Sebastián P. Luque

The comparative energetics and growth strategies of sympatric Antarctic and subantarctic fur seal pups at Îles Crozet

SUMMARY The period of maternal dependence is a time during which mammalian infants must optimise both their growth and the development of behavioural skills in order to successfully meet the demands of independent living. The rate and duration of maternal provisioning, post-weaning food availability and climatic conditions are all factors likely to influence the growth strategies of infants. While numerous studies have documented differences in growth strategies at high taxonomic levels, few have investigated those of closely related species inhabiting similar environments. The present study examined the body composition, metabolism and indices of physiological development in pups of Antarctic fur seals (Arctocephalus gazella) and subantarctic fur seals (Arctocephalus tropicalis), congeneric species with different weaning ages (4 months and 10 months, respectively), during their overlap in lactation at a sympatric breeding site in the Iles Crozet. Body lipid reserves in pre-moult pups were significantly greater (t28=2.73, P<0.01) in subantarctic (26%) than Antarctic fur seals (22%). Antarctic fur seal pups, however, had significantly higher (t26=3.82, P<0.001) in-air resting metabolic rates (RMR; 17.1±0.6 ml O2 kg-1 min-1) than subantarctic fur seal pups (14.1±0.5 ml O2 kg-1 min-1). While in-water standard metabolic rate (SMR; 22.9±2.5 ml O2 kg-1 min-1) was greater than in-air RMR for Antarctic fur seal pups (t9=2.59, P<0.03), there were no significant differences between in-air RMR and in-water SMR for subantarctic fur seal pups (t12=0.82, P>0.4), although this is unlikely to reflect a greater ability for pre-moult pups of the latter species to thermoregulate in water. Pup daily energy expenditure was also significantly greater (t27=2.36, P<0.03) in Antarctic fur seals (638±33 kJ kg-1 day-1) than in subantarctic fur seals (533±33 kJ kg-1 day-1), which corroborates observations that pups of the former species spend considerably more time actively learning to swim and dive. Consistent with this observation is the finding that blood oxygen storage capacity was significantly greater (t9=2.81, P<0.03) in Antarctic (11.5%) than subantarctic fur seal (8.9%) pups. These results suggest that, compared with subantarctic fur seals, Antarctic fur seal pups adopt a strategy of faster lean growth and physiological development, coupled with greater amounts of metabolically expensive behavioural activity, in order to acquire the necessary foraging skills in time for their younger weaning age.

A maximum likelihood approach for identifying dive bouts improves accuracy, precision and objectivity

Foraging behaviour frequently occurs in bouts, and considerable efforts to properly define those bouts have been made because they partly reflect different scales of environmental variation. Methods traditionally used to identify such bouts are diverse, include some level of subjectivity, and their accuracy and precision is rarely compared. Therefore, the applicability of a maximum likelihood estimation method (MLM) for identifying dive bouts was investigated and compared with a recently proposed sequential differences analysis (SDA). Using real data on interdive durations from Antarctic fur seals (Arctocephalus gazella Peters, 1875), the MLM-based model produced briefer bout ending criterion (BEC) and more precise parameter estimates than the SDA approach. The MLM-based model was also in better agreement with real data, as it predicted the cumulative frequency of differences in interdive duration more accurately. Using both methods on simulated data showed that the MLM-based approach produced less biased estimates of the given model parameters than the SDA approach. Different choices of histogram bin widths involved in SDA had a systematic effect on the estimated BEC, such that larger bin widths resulted in longer BECs. These results suggest that using the MLM-based procedure with the sequential differences in interdive durations, and possibly other dive characteristics, may be an accurate, precise, and objective tool for identifying dive bouts.

Recursive Filtering for Zero Offset Correction of Diving Depth Time Series with GNU R Package diveMove

Zero offset correction of diving depth measured by time-depth recorders is required to remove artifacts arising from temporal changes in accuracy of pressure transducers. Currently used methods for this procedure are in the proprietary software domain, where researchers cannot study it in sufficient detail, so they have little or no control over how their data were changed. GNU R package diveMove implements a procedure in the Free Software domain that consists of recursively smoothing and filtering the input time series using moving quantiles. This paper describes, demonstrates, and evaluates the proposed method by using a “perfect” data set, which is subsequently corrupted to provide input for the proposed procedure. The method is evaluated by comparing the corrected time series to the original, uncorrupted, data set from an Antarctic fur seal (Arctocephalus gazella Peters, 1875). The Root Mean Square Error of the corrected data set, relative to the “perfect” data set, was nearly identical to the magnitude of noise introduced into the latter. The method, thus, provides a flexible, reliable, and efficient mechanism to perform zero offset correction for analyses of diving behaviour. We illustrate applications of the method to data sets from four species with large differences in diving behaviour, measured using different sampling protocols and instrument characteristics.

