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Maximising growth during the months after hatching is critical for fishes to surpass predator gape limits, make ontogenetic shifts in diet and increase overwinter survival. Constraints on growth during early life stages can have population and community‐level implications, yet are rarely addressed by habitat restoration or fishery management efforts. To assess environmental controls on larval growth rates, we sampled adult and young‐of‐year (YOY) northern pike (Esox lucius) emigrating from spawning grounds in six tributaries of Lake Michigan. We found that YOY growth rates differed significantly among natal streams, in parallel with variation in hatch date and water temperatures. Within each stream, individual growth rates were positively associated with trophic position, as measured by nitrogen isotope enrichment and gut contents. Earlier hatching individuals also grew faster, but the strength of this relationship varied with warming water temperatures (i.e., 21–27°C). Ageing of adult spawners indicated no differences among streams in average growth rates later in life. Our findings suggest that restoration efforts should replicate ecological conditions found in habitats producing large numbers of fast‐growing YOY. Key habitat attributes include adequate water level throughout the spring spawning season, and stable, warm water temperature conditions. Providing these environments during early life history could enhance the robustness of northern pike populations by boosting fitness from hatching to emigration to adult habitats.

Walleye (Sander vitreus) populations are declining in Wisconsin and neighboring regions, motivating broader interest in walleye biology amidst ecological change. In fishes, growth integrates variation in ecological drivers and provides a signal of changing ecological conditions. We used a 23-year data set of length-at-age from 353 walleye populations across Wisconsin to test whether walleye growth rates changed over time and what ecological factors best predicted these changes. Using hierarchical models, we tested whether spatiotemporal variation in walleye growth was related to adult walleye density (density-dependent effects), water temperature, and largemouth bass (Micropterus salmoides) catch per unit effort (CPUE; predator or competitor effects). The average length of young walleye increased over time, and as a result, time to reach harvestable size declined significantly. In contrast, average lengths of older walleye have remained relatively constant over time. Juvenile walleye length-at-age was positively correlated with largemouth bass CPUE and surface water temperatures, but negatively correlated with adult walleye density. Our finding of widespread and long-term changes in walleye growth rates provides additional insights into how inland fisheries are responding to environmental change.

Corbicula fluminea is invasive in other parts of the world, but in China, it is native and supports important commercial fisheries. Surprisingly little is known about the ecology of native C. fluminea populations in China, including how life-history parameters, such as growth, may respond to widely variable environmental conditions, especially water-level management. A native C. fluminea population that supports a local commercial fishery in Hongze Lake (the 4th-largest freshwater lake in China and the largest impounded lake on the East Route of the South to North Water Transfer Project [ESNT]) was studied. Age, growth, and climate–growth relationships were estimated based on thin-sectioned shells. Sclerochronological techniques were used to detrend individual growth measurement series and to investigate climate factors that influenced growth over time. Six age-classes of C. fluminea were identified. Lee’s phenomenon (i.e., underestimated sizes at earlier age classes in survivors) was evident. A v...

The Safe Operating Space (SOS) of a recreational fishery is the multidimensional region defined by levels of harvest, angler effort, habitat, predation and other factors in which the fishery is sustainable into the future. SOS boundaries exhibit trade-offs such that decreases in harvest can compensate to some degree for losses of habitat, increases in predation and increasing value of fishing time to anglers. Conversely, high levels of harvest can be sustained if habitat is intact, predation is low, and value of fishing effort is moderate. The SOS approach recognizes limits in several dimensions: at overly high levels of harvest, habitat loss, predation, or value of fishing effort, the stock falls to a low equilibrium biomass. Recreational fisheries managers can influence harvest and perhaps predation, but they must cope with trends that are beyond their control such as changes in climate, loss of aquatic habitat or social factors that affect the value of fishing effort for anglers. The SOS illustrates opportunities to manage harvest or predation to maintain quality fisheries in the presence of trends in climate, social preferences or other factors that are not manageable.

Production of biomass is central to the ecology and sustainability of fish assemblages. The goal of this study was to empirically estimate and compare fish assemblage production, production-to-biomass (P/B) ratios and species composition for 25 second- to third-order streams spanning the Appalachian Mountains (from Vermont to North Carolina) that vary in their temperature regimes. Fish assemblage production estimates ranged from 0.15 to 6.79 g m−2 year−1, and P/B ratios ranged from 0.20 to 1.07. There were no significant differences in mean assemblage production across northern cold-water, southern cold-water and southern cool-water streams (p = .35). Two warm-water streams, not included in these comparisons, had the highest mean production and biomass values. Mean assemblage P/B was significantly higher in northern cold-water streams relative to southern cold-water and cool-water streams (p = .01). Species evenness in production declined with stream temperature and differed significantly across the lower latitude cold-water, cool-water and warm-water streams and the higher latitude (i.e. more northern) cold-water streams. Our fish assemblage production estimates and P/B ratios were both lower and higher compared to previously published estimates for similar stream habitats. This study provides empirical fish assemblage production estimates to inform future research on southern Appalachian streams and on the potential impacts of varying temperature regimes on cold-water, cool-water and warm-water fish production in the coming decades as climate change continues to threaten fish assemblages.

Proposals for regulations to improve panfish size structure often lack angler support, in part because of a perceived loss of panfish harvest. We propose that fillet weight and fillet yield, the percentage of the body weight available as fillets, are useful metrics for exploring regulation options and potential outcomes. We determined fillet weight and fillet yield for 321 Bluegill Lepomis macrochirus, 139 Black Crappie Pomoxis nigromaculatus, and 137 Yellow Perch Perca flavescens and developed equations to predict fillet weight from total length. Mean fillet yield was 29.5% for Bluegills, 28.6% for Black Crappies, and 33.1% for Yellow Perch. We used Bluegill size increases associated with a reduction in daily bag limits from 25 fish to 10 fish in seven Wisconsin lakes and then estimated fillet weights to compare the potential total weight of Bluegill fillets available to anglers under both a 10- and a 25-fish daily bag limit. We projected that many anglers might obtain a greater weight of Bluegil...

The habitat concept in inland fisheries has been less studied than wildlife ecology. Since 1950, the cumulative number of publications about “freshwater or inland habitat and fisheries management” has been 60%–95% less than those considering “habitat and wildlife management.” The number of publications about “marine, river, and stream habitat and fisheries management” has also generally exceeded those for “lake habitat and fisheries management.” We provide a perspective comparing inland fish and wildlife habitat management systems and highlight lessons from wildlife ecology that could benefit inland fisheries. We reason that wildlife habitat management has become widespread and accepted because humans share habitats with wildlife and positive/negative responses to habitat restorations/loss are directly observable. We recommend that inland fisheries habitat studies and restorations include opportunities for humans to directly observe the ecological benefits of such practices. To support aquatic habitat man...

