A historical perspective on drift foraging models for stream salmonids

Thirty years ago, Fausch (Can J Zool 62:441–451, 1984) proposed a simple model of optimal positions for drift-feeding salmonids in streams, whereby fish maximize their net energy intake (NEI) by selecting focal points in low water velocity near faster currents that deliver abundant drifting invertebrates. The theory was based on earlier observations in artificial and natural streams describing characteristics of salmonid positions and a conceptual model by Chapman (Am Nat 100:345–357, 1966). A test of this simple drift foraging model in a laboratory stream showed that the growth rate of juvenile trout and salmon increased with NEI, and that the rank of NEI at positions held by coho salmon (Oncorhynchus kisutch) correlated nearly perfectly with their rank in the dominance hierarchy. Fausch (1984) inferred from these findings that positions that optimize NEI, within the constraints of the dominance hierarchy, are the resource for which these stream salmonids compete. In turn, the model was used to test the effects of interspecific competition by coho salmon on the foraging positions held by brook trout (Salvelinus fontinalis) and brown trout (Salmo trutta), and these results were used to infer potential effects of the introduced salmon on resident trout in Lake Michigan tributaries. Though the goals for this model were originally modest, it was tested in the field and further refined by Hughes and Dill (Can J Fish Aquat Sci 47:2039–2048, 1990) and others. During the last 20 years, the general theory has been incorporated into other models, which have been applied widely to analyze salmonid distribution and abundance in streams and rivers and used for management and restoration of habitat and flow regimes to benefit these fishes.     

Global patterns and predictors of tropical reef fish species richness

In the marine realm, the tropics host an extraordinary diversity of taxa but the drivers underlying the global distribution of marine organisms are still under scrutiny and we still lack an accurate global predictive model. Using a spatial database for 6336 tropical reef fishes, we attempted to predict species richness according to geometric, biogeographical and environmental explanatory variables. In particular, we aimed to evaluate and disentangle the predictive performances of temperature, habitat area, connectivity, mid‐domain effect and biogeographical region on reef fish species richness. We used boosted regression trees, a flexible machine‐learning technique, to build our predictive model and structural equation modeling to test for potential ‘mediation effects’ among predictors. Our model proved to be accurate, explaining 80% of the total deviance in fish richness using a cross‐validated procedure. Coral reef area and biogeographical region were the primary predictors of reef fish species richness, followed by coast length, connectivity, mid‐domain effect and sea surface temperature, with interactions between the region and other predictors. Important indirect effects of water temperature on reef fish richness, mediated by coral reef area, were also identified. The relationship between environmental predictors and species richness varied markedly among biogeographical regions. Our analysis revealed that a few easily accessible variables can accurately predict reef fish species richness. They also highlight concerns regarding ongoing environmental declines, with region‐specific responses to variation in environmental conditions predicting a variable response to anthropogenic impacts.     

Mesophotic depths as refuge areas for fishery-targeted species on coral reefs

Coral reefs are subjected to unprecedented levels of disturbance with population growth and climate change combining to reduce standing coral cover and stocks of reef fishes. Most of the damage is concentrated in shallow waters (<30 m deep) where humans can comfortably operate and where physical disturbances are most disruptive to marine organisms. Yet coral reefs can extend to depths exceeding 100 m, potentially offering refuge from the threats facing shallower reefs. We deployed baited remote underwater stereo-video systems (stereo-BRUVs) at depths of 10–90 m around the southern Mariana Islands to investigate whether fish species targeted by fishing in the shallows may be accruing benefits from being at depth. We show that biomass, abundance and species richness of fishery-targeted species increased from shallow reef areas to a depth of 60 m, whereas at greater depths, a lack of live coral habitat corresponded to lower numbers of fish. The majority of targeted species were found to have distributions that ranged from shallow depths (10 m) to depths of at least 70 m, emphasising that habitat, not depth, is the limiting factor in their vertical distribution. While the gradient of abundance and biomass versus depth was steepest for predatory species, the first species usually targeted by fishing, we also found that fishery-targeted herbivores prevailed in similar biomass and species richness to 60 m. Compared to shallow marine protected areas, there was clearly greater biomass of fishery-targeted species accrued in mesophotic depths. Particularly some species typically harvested by depth-limited fishing methods (e.g., spearfishing), such as the endangered humphead wrasse Cheilinus undulatus, were found in greater abundance on deeper reefs. We conclude that mesophotic depths provide essential fish habitat and refuge for fishery-targeted species, representing crucial zones for fishery management and research into the resilience of disturbed coral reef ecosystems.     

