Abundance Of Carnivores Research Articles

The impact of land reform on the status of large carnivores in Zimbabwe.

Large carnivores are decreasing in number due to growing pressure from an expanding human population. It is increasingly recognised that state-protected conservation areas are unlikely to be sufficient to protect viable populations of large carnivores, and that private land will be central to conservation efforts. In 2000, a fast-track land reform programme (FTLRP) was initiated in Zimbabwe, ostensibly to redress the racial imbalance in land ownership, but which also had the potential to break up large areas of carnivore habitat on private land. To date, research has focused on the impact of the FTLRP process on the different human communities, while impacts on wildlife have been overlooked. Here we provide the first systematic assessment of the impact of the FTLRP on the status of large carnivores. Spoor counts were conducted across private, resettled and communal land use types in order to estimate the abundance of large carnivores, and to determine how this had been affected by land reform. The density of carnivore spoor differed significantly between land use types, and was lower on resettlement land than on private land, suggesting that the resettlement process has resulted in a substantial decline in carnivore abundance. Habitat loss and high levels of poaching in and around resettlement areas are the most likely causes. The FTLRP resulted in the large-scale conversion of land that was used sustainably and productively for wildlife into unsustainable, unproductive agricultural land uses. We recommended that models of land reform should consider the type of land available, that existing expertise in land management should be retained where possible, and that resettlement programmes should be carefully planned in order to minimise the impacts on wildlife and on people.

Factors Affecting Red-Legged PartridgeAlectoris rufaAbundance on Big-Game Hunting Estates: Implications for Management and Conservation

The red-legged partridge Alectoris rufa is not only the most important bird game species but also an important prey species for many predators in Iberia. However, its populations have significantly declined in recent decades, principally as the result of agricultural intensification on arable land. Its abundance has also undergone a significant decline in forested areas over the last few decades, where wild ungulate management and abundance have increased. In this scenario, we aimed to test the factors that affect red-legged partridge abundance in relation to high wild ungulate (wild boar and red deer) abundance in south-central Spain. The factors included as predictors were carnivore, wild boar and red deer abundances, vegetation features, nest predation rate and invertebrate availability. Red deer abundance showed a negative relationship with partridge abundance in spring (non-significant negative trends were also evident for carnivore and wild boar), whereas variables related to food availability (grass biomass, Hemipteran abundance and total invertebrate mass) had a positive effect in the same season. Moreover, deer and carnivore abundances and spring nest predation rate were negatively associated with partridge abundance in autumn. Plant biomass and Hemipteran abundance were negatively correlated with wild boar abundance, whereas maximum pasture height was negatively related to red deer and wild boar abundance. Overall, our results show that high ungulate densities may negatively affect partridge abundance, which may be mediated by (i) a reduction in food availability (invertebrate and herbaceous plant biomass) and (ii) nest predation by wild boar. This research has shown that current intensive big-game hunting management schemes in south-central Spain are often incompatible with red-legged partridge conservation, and that these effects should be taken into account when defining big-game management and conservation policies.

Status of the fringing coral reefs in the southern Egyptian coast of the Red Sea

Study of the effect of human impact and sheltering condition on corals and fish assemblages was carried out in twenty nine reef sites at the area between Marsa Umm El-Grifate and Marsa Shuna, Red sea. Total living covers, total coral cover, and total recruitment colonies were recorded and exhibited higher percentages of occurrence onthe exposed and un-impacted sites than on the sheltered and impacted ones. In contrary, the covers of algae, dead and bleached coral colonies were found to be higher on the sheltered and impacted reefs than on the exposed and un-impacted ones. In total, 117 fish species belong to 24 families were recorded. Although, carnivorefish were dominating the food web, the most abundant groups were found to be herbivore and planktivore fishes. Total fish abundance was higher in the shelter sites than in the exposed ones, while the abundance of herbivores, carnivores, and piscivores were higher in the sheltered and impacted sites than in the exposed and unimpactedones. Total coral cover and total recruitments were negatively correlated to algal cover. Total fish abundance was positively correlated to total living cover and negatively correlated to total coral cover. Herbivores fish abundance was positively correlated to total coral cover and total recruitments, but it was negatively correlatedto algal cover. Moreover, planktivores fishes were negatively correlated to the total coral cover and total recruitments. This study strongly recommended to organize the fishing activities along the southern Red Sea, in addition to regulate the rabid coastal development to this part of the Red Sea.

