Impact of a once-through cooling system on the yellow perch stock in the western basin of lake erie

The surplus production model, a conventional fishery stock assessment model, is applied to assess the entrainment and impingement impact of the Monroe Power Plant on the yellow perch standing stock and fishery in the western basni of Lake Erie. Biological parameters of the model are estimated from commercial catch and effort data and entrainment and impingement coefficients are estimated from power plant data. The model is applied to estimate stock biomass, egg production, and larva production; the proportions entrained and impinged are then estimated. The impact of water withdrawal on the equilibrium standing stock and maximum sustainable yield from the fishery is estimated and the impact of increased water withdrawal on the equilibrium standing maximum sustainable yield are larger than the proportion of the standing stock entrained and impinged, but the impact of the Monroe Power Plant is relatively small; it decreases biomass and the maximum sustainable yield of the yellow perch stock by only a few percent. However, there are several power plants impacting the yellow perch stock of the western basin of Lake Erie and the combined impact should be examined.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/24041/1/0000290.pd

Modelling the effect of acidity on mercury uptake by walleye in acidic and circumneutral lakes

An association between acidification of lakes and high mercury concentrations in fishes has been reported. In northern Wisconsin (USA), for example, walleye (Stizostedion vitreum) in naturally acidic lakes have higher mercury concentrations than walleye in circumneutral lakes (Weiner, 1983). In this study a bioenergetic based model for mercury uptake is applied to identify potential causes of higher mercury concentrations in fishes living in acidic lakes. Application of the model to walleye populations in northern Wisconsin indicates that higher mercury concentrations in acidic lakes are most likely a result of both increased concentrations in the water and increased efficiencies of uptake from water. Higher concentrations in the water would result in higher concentrations in the food.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/27524/1/0000568.pd

Contaminant uptake by fish and the potential for transfer to humans modelled over time

A model is developed that enables coupling of contaminant uptake with the growth dynamics of fish, exploitation, and transfer and fate. Contaminant concentration in fish is a function of the properties of the contaminant, concentrations in their food and water, of their growth dynamics, and of the level of exploitation. Exploitation has a large effect on the size and age structure of exploited populations and, therefore, it also has a large effect on contaminant concentrations and potential rates of transfer to humans. It is essential that the biological component of transfer and fate models describe these aspects of contaminant uptake but at the same time the model must be relatively simple and describe uptake as a function of time rather than age.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/26119/1/0000195.pd

Relation between mortality of young walleye (Stizostedion vitreum) and recruitment with different forms of compensation

The relation between mortality of young fish and recruitment is important for assessment of the environmental effects of facilities that kill large numbers of young fish, such as electric power stations and hydropower plants. A simulation model with a bioenergetic growth component was applied to examine the relation between mortality of young and recruitment for walleye (Stizostedion vitreum) with different forms of population regulation, including: food limited growth, food limited growth with size-dependent mortality, and food limited growth with age at maturity dependent on size. With food limited growth small increases in mortality of young reduced recruitment considerably, but the population slowly approached a new equilibrium. If mortality of young increased when growth was food limited, the population approached a new equilibrium of natality and mortality because with fewer individuals there was more food per individual, and individuals were larger in size and produced more eggs; this feedback adjusted natality to equal mortality. With either mortality or age at maturity dependent on size, large increases in mortality of young resulted in only small decreases in recruitment.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/30317/1/0000719.pd

Dynamics of populations with nonoverlapping generations, continuous mortality, and discrete reproductive periods

Simple nonlinear difference equations have been used to describe the growth of populations with nonoverlapping generations; these equations assume mortality and recruitment to be discrete and instantaneous. In reality, mortality is more or less continuous and recruitment is more or less continuous over discrete intervals of time. This information was incorporated into the discrete time form of the logistic equation and the closed form solution was obtained. The population growth rate depends on recruitment, mortality, duration of the lifespan, and timing of the reproductive period. Population stability depends on the population growth rate, and therefore, stability also depends on the above factors. A stable population occurs with high mortality and a relatively short reproductive period. Under certain conditions a relatively small decrease in mortality can cause the dynamical behavior of a population to change drastically.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/31408/1/0000325.pd

