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In this paper, the complex dynamics of a spatial aquatic system in the presence of self- and cross-diffusion are investigated. Criteria for local stability, instability and global stability are obtained. The effect of critical wavelength which can drive a system to instability is investigated. We noticed that cross-diffusion coefficient can be quite significant, even for small values of off-diagonal terms in the diffusion matrix. With the help of numerical simulation, we observed the Turing patterns (spots, strips, spot-strips mixture), regular spiral patterns and irregular patchy structures. The beauty and complexity of the Turing patterns are attributed to a large variety of symmetry properties realized by different values of predator's immunity, rate of fish predation and half saturation constant of predator population. [ABSTRACT FROM AUTHOR]

How predators vary search patterns in response to prey predictability is poorly known. For example, marine invertebrates may be predictable but of low energy value, while fish may be of higher energy value but unpredictable at large (pelagic schools) or small (solitary benthics) spatial scales. We investigated the search patterns of the thick-billed murre ( Uria lomvia), an Arctic seabird feeding on invertebrates, pelagic fish, or benthic fish. Foraging ranges at the Coats Island colony are generally smaller (<240 min per trip) than at larger colonies, and many birds specialize in foraging tactics and diet. Underwater search times for benthic fish were higher than for pelagic fish or invertebrates while above-water search times for pelagic fish were higher than for benthic fish or invertebrates. There were few stops during trips. Total trip time, flying time, number of flights, and number of dives were intercorrelated and increased with prey energy content, suggesting that longer trips involved fewer prey encounters due to selection of higher-quality, but rarer, prey items. Flight times were not Lévy-distributed and seabirds may have used area-restricted searches. The high degree of specialization, apparent absence of information center effects, and reduced above-water searching times may be linked to the relatively small colony size and the resulting short commuting distances to feeding areas, leading to greater prey predictability. We concluded that prey predictability over various scales affected predator search patterns. [ABSTRACT FROM AUTHOR]

This paper deals with the problem of non-selective harvesting of a prey-predator system by using a reasonable catch-rate function instead of usual catch-per-unit-efforthypothesis. Here both the prey and the predator species obey the law of logistic growth. We have taken the predator functional response to prey density in such a form that each predator's functional response to the prey density approaches a constant as the prey population increases. Boundedness of the exploited system is examined. The existence of its steady states and their stability (local and global) are studied using Eigenvalue analysis. The existence of bionomic equilibria has been illustrated using a numerical example. The problem of determining the optimal harvesting policy is then solved by using Pontryagin's maximum principle. [ABSTRACT FROM AUTHOR]

Correlations between time series of the abundance of predator and prey fish species in heavily exploited western North Atlantic marine fisheries vary temporally but are generally positive in southern, warmer waters and negative in northern, colder ones. The correlations provide an index of trophic structure and dynamics. We construct a framework to quantify critical thresholds between states in which the predator–prey correlations are positive or negative. We do so by developing a quantitative model of the distribution of the correlations between predator (15 species) and prey (8 species) functional groups based on the annual predator depletion rates and bottom temperatures (or alternatively species richness). The model accounts for 58% of the variance of the correlations with a root mean square error of 0.3. This index of trophic structure indicates that warmer, species-rich, southern fish populations resist transformation from positive to negative predator–prey correlations at exploitation rates that can be double those in the colder, relatively species-poor, northern areas. The model can be used to set limits for exploitation rates that preserve the functional relationships between predator–prey groups in emerging fisheries, and to assess the potential for and measures required to achieve recovery of degraded fish communities. [ABSTRACT FROM AUTHOR]

Interference among predators decreases per capita foraging rates and has implications for both community dynamics and top-down trophic processes. Interference originates from behavioural interactions among foragers, and these behaviours could be affected by environmental conditions. In experiments on pike foraging alone or among conspecifics in different levels of water turbidity, we expected high turbidity to decrease the perceived risk of intraspecific interactions among pike, and thereby decrease the strength of interference, as turbidity would decrease the visual contact between individuals and act as a refuge from behavioural interactions. The results show that this is not the case, but suggest that interference is induced instead of reduced in high turbidity. Per capita foraging rates do not differ between pike foraging alone or in groups in our clear and moderately turbid treatments, indicating no effect of interference. As high turbidity enhances prey consumption for pike individuals foraging alone, but does not have this effect for pike in groups, high turbidity induces the relative interference effect. We suggest that future evaluations of the stabilizing effects of interference on community dynamics and its reduction of predation impact on top-down trophic cascades should consider potential unexpected effects of environmental conditions. [ABSTRACT FROM AUTHOR]

