2. Biological Setting

Fisheries Terminology

Fisheries Stock Assessment

Management Overview

Inland fishes which are non-migratory are managed at the state level; federal agencies are involved in the management of migratory fishes, commercial fisheries and endangered species. Walleye are considered a non-migratory inland fisheries, and in Wisconsin during the 1980's were managed by the Wisconsin Department of Natural Resources. (This responsibility is now shared by many Tribal agencies.)

In North America fisheries are divided into "cold water" (Salmon, Greyling, Trout), "cool water" (Walleye, Muskellunge, Smallmouth Bass), and "warm water" (Largemouth Bass, Channel Catfish). The lake and river fisheries in Wisconsin are cool water fisheries while in Kansas we have a warm water fishery.

Throughout much of the 20th century it was common practice for state fisheries managers to poison entire lakes and restock them with selected species of gamefish and a limited number of prey species to support them. This happened throughout northern Wisconsin, and is one of the reasons why many lakes have only one or two species of predatory fish and a small number of prey (for example, Walleye as the predator and Yellow Perch as the prey).

There has been an increasing trend in recent years to take other values into consideration when managing inland fisheries, for example conservation of endangered species, biodiversity, maintaining the integrity of genetic stocks and ecosystem functioning. As a result there is a greater tendency to use information from ecology and community ecology to manage in a more "natural" fashion and less reliance on total control of the lake ecosystem.

There has also been an increasing recognition that population models are based on unrealistic assumptions; not all individuals are the same, "maximizing" exploitation rates may leave too little room for error, the environment changes over time so there is no stable carrying capacity, and so on. As a result fisheries managers are developing more rigorous techniques to measure population levels, they are taking into account population structure (size, age, genetic), developing more sophisticated models, and importantly, backing off from the idea of maximizing harvest. For example, in Wisconsin it is now more common to set the take level at 35% of MSY (leaving 65% of the estimated population) rather than 50% (leaving 50% of the estimated population). It is also common to set slot limits for the size of the fish caught in order to protect young fish and the large, highly fecund females. (A slot limit might specify that you can only take fish between 8-12" for example.)

In the next sections we will discuss some of the scientific background that informed fisheries management during the time period covered in "Walleye Wars" in order to understand some of the disagreements and misinformation involved in the conflict.

Walleye Biology

Walleye species account

The scientific name of Walleye is Sander vitreus (it used to be called Stizostedion vitreum and that's what you will find in field guides published up until recently. The older generic name of Sander is now used). Walleye are members of the perch family, Percidae, and their closest relatives are Sauger (which has also been renamed and is now Sander canadensis).

Walleye average around 2 lbs in northern lakes, but can get up to 10 lbs. They are fish predators with large mouths and eyes that are specialized for hunting at night or in murky water. Large females lay many more eggs than small females (a 5 lb female can lay more than 100,000 eggs on the bottom). More information

The native range of Walleye was much smaller than its current range in North America: St. Lawrence-Great Lakes, Arctic, and Mississippi River basins from Quebec to Northwest Territories, and south to Alabama and Arkansas (see map in the Fishbase Summary, originally from Page and Burr 1991).

Walleye have been introduced widely  for sport fishing. click here for map

During the glaciation of North America the area which is now Wisconsin was under the ice sheet, and the fish of the upper Mississippi River basin moved south to refugia in the lower Mississippi basin. This is one of the reasons why northern lakes have relatively few species-- fish species are still moving back up into the upper Mississippi River basin and northern lakes from their Pleistocene refugia. It is also why populations of fish have complex patterns of genetic relatedness-- genetic relatedness between different populations depends upon how each population moved into the region (which particular river it came from), what barriers are present (waterfalls, isolated lake basins) and how long they have been isolated from other populations of Walleye. This makes Walleye populations genetically diverse. It also means that it is important to maintain this diversity at the landscape level in order to make sure the species can survive in a changing environment-- which is a challenge for fish hatcheries in the region.

For a map and detailed account of the genetics see:

C.A. Stepien, D.J. Murphy, R.N. Lohner, O.J. Sepulveda-Villet and A.E. Haponski. 2009. Signatures of vicariance, postglacial dispersal and spawning philopatry: population genetics of the walleye Sander vitreus. Molecular Ecology 18, 3411–3428. click here

Population Models

In order to set fishing quotas, the state fisheries biologists estimated the number of fish in each lake and then modeled how many fish could be taken by sportfishermen without crashing the population. This was important because many of the lakes in northern Wisconsin are relatively small and isolated from other lakes and streams, making them vulnerable to overfishing and reducing the probability that they will be recolonized by fish dispersing from other populations. Lakes were sampled by fisheries biologists before the beginning of the fishing season using mark-recapture techniques. This is done by capturing fish alive, marking them with tags or by cutting a spine on their fin, releasing them, then catching another sample. They then determined how many of the fish in the "recapture" were marked and how many were unmarked-- this ratio allowed them to come up with an estimate of the whole population.