Recreational fisheries are valued at $190B globally and constitute the predominant way in which people use wild fish stocks in developed countries, with inland systems contributing the main fraction of recreational fisheries. Although inland recreational fisheries are thought to be highly resilient and self-regulating, the rapid pace of environmental change is increasing the vulnerability of these fisheries to overharvest and collapse. Here we directly evaluate angler harvest relative to the biomass production of individual stocks for a major inland recreational fishery. Using an extensive 28-y dataset of the walleye ( Sander vitreus ) fisheries in northern Wisconsin, United States, we compare empirical biomass harvest (Y) and calculated production (P) and biomass (B) for 390 lake year combinations. Production overharvest occurs when harvest exceeds production in that year. Biomass and biomass turnover (P/B) declined by ∼30 and ∼20%, respectively, over time, while biomass harvest did not change, causing overharvest to increase. Our analysis revealed that ∼40% of populations were production-overharvested, a rate >10× higher than estimates based on population thresholds often used by fisheries managers. Our study highlights the need to adapt harvest to changes in production due to environmental change.

Minimum length limits (MLLs) combined with reduced bag limits are frequently used by fisheries managers to improve size-structure in Northern Pike Esox lucius populations. We evaluated the effectiveness of a relatively moderate 660-mm MLL and a two-fish-daily bag limit (hereafter, “moderate limit”) and a relatively conservative 813 mm MLL and one-fish-daily bag limit (hereafter, “conservative limit”) on size structure of Northern Pike in Wisconsin lakes. We used a before–after-control–impact design on a series of treatment and reference lakes to test the efficacy of each regulation. Across seven moderate-limit lake pairs, mean and mean maximum total length (i.e., mean of the 10 longest fish) in treatment lakes did not differ relative to reference lakes, where there was no MLL and a five-fish-daily bag limit (relatively liberal; hereafter, “liberal limit”). Across five conservative treatment lakes, there was a significant reduction in mean size relative to references, but mean maximum size increase...

To identify past successes and future opportunities for improved fisheries management in Wisconsin, we synthesized size-structure information on 19 gamefish species from 1944 to 2012, incorporating data on more than 2 million measured individuals. Since the 1940s, mean and mean maximum sizes of five “gamefish” species (Lake Sturgeon Acipenser fulvescens, Largemouth Bass Micropterus salmoides, Smallmouth Bass M. dolomieu, Northern Pike Esox lucius, and Sauger Sander canadensis) have stayed fairly stable, and one (Muskellunge E. masquinongy) initially dropped and then rebounded—most likely as a product of increased catch-and-release fishing and restrictive harvest regulations. In contrast, four “panfish” species (i.e., Bluegill Lepomis macrochirus, Green L. cyanellus, Yellow Perch Perca flavescens, and Black Crappie Pomoxis nigromaculatus), which have not received the same conservation management attention, have experienced substantial and sustained erosions in size over the same period. Regulations for man...

Secondary production is an integrative measure of the accumulation of heterotrophic biomass through time and can be a valuable tool to design, implement, and assess restoration initiatives. To highlight applications of secondary production in restoration contexts, we identify recent papers from the literature, use these to make generalizations about how the concept is applied, and examine why it may not be utilized more commonly. We identified 21 papers that empirically quantified secondary production to compare pre/post-restoration or assess restored sites relative to reference ones. Every study was aquatic, suggesting that secondary production is an underutilized tool in terrestrial restoration studies. We discuss various ways that food web perspectives inform restoration secondary production outcomes, such as through shifts in aquatic basal resource pools and alleviation of nutrient limitation, changes which ripple through food webs supporting higher trophic level production. Despite challenges inherent to calculating secondary production, the approach holds much promise—it is a composite metric simultaneously reflecting components of ecosystem structure and dynamics that restoration initiatives target.

Motivation The BioTIME database contains raw data on species identities and abundances in ecological assemblages through time. These data enable users to calculate temporal trends in biodiversity within and amongst assemblages using a broad range of metrics. BioTIME is being developed as a community-led open-source database of biodiversity time series. Our goal is to accelerate and facilitate quantitative analysis of temporal patterns of biodiversity in the Anthropocene. Main types of variables included The database contains 8,777,413 species abundance records, from assemblages consistently sampled for a minimum of 2 years, which need not necessarily be consecutive. In addition, the database contains metadata relating to sampling methodology and contextual information about each record. Spatial location and grain BioTIME is a global database of 547,161 unique sampling locations spanning the marine, freshwater and terrestrial realms. Grain size varies across datasets from 0.0000000158 km2 (158 cm2) to 100 km2 (1,000,000,000,000 cm2). Time period and grain BioTIME records span from 1874 to 2016. The minimal temporal grain across all datasets in BioTIME is a year. Major taxa and level of measurement BioTIME includes data from 44,440 species across the plant and animal kingdoms, ranging from plants, plankton and terrestrial invertebrates to small and large vertebrates. Software format .csv and .SQL., Global Ecology and Biogeography, 27 (7), ISSN:1466-822X, ISSN:1466-8238

To assess potential effects of climate change on Great Lakes fish populations, we evaluated trends in the reproductive phenology of Yellow Perch Perca flavescens (spring spawner) and Lake Trout Salvelinus namaycush (autumn spawner). For Yellow Perch in Lake Michigan, the estimated reproductive midpoint date (50% of mature females ripe or spent, 50% not yet spawned) took place 6.2 d/decade earlier in the spring near Milwaukee from 1988 to 2012 and 1.8 d/decade earlier in Green Bay from 1980 to 2012. At both locations water temperatures at the spawning sites on the midpoint date showed no trends, but mean water temperatures during the spring at the spawning site and midlake increased over the study period. This suggests that Yellow Perch spawning areas were warming sooner in the spring and that Yellow Perch were spawning earlier to maintain a consistent spawning temperature. Lake Trout phenological patterns were more complex. For Lake Trout in Lake Michigan near Milwaukee, there was a marginally sig...

Aquatic plant communities play critical roles in the form and function of stream ecosystems. In this study, we surveyed the aquatic-plant community along a 39-km reach of the New River, VA, in response to triploid Ctenopharyngodon idella (Grass Carp) stockings to control Hydrilla verticillata (Hydrilla) in Claytor Lake. We utilized drift-net sampling methods and visual observations to document the current plant community in this reach. Nine of 12 aquatic plant species identified in our survey have been documented as preferred forage for Grass Carp. These findings may indicate that migrating Grass Carp could alter the plant community in this reach. We recommend continued monitoring of this system to characterize any future effects of Grass Carp herbivory.

