10 research outputs found
Convergence of marine megafauna movement patterns in coastal and open oceans
Author Posting. © The Author(s), 2017. This is the author's version of the work. It is posted here for personal use, not for redistribution. The definitive version was published in Proceedings of the National Academy of Sciences of the United States of America 115 (2018): 3072-3077, doi:10.1073/pnas.1716137115.The extent of increasing anthropogenic impacts on large marine
vertebrates partly depends on the animalsâ movement patterns.
Effective conservation requires identification of the key drivers of
movement including intrinsic properties and extrinsic constraints
associated with the dynamic nature of the environments the animals
inhabit. However, the relative importance of intrinsic versus
extrinsic factors remains elusive. We analyse a global dataset of
2.8 million locations from > 2,600 tracked individuals across 50
marine vertebrates evolutionarily separated by millions of years
and using different locomotion modes (fly, swim, walk/paddle).
Strikingly, movement patterns show a remarkable convergence,
being strongly conserved across species and independent of body
length and mass, despite these traits ranging over 10 orders of
magnitude among the species studied. This represents a fundamental
difference between marine and terrestrial vertebrates not
previously identified, likely linked to the reduced costs of locomotion
in water. Movement patterns were primarily explained by the
interaction between species-specific traits and the habitat(s) they
move through, resulting in complex movement patterns when
moving close to coasts compared to more predictable patterns
when moving in open oceans. This distinct difference may be
associated with greater complexity within coastal micro-habitats,
highlighting a critical role of preferred habitat in shaping marine
vertebrate global movements. Efforts to develop understanding
of the characteristics of vertebrate movement should consider the
habitat(s) through which they move to identify how movement
patterns will alter with forecasted severe ocean changes, such as
reduced Arctic sea ice cover, sea level rise and declining oxygen
content.Workshops funding granted by the UWA Oceans Institute, AIMS, and
KAUST. AMMS was supported by an ARC Grant DE170100841 and an IOMRC
(UWA, AIMS, CSIRO) fellowship; JPR by MEDC (FPU program, Spain); DWS by
UK NERC and Save Our Seas Foundation; NQ by FCT (Portugal); MMCM by
a CAPES fellowship (Ministry of Education)
The foraging ecology of the short-tailed shearwater puffinus tenuirostris.
The short-tailed shearwater Puffinus tenuirostris is one of the worldâs most abundant seabirds, with a population of around 23 million breeding birds. Despite this abundance we have a limited understanding of their role in the marine ecosystem. This is largely due to the many uncertainties surrounding the trophic interactions, resource requirements and foraging ecology of this wide ranging pelagic seabird. I studied the movement of adults during the short trip (ST) and long trip (LT) component of their dual foraging strategy to determine how they use their marine habitat. ST were primarily confined to neritic (continental shelf) waters 30 to 100 km from their colony, and maximum depth gauges revealed that birds reached a depth of 21 ± 13 m (SD). Analysis of the time spent in area by 39 individuals performing ST revealed that 18 birds employed area restricted searches within circles of a diameter of 14 ± 3 km (SE). Prey returns from area restricted search flights were predominated by bony fish, whereas prey diversity increased for non-area restricted search flights, with more krill and cephalopods. Thus, direct flights were performed when birds were exploiting prey patches dominated by fish, in contrast to the more varied diet returned
when birds covered greater distances. LT flights were highly variable ranging from 11 - 32 days duration, and reaching 912 â 6,952 km from the colony. Foraging trips of extended duration enabled birds to exploit temperate waters further away from the colony, as well as sub Antarctic and Antarctic waters. A wider range of search patterns were performed on LT, as birds either: (1) showed no signs of area restricted search; (2) concentrated area restricted search directly at small scales of within circles of 33 ± 11 km (SE) diameter; or, (3) adopted a hierarchical mode of foraging, where large scales of area restricted search are first performed, followed by nested searches at smaller scales. This variation in foraging behaviour indicates that a range of foraging tactics are employed by the short-tailed shearwater. LT to sub Antarctic and Antarctic waters commonly involved a period of commuting travel to regions with elevated chlorophyll a associated with ocean fronts, where
search effort was increased.
