Marine Top Predators Research Articles

Repeated evolution of durophagy during ichthyosaur radiation after mass extinction indicated by hidden dentition

Marine tetrapods quickly diversified and were established as marine top predators after the end-Permian Mass extinction (EPME). Ichthyosaurs were the forerunner of this rapid radiation but the main drivers of the diversification are poorly understood. Cartorhynchus lenticarpus is a basal ichthyosauriform with the least degree of aquatic adaptation, holding a key to identifying such a driver. The unique specimen appeared edentulous based on what was exposed but a CT scanning revealed that the species indeed had rounded teeth that are nearly perpendicular to the jaw rami, and thus completely concealed in lateral view. There are three dental rows per jaw ramus, and the root lacks infoldings of the dentine typical of ichthyopterygians. The well-developed and worn molariform dentition with three tooth rows supports the previous inference that the specimen is not of a juvenile. The premaxilla and the corresponding part of the dentary are edentulous. Molariform dentition evolved three to five times independently within Ichthyosauriformes in the Early and Middle Triassic. Convergent exploitation of hard-shelled invertebrates by different subclades of ichthyosauriforms likely fueled the rapid taxonomic diversification of the group after EPME.

Circulating nutrient concentrations in free‐ranging Humboldt penguins (Spheniscus humboldti) in Punta San Juan, Peru

Free-ranging Humboldt penguin (HP, Spheniscus humboldti) populations are under pressure from resource competition with industrial fisheries, habitat loss, and El Niño Southern Oscillation events. Foraging patterns for this top marine predator change during periods of aberrant oceanographic conditions and scarce fish stock numbers. These radical dietary fluctuations can lead to poor fertility, early embryonic death, poor hatchability, suppressed immune function, high chick mortality, and illness. To understand the variability of nutrient status in reproductive seasons, we measured select circulating nutrient concentrations (fat-soluble vitamins A, D, E, and carotenoids, fatty acids, amino acids, minerals, and electrolytes) of 105 HP at Punta San Juan, Peru during the first reproductive seasons of 2007 and 2008. We determined significant differences in nutrient status between sexes, years of sampling, and reproductive stages. Males (4.5 ± 0.38 kg) weighed more than females (4.0 ± 0.29 kg) and exhibited higher concentrations of vitamin A (0.71 ± 0.11 vs. 0.61 ± 0.12 µg/ml) and docosahexaenoic acid (6.70 ± 1.61 vs. 5.65 ± 1.59%). Males also displayed lower concentrations of β-carotene (0.01 ± 0.01 vs. 0.012 ± 0.001 µg/ml) and phosphorus (3.43 ± 0.83 vs. 4.40 ± 1.66 mg/dl). Comparison between the 2 years showed most circulating amino acid concentrations were higher in 2007. Significant differences in circulating amino acids and vitamins were also noted between different reproductive stages. These results demonstrate concentrations of nutrients can vary due to the physiological state of the animal, as well as the overall dynamics of their marine ecosystem habitat.

Mercury exposure in relation to foraging ecology and its impact on the oxidative status of an endangered seabird

Mercury is a natural element extensively found in the Earth's crust, released to the atmosphere and waters by natural processes. Since the industrial revolution, atmospheric deposition of Hg showed a three-to-five-fold enrichment due to human activities. Marine top predators such as seabirds are recognized valuable bioindicators of ocean health and sensitive victims of Hg toxic effects. Hg negatively affects almost any aspect of avian physiology; thus, birds prove valuable to study the effect of Hg exposure in vertebrates. The Black-vented Shearwater is endemic to the North-Eastern Pacific Ocean, where it forages along the Baja California Peninsula during the breeding period. The area has no industrial settlement and is in the southern portion of the California Current System (CCS). After observing possible contamination effects in eggshells, we decided to quantify the exposure of breeding birds to Hg and test for possible effects on oxidative status of the species. The concentration of Hg in erythrocytes averaged 1.84 μg/g dw and varied from 1.41 to 2.40 μg/g dw. Males and females had similar Hg concentrations. The individual trophic level (reflected by δ15N) did not explain Hg exposure. In contrast, individuals foraging inshore had higher Hg concentrations than those foraging more offshore (reflected by δ13C). Shearwaters having higher concentrations of Hg had lower activity of the antioxidant enzyme glutathione peroxidase and showed lower non-enzymatic antioxidant capacity. Levels of plasma oxidative damage, superoxide dismutase and catalase were not associated with Hg. Our results indicate that (i) the foraging habitat is the factor explaining Hg exposure and (ii) there is some evidence for potential harmful effects of Hg exposure to this seabird species of conservation concern. CapsuleThe foraging habitat is the factor explaining Hg exposure in seabirds and we observed potential harmful effects of Hg exposure in a seabird species of conservation concern.

