The Experts below are selected from a list of 324 Experts worldwide ranked by ideXlab platform
Marcus Sheaves - One of the best experts on this subject based on the ideXlab platform.
-
Overlooked small and juvenile Piscivores dominate shallow-water estuarine “refuges” in tropical Australia
Estuarine Coastal and Shelf Science, 2009Co-Authors: Ronald Baker, Marcus SheavesAbstract:A model was developed to estimate the relative impacts of different functional groups of Piscivores on the shallow-water estuarine nursery assemblage of tropical north-eastern Australia. Data on variability in the occurrence, number and type of fish in the diet of different Piscivores was combined with estimates of the abundance of each group. The model predicts that previously overlooked small and occasional or ‘minor’ Piscivores, such as sillaginids, ambassids, sparids and small juvenile carangids, inflict mortality on new recruits to shallow-water nursery habitats that is orders of magnitude greater than that imparted by more conspicuous larger Piscivores. Because of their high abundance, a shift in the diet of minor Piscivores to prey on new recruits results in a massive increase in the consumption of fish prey by the piscivore assemblage as a whole. Even if the evidence that minor Piscivores switch to target new recruits was rejected, the model shows that the highly abundant minor Piscivores must still exert a significant proportion of predation mortality experienced by recruiting fishes. As a broad functional group, minor Piscivores occur in most aquatic systems around the globe and are likely to play an important but largely overlooked role as predators that shape communities through predation on critical early life stages of other fishes.
-
Visual surveys reveal high densities of large Piscivores in shallow estuarine nurseries
Marine Ecology Progress Series, 2006Co-Authors: Ronald Baker, Marcus SheavesAbstract:Shallow estuarine nurseries are widely believed to provide juvenile fishes with refuge from predation due to the low numbers of piscivorous fishes. Observations during several years of fieldwork in northeastern Australia indicate that the assemblage of large (≥100 mm) piscivorous fishes within shallow tropical estuarine nurseries may have been considerably underestimated by previous sampling efforts. This study utilised visual surveys of shallow sandy shorelines in the lower reaches of estuaries to estimate the abundance of large Piscivores. Flathead (Platycephalus spp., Platycephalidae) were the only large Piscivores sighted within transects. A total of 296 flathead between 100 and 600 mm TL were observed in waters between 0.02 and 0.62 m deep. The density of flathead observed during the present study (0.04 ind. m -2 ) equated to 1 piscivore ≥100 mm TL for every 10.5 m of shoreline surveyed, and far exceeds density estimates for large Piscivores in shallow estuarine habitats elsewhere in the world. Furthermore, the estimated biomass of flathead (11.56 g m -2 ) was equivalent to comparable biomass estimates of entire fish assemblages from shal- low estuarine habitats in other parts of the world. The densities and depth distribution of these large Piscivores suggests that shallow water nurseries may not provide small fishes with the level of refuge from predation previously assumed.
-
redefining the piscivore assemblage of shallow estuarine nursery habitats
Marine Ecology Progress Series, 2005Co-Authors: Ronald Baker, Marcus SheavesAbstract:It is often suggested that there are few piscivorous fishes in shallow estuarine habitats worldwide, and consequently that these habitats are valuable as nurseries for juvenile fishes because they provide refuge from predation. Information on the dietary habits of predatory fishes from tropical estuaries remains limited to broad summaries that lack quantitative detail on the fish components of the diet. Consequently, it remains unclear which predators in shallow tropical estuarine nurseries target new recruits. To define the assemblage of piscivorous fishes relevant to the functioning of shallow water nurseries, we examined the diets of predatory fishes from shallow (<1.5 m) sandy habitats in the lower reaches of 17 tropical estuaries over 6 yr. In total, 51 taxa from 21 families fed on fish, and the piscivore assemblage included many taxa and size classes that have been previously overlooked. Piscivores ranged in size from 15 to 755 mm and the majority of taxa were piscivorous to some degree from sizes well below 100 mm. All of the smaller Piscivores (<100 mm) mainly preyed on small new recruits, while only some of the larger Piscivores did so. The taxonomic and functional diversity in the piscivore assemblage, and the fish community as a whole, highlights the complexity of the role of predation in the functioning of shallow tropical estuarine nurseries. Despite this complexity, it is apparent that predation has the potential to be a major structuring force on shallow water tropical estuarine fish communities.
