Brett T. van Poorten

Evaluating Short Openings as a Management Tool to Maximize Catch‐Related Utility in Catch‐and‐Release Fisheries

AbstractCatch and release (CR) is an increasingly common strategy for recreational fisheries in which sustaining high catch rates is important. The success of this strategy is reduced if the released fish are temporarily invulnerable to capture due to behavioral changes, as recent research suggests. Here, we explore how temporary fishing closures with short openings might be used in CR fisheries to increase the catch-related utility associated with angler satisfaction from catches. We simulated generic fisheries in single-lake and multiple-lake systems and found that regular, temporary closures could increase catch-related utility—but predominately under the key assumption that angler satisfaction increases disproportionately with increasing catch rates. In the multiple-lake case, a strategy of rotating temporary closures could provide greater catch-related utility than continuously open fisheries, but this would depend upon anglers willingness to redistribute effort from closed waters to open waters. A ...

Estimation of Bioenergetics Parameters for Rainbow Trout (Oncorhynchus mykiss) Using Capture-Recapture Data with Comparison to Estimates from a Laboratory-Based Model

Bioenergetics models provide estimates of growth and consumption in fish and other animals. These estimates can then be used to infer metabolic and population-level consequences of various natural or human-induced environ- mental perturbations to fish populations. Most existing models utilize parameter values and functions derived from labora- tory experiments on similar, closely related populations or species. However, the use of parameters from other species has long been criticized and recent work suggests that certain metabolic rates can vary substantially between closely related species and geographically separated populations of the same species. We evaluate a new model framework (termed the general bioenergetics model) which estimates bioenergetics parameters from length-increment and length-at-age data taken from the same population being modelled. Estimates of growth and consumption from this general model are com- pared with the commonly used Wisconsin bioenergetics model in terms of model fit and predictions resulting from simulated climate warming. Growth estimates using the general bioenergetics model were slightly higher than that of the Wisconsin model but consumption estimates were similar. Both models made similar predictions about effect of climate warming, although there was a consistent difference between model estimates of growth. The findings of this study add weight to the notion that metabolic information through bioenergetics models can be estimated from the population, al- though further validation should be conducted.

Revisiting Beverton–Holt recruitment in the presence of variation in food availability

Understanding density-dependent changes in juvenile survival and growth rates is of great importance because these rates determine recovery rates for imperiled populations and/or sustainable harvest rates. Unfortunately, the mechanisms leading to density dependent survival and growth are among the least understood process in biology and fisheries. Previous work has shown that small fish may vary foraging times to achieve a target growth rate, resulting in the well-known Beverton–Holt recruitment function with variation in food availability affected the initial slope of the recruitment curve. We amend their derivation to show that incorporating fish growth under a variety of evolutionary strategies for balancing foraging time and predation risk still leads to recruitment approximately as expected under the Beverton–Holt recruitment model but that changing food availability affects both the initial slope and maximum recruitment level. We demonstrate that when food availability is known to vary over time, these models often result in a more parsimonious alternative than the standard Beverton–Holt function. Further, Beverton–Holt recruitment is expected when foraging times are adjusted to balance fitness gains from growth against mortality risk. Finally, linking recruitment success to food availability warns that species with high scope for density dependent survival (high compensation ratio or steepness) may be extremely sensitive to changes in available food densities. This work emphasizes the sensitivity of stock-recruitment parameters to food availability and strongly suggests a need to carefully monitor lower trophic levels to better understand and predict dramatic changes in juvenile recruitment and carrying capacity.

Concurrently Assessing Survey Mode and Sample Size in Off-Site Angler Surveys

AbstractOff-site angler surveys are commonly administered via two or more survey modes in the form of a mixed-mode survey. Mixed-mode surveys allow survey administrators to attain the benefits inherent to different survey modes, reduce total survey error, and control survey cost. However, these benefits can only be simultaneously attained after undertaking sample size planning. Sample size planning is a trade-off analysis wherein a researcher concurrently assesses survey administration cost, the accuracy and precision of estimates, the magnitude and direction of biases, and variance of the test statistic to determine an optimal sample size. We used data from an off-site angler survey administered to anglers targeting White Sturgeon Acipenser transmontanus to illustrate a systematic approach to sample size planning. Our survey design included a mixed-mode design with three survey modes (e-mail, mail, and telephone) and a two-phase sampling design that had a first contact and a follow-up contact with a subs...

A Field-based Bioenergetics Model for Estimating Time-Varying Food Consumption and Growth

Abstract Bioenergetics models are often used to describe the implications of changes in growth and consumption of specific wild populations, and yet most parameters are derived from a variety of laboratory studies on other populations or species, leading to questions regarding the validity of predictions. A novel bioenergetics approach was recently developed where many parameters are estimated from the population being modeled, but growth and consumption are assumed invariant over time, which would not hold true when manipulations to the system are known or suspected. In the present paper, a bioenergetics model with many key parameters estimated from field data are presented where temporal deviations in growth rates were directly estimated. A series of rainbow trout Oncorhynchus mykiss and northern pikeminnow Ptychocheilus oregonensis populations, which have undergone various population manipulations, were used to evaluate the model. Further, the model was fit to a series of rainbow trout size-classes sto...

Bioenergetic Approach to Describing Gulf Sturgeon (Acipenser oxyrinchus) Growth in Two Florida Rivers~!2009-02-17~!2010-02-04~!2010-06-03~!

Bioenergetics models are commonly used by scientist and managers to describe energy uptake and metabolism of fish species. Much data is needed to inform these models and often species specific data is unavailable or difficult to acquire, such as in the case with Gulf of Mexico sturgeon. This study applied a new method, developed by Walters and Essington (this issue), to estimate bioenergetics parameters using field observations for Gulf sturgeon populations in the Apalachicola and Suwannee Rivers, Florida, U.S.A. Bioenergetics derived growth curves were compared to growth curves developed using traditional direct aging methods. We obtained bioenergetic parameter estimates for both populations and the bioenergetic method was able to accurately simulate annual variability in Gulf sturgeon growth rates. Further, the bioenergetics growth estimates, which incorporate length-at-age and length-increment data estimated very different growth trajectories than traditional von Bertalanffy curves that used only length-at-age. This indicates that length-atage data alone can lead to errors in growth estimates, resulting in erroneous management advice. Using field data to inform bioenergetic models should be a useful approach for fisheries researchers and managers to describe the growth and energetic characteristics of fish populations.