Oceans of stimuli: an individual-based model to assess the role of olfactory cues and local enhancement in seabirds' foraging behaviour.

Oceans are extremely dynamic environments, which poses challenges for top-predators such as seabirds to find food resources. Yet, seabirds evolved sensorial abilities (olfactory senses) along with complex behaviours (social information transfer through local enhancement) to improve foraging efficiency. Using the Cory's shearwater (Calonectris borealis) as a model species, we developed an individual-based model to explore the complementary role of different searching mechanisms (olfactory foraging and local enhancement) for the optimal foraging behaviour of pelagic seabirds during 1-day foraging trips around breeding colonies. Model outputs were compared with observed patterns of Cory's shearwaters distribution during local foraging trips. Also, the foraging efficiency of virtual individuals was analysed considering hypothetical scenarios of foraging conditions and densities of foraging individuals around breeding colonies. The results support the use of a combination of searching strategies by Cory's shearwaters, which produced representative patterns of space use from tracked individuals, including spatial foraging segregation of neighbouring sub-colonies. Furthermore, while the mechanisms underpinning local enhancement played a key role in mitigating sub-optimal foraging conditions, the use of olfactory senses conferred great adaptive foraging advantages over a wide range of environmental conditions. Our results also indicate a synergistic effect between the two strategies, which suggests that a multimodal foraging strategy is useful to forage in extremely dynamic environments. The developed model provides a basis for further investigation regarding the role of foraging mechanisms in the population dynamics of colonial animals, including the adaptive foraging behaviour of marine top predators to dynamic environmental conditions.

Anthropogenic food resources, sardine decline and environmental conditions have triggered a dietary shift of an opportunistic seabird over the last 30 years on the northwest coast of Spain

Human activities and environmental conditions are the main drivers of ecosystem change. One major alteration near the western Iberian coast has been the collapse of the Atlanto-Iberian sardine Sardina pilchardus stock, with important cascading effects on marine top predators. We investigated the effect of long-term changes in fishery landings, sardine availability and environmental conditions on the diet of the yellow-legged gull Larus michahellis in the northwest coast of Spain, over the last 30 years (1987–2017). Dietary trends of gulls were investigated through the analysis of 5010 pellets that revealed a sharp decline of fish and refuse and a shift to a crustacean-based diet. General additive mixed models showed that both total fish and sardine occurrences in gull pellets were negatively associated with total fishery landings and positively associated with sardine landings, suggesting fish depletion and higher fishing efficiency (i.e. reduced discards) during the study period. The winter North Atlantic Oscillation (NAO) index was also positively related with sardine occurrence in gull pellets, possibly due to low sardine abundance and rough conditions in years with very low NAO values. The refuse decline was most probably caused by the closure of open-air landfills, implemented under the European Union Landfill Directive. Our results suggest that changes in fishing practices and waste disposal were the main factors responsible for the sharp decline of fish and refuse in yellow-legged gull diet.

Cold call: the acoustic repertoire of Ross Sea killer whales (Orcinus orca, Type C) in McMurdo Sound, Antarctica.