Understanding variability in fish production, biomass, production/biomass (P/B) ratios, and their relationship to exploitation is central to fisheries sustainability. At Escanaba Lake, Wisconsin, USA, data from a compulsory creel census (1965–2009) were combined with survey data on fish populations to test for empirical relationships between annual production and exploitation rates of walleye (Sander vitreus). Empirical estimates of walleye production were relatively high and temporally variable in Escanaba Lake. Annual production, biomass, and P/B ratios ranges were 2.4–11.3 kg·ha−1·year−1, 9.1–49.4 kg·ha−1, and 0.15–0.30 year−1, respectively. Walleye production rates were significantly and positively correlated with adult (i.e., age 3+) walleye density — the core metric used to manage walleye populations in the Ceded Territory of Wisconsin. However, adult walleye density correlated best with ages 4–6 production. Annual exploitation based on the percentage of individuals removed from the population was linearly related to annual exploitation based on the percentage of production removed. On average, 100% of annual production was harvested at ∼20% annual exploitation of individuals; thus, higher sustained exploitation rates would deplete walleye biomass in Escanaba Lake over time. A sustainable annual exploitation rate of 20% annually is lower than the 35% limit reference point currently used for walleye management in the Ceded Territory of Wisconsin. Nevertheless, our estimate is strongly concordant with two recent and independent modeling efforts addressing this same topic. We suggest empirical estimates of fish production are a vastly underutilized tool for better understanding sustainable exploitation rates in walleye populations and, likely, fisheries in general.

This study evaluated the effect of reduced aggregate panfish bag limits (from 25 to 10) on the size structure of Bluegill Lepomis macrochirus populations in seven natural lakes in Wisconsin. For assessing the overall significance of treatments, each treatment lake was paired with a control lake in which the regulation was not implemented. Across all lakes, mean total length (TL) of sampled Bluegills was significantly greater in treatment lakes than in control lakes after the regulation was implemented: on average, mean TL increased by 20.3 mm. However, efficacy of reduced bag limits varied substantially across lakes as mean TL improvements ranged from −5.1 to 63.5 mm in individual lakes. This variation could be strongly explained (R2 = 0.81) by lake Secchi depth (lakes with reduced water clarity showed larger improvements in mean TL, R = −0.62) and regulation duration (size structure improved continuously with time after the reduced daily bag limit was implemented, R = 0.75). Reduced bag limits ar...

Understanding the 'value' of nursery habitats is increasingly perceived as essential to conservation management of marine ecosystems globally. Yet, most work on this topic has assumed that population dynamics are temporally and spatially static, which clearly oversimplifies some highly complex and integral ecological processes. We used size-frequency data of fish species from mangrove and seagrass habitats collected at various locations over a >2 yr period to explore demographic structure and variability along with potential factors (such as growth, food abundance, and relative predation risk) that might encourage such variability. While demo - graphics were skewed predominantly towards juveniles, older fish (up to 13 yr) were regularly observed in some mangroves or seagrass beds, indicating relatively complex population demo- graphics. Juvenile habitats varied substantially in both prey abundance and relative predation risk — an effect that appeared to give rise to habitat-specific differences in somatic growth rates and fish densities. Fish population size structure was further related to position within the sea- scape, suggesting complex spatial dynamics in the production of fish biomass. Our results demon- strate that effectively appraising juvenile habitats will be a more convoluted process than previ- ously thought, as greater integration is needed between basic ecological processes (e.g. predation risk and food availability) and population demography. Whereas current approaches often iden- tify and manage single, complete nursery habitats based on those that contribute most individuals to adult populations, our study shows that a more dynamic and spatially-explicit management approach is needed, as nurseries have divergent benefits for separate life stages, species, and locations.

Heterogeneity is increasingly recognized as a foundational characteristic of ecological systems. Under global change, understanding temporal community heterogeneity is necessary for predicting the stability of ecosystem functions and services. Indeed, spatial heterogeneity is commonly used in alternative stable state theory as a predictor of temporal heterogeneity and therefore an early indicator of regime shifts. To evaluate whether spatial heterogeneity in species composition is predictive of temporal heterogeneity in ecological communities, we analyzed 68 community data sets spanning freshwater and terrestrial systems where measures of species abundance were replicated over space and time. Of the 68 data sets, 55 (81%) had a weak to strongly positive relationship between spatial and temporal heterogeneity, while in the remaining communities the relationship was weak to strongly negative (19%). Based on a mixed model analysis, we found a significant but weak overall positive relationship between spatial and temporal heterogeneity across all data sets combined, and within aquatic and terrestrial data sets separately. In addition, lifespan and successional stage were negatively and positively related to temporal heterogeneity, respectively. We conclude that spatial heterogeneity may be a predictor of temporal heterogeneity in ecological communities, and that this relationship may be a general property of many terrestrial and aquatic communities.

A frequent assumption in invasion ecology is that invasive species have enhanced growth rates in their invasive ranges. However, invasions frequently occur in sub-tropical and tropical environments where growth could be higher simply due to climatic conditions rather than novel habitat. In this study, a meta-analysis of growth rates (length-at-age data) was completed for six invasive freshwater fi sh species: common carp Cyprinus carpio , largemouth bass Micropterus salmoides , brown trout Salmo trutta , brown bullhead Ictalurus nebulosus , fl athead catfi sh Pylodictis olivaris and northern snakehead Channa argus . Signifi cant eff ects of climate on growth were observed for all species except common carp, and following normalization of growth for climate eff ects, a range of growth responses between native and invasive populations were revealed. Two species (brown trout, fl athead catfi sh) showed signifi cantly increased growth rates in invasive compared to native ranges, but two species (common carp, largemouth bass) showed signifi cantly faster growth in native ranges, and two other species (northern snakehead, brown bullhead) showed no diff erence in growth rates. No species showed both signifi cantly enhanced growth rates and initial sizes in invasive compared to native ranges. Using the comparative method, countergradient growth variations were apparent for all species within their native ranges and for all but one species in invasive ranges. Invasive populations of freshwater fi sh do not always grow faster when invasive and future studies need to consider growth covariates (e.g. climate and countergradient growth) prior to comparing life-history diff erences between invasive and native populations.

Climate–growth relationships of fish are of increasing research interest. However, few studies have attempted to characterize the extent to which climate–growth relationships may diverge across fundamentally different types of environments. The goal of this study was to examine the effects of climate variability (i.e., temperature, precipitation, global climate indices) on the growth of Freshwater Drum Aplodinotus grunniens and determine the extent to which these relationships differ between lotic and lentic habitats. Freshwater Drum were collected from five river and five reservoir environments in Georgia, Alabama, and Mississippi. Tree-ring techniques were used to standardize annual growth for age (measured using interannual growth increments from otolith sagittae) and growth indices were correlated to annual thermal, hydrologic, and global climate indices. Freshwater Drum expressed distinct and significant climate–growth relationships by water body type. The general pattern observed was that a...

