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The Maugean skate, Zearaja maugeana, is endemic to two isolated western Tasmanian (Australia) estuaries. The species' persistence in one of these estuaries (Bathurst Harbour) is uncertain, while the other estuary (Macquarie Harbour), potentially the remaining stronghold for the species, is an anthropogenically impacted system. Key life‐history parameters were studied to inform conservation actions for this species. Reproductive information was obtained using non‐lethal methodologies, circulating concentrations of sex steroids and ultrasonography. Growth and age parameters were estimated based on vertebral sections from a small sample of individuals. Females and males reached 870 and 760 mm total length, respectively. The species reached a maximum age of at least 10 years. Females and males attained 50% sexual maturity at 665 and 633 mm total length, respectively, probably maturing somewhere between four and six years of age. Females displayed an asynchronous, discontinuous reproductive cycle, being able to reproduce throughout the year, with a probable decline in reproductive activity during summer. No egg cases were observed in‐utero. Males produce sperm all year round, with a peak in testosterone production during spring–autumn. Conservation strategies for Z. maugeana will need to focus on reducing anthropogenic impacts on the environmental health, the primary impacts being altered river flows associated with the production of hydroelectricity and increased nutrient load associated with salmonid aquaculture. There is a need to better understand how reproductive success, egg survival and recruitment are affected by these environmental challenges if the future well‐being of this species is to be secured.

Metabolic rate is intricately linked to the ecology of organisms and can provide a framework to study the behaviour, life history, population dynamics, and trophic impact of a species. Acquiring measures of metabolic rate, however, has proven difficult for large water-breathing animals such as sharks, greatly limiting our understanding of the energetic lives of these highly threatened and ecologically important fish. Here, we provide the first estimates of resting and active routine metabolic rate for the longest lived vertebrate, the Greenland shark (Somniosus microcephalus). Estimates were acquired through field respirometry conducted on relatively large-bodied sharks (33–126 kg), including the largest individual shark studied via respirometry. We show that despite recording very low whole-animal resting metabolic rates for this species, estimates are within the confidence intervals predicted by derived interspecies allometric and temperature scaling relationships, suggesting this species may not be unique among sharks in this respect. Additionally, our results do not support the theory of metabolic cold adaptation which assumes that polar species maintain elevated metabolic rates to cope with the challenges of life at extreme cold temperatures.

Knowledge of the factors shaping the foraging behaviour of species is central to understanding their ecosystem role and predicting their response to environmental variability. To maximise survival and reproduction, foraging strategies must balance the costs and benefits related to energy needed to pursue, manipulate, and consume prey with the nutritional reward obtained. While such information is vital for understanding how changes in prey assemblages may affect predators, determining these components is inherently difficult in cryptic predators. The present study used animal-borne video data loggers to investigate the costs and benefits related to different prey types for female Australian fur seals (Arctocephalus pusillus doriferus), a primarily benthic foraging species in the low productivity Bass Strait, south-eastern Australia. A total of 1,263 prey captures, resulting from 2,027 prey detections, were observed in 84.5 h of video recordings from 23 individuals. Substantial differences in prey pursuit and handling times, gross energy gain and total energy expenditure were observed between prey types. Importantly, the profitability of prey was not significantly different between prey types, with the exception of elasmobranchs. This study highlights the benefit of animal-borne video data loggers for understanding the factors that influence foraging decisions in predators. Further studies incorporating search times for different prey types would further elucidate how profitability differs with prey type.

Hunting large, fast-moving mammals by top predators often involves highly energetic burst locomotion, and studying such behaviour can reveal how physiological capacity shapes predator-prey relationships. Although increasingly sophisticated animal-borne devices have allowed the recording of terrestrial predators’ behaviour (e.g. cheetahs) hunting herbivorous mammals, similar approaches have rarely been applied to marine predators hunting mammals. Here, we deployed video cameras (lasting for 6 h) and accelerometers (lasting for 2 d) on 8 white sharks Carcharodon carcharias aggregating near colonies of long-nosed fur seals Arctocephalus forsteri. Video showed one shark attacking a seal, during which an intensive swimming event (lateral acceleration: 3.7 × g, tailbeat frequency: 3.3 Hz, estimated swim speed: 6.7 m s-1) was recorded. Based on this confirmed event, 7 potential predation events were identified from 150 h of acceleration data. The events occurred at various depths (0-53 m) and primarily at nighttime and during crepuscular periods, partly contrasting with well documented seal-hunting breaching behaviour that occurs primarily during crepuscular periods. This study demonstrates that, despite inherent difficulties, recording infrequent hunting events of top marine predators provides insight into their hunting strategies and maximum locomotor performance.

Resource use and conservation objectives can conflict where protected species and commercially fished species occur together. We tested the potential for a previously overfished deep-sea shark (Centrophorus zeehaani) with very low biological productivity to recover in a network of three reserves. An individual-based simulation model was developed and applied using reproduction and movement data. Without any reserves or reductions in fishing mortality the population will never recover and will fail in 27.9 ± 6.1 years. With three reserves, recovery from 8% of initial numbers to a target of 20% would take 63.1 ± 3.1 years with the network in place. Length of the female cycle, natural mortality, and density dependent female dispersal are uncertain, but could delay recovery time by an additional 16.5, 98.3, or 61.9 years, respectively. Effectiveness of the reserve network was particularly sensitive to location and patchiness of the population. Doubling the size of a reserve where C. zeehaani are abundant would reduce recovery time by 12.5 years; halving it would increase recovery time by 12.0 years. Future re-opening of orange roughy fishing in waters deeper than 750 m would delay recovery of C. zeehaani by 45.9 years. The methods developed here can be used to explore co-management options for target species and protected species in fisheries.

Significance Seismic surveys are used to locate deposits of oil and gas in seabeds throughout the world’s oceans. There are conflicting views on the impact of these surveys on fish fauna and whether they harm commercial catches. To resolve this issue, we conducted an experimental seismic survey and monitored the composition, abundance, behavior, and movement of an assemblage of commercially important demersal fishes on a shelf habitat using acoustic telemetry and underwater video. We found that the seismic survey did not alter fish abundance or behavior in multiple before-after-control-impact and dose–response experimental frameworks. Our work may allay some of the concerns of stakeholders about the negative impacts of seismic surveys on demersal fishes in tropical shelf environments., Seismic surveys are used to locate oil and gas reserves below the seabed and can be a major source of noise in marine environments. Their effects on commercial fisheries are a subject of debate, with experimental studies often producing results that are difficult to interpret. We overcame these issues in a large-scale experiment that quantified the impacts of exposure to a commercial seismic source on an assemblage of tropical demersal fishes targeted by commercial fisheries on the North West Shelf of Western Australia. We show that there were no short-term (days) or long-term (months) effects of exposure on the composition, abundance, size structure, behavior, or movement of this fauna. These multiple lines of evidence suggest that seismic surveys have little impact on demersal fishes in this environment.

