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A simple population model was developed to evaluate the role of plastic and evolutionary life-history changes on sustainable exploitation rates. Plastic changes are embodied in density-dependent compensatory adjustments to somatic growth rate and larval/juvenile survival, which can compensate for the reductions in reproductive lifetime and mean population fecundity that accompany the higher adult mortality imposed by exploitation. Evolutionary changes are embodied in the selective pressures that higher adult mortality imposes on age at maturity, length at maturity, and reproductive investment. Analytical development, based on a biphasic growth model, led to simple equations that show explicitly how sustainable exploitation rates are bounded by each of these effects. We show that density-dependent growth combined with a fixed length at maturity and fixed reproductive investment can support exploitation-driven mortality that is 80% of the level supported by evolutionary changes in maturation and reproductive investment. Sustainable fishing mortality is proportional to natural mortality (M) times the degree of density-dependent growth, as modified by both the degree of density-dependent early survival and the minimum harvestable length. We applied this model to estimate sustainable exploitation rates for North American walleye populations (Sander vitreus). Our analysis of demographic data from walleye populations spread across a broad latitudinal range indicates that density-dependent variation in growth rate can vary by a factor of 2. Implications of this growth response are generally consistent with empirical studies suggesting that optimal fishing mortality is approximately 0.75M for teleosts. This approach can be adapted to the management of other species, particularly when significant exploitation is imposed on many, widely distributed, but geographically isolated populations.

Models of two-patch predator-prey metacommunities are used to explore how the global predator population changes in response to additional mortality in one of the patches. This could describe the dynamics of a predator in an environment that includes a refuge area where that predator is protected and a spatially distinct ("risky") area where it is harvested. The predator's movement is based on its perceived fitness in the two patches, but the risk from the additional mortality is potentially undetectable; this often occurs when the mortality is from human harvesting or from a novel type of top predator. Increases in undetected mortality in the risky area can produce an abrupt collapse of either the refuge population or of the entire predator population when the mortality rate exceeds a threshold level. This is due to the attraction of the risky patch, which has abundant prey due to its high predator mortality. Extinction of the refuge predator population does not occur when the refuge patch has a higher maximum per capita predator growth rate than the exploited patch because the refuge is then more attractive when the predator is rare. The possibility of abrupt extinction of one or both patches from high densities in response to a small increase in harvest is often associated with alternative states. In such cases, large reductions in mortality may be needed to avoid extinction in a collapsing predator population, or to reestablish an extinct population. Our analysis provides a potential explanation for sudden collapses of harvested populations, and it argues for more consideration of adaptive movement in designing protected areas.

Abstract: Future changes to climate in the Great Lakes may have important consequences for fisheries. Evidence suggests that Great Lakes air and water temperatures have risen and the duration of [...]

This special issue honours Rob Peters' outstanding contributions to the field of aquatic ecology. It focuses on the size spectrum approach - in which individual organisms, rather than species, are the most basic biological unit - and highlights applications of this approach to fisheries management. The 21 papers in this issue cover three subject areas: ( i) the use of size spectra to characterize variation in community structure, ( ii) the development of size-based models of ecosystem dynamics to address fisheries questions, and ( iii) applications of size-based theory to examine the consequences of variation in predator-prey size relationships, body size - trophic level relationships, and body size - life history relationships. The empirical studies herein demonstrate the utility of size spectra as indicators of population or community structure and for detecting impacts associated with environmental change. Future research focused on refining size-based sampling methods, standardizing metrics and analytical methods, understanding model sensitivity to the underlying assumptions, and comparative studies across ecosystems will enhance our ability to reliably interpret changes in size spectrum characteristics, thus facilitating their use as indicators of ecological change. [ABSTRACT FROM AUTHOR]

The ability of coldwater species and populations to respond to the predicted temperature increases associated with climate change will largely depend on existing adaptive potential within and among populations. Southern inland populations of Lake TroutSalvelinus namaycushare broadly characterized by two ecotypes (small and large bodied) which differ in their trophic ecology, life history traits, and body size. Using common-garden experiments, we investigated population-specific differences in thermal performance (growth, temperature tolerance, and temperature preference) and whether the differences were consistent between ecotypes. We further explored the role of acclimation temperature on growth and thermal performance in two representative ecotypic populations. The evidence from this study indicated that the differences were population specific rather than ecotype specific. A strong inverse relationship between early growth rate and temperature preference suggests that the differences in early growth among Lake Trout populations are driven by adaptive variation in temperature preference. Acclimation temperature had a greater effect than source population on growth and temperature tolerance, although both significantly influenced temperature preferences. Small-bodied ecotypes were less tolerant of elevated temperatures and exhibited less within-population variation, potentially indicating their greater vulnerability to changing ecological conditions under climate change scenarios. Received September 13, 2011; accepted January 14, 2013 [ABSTRACT FROM PUBLISHER]