El Niño Southern Oscillation drives conflict between wild carnivores and livestock farmers in a semiarid area in Chile

The warm phase of El Niño-Southern Oscillation (ENSO) events results in greatly elevated rainfall in north-central Chile, with dramatic effects on small mammals and vertebrate carnivore abundances. In ensuing cool phases of ENSO, plant cover decreases, followed by small mammal densities, in turn affecting the resource availability for their predators. Wild carnivores such as foxes are one of the main predators of small mammals; when the latter decline, foxes could exhibit functional responses, increasing their consumption of domestic livestock. To our knowledge, the influence of native prey abundance on livestock predation has not been assessed. We hypothesize that periods of scarce native prey increases conflicts between carnivores and farmers outside protected areas, especially during drought years. From 1990 to 2005 we used live trapping to determine monthly density of small mammals in a national park (Bosque Fray Jorge National Park, BFJNP) in north-central Chile; rainfall was also monitored. We calculated an index of predation as the number of sheep predated by foxes annually on one farm (encompassing ca. 45,000 ha) located in the vicinity of BFJNP. Path analysis was carried out to assess factors influencing sheep predation by wild foxes. Factors included precipitation and small mammal density. Small mammal density correlated positively with two years moving average of rainfall. Sheep predation by foxes increased after of two years of low rainfall. Our findings suggest that wild carnivores employ functional responses in response to varying prey availability, shifting from wild to domestic prey during periods of drought, which could have important conservation and management implications.

No Effects of Habitat, Prey Abundance and Competitor Carnivore Abundance on Fecal Cortisol Metabolite Levels in Wildcats (Felis silvestris)

Conservation physiology is an important tool used to understand how variation in the natural environment can evoke a physiological stress response in free-living animals. The aim of this study was to analyze how fecal cortisol metabolite (FCM) levels vary in response to habitat type, prey abundance and interspecific competition in a free-living population of wildcats in northwest Spain. We collected 110 fresh fecal samples from 25 wildcats along 28 transects between May 2005 and June 2009. To determine habitat characteristics and competing carnivore abundance, we defined 110 circular plots with the fresh wildcat scat at the center. For each plot, we sampled habitat variables, competitor carnivore abundance (pine marten [Martes martes] and red fox [Vulpes vulpes]) and prey abundance (wood mice [Apodemus sylvaticus]). Our results indicate that habitat variables, interference competition and main prey abundance did not significantly affect FCM levels in wildcats.

Evaluating noninvasive genetic sampling techniques to estimate large carnivore abundance.

Monitoring large carnivores is difficult because of intrinsically low densities and can be dangerous if physical capture is required. Noninvasive genetic sampling (NGS) is a safe and cost-effective alternative to physical capture. We evaluated the utility of two NGS methods (scat detection dogs and hair sampling) to obtain genetic samples for abundance estimation of coyotes, black bears and Canada lynx in three areas of Newfoundland, Canada. We calculated abundance estimates using program capwire, compared sampling costs, and the cost/sample for each method relative to species and study site, and performed simulations to determine the sampling intensity necessary to achieve abundance estimates with coefficients of variation (CV) of <10%. Scat sampling was effective for both coyotes and bears and hair snags effectively sampled bears in two of three study sites. Rub pads were ineffective in sampling coyotes and lynx. The precision of abundance estimates was dependent upon the number of captures/individual. Our simulations suggested that ~3.4 captures/individual will result in a<10% CV for abundance estimates when populations are small (23-39), but fewer captures/individual may be sufficient for larger populations. We found scat sampling was more cost-effective for sampling multiple species, but suggest that hair sampling may be less expensive at study sites with limited road access for bears. Given the dependence of sampling scheme on species and study site, the optimal sampling scheme is likely to be study-specific warranting pilot studies in most circumstances.