Physiological fitness and exercise capacity decrease with age in humans and rodents, a finding for which, among other causes, the decline of cellular and especially mitochondrial functions with age is held responsible. We investigated changes of escape response to predator attacks in swimming scallops (Aequipecten opercularis) with size using the natural predator Asterias rubens. Aequipecten opercularis swim mainly to avoid predators and a decrease in swimming abilities would increase risk of capture and lower survival. The queen scallop A. opercularis is a very active, epibenthic species with a short lifespan of 8-10 years and a shell height up to 90 mm in the investigated fishing ground around the Isle of Man. No difference in clap rate was found between smaller and bigger A. opercularis individuals, but differences were found in swimming mode (jumping and swimming) and valve opening and closure behaviour between the two size groups in response to predator attack. Smaller individuals showed less jumping movements and closed valves more often and remained closed for longer time than bigger animals. The difference in swimming behaviour is discussed in respect to size and age-dependent changes in morphology and cellular physiology as well as interactions of different main predators (sea stars, crabs) with the different size classes. [ABSTRACT FROM AUTHOR]

Abstract: We explored correlation in diet trends for five piscivorous predators that reproduce on the Pribilof Islands as illustrative of the shifting structure of the Bering Sea ecosystem. We evaluated the size and species of prey consumed by adult female and juvenile northern fur seals (Callorhinus ursinus) and adults and chicks of black-legged kittiwakes (Rissa tridactyla), red-legged kittiwakes (Rissa brevirostris), thick-billed murres (Uria lomvia), and common murres (Uria aalge) from data collected between July and October 1960–2000. Sample sources included stomachs from seals and seabirds collected on pelagic foraging grounds in the eastern Bering Sea, seal scats from rookeries and seabird regurgitations and whole prey from nest sites on St. Paul and St. George Islands of the Pribilof Island archipelago. Typical prey included small fish and invertebrates (⩽20cm for seals and ⩽12cm for seabirds) that concentrate along frontal boundaries of the continental shelf/slope and in the epi-pelagic zone. Squids and fishes including walleye pollock (Theragra chalcogramma), capelin (Mallotus villosus), and sand lance (Ammodytes hexapterus) were variably important in the diet of all five predators. Some prey, such as capelin, were principal in predator diets during the 1960s (seals) and into the early 1980s (seabirds), but declined or disappeared from all predator diets thereafter while others, such as walleye pollock, occurred with increasing frequency from the 1970s forward. As the number of individuals consuming walleye pollock increased, the overall volume of pollock in seabird diets declined. This decline was coincident with a decrease in the age and body size of pollock consumed by both seabirds and fur seals. Squid and pollock were negatively correlated in the diets of their primary consumers, northern fur seals (Pearson''s coefficient −0.71, p=0.016) and thick-billed murres (Pearson''s coefficient=−0.74, p=0.015) from the 1970s forward. Inter-island variation in diet was evident to varying degrees for all predators, with a prevalence of fish on St. Paul Island and invertebrates on St. George Island. Bayesian time-series analysis of synthesized data described significant temporal cross-correlation in diet among northern fur seals, red- and black-legged kittiwakes, and thick-billed murres. For all correlated predators except common murres, beta-binomial modeling indicated that trends in the occurrence of four of the five primary prey (sand lance, capelin, squid, and pollock) evaluated, were significantly associated with eastern Bering Sea time-series trends in sea surface temperature, ice retreat or a combination of both. Data synthesis highlighted potential competition and a scenario for the effects of an altered prey field on the population stability of predators. The association between correlated diet changes among predators and indices of oceanographic shifts in the 1970s and the 1990s allow scrutiny of hypotheses concerning causal mechanisms in population declines. [Copyright &y& Elsevier]