The length-frequency and age distributions, condition factor (K), gonadosomatic index (GSI) and gastrosomatic index (GaSI) of yellow catfish (Peltobagrus fluvidraco) were studied at three sites along the 500-km longitudinal profile of Three Gorges Reservoir. Across all three sites (dam, mid-reservoir and upper reservoir), GSI increased from April through June, with peak values observed in May and June. Mean K and GSI for fish captured near the dam were significantly higher compared to mid-reservoir or upper-reservoir areas. The GaSI index showed no significant variations across sites. However, the length-frequency histogram of yellow catfish in the more riverine upper reservoir was log-normal and skewed towards larger (total length) fish, a pattern that was significantly different from mid-reservoir or near-dam habitats, where fish length data were normally distributed but at a smaller length mode. Age estimations using otolith sagittae revealed that the spawning population was dominated by fish from only two age-classes (1 and 2). This study provides novel insight into population characteristics of fish along the substantial spatial scale of Three Gorges Reservoir. Given the irregular population size-and age-structure and the fact that the species is currently commercially exploited, this population is believed to be susceptible to overfishing. Restricted harvesting during peak reproductive months is recommended and suggested that additional research is needed on recruitment and harvest dynamics of this species throughout Three Gorges Reservoir. Additional research is also required to determine whether the spike in K and GSI at lentic sites is a transient product of recent impoundment or an indicator of optimal hydrologic habitat for the species.

Ontogenetic niche shifts are taxonomically and ecologically widespread across the globe. Consequently, identifying the ecological mechanics that promote these shifts at diverse scales is central to an improved understanding of ecosystems generally. We evaluated multiple potential drivers of ontogenetic niche shifts (predation, growth, maturation, diet shifts, and food availability) for three fish species between connected coral reef and nearshore habitats. In all cases, neither diet compositional change nor sexual maturity functioned as apparent triggers for emigration from juvenile to adult habitats. Rather, the fitness advantages conferred on reef inhabitants (that is, enhanced growth rates) were primarily related to high prey availability on reefs. However, there exists a clear trade-off to this benefit as survival rates for small fishes were significantly reduced on reefs, thereby revealing the potential value of (and rationale behind high juvenile abundances in) nearshore habitat as predation refugia. We ultimately conclude that predation risk functions as the primary early life stage inhibitor of ontogenetic niche shifts towards more profitable adult habitats in these systems. Furthermore, this study provides a case study for how complex, meta-dynamic populations and ecosystems might be better understood through the elucidation of simple ecological trade-offs.

For circumpolar species, little is known on how somatic growth rates can vary at large, transcontinental spatial scales. In this study, a meta-analysis of growth rates was conducted for northern pike (Esox lucius) across North America and Eurasia. Growth rates of northern pike did not differ between North American and 'coastal Eurasian' pike (e.g., UK, Ireland, Sweden), while growth rates for both of these groups were significantly higher compared to 'inland Eurasian' pike (mainly in Russia). There was no difference in growth between lentic and lotic habitats on either continent. In North America, pike growth was positively correlated with temperature, but in Eurasia, pike growth correlated poorly with most climatic variables. Similarly, maximum longevity in pike populations was significantly predicted by latitude in North America, but not in Eurasia. After standardising annual pike growth by the thermal opportunity for growth, a highly significant countergradient growth relationship was found for North American pike, while a significant, but considerably less predictive countergradient growth relationship was found for Eurasian pike. This study provides novel insights into the ecology of a circumpolar species and how populations function at extraordinarily large spatial scales. First, pike appear to be cosmopolitan across hydrologic habitats having fast or slow growth in either lentic or lotic environments. Secondly, continental- scale differences in pike growth rates are suggestive of major genetic and life-history differences. Finally, variable climate-growth relationships and countergradient growth patterns indicate that global climate change is likely to affect circumpolar fishes like pike in complex, nonlinear ways.

Ecological trade-offs by organisms to minimize mortality and maximize growth is a foundational theme in ecology. Yet, these trade-offs are rarely examined within spatially complex, temporally variable ecosystems, such as floodplain rivers. Here, we evaluate ecological trade-offs across space and time for the bluegill (Lepomis macrochirus) in two unregulated river ecosystems in southeastern USA. Life-history differences among spatially segregated main channel and floodplain lake populations were used to assess effects of habitat type on bluegill fitness. Growth, condition, and gonadal somatic index were all significantly enhanced in floodplain lakes relative to the main channel. Furthermore, stomach fullness was significantly higher, and predator densities significantly lower in floodplain lakes thereby providing an ecological explanation for the life-history plasticity observed across the riverscape. However, historical observations suggested that although floodplain lakes are highly productive for bluegills, they are also prone to complete desiccation by drought approximately every 5 years, revealing the ultimate value of channel habitat, which does not dry, as desiccation refugia. Bluegills are faced with a balancing act associated with variation in foraging opportunities, and risks to predation and desiccation, that change in both the temporal and the spatial dimensions of floodplain rivers. The differential responses to these opportunities and risks help to explain why both habitats remain actively populated by bluegills, as well as many other organisms, in these and many other natural rivers.

Secondary production is a composite measure of an animal population's density, biomass, and growth over time. Thus, secondary production converts animal abundance and biomass data into a functional measure of energy flow through an ecosystem. In the present study, we used community secondary production as a composite measure of ecosystem functional response to anthropogenic disturbance, and applied this approach to examine effects of fragmentation on tidal creek ecosystems in The Bahamas. Community fish production decreased from a mean of 901 g m-2 yr-1 in unfragmented creeks to 166 g m-2 yr-1 in downstream areas of fragmented creeks to 29 g m-2 yr-1 upstream of creek blockages in fragmented creeks. when compared with several univariate measures (species richness, evenness, abundance, biomass), community composition (by ordination), and community distribution (via rank-curve analysis), community secondary production appeared to be the most consistent variable for distinguishing between three creek fragmentation categories. These data suggest that small, non-significant declines in diversity or other structural metrics can yield disproportionately large declines in ecosystem function. we suggest community secondary production can be an important component of future assessments of anthropogenic impacts, especially when alterations in diversity or community structure are small, but potentially have dramatic impacts on ecosystem function.

