Phil N. Trathan

An Emperor Penguin Population Estimate: The First Global, Synoptic Survey of a Species from Space

Our aim was to estimate the population of emperor penguins (Aptenodytes fosteri) using a single synoptic survey. We examined the whole continental coastline of Antarctica using a combination of medium resolution and Very High Resolution (VHR) satellite imagery to identify emperor penguin colony locations. Where colonies were identified, VHR imagery was obtained in the 2009 breeding season. The remotely-sensed images were then analysed using a supervised classification method to separate penguins from snow, shadow and guano. Actual counts of penguins from eleven ground truthing sites were used to convert these classified areas into numbers of penguins using a robust regression algorithm. We found four new colonies and confirmed the location of three previously suspected sites giving a total number of emperor penguin breeding colonies of 46. We estimated the breeding population of emperor penguins at each colony during 2009 and provide a population estimate of ∼238,000 breeding pairs (compared with the last previously published count of 135,000–175,000 pairs). Based on published values of the relationship between breeders and non-breeders, this translates to a total population of ∼595,000 adult birds. There is a growing consensus in the literature that global and regional emperor penguin populations will be affected by changing climate, a driver thought to be critical to their future survival. However, a complete understanding is severely limited by the lack of detailed knowledge about much of their ecology, and importantly a poor understanding of their total breeding population. To address the second of these issues, our work now provides a comprehensive estimate of the total breeding population that can be used in future population models and will provide a baseline for long-term research.

Stroke frequency, but not swimming speed, is related to body size in free-ranging seabirds, pinnipeds and cetaceans

It is obvious, at least qualitatively, that small animals move their locomotory apparatus faster than large animals: small insects move their wings invisibly fast, while large birds flap their wings slowly. However, quantitative observations have been difficult to obtain from free-ranging swimming animals. We surveyed the swimming behaviour of animals ranging from 0.5 kg seabirds to 30 000 kg sperm whales using animal-borne accelerometers. Dominant stroke cycle frequencies of swimming specialist seabirds and marine mammals were proportional to mass−0.29 (R2=0.99, n=17 groups), while propulsive swimming speeds of 1–2 m s−1 were independent of body size. This scaling relationship, obtained from breath-hold divers expected to swim optimally to conserve oxygen, does not agree with recent theoretical predictions for optimal swimming. Seabirds that use their wings for both swimming and flying stroked at a lower frequency than other swimming specialists of the same size, suggesting a morphological trade-off with wing size and stroke frequency representing a compromise. In contrast, foot-propelled diving birds such as shags had similar stroke frequencies as other swimming specialists. These results suggest that muscle characteristics may constrain swimming during cruising travel, with convergence among diving specialists in the proportions and contraction rates of propulsive muscles.

Climate change and Southern Ocean ecosystems I: how changes in physical habitats directly affect marine biota

Antarctic and Southern Ocean (ASO) marine ecosystems have been changing for at least the last 30 years, including in response to increasing ocean temperatures and changes in the extent and seasonality of sea ice; the magnitude and direction of these changes differ between regions around Antarctica that could see populations of the same species changing differently in different regions. This article reviews current and expected changes in ASO physical habitats in response to climate change. It then reviews how these changes may impact the autecology of marine biota of this polar region: microbes, zooplankton, salps, Antarctic krill, fish, cephalopods, marine mammals, seabirds, and benthos. The general prognosis for ASO marine habitats is for an overall warming and freshening, strengthening of westerly winds, with a potential pole-ward movement of those winds and the frontal systems, and an increase in ocean eddy activity. Many habitat parameters will have regionally specific changes, particularly relating to sea ice characteristics and seasonal dynamics. Lower trophic levels are expected to move south as the ocean conditions in which they are currently found move pole-ward. For Antarctic krill and finfish, the latitudinal breadth of their range will depend on their tolerance of warming oceans and changes to productivity. Ocean acidification is a concern not only for calcifying organisms but also for crustaceans such as Antarctic krill; it is also likely to be the most important change in benthic habitats over the coming century. For marine mammals and birds, the expected changes primarily relate to their flexibility in moving to alternative locations for food and the energetic cost of longer or more complex foraging trips for those that are bound to breeding colonies. Few species are sufficiently well studied to make comprehensive species-specific vulnerability assessments possible. Priorities for future work are discussed.