The ‘benefits of philopatry’ hypothesis states that helpers in cooperatively breeding species derive higher benefits from remaining home, instead of dispersing and attempting to breed independently. We tested experimentally whether dispersal options influence dispersal propensity in the cooperatively breeding Lake Tanganyika cichlids Neolamprologus pulcher and N. savoryi. Cooperative groups of these fishes breed in densely packed colonies, surrounded by unoccupied, but apparently suitable breeding habitat. Breeding inside colonies and living in groups seems to benefit individuals, for example by early detection and deterrence of predators. We show that despite a slight preference of both species for habitat with a higher stone cover, 40% of the preferred habitat remained unoccupied. On average, the colonies contained a higher number of (1) predators of adults, juveniles and eggs, (2) shelter competitors, and (3) other species including potential food competitors, compared to the outside colony habitat. Apparently, habitat differences cannot explain why these cichlids breed in colonies. Accordingly, dispersal may not be limited by a lack of suitable breeding shelters, but by the relatively higher risk of establishing an outside- compared to a within-colony breeding territory. To test whether cichlids prefer within- to outside-colony breeding territories, we provided breeding shelters inside the colony and at the colony edge and studied helper dispersal. As expected, significantly more shelters were occupied within the colony compared to the edge. New breeding pairs with several helpers occupied these shelters. We conclude that although breeding habitat is plentiful outside the colonies, helpers delay dispersal to obtain a higher quality breeding position within the group or colony eventually, or they disperse in groups. Our results suggest that (1) group augmentation and Allee effects are generally important for dispersal decisions in cooperatively breeding cichlids, consistent with the ‘benefits of philopatry hypothesis’, and (2) habitat saturation cannot fully explain delayed dispersal in these species. [ABSTRACT FROM AUTHOR]

The American brook lamprey (Lampetra appendix) does not feed after metamorphosis from the larval stage, and is typically much smaller than lampreys that feed as parasites or predators of other fishes. However, relatively large "giants" have occasionally been reported from Great Lakes tributaries, and one hypothesis is that they have fed parasitically after metamorphosis. I describe here two additional giant specimens from tributaries of Lake Michigan and Lake Huron. The presence of acanthocephalan parasites in the hindguts of both giants supports the hypothesis that they fed parasitically, because parasites of this group are known only from lampreys that have fed after metamorphosis. [ABSTRACT FROM AUTHOR]

When a predators attack prey, damaged prey tissue releases chemical information that reliably indicates an actively foraging predator. Prey use these semiochemicals to cue anti-predator behaviour and reduce their probability of predation. Here, we test central mudminnows, Umbra limi (Kirtland 1840), for anti-predator behavioural responses to chemical cues in conspecific skin extract. In a field experiment, traps scented with mudminnow skin extract (alarm cue) caught fewer mudminnows than traps scented with water (control). Under controlled laboratory conditions, mudminnows showed a significant reduction in activity and movement to the bottom in response to alarm cues relative to water controls. Reduced activity and increased time on the bottom of the tank are both known components of an anti-predator response. Thus, based on field and lab data, mudminnows exhibited anti-predator behavioural responses to chemical alarm cues released by damaged epidermal tissue. Histological preparations of epidermal tissue did not reveal the presence of specialised “alarm substance” cells for the production of chemical alarm cues. This is the first report of an alarm reaction in an esociform, an order with a long evolutionary history of piscivory. [ABSTRACT FROM AUTHOR]

This review focuses on how predator performance of the invasive largemouth bass [ Micropterus salmoides (Lacepède)] has been, or will be, formed in Japanese freshwaters. Predation impacts of largemouth bass on fish communities appear pervasive in both Japanese as well as North American freshwaters. Factors affecting performance as a piscivorous predator are (1) light intensity and water clarity, (2) oxygen depletion, (3) prey size and gape size, (4) behavioral refuge of prey, (5) weed beds as refuge for prey fish, (6) interaction with bluegill. Size and behavioral refuges requirements are so rigorous that they may have evolved only in some North American prey fish species like bluegill; therefore, most Japanese native fish species are unlikely to be equipped with such refuges. However, refuge habitats like aquatic weed beds could develop in Japanese freshwaters, allowing prey fish species to survive under predation pressure. The density, architecture, and species composition of aquatic plants may affect their suitability as refuges. Studies in Japanese waters have suggested that the presence of rich aquatic vegetation or invasive bluegill in bass-introduced waters have suppressed the predation impact of largemouth bass on fish communities. In addition to these environmental factors, original genotypic and phenotypic traits of the introduced largemouth bass, and hybridization between different lineages of largemouth bass or with Florida bass [ Micropterus floridanus (Lesueur)] may be involved in further adaptation of invasive largemouth bass to Japanese freshwaters. [ABSTRACT FROM AUTHOR]