Inferences regarding animal presence from passive acoustic receiver arrays are driven by the spatial configuration of receivers. Large, dense arrays provide more information, but maintenance of multiple receivers is costly. Configuring acoustic receiver arrays to maximise coverage while minimising cost is therefore paramount. This study used data from a dense acoustic receiver array within a white shark Carcharodon carcharias nursery area on the east coast of Australia to assess how detection data of tagged white sharks in the area was affected by reducing the array size. Receivers were sub-sampled post hoc by simple random sampling, clustered random sampling, and sampling of the top performing receivers. Using the top performing receivers, array size could be reduced by 60% (10 out of 25 receivers) while still detecting a median of 100% of white sharks detected with the full array. With random and clustered sampling methods, a 40% reduction in array size (15 out of 25 receivers) detected a median of 100% of sharks. Reducing the array size by 60% using the top performing receivers resulted in a 35% decrease in the median number of detections per visit of the tagged sharks (67 out of 102.5 detections). In comparison, reducing the array by the same amount with random and clustered sampling methods resulted in a 57% decrease (44 out of 102.5 detections). The post hoc sampling methods used in this study are an empirical approach for optimising placement of limited receiver resources with broad application for establishing cost-effective monitoring.

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.

Individual body size strongly influences the trophic role of marine organisms and the structure and function of marine ecosystems. Quantifying trophic position–individual body size relationships (trophic allometries) underpins the development of size‐structured ecosystem models to predict abundance and the transfer of energy through ecosystems. Trophic allometries are well studied for fishes but remain relatively unexplored for cephalopods. Cephalopods are important components of coastal, oceanic and deep‐sea ecosystems, and they play a key role in the transfer of biomass from low trophic positions to higher predators. It is therefore important to resolve cephalopod trophic allometries to accurately represent them within size‐structured ecosystem models. We assessed the trophic positions of cephalopods in an oceanic pelagic (0–500 m) community (sampled by trawling in a cold‐core eddy in the western Tasman Sea), comprising 22 species from 12 families, using bulk tissue stable isotope analysis and amino acid compound‐specific stable isotope analysis. We assessed whether ontogenetic trophic position shifts were evident at the species‐level and tested for the best predictor of community‐level trophic allometry among body size, taxonomy and functional grouping (informed by fin and mantle morphology). Individuals in this cephalopod community spanned two trophic positions and fell into three functional groups on an activity level gradient: low, medium and high. The relationship between trophic position and ontogeny varied among species, with the most marked differences evident between species from different functional groups. Activity‐level‐based functional group and individual body size are best explained by cephalopod trophic positions (marginal R2 = 0.43). Our results suggest that the morphological traits used to infer activity level, such as fin‐to‐mantle length ratio, fin musculature and mantle musculature are strong predictors of cephalopod trophic allometries. Contrary to established theory, not all cephalopods are voracious predators. Low activity level cephalopods have a distinct feeding mode, with low trophic positions and little‐to‐no ontogenetic increases. Given the important role of cephalopods in marine ecosystems, distinct feeding modes could have important consequences for energy pathways and ecosystem structure and function. These findings will facilitate trait‐based and other model estimates of cephalopod abundance in the changing global ocean.

Knowledge about reproductive movements can be of important conservation value for over-exploited species that are vulnerable when moving between and within key reproductive habitats. Lack of knowledge persists around such movements in the overfished school shark Galeorhinus galeus in Australia. Management assumes all pregnant females migrate between adult aggregations in the Great Australian Bight, South Australia, and nursery areas around Bass Strait and Tasmania. We tracked 14 late-term pregnant females tagged in South Australia using satellite-linked pop-up archival tags to investigate extent, timing, and routes of migrations. We found partial migration, with some females (n = 7) remaining near aggregating areas throughout the pupping season, some migrating to known nursery areas (n = 3), and one migrating ∼3 000 km to New Zealand. We conclude female movements and pupping habitats are less spatially constrained than assumed and propose females use cool-water routes along the shelf break to reduce energy costs of migration. Migrating females using these routes faced greater fishing pressure than sharks in inshore areas and were not protected by inshore shark fishing closures designed to protect them. This study demonstrates the complexity of reproductive movements that can occur in wide-ranging species and highlights the value of explicit movement data.

The Maugean skate (Zearaja maugeana) has only been recorded in two remote and isolated estuaries on the west coast of Tasmania, Australia. While the population status in one of these estuaries (Bathurst Harbour) is uncertain, it is likely that Macquarie Harbour now represents the sole remaining habitat for this species. Environmental conditions, in particular dissolved oxygen levels and benthic biodiversity, in Macquarie Harbour have deteriorated in recent years, impacted by increased nutrient inputs from an expanding salmonid aquaculture industry. These environmental changes are believed to pose a threat to the persistence of the Maugean skate. In assessing the risks for this rare and range-restricted species, it is vital to consider genetic information when developing management strategies. Both mitochondrial and microsatellite markers showed that the species has low genetic diversity; with no detectable genetic diversity in over 3000 base pairs surveyed from the mitochondrial genome, low average microsatellite heterozygosity (0.35 ± 0.11), a low average number of alleles per locus (2.1 ± 0.4) across eight microsatellite loci and no overall population structure within the microsatellite loci (Fst = − 0.002, p = 0.718 ± 0.012). There was also evidence of a recent bottleneck or founder event, which may explain the low observed genetic diversity. While the species may have existed with low genetic diversity for many generations, the results of this study represent a flag for conservation concern for the Maugean skate. Given that Macquarie Harbour may be its last remaining habitat, any threats to the species resulting in local extinction could equate to global loss of this unique skate species.