Ronald Baker - One of the best experts on this subject based on the ideXlab platform.
-
Overlooked small and juvenile Piscivores dominate shallow-water estuarine “refuges” in tropical Australia
Estuarine Coastal and Shelf Science, 2009Co-Authors: Ronald Baker, Marcus SheavesAbstract:A model was developed to estimate the relative impacts of different functional groups of Piscivores on the shallow-water estuarine nursery assemblage of tropical north-eastern Australia. Data on variability in the occurrence, number and type of fish in the diet of different Piscivores was combined with estimates of the abundance of each group. The model predicts that previously overlooked small and occasional or ‘minor’ Piscivores, such as sillaginids, ambassids, sparids and small juvenile carangids, inflict mortality on new recruits to shallow-water nursery habitats that is orders of magnitude greater than that imparted by more conspicuous larger Piscivores. Because of their high abundance, a shift in the diet of minor Piscivores to prey on new recruits results in a massive increase in the consumption of fish prey by the piscivore assemblage as a whole. Even if the evidence that minor Piscivores switch to target new recruits was rejected, the model shows that the highly abundant minor Piscivores must still exert a significant proportion of predation mortality experienced by recruiting fishes. As a broad functional group, minor Piscivores occur in most aquatic systems around the globe and are likely to play an important but largely overlooked role as predators that shape communities through predation on critical early life stages of other fishes.
-
Visual surveys reveal high densities of large Piscivores in shallow estuarine nurseries
Marine Ecology Progress Series, 2006Co-Authors: Ronald Baker, Marcus SheavesAbstract:Shallow estuarine nurseries are widely believed to provide juvenile fishes with refuge from predation due to the low numbers of piscivorous fishes. Observations during several years of fieldwork in northeastern Australia indicate that the assemblage of large (≥100 mm) piscivorous fishes within shallow tropical estuarine nurseries may have been considerably underestimated by previous sampling efforts. This study utilised visual surveys of shallow sandy shorelines in the lower reaches of estuaries to estimate the abundance of large Piscivores. Flathead (Platycephalus spp., Platycephalidae) were the only large Piscivores sighted within transects. A total of 296 flathead between 100 and 600 mm TL were observed in waters between 0.02 and 0.62 m deep. The density of flathead observed during the present study (0.04 ind. m -2 ) equated to 1 piscivore ≥100 mm TL for every 10.5 m of shoreline surveyed, and far exceeds density estimates for large Piscivores in shallow estuarine habitats elsewhere in the world. Furthermore, the estimated biomass of flathead (11.56 g m -2 ) was equivalent to comparable biomass estimates of entire fish assemblages from shal- low estuarine habitats in other parts of the world. The densities and depth distribution of these large Piscivores suggests that shallow water nurseries may not provide small fishes with the level of refuge from predation previously assumed.