The population estimate was then compared to what they considered the maximum population size that a lake could sustain. Fisheries managers used models based on "Maximum Sustainable Yield" or MSY, to manage the Walleye fishery in northern Wisconsin. These models are based on the logistic growth equation and have several important assumptions:

  • Parameters representing reproductive output, life expectancy, and other life history traits are assumed to be the same throughout the population
  • Population models also assume a fixed carrying capacity that does not change over time (stable environment)
  • The goal of harvest models is to maximize net productivity
  • Maximum rate of population increase occurs at a population size of 1/2 K
  • Maintaining population at a size equal to 1/2 K results is fastest replacement rates
  • High replacement rates allow high harvest levels

When you look at this graph remember that it represents a rate, which means that when the curve is steep the population is growing very quickly, but when the curve tapers off the rate of growth is slower. Based on this model fisheries managers assume that every female in the population is the same and the amount of food, nest sites, etc. will always be the same (stable carrying capacity). And they assume that when the population gets large, density dependent factors kick in. Density dependence refers to those things that are more severe when the population size is large (when there is a higher density of individuals): high intraspecific competition for food, mates, and breeding sites; increasing rates of disease and parasites; and other density dependent factors that slow the rate of population growth. In other words, there will be more things that cause more individuals to die and cause fewer individuals to be born, and that will slow down the rate at which the population grows.

Maximum Sustainable Yield

Fisheries managers assume that the population will be growing the fastest before density dependent factors kick in. This theoretically occurs when the population size is at half of the carrying capacity. If you look at the curve, the steepest slope is at 1/2K, which is defined as the "maximum sustainable yield" or MSY. It is assumed that beyond the population size at 1/2K that when you remove individuals through fishing you are reducing density dependent factors and helping the remaining individuals in the population to maintain a high rate of reproduction and survival.

Both graphs modified from: http://hhh.gavilan.edu/jhubbard/

Fisheries Management in Wisconsin

During the early part of the 20th century it was still common for non-Native fishermen to engage in subsistence fishing and for many inland fisheries to be used for commercial harvest. There has been a shift in recent decades as fisheries have become depleted, from subsistence and commercial fisheries to fish farms (aquaculture facilities) for raising fish for commercial sale, and to regulate inland fisheries for recreational sportfishing. Subsistence fishing using high efficiency methods was outlawed and commercial fisheries closed. In the 1970's and 1980's much of the economy of northern Wisconsin was dependent on sportfishing-- many families owned small resorts, and many men were employed during the open season as fishing guides and outfitters. The area around the Ojibwe lands was close enough to Chicago to attract large numbers of weekend fishermen, and opening day saw the influx of mostly male recreational fishermen intent on having a rule-bound "contest" in catching their fish.

Sportfishing has become an even bigger business (just take a look at the "Disney World" experiences available at Bass Pro Shop and Cabela's!) According to the Wisconsin Department of Resources, in 2009:

  • Wisconsin annually sells about 1.4 million fishing licenses to adult anglers.
  • Anglers spent 20.8 million days fishing in Wisconsin in 2006.
  • Nearly 41 percent of Wisconsin residents 16 and over participate in fishing
  • Wisconsin is the second favorite destination spot for nonresident anglers
  • Anglers annually catch 88 million fish and keep 33 million fish of all kinds, releasing the rest to challenge anglers another day.
  • Wisconsin ranks among the top 5 states in terms of numbers of anglers, behind the more populous coastal states of Florida, California and Texas.
  • Fishing generates a $2.75 billion economic impact in Wisconsin
  • More than 30,000 Wisconsin jobs are supported by fishing
  • Fishing related activities and sales generate $200 million in state tax revenues for local and state government. Less than 1 percent is returned to DNR for traditional fisheries management.
  • 381,000 nonresident anglers fished in Wisconsin in 2006, spending a total of 3.8 million days and $280 million on retail goods.

---Wisconsin Department of Natural Resources; U.S. Fish & Wildlife Service; American Sportfishing Association 

In contrast to the recreational fishermen, traditional Ojibwe fishing techniques were "high efficiency" and used to procure fish used as food. Using spearfishing and nets an experienced fisher could take enough fish to feed not only their family but many households in their community. Sportfishing generates a large amount of revenue for the state because there is a tax on boats, motors, and gear, all of which are quite costly for the typical modern sportfishermen, and recreational fishermen often come from other areas and pay for restaurants, boat rental, guides and hotels. The Tribal fishery, in contrast, is local, and tends to be more oriented towards cost effectiveness-- low cost and often homemade gear, and no need for guides, resorts, etc.

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