1. The measurement of energy expenditures in free-ranging animals is essential if we are to understand fully the interaction between a species and its environment. This study examined the validity of heart rate (fH) and doubly labelled water (DLW) as measures of field metabolic rate (FMR) in California Sea Lions (Zalophus californianus). 2. Oxygen consumption and CO2 production were measured over 24 h by direct respirometry in six juvenile sea lions. The respirometer consisted of a hood over a flume in which the sea lions were exercised to various levels for 15 min periods throughout each experiment. The exercise regime produced a mean metabolic rate which was 2.3 times the predicted basal metabolic rate (BMR) with mean maxima of 6.27 times the predicted BMR. 3. Simultaneously with direct respirometry, mean CO2 production was estimated using DLW and 02 consumption was estimated using fH, which had previously been calibrated against 02 consumption. 4. The mean ? SD 02 consumptions from direct respirometry, fH and DLW were 11 80?240, 11.95?2.17 and 15 01?3 77ml min-' kg-' respectively. Paired Student's t-tests showed no significant difference between 02 consumption by direct respirometry and the estimates from DLW andfH. DLW measurements ranged from-10% to +86% of the direct respirometry measurements (mean +36.4%) and fH measurements ranged from-28% to +23% of the direct respirometry measurements (mean +2.7%). 5. The range of estimated metabolic rates fromfH was largely owing to individual differences in the slopes of the linear relationship betweenfH and 02 consumption. The range of metabolic rates from DLW could be partly attributed to the short duration of the experiments (24-25 h) but this was shown not to be the cause of the tendency to overestimate metabolic rate from DLW. It was concluded that both DLW and fH are valid methods for measuring FMR in California Sea Lions although it is possible that FMR could be overestimated when using DLW.

A synthesis of a comprehensive annual study of material processing in the Bly Creek marsh-estuarine basln is described. The project design provides statistical estimates of material fluxes for the water column, salt marsh, and oyster reef subsystems. Fluxes from a freshwater stream, groundwater, and rain are also presented Material processing by the Bly Creek marsh-estuarine basin is constituent-and subsystem-specific Inflows of material via rain, streamwater. and groundwater are small and relatively unin~portant compared to tidal fluxes. The salt marsh dominates the basin in aerial extent and in terms of net material fluxes. Most constituents exhibit significant net annual import to the salt marsh. Only DON is exported from the marsh and from the basin at significant levels. The salt marsh appears to recycle most of the nitrogen and phosphorus needed for marsh grass primary production. Sufficient inorganic particulate material is imported to allow the salt marsh to maintain its elevation with respect to ongoing sea-level rise. As a result of metabolic processes, the oyster reef imports particulate materials and releases dissolved nutrients. The reef is a significant consumer of chl a and produces enough dissolved inorganic nitrogen and phosphorus to support water column primary production The N:P ratio of Bly Creek dissolved inorganic nutrients is lower than that of North Inlet or ocean waters and implies nitrogen conservation or mobilization of particulate phosphorus into orthophosphate. In contrast to human-impacted coastal systems, this prist~ne basin reduces the N : P rat10 as water passes through it Differences in the N:P ratio are probably the result of DON export, denitnfication, and phosphorus import by the basin

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BackgroundThe energy requirements of free-ranging marine mammals are challenging to measure due to cryptic and far-ranging feeding habits, but are important to quantify given the potential impacts of high-level predators on ecosystems. Given their large body size and carnivorous lifestyle, we would predict that northern elephant seals (Mirounga angustirostris) have elevated field metabolic rates (FMRs) that require high prey intake rates, especially during pregnancy. Disturbance associated with climate change or human activity is predicted to further elevate energy requirements due to an increase in locomotor costs required to accommodate a reduction in prey or time available to forage. In this study, we determined the FMRs, total energy requirements, and energy budgets of adult, female northern elephant seals. We also examined the impact of increased locomotor costs on foraging success in this species.ResultsBody size, time spent at sea and reproductive status strongly influenced FMR. During the short foraging migration, FMR averaged 90.1 (SE = 1.7) kJ kg−1d−1 – only 36 % greater than predicted basal metabolic rate. During the long migration, when seals were pregnant, FMRs averaged 69.4 (±3.0) kJ kg−1d−1 – values approaching those predicted to be necessary to support basal metabolism in mammals of this size. Low FMRs in pregnant seals were driven by hypometabolism coupled with a positive feedback loop between improving body condition and reduced flipper stroking frequency. In contrast, three additional seals carrying large, non-streamlined instrumentation saw a four-fold increase in energy partitioned toward locomotion, resulting in elevated FMRs and only half the mass gain of normally-swimming study animals.ConclusionsThese results highlight the importance of keeping locomotion costs low for successful foraging in this species. In preparation for lactation and two fasting periods with high demands on energy reserves, migrating elephant seals utilize an economical foraging strategy whereby energy savings from reduced locomotion costs are shuttled towards somatic growth and fetal gestation. Remarkably, the energy requirements of this species, particularly during pregnancy, are 70–80 % lower than expected for mammalian carnivores, approaching or even falling below values predicted to be necessary to support basal metabolism in mammals of this size.Electronic supplementary materialThe online version of this article (doi:10.1186/s40462-015-0049-2) contains supplementary material, which is available to authorized users.

SUMMARY, increased as water temperature approached 12°C, and suggested a potential thermal limitation in the wild. To determine whether muscle thermogenesis during activity could mitigate this limitation, we measured the active metabolic rate of juveniles swimming at water temperature (T water )5, 12 and 20°C. No significant difference (F0.377, P0.583) in swimming metabolic rate was found among water temperatures, suggesting that thermal disadvantages due to small body size in juvenile sea lions may be circumvented by recycling endogenous heat during locomotor activity.