Three approaches commonly used to quantify diffusive gas exchange across aquatic surfaces were compared in a densely treed, low-wind environment Diffusive surface fluxes of carbon dioxide (CO2) and methane (CH4) from a small boreal reservoir were estimated using (i) surface water concentrations, the thin boundary layer (TBL) equation, and gas transfer velocities (k) calculated using sulfur hexafluoride (SF6); (ii) surface water concentrations, the TBL equation, and k estimated from wind speed; and (iii) static floating chambers (FCs). Comparisons were made during three different approximately 10-day intervals (August 2000, June and September 2001). CO2 and CH4 fluxes estimated from SF6-derived k were on average 1-3 times greater than those determined from wind-estimated k Overall agreement between FC CO2 and CH4 flux estimates and those based on SF6 and wind speed derived kvalues was much weaker, with FC CO2 and CH4 flux estimates ranging from -9 to 23 times those based on SF6 and wind-estimated k values. Chamber deployment likely enhanced gas transfer through disturbance of the surface boundary layer, and results of this study suggest that caution must be exercised concerning the use of FCs on very still water surfaces. Furthermore, findings of this study contradict the common belief that use of wind speed to approximate k is inappropriate for small bodies of water characterized by low winds and surface obstructions.

Reconstruction of the demographic and evolutionary history of populations assuming a consensus tree‐like relationship can mask more complex scenarios, which are prevalent in nature. An emerging genomic toolset, which has been most comprehensively harnessed in the reconstruction of human evolutionary history, enables molecular ecologists to elucidate complex population histories. Killer whales have limited extrinsic barriers to dispersal and have radiated globally, and are therefore a good candidate model for the application of such tools. Here, we analyse a global data set of killer whale genomes in a rare attempt to elucidate global population structure in a nonhuman species. We identify a pattern of genetic homogenisation at lower latitudes and the greatest differentiation at high latitudes, even between currently sympatric lineages. The processes underlying the major axis of structure include high drift at the edge of species' range, likely associated with founder effects and allelic surfing during postglacial range expansion. Divergence between Antarctic and non‐Antarctic lineages is further driven by ancestry segments with up to four‐fold older coalescence time than the genome‐wide average; relicts of a previous vicariance during an earlier glacial cycle. Our study further underpins that episodic gene flow is ubiquitous in natural populations, and can occur across great distances and after substantial periods of isolation between populations. Thus, understanding the evolutionary history of a species requires comprehensive geographic sampling and genome‐wide data to sample the variation in ancestry within individuals.

Eastern Canada-West Greenland (EC-WG) bowhead whales Balaena mysticetus migrate seasonally between northwestern Hudson Bay/Foxe Basin and Gulf of Boothia in summer and Hudson and Davis Straits in winter. Despite recent advances in knowledge of summer diet composition, determining seasonal variation in foraging behaviour of EC-WG bowhead whales remains a priority for understanding how annual metabolic requirements are met, as well as identifying factors driving seasonal habitat selection. We measured stable nitrogen, carbon, and sulfur isotope composition (δ 15 N, δ 13 C, and δ 34 S) along continuously growing baleen plates (n = 14) to assess alternative seasonal foraging hypotheses, namely winter fasting vs. year-round foraging. Synchronous δ 15 N and δ 13 C cycles, with periods of 15 N enrichment corresponding to foraging on the summer grounds, were inconsistent with standard fasting predictions, although δ 15 N cycles could reflect changes in diet-tissue δ 15 N discrimination between periods of intense foraging throughout the open-water season and supplemental protein intake during winter/spring. Correlations between δ 15 N and δ 34 S values, potentially meditated through amino acid metabolism, support this interpretation. Reasonable agreement between baleen isotope oscillations and regional baseline δ 15 N and δ 13 C variation also indicated foraging occurs within isotopically distinct food webs across the summer and winter ranges. We conclude that EC-WG bowhead whales forage throughout their distribution, and conservatively interpret δ 15 N and δ 34 S cycles to reflect reduced food consumption during winter. Foraging outside of periods of peak productivity likely contributes to annual metabolic requirements and winter habitat selection.

