Foraging ecology of ringed seals (Pusa hispida), beluga whales (Delphinapterus leucas) and narwhals (Monodon monoceros) in the Canadian High Arctic determined by stomach content and stable isotope analysis

Stomach content and stable isotope analysis (delta C-13 and delta N-15 from liver and muscle) were used to identify habitat and seasonal prey selection by ringed seals (Pusa hispida; n = 21), beluga whales (Delphinapterus leucas; n = 13) and narwhals (Monodon monoceros; n = 3) in the eastern Canadian Arctic. Arctic cod (Boreogadus saida) was the main prey item of all three species. Diet reconstruction from otoliths and stable isotope analysis revealed that while ringed seal size influenced prey selection patterns, it was variable. Prey-size selection and on-site observations found that ringed seals foraged on smaller, non-schooling cod whereas belugas and narwhals consumed larger individuals in schools. Further interspecific differences were demonstrated by delta C-13 and delta N-15 values and indicated that ringed seals consumed inshore Arctic cod compared to belugas and narwhals, which foraged to a greater extent offshore. This study investigated habitat variability and interseasonal variation in the diet of Arctic marine mammals at a local scale and adds to the sparse data sets available in the Arctic. Overall, these findings further demonstrate the critical importance of Arctic cod to Arctic food webs

Identification of predation events in wild fish using novel acoustic transmitters

Background: Acoustic telemetry is a commonly used tool to gain knowledge about aquatic animal ecology through the study of their movements. In telemetry studies researchers must make inferences regarding the movements and the fates of tagged animals. Until recently, predation has been inferred in telemetry data using a variety of methods including abrupt changes in movement patterns or habitat use. An acoustic telemetry transmitter has been developed to detect predation events of tagged animals, and while they have performed well in controlled laboratory trials, literature regarding the application of these novel transmitters in field settings is limited. The objective of this research was to describe the detection data obtained from field studies using predation tags and propose methods to incorporate this information in decision-making about the fate of tagged animals. We implanted 60 yellow perch (Perca flavescens) with predation transmitters and evaluated their spatial use in a receiver array (34 ha) using a combination of centres of activity, roaming indices, and step length measures to examine detection data. Results: Over 5 months, 19 apparent predation events were identified by the transmitters. Roaming indices and centres of activity revealed a variety of detection patterns, including instances of altered behaviour before and after predation that matched tag-indentified predation events, dropped tags post-predation, and detections that ceased post-predation indicating the predator might have left the array. Based on the observed patterns, probable predation was inferred for 15 of 19 triggered tags, with unclear fates for four fish. Conclusions: Our study provided a framework to assess the fate of animals tagged with predation transmitters and demonstrate how these tags can contribute to telemetry studies. We showed how detections can be categorized using tag status to compare movement metrics among individuals, provided tools to explore space use surrounding predation events, and synthesized this information to inform uncertainty surrounding tag-identified predation events. Predation tags do not remove all uncertainty about the fate of tagged individuals, but combined with other metrics they increase the likelihood of identifying abnormal movements that could otherwise introduce biased detection histories into studies of small-sized fishes

The influence of dynamic environmental interactions on detection efficiency of acoustic transmitters in a large, deep, freshwater lake