How adults allocated time and energy during the entire chick-rearing period was investigated via the simultaneous assessment of adult attendance, adult mass change, the rate of energy delivery to chicks, and chick survival. Adults who reared chicks to good condition spent 80 % of the 90 day chick rearing period performing five - six LT of 13 ± 3 days (SE) duration. The remaining 20 % of time involved 14 ± 3 ST (SE) of one to three days duration. Comparison with chicks of moderate and poor condition revealed that, despite extensive variation in the day to day rate of provisioning, a small change in the proportion of time spent performing ST and LT over the entire chick rearing period can spell the difference between breeding success and failure. By allocating all of the food collected on ST to chicks
birds depleted stored energy reserves, which were replenished on LT. Of the total energy required by chicks from hatching to adult abandonment 75 % was delivered from LT in the form of energy rich stomach oil, with the remainder being supplied in ST meals of raw prey. The advantages of the dual foraging strategy to both adult and chick was demonstrated by considering the daily food requirements of chicks and the likely energy flow from alternate feeding regimes. Under regimes of all ST or all LT, energy flow to chicks could not meet chick energy requirements. This highlights that LT of more than seven days duration are required to accumulate stomach oil. Oil boosts the energy value of meals beyond that achievable in continuous ST foraging. Under continuous ST the estimated rate of food
consumption achieved by adults would not sustain both adult and chick requirements. Therefore the dual strategy enables short-tailed shearwaters to overcome many of the constraints of central-place foraging.
Comparisons between years and short-tailed shearwater colonies revealed extensive variation in the dietary composition of meals returned to chicks, as well as the rate of food delivery. A year of increased ST foraging resulted in an increase in feeding frequency, but not provisioning rate, as smaller meals were returned. In this same year ST meals also contained a high % mass of low energy neritic prey (Australian krill Nyctiphanes australis and cephalopods). These factors reduced the rate of energy flow to chicks compared to other years where fewer ST meals of increased mass contained mostly higher energy fish
(jack mackerel Trachurus declivis and anchovy Engraulis australis). While the rate of chick growth at different ages varied between years, a similar peak mass was gained in all
three years. These findings demonstrate considerable flexibility in the dual foraging strategy of the short-tailed shearwater, providing evidence that adults are able to maintain a suitable rate of energy flow to chicks in years of varied neritic foraging conditions. This is achieved by modifying the time spent performing ST, and the volume of oil returned from LT, likely in response to changing prey availability.
A review of the use of seabirds in fisheries management identified the most commonly used indicators (species and parameters) in environmental, ecological and fisheries management. For the short-tailed shearwater the most useful parameters for identifying the size of pelagic fish stocks in neritic waters include the size and dietary composition of meals returned on ST. The varied importance of pilchard Sardinops sagax
and anchovy Engraulis australis in the diet between years suggest that their occurrence in the diet meals present a potential indicator of the availability of pre-recruits into the South Australian pilchard fishery. The occurrence of Australian Krill in ST meals may also provide a means of investigating the ecological role of upwelling events in neritic waters. The usefulness of provisioning parameters as indicators of prey availability are likely to be limited in this species, due to the extent of flexibility and plasticity in the short-tailed
shearwaters provisioning strategy.
Documenting the extent of flexibility in the foraging strategy, and quantifying the value of the ST and LT component of the dual foraging strategy has provided an insight into the habitat utilisation and prey requirements of this species. This demonstrates that despite the various constraints incurred in sourcing and transporting prey over long distances, dual
foraging presents the most optimal foraging strategy for the delivery of energy to adult and chick. The sheer abundance of this species is evidence that the separation of their foraging
and breeding grounds over 3000 km is a beneficial strategy. An opportunistic diet, and flexibility in foraging suggests that the short-tailed shearwater is more resilient to changes in prey availability than other seabirds in their community. However, we have highlighted that breeding success is sensitive to small changes in the time spent foraging in near and distant waters. Sourcing prey over large spatial scales also exposes birds to feeding conditions over a broader area, increasing their exposure to the potential effects of current and future climate
change. For these reasons the short-tailed shearwater presents a valuable indicator species for short and long-term monitoring programs of both neritic and oceanic ecosystems.Thesis (Ph.D.) -- University of Adelaide, School of Earth and Environmental Sciences, 2010
Correction: Occupancy and detectability modelling of vertebrates in northern Australia using multiple sampling methods.
[This corrects the article DOI: 10.1371/journal.pone.0203304.]
Occupancy and detectability modelling of vertebrates in northern Australia using multiple sampling methods.
