Do gill nets get every fish?

By Gord Ellis

How fish react to nets has been debated for as long as people have been putting mesh in the water. Two decades ago I spent a summer working for the Ministry of Natural Resources (MNR) in northwestern Ontario. It was low-pay field work, but it was also a dream job for an 18-year-old fish geek. The drill was simple: go to a lake, drop in a smattering of index nets, then come back and pull them the next day and take a sample of each fish caught. Those numbers were used to estimate the relative productivity of each lake.

What came out of those nets not only opened my eyes to the average size of fish in each lake (generally larger than those anglers caught), but also the number of walleye, perch, bass, suckers, trout, and whitefish in most "fished-out" lakes. I often wondered how effective nets were at getting fish. Did they capture every fish in the area, or did some of them avoid the mesh?

For the past two years, two biologists from the Minnesota Department of Natural Resources (MDNR) have studied how walleye react to gill nets. Gerry Grant and Paul Radomski learned that walleye are as fickle about nets as they are about the colour of a spinner blade.

The study was conducted with a 10-foot (3-m) gill net in a 42-acre (17-ha) management lake near Brainerd, Minnesota. The water was clear and favourable for filming. Two underwater cameras and four infrared lights were placed about three feet (1.2 m) from the net and cables were run back to shore, where VCRs taped the action. The researchers then went home and waited for morning.

In 36 nights, the cameras filmed 2,300 walleye approaching the net. Just 18 of those fish were caught. The cameras showed that many fish swam right up to the net, and researchers feel sure the fish could see it. "You could watch them sizing the net up," said Radomksi. "Most fish would approach the net slowly, stopping just inches away and backing up from it. Some would bump the mesh with their nose. A few would swim up it or along it before swimming away."

Radomski says many of the fish that did get caught would free themselves by twisting and turning or slowly backing out. Fish caught in the net, often by their teeth, tried to thrust through the mesh. A 1.25-inch (3-cm) square mesh was most effective for catching the small walleye in the lake, yet about half of the fish that contacted mesh of that size managed to escape.

Researchers also learned that large walleye are more difficult to catch than pan-sized fish. The test lake didn't have any big fish when the study began, so 240 walleye up to 26 inches (66 cm) were stocked. Only three have been caught.

Study results raise interesting questions. How far do fish range in a lake? Do gill nets only catch dumb fish? Can walleye learn to avoid nets? And how does water clarity affect how a fish sees a net? The study lake had better visibility than Minnesota's famous Mille Lacs, which was originally going to be the study site. Would the fish have more difficulty eluding the net in a dark-water lake?

Presently, Ontario uses Fall Walleye Index Nets (FWIN) to get population estimates on lakes. The results are often used to make management decisions. Recently, poor FWIN returns in some northeastern Ontario lakes were cited as reasons to put large slot sizes and lower bag limits in place.

"The nets are far less effective than we thought they would be," said Radomski. "We knew gill net numbers were crude before we started, but now we have a better idea of exactly how inefficient they are." The study continues this summer.

Squeers Lake

In 1985, after preliminary studies showed Squeers Lake likely could support a higher harvest, the MNR held the first controlled winter fishery. At the time, the lake held an estimated 8,000 adult lake trout. The nine-day winter fishery attracts about 1,000 anglers. The objective is to determine the maximum harvest that Squeers can sustain without affecting the lake trout's ability to replace itself.

Squeers' lake trout population (which eats plankton and small fish) is representative of approximately 45 per cent of all trout lakes in Ontario. "Planktivorous" lakes produce more trout than other waterbodies due to the lack of whitefish and cisco, which compete for food and space with lakers. They can sustain a higher harvest by anglers. Last fall, MNR's Quetico/ Mille Lacs Unit tagged 900 adult trout on the spawning shoals of Squeers Lake. It was the largest number recorded in the past 10 years. Fisheries technician Jon George says this was due to the adult population of trout increasing from a low of 1,500 in 1995 to 2,400 in 2000, despite an annual winter harvest of between 1,100 and 1,600 fish. This is at least four times the take that was originally seen as sustainable.

George says that part of the reason for the increase in the adult trout population is that anglers catch mostly immature fish. Adult trout tagged in Squeers last fall ranged from 14 to 25 inches (35 to 60 cm), while the average trout anglers caught was about 13 inches (33 cm). Lake trout larger than 25 pounds (10 kg) have been captured in past fisheries and some are still present, yet the majority of them are avoiding hooks.

There are also 400 pike, many of them trophy size, in the lake. Few of these fish are hooked during the fishery and even fewer are landed.

This long-term research is helping the MNR find ways to better manage lake trout in waterbodies similar to Squeers, while allowing for winter fishing and sustainable harvest.

One reason Squeers Lake has been such a success is that it relies on public volunteers to catch fish for the study. Each January, the MNR makes applications available at sporting goods stores and at its district office. People who want to fish Squeers choose from nine days and are entered into a lottery. You can apply in a group of up to four people, you don't need a licence to fish the lake, since you're considered a scientific collector, and you can keep three trout per person. At the end of the day, however, you have to let the MNR measure and sample fish you've caught, while you enjoy a free hot dog and hot chocolate. MNR staff also ask that you record where and how you caught the fish.

It's serious fisheries science, but also a source of positive interaction between the MNR and the angling public. We can always use more of that. For further information on Squeers Lake call Jon George at 807-939-3113; e-mail: jon.george@mnr.gov.on.ca