Background: Acoustic telemetry is an increasingly common method used to address ecological questions about the movement, behaviour, and survival of freshwater and marine organisms. The variable performance of acoustic telemetry equipment and ability of receivers to detect signals from transmitters have been well studied in marine and coral reef environments to inform study design and improve data interpretation. Despite the growing use of acoustic telemetry in large, deep, freshwater systems, detection efficiency and range, particularly in relation to environmental variation, are poorly understood. We used an array of 90 69-kHz acoustic receivers and 8 sentinel range transmitters of varying power output deployed at different depths and locations approximately 100-9500 m apart for 215 days to evaluate how the detection efficiency of acoustic receivers varied spatially and temporally in relation to environmental conditions. Results: The maximum distance that tags were detected ranged from 5.9 to 9.3 km. Shallow tags consistently had lower detection efficiency than deep tags of the same power output and detection efficiency declined through the winter months (December-February) of the study. In addition to the distance between tag and receiver, thermocline strength, surface water velocity, ice thickness, water temperature, depth range between tag and receiver, and number of fish detections contributed to explaining variation in detection efficiency throughout the study period. Furthermore, the most significant models incorporated interactions between several environmental variables and tag-receiver distance, demonstrating the complex temporal and spatial relationships that exist in heterogeneous environments. Conclusions: Relying on individual environmental variables in isolation to interpret receiver performance, and thus animal behaviour, may be erroneous when detection efficiency varies across distances, depths, or tag types. As acoustic telemetry becomes more widely used to study ecology and inform management, it is crucial to understand its limitations in heterogeneous environments, such as freshwater lakes, to improve the quality and interpretation of data. We recommend that in situ range testing and retrospective analysis of detection efficiency be incorporated into study design for telemetry projects. Furthermore, we caution against oversimplifying the dynamic relationship between detection efficiency and environmental conditions for the sake of producing a correction that can be applied directly to detection data of tagged animals when the intended correction may not be justified

Ocean warming has greater and more consistent negative effects than ocean acidification on the growth and health of subtropical macroalgae

Macroalgae are the major habitat-forming organisms in many coastal temperate and subtropical marine systems. Although climate change has been identified as a major threat to the persistence of macroalgal beds, the combined effects of ocean warming and ocean acidification on algal performance are poorly understood. Here we investigate the effects of increased temperature and acidification on the growth, calcification and nutritional content of 6 common subtropical macroalgae; Sargassum linearifolium, Ulva sp., Amphiroa anceps, Corallina officinalis, Delisea pulchra and Laurencia decussata. Algae were reared in a factorial cross of 3 temperatures (23°C [ambient], 26°C and 28°C) and 3 pH levels (8.1 [ambient], 7.8 and 7.6) for 2 wk. The highest (28°C) temperature decreased the growth of all 6 macroalgal species, irrespective of the pH levels. In contrast, the effect of decreased pH on growth was variable. The growth of Ulva sp. and C. officinalis increased, L. decussata decreased, while the remaining 3 species were unaffected. Interestingly, the differential responses of macroalgae to ocean acidification were unrelated to whether or not a species was a calcifying alga, or their carbon-uptake mechanism—2 processes that are predicted to be sensitive to decreased pH. The growth of the calcifying algae (C. officinalis and A. anceps) was not affected by reduced pH but calcification of these 2 algae was reduced when exposed to a combination of reduced pH and elevated temperature. The 3 species capable of uptake of bicarbonate, S. linearifolium, L. decussata and Ulva sp., displayed positive, negative and neutral changes in growth, respectively, in response to reduced pH. The C:N ratio for 5 of the 6 species was unaffected by either pH or temperature. The consistent and predictable negative effects of temperature on the growth and calcification of subtropical macroalgae suggests that this stressor poses a greater threat to the persistence of subtropical macroalgal populations than ocean acidification under ongoing and future climate change

Integrating complementary methods to improve diet analysis in fishery‐targeted species

Developing efficient, reliable, cost‐effective ways to identify diet is required to understand trophic ecology in complex ecosystems and improve food web models. A combination of techniques, each varying in their ability to provide robust, spatially and temporally explicit information can be applied to clarify diet data for ecological research. This study applied an integrative analysis of a fishery‐targeted species group—Plectropomus spp. in the central Great Barrier Reef, Australia, by comparing three diet‐identification approaches. Visual stomach content analysis provided poor identification with ~14% of stomachs sampled resulting in identification to family or lower. A molecular approach was successful with prey from ~80% of stomachs identified to genus or species, often with several unique prey in a stomach. Stable isotope mixing models utilizing experimentally derived assimilation data, identified similar prey as the molecular technique but at broader temporal scales, particularly when prior diet information was incorporated. Overall, Caesionidae and Pomacentridae were the most abundant prey families (>50% prey contribution) for all Plectropomus spp., highlighting the importance of planktivorous prey. Less abundant prey categories differed among species/color phases indicating possible niche segregation. This study is one of the first to demonstrate the extent of taxonomic resolution provided by molecular techniques, and, like other studies, illustrates that temporal investigations of dietary patterns are more accessible in combination with stable isotopes. The consumption of mainly planktivorous prey within this species group has important implications within coral reef food webs and provides cautionary information regarding the effects that changing resources could have in reef ecosystems