Some species may have a larger role than others in the transfer of complex effects of multiple human stressors, such as changes in biomass, through marine food webs. We devised a novel approach to identify such species. We constructed annual interaction-effect networks (IENs) of the simulated changes in biomass between species of the southeastern Australian marine system. Each annual IEN was composed of the species linked by either an additive (sum of the individual stressor response), synergistic (lower biomass compared with additive effects), or antagonistic (greater biomass compared with additive effects) response to the interaction effect of ocean warming, ocean acidification, and fisheries. Structurally, over the simulation period, the number of species and links in the synergistic IENs increased and the network structure became more stable. The stability of the antagonistic IENs decreased and became more vulnerable to the loss of species. In contrast, there was no change in the structural attributes of species linked by an additive response. Using indices common in food-web and network theory, we identified the species in each IEN for which a change in biomass from stressor effects would disproportionately affect the biomass of other species via direct and indirect local, intermediate, and global predator-prey feeding interactions. Knowing the species that transfer the most synergistic or antagonistic responses in a food-web may inform conservation under increasing multiple-stressor impacts.Identificación de las Especies Importantes que Amplifican o Mitigan los Efectos Interactivos de los Impactos Humanos Resumen Algunas especies pueden tener un papel más importante que otras en la transferencia de los efectos complejos de múltiples estresantes humanos, como los cambios en la biomasa por medio de las redes alimenticias marinas. Diseñamos una metodología novedosa para identificar a dichas especies. Construimos una red de efectos anuales de interacción (IEN, en inglés) a partir de los cambios simulados en la biomasa entre especies del sistema marino del sureste de Australia. Cada IEN anual estuvo compuesta por las especies conectadas por una respuesta aditiva (la suma de las respuestas individuales al estresante), sinérgica (una biomasa menor en comparación con los efectos aditivos) o antagónica (una mayor biomasa en comparación con los efectos aditivos) ante los efectos de interacción del calentamiento oceánico, la acidificación oceánica, y las pesquerías. Estructuralmente, durante el periodo de simulación, el número de especies y conexiones en los IEN sinérgicos incrementó y la estructura de la red se volvió más estable. La estabilidad de las IEN antagónicas disminuyó y se volvió más vulnerable ante la pérdida de especies. En contraste, no hubo cambio en los atributos estructurales de las especies conectadas por una respuesta aditiva. Con el uso de índices comunes entre las redes alimenticias y la teoría de redes identificamos a las especies en cada IEN para las cuales un cambio en la biomasa por causa de los efectos estresantes afectaría desproporcionalmente a la biomasa de las otras especies por medio de interacciones de alimentación locales, intermedias y globales del tipo depredador - presa directas o indirectas. Si sabemos cuáles especies transfieren el mayor número de respuestas sinérgicas o antagónicas en una red alimenticia podemos informar a la conservación que está bajo impactos estresantes cada vez mayores.文献中针对学科交叉点的争论就如何结合科学和实践来提高保护成效提出了多种多样的观点。理解这种多样性是处理不平等权力关系、避免只考虑主导观点, 以及确定科学和实践相结合战略的关键。反过来, 科学和实践的结合应促成社会上坚稳可靠、科学上考虑周全的保护决策。为了确定和描述科学家和决策者关于科学和实践如何交叉来改善保护决策的观点, 我们采访了巴西的科学家 (生态学家和保护科学家 (11人) 和决策者 (11人) 。我们利用Q方法学, 要求参与者给出他们对48条科学和实践如何交叉来改善保护决策的表述的赞同度。我们用主成分分析找出了他们共同的观点。科学家和决策者都同意的最主要观点是要重视科学和战略知识的整合来解决环境问题。第二个观点主要由决策者持有, 是在决策过程中要重视科学, 并呼吁进行更多与问题相关的研究。只有科学家认同的第三个观点的特点是不愿意合作, 并认为科学家创造了可以帮助决策者的知识。大多数参与者都同意组织机构应该促进合作, 行动者与来自科学和实践的知识均有重要关系。分歧则在于实践者应担负的具体角色、合作的意愿和组织或机构如何安排才能有效结合科学和实践。我们的结果表明科学家和决策者尚有很大的合作空间, 目前的障碍主要在于现有组织和正式机构的协调安排, 而不是二者之间的消极态度。 【翻译: 胡怡思; 审校: 聂永刚】.

Abundance is commonly used to assess the status of wildlife populations and their responses to changes in management frameworks. Monitoring abundance trends often requires long-term data collection programs, which are not always carried out. One alternative to scientific surveys is to utilize the local ecological knowledge (LEK), from people in continuous interactions with the environment. We developed a semi-quantitative approach to assess shark population trends by using the LEK of non-extractive resource users. We carried out structured interviews with dive guides regarding the abundance trends of six shark species in the Galapagos Marine Reserve (GMR) across decades since the 1980s. Based on dive guides' LEK, we developed a virtual abundance change (VAC) model to assess the changes in abundance across decades. Our VAC analysis showed a 50% decline in hammerhead sharks and 30% decline in whitetip reef sharks. Silky sharks and Galapagos sharks were perceived to suffer an initial decline by 25% and 30% then stabilized. Whale shark abundance did not appear to have changed. Finally, blacktip sharks showed an apparent recovery after a decline by 25%. Furthermore, our VAC results were comparatively similar to empirical datasets from the GMR and neighboring protected areas of the Eastern Tropical Pacific. Our study highlights the value of LEK in assessing the state of marine resources in data-limited management regions. Our VAC method offers an alternative approach by which LEK can provide valuable insights into the historical trends of species abundance.

Knowledge of reproductive movements and sources of recruitment in highly mobile species is important to understand population-level resilience and to manage recovery in populations depleted by human interference. Management of the school shark Galeorhinus galeus (Linnaeus, 1758), a Conservation Dependent species in Australia subject to a national recovery strategy after stock collapse from overfishing, has long assumed obligate female migration to pupping areas in the southeast of their range. We used post-natal elemental signatures of individuals from 3 cohorts born in 1996 to 1998 as a proxy to test whether females use common pupping areas. Environmental or biological factors that differ among pupping areas can give rise to unique trace element signatures in shark vertebrae that act as natural tags and can be used to assess relative contributions from recruitment sources to adult populations. We compared post-natal signatures from sharks caught in 2 regions, South Australia in the northwest of the species’ range and Bass Strait in the southeast, using laser ablation inductively coupled mass spectrometry. Signatures were similar between regions for 1 cohort, suggesting high use of shared or similar pupping areas, but differed for the 2 remaining cohorts. Region of capture could also be accurately predicted (>75%) based on post-natal signatures, refuting the long-held view that all females use common pupping areas. We conclude that female movements and reproductive strategies are likely more plastic than previously assumed, highlighting the need to clarify them and their potential effects on resilience and conservation.

A radio-acoustic positioning system was used to assess the effects of shark cage-diving operators (SCDO) on the fine-scale movements of a non-focal species, the smooth stingray Bathytoshia brevicaudata. The results revealed that the time spent in the array was individually variable, but generally increased when SCDO were present and that the presence of SCDO may have the capacity to elicit changes in the space use of B. brevicaudata. These results indicate that the effects of marine wildlife tourism may extend beyond the focal species of interest.

In comparison to other behaviours, large predators expend relatively large amounts of energy foraging for prey, based on expected high return. Documenting how they manage costs and benefits of feeding is difficult, particularly for marine predators. In July and August of 2004 and 2005, we combined animal-borne video, accelerometry and depth sensors to examine the underwater behaviour during white shark (Carcharodon carcharias) breaching at Seal Island, South Africa (34.1373°S, 18.5825°E)—where sharks launch from the water while attacking Cape fur seals (Arctocephalus pusillus pusillus). We show that breaching begins at depths up to 20 m, is characterised by a brief (~ 7 to 16 s) ascent to the surface during which pitch angle increases by ~ 30° and both tail-beat frequency and swim speed (determined using biomechanical principles) increase by a maximum of 6.5-fold (0.39–2.50 Hz and 1.0–6.5 m s−1, respectively). Sharks also demonstrated the ability to rapidly adjust their approach to the seal during ascent. Dominant tail-beat frequency during breaching was 2.1–4.2 times higher (0.83–1.67 Hz) than during non-predatory ascents (0.4 Hz), suggestive of the large increase in power required to breach. Examination of foraging behaviour through biologger deployments may play an increasingly important role in predicting the resource requirements of large predators and developing appropriate conservation measures, as their populations are generally under threat world-wide.