Age structure, growth, mortality, and density of belugas ( Delphinapterus leucas ) in the Canadian Arctic: responses to environment?

Environmental constraints on life-history traits are expected to increase with seasonality in resources such as food and appropriate breeding habitat. Seasonality is highest at polar latitudes, where environmental constraints can be stronger than biotic factors, such as density and its effect on intraspecific competition. In this study, the age structure, body-length distribution, mortality, and density were studied and compared among five beluga populations of the Canadian Arctic: eastern Beaufort Sea (EBS), Baffin Bay (BB), Cumberland Sound (CS), western (WHB), and eastern Hudson (EHB) Bay, to test the prediction that density-dependent effects on these life-history traits should be inversely related to latitude. Growth, but not mortality, showed a significant positive relationship with latitude. Winter density also increased with winter latitude, consistent with the prediction of greater risk of mortality associated with density-independent effects, such as ice entrapment in winter. Age distributions differed among populations, with animals harvested at the highest-latitude population (EBS) being the oldest and attaining the longest adult body lengths, compared to lower-latitude populations (WHB and EHB). The latitudinal variation in growth, adult body size, and winter density is congruent with the hypothesis that environmental seasonality may impose stronger constraints on life-history traits of beluga with increasing latitude.

Estimation of body volume and body density in California sea lion pups

Body volume was measured directly by the water displacement method and using three different geometric models, consisting of a series of cones and truncated cones, in California sea lion (Zalophus californianus) pups from the Gulf of California. Volume is required for the estimation of density, an indicator of the ratio of fat to lean mass. A model consisting of two cones and four truncated cones predicted body volume with greatest accuracy (volume=1.11+1.06×estimated volume, r 2 =0.90, P<0.001, SEE=0.673, N=274). This model, however, was not adequate to estimate absolute pup body density (mass to volume ratio), as it yielded values poorly correlated with observed body density (r=0.14, P=0.02). However, the regression line of mass on volume indicated that density decreased with volume, so the mass to volume ratio is a biased estimate of density and is not appropriate for comparing whole body density among sea lion pups. The direct analysis of the relationship between body mass and body volume (observed or estimated) through analysis of covariance provided a better tool to compare the relative density among pups of different sex, populations; or born in different years. The results from such analyses are consistent with previous evidence of sex and age effects on body composition.

Ecological monitoring of polar bears and seals in Nunavut a step toward the future.

We deployed satellite transmitters on live ringed seals captured in Hudson Bay in the summer of 2009. Polar bear transmitters have been deployed in Hudson Bay in 2007, 2008, and 2009. This project will provide management information and advice for the Hudson Bay and Foxe Basin ringed seal stocks by: (1) delineating movements that may bring juveniles and possibly adults into areas hunted by other communities, (2) assessing sex- and age-specific site fidelity of individual seals during the breeding season, (3) defining critical foraging habitat, movement and diving behaviour, (4) defining spatio-temporal variation in these aspects of ringed seal foraging ecology to complement ongoing diet studies to address a purported shift in prey of top predators associated with climate change in the greater Hudson Bay region. The project also aims to engage northerners in ecosystem science, develop a community-based monitoring and sampling program for seal, and enhance Arctic science. The final outcome of this combined effort is to provide policy information necessary to inform northerners of how they can adapt to marine ecosystem changes associated with polar warming and the resulting changes to marine mammal distribution and abundance. This project is linked to other Canadian IPY projects: ?GWAMM?. ?Marine Birds?, ?Circumpolar Flaw Lead?, ?Greenland Sharks?, ?Pan-Arctic Beluga?, ?Country Food Safety in a Changing Arctic?, ?People of a Feather and Ice? and internationally within the ESSAR and PAN-AME clusters. Collaborations have been developed to extend the community-based monitoring effort across the Canadian Arctic (Makavik, Fisheries Joint Management Commission, Nunatsiavut-Labrador Inuit Association, Ocean Tracking Network), across international governments (Greenland/Denmark, Russia, United States-Alaska, Norway, Finland), and organizations (Circumpolar Biodiversity Monitoring Program, Sustained Arctic Observing Network, Circumpolar Arctic Flora and Fauna).

Corrigendum — Ontogeny of body size and shape of Antarctic and subantarctic fur seals

In the first sentence of the last paragraph on p. 1280, ‘‘Sparrow and Heywood (1996)’’ should be replaced by ‘‘Kerley (1985)’’, so the sentence should read as follows: Neonates of both species from our study were about a kilogram heavier than those weighed by Kerley (1985), although the difference cannot readily be attributed to any ecological factor because of the small sample size in the latter study.