Multidimensional trace metals and nutritional niche differ between sexually immature and mature common dolphins (Delphinus delphis)

There is a need to understand the links between metals and nutrition for apex marine predators, which may be subject to different ecotoxicological effects at different life stages. We combined stomach content analyses (SCA), prey composition analysis (PCA), the Multidimensional Niche Framework (MNNF) with Bayesian multivariate ellipses, trace metal analysis and nicheROVER to investigate nutrition and trace metals across sex, age, and sexual maturity status in common dolphins (Delphinus delphis) from New Zealand. A broader prey composition niche breadth (SEAc) was estimated for immature compared to mature conspecifics, showing a higher degree of prey and nutrient generalism driven by protein (P) intake. Cd and Zn niche similarities suggests these metals were incorporated through similar prey in both immature and mature dolphins, whereas Hg and Se niche divergence indicates uptake occurred via different prey. Our multidisciplinary assessment demonstrated how nutrients and metal interactions differ in common dolphins depending upon sexual maturity. This approach has relevance when considering how marine pollution, environmental fluctuations and climate change may affect nutritional and trace metal interactions during different reproductive stages within marine predators.fals

Understanding common dolphin and Australasian gannet feeding associations from nutritional and ethological perspectives

Prey detection and subsequent capture is considered a major hypothesis to explain feeding associations between common dolphins and Australasian gannets. However, a current lack of insight on nutritional strategies with respect to foraging behaviours of both species has until now, prevented any detailed understanding of this conspecific relationship. Here we combine stomach content analysis (SCA), nutritional composition of prey, a multidimensional nutritional niche framework (MNNF) and videography to provide a holistic dietary, nutritional, and behavioural assessment of the feeding association between dolphins and gannets in the Hauraki Gulf, New Zealand. Dolphins consumed ten prey species, including grey mullet (Mugil cephalus) as the most representative by wet mass (33.4%). Gannets preyed upon six species, with pilchards (Sardinops pilchardus) contributing most of the diet by wet mass (32.4%) to their diet. Both predators jointly preyed upon pilchard, jack mackerel (Trachurus spp.), arrow squid (genus Nototodarus), and anchovy (Engraulis australis). Accordingly, the MNNF revealed a moderate overlap in the prey composition niche (0.42) and realized nutritional niche (0.52) between dolphins and gannets. This suggests that both predators coexist in a similar nutritional space, while simultaneously reducing interspecific competition and maximizing the success of both encountering and exploiting patchily distributed prey. Behavioural analysis further indicated that dolphin and gannets feeding associations are likely to be mutually beneficial, with a carouselling foraging strategy and larger pod sizes of dolphins, influencing the diving altitude of gannets. Our approach provides a new, more holistic understanding of this iconic foraging relationship, which until now has been poorly understood.fals

Fourier transform infrared (FTIR) analysis identifies microplastics in stranded common dolphins (Delphinus delphis) from New Zealand waters

Here we provide a first assessment of microplastics (MPs) in stomach contents of 15 common dolphins (Delphinus delphis) from both single and mass stranding events along the New Zealand coast between 2019 and 2020. MPs were observed in all examined individuals, with an average of 7.8 pieces per stomach. Most MPs were fragments (77%, n = 90) as opposed to fibres (23%, n = 27), with translucent/clear (46%) the most prevalent colour. Fourier transform infrared (FTIR) spectroscopy revealed polyethylene terephthalate (65%) as the most predominant polymer in fibres, whereas polypropylene (31%) and acrylonitrile butadiene styrene (20%) were more frequently recorded as fragments. Mean fragment and fibre size was 584 μm and 1567 μm, respectively. No correlation between total number of MPs and biological parameters (total body length, age, sexual maturity, axillary girth, or blubber thickness) was observed, with similar levels of MPs observed between each of the mass stranding events. Considering MPs are being increasingly linked to a wide range of deleterious effects across taxa, these findings in a typically pelagic marine sentinel species warrants further investigation.fals

Taking movement data to new depths : Inferring prey availability and patch profitability from seabird foraging behavior