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

Wildlife tourism has been shown to cause behavioural changes to numerous species. Yet, there is still little understanding if behavioural changes have consequences for health and fitness. The current study combined accelerometry and respirometry to show that provisioning whitetip reef sharks (Triaenodon obesus) for tourism increases their daily energy expenditure by elevating activity levels during periods when they normally rest. Field metabolic rate increased by 6.37% on provisioning days compared to non-provisioning days. Since metabolism is a key parameter influencing most biological and ecological processes, this represents some of the clearest evidence to date that ecotourism can impact critical biological functions in wild animals.

We report population genetic structure and fine-scale recruitment processes for the scallop beds (Pecten fumatus) in Bass Strait and the eastern coastline of Tasmania in southern Australia. Conventional population pairwise FST analyses are compared with novel discriminant analysis of principal components (DAPC) to assess population genetic structure using allelic variation in 11 microsatellite loci. Fine-scale population connectivity was compared with oceanic features of the sampled area. Disjunct scallop beds were genetically distinct, but there was little population genetic structure between beds connected by tides and oceanic currents. To identify recruitment patterns among and within beds, pedigree analyses determined the distribution of parent–offspring and sibling relationships in the sampled populations. Beds in northeastern Bass Strait were genetically distinct to adjacent beds (FST 0.003–0.005) and may not contribute to wider recruitment based on biophysical models of larval movement. Unfortunately, pedigree analyses lacked power to further dissect fine-scale recruitment processes including self-recruitment. Our results support the management of disjunct populations as separate stocks and the protection of source populations among open water beds. The application of DAPC and parentage analyses in the current study provided valuable insight into their potential power to determine population connectivity in marine species with larval dispersal.

Dive characteristics and dive shape are often used to infer foraging success in pinnipeds. However, these inferences have not been directly validated in the field with video, and it remains unclear if this method can be applied to benthic foraging animals. This study assessed the ability of dive characteristics from time-depth recorders (TDR) to predict attempted prey capture events (APC) that were directly observed on animal-borne video in Australian fur seals (Arctocephalus pusillus doriferus, n=11). The most parsimonious model predicting the probability of a dive with ≥1 APC on video included only descent rate as a predictor variable. The majority (94%) of the 389 total APC were successful, and the majority of the dives (68%) contained at least one successful APC. The best model predicting these successful dives included descent rate as a predictor. Comparisons of the TDR model predictions to video yielded a maximum accuracy of 77.5% in classifying dives as either APC or non-APC or 77.1% in classifying dives as successful verses unsuccessful. Foraging intensity, measured as either total APC per dive or total successful APC per dive, was best predicted by bottom duration and ascent rate. The accuracy in predicting total APC per dive varied based on the number of APC per dive with maximum accuracy occurring at 1 APC for both total (54%) and only successful APC (52%). Results from this study linking verified foraging dives to dive characteristics potentially opens the door to decades of historical TDR datasets across several otariid species., Summary: We assessed the ability of dive characteristics in Australian fur seals to predict foraging behavior and success that were directly observed on video. TDR data was able to reliably predict presence of prey as well as total successful prey captured per dive.

Empirical testing of optimal foraging models on diving air-breathing animals is limited due to difficulties in quantifying the prey field through direct observations. Here we used accelerometers to detect rapid head movements during prey encounter events (PEE) of free-ranging benthic-divers, Australian fur seals, Arctocephalus pusillus doriferus. PEE signals from accelerometer data were validated by simultaneous video data. We then used PEEs as a measure of patch quality to test several optimal foraging model predictions. Seals had longer bottom durations in unfruitful dives (no PEE) than those with some foraging success (PEE ≥ 1). However, when examined in greater detail, seals had longer bottom durations in dives with more PEEs, but shorter bottom durations in bouts (sequences of dives) with more PEEs. Our results suggest that seals were generally maximizing bottom durations in all foraging dives, characteristic of benthic divers. However, successful foraging dives might be more energetically costly (e.g. digestive costs), thus resulting in shorter bottom durations at the larger scale of bouts. Our study provides a case study of how the foraging behaviour of a central place forager foraging in a fairly homogeneous environment, with relatively high travel costs, may deviate from current foraging models under different situations. Future foraging models should aim to integrate other aspects (e.g. diet) of the foraging process for more accurate predictions.

Understanding the way catchability of exploited fish species varies due to changes in individual fish behaviour is a seldom addressed but important requisite for extracting accurate information on fish abundance from catch per unit effort (cpue) data, particularly from baited gears. In this study, cpue data analysis was combined with analysis of movement and activity data from acoustic telemetry tags to determine the nature of seasonal changes in cpue of the recreationally caught sand flathead ( Platycephalus bassensis ) in a coastal bay and estuary in southeast Tasmania, Australia. Water temperature had a significant influence on cpue of sand flathead with lower catches at lower temperatures. Yet, even at the relatively small scale of this study (10 s of km), the mechanisms in which temperature affects cpue were highly area specific. In the shallow, estuarine part of the study area, changes in cpue were driven by changes in availability, due to seasonal movements of fish in and out of the area. In the deeper bay at the mouth of the estuary, on the other hand, changes in cpue with temperature were most likely driven by temperature-related changes in activity. At lower temperatures, fish were less active, indicating that fish will have a lower probability of encountering bait as well as lower feeding motivation due to lower metabolic debt. This shows the importance of the inclusion of an environmentally influenced catchability parameter in stock assessment models that utilize cpue data from baited gear types, which is often only done implicitly on a coarse temporal scale by accounting for changes in cpue with season. Our study furthermore highlights the usefulness of acoustic telemetry in a fisheries context beyond the basic study of fish movement, allowing the monitoring of activity levels of exploited fish in relation to environmental parameters in the field.