Global climate drives southern right whale (Eubalaena australis) population dynamics

Sea surface temperature (SST) time-series from the southwest Atlantic and the El Niño 4 region in the western Pacific were compared to an index of annual calving success of the southern right whale (Eubalaena australis) breeding in Argentina. There was a strong relationship between right whale calving output and SST anomalies at South Georgia in the autumn of the previous year and also with mean El Niño 4 SST anomalies delayed by 6 years. These results extend similar observations from other krill predators and show clear linkages between global climate signals and the biological processes affecting whale population dynamics.

Corticosterone Predicts Foraging Behavior and Parental Care in Macaroni Penguins

Corticosterone has received considerable attention as the principal hormonal mediator of allostasis or physiological stress in wild animals. More recently, it has also been implicated in the regulation of parental care in breeding birds, particularly with respect to individual variation in foraging behavior and provisioning effort. There is also evidence that prolactin can work either inversely or additively with corticosterone to achieve this. Here we test the hypothesis that endogenous corticosterone plays a key physiological role in the control of foraging behavior and parental care, using a combination of exogenous corticosterone treatment, time-depth telemetry, and physiological sampling of female macaroni penguins (Eudyptes chrysolophus) during the brood-guard period of chick rearing, while simultaneously monitoring patterns of prolactin secretion. Plasma corticosterone levels were significantly higher in females given exogenous implants relative to those receiving sham implants. Increased corticosterone levels were associated with significantly higher levels of foraging and diving activity and greater mass gain in implanted females. Elevated plasma corticosterone was also associated with an apparent fitness benefit in the form of increased chick mass. Plasma prolactin levels did not correlate with corticosterone levels at any time, nor was prolactin correlated with any measure of foraging behavior or parental care. Our results provide support for the corticosterone-adaptation hypothesis, which predicts that higher corticosterone levels support increased foraging activity and parental effort.

Characterization of the Antarctic Polar Frontal Zone to the north of South Georgia in summer 1994

The Polar Front (PF) forms the southern boundary to the Polar Frontal Zone (PFZ) along the northern edge of the Antarctic Circumpolar Current (ACC). In a number of areas the position of the PF (and thus the PFZ) is known to be influenced by topographic steering, while local bathymetry has also been implicated in the movement and retention of various associated mesoscale features. In this paper we examine the structure and position of the PF as it passes over the rugged bathymetry to the north of the Scotia Sea. Results are presented from an oceanographic transect crossing the PF to the northwest of South Georgia and from a pair of shorter transects south of the PF but north and east of the first. Associated with the PF was a narrow, high-speed flow embedded in broader, slower moving regions. This high-speed flow was found to have a geostrophic component of velocity that was slower than estimates for other regions of the PF. Comparisons with output from recent oceanographic models were found to be consistent with the physical observations. A second examination of the region after a period of 30 days suggested that the surface expression of the PF had shifted southward by approximately 35 km but that the PF was essentially in the same position over the southern edge of the Maurice Ewing Bank. An advanced very high resolution radiometer image taken during the cruise provided additional information about the position of the surface expression of the PF and the extent of mesoscale features that were present to the north of the study area. Immediately to the north of South Georgia, water in the eastward flow of the ACC meets colder, more saline water flowing west along the north coast of the island. The area where these two flows meet was found to be variable over the 30-day timescale of the cruise. This area is known to be of major biological significance, and variability in the local oceanography is possibly of crucial importance to many predator species breeding at the northern end of South Georgia.

Where do penguins go during the inter-breeding period? Using geolocation to track the winter dispersion of the macaroni penguin.

Although penguins are key marine predators from the Southern Ocean, their migratory behaviour during the inter-nesting period remains widely unknown. Here, we report for the first time, to our knowledge, the winter foraging movements and feeding habits of a penguin species by using geolocation sensors fitted on penguins with a new attachment method. We focused on the macaroni penguin Eudyptes chrysolophus at Kerguelen, the single largest consumer of marine prey among all seabirds. Overall, macaroni penguins performed very long winter trips, remaining at sea during approximately six months within the limits of the Southern Ocean. They departed from Kerguelen in an eastward direction and distributed widely, over more than 3.106 km2. The penguins spent most of their time in a previously unrecognized foraging area, i.e. a narrow latitudinal band (47–49° S) within the central Indian Ocean (70–110° E), corresponding oceanographically to the Polar Frontal Zone. There, their blood isotopic niche indicated that macaroni penguins preyed mainly upon crustaceans, but not on Antarctic krill Euphausia superba, which does not occur at these northern latitudes. Such winter information is a crucial step for a better integrative approach for the conservation of this species whose world population is known to be declining.