Funded byNatural Environment Research Council. Grant Number: NE/K007440/1 and Marine Scotland Science and Seabird Tracking and Research (STAR) Project led by the Royal Society for the Protection of Birds (RSPB)Peer reviewedPublisher PD

Per- and polyfluoroalkyl substances (PFAS), trace elements and life history parameters of mass-stranded common dolphins (Delphinus delphis) in New Zealand

Profiles of 33 PFAS analytes and 12 essential and non-essential trace elements were measured in livers of stranded common dolphins (Delphinus delphis) from New Zealand. PFAS concentrations reported were largely comparable to those measured in other marine mammal species globally and composed mostly of long-chain compounds including perfluorooctanesulfonic acid (PFOS), perfluorododecanoic acid (PFDoDA), perfluorotridecanoic acid (PFTrDA) and perfluorooctanesulfonamide (FOSA). PFAS profiles did not vary significantly by location, body condition, or life history. Notably, significant positive correlations were observed within respective PFAS and trace elements. However, only negative correlations were evident between these two contaminant types, suggesting different exposure and metabolic pathways. Age-associated concentrations were found for PFTrDA and four trace elements, i.e. silver, mercury, cadmium, selenium, indicating differences in the bioaccumulation biomagnification mechanisms. Overall, our results contribute to global understanding of accumulation of PFAS by offering first insights of PFAS exposure in cetaceans living within South Pacific Australasian waters.fals

Energetic and physical limitations on the breaching performance of large whales

The considerable power needed for large whales to leap out of the water may represent the single most expensive burst maneuver found in nature. However, the mechanics and energetic costs associated with the breaching behaviors of large whales remain poorly understood. In this study we deployed whale-borne tags to measure the kinematics of breaching to test the hypothesis that these spectacular aerial displays are metabolically expensive. We found that breaching whales use variable underwater trajectories, and that high-emergence breaches are faster and require more energy than predatory lunges. The most expensive breaches approach the upper limits of vertebrate muscle performance, and the energetic cost of breaching is high enough that repeated breaching events may serve as honest signaling of body condition. Furthermore, the confluence of muscle contractile properties, hydrodynamics, and the high speeds required likely impose an upper limit to the body size and effectiveness of breaching whales

Immature gannets follow adults in commuting flocks providing a potential mechanism for social learning

Group travel is a familiar phenomenon among birds but the causes of this mode of movement are often unclear. For example, flocking flight may reduce flight costs, enhance predator avoidance or increase foraging efficiency. In addition, naive individuals may also follow older, more experienced conspecifics as a learning strategy. However, younger birds may be slower than adults so biomechanical and social effects on flock structure may be difficult to separate. Gannets are wide‐ranging (100s–1000s km) colonial seabirds that often travel in V or echelon‐shaped flocks. Tracking suggests that breeding gannets use memory to return repeatedly to prey patches 10s–100s km wide but it is unclear how these are initially discovered. Public information gained at the colony or by following conspecifics has been hypothesised to play a role, especially during early life. Here, we address two hypotheses: 1) flocking reduces flight costs and 2) young gannets follow older ones in order to locate prey. To do so, we recorded flocks of northern gannets commuting to and from a large colony and passing locations offshore and used a biomechanical model to test for age differences in flight speeds. Consistent with the aerodynamic hypothesis, returning flocks were significantly larger than departing flocks, while, consistent with the information gathering hypothesis, immatures travelled in flocks more frequently than adults and these flocks were more likely to be led by adults than expected by chance. Immatures did not systematically occupy the last position in flocks and had similar theoretical airspeeds to adults, making it unlikely that they follow, rather than lead, for biomechanical reasons. We therefore conclude that while gannets are likely to travel in flocks in part to reduce flight costs, the positions of immatures in those flocks may result in a flow of information from adults to immatures, potentially leading to social learning

Hunting between the air and the water : the Australasian gannet (Morus serrator) : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Ecology at Massey University, Auckland, New Zealand

