Ontogeny of oxygen stores and physiological diving capability in Australian sea lions

1.For air-breathing animals in aquatic environments, foraging behaviours are often constrained by physiological capability. The development of oxygen stores and the rate at which these stores are used determine juvenile diving and foraging potential.2. We examined the ontogeny of dive physiology in the threatened Australian sea lion Neophoca cinerea. Australian sea lions exploit benthic habitats; adult females demonstrate high field metabolic rates (FMR), maximize time spent near the benthos, and regularly exceed their calculated aerobic dive limit (cADL). Given larger animals have disproportionately greater diving capabilities; we wanted to determine the extent physiological development constrained diving and foraging in young sea lions.3. Ten different mother/pup pairs were measured at three developmental stages (6, 15 and 23 months) at Seal Bay Conservation Park, Kangaroo Island, South Australia. Hematocrit (Hct), haemoglobin (Hb) and plasma volume were analyzed to calculate blood O2 stores and myoglobin was measured to determine muscle O2. Additionally, FMR\u27s for nine of the juveniles were derived from doubly-labelled water measurements.4. Australian sea lions have the slowest documented O2 store development among diving mammals. Although weaning typically occurs by 17&middot;6 months, 23-month juveniles had only developed 68% of adult blood O2. Muscle O2 was the slowest to develop and was 60% of adult values at 23 months.5. We divided available O2 stores (37&middot;11 &plusmn; 1&middot;49 mL O2 kg&minus;1) by at-sea FMR (15&middot;78 &plusmn; 1&middot;29 mL O2 min&minus;1 kg&minus;1) to determine a cADL of 2&middot;33 &plusmn; 0&middot;24 min for juvenile Australian sea lions. Like adults, young sea lions regularly exceeded cADL\u27s with 67&middot;8 &plusmn; 2&middot;8% of dives over theoretical limits and a mean dive duration to cADL ratio of 1&middot;23 &plusmn; 0&middot;10.6. Both dive depth and duration appear impacted by the slow development of oxygen stores. For species that operate close to, or indeed above their estimated physiological maximum, the capacity to increase dive depth, duration or foraging effort would be limited. Due to reduced access to benthic habitat and restricted behavioural options, young benthic foragers, such as Australian sea lions, would be particularly vulnerable to resource limitation.<br /

Locomotion in diving elephant seals: physical and physiological constraints

To better understand how elephant seals (Mirounga angustirostris) use negative buoyancy to reduce energy metabolism and prolong dive duration, we modelled the energetic cost of transit and deep foraging dives in an elephant seal. A numerical integration technique was used to model the effects of swim speed, descent and ascent angles, and modes of locomotion (i.e. stroking and gliding) on diving metabolic rate, aerobic dive limit, vertical displacement (maximum dive depth) and horizontal displacement (maximum horizontal distance along a straight line between the beginning and end locations of the dive) for aerobic transit and foraging dives. Realistic values of the various parameters were taken from previous experimental data. Our results indicate that there is little energetic advantage to transit dives with gliding descent compared with horizontal swimming beneath the surface. Other factors such as feeding and predator avoidance may favour diving to depth during migration. Gliding descent showed variable energy savings for foraging dives. Deep mid-water foraging dives showed the greatest energy savings (approx. 18%) as a result of gliding during descent. In contrast, flat-bottom foraging dives with horizontal swimming at a depth of 400 m showed less of an energetic advantage with gliding descent, primarily because more of the dive involved stroking. Additional data are needed before the advantages of gliding descent can be fully understood for male and female elephant seals of different age and body composition. This type of data will require animal-borne instruments that can record the behaviour, three-dimensional movements and locomotory performance of free-ranging animals at depth

Fishing for data in the Ross Sea

The public perceives a certification by the Marine Stewardship Council (MSC) to mean an environmentally friendly fishery, not one characterized by the \u201cdearth of key data\u201d. Significant data deficiencies lead to conclude that an eco-friendly label for the fishery of Ross Sea Antarctic toothfish (Dissostichus mawsoni) is scientifically indefensible. Credible life history data are missing: spawning areas, eggs, and larvae have never been found, spawning intervals are unknown, and most density-dependent aspects of ecological relationships are undetermined. Stock assessment is problematic because severe Antarctic pack ice conditions for more than 9 months a year prevent scientists from effectively using standard models, which require random tagging over time, space, and age classes. The number of fish harvested by illegal, unregulated, and unreported fisheries is likely substantial. Finally, ecosystem effects of removing 50% of spawning biomass of this slow-to-mature species are unlikely to be neutral. The large, adult toothfish targeted by the fishery are a key structural link in the food web of the Ross Sea, currently the most pristine marine area on Earth. Instead of a certification that lacks proper data, a moratorium should be placed on further Ross Sea fishing until the quality of science at least equals that of certified fisheries elsewhere