Early post-settlement mortality is one of the main processes determining distribution and abundance patterns of marine benthic invertebrates. Most scallops have an attached phase as spat before they release the byssus and move onto the soft sediments. Thus, spat differ from other stages of life in their use of microhabitat, lack of mobility, and therefore in their vulnerability to mortality processes such as predation. However, the contribution of predation to explain levels of mortality experienced by spat and early juvenile scallops is unknown. Complex habitats such as seagrasses and algae provide a substrate upon which spat can attach and might confer an advantage as a refuge from predation. This study investigates the contribution of early post-settlement predation on abundance of Pecten fumatus and determines the role of the algae Hincksia sordida as a refuge from predation. Data were collected using field observations, a predator exclusion experiment, and tethering techniques. Mortality of up to 85% during the first weeks after settlement appeared to have prevented the establishment of an adult population at our study site. Mats of the macroalgae H. sordida provided a settlement substrate for P. fumatus spat. However, increased algal biomass did not provide greater protection from predation to juvenile scallops than lower algal biomass. Our study suggests that prey survival in submersed vegetation is likely to be dynamic among years, and affected by prey behaviour and density as well as the characteristics of the submerged vegetation.

Protecting essential habitats through the implementation of area closures has been recognized as a useful management tool for rebuilding overfished populations and minimizing habitat degradation. School shark ( Galeorhinus galeus ) have suffered significant stock declines in Australia; however, recent stock assessments suggest the population may have stabilized and the protection of closed nursery areas has been identified as a key management strategy to rebuilding their numbers. Young-of-the-year (YOY) and juvenile G. galeus were acoustically tagged and monitored to determine ontogenetic differences in residency and seasonal use of an important protected nursery area (Shark Refuge Area or SRA) in southeastern Tasmania. Both YOY and juvenile G. galeus showed a distinct seasonal pattern of occurrence in the SRA with most departing the area during winter and only a small proportion of YOY (33%) and no juveniles returning the following spring, suggesting areas outside the SRA may also be important during these early life-history stages. While these behaviors confirm SRAs continue to function as essential habitat during G. galeus early life history, evidence of YOY and juveniles emigrating from these areas within their first 1–2 years and the fact that few YOY return suggest that these areas may only afford protection for a more limited amount of time than previously thought. Determining the importance of neighbouring coastal waters and maintaining the use of traditional fisheries management tools are therefore required to ensure effective conservation of G. galeus during early life history.

1. Body size is a key determinant of metabolic rate, but logistical constraints have led to a paucity of energetics measurements from large water-breathing animals. As a result, estimating energy requirements of large fish generally relies on extrapolation of metabolic rate from individuals of lower body mass using allometric relationships that are notoriously variable. Swim-tunnel respirometry is the 'gold standard' for measuring active metabolic rates in water-breathing animals, yet previous data are entirely derived from body masses

Seismic surveys map the seabed using intense, low-frequency sound signals that penetrate kilometers into the Earth's crust. Little is known regarding how invertebrates, including economically and ecologically important bivalves, are affected by exposure to seismic signals. In a series of field-based experiments, we investigate the impact of exposure to seismic surveys on scallops, using measurements of physiological and behavioral parameters to determine whether exposure may cause mass mortality or result in other sublethal effects. Exposure to seismic signals was found to significantly increase mortality, particularly over a chronic (months postexposure) time scale, though not beyond naturally occurring rates of mortality. Exposure did not elicit energetically expensive behaviors, but scallops showed significant changes in behavioral patterns during exposure, through a reduction in classic behaviors and demonstration of a nonclassic "flinch" response to air gun signals. Furthermore, scallops showed persistent alterations in recessing reflex behavior following exposure, with the rate of recessing increasing with repeated exposure. Hemolymph (blood analog) physiology showed a compromised capacity for homeostasis and potential immunodeficiency, as a range of hemolymph biochemistry parameters were altered and the density of circulating hemocytes (blood cell analog) was significantly reduced, with effects observed over acute (hours to days) and chronic (months) scales. The size of the air gun had no effect, but repeated exposure intensified responses. We postulate that the observed impacts resulted from high seabed ground accelerations driven by the air gun signal. Given the scope of physiological disruption, we conclude that seismic exposure can harm scallops.

Understanding how aquatic species respond to extremes of DO and temperature is crucial for determining how they will be affected by climate change, which is predicted to increasingly expose them to levels beyond their optima. In this study we used novel animal-borne DO, temperature and depth sensors to determine the effect of extremes of DO and temperature on the vertical habitat use of Atlantic salmon Salmo salar in aquaculture cages. Salmon showed a preference for temperatures around 16.5 to 17.5 °C, however, selection of preferred temperatures was trumped by active avoidance of low DO (20.1 °C), which led to a considerable contraction in the available vertical habitat. Despite their avoidance behavior, fish spent a large amount of time in waters with suboptimal DO (

We have little empirical evidence of how large-scale overlaps between large numbers of marine species may have altered in response to human impacts. Here, we synthesized all available distribution data (>1 million records) since 1992 for 61 species of the East Australian marine ecosystem, a global hot spot of ocean warming and continuing fisheries exploitation. Using a novel approach, we constructed networks of the annual changes in geographical overlaps between species. Using indices of changes in species overlap, we quantified changes in the ecosystem stability, species robustness, species sensitivity and structural keystone species. We then compared the species overlap indices with environmental and fisheries data to identify potential factors leading to the changes in distributional overlaps between species. We found that the structure of the ecosystem has changed with a decrease in asymmetrical geographical overlaps between species. This suggests that the ecosystem has become less stable and potentially more susceptible to environmental perturbations. Most species have shown a decrease in overlaps with other species. The greatest decrease in species overlap robustness and sensitivity to the loss of other species has occurred in the pelagic community. Some demersal species have become more robust and less sensitive. Pelagic structural keystone species, predominately the tunas and billfish, have been replaced by demersal fish species. The changes in species overlap were strongly correlated with regional oceanographic changes, in particular increasing ocean warming and the southward transport of warmer and saltier water with the East Australian Current, but less correlated with fisheries catch. Our study illustrates how large-scale multispecies distribution changes can help identify structural changes in marine ecosystems associated with climate change.

In broadcast spawners, low densities and poor spawning synchronization can reduce fertilization success. In wild populations, individuals in close proximity tend to spawn more synchronously than those further apart, sug- gesting that low spawner densities may reduce gamete pro- duction by lessening the efficacy of pheromone signalling. This study assessed the role of adult density in aggregation patterns and spawning synchronization in a semi-sessile, hermaphroditic scallop, Pecten fumatus. The study was carried out in Great Bay, Tasmania, Australia (147.335 W, 43.220 S) in 2010-2012 by assessing (1) the relationship between density, small-scale aggregation patterns and near- est neighbour distance (NND), (2) the temporal pattern of spawning synchronization, and (3) the effect of site density and conspecific proximity on the probability of spawn- ing. Densities observed in the field ranged from 1.455 to 0.021 ind m −2 . Sites with lower densities had less small- scale aggregation and greater NNDs. Patterns of small- scale aggregation and NNDs in P. fumatus were compara- ble to those observed in a gonochoristic species. Spawning synchronization was highly variable, ranging between 3.5

