Almost 1.6 million people went fishing in Wisconsin in , spending over 1.6 billion dollars on equipment and other expenses, and providing almost $200 million in both federal and state taxes. Fishery managers must balance the desire of anglers, who provide such large economic benefits, to have a successful fishing experience with the fact that high harvest rates can deplete a fish population and increase the risk of extirpation. To allow for sustainable exploitation of the fish, managers may create restrictions and regulations about the number and type of fish that may be removed, as well as stock the lake with additional fish, which anglers often request. However, because of the limited financial resources available to fishery managers, as well as the growing awareness of problems caused by stocking, managers must decide which lakes should receive stock, and the quantity of stock for individual lakes.
Across the United States, government agencies stocked about 1.75 billion fish in 2004. While this is not the highest number of individual fish that has ever been stocked, it is the largest quantity by mass since the data set began in the 1930s. The increasing mass of stocked fish is largely due to the pressure to meet the desires of anglers because of the economic benefits they bring to a given region. Anglers prefer to catch large trophy fish; therefore managers have chosen to stock larger sized fish. Stocking can be an effective way to increase the fish population in lakes that suffer from overfishing or habitat loss, and therefore have low natural recruitment. Stocking may also increase species richness if a variety of species are stocked and they are able to coexist with native species. According to the Wisconsin Department of Natural Resources, other benefits of stocking include the restoration of fish populations following fish kills or human caused declines, and increased recreational opportunities in lakes across the state.
While stocking has remained a popular management strategy, there have been increasing concerns among the scientific community about the unintended problems stocking may create. For example, if a stocked species that is introduced to a lake is a better competitor than native species, stocking may drive the native fish population to extirpation or extinction. Another concern is that increased stocking rates will attract more anglers to the fishery, and lead to an increase in angling rates. In this case, even though the fish population is increased at a higher rate through stocking, it is also decreased at a higher rate by the anglers, resulting in an overall decrease in the fish population.
Managers who want to avoid these problems may seek alternatives to stocking at high rates. One option would be limiting shoreline development, to reduce loss of coarse woody habitat. Coarse woody habitat (CWH), also known as coarse woody debris, refers to trees and large branches that have fallen into aquatic ecosystems and can be used as a nesting site for fish, for protection of young fish from predators, and for adult fish to ambush prey. Several species, such as largemouth bass and black crappies, prefer CWH as their nesting site and may have disrupted nesting behavior due to shoreline development. As shoreline development, which includes logging, creating beachfront property, or creating artificial beaches, increases, coarse woody habitat decreases, because shoreline development often requires the removal of trees and vegetation in order to provide lake access and aesthetically pleasing lawns. Thus, shoreline development decreases the flow of CWH into lakes and is likely to result in a decline in fish populations.
While removing CWH from a lake has immediate negative effects, the recovery process seems to occur on a much slower timescale. One lake that had experienced clear cutting over 100 years ago was still suffering reduced species diversity and other negative impacts at the time of the study. This long lasting effect could be due to the fact that some changes are irreversible. For example, if a fish species was extirpated because of loss of CWH, adding CWH cannot bring it back. Some aspects of the loss of CWH in aquatic ecosystems are unclear, but studies have agreed that it decreases the population of benthivorous fish. Preserving, and perhaps even enhancing, CWH may therefore be a potential management strategy, both in terms of maintaining a sustainable fishery and maintaining the genetic diversity of the ecosystem.
There is currently a gap between the recommendations of ecologists and the decisions of fishery managers, as mangers continue stocking at high rates, and shoreline development continues, despite the growing ecologic concerns raised by the scientific community. The immediate economic gains from development and stocking are difficult to refuse, even when they may present dangers to the ecosystem. For every $1 that is spent on stocking, $9 in taxes is generated, making stocking programs incredibly attractive from an economic standpoint. Anglers often target a specific fish species and if that species is not stocked, they may switch fishing sites, causing the initial site to lose money. Additionally, as the size of average fish caught increases, there is also an increase in local jobs and average income near the fishing site, which provides a strong case for stocking large fish. Therefore, eliminating stocking programs could have a detrimental effect on the region’s economy if other solutions are not created.
One method to assess management strategies before committing to a plan is through mathematical models. Models can be used to predict how changes in management strategy will affect various components of the fishery, giving managers the opportunity to compare management strategies before enacting them in the real world. Thus, models provide valuable information about fisheries that could not be otherwise obtained due to the difficulty in adequately monitoring thousands of lakes in a region. As more research is conducted, fishery models are becoming more realistic and therefore more useful in understanding lake ecosystems and choosing management strategies for fisheries.
To evaluate combinations of variables, primarily shoreline development and harvest rate, we are using a model that builds on the social and biological submodels developed by Van Poorten by adding a shoreline development component based on a CWH-focused model. Thus there are three broad components being considered: biological, management decisions, and shoreline development. We have chosen to examine several harvest rate and shoreline development scenarios through the model, to represent lakes at different levels of exploitation. Using these scenarios, we have analyzed stocking expenses, resiliency of the lake, represented by an index of fish intra-population genetic diversity an index of fish intra-population genetic diversity, and regional economic gain, which tends to be greater at higher fishing and development levels. By considering the tradeoffs between economic gain and loss, as well as environmental considerations, we have evaluated management strategies to determine optimal management and sustainability at different situations.