Simulation of fish population responses to exploitation

A model that couples Larkin's predator-prey model, Ivlev's feeding model, Ursin's growth equation and the exponential mortality model was applied for simulation of the responses of fish populations to exploitation. Simulations were done without food-limited growth, with food-limited growth, with food limited growth and size-specific mortality, and with food-limited growth and age at maturity a function of size. Without food-limited growth there was no compensation for exploitation and the population became extinct with an increase in mortality. With food-limited growth the population compensated for fishing mortality; as abundance decreased, size increased, and production of eggs by the population increased. With either mortality or age at maturity a function of size, compensation was much higher than with food-limited growth alone. Recruitment decreased with increase in exploitation. There was an association between numbers of spawners and recruits, but both the number of spawners and the number of recruits were determined by food limited growth. If age at maturity is a function of size, there are fluctuations in population abundance when fishing mortality is low, but not when fishing mortality is high.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/29191/1/0000245.pd

Simulation of the potential for life history components to regulate walleye population size

A bioenergetic life history simulation model was applied to identify components of the walleye (Stezostedion vitrium) life history that had a potential for population regulation. The model combined a predator-prey model, a bioenergetic growth model, a relation between mortality and size, and the exponential mortality model to produce a feedback relation among abundance, food concentration, growth, and mortality. Larval mortality, juvenile mortality, and age at maturity were identified as factors with a potential for compensation. As the number of larvae increased, the number of young-of-year () increased to a maximum and then decreased with further increase in the number of larvae. This occurred because as the number of larvae increased, food concentration decreased, growth rate decreased, and mortality, which was size dependent, increased. As the number of juveniles increased, the number of recruits increased to a maximum, and then with further increase in the number of juveniles the number of recruits decreased. Age at maturity increased exponentially with increase in the number of juveniles because growth decreased. Change in mortality of both adults and had little potential for compensation.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/28063/1/0000504.pd

Simple models for exploitative and interference competition

Competition is exploitative when species compete for the same limited resource, and interference when species deplete one another's resources by interferences such as aggressive displays or fighting. If pure exploitative competition is defined as an effect on the carrying capacity, and if pure interference competition is defined as an effect on the rate of increase per individual, then the logistic equation can be modified to describe both pure exploitative and pure interference competition. Both models have identical equilibrium properties and very similar trajectories; it would be difficult to distinguish between these two types of competition using only data on abundances. However, for pure interference competition the relation between the rate of change per individual of one species and abundance of the second is linear, whereas for pure exploitative competition the relation between the rate of change per individual of one species and abundance of the second is non-linear; this is an important consideration when exploiting competitive species.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/26823/1/0000382.pd

Dynamics of fisheries that affect the population growth rate coefficient

Conventional surplus production models indicate that destruction of fish populations by overfishing is difficult, if not impossible, but catastrophic declines in abundance of exploited populations are common. Surplus production models also do not predict large continuing fluctuations in yield, but large fluctuations in yield are common. Conventional surplus production models assume that fisheries do not impact the population's capacity to increase, but changes in age structure or a decrease in age-specific fecundity resulting from fishing can decrease the coefficient of increase. A surplus production model is developed in which fishing reduces the capacity of a population to increase; the model is applied to describe the fluctuations observed in yield of lake herring ( Coregonus artedii ) from the upper Great Lakes. The fisheries of the Great Lakes were decimated by the combined effects of heavy fishing and a changing environment. For some species, yield increased to high levels and then the fisheries collapsed; for other species, yield and effort fluctuated greatly.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/41272/1/267_2005_Article_BF01866934.pd

Adjusting catch curves for gill net selection with the logistic distribution

The normal distribution often is used to describe gill net selection but the normal distribution cannot be integrated in closed form. The logistic distribution, which is a probability distribution similar in shape to the normal distribution, has a probability density function which can be integrated in closed form so that a term for gear selection can be included in the equation describing population size as a function of age. The logistic distribution was applied to the catch curve of Lake Michigan chubs (Coregonus spp.) to adjust it for gill net selection. Yield per 1000 recruits as a function of mean selection age and of fishing mortality was calculated from the adjusted catch curve; these results were compared with yields calculated by conventional methods.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/24522/1/0000801.pd