Isolation from predators can lead to the reduction or loss of ancestral behavioral defenses in prey, but does not always do so. Predators introduced to populations that have experienced relaxed selection from some ancestral predators can favor the evolution of antipredator behavior that has been lost. We examined these possibilities by eliciting antipredator behavior in three populations of threespine stickleback fish, Gasterosteus aculeatus: an oceanic population thought to resemble the ancestral form, and two populations historically (up to 20 000 yr) devoid of piscine predators (relaxed selection), one of which has been stocked with salmonids for nearly 25 yr (reversed selection). We used three kinds of predator models: a sculpin (ambush predator), a rainbow trout (chasing predator), and an overhead silhouette of an arctic tern. Stickleback reacted differently to the three models, indicating that they distinguished among them. Individuals from all populations responded similarly to the tern model. The ancestral population showed the weakest response to the sculpin model despite being the only population that encounters these predators naturally. Stickleback from the trout-free population displayed slightly reduced responses to the trout model, and recovery times like those in the ancestral population providing only weak evidence for loss of the ancestral antipredator repertoire. Fish from the reverse-selected population exhibited fascinating, elevated responses to both the trout and sculpin models relative to the other two populations. These findings offer initial evidence of (1) a partial alteration of the ancestral behavioral repertoire during a long period of relaxed selection from piscine predators, and (2) rapid acquisition of extreme responses to piscine predators under reverse selection. [ABSTRACT FROM AUTHOR]

While qualitative observations of jellyfish intraguild predation abound in the literature, there are only few rate measurements of these interactions. We quantified predation rates among two common jellyfish in northern boreal waters, Cyanea capillata and its prey Aurelia aurita, both of which also feed on crustacean zooplankton and fish larvae. A series of incubation experiments using a wide range of prey concentrations (0.38–3.8 m−3) in large containers (2.6 m3) was carried out. By replenishing the prey continuously as they were captured we maintained a nearly constant prey concentrations. Ingestion rates increased linearly up to prey concentrations of 1.92 m−3, yielding maximum clearance rates of ∼2.37 ± 0.39 m3 predator−1 h−1 for C. capillata predators 16 ± 2.3 cm in diameter. Mean ingestion rate at saturated prey concentrations (1.92–3.85 m−3) was 4.01 ± 0.78 prey predator−1 h−1. Behavioral observations suggested that predators did not alter their swimming behavior during meals, and thus that feeding rates were generally handling limited rather than encounter limited. Predators captured more prey than needed, and semi-digested prey was often discarded when fresh prey was encountered. [ABSTRACT FROM AUTHOR]

1. Ecologists have struggled to describe general patterns in the impacts of predators on stream prey, particularly at large, realistic spatial and temporal scales. Among the confounding variables in many systems is the presence of multiple predators whose interactions can be complex and unpredictable. 2. We studied the interactions between brook trout ( Salvelinus fontinalis) and larval two-lined salamanders ( Eurycea bislineata), two dominant vertebrate predators in New England stream systems, by examining patterns of two-lined salamander abundance in stream reaches above and below waterfalls that are barriers to fish dispersal, by measuring the effects of trout on salamander density and activity using a large-scale manipulation of brook trout presence, and by conducting a small-scale laboratory experiment to study how brook trout and larval two-lined salamanders affect each other's prey consumption. 3. We captured more salamanders above waterfalls, in the absence of trout, than below waterfalls where trout were present. Salamander density and daytime activity decreased following trout addition to streams, and salamander activity shifted from aperiodic to more nocturnal with fish. Analysis of stomach contents from our laboratory experiment revealed that salamanders eat fewer prey with trout, but trout eat more prey in the presence of salamanders. 4. We suggest that as predators in streams, salamanders can influence invertebrate prey communities both directly and through density- and trait-mediated interactions with other predators. [ABSTRACT FROM AUTHOR]