Integrating complementary methods to improve diet analysis in fishery-targeted species

Developing efficient, reliable, cost-effective ways to identify diet is required to understand trophic ecology in complex ecosystems and improve food web models. A combination of techniques, each varying in their ability to provide robust, spatially and temporally explicit information can be applied to clarify diet data for ecological research. This study applied an integrative analysis of a fishery-targeted species group—Plectropomus spp. in the central Great Barrier Reef, Australia, by comparing three diet-identification approaches. Visual stomach content analysis provided poor identification with ~14% of stomachs sampled resulting in identification to family or lower. A molecular approach was successful with prey from ~80% of stomachs identified to genus or species, often with several unique prey in a stomach. Stable isotope mixing models utilizing experimentally derived assimilation data, identified similar prey as the molecular technique but at broader temporal scales, particularly when prior diet information was incorporated. Overall, Caesionidae and Pomacentridae were the most abundant prey families (\u3e50% prey contribution) for all Plectropomus spp., highlighting the importance of planktivorous prey. Less abundant prey categories differed among species/color phases indicating possible niche segregation. This study is one of the first to demonstrate the extent of taxonomic resolution provided by molecular techniques, and, like other studies, illustrates that temporal investigations of dietary patterns are more accessible in combination with stable isotopes. The consumption of mainly planktivorous prey within this species group has important implications within coral reef food webs and provides cautionary information regarding the effects that changing resources could have in reef ecosystems

Global trends in aquatic animal tracking with acoustic telemetry

Acoustic telemetry (AT) is a rapidly evolving technique used to track the movements of aquatic animals. As the capacity of AT research expands it is important to optimize its relevance to management while still pursuing key ecological questions. A global review of AT literature revealed region-specific research priorities underscoring the breadth of how AT is applied, but collectively demonstrated a lack of management-driven objectives, particularly relating to fisheries, climate change, and protection of species. In addition to the need for more research with direct pertinence to management, AT research should prioritize ongoing efforts to create collaborative opportunities, establish long-term and ecosystem-based monitoring, and utilize technological advancements to bolster aquatic policy and ecological understanding worldwide

Investigation of coral trout (Plectropomus spp.) movement patterns and resource use: a multidisciplinary approach using acoustic telemetry and dietary indicators