Ecosystems are intricately linked by the flow of organisms across their boundaries, and such connectivity can be essential to the structure and function of the linked ecosystems. For example, many coral reef fish populations are maintained by the movement of individuals from spatially segregated juvenile habitats (i.e., nurseries, such as mangroves and seagrass beds) to areas preferred by adults. It is presumed that nursery habitats provide for faster growth (higher food availability) and/or low predation risk for juveniles, but empirical data supporting this hypothesis is surprisingly lacking for coral reef fishes. Here, we investigate potential mechanisms (growth, predation risk, and reproductive investment) that give rise to the distribution patterns of a common Caribbean reef fish species, Haemulon flavolineatum (French grunt). Adults were primarily found on coral reefs, whereas juvenile fish only occurred in non-reef habitats. Contrary to our initial expectations, analysis of length-at-age revealed that growth rates were highest on coral reefs and not within nursery habitats. Survival rates in tethering trials were 0% for small juvenile fish transplanted to coral reefs and 24-47% in the nurseries. As fish grew, survival rates on coral reefs approached those in non-reef habitats (56 vs. 77-100%, respectively). As such, predation seems to be the primary factor driving across-ecosystem distributions of this fish, and thus the primary reason why mangrove and seagrass habitats function as nursery habitat. Identifying the mechanisms that lead to such distributions is critical to develop appropriate conservation initiatives, identify essential fish habitat, and predict impacts associated with environmental change.

Impoundment of rivers by dams is widespread and one of the most devastating anthropogenic impacts to freshwater environments. Linking theoretical and applied research on river impoundment requires an improved capacity for predicting how varying degrees of impoundment affects a range of species. Here, growth of 14 North American sunfish species resilient to river impoundment was compared in rivers versus impoundments. Growth response to river impoundment varied widely, but consistently among taxa: five species (shadow bass, rock bass, flier, redbreast sunfish and green sunfish) showed significantly higher growth in riverine ecosystems, four species (largemouth bass, smallmouth bass, spotted bass and longear sunfish) showed significantly higher growth in impounded ecosystems, and five species (bluegill, black crappie, white crappie, redear sunfish and warmouth) displayed no difference in growth between rivers and impoundments. Furthermore, significant linear models were developed for predicting growth of two species (largemouth bass, R2 = 0.75 and warmouth, R2 = 0.44) based on a physiographically specific index of reservoir retention time. For another species (white crappie), growth could not be predicted by the retention time index in Central Lowlands rivers (R2 = 0.001), but was strongly predicted by this factor in southeastern Coastal Plain rivers (R2 = 0.76) showing how impacts of impoundment, and prediction of its consequences, can vary across river landscape types. Further analysis of fish growth in response to river impoundment, regulation and fragmentation could greatly enhance conservation biology, restoration ecology and basic land use decisions in riverine landscapes. Copyright © 2010 John Wiley & Sons, Ltd.

Predicting mercury (Hg) concentrations of fishes at large spatial scales is a fundamental environmental challenge with the potential to improve human health. In this study, mercury concentrations were examined for five species across 161 lakes and ecosystem, and watershed parameters were investigated as explanatory variables in statistical models. For all species, Hg concentrations were significantly, positively related to wetland coverage. For three species (largemouth bass, pike, and walleye), Hg concentrations were significantly, negatively related to lake trophic state index (TSI), suggestive of growth biodilution. There were no significant relationships between ecosystem size and mercury concentrations. However, Hg concentrations were strongly, positively related to ecosystem size across species. Scores of small or remote lakes that have never been tested could be prioritized for testing using models akin to those presented in this article. Such an approach could also be useful for exploring how Hg concentrations of fishes might respond to natural or anthropogenic changes to ecosystems over time.

Large-scale habitat preferences of riverine taxa are not always revealed by examining community data. Here, we show how lipid and growth can be used to evaluate hydrologic habitat preferences of fishes resilient to river fragmentation (i.e. species that can tolerate river fragmentation by dams, but not collapse). Lipid content was examined for seven fishes in a major southeastern USA reservoir and its largest lotic tributary over the 5 years. Controlling for effects of sex, size and year of collection, largemouth bass, spotted bass and black crappie had significantly higher lipid in lentic habitat. Conversely, channel catfish and freshwater drum had significantly higher lipid in lotic habitat. There were no significant differences in lipid of bluegill and blacktail shiner between hydrologic habitat types. Fish growth produced concordant results as largemouth bass and spotted bass had significantly faster growth in lentic habitat, whereas channel catfish and freshwater drum had significantly faster growth in lotic habitat. We were also able to document a synchronous spike in lipids of these species in both habitat types during a major drought. We surmise that the spike was driven by enhanced primary production, predator-prey concentration and possibly also reduced reproduction during intense drought. Two conclusions are drawn from this study as a whole. First, long-term lipid and growth observations hold promise for evaluating ecological effects of droughts over long time spans. Second, population characteristics are excellent indicators of habitat preferences and could be used more broadly to elucidate how organisms react to river ecosystem fragmentation and restoration initiatives.

The role of climate variability in the ecology of freshwater fishes is of increasing interest. However, there are relatively few tools available for examining how freshwater fish populations respond to climate variations. Here, I apply tree-ring techniques to incremental growth patterns in largemouth bass (Micropterus salmoides Lacepede) otoliths to explore relationships between annual bass growth and various climate metrics in the southeastern USA. Among six rivers and seven reservoirs in Georgia, Alabama, and Mississippi, strong correlations between annual bass growth indices and climate were detected (73 of 96 possible correlations were significant at a < 0.05). All but two ecosystems exhibited the following pattern: annual bass growth was significantly negatively correlated with annual precipitation metrics, and significantly positively correlated with annual temperature metrics. Based on multiple regressions, climate, on average, accounted for 50% of variability (R 2 )i n bass growth, although these values ranged from 28% to 65% depending on the ecosystem. Furthermore, every population showed significant correlations with at least one of the following global climate factors: El Nino-Southern Oscillation (ENSO), North Atlantic Oscillation (NAO), and the Arctic Oscillation (AO). Largemouth bass growth in the southeast is apparently influenced by climate in major ways. Fish ecologists and managers in the region should be aware of the strong links between annual climate conditions and annual fish growth.

We present long-term growth trends for 13 freshwater mussel species from two unregulated rivers and one regulated river in the southeastern U.S. Coastal Plain. We also collected baldcypress (Taxodium distichum (L.) Rich.) tree cores adjacent to mussel collection sites in one river and directly compared tree and mussel chronologies in this river. To extend our analysis spatially, we examined published baldcypress chronologies from six other unregulated rivers throughout the region. Biochronologies were developed using standard dendrochronology techniques and we explored relationships between annual growth and a suite of streamflow variables in each river. Growth of mussels in unregulated rivers was negatively correlated with annual flood pulse count and May and June discharge, but positively correlated with annual low pulse count and annual number of hydrographic reversals. Baldcypress growth in unregulated rivers was positively correlated with May and June discharge and negatively correlated with annual low pulse count. Mussel growth in the regulated river was not correlated with any streamflow variable suggesting that biological rhythms are decoupled from hydrologic variations in this system. This study shows how interannual variability in streamflow can benefit diverse taxa in floodplain rivers over long periods and how river regulation can disrupt these relationships.