Understanding the links between external variables such as habitat and interactions with conspecifics and animal space-use is fundamental to developing effective management measures. In the marine realm, automated acoustic tracking has become a widely used method for monitoring the movement of free-ranging animals, yet researchers generally lack robust methods for analysing the resulting spatial-usage data. In this study, acoustic tracking data from male and female broadnose sevengill sharks Notorynchus cepedianus, collected in a system of coastal embayments in southeast Tasmania were analyzed to examine sex-specific differences in the sharks' coastal space-use and test novel methods for the analysis of acoustic telemetry data. Sex-specific space-use of the broadnose sevengill shark from acoustic telemetry data was analysed in two ways: The recently proposed spatial network analysis of between-receiver movements was employed to identify sex-specific space-use patterns. To include the full breadth of temporal information held in the data, movements between receivers were furthermore considered as transitions between states of a Markov chain, with the resulting transition probability matrix allowing the ranking of the relative importance of different parts of the study area. Both spatial network and Markov chain analysis revealed sex-specific preferences of different sites within the study area. The identification of priority areas differed for the methods, due to the fact that in contrast to network analysis, our Markov chain approach preserves the chronological sequence of detections and accounts for both residency periods and movements. In addition to adding to our knowledge of the ecology of a globally distributed apex predator, this study presents a promising new step towards condensing the vast amounts of information collected with acoustic tracking technology into straightforward results which are directly applicable to the management and conservation of any species that meet the assumptions of our model.

Understanding the patterns of large-scale movements of highly mobile marine predators is essential to understanding the impacts of anthropogenic pressures on the animals and the ecosystems they frequent. The broadnose sevengill shark Notorynchus cepedianus is one of the most important apex predators in temperate coastal areas around the world, yet little is known of its seasonal large-scale movements. Five male and five female sevengill sharks were equipped with pop-up satellite archival tags (PSATs) in a coastal embayment in southern Tasmania, that collected depth and temperature data during winter, when the animals leave the coastal embayment, resulting in a dataset covering a total of 818 d. Animal tracks indicated that males moved northwards into warmer waters, whereas females remained in southern waters. Three of the females stayed in the Tasmanian coastal areas while the other two left, with one of them moving into deeper waters of up to 360 m depth at the southern edge of the Tasmanian shelf before returning to the Tasmanian coast. These sex-specific differences in large-scale movement could potentially lead to the differential exploitation of the sexes when the sharks leave the protected areas where they were tagged. Both males and females switched between diel vertical migration and reverse diel vertical migration over the course of their tracks and displayed oscillatory vertical movements, probably linked to foraging. These vertical movements persisted throughout the tracks, suggesting that sevengill sharks foraged continuously during their migration rather than switching between transiting and foraging modes.

An understanding of the influence of life history on dispersal capability is central to a range of disciplines within ecology and evolution. While studies have investigated this question by contrasting spatial population structuring in taxa that differ in life history, in the vast majority such comparisons differ in space and time, and therefore environmental factors may have contributed. Here, population structure of a holobenthic (i.e. direct developing) octopus, Octopus pallidus , was investigated genetically. This was compared to existing genetic data for a co-occurring merobenthic (i.e. planktonic larvae) species, Macroctopus maorum . Greater spatial genetic structuring was evident in O. pallidus than M. maorum . Patterns were consistent with isolation by distance in O. pallidus , but appeared related to oceanographic circulation systems in M. maorum , suggesting distance-dependent adult dispersal and current-mediated larval dispersal, respectively. Genetic population structuring in O. pallidus also largely corroborated inferences based on stylet microchemistry, indicating the utility of these environmental signatures. This study enables stronger predictions to be made regarding the dispersal capabilities and spatial population structuring of other cephalopods based on life history.

Site fidelity and migratory movements of vertebrate animals occur at many spatial and temporal scales. Larger migratory movements tend to occur in species that live in seasonal environments in which food supplies vary markedly, while species found in thermally stable environments are more site-attached. In the marine environment, seasonal migrations are often associated with predictable temporary aggregations that have largely been targeted for exploitation. We employed passive acoustic telemetry to investigate inter- and intraseasonal site fidelity of zebra sharks to an aggregation site in southeast Queensland, Australia, close to the southern latitudinal extent of this species' range. We tracked 10 zebra sharks over two aggregation seasons (21 months). We applied a generalized linear mixed-effects model to investigate the presence/absence of these zebra sharks with respect to several environmental variables. We found that different environmental factors were associated with site fidelity of zebra sharks at different temporal levels and that these may be indicative of the mechanisms driving the movements. Seasonal patterns may be driven by endogenous systems, and cues such as photoperiod and water temperature are likely to be important. Intraseasonal patterns are more likely to be indicative of direct behavioural responses to changes in environmental conditions such as increased wave heights, as well as foraging bouts away from a core refuge. Understanding the relative contributions of these environmental parameters, as well as biological factors, will be important for making predictions of site fidelity and movements of migratory marine vertebrates under differing future scenarios such as increases in sea temperature.

Environmental DNA (eDNA) techniques have only recently been applied in the marine environment to detect the presence of marine species. Species-specific primers and probes were designed to detect the eDNA of the endangered Maugean skate (Zearaja maugeana) from as little as 1 L of water collected at depth (10-15 m) in Macquarie Harbour (MH), Tasmania. The identity of the eDNA was confirmed as Z. maugeana by sequencing the qPCR products and aligning these with the target sequence for a 100% match. This result has validated the use of this eDNA technique for detecting a rare species, Z. maugeana, in the wild. Being able to investigate the presence, and possibly the abundance, of Z. maugeana in MH and Bathurst harbour (BH), would be addressing a conservation imperative for the endangered Z. maugeana. For future application of this technique in the field, the rate of decay was determined for Z. maugeana eDNA under ambient dissolved oxygen (DO) levels (55% saturation) and lower DO (20% saturation) levels, revealing that the eDNA can be detected for 4 and 16 hours respectively, after which eDNA concentration drops below the detection threshold of the assay. With the rate of decay being influenced by starting eDNA concentrations, it is recommended that samples be filtered as soon as possible after collection to minimize further loss of eDNA prior to and during sample processing.

Zooplankton underpin the health and productivity of global marine ecosystems. Here we present evidence that suggests seismic surveys cause significant mortality to zooplankton populations. Seismic surveys are used extensively to explore for petroleum resources using intense, low-frequency, acoustic impulse signals. Experimental air gun signal exposure decreased zooplankton abundance when compared with controls, as measured by sonar (∼3-4 dB drop within 15-30 min) and net tows (median 64% decrease within 1 h), and caused a two- to threefold increase in dead adult and larval zooplankton. Impacts were observed out to the maximum 1.2 km range sampled, which was more than two orders of magnitude greater than the previously assumed impact range of 10 m. Although no adult krill were present, all larval krill were killed after air gun passage. There is a significant and unacknowledged potential for ocean ecosystem function and productivity to be negatively impacted by present seismic technology.

