Unsteady-state gas exchange and storage in diving marine mammals: the harbor porpoise and gray seal.

Breath-by-breath measurements of end-tidal O(2) and CO(2) concentrations in harbor porpoise reveal that the respiratory gas exchange ratio (R(R); CO(2) output/O(2) uptake) of the first lung ventilation in a breathing bout after a prolonged breath-hold is always well below the animal's metabolic respiratory quotient (RQ) of 0.85. Thus the longest apneic pauses are always followed by an initial breath having a very low R(R) (0.6-0.7), which thereafter increases with each subsequent breath to values in excess of 1.2. Although the O(2) stores of the body are fully readjusted after the first three to four breaths following a prolonged apneic pause, a further three to four ventilations are always needed, not to load more O(2) but to eliminate built-up levels of CO(2). The slower readjustment of CO(2) stores relates to their greater magnitude and to the fact that they must be mobilized from comparatively large and chemically complex HCO/CO(2) stores that are built up in the blood and tissues during the breath-hold. These data, and similar measurements on gray seals (12), indicate that it is the readjustment of metabolic RQ and not O(2) stores per se that governs the amount of time an animal must spend ventilating at the surface after a dive.

Gas exchange and heart rate in the harbour porpoise, Phocoena phocoena.

The respiratory physiology, heart rates and metabolic rates of two captive juvenile male harbour porpoises (both 28 kg) were measured using a rapid-response respiratory gas analysis system in the laboratory. Breath-hold durations in the laboratory (12 +/- 0.3 s, mean +/- SEM) were shorter than field observations, although a few breath-holds of over 40 s were recorded. The mean percentage time spent submerged was 89 +/- 0.4%. Relative to similarly-sized terrestrial mammals, the respiratory frequency was low (4.9 +/- 0.19 breaths.min-1) but with high tidal volumes (1.1 +/- 0.011), enabling a comparatively high minute rate of gas exchange. Oxygen consumption under these experimental conditions (247 +/- 13.8 ml O2.min-1) was 1.9-fold higher than predicted by standard scaling relations. These data together with an estimate of the total oxygen stores predicted an aerobic dive limit of 5.4 min. The peak end-tidal O2 values were related to the length of the previous breath-hold, demonstrating the increased oxygen uptake from the lung for the longer dives. Blood oxygen capacity was 23.5 +/- 1.0 ml.100 ml-1, and the oxygen affinity was high, enabling rapid oxygen loading during ventilation.

Interspecific microsatellite markers for the study of pinniped populations.

Microsatellites have rapidly become the marker of choice for a wide variety of population genetic studies. Here we describe 20 pinniped microsatellite markers which have been tested across 18 pinniped species. The majority of these markers have broad utility in all pinnipeds and provide a strong base for detailed population genetic studies in the Pinnipedia.

Molecular scatology: the use of molecular genetic analysis to assign species, sex and individual identity to seal faeces.

Seals and commercial fisheries are potential competitors for fish and cephalopods. Research into the diet of British seal species has been based on conventional dietary analyses, but these methods often do not allow assignment of species identity to scat samples. We present a protocol for obtaining DNA from seal scat (faecal) samples which can be used in polymerase chain reactions to amplify both nuclear and mitochondrial DNA. This can provide a method of identifying the species, sex and individual identity of the seal, from a particular scat sample. Combined with conventional dietary analyses these techniques will allow us to assess sources of variation in seal diet composition. Scat samples have been collected from intertidal haul-out sites around the inner Moray Firth, north-east Scotland. We have assessed methods to extract and purify faecal DNA, a combination of DNA from the individual seal, prey items, and gut bacteria, for use in PCR. Controls using faecal and blood samples from the same individual have enabled microsatellite primer sets from four pinniped species to be tested. Approximately 200 scat samples have been examined for species identity and individual matches. This study will provide essential information for the assessment of interactions between seals and commercial or recreational fisheries.

The metabolic characteristics of the locomotory muscles of grey seals (Halichoerus grypus), harbour seals (Phoca vitulina) and Antarctic fur seals (Arctocephalus gazella).

It is not known precisely how marine mammals are able to maintain muscle function during active swimming in breath-hold dives, when ventilation stops and heart rate falls. Examination of muscle biochemistry and histochemistry can provide information on the relative importance of different metabolic pathways, the contractile potential of the muscle fibres, the oxygen storage capacity of the muscle and the capillary distribution in these animals. In this study, samples of locomotory muscle were taken from wild grey seals (Halichoerus grypus), harbour seals (Phoca vitulina) and Antarctic fur seals (Arctocephalus gazella); Wistar rat muscle was analysed for comparative purposes. Activities of citrate synthase and beta-hydroxyacyl CoA dehydrogenase were higher in the harbour seal muscle than in the grey seal muscle, suggesting that harbour seals have a greater aerobic capacity. Both phocid muscles had a greater reliance on fatty acid oxidation than the fur seal or rat muscles. The myoglobin data demonstrate that the grey seals have the highest oxygen storage capacity of the three pinniped species, which correlates with their greater diving ability. Myoglobin levels were higher in all three pinniped species than in the Wistar rat. The fibre type compositions suggest that the muscles from the fur seals have higher glycolytic capacities than those of the phocid seals [fur seal pectoralis, 7% slow-twitch oxidative fibres (SO), 25% fast-twitch oxidative glycolytic fibres (FOG), 68% fast-twitch glycolytic fibres (FG); grey seal 57% SO, 5% FOG, 38% FG; area per cents]. However, the pectoralis muscle of the fur seal, although the most glycolytic of the pinniped muscles studied, has the highest capillary density, which indicates a high capacity for fuel distribution. These results show that, while pinniped muscle has an increased oxygen storage potential compared with the muscle of a typical terrestrial mammal, there are no distinct adaptations for diving in the enzyme pathways or fibre type distributions of the pinniped muscle. However, the muscle characteristics of each species can be related to its diving behaviour and foraging strategy.

Gas exchange of captive freely diving grey seals (Halichoerus grypus).

When at sea, phocids dive for long periods and spend a high percentage of their time submerged. This behaviour requires some combination of an increased oxygen storage capacity, rapid oxygen loading at the surface and reduced oxygen utilisation when submerged. To assess these adaptations, breath-by-breath ventilation was studied in four adult grey seals (two male, two female, 160-250 kg), freely diving in a large outdoor tank where surface access was restricted to one breathing hole. The dive patterns obtained were similar to those recorded from freely diving wild grey seals. Respiratory frequency during the surface periods was 40% higher than that estimated from allometric relationships (19.4 +/- 0.7 breaths min-1), and tidal volume (6.3 +/- 1.21) was approximately five times higher than that estimated from allometric relationships. These adaptations produce a high minute volume and enable gas exchange to occur at the surface. Mean oxygen consumption rate (VO2, measured for a dive+surface cycle) decreased with increasing dive duration. The aerobic dive limit was estimated as 9.6 min for a 150 kg grey seal (using the overall average VO2 of 5.2 ml O2 min-1 kg-1), which is consistent with results from freely diving wild grey seals (only 6% of dives exceeded 10 min). End-tidal oxygen values varied during a surface period, following a U-shaped curve, which suggests that there is limited oxygen uptake from the lung and/or blood oxygen stores during dives. This result was unexpected and indicates that these seals are utilising substantial physiological responses to conserve oxygen, even during shallow voluntary diving.