Indirect Effects of Sika Deer on Japanese Badgers

Recently, the range of the deer has expanded worldwide, with dramatic increases in abundance; yet relatively little is known about how these increases influence other mammals at high trophic levels. A recent study showed that high deer density exerts cascading effects on raccoon dogs, omnivorous carnivores, because of any increase in their prey abundance in Oku-Nikko, Japan. Here, we examined the diet of Japanese badgers, another omnivorous carnivore, outside a deer-proof fence and compared carnivore abundance inside and outside the fence in Oku-Nikko, to assess whether high deer density outside the fence influences the carnivore. Earthworms and insects, the population of which increased by high deer density, were frequently found in badger fecal samples outside the fence. Outside the fence, the deer density was 13.5/km2 and the badger relative density was 0.16, whereas inside the fence, the deer density was only 2.3/km2 and the badger relative density was 0.01. A statistical test showed that this inverse relationship was significant. We propose that the grazing pressure associated with high deer density impacts habitat conditions, increasing earthworm and insect abundance, which then increases omnivorous carnivore foraging opportunities and population densities.

Small carnivores of Biligiri Rangaswamy Temple Tiger Reserve, Karnataka, India

During the present study in Biligiri Rangaswamy Temple Tiger Reserve (BRT), nine species of small carnivores viz., Jungle Cat Felis chaus, Rusty-spotted Cat Prionalilurus rubiginosus, Leopard Cat Prionailurus bengalensis, Small Indian Civet Viverricula indica, Asian Palm Civet Paradoxurus hermaphroditus, Striped-necked Mongoose Herpestes vitticollis, Ruddy Mongoose Herpestes smithii, Common Mongoose Herpestes edwardsii and Smooth-coated Otter Lutrogale perspicillata, were recorded using camera-trapping technique, transect walks, and night surveys. Vegetation type strongly influences the presence and abundance of each species. The most sightings of small carnivores occurred in dry deciduous forests. Among all the species, the Asian Palm Civet was the most abundant and was followed by the small Indian Civet. Compared to many other forests or regions in India, the sight records of the Rusty-spotted Cat were relatively higher in BRT. Although we were unable to use statistical methods to search for higher levels of interdependencies between forest types and small carnivore abundance, our study sheds light on patterns of small carnivore distribution in this unique habitat which bridges the Western Ghats and the Eastern Ghats.

Evidence that vulture restaurants increase the local abundance of mammalian carnivores in South Africa

Vulture restaurants are used worldwide as a conservation tool to provide threatened vultures with a source of supplementary carrion free from anthropogenic contaminants such as poisons and veterinary drugs. While the impacts of supplementary feeding sites on ecosystem and scavenging community dynamics have been investigated in Europe, no information is currently available for southern Africa. This study presents evidence that providing supplementary carrion for vultures stimulated an increase in local abundance of two species of mammalian carnivores, the brown hyaena (Hyaena brunnea) and the black-backed jackal (Canis mesomelas). These findings require that the wider impacts of providing supplementary carrion for conserving threatened species are fully investigated.

Can occupancy-abundance models be used to monitor wolf abundance?

Estimating the abundance of wild carnivores is of foremost importance for conservation and management. However, given their elusive habits, direct observations of these animals are difficult to obtain, so abundance is more commonly estimated from sign surveys or radio-marked individuals. These methods can be costly and difficult, particularly in large areas with heavy forest cover. As an alternative, recent research has suggested that wolf abundance can be estimated from occupancy–abundance curves derived from “virtual” surveys of simulated wolf track networks. Although potentially more cost-effective, the utility of this approach hinges on its robustness to violations of its assumptions. We assessed the sensitivity of the occupancy–abundance approach to four assumptions: variation in wolf movement rates, changes in pack cohesion, presence of lone wolves, and size of survey units. Our simulations showed that occupancy rates and wolf pack abundances were biased high if track surveys were conducted when wolves made long compared to short movements, wolf packs were moving as multiple hunting units as opposed to a cohesive pack, and lone wolves were moving throughout the surveyed landscape. We also found that larger survey units (400 and 576 km2) were more robust to changes in these factors than smaller survey units (36 and 144 km2). However, occupancy rates derived from large survey units rapidly reached an asymptote at 100% occupancy, suggesting that these large units are inappropriate for areas with moderate to high wolf densities (>15 wolves/1,000 km2). Virtually-derived occupancy–abundance relationships can be a useful method for monitoring wolves and other elusive wildlife if applied within certain constraints, in particular biological knowledge of the surveyed species needs to be incorporated into the design of the occupancy surveys. Further, we suggest that the applicability of this method could be extended by directly incorporating some of its assumptions into the modelling framework.