Killer whales (Orcinus orca) are top marine predators occurring globally. In Antarctic waters, five ecotypes have been described, with Type C being the smallest form of killer whale known. Acoustic recordings of nine encounters of Type C killer whales were collected in 2012 and 2013 in McMurdo Sound, Ross Sea. In a combined 3.5 h of recordings, 6386 killer whale vocalizations were detected and graded based on their signal-to-noise ratio. Spectrograms of the highest-quality calls were examined for characteristic patterns yielding a catalogue of 28 call types (comprising 1250 calls). Acoustic parameters of each call were measured and summarized by call type. Type C killer whales produced complex calls, consisting of multiple frequency-modulated, amplitude-modulated and pulsed components. Often, two components occurred simultaneously, forming a biphonation; although the biphonic components did not necessarily start and end together, with one component lasting over several others. The addition and deletion of components yielded call subtypes. Call complexity appears stable over time and may be related to feeding ecology. Characterization of the Type C acoustic repertoire is an important step for the development of passive acoustic monitoring of the diverse assemblage of killer whale ecotypes in Antarctica's rapidly changing marine ecosystems.

Concentration of trace elements in long-finned pilot whales stranded in northern Patagonia, Chile

The use of trace metals and rare-earth elements (REEs) is increasing in the mining, metallurgic, electronic, and automobile industries due to their magnetic, heat-resistant, and phosphorescent properties. While large amounts of these metals are released to the environment, the toxic consequences in marine organisms are poorly understood. In Chile a mass stranding event of long-finned pilot whales (LFPW) (Globicephala melas) occurred in 2016 due to unknown consequences. Al, Ce, Cr, Cu, Tl, and Zn concentrations were analyzed in LFPW blubber tissue and correlated with body size and age class of individuals. While Al and Zn were higher in juvenile individuals, Ce, Cu, Cr, and Tl were higher in adults. This study provides the first base line of trace metals and REE in LFPW from the southern hemisphere and demonstrates the existence and persistence of trace elements in marine top predators from remote ecosystems like the Chilean Patagonia.

Drivers of spatiotemporal variability in bycatch of a top marine predator: First evidence for the role of water turbidity in protected species bycatch

Abstract Bycatch of protected species in static net fisheries is a global conservation concern and is currently considered the dominant anthropogenic threat facing many marine mammal species. Effective bycatch mitigation remains challenging, contingent on an understanding of the underlying mechanisms that cause individuals to become entangled. We combined data collected by scientific observers and fishers to identify predictors of seal bycatch in static net fisheries along the west, southwest and south coasts of Ireland. We first analysed the broad regional and seasonal trends in seal bycatch before identifying environmental variables that could explain these patterns. Based on negative binomial generalized linear mixed effects models, seal bycatch significantly varied with season and decreased with greater distance to major seal colonies and in clearer, less turbid water. Synthesis and applications. Our results suggest that distance to major seal colonies was a significant driver of spatial variation in seal bycatch, and water turbidity a major driver of seasonal trends. These findings will enable us to identify future bycatch risk and target mitigation measures effectively. This is the first study to identify the effect of water turbidity on bycatch of a protected marine species. Increasing net visibility in turbid waters may provide a novel approach to mitigating against protected species bycatch in static net fisheries.

Environment-sensitive mass changes influence breeding frequency in a capital breeding marine top predator.

