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Sawfishes are among the most threatened families of marine fishes and are susceptible to incidental capture in net fisheries. Since bycatch reduction devices currently used in trawl fisheries are not effective at reducing sawfish catches, new methods to minimise sawfish bycatch are needed. Ideally, these should affect sawfish behaviour and prevent contact with the fishing gear. We tested the effects of electric fields on sawfish behaviour to assess the potential of electric pulses in mitigating sawfish bycatch. Experiments were conducted in a tank where 2 electrodes were suspended in the water column, connected to a pulse generator, and placed across the swimming path of sawfish. Two largetooth sawfish Pristis pristis were tested in control conditions, in the presence of a baseline pulse, and of 5 variations of that pulse where 1 parameter (polarity, voltage, frequency, pulse shape, pulse duration) was altered at a time. Conditional inference trees were used to identify the effects of various parameters (e.g. treatment, individual) on reaction type, reaction distance, twitching presence and duration, and inter-approach times. Sawfish reacted to electric fields, but reaction distances were small (typically

Accuracy in representing, communicating and reporting science is critical to the translation of science into knowledge. Any lack of accuracy degrades the quality and reliability of consequent decisions. One common cause of inaccuracy is the use of superseded paradigmatic concepts with a lack of careful validation. This leads to evidentiary dissonance (an apparent abundance of evidence with little basis in actual reported scientific findings). We illustrate the nature and consequences of evidentiary dissonance using the example of estimates of the value of mangroves to fisheries, which are key motivators of decision-making around land-use activities in mangroves systems, mangrove restoration and disturbance offset initiatives. Causes include the use of inappropriate or inaccurate data and inadequate support for reasoning used to develop estimates of fisheries value. Evidentiary dissonance in linking estimates to scientific understanding has produced a citable and cited body of work with tenuous foundations in current ecological understanding, and a body of literature that is likely to lead to unrealistic expectations, misdirected and wasted resources, and perverse management outcomes.

The known distribution of manta rays in Australian waters is patchy, with records primarily centred around tourism hotspots. We collated 11,614 records of Mobula alfredi from photo-ID databases (n = 10,715), aerial surveys (n = 378) and online reports (n = 521). The study confirms an uninterrupted coastal distribution from north of 26 degrees S and 31 degrees S on the west and east coasts, respectively. More southerly M. alfredi records relate to warm-water events with a southernmost extent at 34 degrees S. Coastal sightings of Mobula birostris were rare (n = 32), likely reflecting a preference for offshore waters, but encompass a wider latitudinal extent than M. alfredi of 10-40 degrees S.

The presence of lipids and urea in elasmobranch tissues can affect carbon (δ¹³C) and nitrogen (δ¹⁵N) stable isotope values, introducing bias in food web interpretations. Information on how lipids and urea affect δ¹³C/δ¹⁵N is only available for < 5% of similar to 1150 described elasmobranch species and results are highly variable among existing studies. Here, we investigate the effects of lipid and urea extraction on δ¹³C, δ¹⁵N, and C:N ratios in muscle and blood plasma of two batoids (Pastinachus ater and Himantura australis) and examine the influence of lipid/urea extraction on isotopic niche size and overlap. Lipid extraction (LE) did not affect δ¹³C, δ¹⁵N, or C:N ratios, suggesting low lipid content. Urea extraction (UE), however, increased δ¹⁵N and C:N in muscle. The similar to 1 parts per thousand δ¹⁵N increase represents a shift of similar to 0.5 trophic levels relative to bulk samples, highlighting the importance of UE to accurately assess trophic positions. Although there was no effect of any treatment on niche size, the probability of P. ater occurring within the niche of H. australis increased following UE. Overall, results suggest that urea should be removed from muscle prior to analysis, but LE is not required. Given the interspecific variability in the effects of lipid/urea on elasmobranch δ¹³C/δ¹⁵N, more studies are needed to assess the effects of lipid and urea on a broader range of species to produce a generalized understanding. Where no species-specific data are available, we recommend pilot samples are analyzed to determine if LE is needed prior to preparation of the overall sample set.

REPLYING TO H. Murua et al. Nature https://doi.org/10.1038/s41586-021-03396-4 (2021) Our previously published paper1 provided global fine-scale spatiotemporal estimates (1° × 1°; monthly) of overlap and fishing exposure risk (FEI) between satellite-tracked shark space use and automatic identification system (AIS) longline fishing effort. We did not assess shark mortality directly, but in addition to replying to the Comment by Murua et al.2, we confirm—using regression analysis of spatially matched data—that fishing-induced pelagic shark mortality (catch per unit effort (CPUE)) is greater where FEI is higher. We focused on assessing shark horizontal spatiotemporal overlap and exposure risk with fisheries because spatial overlap is a major driver of fishing capture susceptibility and previous shark ecological risk assessments (ERAs) assumed a homogenous shark density within species-range distributions3,4,5 or used coarse-scale modelled occurrence data, rather than more ecologically realistic risk estimates in heterogeneous habitats that were selected by sharks over time. Furthermore, our shark spatial exposure risk implicitly accounts for other susceptibility factors with equal or similar probabilities to those commonly used in shark ERAs3,5.

REPLYING TO A. V. Harry & J. M. Braccini Nature https://doi.org/10.1038/s41586-021-03463-w (2021) Our global analysis1 estimated the overlap and fishing exposure risk (FEI) using the space use of satellite-tracked sharks and longline fishing effort monitored by the automatic identification system (AIS). In the accompanying Comment, Harry and Braccini2 draw attention to two localized shark–longline vessel overlap hotspots in Australian waters, stating that 47 fishing vessels were misclassified as longline and purse seine vessels in the Global Fishing Watch (GFW)3 2012–2016 AIS fishing effort data product that we used. This, they propose2, results in misidentifications that highlight fishing exposure hotspots that are subject to an unexpected level of sensitivity in the analysis and they suggest that misidentifications could broadly affect the calculations of fishing exposure and the central conclusions of our study1. We acknowledged in our previously published paper1 that gear reclassifications were likely to occur for a small percentage of the more than 70,000 vessels studied, however, here we demonstrate that even using much larger numbers of vessel reclassifications than those proposed by Harry and Braccini2, the central results and conclusions of our paper1 do not change.

Non-lethal methods for deriving age estimates from species of conservation significance or those supporting catch-and-release sport fisheries can assist in their sustainable management. In this study we tested if dorsal spines provide equivalent age estimates to otoliths for two species of large tropical snappers (Lutjanus goldiei and L. fuscescens, Lutjanidae) that support a catch-and-release sport fishery in remote parts of Papua New Guinea. Comparison of putative age estimates from sections taken at the base, mid and tip of the dorsal spine revealed that the base sections provided the most similar ages to otoliths, while mid and tip sections underestimated otolith age, especially for older individuals. Dorsal spine base-sections provided equivalent age estimates to otoliths for both species across the full range of ages examined (up to 17 for L. goldiei, and 14 for L. fuscescens). Like other lutjanids, these species show a wide range in length-at-age. This means that small fish are not necessarily young fish, and recruitment could potentially fail for more than a decade before anglers or guides notice a lack of smaller fish in their captures, by which time the opportunity to identify and reverse the cause of recruitment failure may have passed. Dorsal spines provide an effective and minimally-harmful means of monitoring population age structure to ensure ongoing recruitment to the fishery, and offer the opportunity for engagement of anglers, guides, and community members in the sustainable management of this fishery.