Estimating seasonal abundance and habitat use of small carnivores in the Western Ghats using an occupancy approach

Abstract:Rigorous population studies on many small carnivores are lacking in India. Presence-absence models with habitat covariates were applied to estimate seasonal occupancy and abundance of nine small-carnivore species from camera-trap data in Mudumalai Tiger Reserve (2010 and 2011). We deployed 25 camera-trap stations in the deciduous forest, 21 in the semi-evergreen forest and 26 in the dry thorn forest. In total, 7380 trap-nights yielded 448 photographs of small carnivores: jungle cat (n = 72), leopard cat (n = 6), rusty-spotted cat (n = 11), small Indian civet (n = 89), common palm civet (n = 37), brown palm civet (n = 20), stripe-necked mongoose (n = 66), ruddy mongoose (n = 96) and Indian grey mongoose (n = 51). In the dry season, rusty-spotted cat was the rarest carnivore with an average abundance (λmean) of 0.24 ± 0.26, while ruddy mongoose was the most abundant (λmean = 0.90 ± 0.40). In the wet season, leopard cat was the rarest species (λmean = 0.048 ± 0.041) while grey mongoose was the most abundant (λmean = 0.68 ± 0.35). Abundance of jungle cat, common palm civet, ruddy mongoose and grey mongoose increased in the dry thorn forest whereas in the dry season abundance of small Indian civet decreased in this forest type. Abundance of leopard cat and small Indian civet was not influenced by habitat in the wet season. Deciduous forest was positively associated with abundance of rusty-spotted cat. Deciduous and semi-evergreen forests had a positive effect on abundance of stripe-necked mongoose while the latter was a positive predictor of abundance and occupancy for brown palm civet. Improved modelling approaches can account for the spatio-temporal variation in habitat use of small carnivores occupying specialized niches in heterogeneous tropical forests of southern India.

Effect of wildlife refuges on small carnivores in a hunting area in Mediterranean habitat

Most of Spain is managed for game hunting, an economic activity that is commonly related to predator control. This practice can affect the diversity and abundance of wild carnivores if, despite that hunting is legally focused on some target species, other species are illegally removed. This note evaluates the changes in the structure of carnivore assemblage between wildlife refuges (no predator control) and private areas managed for game production where, because of little regulation, foxes and crows can be eliminated. Our aim is to test if predator control produces a significant change in the presence of foxes (the target species) or whether it also affects other carnivores. Download the complete issue.

Compensatory heterogeneity in spatially explicit capture-recapture data.

Spatially explicit capture-recapture methods, used widely to estimate the abundance of large carnivores, allow for movement within home ranges during sampling. Probability of detection is a decreasing function of distance from the home range center, with one parameter for magnitude and another for spatial scale. Sex-based and other differences in home range size potentially cause heterogeneity in individual detection and bias in estimates of density. The two parameters of detection have hitherto been treated as independent, but we suggest that an inverse relation is expected when detection probability depends on time spent near the detector. Variation in the spatial scale of detection is then compensated by reciprocal variation in the magnitude parameter. We define a net measure of detection ("single-detector sampling area," a(0)), and show by simulation that its coefficient of variation (CV) is a better predictor of bias than the CV of either component or the sum of their squared CVs. In an example using the grizzly bear Ursus arctos, the estimated sex variation in a(0) was small despite large variation in each component. From the simulations, the relative bias of density estimates was generally negligible (< 5%) when CV(a(0)) < 30%. Parameterization of the detection model in terms of a(0) and spatial scale can be more parsimonious and significantly aids the biological interpretation of detection parameters.

Population density and abundance of sympatric large carnivores in the lowland tropical evergreen forest of Indian Eastern Himalayas

Low density occurrence of large carnivore species and direct hunting of predators and prey make carnivore conservation complex. Vital baseline information on population status of large carnivores is still deficient in most forests of eastern Himalaya, which are known to be the biodiversity hotspots. To fill this information gap, we estimated the large carnivore population status and abundance in an intricate eastern Himalayan lowland tropical forest in Pakke Tiger Reserve, Arunachal Pradesh. Population status and abundance estimates of tigers and leopards were made through individual identification using closed capture-recapture sampling. To estimate the dhole abundance photographic encounter rate was used. For individually non-identifiable species photographic rate seemed to correlate well with animal abundance. The estimated tiger and leopard density through 1/2 MMDM was 2.14±0.04/100km2 and 2.99±1.13/100km2 respectively. Maximum likelihood estimates shows density of tiger 1.86±0.7 and for leopard 2.82±1.2.The estimated dhole abundance was (N) 10.6±0.94, and density 6.62±0.58 individuals in 100km2. Further, occupancy estimation of large carnivores may be tried along with assessing the comparative efficacy of other population estimation methods to establish better monitoring methods for this region.