We studied the compartmentalization of cadmium and zinc in the oligochaete Tubifex tubifex. The subcellular distribution was followed over time and levels of metallothionein-like proteins were measured. The impact of the speciation on the trophic transfer was studied by calculating the assimilation efficiencies of metals from Tubificidae fed to carp. It was found that carp were able to assimilate 9.8% of the cadmium. The expected assimilated amount of cadmium, based on the subcellular fractions which are thought to be trophically available, is however 72%. The zinc assimilation results suggest that the debris fraction is at least partially available to predators. Differential centrifugation techniques provide information about the tissue compartmentalization in aquatic organisms but it is not straightforward to directly link internal speciation in prey items to the actual assimilation in the predator. The possible impact that the compartmentalization of cadmium in T. tubifex will have on the toxicity to the organism is also discussed. [Copyright &y& Elsevier]

Many top-predator fish stocks in both freshwater and marine systems have collapsed as a result of overharvesting. Consequently, some of these communities have shifted into seemingly irreversible new states. We showed, for predators feeding on prey that exhibit food-dependent growth, that culling of fish prey may promote predator recovery. We removed old stunted individuals of a prey-fish species in a large, low-productive lake, which caused an increase in the availability of small-sized prey and allowed the predator to recover. The shift in community state has been sustained for more than 15 years after the cull ended and represents an experimental demonstration of an alternative stable state in a large-scale field system. Because most animals exhibit food-dependent growth, shifts into alternative stable states resulting from overcompensating prey growth may be common in nature and may require counterintuitive management strategies. [ABSTRACT FROM AUTHOR]

The present study reports the annual variation in consumption of the sea urchin Strongylocentrotus intermedius by avian predators on a rocky shore where the culture of sea urchins has been conducted. Carrion crow and a few gull species were the most abundant avian predators and consumed a large number of sea urchins. Crows consumed mostly natural sea urchins, approximately 36 kg ww/ha per year on the intertidal rocky bench, but the gull species consumed mostly cultured sea urchins, approximately 100 kg ww/ha per year in the culture area. The seasonal variation in the amount of sea urchins consumed by crows was higher than that by the gull species, presumably because of the difference in foraging behavior in association with the seasonal tidal cycle. The natural sea urchins consumed are an allochthonous input from the subtidal to the intertidal habitat, and thus, crow predation may not affect the natural and the cultured populations of the sea urchin. The gull species consumed much of the cultured sea urchin, and thus, may be regarded as an effective predator causing damage to sea urchin culture. The results suggest that further studies are needed to determine why the gull species selectively feed on cultured sea urchins. [ABSTRACT FROM AUTHOR]

Intertidal mudflats are important nursery grounds for juveniles of many fish species. However, they are being used increasingly to farm bivalve molluscs, which produce large amounts of organic “fluff”, overlying the mud. Fish such as sole, Solea solea, hide in this fluff from potential predators, but the energy consumed by respiring the fluff may be high due to its biorheological properties. We developed an ichthyoviscometer. It incorporates a freshly killed fish as a viscometer, and we developed it to measure the rheological properties of fluids and suspensions, including fluff, at scales encompassing those in gill ventilation. We have shown that the rheological behaviour of fluff is close to that of a gel with a yield stress strongly dependent on particulate organic matter concentration ([POM]). This has allowed us to model fluff flow through the gill channels in living sole as a function of fish size and [POM], showing that in a 26-g sole, fluff would halve flow at a [POM] value of 3.2 g l−1, and stop it at 3.4. [ABSTRACT FROM AUTHOR]

Here long-term monitoring data taken at 33 sites in southern and central California coast and islands were used to evaluate the size structure of the large intertidal limpet, Lottia gigantea in restricted-access and in easily accessible intertidal zones that encompass a wide range of ecological variables. Using multi-dimensional analysis of population size structures, we found that sites on islands and strictly protected mainland sites have significantly larger median limpet sizes and a greater range of limpet sizes than unprotected mainland sites, while no pattern occurs in latitudinal or regional comparison of sites. Although intertidal predators such as oystercatchers were not the primary focus of the monitoring efforts, extensive natural history notes taken during sampling visits support the argument that predation was not a primary cause for the size structure differences. Finally, substratum differences were determined not to have biased the observation of larger limpets in protected sites. In regard to human interactions with limpets, we conclude that the degree of enforcement against poaching is the better predictor of limpet size structure than proximity to population centers or visitation to intertidal sites. [ABSTRACT FROM AUTHOR]