Understanding the range of habitats needed to complete life-cycles is essential for the effective conservation and management of species. We combined otolith microchemistry, acoustic tracking, and underwater video to determine patterns of seascape use by an assemblage of tropical snappers, including two little-known species of high economic importance, the Papuan black bass (Lutjanus goldiei) and spot-tail snapper (Lutjanus fuscescens). All species appeared to have marine larval phases, and post-settlement distributions broadly overlapped across the coastal seascape. However, species and life stages were distributed along a gradient from freshwater to coastal waters. Lutjanus fuscescens is primarily a freshwater species post-settlement, but larger individuals move into brackish estuaries and even coastal waters at times. Lutjanus goldiei appear to recruit to low salinity or freshwater areas. Larger individuals tend to have home-ranges centred on brackish estuaries, while making regular movements into both coastal waters and freshwater. Lutjanus argentimaculatus also ranged widely from fresh to coastal waters, but juveniles were most common in the saline parts of estuaries. Ontogenetic shifts by L. argentimaculatus were similar to those reported from other regions, despite vast differences in the spatial proximity of seascape components. The wide-ranging seascape movements of our target species highlight the importance of maintaining effective connectivity between marine, estuarine, and freshwaters in the region to maintain ecosystem function and support sustainable sport fisheries. The combined approaches resolved some of the ambiguities of individual methods and provide a powerful approach to understanding seascape use by coastal fishes.

Wildlife tourism is a growing industry, with significant conservation and socio-economic benefits. Concerns have however been raised about the possible impacts of this industry on the long-term behaviour, health and fitness of the animal species tourists come to see (the target species), particularly when those species are regularly fed to improve the tourism experience. Information on the contribution of food rewards to the diet of the target species at feeding sites is critical to assess the dependency on handouts and to identify possible health/fitness problems that might be associated, if handouts become the main part of animals' diets. Here, we use stable isotopes (δ13C and δ15N) to evaluate the importance of handouts for a marine predator, the bull shark (Carcharhinus leucas), at a feeding site (Fiji) where shark feeds occur 5 days/week and sharks (up to 75 individuals/dive) are fed ~200 kg of tuna heads/day. There was no evidence of incorporation of food provided, even for individuals that regularly consume food rewards. Results, when combined with those from previous studies on bull shark movements and feeding rates at our study site, show that current levels of provisioning likely have no long-term impacts on bull shark diet or behaviour. This study also demonstrates the applicability of stable isotope analysis to assess and monitor the contribution of food rewards to wildlife, and highlights the benefits of using multi-sources of information to gain a holistic understanding of the effects of provisioning predators.

1. Knowledge of trophic structure is important to understand sources and pathways of energy resources in community ecology and to identify determinants of ecosystem changes. Yet, little is known from rivers of African savanna receiving large inputs of terrestrial organic matter and nutrients by large mammalian herbivores. 2. We used Stable Isotope (δ13C and δ15N) Bayesian Ellipses in R (SIBER) and Layman's community‐wide metrics to describe seasonal variation in trophic niches and trophic structures in midorder river reaches in the Mara River (Kenya) that differed in environmental conditions (agricultural vs. forested) and amounts of organic matter and nutrients (low vs. high inputs by livestock and hippopotami, Hippopotamus amphibius). These analyses were supplemented with data on the trophic diversity of macroinvertebrate functional feeding groups (FFGs) and fish trophic guilds. 3. The δ13C and δ15N of basal resources and consumers differed between sites and changed with seasons. Sites in agricultural areas that were utilised by livestock and a site with hippopotami had higher δ13C than the forested site due to the presence of C4 carbon from egestion and excretion by the grazers. 4. The forested site recorded the most taxon‐rich and trophic‐diverse invertebrate community, suggesting both autochthonous and allochthonous sources of energy were available. Agricultural sites and the site with hippopotami recorded high abundances of collector taxa in response to large inputs of organic matter. Fish trophic guilds were less diverse and were dominated by insectivores. 5. The food web at the forested site had the widest trophic niche size and highest isotopic trophic diversity compared to sites in areas with large mammalian herbivores. Invertebrate and fish trophic niche sizes changed according to food resources varying with space and time. Invertebrates had higher δ13C values during the dry season. In contrast, fish showed higher δ13C values during the wet season, and trophic niche sizes were constricted and considerably overlapping, suggesting feeding on a narrow range of food sources with high trophic redundancy. 6. This study showed that increased terrestrial organic matter by large mammalian herbivores affected trophic diversity and niche sizes for aquatic consumers in rivers draining the African savanna. Linking the density of terrestrial large mammalian herbivores to aquatic ecosystem structure and function could help manage their populations sustainably.

Predators play a crucial role in the structure and function of ecosystems. However, the magnitude of this role is often unclear, particularly for large marine predators, as predation rates are difficult to measure directly. If relevant biotic and abiotic parameters can be obtained, then bioenergetics modelling offers an alternative approach to estimating predation rates, and can provide new insights into ecological processes. We integrate demographic and ecological data for a marine apex predator, the broadnose sevengill shark Notorynchus cepedianus, with energetics data from the literature, to construct a bioenergetics model to quantify predation rates on key fisheries species in Norfolk Bay, Australia. We account for the uncertainty in model parameters by incorporating parameter confidence through Monte Carlo simulations and running alternative variants of the model. Model and parameter variants provide alternative estimates of predation rates. Our simplest model estimates that ca. 1130 ± 137 N. cepedianus individuals consume 11,379 (95% CI: 11,111–11,648) gummy sharks Mustelus antarcticus (~21 tonnes) over a 36-week period in Norfolk Bay, which represents a considerable contribution to total predation mortality on this key fishery species. This study demonstrates how the integration of ecology and fisheries science can provide information for ecosystem and fisheries management.

Tiger sharks were sampled off the western (Ningaloo Reef, Shark Bay) and eastern (the Great Barrier Reef; GBR, Queensland and New South Wales; NSW) coastlines of Australia. Multiple tissues were collected from each shark to investigate the effects of location, size and sex of sharks on δ13C and δ15N stable isotopes among these locations. Isotopic composition of sharks sampled in reef and seagrass habitats (Shark Bay, GBR) reflected seagrass-based food-webs, whereas at Ningaloo Reef analysis revealed a dietary transition between pelagic and seagrass food-webs. In temperate habitats off southern Queensland and NSW coasts, shark diets relied on pelagic food-webs. Tiger sharks occupied roles at the top of food-webs at Shark Bay and on the GBR, but not at Ningaloo Reef or off the coast of NSW. Composition of δ13C in tissues was influenced by body size and sex of sharks, in addition to residency and diet stability. This variability in stable isotopic composition of tissues is likely to be a result of adaptive foraging strategies that allow these sharks to exploit multiple shelf and offshore habitats. The trophic role of tiger sharks is therefore both context- and habitat-dependent, consistent with a generalist, opportunistic diet at the population level.