Feeding modes in stream salmonid population models: is drift feeding the whole story?

Drift-feeding models are essential components of broader models that link stream habitat to salmonid populations and community dynamics. But is an additional feeding mode needed for understanding and predicting salmonid population responses to streamflow and other environmental factors? We addressed this question by applying two versions of the individual-based model inSTREAM to a field experiment in which streamflow was varied in experimental units that each contained a stream pool and the adjacent upstream riffle. The two model versions differed only in the feeding options available to fish. Both versions of inSTREAM included drift feeding; one also included a search feeding mode to represent feeding in which food availability is largely independent of streamflow, such as feeding from the benthos, or feeding from the water column or the water’s surface in low water velocities. We compared the abilities of the two model versions to fit the observed distributions of growth by individual rainbow trout (Oncorhynchus mykiss) in the field experiment. The version giving fish the daily choice between drift or search feeding better fit observations than the version in which fish fed only on drift. Values for drift and search food availability from calibration to the individual mass changes of fish in experimental units with unaltered streamflow yielded realistic distributions of individual growth when applied to experimental units in which streamflow was reduced by 80 %. These results correspond with empirical studies that show search feeding can be an important alternative to drift feeding for salmonids in some settings, and indicate that relatively simple formulations of both processes in individual-based population models can be useful in predicting the effects of environmental alterations on fish populations.     

Relating fish biomass to habitat and chemistry in headwater streams of the northeastern United States

Stream pH and stream habitat have both been identified as important environmental features influencing total fish biomass in streams, but few studies have evaluated the relative influence of habitat and pH together. We measured total fish biomass, stream habitat, and stream pH in sixteen sites from three tributary systems in the northeastern United States. The habitat metrics included total pool area, a cover score, large wood frequency, and stream temperature. We created and compared nine linear models relating total fish biomass in summer to stream pH and stream habitat using Akaike’s Information Criterion (AIC) analysis. The best (most parsimonious) models included pool area and stream pH. These results and a separate comparison of three regressions (low-flow pH, pool area, and these two metrics together versus total fish biomass) suggest that both habitat and stream buffering capacity affect the total biomass of fish in northeastern US headwater streams. When stream pH is adequate (low-flow pH greater than at least 5.7), physical habitat is likely to be more important, but under lower pH conditions, habitat is likely to be less effective in accounting for the total biomass of fish in these streams. This work demonstrates the continued effects of stream acidification in the northeastern US and more generally, it illustrates the importance of considering both physical and chemical conditions of a stream when evaluating the factors influencing fish communities.     

Do trappers understand marten habitat?

Previous studies of the effects of fur trapping on marten populations have not considered habitat variation and how trappers use available habitat. We investigated the behavior of fur trappers with respect to roads, waterways, and the forest habitats on trap lines, using registered trap lines in northern Ontario as a study system. The objectives of this study were to 1) develop models for predicting trap location based on access and habitat features, 2) determine whether trappers target the same habitat preferred by American marten, and 3) investigate effects of spatial resolution on predictive models, using a geographic information system (GIS) for coarse resolution variables and direct forest mensuration for fine resolution variables. Distance to roads and water were by far the most influential factors in logistic models for predicting trap presence, accounting for 51.2–61.7% of the observed deviance. At a coarse spatial resolution, trappers selected sites that were close to vehicular access, and in older mixed wood forest stands. Similarly, at a coarse resolution, marten selected old stands, but dominated by coniferous trees. At a finer spatial resolution, trappers selected sites with high basal area of trees, pronounced proportion of black spruce, high canopy cover, and high density of coarse woody debris, consistent with previous studies on marten habitat selection at a fine resolution. Although coarse resolution models are easily applicable because of the wide availability of GIS land cover data, fine resolution models had greater predictive power when considering habitat variables. By quantifying trapper behaviors, these results suggest that the effectiveness of marten sanctuaries used in forest management depend not only on the age and species composition of forest stands left unlogged, but also on the degree to which they are accessible to trappers. © 2012 The Wildlife Society.     