Understanding how co-occurring species within comparable trophic guilds (sympatry) partition resources provides fundamental information about their ecological roles within an ecosystem. Despite morphological and biological similarities, resources may be selected and exploited independently, leading to alternative interactions and influences within the ecosystem. Studying movement and dietary patterns directly relates to an animal's resource use, and is a valuable approach to characterise preferred prey and habitat within and between sympatric species. Expanding knowledge of resource use is essential to address how animals are affected by, and how they might respond to, an increasingly variable environment, and is necessary to implement ecosystem-based management practices. Coral trout or coralgrouper (Plectropomus spp.) are iconic and economically significant mesopredatory reef fishes within Australia's Great Barrier Reef (GBR) and throughout the Indo-Pacific region. Despite the importance of Plectropomus spp. in the Queensland Coral Reef Fin Fish Fishery, investigations focussed on their ecology are surprisingly limited. Much of the behavioural-based research has been conducted in scenarios of captivity, is biased by confounding sampling limitations, or only provides short-term, data-poor perspectives. Consequently, interpretations of findings are often applicable only to certain periods or locations, or are only based on patterns from a small number of individuals. This hinders the ability of managers to evaluate how fishing pressure, protection initiatives, and environmental fluctuations or disturbances might impact populations. Furthermore, research is overwhelmingly directed at P. leopardus (or grouped as Plectropomus spp.) which forms the majority of commercial catches on the GBR. Nevertheless, other species such as P. maculatus and P. laevis are readily captured by both recreational and commercial sectors, but their resource selection patterns and interactions with P. leopardus are unknown. The research in this thesis employed two methodological approaches – passive acoustic telemetry and stable isotope analysis, to study movement and dietary patterns, respectively, in three exploited species of coral trout – P. leopardus, P. maculatus, and P. laevis. The research was conducted at three primary locations – Orpheus Island, four mid-shelf/offshore reefs in the Townsville region (Townsville reefs), and the Marine and Aquaculture Research Facilities Unit (MARFU) at James Cook University. Samples and data were collected over the course of three years (2013-2015) providing extensive ecological and behavioural information from more than 300 individual Plectropomus. The overall aim of this research was to quantify, qualify, and compare long-term movement and dietary patterns of sympatric Plectropomus spp. By using multiple approaches, this thesis showed that broad resource selection trends differ between sympatric species, but interestingly, the way they differ is unique to each species pairing. At the Townsville reefs, P. laevis moved greater distances and had increased variability in depth use compared to P. leopardus. Movement patterns were correlated with distinct dietary niches between species, particularly when colour phases of P. laevis (footballer and blue-spot) were separated. The limited isotopic niche overlap between species was not correlated with fish size, indicating alternate prey selection, feeding styles, or energetic requirements engrained at a species level. Based on results from an aquarium-based stable isotope feeding trial, the trophic position of P. leopardus in the wild varied little between sampling locations and time periods. Similarly, the isotopic niches between species remained constant for several tissues (a proxy to feeding timeline) and at several reefs, suggesting feeding pressures exerted by each species is consistent within the region. Consequently, it is hypothesised that both P. laevis and P. leopardus will respond to environmental or humaninduced disturbances in similar ways within and across compatible reefs. At Orpheus Island, P. maculatus shared the same home range size as P. leopardus, however P. maculatus remained deeper in the water column throughout daily and monthly periods. These spatial patterns were correlated to overlapping isotopic niches - or similar prey selection. These trends indicate a high potential for competition that may be mediated by spatial or habitat partitioning. Overall, this research highlights the need for greater species-specific consideration relative to conservation and management initiatives since Plectropomus spp. readily demonstrate distinct behavioural patterns, and will likely respond to disturbances differently. Without fundamental knowledge of how co-occurring species select and partition resources, their interactions and impacts throughout the reef ecosystem remain unknown. Not only did this thesis provide new information about each species, it produced preliminary evidence that interactions between species may shape how resources are utilised on coral reefs

Investigation of coral trout (Plectropomus spp.) movement patterns and resource use: a multidisciplinary approach using acoustic telemetry and dietary indicators