Appendix 1 and 2 removed due to copyright restrictions: Machovsky Capuska, G.E., Huynen, L., Lambert, D., Raubenheimer, D. (2011), UVS is rare in seabirds, Vision Research, 51, 1333-1337 Shuckard, R., Melville, D.S., Cook, W., Machovsky Capuska, G.E. (2012), Diet of the Australasian gannet (Morus serrator) at Farewell Spit, New Zealand, Notornis, 59, 66-70Australasian gannets (Morus serrator) are the second rarest member of the seabird group Sulidae. Among the three species of gannets worldwide, they are the only species that regularly breeds in southeastern Australia and New Zealand. Like all gannets, M. serrator face considerable challenges in foraging, relying on sparsely and patchily distributed pelagic prey, which move in a 3D environment. Whereas most predators are specialise hunters in one media, gannets have to hunt within a complex air-water interface. The aim of the present thesis is to examine the hunting strategies of Australasian gannets, with particular emphasis on how these birds use both aerial and aquatic adaptations to locate and capture prey. The acquisition of information concerning food sources was analysed using GPS data loggers, field observations and high resolution video footage. I tested the hypothesis that gannets obtain information of food resources from their partners using bill fencing as referential signals analogous to the waggle dance in honeybees (Apis mellifera) (Chapter 2). Results did not support this hypothesis but suggested that Australasian gannets use a combination of strategies, probably including memory that facilitates their return to locations where prey was previously captured (Chapter 3) and local enhancement to locate active feeding sites (Chapter 2). The impact of intraspecific competition for local resources was studied between large (Cape Kidnappers, 7,300 breeding pairs) and small (Farewell Spit, 3,900 breeding pairs) colonies in New Zealand using GPS data loggers (Chapter 3). Results indicated that gannets from the larger colony invested more in foraging (greater foraging times and foraging distances). This is consistent with previous studies of other gannet species, suggesting that M. serrator experience intraspecific competition for food when living in large colonies. Pelagic prey are able to evade predation by descending to depths beyond the reach of diving birds. Among the adaptations evolved by gannets for dealing with this challenge is plunge-diving, where the bird uses gravity in the aerial phase of the hunt to gain speed and momentum for descending into the water column. I conducted a fine scaled analysis using videography of the aerial and aquatic phases of this highly specialised hunting strategy. Analysis of the aerial phase (Chapter 4) showed that the initiation of plunge dives are synchronised among members of foraging groups, suggesting a form of group-level behaviour in which gannets might benefit from the sensory experiences (prey detection) of conspecifics. The analysis also showed that gannets adapt the aerial phase of their dives in presence vs. absence of heterospecific predators. In the aquatic phase (Chapter 5), gannets perform short and shallow V-shaped dives and long and deep U-shaped dives in pursuit of pelagic fish and squid. My findings revealed that gannets adjusted their dive shape in relation to the depth of their prey rather than prey type, as previously hypothesised. Although the maximum number of prey captured per dive by the gannets was higher than previously reported, reaching up to five fish in a single U-shaped dive, the results presented herein suggest that the two dive profiles were equally profitable. To examine the role of underwater vision in prey capture, I used underwater video footage, photokeratometry and infrared video photorefraction (Chapter 6). Analysis of video footage confirmed that there are two distinct phases in the underwater component of plunge dives in Australasian gannets, an initial phase in which the bird is propelled through the water column by the momentum of the plunge (M phase) and a phase in which it is actively propelled by wing flapping (WF phase). The highest prey capture rate was observed during the WF phase, a result that suggests the use of vision in underwater prey pursuit. I therefore used photokeratometry and video photorefraction to test whether gannets are able to adapt optically in the transition from aerial to aquatic media. My measurements showed that underwater visual accommodation in the gannets was attained within 2 - 3 frames (80 - 120 ms) of submergence, a remarkably short timescale in relation to the optics of most vertebrate eyes. The preceding chapters demonstrate some highly effective behavioural and sensory capacities used by gannets in foraging. In Chapter 7 I demonstrate evidence of fatal injuries due to collision between conspecifics in plunge-diving Australasian and Cape gannets (M. capensis). The analysis also revealed a case of attempted underwater kleptoparasitism, in which a diving bird targeted a previously captured fish in the beak of another gannet. This novel observation suggests a further challenge for hunting gannets, namely to retain prey following the capture