The trade-off between survival and reproduction in resource-limited iteroparous animals can result in some individuals missing some breeding opportunities. In practice, even with the best observation regimes, deciding whether 'missed' years represent real pauses in breeding or failures to detect breeding can be difficult, posing problems for the estimation of individual reproductive output and overall population fecundity. We corrected fecundity estimates by determining whether breeding had occurred in skipped years, using long-term capture-recapture observation datasets with parallel longitudinal mass measurements, based on informative underlying relationships between individuals' mass, breeding status and environmental drivers in a capital breeding phocid, the grey seal. Bayesian modelling considered interacting processes jointly: temporal changes in a phenotypic covariate (mass); relationship of mass to breeding probability; effects of maternal breeding state and mark type on resighting. Full reproductive histories were imputed, with the status of unobserved animals estimated as breeding or non-breeding, accounting for local environmental variation. Overall fecundity was then derived for Scottish breeding colonies with contrasting pup production trends. Maternal mass affected breeding likelihood. Mothers with low body mass at the end of breeding were less likely to bear a pup the following year. Successive breeding episodes incurred a cost in reduced body mass which was more pronounced for North Rona, Outer Hebrides (NR) mothers. Skipping breeding increased subsequent pupping probability substantially for low mass females. Poor environmental conditions were associated with declines in breeding probability at both colonies. Seal mass gain between breeding seasons was (a) negatively associated with lagged North Atlantic Oscillation for seals at NR and (b) positively associated with an index of seal prey (Ammodytes spp) abundance at Isle of May, Firth of Forth (IM). Overall fecundity was marginally greater at IM (increasing/stable pup production) than at NR (decreasing). No effects of mass were detected on maternal survival. Skipping breeding in female grey seals appears to be an individual mass-dependent constraint moderated by previous reproductive output and local environmental conditions. Different demographic trends at breeding colonies were consistent with the fecundities estimated using this method, which is general and adaptable to other situations.

Impacts of extreme ocean warming on the early development of a marine top predator: The Guadalupe fur seal

From fall 2013 through 2015, a large-scale, multi-year warm water anomaly occurred in the northeast Pacific Ocean. The phenomenon had negative impacts on some oceanic predators, including higher mortalities and poor body conditions. We studied the effect of this warm water anomaly on the weight gain of Guadalupe fur seal (Arctocephalus philippii townsendi) neonates off the coast of the Baja California Peninsula, Mexico. Individuals were captured, marked, and weighed every 13–15 days, up to 60 days of age, during the early nursing seasons (mid-June to mid-August) of 2014–2016 at this subspecies’ only reproductive colony, located on Guadalupe Island. The body weight was measured at each capture and recapture. A hierarchical Bayesian model was used to explore the impact of sea surface temperature (SST) anomalies on the neonates’ weights. The hierarchical structure included connected models for the spring-summer SST trend around the colony, the neonatal body weight gain with age, and the relationship between the anomalies of both variables. Marked neonates were also tracked in order to estimate survival rates during first two months of age. Overall, positive SST anomalies had a negative effect on neonatal body weight gain. The northeast Pacific Marine Heatwave precipitated the lowest weights at birth and the slowest weight gain in 2014, as well as low weights and the lowest survival rate in 2015, likely due to the persistence of the warm anomalies. The evident sensitivity of Guadalupe fur seal neonates to regional warming conditions highlights their vulnerability under scenarios of climate change, which could impede this subspecies’ continued recovery from near extinction.

Marine top predators as climate and ecosystem sentinels

The rapid pace of environmental change in the Anthropocene necessitates the development of a new suite of tools for measuring ecosystem dynamics. Sentinel species can provide insight into ecosystem function, identify hidden risks to human health, and predict future change. As sentinels, marine apex (top) predators offer a unique perspective into ocean processes, given that they can move across ocean basins and amplify trophic information across multiple spatiotemporal scales. Because use of the terms “ecosystem sentinel” and “climate sentinel” has proliferated in the scientific literature, there is a need to identify the properties that make marine predators effective sentinels. We provide a clear definition of the term “sentinel”, review the attributes of species identified as sentinels, and describe how a suite of such sentinels could strengthen our understanding and management of marine ecosystems. We contend that the use of marine predators as ecosystem sentinels will enable rapid response and adaptation to ecosystem variability and change.