Understanding where species occur and how difficult they are to detect during surveys is crucial for designing and evaluating monitoring programs, and has broader applications for conservation planning and management. In this study, we modelled occupancy and the effectiveness of six sampling methods at detecting vertebrates across the Top End of northern Australia. We fitted occupancy-detection models to 136 species (83 birds, 33 reptiles, 20 mammals) of 242 recorded during surveys of 333 sites in eight conservation reserves between 2011 and 2016. For modelled species, mean occupancy was highly variable: birds and reptiles ranged from 0.01-0.81 and 0.01-0.49, respectively, whereas mammal occupancy was lower, ranging from 0.02-0.30. Of the 11 environmental covariates considered as potential predictors of occupancy, topographic ruggedness, elevation, maximum temperature, and fire frequency were retained more readily in the top models. Using these models, we predicted species occupancy across the Top End of northern Australia (293,017 km2) and generated species richness maps for each species group. For mammals and reptiles, high richness was associated with rugged terrain, while bird richness was highest in coastal lowland woodlands. On average, detectability of diurnal birds was higher per day of surveys (0.33 ± 0.09) compared with nocturnal birds per night of spotlighting (0.13 ± 0.06). Detectability of reptiles was similar per day/night of pit trapping (0.30 ± 0.09) as per night of spotlighting (0.29 ± 0.11). On average, mammals were highly detectable using motion-sensor cameras for a week (0.36 ± 0.06), with exception of smaller-bodied species. One night of Elliott trapping (0.20 ± 0.06) and spotlighting (0.19 ± 0.06) was more effective at detecting mammals than cage (0.08 ± 0.03) and pit trapping (0.05 ± 0.04). Our estimates of species occupancy and detectability will help inform decisions about how best to redesign a long-running vertebrate monitoring program in the Top End of northern Australia
Trophodynamics of the eastern Great Australian Bight ecosystem : ecological change associated with the growth of Australia\u27s largest fishery
We used the Ecopath with Ecosim software to develop a trophic mass-balance model of the eastern Great Australian Bight ecosystem, off southern Australia. Results provide an ecosystem perspective of Australia's largest fishery, the South Australian sardine fishery, by placing its establishment and growth in the context of other dynamic changes in the ecosystem, including: the development of other fisheries; changing abundances of apex predator populations and oceanographic change. We investigated the potential impacts of the sardine fishery on high tropic level predators, particularly land-breeding seals and seabirds which may be suitable ecological performance indicators of ecosystem health. Results indicate that despite the rapid growth of the sardine fishery since 1991, there has likely been a negligible fishery impact on other modelled groups, suggesting that current levels of fishing effort are not impacting negatively on the broader ecosystem structure and function in the eastern Great Australian Bight. Results highlight the importance of small pelagic fish to higher trophic levels, the trophic changes that have resulted from loss and recovery of apex predator populations, and the potential pivotal role of cephalopod biomass in regulating âbottom-upâ trophic processes. The ability to resolve and attribute potential impacts from multiple fisheries, other human impacts and ecological change in this poorly understood region is highlighted by the study, and will be critical to ensure future ecologically sustainable development within the region.Simon D. Goldsworthy, Brad Page, Paul J. Rogers, Cathy Bulman, Annelise Wiebkin, Lachlan J. McLeay, Luke Einoder, Alastair M.M. Baylis, Michelle Braley, Robin Caines, Keryn Daly, Charlie Huveneers, Kristian Peters, Andrew D. Lowther, Tim M. War
Feeding strategies of the Short-tailed Shearwater vary by year and sea-surface temperature but do not affect breeding success
To understand how animals cope with environmental variability it is necessary to identify the degree of flexibility in a species' diet and foraging mode and the consequences of this flexibility for reproduction. We examined rates of feeding and energy delivery to chicks by a long-lived pelagic seabird, the Short-tailed Shearwater (Puffinus tenuirostris). Individual adults alternated between foraging trips of short and long duration in a dual foraging strategy, but the allocation of time on those trips varied significantly from year to year. In two years when sea-surface temperatures of feeding grounds exploited during short trips were cooler (2005, 2006) adults initially fed their chick more often, then feeding decreased through the chick-rearing period. In the following year of warmer sea-surface temperature (2007), the number of feedings per day was initially low but increased through chick rearing. Despite varied feeding patterns, breeding success was consistently high, yet in 2006 the chicks' poor condition indicates the capacity for buffering chicks from these effects was lower than in other years. The relative contribution of short and long trips to the amount of energy delivered to chicks also varied by year. During local food shortages, shearwaters appeared to deliver more oil from long trips and increased the frequency of short trips. Yet in 2006, low-calorie prey from short trips coincided with low volume of stomach oil from long trips, resulting in chicks' poorer condition. Oil volume and increased short-trip foraging provide potential mechanisms of flexibility enabling adults to buffer prey delivery to chicks during food shortages.Luke D. Einoder, Bradley Page and Simon D. Goldsworth
Convergence of marine megafauna movement patterns in coastal and open oceans
Data and code used in Sequeira et al., "Convergence of marine megafauna movement patterns in coastal and open oceans", Proceedings of the National Academy of Sciences (2018).Peer reviewe