Habitat valuation can provide an objective basis for the prioritisation of conservation and restoration actions. The attribution of fisheries production to particular habitat units is an important measure of value, but is difficult to estimate. Using the case study of habitat use by juvenile banana prawns in a tropical estuary, we assessed the potential to produce valid value estimates at two spatio-conceptual scales: estuary reach and whole estuary. Additionally, we also explore the potential to produce meaningful value estimates at the scale of whole estuary contribution to the offshore fisheries stock. A diversity of potential and actual sources of error and logical problems means that quantification at any scale is at best of uncertain validity and produces estimates that are likely to produce unreliable results if treated as quantitative inputs to production models. Estimates for the whole estuary were the most viable, although still requiring substantial assumptions that may or may not be reasonable in particular situations. Estimates for individual habitats required the unreasonable assumption of limited prawn movement, while estimates of contribution of an estuary to the fishery required difficult-to-obtain and usually unavailable information. Because low occupancy habitats can have trophic value, we also used stable isotope analysis to assess the importance of mangroves and saltmarshes to prawn nutrition. No particular habitat was of critical trophic importance, again suggesting that the habitat-production link is most usefully assessed at the whole-of-estuary scale. While valuable and required to support targeted ecosystem management and protection and restoration efforts, valid estimates of the contribution of particular units to fisheries are likely to be unachievable in many situations.

The known distribution of manta rays in Australian waters is patchy, with records primarily centred around tourism hotspots. We collated 11,614 records of Mobula alfredi from photo-ID databases (n = 10,715), aerial surveys (n = 378) and online reports (n = 521). The study confirms an uninterrupted coastal distribution from north of 26°S and 31°S on the west and east coasts, respectively. More southerly M. alfredi records relate to warm-water events with a southernmost extent at 34°S. Coastal sightings of Mobula birostris were rare (n = 32), likely reflecting a preference for offshore waters, but encompass a wider latitudinal extent than M. alfredi of 10-40°S.

1. Essential habitats are areas required to support specific functions, such as providing foraging grounds, shelter or used for reproductive purposes. For mobile aquatic species that move throughout numerous components of the seascape, identifying essential habitats within a species' broader distribution range is crucial to under-standing their ecology and provide vital information needed to underpin effective conservation and management (e.g. the implementation of protected areas). 2. In Tasmania (Australia), a number of coastal habitats have been declared shark refuge areas (SRAs), where fishing for elasmobranchs (sharks, rays and skates) is prohibited. 3. Chimaeras are relatives of elasmobranchs (class Chondrichthyes) and share traits that predispose many elasmobranch species to be vulnerable to overfishing (e.g. slow growth rates and low reproductive output). However, fishing for elephantfish Callorhinchus milii (the chimaera species found in coastal Tasmania) is still permitted in SRAs. 4. Here, a combination of acoustic tracking, catch data and reproductive information was used to determine the significance of the SRA coastal habitats for C. milii. 5. Results suggest that these areas are essential habitats for reproduction and likely important for other purposes, such as foraging. 6. Given that a key strategy in managing fish stocks is protecting areas important for reproduction, and the importance of these coastal areas of Tasmania for C. mili reproductive purposes, we recommend including C. mili in current SRAs, and decreeing these areas as chondrichthyan refuge areas. Fil: Barnett, Adam. Deakin University; Australia. James Cook University; Australia Fil: McAllister, Jamie D.. Institute For Marine And Antarctic Studies; Australia Fil: Semmens, Jayson. Institute For Marine And Antarctic Studies; Australia Fil: Abrantes, Kátya. James Cook University; Australia Fil: Sheaves, Marcus. James Cook University; Australia Fil: Awruch, Cynthia Andrea. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Centro Nacional Patagónico. Centro para el Estudio de Sistemas Marinos; Argentina. University of Tasmania; Australia

Quantification of key pathways sustaining ecosystem function is critical for underpinning informed decisions on development approvals, zoning and offsets, ecosystem restoration and for meaningful environmental assessments and monitoring. To develop a more quantitative understanding of the importance and variation in food webs and nutrient flows in tropical estuaries, we investigated the spatio-temporal distribution of biomass of fish across 28 mangrove-lined estuaries in tropical Australia. We evaluated the extent to which nekton biomass in tropical estuaries responded to spatial and temporal factors and to trophic identity. Biomass was dominated by two trophic groups, planktivores and macrobenthos feeders. Contributions by other trophic groups, such as detritivores and microbenthos feeders, were more variable. Total biomass and the biomass of all major trophic groups were concentrated in downstream reaches of estuaries. The consistent concentration of biomass downstream, and spatio-temporal differences in the contributions by the different trophic groups, indicates substantial differences in food web structure, differences in the contributions from different sources of nutrition and probably unequal flow of productivity into higher levels of the food web in different parts of the estuary. In turn, this suggests substantial qualitative and quantitative differences in ecosystem-supporting processes in different estuary reaches.

The Niugini black bass, Lutjanus goldiei Bloch, is an estuarine and freshwater fish species endemic to New Guinea and the surrounding islands. It is the focus of a growing sport fishing industry that has the potential to provide long-standing benefits to local people. Plantation agriculture, mining and logging are expanding in many catchments where L. goldiei is found, creating the potential for these industries to impact on L. goldiei and the environments it relies on. Understanding of the current status of the species, including its biology, ecology and distribution, is essential for its sustainable management. However, very little is known about the species. Here, the published literature, unpublished data and interviews with anglers and fisheries officers were used to draw together existing knowledge, assess the current conservation status, make a preliminary analysis of threats and identify key areas for research that will support the sustainable development of the L. goldiei sport fishing industry while fostering positive conservation outcomes.

Effective ocean management and the conservation of highly migratory species depend on resolving the overlap between animal movements and distributions, and fishing effort. However, this information is lacking at a global scale. Here we show, using a big-data approach that combines satellite-tracked movements of pelagic sharks and global fishing fleets, that 24% of the mean monthly space used by sharks falls under the footprint of pelagic longline fisheries. Space-use hotspots of commercially valuable sharks and of internationally protected species had the highest overlap with longlines (up to 76% and 64%, respectively), and were also associated with significant increases in fishing effort. We conclude that pelagic sharks have limited spatial refuge from current levels of fishing effort in marine areas beyond national jurisdictions (the high seas). Our results demonstrate an urgent need for conservation and management measures at high-seas hotspots of shark space use, and highlight the potential of simultaneous satellite surveillance of megafauna and fishers as a tool for near-real-time, dynamic management., Data analysis was funded in part by the Marine Biological Association (MBA) and the UK Natural Environment Research Council (NERC) (NE/R00997X/1) (to D.W.S.) with additional research support from the Save Our Seas Foundation and the NERC Oceans 2025 Strategic Research Programme, in which D.W.S. was a principal investigator. D.W.S. was supported by an MBA Senior Research Fellowship, N.Q. by European Regional Development Fund (FEDER) via the Programa Operacional Competitividade e Internacionalização (COMPETE), National Funds via Fundação para a Ciência e a Tecnologia (FCT) under PTDC/MAR/100345/2008 and COMPETE FCOMP-01-0124-FEDER-010580 (to N.Q. and D.W.S.), and Norte Portugal Regional Operational Programme (NORTE 2020) under the PORTUGAL 2020 Partnership Agreement through the European Regional Development Fund (ERDF) in project MarInfo (NORTE-01-0145-FEDER-000031). Additional support was provided by an FCT Investigator Fellowship IF/01611/2013 (N.Q.), FCT Doctoral Fellowship PD/BD/52603/2014 (M.V.), PTDC/MAR-BIO/4458/2012, Xunta de Galicia - Isabel Barreto Program 2009-2012 (G.M.), Australian Research Council (ARC) grant DE170100841 and operational funds from the Australian Institute for Marine Science (AIMS) (both to A.M.M.S.).

