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A decline in the size of fish within a population is concerning. Large-sized fish are ecologically important and valued for social and economic reasons. Following widespread collapses from angling overharvest, the densities of Walleyes Sander vitreus in Albertas lakes increased rapidly with large-minimum-size limits. Anglers were unhappy, however, as catch rates increased (>1 Walleyes*hour-1) but fish remained small and did not exceed the minimum size limit. The two alternate explanations for the small, yet old Walleyes were either compensatory growth because of high density (stunting) or size-selective mortality (overfishing). Size-selective mortality has evolutionary consequences. Paradoxically, the management solutions for these problems are in opposition (more harvest versus less harvest), and a wrong diagnosis could exacerbate the problem. I used nested hypotheses, and implemented active adaptive management at several Alberta lakes, to diagnose the causal mechanism creating the small fish problem. For inferences on the source of the mortality, I analysed backcalculated growth rates from pelvic fins. Walleyes that had fast-growth to an early maturity, and then subsequent slow-growth, had greater survival. This hockey stick-shaped growth allows for successful reproduction while the Walleyes remain below the minimum size limit, avoiding harvest. Using changes to sport fishing regulations, I then modified angler effort and harvest at four different Alberta lakes to increase or decrease size-selective harvest and Walleye densities. I found that size-selective mortality from angling rapidly truncated the population-size structure. With concerns of evolutionary consequences because of evidence of size selective harvest, I used an age- and size-structured, single-species model, parameterized with data from Albertas Walleye fisheries, to evaluate the selectiveness of various management regulations. I found that the 50-cm minimum size limit used to recover Albertas Walleye populations did indeed select for the hockey stick life history, although this regulation allowed for sustainable populations (>5 Walleyes*hectare-1) and angler effort up to 16 angler-hours*ha-1*year-1. The optimal regulation to reduce life history selection and allow for population sustainability was a 40-50 cm harvest-tag regulation. This regulation reversed the selection for the hockey stick life history, yet produced sustainable fish densities and allowed angler effort up to 30 angler-hours*ha-1*year-1. However, increasing angler-noncompliance reduced the sustainability of this regulation. / Wildlife Ecology and Management

<p>Forest management involves numerous stochastic elements. To sustainably manage forest resources, it is crucial to acknowledge these sources as uncertainty or risk, and incorporate them in adaptive decision-making. Here, I developed several stochastic programming models in the form of passive or active adaptive management for natural mixed-species hardwood forests in Indiana. I demonstrated how to use these tools to deal with time-invariant and time-variant natural disturbances in optimal planning of harvests.</p> <p> Markov decision process (MDP) models were first constructed based upon stochastic simulations of an empirical forest growth model for the forest type of interest. Then, they were optimized to seek the optimal or near-optimal harvesting decisions while considering risk and uncertainty in natural disturbances. In particular, a classic expected-criterion infinite-horizon MDP model was first used as a passive adaptive management tool to determine the optimal action for a specific forest state when the probabilities of forest transition remained constant over time. Next, a two-stage non-stationary MDP model combined with a rolling-horizon heuristic was developed, which allowed information update and then adjustments of decisions accordingly. It was used to determine active adaptive harvesting decisions for a three-decade planning horizon during which natural disturbance probabilities may be altered by climate change.</p> <p> The empirical results can be used to make some useful quantitative management recommendations, and shed light on the impacts of decision-making on the forests and timber yield when some stochastic elements in forest management changed. In general, the increase in the likelihood of damages by natural disturbance to forests would cause more aggressive decisions if timber production was the management objective. When windthrow did not pose a threat to mixed hardwood forests, the average optimal yield of sawtimber was estimated to be 1,376 ft³/ac/acre, while the residual basal area was 88 ft²/ac. Assuming a 10 percent per decade probability of windthrow that would reduce the stand basal area considerably, the optimal sawtimber yield per decade would decline by 17%, but the residual basal area would be lowered only by 5%. Assuming that the frequency of windthrow increased in the magnitude of 5% every decade under climate change, the average sawtimber yield would be reduced by 31%, with an average residual basal area slightly around 76 ft²/ac. For validation purpose, I compared the total sawtimber yield in three decades obtained from the heuristic approach to that of a three-decade MDP model making <i>ex post</i> decisions. The heuristic approach was proved to provide a satisfactory result which was only about 18% lower than the actual optimum.</p> These findings highlight the need for landowners, both private and public, to monitor forests frequently and use flexible planning approaches in order to anticipate for climate change impacts. They also suggest that climate change may considerably lower sawtimber yield, causing a concerning decline in the timber supply in Indiana. Future improvements of the approaches used here are recommended, including addressing the changing stumpage market condition and developing a more flexible rolling-horizon heuristic approach.