No abstract

Although predators influence behavior of prey, analyses of electronic tracking data in marine environments rarely consider how predators affect the behavior of tracked animals. We collected an unprecedented dataset by synchronously tracking predator (killer whales, N = 1; representing a family group) and prey (narwhal, N = 7) via satellite telemetry in Admiralty Inlet, a large fjord in the Eastern Canadian Arctic. Analyzing the movement data with a switching-state space model and a series of mixed effects models, we show that the presence of killer whales strongly alters the behavior and distribution of narwhal. When killer whales were present (within about 100 km), narwhal moved closer to shore, where they were presumably less vulnerable. Under predation threat, narwhal movement patterns were more likely to be transiting, whereas in the absence of threat, more likely resident. Effects extended beyond discrete predatory events and persisted steadily for 10 d, the duration that killer whales remained in Admiralty Inlet. Our findings have two key consequences. First, given current reductions in sea ice and increases in Arctic killer whale sightings, killer whales have the potential to reshape Arctic marine mammal distributions and behavior. Second and of more general importance, predators have the potential to strongly affect movement behavior of tracked marine animals. Understanding predator effects may be as or more important than relating movement behavior to resource distribution or bottom-up drivers traditionally included in analyses of marine animal tracking data.predator-prey dynamics | sea ice | biologging | climate change | trait-mediated effects C onsumptive effects (alternatively termed "density-mediated effects") of predators on prey refer to the mortality incurred when predators kill and consume prey during predation events. They can control prey populations and in certain circumstances, restructure ecosystems through trophic cascades (1-3). Nonconsumptive effects (also termed "trait-mediated effects") can similarly affect prey populations by altering species' behavior and space use under perceived or real predation risk, which are associated with decreased fitness through loss of access to key foraging areas, disrupted social structure, increased energy expenditure and stress imposed by persistent vigilance and escape behaviors, and decreased reproductive success (3-7). Nonconsumptive effects are sublethal (8, 9), but because they can impact many individuals in a population simultaneously, the cumulative effect may exceed consumptive effects (8,(10)(11)(12).In terrestrial systems, movement data collected by electronic telemetry tracking tags have been used to clearly show that carnivores affect prey species' use of space and habitat selection (13-15), and these nonconsumptive effects can negatively impact population dynamics (10, 13, 11). When large enough, such effects have even been suggested to lead to trophic cascades (16,17,3). However, there is disagreement about whether nonconsumptive effects ...

No abstract

Killer whales in the Eastern Canadian Arctic (ECA) prey on narwhal, beluga, bowhead whales and seals, while further south in the north-west Atlantic (NWA), killer whales off the coast of Newfoundland and Labrador prey on both marine mammals and fish. Bulk and amino acid (AA) specific isotopic composition of dentinal collagen in teeth of 13 ECA/NWA killer whales were analysed to assess the degree, if any, of dietary specialization of killer whales across the region. Dentine was sampled from within annual growth layer groups (GLGs) to construct chronological profiles of stable nitrogen (d 15 N) and carbon (d 13 C) isotopic compositions for individual whales spanning 3-25 years. Interannual isotopic variation across GLGs was less than that among individuals, and median bulk d 15 N values differed by up to 5‰ among individuals. Significant correlation between bulk d 15 N values and baseline (source AA) d 15 N values indicates much of the observed isotopic variation among individuals reflects foraging within isotopically distinct food webs, rather than diet differences. This interpretation is supported by consistent differences in bulk d 13 C values between the two individuals with lowest source AA d 15 N values and the remaining whales. After accounting for baseline isotopic variation, comparable d 15 N values among individuals indicates similar trophic-level diet, although uncertainties in relative trophic 15 N enrichment of individual AAs currently limits trophic position estimates for top consumers. Further research is required to clarify seasonal movement patterns and possible diet shifts of ECA/NWA killer whales to better define their role in marine ecosystems across the region.

The effects of predator intimidation on habitat use and behavior of prey species are rarely quantified for large marine vertebrates over ecologically relevant scales. Using state space movement models followed by a series of step selection functions, we analyzed movement data of concurrently tracked prey, bowhead whales (Balaena mysticetus;n= 7), and predator, killer whales (Orcinus orca; n= 3), in a large (63,000 km2), partially ice-covered gulf in the Canadian Arctic. Our analysis revealed pronounced predator-mediated shifts in prey habitat use and behavior over much larger spatiotemporal scales than previously documented in any marine or terrestrial ecosystem. The striking shift from use of open water (predator-free) to dense sea ice and shorelines (predators present) was exhibited gulf-wide by all tracked bowheads during the entire 3-wk period killer whales were present, constituting a nonconsumptive effect (NCE) with unknown energetic or fitness costs. Sea ice is considered quintessential habitat for bowhead whales, and ice-covered areas have frequently been interpreted as preferred bowhead foraging habitat in analyses that have not assessed predator effects. Given the NCEs of apex predators demonstrated here, however, unbiased assessment of habitat use and distribution of bowhead whales and many marine species may not be possible without explicitly incorporating spatiotemporal distribution of predation risk. The apparent use of sea ice as a predator refuge also has implications for how bowhead whales, and likely other ice-associated Arctic marine mammals, will cope with changes in Arctic sea ice dynamics as historically ice-covered areas become increasingly ice-free during summer.