Fish are starting to wise up to anglers' tricks
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 "streetwise", 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. "They said the fish were getting a bit too smart," 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.
"Fish in the remote river were very sensitive to anglers," says Hayes. "They would hide and would not come back. And once fish had been caught, they were more difficult to catch next time." 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 "catch and return" 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. "The agency might have to consider 'resting' rivers between fishing parties," says Hayes.
Author: Andy Coghlan
Source: Fish & Game New Zealand (Special issue 11, p 44)
New Scientist issue: 26 August 2000
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