We generated a standard weight (Ws ) equation for the blacktail redhorse Moxostoma poecilurum by use of the empirical percentile (EmP) method. Length and weight data were compiled from 3,098 individuals representing 60 populations across five states in the southeastern USA. These data were subsequently used to create the Ws equation. The species' total length (TL) constraints (130–450 mm) were used to produce the final Ws equation: log10 Ws = −5.182 + 3.087 · log10TL. No length-related bias could be detected from the equation, indicating that it is a strong Ws equation. A separate data set from 42 populations and 179 individuals was used to validate the Ws equation. We recommend use of this equation for assessment of blacktail redhorse population dynamics, and we contend that creation of EmP Ws equations for other nongame fishes would be useful in management of fish communities as a whole.

We examined the usefulness of dendrochronological cross-dating methods for studying long-term, interannual growth patterns in freshwater mussels, including validation of annual shell ring formation. Using 13 species from three rivers, we measured increment widths between putative annual rings on shell thin sections and then removed age-related variation by standardizing measurement time series using cubic splines. Initially, cross dating was a valuable quality control technique allowing us to correct interpretive and measurement errors in 16% of specimens. For all species, growth varied among years but was highly synchronous among individuals. Standardized measurement time series of 94% of individuals were significantly correlated with species master chronologies, and mean interseries correlations ranged from 0.37 to 0.96. Growth was also synchronous among species, even from different rivers, and growth was negatively correlated with mean annual streamflow for most species except Quadrula pustulosa from a regulated dam tailrace. Highly synchronous growth and the strong relationship to streamflow showed that large-scale environmental signals generated non-age-related variation in mussel growth giving strong support for annual formation of the growth increments we measured. Cross dating can be a valuable technique for studying freshwater mussel growth providing quality control, validation of annual rings, and reconstruction of long-term growth histories.

We compared Hg concentrations in fishes from the regulated Black Warrior River and the unregulated Sipsey River in west Alabama whose neighboring watersheds receive equivalent atmospheric Hg deposition. Average fish fillet Hg concentrations were 3-fold higher in the unregulated river compared to the regulated river. Between river differences in Hg fish concentrations likely originate from structural (e.g., species composition) and functional (e.g., energy flow pathways) differences between the two ecosystems. We tested the generality of these findings by comparing largemouth bass Hg concentrations among unregulated rivers (n=6) and reservoirs (n=11) throughout the southern Coastal Plain geologic region. ANCOVA revealed that at a given bass length, Hg concentrations were approximately 1.75 times higher in unregulated rivers compared to regulated rivers. Aerial deposition of Hg was not correlated to largemouth bass Hg concentrations. We suggest that the link between atmospheric Hg deposition and fish Hg concentrations is significantly modulated by the structure and function of aquatic ecosystems and this accounts for much of the variation in fish Hg concentrations among systems. Unregulated floodplain-rivers in the south have some of the highest fish Hg concentrations on record and should be intensely monitored to establish human consumption risks.

Ecosystem fragmentation is one of the most damaging anthropogenic impacts to aquatic and terrestrial eco- systems worldwide. In this study, we analyzed population-level characteristics of a resilient top predator, the gray snap- per (Lutjanus griseus), across a gradient of fragmentation in Bahamian tidal creeks. Analysis of hydrologic connectivity (the inverse of fragmentation) and site-specific population parameters revealed that varying degrees of connectivity translated into predictable characteristics in fish populations. Less-fragmented systems produced fast-growing snapper with high condition factors, whereas more fragmented tidal creeks yielded slow-growing snapper with low condition factors. Underlying reasons for growth rate differences likely originated from structural and functional shifts in tidal creek ecosystems following fragmentation. Such ecosystem-level shifts were reflected by low per-individual volumes of consumed prey, as well as increased parasite infestations. Results indicated that aquatic ecosystem fragmentation may affect long-term fitness and viability of resilient species capable of persisting in fragmented habitats. Our results from estuarine tidal creeks compare well with studies on fragmentation of freshwater streams by dams and suggest that population-level consequences following ecosystem fragmentation may be generalizable between seemingly disparate aquatic environments. Resume : La fragmentation des ecosystemes est a l'echelle globale l'un des impacts anthropiques les plus nocifs pour les ecosystemes aquatiques et terrestres. Nous analysons dans notre etude les caracteristiques a l'echelle de la popula- tion chez un predateur resilient de niveau superieur, le vivaneau sandre gris (Lutjanus griseus), le long d'un gradient de fragmentation dans des cours d'eau a marees des Bahamas. L'analyse de la connectivite hydrologique (l'inverse de la fragmentation) et des parametres demographiques specifiques aux sites montre que les divers degres de connectivite se refletent dans des caracteristiques previsibles des populations de poissons. Les systemes moins fragmentes produisent des vivaneaux a croissance rapide et a coefficient de condition eleve, alors que les cours d'eau a marees plus fragmen- tes contiennent des vivaneaux a croissance lente et a coefficient de condition bas. Ces differences dans la croissance s'expliquent vraisemblablement par des changements structuraux et fonctionnels dans les ecosystemes des cours d'eau a marees apres la fragmentation. De tels changements a l'echelle de l'ecosysteme se traduisent par une consommation in- dividuelle de faibles volumes de proies et des taux accrus d'infestations parasitaires. La fragmentation des ecosystemes aquatiques peut ainsi affecter la fitness a long terme et la viabilite des especes resilientes capables de survivre dans les habitats fragmentes. Nos resultats obtenus dans les cours d'eau a marees se comparent bien a ceux d'etudes sur la frag- mentation des cours d'eau par les barrages en milieu d'eau douce; cela laisse esperer que les consequences de la frag- mentation des ecosystemes a l'echelle des populations puissent etre generalisables pour des environnements aquatiques a premiere vue disparates. (Traduit par la Redaction) Rypel and Layman 339

Three yellow sandshell mussels, Lampsilis teres (Rafinesque, 1820), were observed in Lake Tuscaloosa, Alabama, and the temporal display pattern of their mantle-flap lures was investigated in situ. All three gravid females fully displayed their mantle-flap lures after dark during each nighttime visit (N = 3) but none displayed their lures during daytime (N = 3). An encounter between a mantle-lure and a largemouth bass was observed. These observations are the first reported of in situ mantle-flap lure displays and fish host encounters for L. teres, and support previous studies of diel display patterns in other mantle-lure displaying mussels. This diel lure display may be related to the ecology of the fish hosts they seek to attract. Future daytime and, especially, nighttime field observations of bivalve mussels with mantle-flap lures may greatly improve understanding of their reproductive ecology.