Identifying foraging habitats of adult female long-nosed fur seal Arctocephalus forsteri based on vibrissa stable isotopes

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 628:223-234 (2019) - DOI: https://doi.org/10.3354/meps13113 Identifying foraging habitats of adult female long-nosed fur seal Arctocephalus forsteri based on vibrissa stable isotopes Dahlia Foo1,*, Mark Hindell1, Clive McMahon2, Simon Goldsworthy3 1Institute for Marine and Antarctic Studies, University of Tasmania, Hobart, Tasmania 7004, Australia 2Sydney Institute of Marine Science, Mosman, New South Wales 2088, Australia 3Aquatic Sciences Centre, South Australian Research and Development Institute, West Beach, South Australia 5024, Australia *Corresponding author: dahlia.foo@utas.edu.au ABSTRACT: We investigated how foraging ecotypes of female long-nosed fur seals Arctocephalus forsteri could be identified from vibrissa stable isotopes. We collected regrowths of vibrissae from adult females (n = 18) from Cape Gantheaume, Kangaroo Island, South Australia, from 2 breeding seasons (2016, 2017). The period represented by the regrowth was known, and 8 individuals were administered with 15N-enriched glycine as a biomarker to mark the start date of the regrowth. Non-glycine-marked and glycine-marked vibrissae were used to estimate the rate of the individual vibrissa regrowth. Using individual growth rates (0.18 ± 0.04 mm d-1), we reconstructed a stable isotope (δ13C and δ15N) time series for each regrowth and allocated them to corresponding at-sea locations either based on geolocation tracks (n = 14) or foraging habitat type (shelf or oceanic) based on diving data (n = 2) of the sampled seals. Mean (±SD) δ15N from vibrissa segments was higher when females foraged on the continental shelf region (16.1 ± 0.7‰, n = 29) compared to oceanic waters (15.1 ± 0.7‰, n = 106) in 2017, whereas it was similar in both regions in 2016 (shelf: 15.3 ± 0.4‰, n = 13; oceanic: 15.4 ± 0.4‰, n = 15). Based on the stable isotope signatures of vibrissa segments, model-based clustering analysis correctly classified 79.8% as originating from shelf or oceanic foraging habitats. This demonstrates the potential of using vibrissa stable isotopes for studying the foraging ecology of an important top marine predator. KEY WORDS: Isoscape · Foraging strategies · Trophic dynamics · Continental shelf · Oceanic · Marine top predators Full text in pdf format Supplementary material PreviousCite this article as: Foo D, Hindell M, McMahon C, Goldsworthy S (2019) Identifying foraging habitats of adult female long-nosed fur seal Arctocephalus forsteri based on vibrissa stable isotopes. Mar Ecol Prog Ser 628:223-234. https://doi.org/10.3354/meps13113 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 628. Online publication date: October 10, 2019 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2019 Inter-Research.

Evidence for non-random co-occurrences in a white shark aggregation

Groups or aggregations of animals can result from individuals being attracted to a common resource or because of synchronised patterns of daily or seasonal activity. Although mostly solitary throughout its distribution, white sharks (Carcharodon carcharias) seasonally aggregate at a number of sites worldwide to feed on calorie-rich pinnipeds. At the Neptune Islands, South Australia, large numbers of white sharks can be sighted throughout the year, including during periods of low seal abundance. We use a combination of photo-identification and network analysis based on co-occurrence of individuals visiting the site on the same day to elucidate the population structure and aggregatory behaviour of Australia’s largest aggregation of sub-adult and adult white sharks. We photo-identified 282 sharks (183 males, 97 females, 2 unknown) over a 4.5-year period (June 2010–November 2014) and found that white sharks did not randomly co-occur with their conspecifics, but formed four distinct communities. Tendency to co-occur varied across months with males co-occurring with more individuals than females. Sex-dependent patterns of visitation at the Neptune Islands and resulting intraspecific competition likely drive the observed community structure and temporal variability in co-occurrences. This study provides new insights into the aggregatory behaviour of white sharks at a seal colony and shows for the first time that white shark co-occurrence can be non-random. White sharks are top marine predators that are typically solitary but can also form aggregations around seal colonies to feed. Using a combination of photo-identification and network analysis, we investigated the co-occurrence patterns of white sharks. We showed, for the first time, that white sharks form non-random associations with conspecifics. We hypothesise that the observed sex-dependant variations in co-occurrence are linked to intraspecific competition for resources, providing new insights into the aggregatory behaviour of white sharks at a seal colony. Our study adds to the growing literature of animals showing non-random interaction or co-occurrence patterns, providing important comparative knowledge for other researchers as it broadens our knowledge to marine top predators.

