Study sheds light on walleye mortality

[Hamilton Reef]

Study sheds light on walleye mortality

http://www.greenbaypressgazette.com/app ... 10722/1233

03/11/07 By Jim Lee Gannett Wisconsin Newspapers jlee77@charter.net

MILLE LACS, Minn. — "Well, there's one for the eagles."

That resigned comment has emanated from more than one Wisconsin walleye angler while releasing an injured, undersized fish.

The belief that a bleeding fish will die and become food for fish-eating raptors or turtles is a common assumption.

While there is little doubt eagles and osprey dine on anglers' castoffs, there is a nagging question as to how frequently walleyes are released with fatal results.

"Hooking mortality was most associated with water temperature, bleeding, fish length, hook location and fish floating upon release," concluded a Minnesota study that examined walleye hooking results on Mille Lacs, a renowned 132,000-acre walleye lake in north-central Minnesota.

"Very few walleyes died in the spring, when the water is cold," said Keith Reeves, a fisheries research biologist with the Minnesota Department of Natural Resources and co-author of the study.

"When water temperatures topped 70 degrees, fish started dying from hooking mortality."

Minnesota is taking a close look at the situation because, similar to Wisconsin, it has treaty resource management obligations with Chippewa bands on many of its northern lakes, and because the state has implemented slot-size restrictions in key walleye waters to limit sport angler harvest and improve the walleye fishery.

Slot-size restrictions (which protect fish within certain length parameters) and minimum size regulations (such as requiring walleye to be at least 15 inches long in order to be kept) result in a considerable release of fish.

Theoretically, if fish can't be released safely, there may not be sufficient benefit to justify length restrictions.

It may be easier on the resource to allow an angler to catch three walleyes of any size and quit fishing than to catch and release 20 to 30 sub-legal fish while searching for fish of the correct size.

Preliminary findings from two Minnesota studies indicate hooking mortality is a problem, but it is not considered significant.

"Hooking mortality in the recreational, non-tournament walleye fishery at Mille Lacs was generally less than 5 percent," the study compiled by Reeves and biologist Richard Bruesewitz concluded.

"During cool-water fishing in May, hooking mortality was estimated at 0 percent. Even during the highest water temperatures in summer when most anglers are using live bait, we estimated hooking mortality to be less than 15 percent."

Deeply hooked fish were most likely to die, with smaller walleyes more susceptible.

"As fish size increases, relative hook size decreases, penetration decreases and organ damage is minimized," the study said.

Many walleye anglers prefer jigs to single hooks when presenting bait such as minnows, leeches or nightcrawlers.

There was no difference in mortality between walleyes hooked deep with a jig or single hook, but jigs were less likely to be found in a deep-hooking situation, the study found.

A similar study is being completed on Rainy Lake, a deeper 200,000-acre border lake shared by Minnesota and Canada where anglers are required to release walleyes between 17 and 28 inches.

"We wanted to see how well walleyes survived if caught in deep water, particularly in late summer," said Kevin Peterson, area fisheries supervisor for the Minnesota DNR at International Falls.

A team of volunteer anglers caught and released walleyes from an average depth of 35 feet. The fish were held in nets in the same area for five days for observation.

"We did observe some mortality," Peterson said, "but it was little more than we typically see in colder water and shallower water."

The study showed "the vast majority of walleyes that are released do survive," Peterson said.

As further proof, he noted the slot-size restriction was implemented in 1994 in an effort to resurrect a declining walleye fishery.

"Anglers on Rainy Lake are telling us the walleye fishing has never been better," Peterson said.