This paper evaluates the feasibility of using flatbed scanners and free computer software for image analysis of fish otoliths. Scanned images of whole and cross-sectioned otoliths from bluegill Lepomis macrochirus, freshwater drum Aplodinotus grunniens, largemouth bass Micropterus salmoides, warmouth L. gulosus, and white crappie Pomoxis annularis provided adequate resolution for visualizing and counting annuli as well as for measuring interannual growth increments. I found concordant relationships between interannual growth measurements taken with a microscope-based image analysis system and those taken with the scanning technique. The use of flatbed scanners for age and growth analyses could substantially reduce costs, and such scanners may already be available for many persons interested in otolith image analysis. This could widen the access to otolith research for those who previously could not afford imaging equipment. Depending on user experience and computer and scanner speeds, 25–40 alrea...

We collected and analyzed 955 individual fish (six species) for sexual differences in PCB bioaccumulations from a southeastern, USA reservoir. Using 2-way ANCOVAs, we found significant differences in fillet PCB concentrations between sexes for channel catfish ( Ictalurus punctatus ), largemouth bass ( Micropterus salmoides ) and spotted bass ( Micropterus punctulatus ). Striped bass ( Morone saxatilus ), black crappie ( Pomoxis nigromaculatus ) and freshwater drum ( Aplodinotus grunniens ) did not display differences between sexes in PCB concentrations. We suspect that sexual differences may be due to biological differences in reproduction, relative motility and lipid deposition. For one species (striped bass), sexual differences in PCB concentrations were inconsistent with a study in the Hudson River suggesting that sexual differences in bioaccumulations can change across ecosystems. Two species which did show sexual differences, largemouth bass and channel catfish, are often chosen as representative species (e.g., “piscivore” and “benthivore”) in contaminant monitoring in many USA states indicating human consumption and risk management decisions would be improved if an equal number of male and female fish were included in composite PCBs analysis. This could reduce variability in fish PCBs data from which consumption advisories are based.

We evaluated the influence of water depth on relative predation risk for mojarra (Eucinostomus spp.) in six tidal creeks on Andros Island, Bahamas. Relative predation risk was determined using a tethering protocol combined with underwater visual census. In one experiment, we found that relative predation risk increased predictably with water depth (r2 = 0.83), and survival of tethered mojarra decreased with water depth (r2 = 0.71). We identified three depth zones containing differing levels of predation threat: refugia (0–19 cm), transition (20–69 cm), and predation (> 70 cm). Predation on mojarra rarely occurred within the refugia zone (2% eaten) and always in the predation zone (100% eaten). Additional factors not examined in this study (e.g., mangrove complexity, predator density) likely drive variability of relative predation risk within the transition zone. In a second experiment, we directly examined influence of water depth on relative predation risk at fixed locations from high tide to low tide in a single creek. Mean relative predation risk was significantly higher during higher tides at deeper water depths. Results provide experimental evidence that exploitation of shallow water refugia by motile prey can significantly reduce predation risk. We expect the distribution of motile fishes is at least partially influenced by spatially-dynamic shallow water refugia.

I examined sexual dimorphism in the long-lived Aplodinotus grunniens (freshwater drum) from five lakes and four rivers in Alabama. Using the Von Bertalanffy growth function combined with nonparametric statistics, I found males and females had similar annual growth rates from years 0–4 years of age, but then showed significantly different growth rates across subsequent ages. Female drum grew significantly faster through adulthood, and ultimately attained significantly larger sizes (L∞ = 510.8 mm, TL) compared to males (L∞ = 385.3 mm, TL). This study highlights the difference gender can have in evaluation and interpretation of population characteristics, especially for long-lived and highly fecund fishes such as freshwater drum.

We observed diel patterns in CPUE, size and age-structure for freshwater drum (Aplodinotus grunniens) from Alabama waters during May–July 2003 . Drum were significantly more susceptible to capture along shoreline habitat at night. CPUE of freshwater drum was often zero during the day and increased up to 84.5 fish * h−1 at night suggesting that many drum shift location to nearshore habitat after dark. Drum captured at night were also significantly smaller and younger that drum captured during the day. Age-0 drum were the most abundant age-class in nighttime samples whereas age-8 drum were the most abundant age-class in daytime samples. The dynamic interplay between food availability and predation on juvenile fish likely drives diel habitat shifts of freshwater drum.

The hydroperiod of ephemeral wetlands is often the most important characteristic determining amphibian breeding success, especially for species with long development times. In mesic and wet pine flatwoods of the southeastern United States, ephemeral wetlands were a common landscape feature. Reticulated flatwoods salamanders (Ambystoma bishopi), a federally endangered species, depend exclusively on ephemeral wetlands and require at least 11 weeks to successfully metamorphose into terrestrial adults. We empirically modeled hydroperiod of 17 A. bishopi breeding wetlands by combining downscaled historical climate-model data with a recent 9-year record (2006–2014) of observed water levels. Empirical models were subsequently used to reconstruct wetland hydrologic conditions from 1896–2014 using the downscaled historical climate datasets. Reconstructed hydroperiods for the 17 wetlands were highly variable through time but were frequently unfavorable for A. bishopi reproduction (e.g., only 61% of years, using a conservative estimate of development time [12 weeks], were conducive to larval development and metamorphosis). Using change-point analysis, we identified significant shifts in average hydroperiod over the last century in all 17 wetlands. Mean hydroperiods were shorter in recent years than at any other point since 1896, and thus less suitable for A. bishopi reproduction. We suggest that climate change will continue to impact the reproductive success of flatwoods salamanders and other ephemeral wetland breeders by reducing the number of years these wetlands have suitable hydroperiods. Consequently, we emphasize the importance of conservation and management for mitigating other forms of habitat degradation, especially maintenance of high quality breeding sites where reproduction can occur during appropriate environmental conditions.

We analyzed variations in the age and growth of freshwater drum Aplodinotus grunniens in Alabama rivers and reservoirs. Lotic environments produced significantly more robust freshwater drum (associated with higher growth rates) than did lentic settings. Shorter reservoir retention times (more lotic reservoirs) also produced more robust and faster-growing freshwater drum, which supported the hypothesis that hydraulic-based habitat was an important variable in determining freshwater drum condition and growth. Linear declines in relative weight and percent lipid were revealed along a hydrologic gradient in Lake Logan Martin and were strongest in older freshwater drum. Von Bertalanffy predictions supported these results but also exposed a unique caveat: If freshwater drum lived long enough (>12 years), they were ultimately able to grow to larger sizes (>L ∞) in reservoirs. Freshwater drum may be capable of moving between available lentic and lotic habitats during their lifetime to maximize invertebra...

The endangered vermilion darter (Etheostoma chermocki) is endemic to the Black Warrior River system, Mobile Basin, Alabama. Collections of specimens obtained from October 1969 to January 2000 were evaluated to determine life history characteristics. Standard length was significantly correlated with body mass, gonad mass, and clutch size. Sex ratio (2:1) was in favor of females. Length frequency distribution and enumeration of otolith annuli revealed four different age classes (0 to 3). Vermilion darters matured at the end of the first year of life. Gonadosomatic index indicated reproduction occurred from March to June. Mean clutch size was 65 oocytes per female, and mean oocyte diameter was 1.14 mm. The vermilion darter is a generalist benthic invertivore, predominantly consuming larval chironomids, tipulids, and hydropsychids. Diet breadth was greatest during warmer months and least during colder months.