Copyright of Canadian Journal of Fisheries & Aquatic Sciences is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Canadian Journal of Fisheries & Aquatic Sciences is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In this study, we examine the divergence in growth and maturation between two populations of smallmouth bass (Micropterus dolomieu) introduced from a common source a century ago. To determine if the divergence in maturation is simply a plastic response to differences in growth rate, we use a new approach to estimate and then compare the probabilistic maturation reaction norms (PMRNs) for each population. The PMRNs for 5-year-old males are similar in the two populations, suggesting that the observed divergence in maturation is largely a plastic response to growth rate differences. For one population, we document the time course of maturation changes for the 60-year period from 1937 through 1990; while the mean length at maturation for 5-year-old males exhibits a steady downward trend (beginning at 31 cm and ending at 26 cm), their PMRNs vary over a much narrower range (25–27 cm) and do not exhibit a consistent temporal trend. These observations are consistent with the hypothesis that most of the observed change in maturation since introduction is a product of phenotypic plasticity, driven by environmentally based differences in growth rate. Our study provides an instructive example of how the PMRN approach can be used to isolate the role of growth rate variation in generating life history differences. [ABSTRACT FROM AUTHOR]

Throughout his career, Ray Beverton displayed an interest in the life history diversity in marine and freshwater fish. The papers collected here describe recent research directed at documenting this diversity and understanding both its consequences and the processes that generate it. There are three themes: factors that direct life history dynamics; fishing as a force that redirects life history dynamics; and roles for life history statics in conservation management. The "dynamics" papers show that fish life histories can evolve in response to both natural and harvest-induced selective pressures. Evolution in response to harvesting can be rapid, with potentially dramatic effects on population dynamics and sustainable exploitation. The "statics" articles demonstrate how maturity traits combine with shifts in habitat use to shape the sensitivity of a population to habitat loss. Life history shifts can dramatically alter the safety of harvesting policies that were prudent in the past; shifts of the predators or prey of a harvested species can be as important as shifts in the harvested species itself. Further work on the ecological circumstances that favour different degrees of plastic or genetic life history responses to human impacts are needed to prevent inadvertent induction of long-lasing evolutionary changes in fish life histories. [ABSTRACT FROM AUTHOR]

Copyright of Canadian Journal of Fisheries & Aquatic Sciences is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Current models of the offshore thermal structure in lakes suggest that the thermal regime inshore should vary seasonally, and should vary systematically from upwind to downwind littoral sites. To test these hypotheses, we measured mean temperature and short-term (<2 days) temporal variability in water temperature at 23 shallow littoral sites in four basins of Lake Opeongo, Ontario, Canada. Water temperature in the littoral zone was most variable, both spatially and temporally, in the spring. Spring water temperature differed by as much as 7–15°C among littoral sites in different basins (median difference among sites = 2–4°C). Downwind sites were generally warmer and had more constant temperature than upwind sites, but the magnitude of these differences varied among basins of different sizes and shapes. Simple calculations of growth rates and of fish hatching times suggest that the observed variability in water temperature would result in differences in the productivity of different portions of the littoral zone.Les modèles actuels qui expliquent la structure thermique des eaux au centre des lacs laissent croire que le régime thermique près des berges doit varier d'une saison à l'autre et qu'il doit se modifier de façon systématique depuis les sites littoraux au vent jusqu'aux sites sous le vent. Pour éprouver ces hypothèses, nous avons mesuré la température moyenne et la variabilité temporelle à court terme (<2 jours) de la température de l'eau à 23 sites littoraux peu profonds dans 4 bassins du lac Opeongo, Ontario, Canada. La température de l'eau du littoral est le plus variable au printemps, tant dans l'espace que dans le temps. Nous avons observé des différences de température d'un site à l'autre allant jusqu'à 7–15°C selon les bassins (l'écart médian entre les sites = 2–4°C). Les sites sous le vent sont généralement plus chauds et ont des températures plus constantes que les sites au vent, bien que l'importance de ces écarts varie dans les bassins de tailles et de formes différentes. Des calculs simples des taux de croissance des poissons et des temps d'éclosion de leurs oeufs laissent présumer que la variabilité observée dans la température peut générer des différences de productivité dans les diverses sections de la zone littorale.[Traduit par la Rédaction] [ABSTRACT FROM AUTHOR]