Shark nurseries are susceptible to environmental fluctuations in salinity because of their shallow, coastal nature; however, the physiological impacts on resident elasmobranchs are largely unknown. Gummy sharks (Mustelus antarcticus) and school sharks (Galeorhinus galeus) use the same Tasmanian estuary as a nursery ground; however, each species has distinct distribution patterns that are coincident with changes in local environmental conditions, such as increases in salinity. We hypothesized that these differences were directly related to differential physiological tolerances to high salinity. To test this hypothesis, we exposed wild, juvenile school and gummy sharks to an environmentally relevant hypersaline (120% SW) event for 48 h. Metabolic rate decreased 20-35% in both species, and gill Na(+)/K(+)-ATPase activity was maintained in gummy sharks but decreased 37% in school sharks. We measured plasma ions (Na(+), K(+), Cl(-)) and osmolytes [urea and trimethylamine oxide (TMAO)], and observed a 33% increase in plasma Na(+) in gummy sharks with hyperosmotic exposure, while school sharks displayed a typical ureosmotic increase in plasma urea (∼20%). With elevated salinity, gill TMAO concentration increased by 42% in school sharks and by 30% in gummy sharks. Indicators of cellular stress (heat shock proteins HSP70, 90 and 110, and ubiquitin) significantly increased in gill and white muscle in both a species- and a tissue-specific manner. Overall, gummy sharks exhibited greater osmotic perturbation and ionic dysregulation and a larger cellular stress response compared with school sharks. Our findings provide physiological correlates to the observed distribution and movement of these shark species in their critical nursery grounds.

The generalized energy budget for fish (i.e., Energy Consumed = Metabolism + Waste + Growth) is as relevant today as when it was first proposed decades ago and serves as a foundational concept in fish biology. Yet, generating accurate measurements of components of the bioenergetics equation in wild fish is a major challenge. How often does a fish eat and what does it consume? How much energy is expended on locomotion? How do human-induced stressors influence energy acquisition and expenditure? Generating answers to these questions is important to fisheries management and to our understanding of adaptation and evolutionary processes. The advent of electronic tags (transmitters and data loggers) has provided biologists with improved opportunities to understand bioenergetics in wild fish. Here, we review the growing diversity of electronic tags with a focus on sensor-equipped devices that are commercially available (e.g., heart rate/electrocardiogram, electromyogram, acceleration, image capture). Next, we discuss each component of the bioenergetics model, recognizing that most research to date has focused on quantifying the activity component of metabolism, and identify ways in which the other, less studied components (e.g., consumption, specific dynamic action component of metabolism, somatic growth, reproductive investment, waste) could be estimated remotely. We conclude with a critical but forward-looking appraisal of the opportunities and challenges in using existing and emerging electronic sensor-tags for the study of fish energetics in the wild. Electronic tagging has become a central and widespread tool in fish ecology and fisheries management; the growing and increasingly affordable toolbox of sensor tags will ensure this trend continues, which will lead to major advances in our understanding of fish biology over the coming decades.

In theory, predators should attempt to match the distribution of their prey, and prey to avoid areas of high predation risk. However, there is a scarcity of empirical knowledge on predator and prey spatial use when both are moving freely in their natural environment. In the current study, we use information collated on a predators' diet, its population structure, as well as predator and prey relative abundance, and track the movements of predator and prey simultaneously to compare habitat use and evaluate predation pressure. The study was conducted in elasmobranch protected areas of coastal Tasmania, Australia. The species considered were the broadnose sevengill shark Notorynchus cepedianus, the apex predator in the area, and five chondrichthyan prey species. Notorynchus cepedianus and its prey show similar seasonality in the use of these coastal areas: more abundant in warmer months and absent in winter. Predator and prey also showed high spatial overlap and similar habitat use patterns. These similar movement patterns of predator and prey combined with the additional ecological information (diet, population structure of predator, relative abundance of predator and prey) suggests that N. cepedianus move into coastal areas to exploit seasonally abundant prey. Also, while in protected areas, chondrichthyans are subjected to high predation pressure. Overall, results illustrate the value of simultaneously recording and integrating multiple types of information to explore predator–prey relationships and predation pressure.

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.

Despite the ecological and increasing commercial significance of cephalopods worldwide, little attention has been paid to developing techniques that investigate the movement of early life-history stages. We evaluated the potential of mass-marking giant Australian cuttlefish Sepia apama hatchlings, via immersion of eggs in water enriched in 137Ba isotope. Eggs were immersed in several 137Ba concentrations, for varying durations, and at different stages of development. Statoliths of hatchlings from each combination of 137Ba concentration (0.3 and 1 ig l–1) and immersion time (2, 5 and 8 d) produced lower mean 138Ba:137Ba values than control hatchlings, and mark success was generally high (70–100% of statoliths were unequivocally marked across all treatments). Development stage was an important factor, with statoliths successfully marked only for eggs immersed in 137Ba at 10 wk of age. These results suggest that marking of statoliths via enriched isotope immersion offers considerable potential for understanding juvenile dispersal and connectivity of cephalopod populations in nature.

Doubleday, Z. A., White, J., Pecl, G. T., and Semmens, J. M. 2011. Age determination in merobenthic octopuses using stylet increment analysis: assessing future challenges using Macroctopus maorum as a model. – ICES Journal of Marine Science, 68: 2059–2063. Stylet increment analysis (SIA) is a method recently developed to age octopuses; it involves the enumeration of daily growth increments within stylets (an internal shell). To examine the potential of SIA in a merobenthic octopus species, SIA was applied to Macroctopus maorum collected from southeast Australia and New Zealand (n = 147). The stylets had clear concentric growth increments and a core-like region. However, low increment counts (≤224 d) produced non-feasibly high (≤21.7% body weight per day) instantaneous growth rates, based on the assumption that increment number relates to age (d). In the light of these results, the issues surrounding the application of SIA to merobenthic octopuses is discussed, particularly in relation to the lack of understanding in regard to stylet development in the early life history stages and the importance of validating age at first increment formation.

Many salmon populations in both the Pacific and Atlantic Oceans have experienced sharply decreasing returns and high ocean mortality in the past two decades, with some populations facing extirpation if current marine survival trends continue. Our inability to monitor the movements of marine fish or to directly measure their survival precludes experimental tests of theories concerning the factors regulating fish populations, and thus limits scientific advance in many aspects of fisheries management and conservation. Here we report a large-scale synthesis of survival and movement rates of free-ranging juvenile salmon across four species, 13 river watersheds, and 44 release groups of salmon smolts (>3,500 fish tagged in total) in rivers and coastal ocean waters, including an assessment of where mortality predominantly occurs during the juvenile migration. Of particular importance, our data indicate that, over the size range of smolts tagged, ( i ) smolt survival was not strongly related to size at release, ( ii ) tag burden did not appear to strongly reduce the survival of smaller animals, and ( iii ) for at least some populations, substantial mortality occurred much later in the migration and more distant from the river of origin than generally expected. Our findings thus have implications for determining where effort should be invested to improve the accuracy of salmon forecasting, to understand the mechanisms driving salmon declines, and to predict the impact of climate change on salmon stocks.

