D24—Lancaster Farming, Saturday, April 2,1983
UNIVERSITY PARK - When it
comes to conserving energy, wild
trout are among nature’s smartest
creatures. Wild trout know how to
save energy and only the most
efficient ones grow year by year.
For example, says Robert
Bachman, fisheries biologist at
Penn State, smart trout save their
energy by intercepting food as
close as possible to their feeding
sites. Then they drop quickly to the
stream bottom, where there is less
current, in returning upstream to
“home base.” Most food is in the
drift, meaning it drifts with the
current.
Over three seasons, April
through November, Bachman
discovered that wild trout spent
over 85 percent of their time in “sit
and wait” feeding sites. He studied
free-ranging wild brown trout from
camouflaged towers at the Spruce
Creek Fisheries Research Area in
central Pennsylvania.
World Record
Bachman’s studies set
something of a world record in
Egg production rises
HARRISBURG - February,
1983 egg production in Penn
sylvania totaled 367 million ac
cording to the Pennsylvania Crop
Reporting Service. This was up
seven percent from the 343 million
eggs produced in February 1962.
The February average of 18.1
million layers was seven percent
above a year ago. Egg production
per 100 layers was 2,032 compared
Just how smart are those trout?
observing a single group of wild
trout - over 100 of them - without
handling or marking the fish. He
was supporting in his studies at
Penn State by .the Cooperative
Fishery Research Unit, now
merged into the Cooperative Fish
and Wildlife Research Unit.
He claims the speed of a trout’s
growth, and how big it gets,
depends on the difference between
the energy gained from the food
and the energy spent in catching it.
He noticed that hatchery trout,
brought into the research site, used
up more energy than they gained -
mostly due to wasted movements.
Thus, they didn’t survive well in
the wild.
Feeding sites used by any one
trout, typically six to eight for each
fish, changed very little with time
of day, season, or even as the trout
grew, he affirmed. The area en
closing the trout’s home range
averaged less than 200 square feet.
These sites usually were
established when the trout were six
months to a year old.
with 2,034 in February 1962.
The nation’s laying flocks
produced 5.35 billion eggs during
February 1963, up fractionally
from a year earlier. The number of
layers on hand during February
1963 was 281 million, compared
with 288 million a year earlier. Egg
production per 100 layers during
February was 1,899 compared with
1,850 a year earlier.
“Home ranges of different in
dividuals overlapped,” he said,
“and we often found four or five
trout using the same feeding site
on a time-sharing basis. Such
feeding sites became the focus of
fights.”
Fight for Feed
Bachman explained that a trout
usually tries to chase away
another trout approaching its
feeding site. It appears that each
trout knows its neighbors, he
added, since fighting between
them is brief and not very costly in
energy.- But fights between
strangers or neighbors of nearly
the same age and size are often
long and burn off energy.
“Trout seem to know in
stinctively that energy costs can be
reduced by quickly driving away
competitors or by occupying less
busy feeding sites," he stated.
“Trout usually take only about
one second to intercept food
floating downstream but often take
as long as eight to ten seconds in
returning upstream," he added.
“Then once again they take up
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energy-saving sites provided by
rocks sheltering them from the
current, where they can watch for
oncoming food.”
Feeding rates were found to
decline as the fish grew older. The
larger trout gradually omitted
more and more of the smaller food
items from their diet. Bachman
said the trout apparently were able
to judge when a food item was
large enough to warrant the
energy needed to catch it. In
general, the wild trout were very
good at balancing their energy
budgets.
Growth stopped, or continued
very slowly, when trout reached a
size where the energy from food
balanced the energy spent getting
it. One such trout, named
“Yellowfin,” was seen in the same
area six consecutive summers.
“Yellowfin" grew only two inches
in a 50-month period - but was the
most dominant trout in the study
area during that time.
Bachman said only one trout in a
thousand grows to trophy size. He
thinks that certain special areas of
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a stream provide a place where a
trout can ambush small fish as
they pass by. Such areas tend to
grow big fish. However, most trout
are drift feeders for all of their
lives and never attain trophy size,
regardless of their age.
The hatchery trout brought into
the stream were much less “cost
conscious” than the wild ones.
Hatchery trout changed position
more than three times as often as
wild trout and used energy-saving
sites less often than wild trout.
Moreover, hatchery trout were
less likely to return to feeling sites
after an encounter with another
trout, wild or hatchery. As a result,
hatchery trout failed to become
part of the established “pecking
order” and did not settle into a
permanent home range.
“With all their moving around,
one might assume that the hat
chery trout were seeking food
more diligently that the wild trout.
Our results showed, however, that
hatchery trout fed only one-fourth
to one-half as often as wild ones. So
they use up more energy than they
gain,” he added.
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