Abstract: We studied in a laboratory experiment using stream tanks if two percid prey fish, the perch (Perca fluviatilis) and the ruffe (Gymnocephalus cernuus), can recognize and respond to increased predation risk using odors of two piscivores, the pike (Esox lucius) and the burbot (Lota lota). Burbot is night-active most of the year but pike hunts predominantly visually whenever there is enough light. Perch is a common day-active prey of pike and dark-active ruffe that of burbot. We predicted that besides recognizing the predator odors, the prey species would respond more strongly to odors of the predator which share the same activity pattern. Both perch and ruffe clearly responded to both predator fish odors. They decreased movements and erected the spiny dorsal fins. Fin erection showed clearly the black warning ornamentation in the fin and thus erected fin may function besides as mechanical defense also as warning ornament for an approaching predator. No rapid escape movements were generally observed. Both perch and ruffe responded more strongly to pike odor than to burbot. There were no clear differences in response between day and night. In conclusion, we were able to verify clear predator odor recognition by both prey fish. Both perch and ruffe responded to both predator odors and it seemed that pike forms a stronger threat for both prey species. Despite of diel activity differences both perch and ruffe used the same antipredatory strategies, but the day-active perch seemed to have a more flexible antipredatory behavior by responding more strongly to burbot threat during the night when burbot is active. [Copyright &y& Elsevier]

Invasive species often cause the decline of native prey or competitors. We highlight a contrasting example of the large-scale recovery of a native species and the concurrent decline and likely displacement of an established invasive competitor. Invasive American mink Mustela vison became widespread in the British Isles at the same time as native Eurasian otters Lutra lutra were declining as a result of water pollution. In common with other invasive predators, mink cause conservation problems for a range of native prey species, most notably water voles Arvicola terrestris. Recent trends in the distribution of native otters and invasive mink in north-east England were examined using a novel regression modelling approach to analyse presence/absence data from field surveys, corroborated by contemporary predator culling records. Between 1991 and 2002, the percentage of sites where mink signs were found decreased from 80% to 20%, while otter signs increased from 18% to 80%. Annual indices of mink captures on shooting estates increased between 1980 and 1996, but were followed by a decline thereafter. Indices of the incidence of native otters were significantly related to those indicating the decline or displacement of invasive mink. This large-scale field study is supportive of localized experimental evidence for the return of dominant, native otters being concurrent with the decline of the invasive alien mink. The recovery of a dominant native species may represent a reversal of the mesopredator release that allowed invasive mink to establish and may eventually serve to mitigate their impact on native prey species. [ABSTRACT FROM AUTHOR]

The North Sea ecosystem of the early 1980s differed substantially from that of the early 1990s. The current North Sea multispecies fisheries assessment models are parameterized by fish diet data sets that reflect both ecosystem states, as the stomachs were sampled in 1981 and 1991. In this study, multispecies virtual population analysis (MSVPA) was parameterized with either diet data set, leading to different model food webs, each representing the predator's diet selection behavior and spatiotemporal overlap with their prey in the two respective ecosystem states. The impact of these changes in predator preferences and spatiotemporal overlap on recruitment success and on stock developments could be demonstrated by using either stomach data set to estimate historic and future spawning stock biomass and recruitment trajectories. The observed changes in the food web mainly impacted the hindcasted recruitment trajectories, whereas spawning stock biomass estimates were quite robust. In the prediction runs, the differences in the survival rate of the recruits decided whether fish stocks of commercially important species (e.g., Gadus morhua, Merlangius merlangus) would recover or collapse in the near future. [ABSTRACT FROM AUTHOR]

1. Shelter is of major importance to many animals in providing protection against both the physical environment and potential predators. 2. We hypothesized that animals without shelter suffer metabolic costs associated with a need for increased vigilance and preparedness to escape attacks from predators or competitors. This possibility was tested by comparing the standard metabolic rates of inactive postdigestive juvenile Atlantic salmon, Salmo salar, held either with or without a shelter, which took the form of a semicircular ledge under which the fish could fit comfortably. 3. The ledges were semitransparent (so did not substantially reduce light levels) and provided no protection against the minimal water velocities in the testing arena. Nonetheless, absence of ledge shelter resulted in a 30% higher rate of oxygen consumption. 4. Fish without a ledge shelter typically positioned themselves against vertical walls of the observation arena, which presumably afforded the best available sheltering option, and adopted a significantly darker coloration (indicative of greater stress) than those under ledges. Fish with ledges rested outside and adjacent to rather than beneath the shelter. Therefore, it seems that awareness that a shelter is readily available, rather than the act of sheltering, results in reduced metabolism. 5. We conclude that the presence of appropriate shelter not only reduces the risk of predation but also provides a metabolic benefit to fish that is likely to have implications for growth performance and activity budgets. Standard metabolic rate can be a function of habitat structure. [ABSTRACT FROM AUTHOR]