Habitat valuation can provide an objective basis for the prioritisation of conservation and restoration actions. The attribution of fisheries production to particular habitat units is an important measure of value, but is difficult to estimate. Using the case study of habitat use by juvenile banana prawns in a tropical estuary, we assessed the potential to produce valid value estimates at two spatio-conceptual scales: estuary reach and whole estuary. Additionally, we also explore the potential to produce meaningful value estimates at the scale of whole estuary contribution to the offshore fisheries stock. A diversity of potential and actual sources of error and logical problems means that quantification at any scale is at best of uncertain validity and produces estimates that are likely to produce unreliable results if treated as quantitative inputs to production models. Estimates for the whole estuary were the most viable, although still requiring substantial assumptions that may or may not be reasonable in particular situations. Estimates for individual habitats required the unreasonable assumption of limited prawn movement, while estimates of contribution of an estuary to the fishery required difficult-to-obtain and usually unavailable information. Because low occupancy habitats can have trophic value, we also used stable isotope analysis to assess the importance of mangroves and saltmarshes to prawn nutrition. No particular habitat was of critical trophic importance, again suggesting that the habitat-production link is most usefully assessed at the whole-of-estuary scale. While valuable and required to support targeted ecosystem management and protection and restoration efforts, valid estimates of the contribution of particular units to fisheries are likely to be unachievable in many situations.

Ecotourism ventures in developing countries are often among the few alternatives for enhancing sustainable livelihoods without altering traditional ways of life. The best way forward is to continually develop and implement best practice guidelines and, in particular, to flexibly develop them to suit individual cases. We conduct a multidisciplinary assessment of best practice guidelines required to develop and sustain sportfishing tourism in developing countries, while enhancing local livelihoods and promoting environmental stewardship. In general, best practice guidelines should be developed around a sustainable livelihood framework that includes short-term coping mechanisms and longer-term capacity building. Sportfishing development that conforms to ecological and socially orientated criteria, founded on site-specific research that captures local environmental and social complexities, has the potential to provide mutual benefits to tourists and local people, fuelling community development and enhancing the cultural experience of tourists. Best practice guidelines for sportfishing that do not address these dimensions are unlikely to result in a viable industry. Given the current interest and growth of sportfishing in developing countries, the proposed guidelines can help a range of end users manage, conserve and maximize livelihood benefits from their fishery.

The tropical savannas of Africa have witnessed a dramatic reduction in native large mammalian herbivore populations. The consequences of these changes for terrestrial-aquatic food-web linkages are poorly documented. We used natural abundances of stable carbon and nitrogen isotopes (δ¹³C, δ¹⁵N) to determine spatial and temporal patterns in the importance of herbivore-mediated subsidies for consumers in the Mara River, Kenya. Potential primary producers (terrestrial C3 and C4 producers and periphyton) and consumers (invertebrates and fish) were collected during dry and wet seasons from different sites along the river, representing a gradient from forested highlands to natural savanna grasslands with high herbivore densities across mixed agricultural and livestock-dominated zones. Bayesian mixing models were used to estimate the relative contributions of terrestrial and algal sources of organic carbon supporting consumer trophic groups. Organic carbon sources differed for consumer groups and sites and with season. Overall, periphyton was the major energy source for most consumer groups during the dry season, but with wide 95% confidence intervals. During the wet season, the importance of terrestrial-derived carbon for consumers increased. The importance of C3 producers declined from 40 and 41% at the forested upper reaches to 20 and 8% at river reaches receiving hippo inputs during the dry and wet seasons, respectively. The reciprocal increase in the importance of C4 producers was higher than expected based on areal cover of riparian vegetation that was mainly C3. The importance of C4 producers notably increased from 18 and 10% at the forested upper reaches to 33 and 58% at river reaches receiving hippo inputs during the dry and wet seasons, respectively. This study highlights the importance of large herbivores to the functioning of riverine ecosystems and the potential implications of their loss from savanna landscapes that currently harbor remnant populations. Although the importance of C4 terrestrial carbon in most river systems has been reported to be negligible, this study shows that its importance can be mediated by large herbivores as vectors, which enhance energetic terrestrial-aquatic linkages in rivers in savanna landscapes. ispartof: Ecosystems vol:18 issue:4 pages:686-706 status: published

Intertidal crabs are abundant, key components of tropical estuaries whose trophic interactions provide a direct and identifiable link within the ecosystem. Our study investigated spatial variability in food resource use of intertidal crabs, using stable isotope (δ13C and δ15N) values. This was done for two genera with contrasting feeding strategies (specialist Uca vs. generalist Metopograpsus) within and among locations in North Queensland, Australia. Uca coarctata, Uca seismella, Metopograpsus frontalis, and Metopograpsus latifrons occupied distinct isotopic niches, as quantified by standard ellipse areas. Bayesian mixing models suggested a diet supported by microphytobenhos for Uca species and a more depleted source for Metopograpsus species. Evidence for opportunistic feeding at higher trophic levels by Metopograpsus spp. was reflected by higher δ15N values compared to Uca species. Differences in diet between Uca and Metopograpsus, based on isotopic data, were maintained among ten locations across five estuaries. Food resource use was more variable for Metopograpsus spp. compared to Uca spp. among locations, reflecting the opportunistic feeding of the former. Sewage pollution was echoed in augmented δ15N values of all species. Results revealed separate trophic niches for both generalist and specialist feeding intertidal crab species across the estuarine landscape. The isotopic patterns of Uca spp. and Metopograpsus spp. fitted within the wider intertidal crab community, with generally low overlap among species within individual habitats. The greater flexibility in food resource use by generalists among locations could potentially provide a buffer against changes in food availability. We argue that patterns in food-resource use need to be considered in response to anthropogenic changes in the estuarine landscape.