Dive behaviour and foraging effort of female Cape fur seals Arctocephalus pusillus pusillus.

While marine top predators can play a critical role in ecosystem structure and dynamics through their effects on prey populations, how the predators function in this role is often not well understood. In the Benguela region of southern Africa, the Cape fur seal (Arctocephalus pusillus pusillus) population constitutes the largest marine top predator biomass, but little is known of its foraging ecology other than its diet and some preliminary dive records. Dive information was obtained from 32 adult females instrumented with dive recorders at the Kleinsee colony (29°34.17′ S, 16°59.80′ E) in South Africa during 2006–2008. Most dives were in the depth range of epipelagic prey species (less than 50 m deep) and at night, reflecting the reliance of Cape fur seals on small, vertically migrating, schooling prey. However, most females also performed benthic dives, and benthic diving was prevalent in some individuals. Benthic diving was significantly associated with the frequency with which females exceeded their aerobic dive limit. The greater putative costs of benthic diving highlight the potential detrimental effects to Cape fur seals of well-documented changes in the availability of epipelagic prey species in the Benguela.

New non-breeding colonies of the South American fur seal in central Chile. Is the distribution in the southeastern Pacific waters extending?

The South American fur seal (SAFS), Arctocephalus australis, has an estimated abundance of 219,000 individuals. The distribution range of this top marine predator along the Pacifc coast of South America is discontinuous, with a gap between 29°02’S-43°36’S, whereas the Atlantic coast presents a continuous distribution. Little is known aboutthe population dynamics of the species in Chile, as there have been few observations of vagrant individuals within the distribution gap and partial population censuses on dates that do not fit with the reproductive season in northern andsouthern Chile. The aim of this study is to identify the presence of A. australis colonies and summarize the sightings in central Chile. Aerial censuses were performed between 32°12’S-39°24’S during the austral winter and summer (2015) and between 41°44’S-44°55’S during summer (2013, 2016-2018). Official stranding records were also included to complementthe research sightings. We registered a total of 54 SAFS in the Chilean distribution gap, most of them during winter (89%) and with a higher proportion of females (72%). Two non-breeding colonies were found in the Biobío Region during the winter of 2015, Islote del Trabajo (38°25’S) and Islote Quechol (38°26’S), with 27 ± 1 and 16 ± 0 individuals, respectively. The sightings of adult individuals suggest their arrival at these latitudes to carry out foraging and resting activities, probably from Guafo Island (43°36’S). The last Pleistocene glaciation, hunting activities during the eighteenth century and ENSO events could have conditioned the current abundance and range of distribution of A. australis in South America; therefore, the establishment of new non-breeding colonies in the gap of distribution could lead to new breeding grounds in thefuture.

A matter of taste: Spatial and ontogenetic variations on the trophic ecology of the tiger shark at the Galapagos Marine Reserve.

Sharks are top predators across ocean food webs and have a major ecological role in marine ecosystems. Investigating the trophic ecology of this group of species is thus essential to understand ecosystem functioning and inform specific management actions aimed at shark conservation. The Galapagos Islands represent one of the last ocean wildernesses, where populations of sharks and other top marine predators come close to a pristine status. Here we provide the first study on the trophic ecology of the tiger shark (Galeocerdo cuvier) within the Galapagos Marine Reserve (GMR), using a combination of stable isotope analysis, satellite tracking, and passive acoustic telemetry to investigate ontogenetic and spatial variations at two regions. The mean estimated δ13C and δ15N at Isabela island (western region) were -13.9 ± 0.5‰ and 13.7 ± 0.7‰; and for Santa Cruz island (central region) were -13.8 ± 0.3‰ and 13.4 ± 0.7‰, respectively. Green sea turtles (Chelonia mydas) were the main prey item for large tiger sharks (>280 cm TL), while smaller sharks mainly fed on squid and pelagic fish. Tiger sharks exhibited a high degree of philopatry around green sea-turtle nesting areas, with the majority of sharks detected around green sea-turtle nesting areas for at least 10 months after their capture date, and some individuals were even present during the entire three-year study period. Although we did not report statistically significant differences between the two regions, isotopic and electronic tagging data suggest that tiger sharks in the Galapagos could be segregated into specific populations separated by geographical scales of <100 km. The high productivity of the archipelago, along with the protection from industrial fishing granted by the GMR, result in abundant and predictable sources of prey. This high food abundance, combined with the presence of suitable habitats throughout the tiger shark life cycle, might result in a reduction of migratory behaviours when compared to movement patterns of tiger sharks in other ocean basins. Additional studies using genetic tools could provide further evidence on the presence of separate management units, as it has been recently revealed for other shark species inhabiting the GMR.