Relative Importance of Coral Cover,Habitat Complexity and Diversity in Determining the Structure of Reef Fish Communities

The structure of coral reef habitat has a pronounced influence on the diversity, composition and abundance of reef-associated fishes. However, the particular features of the habitat that are most critical are not always known. Coral habitats can vary in many characteristics, notably live coral cover, topographic complexity and coral diversity, but the relative effects of these habitat characteristics are often not distinguished. Here, we investigate the strength of the relationships between these habitat features and local fish diversity, abundance and community structure in the lagoon of Lizard Island, Great Barrier Reef. In a spatial comparison using sixty-six 2m² quadrats, fish species richness, total abundance and community structure were examined in relation to a wide range of habitat variables, including topographic complexity, habitat diversity, coral diversity, coral species richness, hard coral cover, branching coral cover and the cover of corymbose corals. Fish species richness and total abundance were strongly associated with coral species richness and cover, but only weakly associated with topographic complexity. Regression tree analysis showed that coral species richness accounted for most of the variation in fish species richness (63.6%), while hard coral cover explained more variation in total fish abundance (17.4%), than any other variable. In contrast, topographic complexity accounted for little spatial variation in reef fish assemblages. In degrading coral reef environments, the potential effects of loss of coral cover and topographic complexity are often emphasized, but these findings suggest that reduced coral biodiversity may ultimately have an equal, or greater, impact on reef-associated fish communities.     

Fish habitat rehabilitation using wood in the world

To provide river managers and researchers with practical knowledge about fish rehabilitation, various studies of fish habitat rehabilitation that used wood were reviewed. The review focuses on fish responses, wood installation methods, and geomorphic features of the rehabilitation sites. Most studies were conducted in moderately sized (small and medium) streams with relatively high bed gradients and aimed to improve the habitats of salmonid species. In this stream type, structures spanning the full (log dam) and partial (log deflector) width of the river were most common, and wood structures that created pools and covers were successful in improving fish habitat. Some projects were conducted in moderately sized low-gradient streams, in which wooden devices used to create instream cover were effective for fish assemblages. There were few studies in other aquatic ecosystems. However, well-designed large wood structures, known as engineered log jams, were used in rehabilitation projects for large rivers. In slack-water or lentic systems such as side-channels, estuaries, and reservoirs, small and large wood structures that created cover were used to improve habitat for many fish species. For successful fish habitat rehabilitation projects, the hydrogeomorphic conditions of rehabilitation sites should be carefully examined to avoid physical failure of wood structures. Although artificial wood structures can be used to improve fish habitat in various aquatic ecosystems, they should be considered to be a complementary or interim habitat enhancement technique. The recovery of natural dynamic processes at the watershed scale is the ultimate target of restoration programs.     

Habitat correlates of the distribution and biomass of Seychelles' reef fishes

Synopsis Relationships between quantitative measures of habitat type and the biomass of Chaetodon, Scarus and Parupeneus species were investigated across 35 reef sites in the Inner Seychelles Group. Multiple regression was used to determine the proportion of variance in biomass between sites which could be explained by depth, exposure, vertical relief, topographic complexity, live coral cover, coral rubble cover, rock cover, sand cover, underlying carbonate substrate, underlying sand substrate, underlying rock substrate and an index of fishing intensity. A significant proportion of the variance in biomass was explained by habitat variables and the index of fishing intensity for 7 of 12 Chaetodon species (23–52% of variance explained), 3 of 6 Parupeneus species (33–40%), and 10 of 13 Scarus species (14–46%). Within genera, different groups of habitat variables explained the variance in biomass for different species and, of the variables studied, only the proportion of underlying sand substrate failed to explain a significant proportion of the variance in biomass for any species. Quantitative relationships between the biomass of Chaetodon and habitat were often in accordance with those suggested by previous studies of their ecology, life-history and distribution at other Indo-Pacific locations. However, the habitat associations of the Parupeneus and some Scarus species have not been studied at other locations and clearly warrant further investigation. It was concluded that habitat was an important determinant of the distribution of many Seychelles reef fishes, but that the habitat variables examined were rarely the most important determinant of biomass. However, the inclusion of a procedure to collect habitat data provided a useful means by which to reduce the unexplained variance associated with visual census biomass estimates and therefore improves the possibility of elucidating the effects of other factors on the biomass of Seychelles reef fishes.     