Sharks are a diverse group of mobile predators that forage across varied spatial scales and have the potential to influence food web dynamics. The ecological consequences of recent declines in shark biomass may extend across broader geographic ranges if shark taxa display common behavioural traits. By tracking the original site of photosynthetic fixation of carbon atoms that were ultimately assimilated into muscle tissues of 5,394 sharks from 114 species, we identify globally consistent biogeographic traits in trophic interactions between sharks found in different habitats. We show that populations of shelf-dwelling sharks derive a substantial proportion of their carbon from regional pelagic sources, but contain individuals that forage within additional isotopically diverse local food webs, such as those supported by terrestrial plant sources, benthic production and macrophytes. In contrast, oceanic sharks seem to use carbon derived from between 30° and 50° of latitude. Global-scale compilations of stable isotope data combined with biogeochemical modelling generate hypotheses regarding animal behaviours that can be tested with other methodological approaches., This research was conducted as part of C.S.B.’s Ph.D dissertation, which was funded by the University of Southampton and NERC (NE/L50161X/1), and through a NERC Grant-in-Kind from the Life Sciences Mass Spectrometry Facility (LSMSF; EK267-03/16). We thank A. Bates, D. Sims, F. Neat, R. McGill and J. Newton for their analytical contributions and comments on the manuscripts.

Mangroves are traditionally considered to provide important nutrition to tropical estuarine consumers. However, there is still controversy about this, and the extent and importance of these inputs are largely unquantified. In particular, there is no information for food webs of small estuaries that dominate wet–dry tropical coasts, where freshwater inflow is intermittent, leading to highly seasonal inputs of nutrients from terrestrial systems. Since the relative importance of the different sources depends on the type and extent of different habitats and on hydrological and topographic conditions, results from other regions/type of systems cannot be extrapolated to these estuaries. Here, δ13C is used to determine the importance of mangrove-derived carbon for Penaeus merguiensis (detritivore; shrimp), Ambassis vachellii (planktivore; fish), and Leiognathus equulus (benthivore; fish) from six small wet–dry tropical estuaries that differ in mangrove (C3) cover and in type of terrestrial vegetation adjacent to the estuary. Bayesian mixing models confirmed that mangrove material was important to consumers in all estuaries. There was a gradient in this importance that agreed with the extent of mangrove forests in the estuaries, as C3 sources were the most important contributors to animals from the three estuaries with the greatest (>40 %) mangrove cover. There was also evidence of incorporation of C3 material for the three estuaries with lower (

Trophic studies are key components in animal ecology and fisheries research. Although stomach samples are often obtained from fisheries, diet studies that consider the influence of fisheries on dietary results are still lacking. Here, the diet of the draughtboard shark Cephaloscyllium laticeps, an abundant mesopredator in Tasmanian waters, was investigated. Stomach samples were obtained from gillnet and craypot fisheries sourced from 4 regions: central (100% gillnet), east coast (63% gillnet, 37% craypot), northwest (100% gillnet), and southwest Tasmania (100% craypot). Overall, C. laticeps consumed the same prey types in all regions, but the importance of some prey varied significantly between regions. Generalized linear models showed that region was the main factor affecting prey abundance in the diet. Fishing method had some influence on the abundance of some prey (crabs, octopus, and other molluscs (gastropods and bivalves)), but the effect of fishing method on pot-related species such as Jasus edwardsii (lobster) and octopus was not as prevalent as expected. The common occurrence of C. laticeps as a bycatch species and its high consumption of targeted fishery species (lobsters and octopus) indicates that C. laticeps has a strong interaction with the fisheries. Therefore, the relationship between these fishery species and C. laticeps should be considered in food web studies in Tasmanian waters. Fil: Barnett, Adam. Deakin University. School Of Life And Environmental Sciences; Australia. James Cook University. School of Marine and Tropical Biology. Estuary and Tidal Wetland Ecosystems Research Group. Centre for Tropical Water & Aquatic Ecosystem Research; Australia. OceansIQ; Australia Fil: Yick, Jonah L.. Inland Fisheries Service; Australia Fil: Abrantes, Kátya G.. James Cook University. School of Marine and Tropical Biology. Estuary and Tidal Wetland Ecosystems Research Group. Centre for Tropical Water & Aquatic Ecosystem Research; Australia Fil: Awruch, Cynthia Andrea. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Nacional Patagónico; Argentina. University of Tasmania. School of Zoology; Australia

Intrapopulation differences in diet and/or movement are important for understanding the role mobile predators play in different systems. However, ecological studies traditionally overlook individual differences. δ13C and δ15N were used in conjunction with diet and movement information to identify intrapopulation differences in diet and movement patterns of the apex predator broadnose sevengill shark Notorynchus cepedianus in southeast Tasmania. Sevengill samples from 3 inshore and 3 offshore sites were collected, and δ13C and δ15N compared between sites, sizes and sexes. Individuals captured offshore had lower δ15N than those captured inshore, indicating some degree of spatial segregation. Sevengills also had variable δ13C and δ15N within coastal habitats, suggesting intrapopulation differences in diet or migration schedules. In comparison to their main prey, most individuals had δ15N lower than expected for a top predator, also suggesting that they do not reside permanently in these areas, as their tissue was not in isotopic equilibrium with their known prey. This is in agreement with tracking data that showed seasonal use of coastal areas, with most animals leaving for the colder months but returning the following year. There was also a group of females with relatively high δ13C that suggests greater association to coastal habitats, again in agreement with tracking data, as some tagged females remained in the coastal areas over winter. Overall, together with diet and tracking information, results indicate that there are differences in movement and possibly diet in this sevengill population. This multimethods approach allowed a better understanding of sevengill ecology than the use of any one of the techniques alone.

Establishing the ecological role of predators within an ecosystem is central to understanding community dynamics and is useful in designing effective management and conservation strategies. We analysed differences in the trophic ecology of four species of reef sharks (Carcharhinus melanopterus, Carcharhinus amblyrhynchos, Triaenodon obesus and Negaprion acutidens) at Ningaloo Reef, Western Australia, by analysing tissue stable isotopes (δ15N and δ13C). We also monitored animals using acoustic telemetry to determine long-term residency patterns in a bay at the southern end of the reef, Coral Bay. Overall, mean δ13C was similar among species, ranging between −10.9 and −11.8‰, suggesting a food-web dependency on coastal producers. Classification and regression tree analysis identified an effect of species on δ15N that separated C. amblyrhynchos and C. melanopterus from N. acutidens and T. obesus. For C. amblyrhynchos and C. melanopterus, animals were also divided by size classes, with smaller sharks having lower average δ15N than larger animals; this suggests that δ15N increases with size for these two species. Juvenile C. melanopterus, juvenile N. acutidens and adult T. obesus had trophic levels of 3.7, for juvenile C. amblyrhynchos and adult C. melanopterus it was 4, and adult C. amblyrhynchos had a value of 4.3. Trophic-level estimates for C. melanopterus and C. amblyrhynchos corroborate previous conclusions based on diet studies. We found no evidence for a difference in isotopic composition between resident and non-resident sharks. The lack of variation in isotopic composition was consistent with high mean residency of these species recorded using acoustic telemetry, which was 79% (±0.09 SE) of days monitored for T. obesus, followed by N. acutidens (57 ± 19.55%), C. amblyrhynchos (54 ± 13%) and C. melanopterus (33 ± 8.28%). High δ13C composition in reef sharks and long-term residency behaviour suggest that coastal marine reserves might provide effective conservation refuges for some species.