Understanding how co-occurring species within comparable trophic guilds (sympatry) partition resources provides fundamental information about their ecological roles within an ecosystem. Despite morphological and biological similarities, resources may be selected and exploited independently, leading to alternative interactions and influences within the ecosystem. Studying movement and dietary patterns directly relates to an animal's resource use, and is a valuable approach to characterise preferred prey and habitat within and between sympatric species. Expanding knowledge of resource use is essential to address how animals are affected by, and how they might respond to, an increasingly variable environment, and is necessary to implement ecosystem-based management practices. Coral trout or coralgrouper (Plectropomus spp.) are iconic and economically significant mesopredatory reef fishes within Australia's Great Barrier Reef (GBR) and throughout the Indo-Pacific region. Despite the importance of Plectropomus spp. in the Queensland Coral Reef Fin Fish Fishery, investigations focussed on their ecology are surprisingly limited. Much of the behavioural-based research has been conducted in scenarios of captivity, is biased by confounding sampling limitations, or only provides short-term, data-poor perspectives. Consequently, interpretations of findings are often applicable only to certain periods or locations, or are only based on patterns from a small number of individuals. This hinders the ability of managers to evaluate how fishing pressure, protection initiatives, and environmental fluctuations or disturbances might impact populations. Furthermore, research is overwhelmingly directed at P. leopardus (or grouped as Plectropomus spp.) which forms the majority of commercial catches on the GBR. Nevertheless, other species such as P. maculatus and P. laevis are readily captured by both recreational and commercial sectors, but their resource selection patterns and interactions with P. leopardus are unknown. The research in this thesis employed two methodological approaches – passive acoustic telemetry and stable isotope analysis, to study movement and dietary patterns, respectively, in three exploited species of coral trout – P. leopardus, P. maculatus, and P. laevis. The research was conducted at three primary locations – Orpheus Island, four mid-shelf/offshore reefs in the Townsville region (Townsville reefs), and the Marine and Aquaculture Research Facilities Unit (MARFU) at James Cook University. Samples and data were collected over the course of three years (2013-2015) providing extensive ecological and behavioural information from more than 300 individual Plectropomus. The overall aim of this research was to quantify, qualify, and compare long-term movement and dietary patterns of sympatric Plectropomus spp. By using multiple approaches, this thesis showed that broad resource selection trends differ between sympatric species, but interestingly, the way they differ is unique to each species pairing. At the Townsville reefs, P. laevis moved greater distances and had increased variability in depth use compared to P. leopardus. Movement patterns were correlated with distinct dietary niches between species, particularly when colour phases of P. laevis (footballer and blue-spot) were separated. The limited isotopic niche overlap between species was not correlated with fish size, indicating alternate prey selection, feeding styles, or energetic requirements engrained at a species level. Based on results from an aquarium-based stable isotope feeding trial, the trophic position of P. leopardus in the wild varied little between sampling locations and time periods. Similarly, the isotopic niches between species remained constant for several tissues (a proxy to feeding timeline) and at several reefs, suggesting feeding pressures exerted by each species is consistent within the region. Consequently, it is hypothesised that both P. laevis and P. leopardus will respond to environmental or humaninduced disturbances in similar ways within and across compatible reefs. At Orpheus Island, P. maculatus shared the same home range size as P. leopardus, however P. maculatus remained deeper in the water column throughout daily and monthly periods. These spatial patterns were correlated to overlapping isotopic niches - or similar prey selection. These trends indicate a high potential for competition that may be mediated by spatial or habitat partitioning. Overall, this research highlights the need for greater species-specific consideration relative to conservation and management initiatives since Plectropomus spp. readily demonstrate distinct behavioural patterns, and will likely respond to disturbances differently. Without fundamental knowledge of how co-occurring species select and partition resources, their interactions and impacts throughout the reef ecosystem remain unknown. Not only did this thesis provide new information about each species, it produced preliminary evidence that interactions between species may shape how resources are utilised on coral reefs

Summer foraging behaviour of shallow-diving seabirds and distribution of their prey, Arctic cod (Boreogadus saida), in the Canadian Arctic

Productive areas in the Canadian Arctic seasonally provide top predators with accessible and often predictable sources of energy. Arctic cod (Boreogadus saida) aggregate in shallow bays during the summer and are exploited by seabirds and marine mammals. Information concerning how prey is presented to predatory seabirds, and the cues seabirds use to optimize foraging potential, is limited. Hydroacoustic surveys were completed in Allen Bay, Nunavut, to determine the presence, density, abundance, and depth of Arctic cod schools in relation to shallow-diving seabirds. Schools were also documented using standardized protocols to examine the influence of environmental variables, such as wind, ice, tidal states and seabird behaviour. The presence of schools was a significant predictor of the distribution of northern fulmars (Fulmarus glacialis) but not black-legged kittiwakes (Rissa tridactyla). Glaucous gulls (Larus hyperboreus) associated with northern fulmars are likely optimizing chances of stealing Arctic cod. The density, size and depth of schools did not significantly affect the distribution of the seabirds. We speculate that Arctic cod from demersal schools separate to feed at the surface in satellite schools (groups of dispersed fish), thus reducing competition but increasing the risk of predation.Keywords: Satellite schools; schooling; predators; northern fulmar; black-legged kittiwake; glaucous gull(Published: 3 September 2012)Citation: Polar Research 2012, 31, 15894, http://dx.doi.org/10.3402/polar.v31i0.1589