WOODRUFF, Wis. – As soon as the lakes thaw, state fisheries crews begin surveys that are the cornerstone of the state’s system to manage waters in the ceded territory of northern Wisconsin.
“We plan to get in the lakes with fyke nets as quickly as possible after ice-out, and we’ll leave nets out through the peak of the walleye spawning period,” says Dennis Scholl, who leads a team of biologists and technicians responsible for conducting fishery assessments on a number of northern lakes.
The netting surveys are the first step in a year-long, multi-step process to assess fish populations and to monitor the sport fishery in each lake. Most surveys target walleyes because of their importance to tribal fishery and sport anglers, but information is also collected on other gamefish and non-game species.
As part of a 1983 federal Appellate Court decision affirming Chippewa off-reservation hunting, fishing, and gathering rights, the six bands of Wisconsin Chippewa set annual harvest quotas for off-reservation lakes in the Wisconsin Ceded Territory. To assure the combined tribal and recreational angler harvest does not exceed a sustainable level, the state revises recreational bag limits in lakes declared for harvest by the Chippewa bands. Those recreational angling bag limits for walleyes will soon be announced for 2007.
“Many people assume that the reduced bag limits are a response to some damage that’s occurred in the fishery, when in actuality they are only a preventive measure to assure that the total combined sport and tribal harvest for the year does not reach an unsafe level,” Scholl says. After about 18 years of experience with the current harvest management system, we know that, in general, it’s working. The surveys are a critical part of that system.”
Due to staff and funding limitations, only a small proportion of the 800+ walleye lakes can be surveyed in any one year. So, DNR biologists focus on lakes that are most heavily targeted by tribal spearers and sport anglers, and then use a conservative formula to generate tribal harvest quotas and sport bag limits for lakes lacking current surveys.
Lakes scheduled to be surveyed in 2007 in northeastern and north central Wisconsin include: Moen Chain and Hat Rapids Flowage in Oneida County; Trout, Little Arbor Vitae, and North and South Twin in Vilas County, Metonga in Forest County, Fay in Florence County, and Spider in Iron County.
Lakes scheduled to be surveyed for 2007 in northwestern Wisconsin include: Lower Eau Claire and Cranberry in Douglas County, Middle Eau Claire and Owen in Bayfield County, Lipsett and Big McKenzie in Burnett County, Magnor and Wapogasset in Polk County, and Sand in Sawyer County.
The survey process begins when crews stretch large fyke nets perpendicular to the shore where adult walleyes, muskies, and other gamefish congregate in spawning areas. The crews measure the fish they collect, determine their sex by the presence of eggs or milt, mark the fish by finclipping or tagging, and then remove a scale or dorsal fin spine sample for later analysis to determine the fish’s age, before releasing them.
A short time later, crews return to the same lakes in what are known as “recapture runs” to see how many of the same fish they catch. The crews use boats equipped to deliver an electric current in the water that stuns the fish and sends them to the surface. Crews then scoop them up with nets and place them in a tank filled with water. The crews do one entire circuit of the shore with the electrofishing boats, and again record data on fish size, age and sex before releasing them. The key information they collect includes the number and proportion of fish that were marked in the earlier fyke netting.
“The basic method for doing population estimates is to look at the ratio of marked to ummarked fish among those in a recapture sample, and that ratio is theoretically the same as the ratio of marked to unmarked fish in the population as a whole,” Scholl says.
Based on the population estimates for a lake, biologists calculate the “total allowable catch,” or TAC, which is the number of the adult population that can be safely harvested by all fishing methods combined, both sport and tribal, Scholl says. Because tribal harvest methods like spearing and netting are considered to be intensive harvest methods, biologists apply additional safety factors to the TAC to determine the “safe harvest” level for walleyes and muskies. Limits on the tribal harvest are calculated based on the safe harvest level for each lake.
If a population estimate hasn’t been done within the last two years on a lake, biologists use a mathematical model to generate a safe harvest figure for lakes, based on numerous population estimates from prior years. The model is intentionally designed to yield a more conservative estimate than would be generated after a survey, and results in a 1 in 40 risk of over harvest.
Another component of the overall study is the “creel survey,” where a creel survey technician counts and interviews anglers throughout the fishing season. Creel surveys provide information on catch and harvest rates, fishing pressure, and total angling exploitation. Exploitation is the percent of the spring adult population that ends up being harvested during that fishing season. That information will help manage the walleye populations over the long-term, and help monitor whether the regulatory system is working.
FOR MORE INFORMATION CONTACT: Dennis Scholl - (715) 358-9210 or Mike Keniry - (715) 685-2927
Article Source:
http://justnorth.com/Articles/tabid/105/articleType/AuthorView/authorID/12/justnorth.aspx