Utilization of algae for decorating by the intertidal majid crab Tiarinia cornigera was examined by laboratory experiments in relation to availability of algae, presence of a predator, and the presence of conspecific and heterospecific crabs. Different availabilities of decorating materials had a positive correlation on decorating amount by juveniles, while the correlation was not so clear in subadults. The amount of decorating decreased with increasing density of conspecific crabs in the presence of a predator, but there was so clear relationship in the absence of a predator. The decrease in decorating under high density could be due to intraspecific aggression, because the superior crab, in fighting, was found to be decorated with more algae. Tiarinia cornigera was found to be superior to the co-occurring different majid species Micippa platipes in fighting. When T. cornigera and M. platipes were housed together, the former was decorated with more algae than the latter in the presence of a predator, but in the absence of a predator, the amount of algae was not different. Thus, presence of a predator may motivate intraspecific competition in T. cornigera as well as interspecific competition between T. cornigera and M. platipes for decorating materials. [ABSTRACT FROM AUTHOR]

Mathematical models examine the relationship between harvesting effort and stock size for a predator species when the prey adapts to the risk of predation. In one set of models, the prey can increase its own reproductive rate if it increases its vulnerability to the predator. In the second set of models, each of two prey species has fixed characteristics, but changes in the average characteristics within the prey trophic level occur via shifts in the relative abundance of the two species. In both models, the equilibrium predator population can increase as harvest of that species increases. In the case of two-prey models, the predator's equilibrium population always increases with an increased harvest rate if the two prey coexist and share a single resource. The predator's equilibrium population often decreases from its maximum size to zero over a very small range of harvest rates, once those rates become high enough. Because increased stock size is often used to justify increased harvest rates, this relationship poses a risk that harvest rate will increase to the point where the stock quickly collapses. The results are relevant to understanding changes in the population size of a species experiencing declining environmental conditions. [ABSTRACT FROM AUTHOR]

Parabroteas sarsi is a predaceous calanoid copepod that inhabits both shallow temporary fishless ponds and deep fish lakes of Patagonia and Antarctica. The aim of this study was to analyse the effect of P. sarsi on the plankton structure of a deep Andean lake (>100 m depth) and the zooplankton vertical distribution in order to asses a possible vertical refuge of the predatory copepod against visual fish predation. We tested the extent to which the trophic cascade effect of this predator propagates through the food web. We carried out a vertical sampling in Lake Rivadavia (Patagonia, Argentina) in order to assess zooplankton distribution. P. sarsi showed a vertical distribution towards deeper layers of the water column both at midday and at night, indicating that the copepod had an effective refuge against visual predation. Additionally, we carried out both field and laboratory experiments with the presence of P. sarsi. The predator was observed to affect significantly the survival of the copepod Boeckella michaelseni both in laboratory and field experiments. On the contrary, rotifers and adults of Daphnia cf. commutata were not substantially affected by the predator. B. michaelseni mouthparts revealed an omnivorous diet; therefore a broad phytoplanktonic size spectrum could be affected by this copepod. However, no cascade effect was observed due to the presence of P. sarsi despite the decrease of B. michaelseni abundance. [ABSTRACT FROM AUTHOR]

The objective of this study was to determine whether juvenile Chinook salmon Oncorhynchus tshawytscha are negatively influenced by the intraperitoneal implantation of acoustic transmitters. We evaluated swimming performance and predator avoidance of juvenile salmonids implanted with acoustic transmitters that weighed up to 6.7% of the fish's body weight in air. Critical swimming speeds (Ucrit) of tagged, sham-tagged (surgery but no tag), and control fish were measured in a respirometer to determine tag effects on swimming performance. Swimming performance was similar among treatment groups at 1-d and 21-d postsurgery intervals. Predator avoidance of fish implanted with active tags was evaluated to determine whether tagged fish were impaired by the operation of the tags or predators were attracted to the signals emitted from the tags. Predator avoidance was evaluated by comparing the proportion of each treatment group consumed (active tag, inactive tag, sham, and control) during exposure to piscivorous adult rainbow trout O. mykiss. Surgical implantation of acoustic tags in juvenile fall Chinook salmon did not significantly affect swimming performance. Implantation of acoustic transmitters (active and inactive) did not result in greater predation susceptibility in tagged fish than in untagged fish. [ABSTRACT FROM AUTHOR]

