is no commercial fishing for bass, we were assessing
the evolutionary impacts of recreational fishing.”

Philipp explained that the perception among anglers is that
catch-and-release has no negative impact on the population. During the
spawning season, however, if bass are angled and held off of their nests for
more than a few minutes, when they are returned to the lake, it’s too late;
other fish have found the nest and are quickly eating the babies.

Philipp recommends that to preserve bass populations across North America,
management agencies need to protect the nesting males during the spawning
season. “There should be no harvesting bass during the reproductive period.
That makes sense for all wildlife populations. You don’t remove the adults
during reproduction.
“One of the big issues for concern is the explosion of tournaments. Lots of
bass tournaments are held during the springtime because there are lots of
big fish available. In tournaments you put fish into live wells, and yes,
they’re released, but they could be held for up to 8 hours first. They’re
brought back to the dock, miles from their nest. So, basically, if a fish is
caught in a tournament and brought into the boat and put into a live well,
his nest is destroyed.”

Philipp recommended that if fishing tournaments were held during the
spawning season, then regulations should require that there be immediate
catch-and-release, eliminating the use of tournament weigh-ins.

Philipp urges management agencies to go even further and suggests that a
portion of each lake could be set aside as a bass spawning sanctuary, where
all fishing would be prohibited until after bass reproduction is complete.
In the rest of the lake, mandatory catch-and-release regulations could be
put into place during that same reproductive period. In Illinois, the bass
reproduction period is from about April 1 through June 15. Philipp said that
in that way, anglers could help protect the long-term future of the resource
without completely restricting fishing.

“The potential for angling to have long-term evolutionary impacts on bass
populations is real. If we truly want to protect this valuable resource into
the future, then we need to understand that and adjust our management
strategies,” Philipp said.

Others on the University of Illinois research team include Steven Cooke,
Julie Claussen, Jeffrey Koppelman, Cory Suski, and Dale Burkett. Selection
for Vulnerability to Angling in Largemouth Bass was published in
Transactions of the American Fisheries Society 138:189-199, 2009.