What goes in, must come out: Combining scat‐based molecular diet analysis and quantification of ingested microplastics in a marine top predator

Abstract Microplastics (plastic particles &lt;5 mm in size) are highly available for ingestion by a wide range of organisms, either through direct consumption or indirectly, via trophic transfer, from prey to predator. The latter is a poorly understood, but potentially major, route of microplastic ingestion for marine top predators. We developed a novel and effective methodology pipeline to investigate dietary exposure of wild top predators (grey seals; Halichoerus grypus) to microplastics, by combining scat‐based molecular techniques with a microplastic isolation method. We employed DNA metabarcoding, a rapid method of biodiversity assessment, to garner detailed information on prey composition from scats, and investigated the potential relationship between diet and microplastic burden. Outcomes of the method development process and results of both diet composition from metabarcoding analysis and detection of microplastics are presented. Importantly, the pipeline performed well and initial results suggest the frequency of microplastics detected in seal scats may be related to the type of prey consumed. Our non‐invasive, data‐rich approach maximizes time and resource–efficiency, while minimizing costs and sample volumes required for analysis. This pipeline could be used to underpin a much‐needed increase in understanding of the relationship between diet composition and rates of microplastic ingestion in high trophic level species.

Defining areas of intensive foraging activity for a top marine predator, the Antarctic fur seal: Compromises between effort and accuracy

Defining areas of intensive foraging activity for a top marine predator, the Antarctic fur seal: Compromises between effort and accuracy

Hunting behaviour of white sharks recorded by animal-borne accelerometers and cameras

ABSTRACT: 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.

Variable sea-ice conditions influence trophic dynamics in an Arctic community of marine top predators.

Sea‐ice coverage is a key abiotic driver of annual environmental conditions in Arctic marine ecosystems and could be a major factor affecting seabird trophic dynamics. Using stable isotope ratios of carbon (δ13C) and nitrogen (δ15N) in eggs of thick‐billed murres (Uria lomvia), northern fulmars (Fulmarus glacialis), glaucous gulls (Larus hyperboreus), and black‐legged kittiwakes (Rissa tridactyla), we investigated the trophic ecology of prebreeding seabirds nesting at Prince Leopold Island, Nunavut, and its relationship with sea‐ice conditions. The seabird community of Prince Leopold Island had a broader isotopic niche during lower sea‐ice conditions, thus having a more divergent diet, while the opposite was observed during years with more extensive sea‐ice conditions. Species' trophic position was influenced by sea ice; in years of lower sea‐ice concentration, gulls and kittiwakes foraged at higher trophic levels while the opposite was observed for murres and fulmars. For murres and fulmars over a longer time series, there was no evidence of the effect of sea‐ice concentration on species' isotopic niche. Results suggest a high degree of adaptation in populations of high Arctic species that cope with harsh and unpredictable conditions. Such different responses of the community isotopic niche also show that the effect of variable sea‐ice conditions, despite being subtle at the species level, might have larger implications when considering the trophic ecology of the larger seabird community. Species‐specific responses in foraging patterns, in particular trophic position in relation to sea ice, are critical to understanding effects of ecosystem change predicted for a changing climate.