Quantifying the direct and indirect effects of flow‐related disturbance on stream fish assemblages

相似文献   

Variability in the distribution and abundance of stream salmonids, and the associated use of habitat models

The effective management of salmonid fisheries requires that the factors influencing variation in the abundance of stream populations are understood. The use of habitat models to explain the spatial component of population variance offers potential for management, but has not previously been set in the context of long term variation in population abundance because of the lack of suitable data sets. This paper examines contributions of spatial and temporal factors lo fish density variance using a 10-year data set from five tributaries of the River Conwy, North Wales. Recently developed habitat models were applied to the data to test their ability to explain nominal spatial variance. Spatial variance accounted for between 21 and 62% of the overall variance of salmonid abundance, and habitat models explained up to 95% of the spatial variance component. Synchrony in population variation amongst sites within and between tributaries is described, and some of the factors that may influence this are discussed.     

Limited transferability of stream‐fish distribution models among river catchments: reasons and implications

相似文献   

Biodiversity and fish farming intensification in French fishpond systems

Fishponds are artificial ecosystems in which biodiversity may be strongly affected by fish farming management. We studied biodiversity variation along a gradient of fish farming intensification within a 180-pond sample of a French region to establish whether biodiversity primarily depended on extensive management with the alternative hypothesis that some habitat characteristics could compensate for the effect of intensification. We compared the relationships of three biodiversity indicators (breeding birds, protected plants, macrophytes) to an index of intensification and to habitat characteristics likely to influence each indicator. In all selected indicators, species richness did not vary according to the composite intensification gradient. Protected plant richness was best explained by periodic drainage, which could thus benefit biodiversity in intensified fishponds provided that shallow littoral areas are still present. Bird richness was linked to macrophyte cover and probably to reed bed areas. Macrophyte richness and coverage were negatively influenced by low water transparency and high fish biomass which seemed likely to affect bird habitat above 350–400 kg/ha. Aquatic vegetation, which may reflect interactive effects of environmental factors and fish farming management, may then contribute to assessment of the ecological status of fishponds under the E.U. Water Framework Directive.     

Proximate composition,energetic value,and relative abundance of prey fish from the inshore eastern Bering Sea: implications for piscivorous predators

Changing ocean conditions and subsequent shifts in forage fish communities have been linked to numerical declines of some piscivorous marine birds and mammals in the North Pacific. However, limited information about fish communities is available for some regions, including nearshore waters of the eastern Bering Sea, where many piscivores reside. We determined proximate composition and energetic value of a suite of potential forage fish collected from an estuary on the Yukon-Kuskokwim Delta, Alaska, during 2002 and 2003. Across species, energy density ranged from 14.5 to 20.7 kJ g⁻¹ dry mass and varied primarily as a function of lipid content. Total energy content was strongly influenced by body length and we provide species-specific predictive models of total energy based on this relationship; some models may be improved further by incorporating year and date effects. Based on observed energetic differences, we conclude that variation in fish size, quantity, and species composition of the prey community could have important consequences for piscivorous predators.     