-
piscivory and the functioning of shallow tropical estuarine nursery grounds
2006Co-Authors: Ronald BakerAbstract:Shallow estuarine habitats around the world are considered important nurseries for a diverse range of fish and crustaceans of ecological and economic importance. One of the key features believed to contribute to the nursery value of these habitats is that they contain few predatory fishes, and thus provide juveniles with a refuge from predation. Despite its global application, there is very little direct evidence to support the shallowwater refuge paradigm. Within tropical estuarine systems our current knowledge of the role predation may play in structuring juvenile fish faunas and the functioning of shallow water nurseries is limited to broad summaries of the general dietary habits of a limited range of large piscivorous fishes. Small and occasional or ‘minor’ Piscivores, those predators which on average have a low occurrence of fish in their diet, have largely been ignored. Additionally, there is a lack of quantitative detail on dietary composition and on spatial and temporal patterns in the consumption of fish prey. Such details are needed to clarify the importance of predation on particularly vulnerable or critical life stages such as new recruits. Understanding the processes that drive systems such as estuarine nurseries is critical for the effective management and protection of these important systems into the future. The goal of this thesis is to gain a clearer insight into the role of piscivory within shallow tropical estuarine nursery grounds, and by doing so, to significantly enhance our understanding of the functioning of these important systems. To define the assemblage of piscivorous fishes relevant to the functioning of shallow water nurseries, the diets of almost 5000 predatory fishes collected over 6 years from shallow (<1.5m) sandy habitats in the lower reaches of 17 tropical estuaries were examined. The piscivore assemblage was diverse in terms of taxonomic composition, size structure and predation strategies. Fifty-one taxa were found to have fed on fish, and the piscivore assemblage included many taxa and size classes that have been previously overlooked. The majority of taxa were piscivorous to some degree from sizes well below 100 mm. All of the smaller Piscivores (<100 mm) preyed mainly on small new recruits. The larger more widely recognised Piscivores preyed on a broader range of fish prey, however few of these consumed significant numbers of small new recruits. The suggestion that shallow-waters in tropical estuaries contain few piscivorous fishes fails to recognise the potential importance of the abundant and diverse assemblage of small and minor Piscivores that utilise these habitats. The potential importance of previously overlooked occasional or minor Piscivores as predators of new recruits was explored by relating recruit abundance to predator diets, and by examining spatial and temporal patterns in the consumption of fish prey. The high spatial patchiness of new recruits made it difficult to correlate their abundance with their consumption by minor Piscivores. However, the low average occurrence of fish in the diet of minor Piscivores was a poor reflection of the spatial and temporal patterns in predation pressure by these on new recruits to shallow nursery habitats. Most of the time, minor Piscivores did not consume fish prey but occasionally a large proportion of them did so. When minor Piscivores consumed fish prey, they preyed mainly on small new recruits. Small new recruits were only occasionally abundant, with temporally patchy recruitment to shallow estuarine nurseries. Thus, the low average occurrence of fish in the diet of minor Piscivores suggests that while these predators may derive little of their nutritional requirements from fish prey, they may switch to heavily target new recruits. Given that many of the minor Piscivores are highly abundant and are themselves small juvenile fishes occupying the shallow nursery habitats, they are potentially major sources of mortality for fish recruiting to shallow estuarine nurseries. The abundance of large (≥100 mm TL) piscivorous fishes in shallow water habitats where they appeared to have previously been underestimated was determined by visual census. Although flathead (Platycephalus spp., Platycephalidae) were the only large Piscivores sighted within the transects, the density observed (0.04 ind. m-2) equated to one piscivore for every 10.5 m of shoreline surveyed. This exceeds density estimates for large Piscivores in shallow estuarine habitats elsewhere in the world by orders of magnitude. Furthermore, the estimated biomass of flathead (11.56 g m-2) was equivalent to comparable biomass estimates of entire fish assemblages from shallow estuarine habitats in other parts of the world. The densities and depth distribution of these large Piscivores, combined with the diverse and abundant assemblage of small and occasional Piscivores, suggests that shallow water nurseries may not provide small fishes with the level of refuge from predation previously assumed. The hypothesis that predation pressure on small fishes is lower in shallow waters than in adjacent deeper water was directly tested by a series of tethering experiments. Over 6 months 17 replicate experimental trials were conducted, deploying a total of 183 tethered fish prey across a depth gradient (0.2 – 3 m) in the lower reaches of a tropical estuary. Despite the clear and consistent patterns found in previous studies elsewhere in the world, there was no evidence of lower predation pressure in the shallow relative to the adjacent deeper waters in the tropical estuaries examined. Given the complexity and diversity of the piscivore assemblage in these estuaries it is hardly surprising that