Stable isotope analysis is increasingly used in ecological studies. Because lipid content influences δ13C, lipids should be removed from lipid-rich samples before δ13C analysis. To account for differences in δ13C arising from differences in lipid content, relationships between lipid content, C:N ratio and Δδ13C with lipid removal can be used to normalise lipid content to uniform levels. We investigate these relationships for salmonid muscle and evaluate the suitability of previously published normalisation equations for these fish. Salmonids with a wide range of condition (muscle lipid content = 3–35% of dry weight) were considered. There were no consistent relationships between lipid content or C:N ratio and Δδ15N. There were linear relationships between C:N ratio and lipid content (L = −16.53 + 6.27 × C:N); C:N ratio and Δδ13C (Δδ13C = −1.87 + 0.65 × C:N); and lipid content and Δδ13C (Δδ13C = 0.01 + 0.10 × L), which should be used on salmonid stable isotope studies.

Atlantic salmon, Salmo salar , and rainbow trout, Oncorhynchus mykiss , are farmed in Tasmania, Australia, where fish sometimes escape into the natural environment. If escapees are able to survive and feed on native fauna, it is likely that they will have ecosystem impacts. Stomach content, body condition (muscle lipid content and Fulton’ K), stable isotope, and fatty acid analysis were used to determine if escaped salmonids feed on native fauna. Results indicate that, in general, escaped salmonids do not feed on native fauna. Salmonids loose condition after escaping, and escapee stomachs were mostly empty or contained non-nutritious material or feed pellets. Nevertheless, almost a quarter of rainbow trout stomachs contained native fauna. The majority of escapees had biochemical composition similar to caged animals, indicating that these fish had not switched to feed on local food sources. However, a small fraction of escapees conclusively showed changes in biochemical parameters indicative of a shift to feeding on native fauna. Given the numbers and frequency of escapes, this can have an important impact on native species and on the ecology of Macquarie Harbour.

In the dive tourism industry, shark provisioning has become increasingly popular in many places around the world. It is therefore important to determine the impacts that provisioning may have on shark behaviour. In this study, eight adult whitetip reef sharks Triaenodon obesus were tagged with time-depth recorders at Osprey Reef in the Coral Sea, Australia. Tags collected time and depth data every 30 s. The absolute change in depth over 5-min blocks was considered as a proxy for vertical activity level. Daily variations in vertical activity levels were analysed to determine the effects of time of day on whitetip reef shark behaviour. This was done for days when dive boats were absent from the area, and for days when dive boats were present, conducting shark provisioning. Vertical activity levels varied between day and night, and with the presence of boats. In natural conditions (no boats present), sharks remained at more constant depths during the day, while at night animals continuously moved up and down the water column, showing that whitetip reef sharks are nocturnally active. When boats were present, however, there were also long periods of vertical activity during the day. If resting periods during the day are important for energy budgets, then shark provisioning may affect their health. So, if this behaviour alteration occurs frequently, e.g., daily, this has the potential to have significant negative effects on the animals’ metabolic rates, net energy gain and overall health, reproduction and fitness.

Combining movement behaviour with other ecological information of predators and their prey is essential for an adequate understanding of ecosystem dynamics. The movement patterns of broadnose sevengill sharks, Notorynchus cepedianus, were monitored with acoustic and satellite technology in coastal areas of southeast Tasmania, Australia. Individuals were tagged in two habitats (Norfolk Bay and the Derwent Estuary) for which we had ecological information such as diet, population structure and abundance. Notorynchus cepedianus showed seasonal site fidelity in the use of the coastal habitats. The general pattern was for sharks to exit coastal areas over winter and females to return the following spring and males in summer. Their movement into these coastal areas coincided with high seasonal abundance of their known prey species during summer, suggesting feeding site fidelity. Individuals tagged in two coastal areas showed low spatial and dietary overlap, suggesting localized site fidelity and fine spatial scale resource partitioning. This has rarely been reported for large mobile predators. Both satellite and acoustic methods showed that males make northerly migrations during winter to distances of at least 1000 km. The combined use of tracking, diet and abundance information demonstrated that N. cepedianus are likely to exert significant predation pressure on prey inhabiting these areas during summer. Overall, this study highlights the benefit of complementing movement data with other ecological information to understand the habitat use of large mobile predators and their potential influences on ecosystem structure and function.

The diet of the broadnose sevengill shark Notorynchus cepedianus was investigated over 3 years from 2 coastal locations in south-east Tasmania: the Derwent Estuary and Norfolk Bay. In general, individuals from both locations consumed the same broad dietary categories (sharks, batoids, teleosts and mammals). However, within these categories, species composition differed. Variations in chondrichthyan prey consumed matched estimations of prey abundance: Mustelus antarcticus was the primary prey in Norfolk Bay, where it was also the most abundant prey species; similarly, Squalus acanthias was an important prey and the most abundant in the Derwent Estuary. A decline in the catch rates of N. cepedianus and elasmobranch prey, in particular M. antarcticus over 3 years coincided with declines in dietary occurrence of M. antarcticus. Also, N. cepedianus and M. antarcticus abundances were both higher in Norfolk Bay than the Derwent Estuary. The correla- tion with diet and estimations of predator and prey relative abundance suggests N. cepedianus may move into coastal areas to exploit regular seasonal abundant resources, but they can also be versatile opportunistic predators that exploit a temporarily abundant resource.

δ13C was used to identify seasonal variations in the importance of autochthonous and allochthonous sources of productivity for fish communities in intermittently connected estuarine areas of Australia’s dry tropics. A total of 224 fish from 38 species were collected from six intermittently connected estuarine pools, three in central Queensland (two dominated by C3 forest and one by C4 pasture) and three in north Queensland (one dominated by C3 and two by C4 vegetation). Samples were collected before and after the wet season. Fish collected in the two forested areas in central Queensland had the lowest δ13C, suggesting a greater incorporation of C3 terrestrial material. A seasonal variation in δ13C was also detected for these areas, with mean δ13C varying from −20 to −23‰ from the pre- to the post-wet season, indicating a greater incorporation of terrestrial carbon after the wet season. Negative seasonal shifts in fish δ13C were also present at the pasture site, suggesting a greater dependence on carbon of riparian vegetation (C3 Juncus sp.) in the post-wet season. In north Queensland, terrestrial carbon seemed to be incorporated by fish in the two C4 areas, as δ13C of most species shifted towards slightly heavier values in the post-wet season. A two-source, one-isotope mixing model also indicated a greater incorporation of carbon of terrestrial origin in the post-wet season. However, no seasonal differences in δ13C were detected for fish from the forested area of north Queensland. Overall, hydrologic connectivity seemed to be a key factor in regulating the ultimate sources of carbon in these areas. It is therefore important to preserve the surrounding habitats and to maintain the hydrologic regimes as close to natural conditions as possible, for the conservation of the ecological functioning of these areas.

Stable isotope composition of organisms from different trophic groups collected from a semi-isolated wetland pool in the Ross River estuary, northern Australia, was analysed to determine if there was a consistent relationship between δ13C, δ15N and trophic level that could be used to assign trophic positions. A strong linear negative relationship between δ13C and δ15N was detected for the three trophic levels considered (primary producers, primary consumers and secondary consumers). This relationship was consistent among trophic levels, differing only in height, that is, on δ15N values, which indicate trophic positions. A difference of 3.6–3.8‰ between trophic levels was present, suggesting a δ15N fractionation of approximately 3.7‰, a value slightly higher than the commonly assumed δ15N fractionation of approximately 3.4‰. The relationship between δ13C and δ15N was similar for invertebrate and fish primary consumers, indicating similar δ15N trophic fractionation for both groups, meaning trophic positions and trophic length could be reliably calculated based on either invertebrates or fish.