Shelter availability affects behaviour, size-dependent and mean growth of juvenile Atlantic salmon

1. Anthropogenic disturbances of the physical habitat and corresponding effects on fish performance are key issues in stream conservation and restoration. Reduced habitat complexity because of increased sediment loadings and canalization is of particular importance, but it is not clear to what extent fish populations are influenced directly by changes in the physical environment, or indirectly through changes in the biotic environment affecting the food availability. 2. Here, we test for the direct effect of habitat complexity on the performance (growth) of juvenile Atlantic salmon by manipulating shelter availability (interstitial spaces in the substrate) across 20 semi‐natural stream channels without altering the substrate composition, and stocking each channel with a common density of fish. A simple method for measuring salmonid shelters using flexible PVC tubes was developed and tested. Daytime sheltering behaviour and growth rates were compared across the channels differing in shelter availability. 3. Measured shelter availability was strongly negatively correlated with observed number of fish not finding shelters and mass loss rates of the fish (growth performance) increased with decreasing number of measured shelters. Number and mean depth of interstitial spaces explained up to 68% and 24% of the among‐channel variation in sheltering behaviour and growth performance, respectively. Furthermore, negative effects of shelter reduction increased with fish body size. Thus, changes in habitat structure may even influence the size selection gradients. 4. Shelter availability is an easily measured variable, possibly affecting the population demographics and long‐term evolutionary processes, and is therefore a key habitat factor to be considered in stream restoration and habitat classification.     

Diel Habitat Partitioning by Bull Charr and Cutthroat Trout During Fall and Winter in Rocky Mountain Streams

We used underwater observation to determine diel habitat partitioning between bull charr, Salvelinus confluentus, and cutthroat trout, Oncorhynchus clarki, during fall and winter (0.1–8.3°C) in two Rocky Mountain streams that differed in habitat availability. The majority (>70%) of both species emerged from concealment cover at night, though bull charr exhibited a greater tendency for nocturnal behavior than cutthroat trout. Differences in day and night counts were most pronounced at temperatures <3°C, when very few fish of either species were observed in the water column during the day, but both species were common at night. Both species used concealment cover of large woody debris and boulder substrate crevices in deep pools during the day. At night, fish emerged from cover and habitat use shifted to shallow water with low cover. Microhabitat partitioning among species and size classes occurred at night, cutthroat trout moving into shallower, faster water that was farther from cover compared to bull charr. Smaller fish of both species occupied focal positions in slower, shallower water closer to the substrate than larger fish. Large, mixed-species aggregations also were common in beaver ponds both day and night. High variation in diel and site-specific winter habitat use suggests the need for caution in developing habitat suitability criteria for salmonids based solely on daytime observations or on observations from a few sites. Our results support the need to incorporate nocturnal habitat use and partitioning in studies of salmonid ecology.     

Non‐reef habitats in a tropical seascape affect density and biomass of fishes on coral reefs

Nonreef habitats such as mangroves, seagrass, and macroalgal beds are important for foraging, spawning, and as nursery habitat for some coral reef fishes. The spatial configuration of nonreef habitats adjacent to coral reefs can therefore have a substantial influence on the distribution and composition of reef fish. We investigate how different habitats in a tropical seascape in the Philippines influence the presence, density, and biomass of coral reef fishes to understand the relative importance of different habitats across various spatial scales. A detailed seascape map generated from satellite imagery was combined with field surveys of fish and benthic habitat on coral reefs. We then compared the relative importance of local reef (within coral reef) and adjacent habitat (habitats in the surrounding seascape) variables for coral reef fishes. Overall, adjacent habitat variables were as important as local reef variables in explaining reef fish density and biomass, despite being fewer in number in final models. For adult and juvenile wrasses (Labridae), and juveniles of some parrotfish taxa (Chlorurus), adjacent habitat was more important in explaining fish density and biomass. Notably, wrasses were positively influenced by the amount of sand and macroalgae in the adjacent seascape. Adjacent habitat metrics with the highest relative importance were sand (positive), macroalgae (positive), and mangrove habitats (negative), and fish responses to these metrics were consistent across fish groups evaluated. The 500‐m spatial scale was selected most often in models for seascape variables. Local coral reef variables with the greatest importance were percent cover of live coral (positive), sand (negative), and macroalgae (mixed). Incorporating spatial metrics that describe the surrounding seascape will capture more holistic patterns of fish–habitat relationships on reefs. This is important in regions where protection of reef fish habitat is an integral part of fisheries management but where protection of nonreef habitats is often overlooked.     