Climatic variations are known to engender life-history diversification of species and populations at large spatial scales. However, the extent to which microgeographic variations in climate (e.g., those occurring within a single large ecosystem) can also drive life-history divergence is generally poorly documented. We exploited a spatial gradient in water temperatures at three sites across a large montane lake in southwest China (Lake Erhai) to examine the extent to which life histories of a short-lived fish species (icefish, Neosalanx taihuensis) diversified in response to thermal regime following introduction 25 y prior. In general, warmwater icefish variants grew faster, had larger adult body size and higher condition and fecundity, but matured at smaller sizes. Conversely, coldwater variants had smaller adult body size and lower condition, but matured at larger sizes and had larger eggs. These life-history differences strongly suggest that key ecological trade-offs exist for icefish populations exposed to different thermal regimes, and these trade-offs have driven relatively rapid diversification in the life histories of icefish within Lake Erhai. Results are surprisingly concordant with current knowledge on life-history evolution at macroecological scales, and suggest that improved conservation management might be possible by focusing on patterns operating at microgeographical, including, within-ecosystem scales. Published version

Various species of aquatic animals have complex life cycles and utilize differenthabitats during consecutive phases of their life cycles. For example, many marine fish speciesoccupy different habitat types during juvenile and adult life stages. Juveniles of some speciesrecruit to inshore nursery habitats such as mangroves and seagrass beds, whereas large adultstend to dominate coral reefs. The mechanisms underlying apparent cross-habitat distribution pat-terns by life stage remain uncertain for many species. Here, we investigated potential mecha-nisms that produce a 5-phase, and possibly even a 6-phase life cycle pattern in a common Carib-bean coral reef fish species Haemulon flavolineatum (French grunt) across multiple coastalhabitats. At each discrete life stage, individuals were faced with important and stage-specific eco-logical trade-offs that could significantly augment fitness. Pelagic larvae settled on rubble habitatsnear bay entrances where they reached an optimum between predation risk (survival) and foodabundance (growth). Individuals subsequently shifted to seagrass beds, likely as a result of in -creased food resources, followed by a shift to mangroves as predation refugia. Before the uni-directional movement between bays and coral reefs, some fishes shifted from mangroves to boul-der/notch habitats. Likely, this habitat serves as an intermediate stop before their final shift to thecoral reef, where they reach maturity and reproduce. This study reveals ecological linkages andflows among habitat types that are of direct conservation importance to these ecosystems. Further-more, the identification of mechanisms that give rise to cross-habitat distribution patterns of mar-ine fishes in general might lead to enhanced conservation management solutions to declines infisheries at larger scales.KEY WORDS: Ontogenetic habitat shifts · Life cycle · Nursery · Food abundance · Condition ·Maturation · Trade-offs

Understanding general rules governing macroecological body size variations is one of the oldest pursuits in ecology. However, this science has been dominated by studies of terrestrial vertebrates, spurring debate over the validity of such rules in other taxonomic groups. Here, relationships between maximum body size and latitude, temperature, and elevation were evaluated for 29 North American freshwater fish species. Bergmann's rule (i.e., that body size correlates positively with latitude and negatively with temperature) was observed in 38% of species, converse Bergmann's rule (that body size correlates negatively with latitude and positively with temperature) was observed in 34% of species, and 28% of species showed no macroecological body size relationships. Most notably, every species that expressed Bergmann's rule was a cool- or cold-water species while every species that expressed converse Bergmann's rule was a warm-water species, highlighting how these patterns are likely connected to species thermal niches. This study contradicts previous research suggesting Bergmann's rule does not apply to freshwater fishes, and is congruent with an emerging paradigm of variable macroecological body size patterns in poikilotherms.

The amount of energy allocated to growth versus other functions is a fundamental feature of an organism’s life history. Constraints on energy availability result in characteristic trade-offs among life-history traits and reflect strategies by which organisms adapt to their environments. Freshwater mussels are a diverse and imperiled component of aquatic ecosystems but little is known about their growth and longevity. Generalized depictions of freshwater mussels as ‘long-lived and slow-growing’ may give an unrealistically narrow view of life-history diversity which is incongruent with the taxonomic diversity of the group and can result in development of inappropriate conservation strategies. We investigated relationships among growth, longevity, and size in 57 species and 146 populations of freshwater mussels using original data and literature sources. In contrast to generalized depictions, longevity spanned nearly two orders of magnitude, ranging from 4 to 190 years, and the von Bertalanffy growth constant, K , spanned a similar range (0.02–1.01). Median longevity and K differed among phylogenetic groups but groups overlapped widely in these traits. Longevity, K , and size also varied among populations; in some cases, longevity and K differed between populations by a factor of two or more. Growth differed between sexes in some species and males typically reached larger sizes than females. In addition, a population of Quadrula asperata exhibited two distinctly different growth trajectories. Most individuals in this population had a low-to-moderate value of K (0.15) and intermediate longevity (27 years) but other individuals showed extremely slow growth (K = 0.05) and reached advanced ages (72 years). Overall, longevity was related negatively to the growth rate, K ,a ndK explained a high percentage of variation in longevity. By contrast, size and relative shell mass (g mm −1 shell length) explained little variation in longevity. These patterns remained when data were corrected for phylogenetic relationships among species. Path analysis supported the conclusion that K was the most important factor influencing longevity both directly and indirectly through its effect on shell mass. The great variability in age and growth among and within species shows that allocation to growth is highly plastic in freshwater mussels. The strong negative relationship between growth and longevity suggests this is an important trade-off describing widely divergent life-history strategies. Although life-history strategies may be constrained somewhat by phylogeny, plasticity in growth among populations indicates that growth characteristics cannot be generalized within a species and management and conservation efforts should be based on data specific to a population of interest.

We evaluated whether growth rates of six fish species correlated with PCB concentrations in a moderately-to-heavily polluted freshwater ecosystem. Using a large dataset (n = 984 individuals), and after accounting for growth effects related to fish age, habitat, sex, and lipids, growth correlated significantly, but positively with lipid-corrected PCB concentrations for 4 of 6 species. Remaining species showed no correlations between growth and PCBs. Comparisons with regional, lentic growth averages for four species confirmed growth was on par and in three of four cases higher than regional averages in the PCB-polluted ecosystem. We conclude that for these species, at the range of concentrations examined, these PCBs do not exert negative impacts on growth. Rather, factors often cited as influential to growth were also driving growth trends in this study. Future studies that evaluate whether pollution affects growth must account for major growth drivers prior to attributing growth differentials to pollution alone.