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.

Small temperature increases will benefit the growth of many cold-blooded animals, but laboratory studies indicate that warming can eventually exceed physiological limits, resulting in reduced growth. Evidence shows that this may have already happened for a fish species—the banded morwong—in the Tasman Sea. Climate change can affect organisms both directly, by affecting their physiology, growth, and behaviour1, and indirectly, for example through effects on ecosystem structure and function1,2. For ectotherms, or ‘cold-blooded’ animals, warming will directly affect their metabolism, with growth rates in temperate species predicted to increase initially as temperatures rise, but then decline as individuals struggle to maintain cardiac function and respiration in the face of increased metabolic demands3,4. We provide evidence consistent with this prediction for a marine fish (Cheilodactylus spectabilis) in the Tasman Sea; one of the most rapidly warming regions of the Southern Hemisphere ocean5. We estimated changes in the species’ growth rate over a 90-year period using otoliths—bony structures that fish use for orientation and detection of movement—and compared these changes to temperature trends across the species’ distribution. Increasing temperatures coincide with increased growth for populations in the middle of the species range, but with reduced growth for those at the warm northern edge of the species’ distribution, indicating that temperatures may have already reached levels associated with increased metabolic costs. If warming continues, the direct metabolic effects of increasing temperatures on this species may lead to declining productivity and range contraction.

Species occupying high trophic positions with a small population size, limited diet and restricted range are vulnerable to extinction. The endangered Maugean skate (Zearaja maugeana) in Macquarie Harbour is potentially threatened by changing benthic environmental conditions (declining dissolved oxygen concentrations and decreased macrofaunal diversity). To inform investigations on potential indirect impacts of benthic environmental changes on the Maugean skate and its prey, non-lethal techniques were used to identify dietary composition and trophic position of the species. The Maugean skate occupies a high trophic position (3.70) in the food web, with both stable-isotope (median 86% contribution to isotopic signatures, credible interval (CI)=44–100%) and stomach-content analysis showing crustaceans, particularly brachyuran crabs (58.5% index of relative importance), as the dominant prey type. Aquaculture feed from salmonid fish farms operating in the harbour was not found to be important in skate diet. This study showed that the Maugean skate consumes a small number of benthic prey species, highlighting its vulnerability to changing environmental conditions in the harbour.

Acoustic telemetry has emerged as a leading approach to infer diel, tidal and lunar rhythmicity in the movements of aquatic organisms in a range of taxa. Typically, studies examine the relative frequency of detections from individuals tagged with acoustic transmitters, and then infer patterns in the species’ behaviour, but studies to date have not controlled for factors that may influence tag detection patterns in the absence of animal behaviour. We compared patterns in acoustic detections from tagged cuttlefish Sepia apama and several fixed-location control tags, and used these data to highlight the danger of misinterpreting patterns in the absence of adequate controls. Cuttlefish and control tags displayed similar detection patterns, and correcting cuttlefish-detection data for the influence of environmental factors resulted in the opposite pattern of cuttlefish activity displayed prior to correction. This study highlights the danger of using acoustic data to infer animal behaviour in the absence of adequate controls.

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.

1. Estimating the metabolic rate of animals in nature is central to understanding the physiological, behavioural and evolutionary ecology of animals. Doubly labelled water and heart-rate methods are the most commonly used approaches, but both have limitations that preclude their application to some systems. 2. Accelerometry has emerged as a powerful tool for estimating energy expenditure in a range of animals, but is yet to be used to estimate field metabolic rate in aquatic taxa. We combined two-dimensional accelerometry and swim-tunnel respirometry to estimate patterns of energy expenditure in giant Australian cuttlefish Sepia apama during breeding. 3. Both oxygen consumption rate (Vo2) and swimming speed showed strong positive associations with body acceleration, with coefficients of determination comparable to those using similar accelerometers on terrestrial vertebrates. Despite increased activity during the day, field metabolic rate rarely approached Vo2, and night-time Vo2 was similar to that at rest. 4. These results are consistent with the life-history strategy of this species, which has a poor capacity to exercise anaerobically, and a mating strategy that is visually based. With the logistical difficulties associated with observation in aquatic environments, accelerometry is likely to prove a valuable tool for estimating energy expenditure in aquatic animals.

Dietary information of apex predators is crucial to understanding community dynamics and ecosystem processes. However, as dietary studies traditionally involve lethal sampling, obtaining this essential information can have repercussions on predator populations and the structure and functioning of marine ecosystems. With stronger emphasis being placed on conservation of species that are vulnerable to overexploitation, the need for non-destructive methods of sampling is imperative, as is the requirement to maximize the information obtained from each sample. Stomach flushing (gastric lavage) and DNA analysis of stomach contents methods were tested on the broadnose sevengill shark Notorynchus cepedianus Peron 1807. Acoustic tracking and recaptures of sharks implied high survivorship post-fishing and stomach flushing. From 85 prey items collected, 36 (43%) could be identified to species level using morphological analysis. After DNA analysis, a further 35 items were identified to species level, doubling the information obtained from these stomachs. The number of N. cepedianus that were confirmed to have eaten gummy sharks Mustelus antarcticus Gunther 1870 also doubled after DNA analysis. Without DNA analysis (of stomach contents) the importance of M. antarcticus in the diets of N. cepedianus would have been substantially underestimated. In addition, the non-lethal approach provides an opportunity to obtain meaningful information from non-harvested, endangered or rare species or sampling of species within protected areas.

Adult sex ratios (ASRs) and population size are two of the most fundamental parameters in population biology, as they are the main determinants of genetic and demographic viability, and vulnerability of a population to stochastic events. Underpinning the application of population viability analysis for predicting the extinction risk of populations is the need to accurately estimate parameters that determine the viability of populations (i.e. the ASR and population size). Here we demonstrate that a lack of temporal information can confound estimation of both parameters. Using acoustic telemetry, we compared differences in breeding durations of both sexes for a giant Australian cuttlefish Sepia apama breeding aggregation to the strongly male-biased operational sex ratio (4:1), in order to estimate the population ASR. The ratio of breeding durations between sexes was equal to the operational sex ratio, suggesting that the ASR is not strongly male-biased, but balanced. Furthermore, the short residence times of individuals at the breeding aggregation suggests that previous density-based abundance estimates have significantly underestimated population size. With the current wide application of population viability analysis for predicting the extinction risk of populations, tools to improve the accuracy of such predictions are vital. Here we provide a new approach to estimating the fundamental ASR parameter, and call for temporal considerations when estimating population size.