Responding to climate change: Adélie Penguins confront astronomical and ocean boundaries

Long-distance migration enables many organisms to take advantage of lucrative breeding and feeding opportunities during summer at high latitudes and then to move to lower, more temperate latitudes for the remainder of the year. The latitudinal range of the Adélie Penguin (Pygoscelis adeliae) spans approximately 22 degrees. Penguins from northern colonies may not migrate, but due to the high latitude of Ross Island colonies, these penguins almost certainly undertake the longest migrations for the species. Previous work has suggested that Adélies require both pack ice and some ambient light at all times of year. Over a three-year period, which included winters of both extensive and reduced sea ice, we investigated characteristics of migratory routes and wintering locations of Adélie Penguins from two colonies of very different size on Ross Island, Ross Sea, the southernmost colonies for any penguin. We acquired data from 3-16 geolocation sensor tags (GLS) affixed to penguins each year at both Cape Royds and Cape Crozier in 2003-2005. Migrations averaged 12760 km, with the longest being 17 600 km, and were in part facilitated by pack ice movement. Trip distances varied annually, but not by colony. Penguins rarely traveled north of the main sea-ice pack, and used areas with high sea-ice concentration, ranging from 75% to 85%, about 500 km inward from the ice edge. They also used locations where there was some twilight (2-7 h with sun < 6 degrees below the horizon). We report the present Adélie Penguin migration pattern and conjecture on how it probably has changed over the past approximately 12000 years, as the West Antarctic Ice Sheet withdrew southward across the Ross Sea, a situation that no other Adélie Penguin population has had to confront. As sea ice extent in the Ross Sea sector decreases in the near future, as predicted by climate models, we can expect further changes in the migration patterns of the Ross Sea penguins.

Pollution, habitat loss, fishing, and climate change as critical threats to penguins

Cumulative human impacts across the worlds oceans are considerable. We therefore examined a single model taxonomic group, the penguins (Spheniscidae), to explore how marine species and communities might be at risk of decline or extinction in the southern hemisphere. We sought to determine the most important threats to penguins and to suggest means to mitigate these threats. Our review has relevance to other taxonomic groups in the southern hemisphere and in northern latitudes, where human impacts are greater. Our review was based on an expert assessment and literature review of all 18 penguin species; 49 scientists contributed to the process. For each penguin species, we considered their range and distribution, population trends, and main anthropogenic threats over the past approximately 250 years. These threats were harvesting adults for oil, skin, and feathers and as bait for crab and rock lobster fisheries; harvesting of eggs; terrestrial habitat degradation; marine pollution; fisheries bycatch and resource competition; environmental variability and climate change; and toxic algal poisoning and disease. Habitat loss, pollution, and fishing, all factors humans can readily mitigate, remain the primary threats for penguin species. Their future resilience to further climate change impacts will almost certainly depend on addressing current threats to existing habitat degradation on land and at sea. We suggest protection of breeding habitat, linked to the designation of appropriately scaled marine reserves, including in the High Seas, will be critical for the future conservation of penguins. However, large-scale conservation zones are not always practical or politically feasible and other ecosystem-based management methods that include spatial zoning, bycatch mitigation, and robust harvest control must be developed to maintain marine biodiversity and ensure that ecosystem functioning is maintained across a variety of scales.

Interspecific variations in the gastrointestinal microbiota in penguins

Despite the enormous amount of data available on the importance of the gastrointestinal (GI) microbiota in vertebrate (especially mammals), information on the GI microbiota of seabirds remains incomplete. As with many seabirds, penguins have a unique digestive physiology that enables them to store large reserves of adipose tissue, protein, and lipids. This study used quantitative real‐time polymerase chain reaction (qPCR) and 16S rRNA gene pyrosequencing to characterize the interspecific variations of the GI microbiota of four penguin species: the king, gentoo, macaroni, and little penguin. The qPCR results indicated that there were significant differences in the abundance of the major phyla Firmicutes, Bacteroides, Actinobacteria, and Proteobacteria. A total of 132,340, 18,336, 6324, and 4826 near full‐length 16S rRNA gene sequences were amplified from fecal samples collected from king, gentoo, macaroni, and little penguins, respectively. A total of 13 phyla were identified with Firmicutes, Bacteroidetes, Proteobacteria, and Fusobacteria dominating the composition; however, there were major differences in the relative abundance of the phyla. In addition, this study documented the presence of known human pathogens, such as Campylobacter, Helicobacter, Prevotella, Veillonella, Erysipelotrichaceae, Neisseria, and Mycoplasma. However, their role in disease in penguins remains unknown. To our knowledge, this is the first study to provide an in‐depth investigation of the GI microbiota of penguins.