no clear patterns emerged. The findings suggest that the shallow-water refuge paradigm may be too simplistic for diverse and complex tropical estuarine nursery grounds. Finally, a model was constructed to estimate the relative importance of different members of the diverse shallow water piscivore assemblage within tropical estuaries. Data on variability in the occurrence, number and type of fish in the diet of different Piscivores was combined with estimates of the abundance of each group gained from block-net sampling an intertidal marsh over 2 years. The model predicts that previously overlooked small and occasional Piscivores have the potential to have orders of magnitude greater impacts than more conspicuous larger Piscivores on new recruits utilising shallow tropical estuarine habitats as nurseries. Because of their sheer abundance, a switch by the minor Piscivores to target new recruits results in a massive increase in the consumption of fish prey by the piscivore assemblage. As a broad functional group, minor Piscivores occur in many systems around the globe, and are likely to play important roles in these systems as predators that shape communities by targeting the critical early life stages of other fishes. This study revealed a diverse assemblage of Piscivores with the potential to cause significant mortality on new recruits to shallow water habitats. Many of the Piscivores with the greatest potential to shape community structure through predation on new recruits are themselves small juvenile fishes utilising shallow water habitats as nurseries. In contrast to the idea that shallow waters provide refuge from predation, heavy predation on new recruits entering the nursery may represent a significant input of energy and nutrients from coastal waters to estuarine systems and may act to enhance the productivity and hence the nursery ground value of these systems.
-
redefining the piscivore assemblage of shallow estuarine nursery habitats
Marine Ecology Progress Series, 2005Co-Authors: Ronald Baker, Marcus SheavesAbstract:It is often suggested that there are few piscivorous fishes in shallow estuarine habitats worldwide, and consequently that these habitats are valuable as nurseries for juvenile fishes because they provide refuge from predation. Information on the dietary habits of predatory fishes from tropical estuaries remains limited to broad summaries that lack quantitative detail on the fish components of the diet. Consequently, it remains unclear which predators in shallow tropical estuarine nurseries target new recruits. To define the assemblage of piscivorous fishes relevant to the functioning of shallow water nurseries, we examined the diets of predatory fishes from shallow (<1.5 m) sandy habitats in the lower reaches of 17 tropical estuaries over 6 yr. In total, 51 taxa from 21 families fed on fish, and the piscivore assemblage included many taxa and size classes that have been previously overlooked. Piscivores ranged in size from 15 to 755 mm and the majority of taxa were piscivorous to some degree from sizes well below 100 mm. All of the smaller Piscivores (<100 mm) mainly preyed on small new recruits, while only some of the larger Piscivores did so. The taxonomic and functional diversity in the piscivore assemblage, and the fish community as a whole, highlights the complexity of the role of predation in the functioning of shallow tropical estuarine nurseries. Despite this complexity, it is apparent that predation has the potential to be a major structuring force on shallow water tropical estuarine fish communities.
Shaun K Wilson - One of the best experts on this subject based on the ideXlab platform.
-
exploitation and habitat degradation as agents of change within coral reef fish communities
Global Change Biology, 2008Co-Authors: Nicholas Polunin, Shaun K Wilson, R P Fisher, Nicholas A J Graham, Nicholas K Dulvy, Rachel A Turner, A Cakacaka, Stephen P RushtonAbstract:Over-exploitation and habitat degradation are the two major drivers of global environmental change and are responsible for local extinctions and declining ecosystem services. Here we compare the top-down effect of exploitation by fishing with the bottom-up influence of habitat loss on fish communities in the most diverse of ecological systems, coral reefs. Using a combination of multivariate techniques and path analyses, we illustrate that the relative importance of coral cover and fishing in controlling fish abundance on remote Fijian reefs varies between species and functional groups. A decline in branching Acropora coral is strongly associated with a decline in abundance of coral-feeding species, and a decrease in coral-associated habitat complexity, which has indirectly contributed to reduced abundance of small-bodied damselfish. In contrast, reduced fishing pressure, brought about by declining human populations and a shift to alternate livelihoods, is associated with increased abundance of some Piscivores and fisheries target species. However, availability of prey is controlled by coral-associated habitat complexity and appears to be a more important driver of total piscivore abundance compared with fishing pressure. Effects of both fishing and coral loss are stronger on individual species than functional groups, as variation in the relative importance of fishing or coral loss among species within the same functional group attenuated the impact of either of these potential drivers at the functional level. Overall, fishing continues to have an influence on Fijian fish communities; however, habitat loss is currently the overriding agent of change. The importance of coral loss mediated by climate change is expected to have an increasing contribution to fish community dynamics, particularly in remote locations or where the influence of fishing is waning.