Experimental studies of the foraging ecology of drift-feeding fishes have been limited in scope because of the lack of systems for dispensing suitable prey items to a number of patches with complex and controlled spatio-temporal patterns of delivery rate. Here, tests are reported of a computer-controlled feeding system that performs this requirement with considerable flexibility. [ABSTRACT FROM AUTHOR]

Juvenile brown trout Salmo trutta from natural populations reacted to the presence of piscivorous brown trout by increasing the use of refuges. In contrast, second-generation hatchery fish and the offspring of wild fish raised under hatchery conditions were insensitive to predation risk. The diel pattern of activity also differed between wild and hatchery brown trout. Second-generation hatchery fish were predominantly active during daytime regardless of risk levels. Wild fish, however, showed a shift towards nocturnal activity in the presence of predators. These findings emphasize the potential role of domestication in weakening behavioural defences. They support the idea that the behavioural divergence between wild and domesticated individuals can arise from a process of direct or indirect selection on reduced responsiveness to predation risk, or as a lack of previous experience with predators. [ABSTRACT FROM AUTHOR]

Prior work has demonstrated that, following a predator inspection visit of their own, guppies prefer to associate with individuals who inspected a predator most closely. Based on this work, as well as studies of social learning in the context of mate choice, we predicted that male guppies that observed but did not participate in an inspection trial would subsequently choose to associate with the closer of two inspectors. Our experimental protocol consisted of three treatments: a control test in which an observer watched two fish consecutively, only one of which was exposed to a predator, a sequential test in which an observer watched two fish consecutively, both of which were exposed to the predator, and a social test in which an observer watched two fish inspect simultaneously. We found no preferences by the observer for either of the fish in any of the trials. Our results suggest that direct interaction is a critical component to the development of preferences in male guppies. We discuss our findings in light of game theoretical treatments of cooperation. [ABSTRACT FROM AUTHOR]

Examines the pattern and prevalence of predator damage on Atlantic salmon returning to a river system in Scotland. Types of damage; Factors causing the damage in salmon; Multispecies nature of interactions between salmon and their predators; Role of damage levels in assessing the impact of different predators on salmonid population dynamics.

Fish exhibit a wide variety of behavior, including swimming and schooling. Animating a school of fish is difficult because of the large number of fish and because a school of fish often swims in distinctive and coordinated patterns, particularly when they are attacked by a predator. Previous work in computer graphics has not provided satisfactory models to simulate the many distinctive interactions between a school of prey fish and their predator. In this paper, we present a fish school escape behavior model that can simulate 12 fish escape maneuvers identified in biological studies: compact, avoid, fast avoid, skitter, fountain, flash, ball, split, join, herd, vacuole, and hourglass. This behavior animation model can free an animator from dealing with the low‐level animations but instead controls the fish behavior on a higher level by modifying a state machine and a small set of system parameters. We present a fish school behavior model that can simulate 12 fish escape maneuvers identified in biological studies: compact, avoid, fast avoid, skitter, fountain, flash, ball, split, join, herd, vacuole, and hourglass and a state machine model to simulate the many distinctive interactions between a school of prey fish and their predator. [ABSTRACT FROM AUTHOR]

The article reports on a study by marine biologists at the Line Islands south of Hawaii, which showed that reef-dwelling fish at the two primeval atolls of Kingman and Palmyra, which are virtually untouched by humans, have short lives. The scientists found that huge predators, such as large jacks, sharks and snappers, dominate the ecosystem. About 85 percent of the estimated mass of all fish was found to be made up of predators. These findings suggest that intensive fishing in other waters has affected predator-prey dynamics.

The article reports on the findings of the study regarding the physiological effect of heave metals of fish sense such as those of salmon. The study has indicated that salmon lose their sense of smell, which is necessary to avoid predators, if there are even very low levels of copper in the water. Contrary to the belief that heavy metals such as copper and zinc were too low to affect aquatic organisms, the study proves that leeches in Lake Ontario were unable to smell their food, while fathead minnows could not perceive their own eggs and ate them instead of protecting them.