Importance of fish behaviour in modelling conservation problems: food limitation as an example

Simulation experiments using the inSTREAM individual-based brown trout Salmo trutta population model explored the role of individual adaptive behaviour in food limitation, as an example of how behaviour can affect managers' understanding of conservation problems. The model includes many natural complexities in habitat (spatial and temporal variation in characteristics such as depth and velocity, temperature, hiding and feeding cover, drift-food supply and predation risk), fish physiology (especially, how food intake and growth vary with hydrodynamics, cover, fish size and temperature) and behaviour. When drift-food concentration was increased over a wide range in 7 year simulations, the simulated population was always food limited. In fact, as food supply increased, the population increased at an increasing rate and consumed a higher percentage of the food supply, apparently because higher food concentrations make more stream area energetically profitable for drift feeders. The behaviour most responsible for this response was activity selection: when food was abundant, fish chose to feed less frequently and more nocturnally, thereby reducing predation mortality so more fish survived longer. These results indicate that the traditional concept of food limitation, that food availability stops limiting population size when it exceeds some threshold level, may not be useful and can be misleading. Results also strongly contradict the concept that a salmonid population is not food limited if the total food supply is greater than the population's consumption. Explicit consideration of adaptive behaviour produced a novel but believable understanding of food effects on salmonid populations. Published 2011. This article is a U.S. Government work and is in the public domain in the USA.     

Covariation of stream community structure and biomass of algae, invertebrates and fish with forest cover at multiple spatial scales

1. To evaluate the spatial extent of the effects of forest cover on stream ecosystems, we measured algae, invertebrate, and fish biomass and invertebrate and fish community structure in 38 small first- to third-order streams in the National Capital Region of Canada along with forest cover at different spatial scales.
2. We considered 55 spatial scales of forest cover including several buffer widths (doubling 10–320 m) and lengths (doubling 10–1280 m, entire riparian distance upstream from sampling area) and entire catchments to determine which spatial scale maximized the correlation with biomass and metrics of community structure.
3. The proportion of variability in biomass and structural metrics explained by forest cover generally increased with increasing scale, suggesting that catchment-wide disturbances are the most influential determinants of benthic and fish communities.
4. Catchment forest cover explained more variation in algal (adjusted r ²   =   0.54), invertebrate (adjusted r ²   =   0.51) and fish (adjusted r ²   =   0.33) biomass than structural metrics of invertebrates and fish (adjusted r ²   =   0.08–0.27).
5. Analyses of the partial effects of forest cover at three scales (reach, riparian and the entire catchment) on biomass and community structure metrics identified catchment and reach scales as being most influential and never detected a significant partial effect of forest cover at the riparian scale.
6. These results suggest that maintenance or protection of reach and riparian buffers alone will not sufficiently protect stream function and structure from catchment-wide impacts.     

Microhabitat selection in the common lizard: implications of biotic interactions,age, sex,local processes,and model transferability among populations

Modeling species' habitat requirements are crucial to assess impacts of global change, for conservation efforts and to test mechanisms driving species presence. While the influence of abiotic factors has been widely examined, the importance of biotic factors and biotic interactions, and the potential implications of local processes are not well understood. Testing their importance requires additional knowledge and analyses at local habitat scale. Here, we recorded the locations of species presence at the microhabitat scale and measured abiotic and biotic parameters in three different common lizard (Zootoca vivipara) populations using a standardized sampling protocol. Thereafter, space use models and cross‐evaluations among populations were run to infer local processes and estimate the importance of biotic parameters, biotic interactions, sex, and age. Biotic parameters explained more variation than abiotic parameters, and intraspecific interactions significantly predicted the spatial distribution. Significant differences among populations in the relationship between abiotic parameters and lizard distribution, and the greater model transferability within populations than between populations are in line with effects predicted by local adaptation and/or phenotypic plasticity. These results underline the importance of including biotic parameters and biotic interactions in space use models at the population level. There were significant differences in space use between sexes, and between adults and yearlings, the latter showing no association with the measured parameters. Consequently, predictive habitat models at the population level taking into account different sexes and age classes are required to understand a specie's ecological requirements and to allow for precise conservation strategies. Our study therefore stresses that future predictive habitat models at the population level and their transferability should take these parameters into account.