Estimating the abundance of rare and elusive carnivores from photographic‐sampling data when the population size is very small

AbstractConservation and management agencies require accurate and precise estimates of abundance when considering the status of a species and the need for directed actions. Due to the proliferation of remote sampling cameras, there has been an increase in capture–recapture studies that estimate the abundance of rare and/or elusive species using closed capture–recapture estimators (C–R). However, data from these studies often do not meet necessary statistical assumptions. Common attributes of these data are (1) infrequent detections, (2) a small number of individuals detected, (3) long survey durations, and (4) variability in detection among individuals. We believe there is a need for guidance when analyzing this type of sparse data. We highlight statistical limitations of closed C–R estimators when data are sparse and suggest an alternative approach over the conventional use of the Jackknife estimator. Our approach aims to maximize the probability individuals are detected at least once over the entire sampling period, thus making the modeling of variability in the detection process irrelevant, estimating abundance accurately and precisely. We use simulations to demonstrate when using the unconditional‐likelihood M0 (constant detection probability) closed C–R estimator with profile‐likelihood confidence intervals provides reliable results even when detection varies by individual. If each individual in the population is detected on average of at least 2.5 times, abundance estimates are accurate and precise. When studies sample the same species at multiple areas or at the same area over time, we suggest sharing detection information across datasets to increase precision when estimating abundance. The approach suggested here should be useful for monitoring small populations of species that are difficult to detect.

Conservation value of forest fragments for medium-sized carnivores in a silvopastoral system in Colombia

Silvopastoral cattle ranching is seen as a viable land use management system, which unlike traditional land use systems preserve forested areas and prevent loss of important habitats for carnivores. We evaluated carnivore abundance and habitat use in a 50-year silvopastoral system located in the Cordoba department, Caribbean region of Colombia. Transects and track plots were established both in forest fragments and pastures within the silvopastoral system and were sampled for carnivore signs. Crab-eating raccoon, Crab-eating fox, and Gray fox were the most abundant species and showed higher preference for forest than pastures. Our results reflect the importance of forest cover within livestock systems and highlight the potential of these land use systems for carnivore and tropical dry forest conservation in fragmented landscapes.

Predators and livestock reduce bird nest survival in intensive Mediterranean farmland

High nest predation is one of the factors potentially driving farmland bird declines, particularly in the case of ground-nesting species. Accordingly, recent calls have been made to address predation in agri-environment schemes, but this is hindered by limited understanding of how processes operating at different scales affect predation patterns and how additional factors such as livestock trampling contribute to reduced nest survival. Using an artificial nest experiment, we assessed how field management, landscape composition and configuration, and the abundance of potential avian predators and mammalian carnivores affected predation and trampling rates in grassland fields (pastures and fallows) embedded in intensive Mediterranean farmland. Mean predation and trampling rates per field were 0.18 ± 0.23 SD and 0.12 ± 0.17 SD, respectively. However, there was strong spatial variation, with high nest losses (>50 %) occurring in about one quarter of the fields. Variation in failure rates was mainly related to livestock grazing and predator abundances, while the effects of landscape context were negligible. Predation and trampling rates were highest in fields with short swards. Predation rate was positively related to the abundance of Egyptian mongooses and dogs. To increase nest survival, agri-environment schemes designed for ground-nesting birds should contribute for maintaining low stocking density. Further evaluation is required on the need for controlling populations of fast-expanding generalist predators such as mongooses.