Carbon and nitrogen isotopic composition was used to identify the main sources of carbon and describe the main trophic pathways in Deluge Inlet, a near-pristine mangrove estuary in tropical north Queensland, Australia. Producers' δ13C varied from −28.9‰ for mangroves to −18.6‰ for seagrass. Animals were also well separated in δ13C (−25.4‰ to −16.3‰ for invertebrates and −25.2‰ to −17.2‰ for fish), suggesting considerable differences in ultimate sources of carbon, from a substantial reliance on mangrove carbon to an almost exclusive reliance on seagrass. In general, invertebrates had lower δ15N than fish, indicating lower trophic levels. Among fish, δ15N values reflected well the assumed trophic levels, as species from lower trophic levels had lower δ15N than species from higher trophic levels. Trophic levels and trophic length were estimated based on δ15N of invertebrate primary consumers (6.1‰), with results suggesting a food web with four trophic levels. There was also evidence of a high level of diet overlap between fish species, as indicated by similarities in δ13C for fish species of higher trophic levels. Stable isotope data was also useful to construct a general model for this food web, where five main trophic pathways were identified: one based on both mangrove and microphytobenthos, one on plankton, two on both microphytobenthos and seagrass, and one based mainly on seagrass. This model again suggested the presence of four trophic levels, in agreement with the value calculated based on the difference in δ15N between invertebrate primary consumers and top piscivores.

Carbon and nitrogen stable isotope composition of a range of organisms collected from two intermittently connected floodplain pools in the Ross River estuary were analysed to assess the extent to which carbon fixed by terrestrial wetland producers is incorporated into adjacent aquatic food webs. The two pools differed in surrounding vegetation with one surrounded by mangroves and the other by the salt couch Sporobolus virginicus. At both pools, animals showed differences in δ13C, indicating differences in sources of carbon. Since δ13C values of C3 mangroves (−29.7 to −26.3‰) were very different from those of the C4 salt couch (−16.3 to −15.4‰), it was possible to determine the importance of terrestrial wetland producers by comparing isotope values of consumers between sites, in a species by species approach. Most animal species collected showed lower δ13C at the mangrove pool than at the Sporobolus pool, which indicates a greater incorporation of mangrove carbon at the mangrove pool. However, the animals’ isotopic shifts were also similar to that shown by epiphytes, and hence the differences in animal δ13C could also be a result of a dependence on these producers. The IsoSource model was useful to clarify this question, indicating that mangrove and salt marsh material was a crucial contributor to the diet of several fish and invertebrate species at both sites, indicating that carbon of terrestrial origin is incorporated in the estuarine food web.

Although urban development impacts wetlands around the world, until now there have been no studies of its effects on coastal wetlands in tropical regions of developed countries such as Australia. In fact the ecological value of such wetlands is poorly understood. This study provides an initial step in evaluating the ecological value of urbanised, tropical coastal wetlands by determining (a) the extent to which a remnant wetland, in a highly urbanised estuary in northern Australia, is used by juvenile commercial penaeid shrimps, and (b) the extent to which the shrimps rely on food chains based on wetland plants versus marine based food chains. Juvenile penaeids were abundant in the 11 wetland pools sampled. Catches included 5 commercial penaeids with two species, Fenneropenaeus merguiensis and Metapenaeus bennetae, comprising half the catch. Densities in the wetland pools were usually substantially higher than in adjacent estuarine habitats. Stable isotope analysis indicated that much of the nutrition of juvenile shrimps was supplied by marine primary producers (phytoplankton, epiphytic and epilithic algae, microphytobenthos, green filamentous algae) however the locally abundant saltmarsh grass Sporobolus virginicus was also a major contributor. In contrast, there was little indication of nutritional support from mangrove carbon. The lack of importance of mangrove carbon is surprising because the catches of F. merguiensis are often closely linked to the area or extent of mangroves, suggesting that aspects of mangrove systems other than the supply of mangrove carbon may determine the distribution of juvenile F. merguiensis.

A series of laboratory experiments was conducted at Inhaca Island Marine Biological Station, Mozambique, in order to assess the separate effects of turbidity, prey density, substrate type, pneumatophore density, and the combined effects of turbidity with the latter three, on rate of predation by the thorn fish Terapon jarbua (Forskal, 1775) on white shrimp Penaeus indicus and brown shrimp Metapenaeus monoceros. Significant interactions between turbidity and the other three factors on shrimp predation for both prey species were detected. Regardless of prey density, increasing turbidity decreased predation on P. indicus, but not on M. monoceros, for which increasing densities reduced the protective effect of turbidity. Increasing prey density increased predation on P. indicus in clear water, and increased predation on M. monoceros in low and high, but not in intermediate turbidity or clear water. The presence of a substrate suitable for burying decreased predation on M. monoceros in clear water, but not in the turbidity levels used. In clear water, solely sandy-shell substrate afforded protection to P. indicus, while in turbid water, no substrate offered significant protection and muddy substrate even increased prey vulnerability to fish probably as a result of increased preys' locomotor activity. Raising pneumatophores density seems to lower the protective value of turbidity for both species. In clear water, only low and high structure density provided a deterrent effect on predation on P. indicus; in turbid water, intermediate and higher structure density increased predation. Increasing structural complexity reduced predation on M. monoceros linearly in clear water; but in low turbid water it increased. In high turbid waters, the increase was only significant in intermediate pneumatophore density. High structural complexities impair the pursuing capacity of fish and thus decreased predation rates. The results indicate that the effective provision of shelter of different habitats depends not only on the various environmental parameters analysed, but also on the way they interact and on the behaviour of prey and predator as well.

Quantitative tools to describe biological communities are important for conservation and ecological management. The analysis of trophic structure can be used to quantitatively describe communities. Stable isotope analysis is useful to describe trophic organization, but statistical models that allow the identification of general patterns and comparisons between systems/sampling periods have only recently been developed.Here, stable isotope-based Bayesian community-wide metrics are used to investigate patterns in trophic structure in five estuaries that differ in size, sediment yield and catchment vegetation cover (C3/C4): the Zambezi in Mozambique, the Tana in Kenya and the Rianila, the Betsiboka and Pangalanes Canal (sampled at Ambila) in Madagascar.Primary producers, invertebrates and fish of different trophic ecologies were sampled at each estuary before and after the 2010–2011 wet season. Trophic length, estimated based on d15N, varied between 3•6 (Ambila) and 4•7 levels (Zambezi) and did not vary seasonally for any estuary. Trophic structure differed the most at Ambila, where trophic diversity and trophic redundancy were lower than at the other estuaries. Among the four open estuaries, the Betsiboka and Tana (C4-dominated) had lower trophic diversity than the Zambezi and Rianila (C3-dominated), probably due to the high loads of suspended sediment, which limited the availability of aquatic sources.There was seasonality in trophic structure at Ambila and Betsiboka, as trophic diversity increased and trophic redundancy decreased from the prewet to the postwet season. For Ambila, this probably resulted from the higher variability and availability of sources after the wet season, which allowed diets to diversify. For the Betsiboka, where aquatic productivity is low, this was likely due to a greater input of terrestrial material during the wet season.The comparative analysis of community-wide metrics was useful to detect patterns in trophic structure and identify differences/similarities in trophic organization related to environmental conditions. However, more widespread application of these approaches across different faunal communities in contrasting ecosystems is required to allow identification of robust large-scale patterns in trophic structure. The approach used here may also find application in comparing food web organization before and after impacts or monitoring ecological recovery after rehabilitation.

