杏吧原创

ANGLING folklore that claims fish learn how to avoid capture seems to be
true. A study of trout fishing published last week in New Zealand demonstrates
for the first time that fish constantly exposed to anglers become 鈥渟treetwise鈥�,
staying out of sight and avoiding the bait. Likewise, fish caught once remember
to avoid falling for the same ruse again for at least a month.

John Hayes and Roger Young of the Cawthron Institute in Nelson investigated
the phenomenon after veteran anglers complained that fish were becoming harder
to catch. 鈥淭hey said the fish were getting a bit too smart,鈥� says Hayes.

The researchers set out to catch brown trout that were old hands in the
heavily fished Owen River near Murchison and naive trout in a remote river of
the Kahurangi National Park, which is usually inaccessible to anglers. They
asked two experienced anglers to visit each river on four fishing trips over a
single season. On each three-day trip, observers recorded the number of fish
caught and marked them with a coloured tag to identify them the next time.

Despite the fished stretches of the two rivers having the same density of
trout, the savvy fish from the Owen were far trickier to land. Only 58 were
caught in the Owen, compared with 157 in the remote river.

Trout in the remote region, which had never encountered anglers before,
showed a distinct pattern of learning. They went to ground after being caught,
failing to appear again until subsequent trips. On the first day in the remote
site, each angler would typically catch 10 fish. But the haul vanished almost to
nothing on the third day.

鈥淔ish in the remote river were very sensitive to anglers,鈥� says Hayes. 鈥淭hey
would hide and would not come back. And once fish had been caught, they were
more difficult to catch next time.鈥� The pattern was mixed on the Owen, depending
less on the anglers and more on higher water temperatures, which encourage the
fish to feed.

Fish & Game New Zealand, the government agency that commissioned the
research, operates a 鈥渃atch and return鈥� policy to preserve stocks. But it may
now change its management strategy as it fears trout fishing holidays could
become less popular if the savvy trout are too difficult to catch. 鈥淭he agency
might have to consider `resting鈥� rivers between fishing parties,鈥� says Hayes.