Geo-Spatial Aspects of Acceptance of Illegal Hunting of Large Carnivores in Scandinavia

Human-carnivore conflicts are complex and are influenced by: the spatial distribution of the conflict species; the organisation and intensity of management measures such as zoning; historical experience with wildlife; land use patterns; and local cultural traditions. We have used a geographically stratified sampling of social values and attitudes to provide a novel perspective to the human – wildlife conflict. We have focused on acceptance by and disagreements between residents (measured as Potential Conflict Index; PCI) towards illegal hunting of four species of large carnivores (bear, lynx, wolf, wolverine). The study is based on surveys of residents in every municipality in Sweden and Norway who were asked their opinion on illegal hunting. Our results show how certain social values are associated with acceptance of poaching, and how these values differ geographically independent of carnivore abundance. Our approach differs from traditional survey designs, which are often biased towards urban areas. Although these traditional designs intend to be representative of a region (i.e. a random sample from a country), they tend to receive relatively few respondents from rural areas that experience the majority of conflict with carnivores. Acceptance of poaching differed significantly between Norway (12.7–15.7% of respondents) and Sweden (3.3–4.1% of respondents). We found the highest acceptance of illegal hunting in rural areas with free-ranging sheep and strong hunting traditions. Disagreements between residents (as measured by PCI) were highest in areas with intermediate population density. There was no correlation between carnivore density and either acceptance of illegal hunting or PCI. A strong positive correlation between acceptance of illegal hunting and PCI showed that areas with high acceptance of illegal hunting are areas with high potential conflict between people. Our results show that spatially-stratified surveys are required to reveal the large scale patterns in social dynamics of human-wildlife conflicts.

Asynchronous food‐web pathways could buffer the response of Serengeti predators to El Niño Southern Oscillation

Understanding how entire ecosystems maintain stability in the face of climatic and human disturbance is one of the most fundamental challenges in ecology. Theory suggests that a crucial factor determining the degree of ecosystem stability is simply the degree of synchrony with which different species in ecological food webs respond to environmental stochasticity. Ecosystems in which all food-web pathways are affected similarly by external disturbance should amplify variability in top carnivore abundance over time due to population interactions, whereas ecosystems in which a large fraction of pathways are nonresponsive or even inversely responsive to external disturbance will have more constant levels of abundance at upper trophic levels. To test the mechanism underlying this hypothesis, we used over half a century of demographic data for multiple species in the Serengeti (Tanzania) ecosystem to measure the degree of synchrony to variation imposed by an external environmental driver, the El Niño Southern Oscillation (ENSO). ENSO effects were mediated largely via changes in dry-season vs. wet-season rainfall and consequent changes in vegetation availability, propagating via bottom-up effects to higher levels of the Serengeti food web to influence herbivores, predators and parasites. Some species in the Serengeti food web responded to the influence of ENSO in opposite ways, whereas other species were insensitive to variation in ENSO. Although far from conclusive, our results suggest that a diffuse mixture of herbivore responses could help buffer top carnivores, such as Serengeti lions, from variability in climate. Future global climate changes that favor some pathways over others, however, could alter the effectiveness of such processes in the future.

Patterns in Stream Fish Assemblage Structure and Function Associated With a PCB Gradient

Stream fish assemblage structure and function were examined for significant response along a polychlorinated biphenyl (PCB) gradient from two PCB-contaminated streams (Clear Creek and Richland Creek watershed) at three locations and a control stream (Little Indian Creek), Indiana, USA. Fish were sampled in the summer months of 1995 and from 1999 to 2002. 51 fish assemblage attributes-including structure (i.e., fish composition) and function (i.e., trophic, reproductive, condition guilds), biomass, and index of biotic integrity (IBI) metric scores-were evaluated for significance according to an increasing PCB gradient. Eight biomass attributes of fish assemblages decreased with increasing PCB concentration: number of species biomass, number of sunfish biomass, percent sunfish biomass, number of sucker biomass, percent sucker biomass, biomass of sensitive species, percent sensitive species biomass, and percent carnivore biomass. Three biomass attributes increased with PCB concentration: percent minnow biomass, percent pioneer species biomass, and percent tolerant species biomass. Seven species composition and relative abundance characters decreased with increasing PCB concentration: number of species; number of darter, madtom, and sculpin; number of darter; number of sunfish; number of sucker; number of sensitive species; and percent individuals as carnivores. Percent individuals as pioneer species increased with increasing PCB concentration. Two IBI metrics, percent individuals as headwater species and number of minnow species, increased as PCB concentrations increased, whereas number of sucker species and percent individuals as pioneer species decreased with increasing PCB concentration class. We observed a direct response between decreased relative abundance and biomass of carnivores and increased relative abundance minnows as the PCB gradient increased. Total IBI score did not detect subtle changes to the fish community that were observed along a PCB gradient, whereas diagnostic analysis of the individual metrics did.