Deluge Inlet is a small, tide-dominated estuary on Australia’s north-east tropical coast, located in the central part of the Hinchinbrook Island National Park, Australia’s largest island National Park. It is situated in Australia’s humid tropical zone, and experiences an intense summer wet season and regular impacts of tropical cyclones. Protection by National Parks, World Heritage and Wild Rivers legislation means it remains in near pristine condition. Deluge Inlet sports substantial biodiversity in the form of extensive mangrove forests, seagrass beds, and complex marine mammal, reptile, fish and invertebrate assemblages, all supported by a mosaic of highly interconnected habitat types. The mix of habitats and rich biodiversity makes Deluge Inlet an important nursery for many species, and supports complex food webs. Current threats are from increasing fishing and boating pressure, and effective governance will be needed to ensure Deluge Inlet remains in near-pristine condition into the future.

Information on the fine-scale movement of predators and their prey is important to interpret foraging behaviours and activity patterns. An understanding of these behaviours will help determine predator-prey relationships and their effects on community dynamics. For instance understanding a predator's movement behaviour may alter pre determined expectations of prey behaviour, as almost any aspect of the prey's decisions from foraging to mating can be influenced by the risk of predation. Acoustic telemetry was used to study the fine-scale movement patterns of the Broadnose Sevengill shark Notorynchus cepedianus and its main prey, the Gummy shark Mustelus antarcticus, in a coastal bay of southeast Tasmania. Notorynchus cepedianus displayed distinct diel differences in activity patterns. During the day they stayed close to the substrate (sea floor) and were frequently inactive. At night, however, their swimming behaviour continually oscillated through the water column from the substrate to near surface. In contrast, M. antarcticus remained close to the substrate for the entire diel cycle, and showed similar movement patterns for day and night. For both species, the possibility that movement is related to foraging behaviour is discussed. For M. antarcticus, movement may possibly be linked to a diet of predominantly slow benthic prey. On several occasions, N. cepedianus carried out a sequence of burst speed events (increased rates of movement) that could be related to chasing prey. All burst speed events during the day were across the substrate, while at night these occurred in the water column. Overall, diel differences in water column use, along with the presence of oscillatory behaviour and burst speed events suggest that N. cepedianus are nocturnal foragers, but may opportunistically attack prey they happen to encounter during the day.

Little is known on the degree to which terrestrial organic matter delivered to tropical estuaries contributes to estuarine consumers. Here, stable isotope analysis is used to constrain this contribution for contrasting east African estuaries whose catchments differ in relative C3/C4 vegetation cover. As these two types of vegetation differ strongly in d13C, we anticipated that terrestrial subsidies would be reflected in a gradient in estuarine consumer d13C values, following the relative importance of C3 (characterised by low d13C) vs. C4 (characterised by high d13C) cover. Five estuaries were sampled for aquatic biogeochemical parameters, primary producers and consumers of different trophic ecologies: the Zambezi (catchment with a C3/C4 cover of 61/39%) in Mozambique, the Tana in Kenya (36/64%) and the Betsiboka (42/58%), Rianila (85/15%) and Canal des Pangalanes (C3-dominated) in Madagascar. Sampling was done before and after the 2010/2011 wet season. There were positive relationships between the proportion of C4 cover in the catchment and turbidity, d13CDIC, d13CDOC, d13CPOC and d15NPN. There were also significant positive relationships between d13CPOC and consumer d13C and between d15NPN and consumer d15N for all consumer trophic guilds, confirming the incorporation of organic material transported from the catchments by estuarine consumers, and implying that this material is transported up to high trophic level fish. Bayesian mixing models confirmed that C4 material was the most important source for the highly turbid, C4-dominated estuaries, contributing up to 61–91% (95% CI) to phytodetritivorous fish in the Betsiboka, whereas for the less turbid C3-dominated estuaries terrestrial subsidies were not as important and consumers relied on a combination of terrestrial and aquatic sources. This shows that the ecology of the overall catchment affects the estuaries at the most basic, energetic level, and activities that alter the turbidity and productivity of rivers and estuaries can affect food webs well beyond the area of impact.

Prawn fisheries are among the main sources of income in several tropical countries, where juveniles of many species inhabit estuarine wetlands. Although plants in these wetlands are considered to be essential food sources for juvenile prawns, some studies suggest that wetland producers are of limited importance. In the present study, δ13C and δ15N were used to identify differences in diet between penaeid species and size classes, and to determine if terrestrial wetland producers are important for nutrition. Two estuarine floodplain pools were sampled: one surrounded by mangroves and one surrounded by salt marsh. There were differences in diet between species and size classes. As mangrove δ13C (–29.7 to –26.3‰) was very different from salt marsh δ13C (–16.3 to –15.4‰), the importance of these producers was examined by comparing the isotopic composition of the prawns between sites and by using the IsoSource model. Although aquatic sources were the most important, salt marsh grass was also a significant contributor, supporting the hypothesis that these wetland producers are important for juvenile prawn nutrition. There was no evidence that mangrove material was of major importance for any species, suggesting that mangrove productivity is not the primary reason for the occurrence of penaeid prawns in mangrove habitats.

Estuarine floodplain wetland pools occur adjacent to marine coasts and estuaries throughout the world. In Australia’s dry tropics and sub-tropics, low and irregular rainfall means estuarine wetland pools are isolated for much of the time, resulting in varied within-pool conditions, with chemistry ranging from fresh to hypersaline, depending on the balance between freshwater and marine inputs and the time between connections. Varied physical conditions and irregular connectivity provide the potential for substantial faunal difference among pools. The present study compares the compositions and structures of the fish fauna of a broad cross section of estuarine wetland pools adjacent to the estuary of the Fitzroy River, one of the largest rivers in Australia’s dry tropical/subtropical zone. Ten pools were sampled between February 2004 and May 2005. The total species richness was low, with the 6123 fish recorded over the study, comprising only 44 species. This low species richness was reflected at the individual pool level, with a maximum total richness of 25 species in a single pool. Different pools had faunas that differed as a function of the proportion of the community comprised of marine spawned, compared with freshwater spawned, species. This was a reflection of the extent of connectivity to freshwater and marine systems, which determined both the physical nature of pools and the sources of faunal supply. Despite faunal differences among pools, at a functional level pool fish faunas were dominated by detritivores, regardless of pool type, size, season or connectedness.