Zhengwen Liu - One of the best experts on this subject based on the ideXlab platform.
-
submerged macrophytes facilitate dominance of omnivorous fish in a subtropical shallow lake implications for lake restoration
Hydrobiologia, 2016Co-Authors: Zhengwen Liu, Wei Zhen, Baohua Guan, Feizhou Chen, Ping Zhong, Franco Teixeira De Mello, Erik JeppesenAbstract:Biomanipulation based on removal of coarse fish, piscivorous fish stocking and sometimes also planting of submerged macrophytes has been used to restore temperate eutrophic shallow lakes. However, in warmer lakes, omnivorous fish are more abundant and apparently less well controlled by the Piscivores. We investigated the food web structure and energy pathways of fish in the restored part of subtropical Lake Wuli, China, using gut contents analysis (GCA) and the IsoSource model based on stable isotope analysis (SIA) data. We found that omnivores dominated the fish community in terms of numbers. GCA showed that cyclopoid copepods constituted the main food item for the planktivores, while all adult omnivorous fish fed mainly on macrophytes. The IsoSource SIA model supported these results. Furthermore, Piscivores consumed shrimps rather than juvenile omnivores, and the SIA analysis revealed no trophic links between Piscivores and adult omnivores or zooplanktivores. We conclude that macrophytes constituted an important food item for omnivores, potentially promoting population growth of omnivores as control by Piscivores was weak. This may yield a high predation pressure on both zooplankton and on macrophytes, possibly preventing the establishment of a stable macrophyte state following restoration of eutrophic lakes unless the fish density is regularly controlled.
Stephen P Rushton - One of the best experts on this subject based on the ideXlab platform.
-
exploitation and habitat degradation as agents of change within coral reef fish communities
Global Change Biology, 2008Co-Authors: Nicholas Polunin, Shaun K Wilson, R P Fisher, Nicholas A J Graham, Nicholas K Dulvy, Rachel A Turner, A Cakacaka, Stephen P RushtonAbstract:Over-exploitation and habitat degradation are the two major drivers of global environmental change and are responsible for local extinctions and declining ecosystem services. Here we compare the top-down effect of exploitation by fishing with the bottom-up influence of habitat loss on fish communities in the most diverse of ecological systems, coral reefs. Using a combination of multivariate techniques and path analyses, we illustrate that the relative importance of coral cover and fishing in controlling fish abundance on remote Fijian reefs varies between species and functional groups. A decline in branching Acropora coral is strongly associated with a decline in abundance of coral-feeding species, and a decrease in coral-associated habitat complexity, which has indirectly contributed to reduced abundance of small-bodied damselfish. In contrast, reduced fishing pressure, brought about by declining human populations and a shift to alternate livelihoods, is associated with increased abundance of some Piscivores and fisheries target species. However, availability of prey is controlled by coral-associated habitat complexity and appears to be a more important driver of total piscivore abundance compared with fishing pressure. Effects of both fishing and coral loss are stronger on individual species than functional groups, as variation in the relative importance of fishing or coral loss among species within the same functional group attenuated the impact of either of these potential drivers at the functional level. Overall, fishing continues to have an influence on Fijian fish communities; however, habitat loss is currently the overriding agent of change. The importance of coral loss mediated by climate change is expected to have an increasing contribution to fish community dynamics, particularly in remote locations or where the influence of fishing is waning.
