020406080100120

SLI)

'I)E

-c

a

Ea

-ULI

I

Time (mm)

Figure 2. Seawater depth and average seal heart rate were recordedeach 30 seconds by the diving computer during free diving ofmonitored Weddell seals. [Heart rate (HR) is measured in beats perminute (bpm).]

Although depth and ECG were recorded on four seals, oneseal far surpassed all others in the quality and quantity of dataproduced, and the majority of our data came from this seal. Thisseal had heart rate and depth recorded every 30 seconds for

over 94 hours, providing a total of 22,700 data points. Duringthis time the seal produced a wide variety of dive lengths anddepths; the longest dive was 52 minutes and the deepest was486 meters. Figure 2 provides a sample of heart rate and sea-water depths during free diving. With each submersion a bra-dycardia was evident.

We also used our diving computer to control other underseameasurements. In addition to heart rate and depth measure-ments the computer initiated and controlled an aortic bloodsampling roller pump. We obtained 40 arterial blood samplesduring undersea free diving at depths up to 350 meters.

This research was supported by National Science Foundationgrant DPP 81-00212.

References

Kanwisher, J. W., C. Gabrielson, and N. Kanwisher. 1981. Free andforced diving in birds. Science, 211,717.

Kooyman, C. L., and W. B. Campbell. 1972. Heart rates in freely divingWeddell seals, Leptonychotes weddelli. Comparative Biochemistry andPhysiology, 43A,31-36.

Kooyman, C. L., E. A. Wahrenbrock, M. A. Castellini, R. A. Davis,and E. E. Sinnett. 1980. Aerobic and anaerobic metabolism duringvoluntary diving in Weddell seals: Evidence of preferred pathwaysfrom blood chemistry and behavior. Journal of Comparative Physiology,138,335-346.

Ecology of Weddell seals in McMurdoSound 1982-1983

J. WARD TESTA, SUZANNE BRAUN,and DONALD B. SINIFF

University of MinnesotaDepartment of Ecology and Behavioral Biology

Minneapolis, Minnesota 55455

R. REICHLE

University of MinneotaCedar Creek Bioelectronics Laboratory

Minneapolis, Minnesota 55455

LISA FERM

Hubbs Sea World Research InstituteSan Diego, California 92109

JIMMY D. WINTER

State University of New York-FredoniaFredonia, New York 14063

214

Research on McMurdo Sound's Weddell seal population con-tinued in three main areas during the 1982-1983 field season.(1) Tagging and census work provided the long-term focus forour population dynamics research at McMurdo Sound. (2) Astudy was made of concurrent distribution of seals and a con-spicuous prey species, the antarctic cod (Dissostichus rnawsoni),which may be an important food source to breeding adultsduring the nonbreeding season (Calhaem and Christoffel 1969).(3) The distribution and behavior of juvenile seals (less than 5years old) were studied to understand age-class interactionsand their effects on population dynamics.

Population demographic studies continued with tagging ofall pups born in the 1982-1983 season and retagging of adultsand subadults that had lost a single tag; an effort to increase theproportion of tagged adult males to make our population esti-mates of that group more precise was successful. Seven cen-suses were conducted and the results indicate a population sizeof around 650 adult-size females and over 200 adult males. Pupproduction this season was 385. These figures are comparableto those of the last 3 years and indicate a fairly stable population,though it is much reduced from the 1960's and early 1970's(DeMaster 1978; Siniff et al. 1977; Stirling 1969). Harvest of sealsby the New Zealand Antarctic Research Programme was re-duced to 36, and their cooperation made material from the killavailable for analyses of age structure and genetic compositionof the population. Electrophoretic analysis of that material was

ANTARCTIC JOURNAL

EI

Figure 1. Radio transmitter attached to the pelage of a weanedWeddell seal pup.

conducted at the Savannah River Ecolog y Laboratory in April1983 and the results are in preparation.

This season we surveyed locations in McMurdo Sound tocompare the distribution antarctic cod and seal population. Aseries of holes was drilled, each was fished for a 24-hour periodbetween late October and early December, and the distributionof cod was compared to seal distribution and bathymetriccharacters. Not surprisingly, cod concentrations were well re-moved from breeding seal colonies. Additionally, seal scatscollected at the same time from various areas both in and awayfrom the colonies show greater predation by seals on small fishand crustaceans than on cod. Small, midwater fish dominatedstomach samples from seals killed by the New Zealand Ant-arctic Research Program as well (Dearborn 1965 and this study).The paucity of cod remains in scat and stomach samples doesnot preclude interaction between the two species. The exclusivedistribution of Weddell seals and antarctic cod suggests (1) thatseals are effectively depleting the cod population from localareas (2) that cod avoid seal concentrations, or (3) their pre-ferred habitats simple do not overlap at this season.

The distribution of adult and subadult age classes inMcMurdo Sound was studied by aerial survey transects and tagsightings in areas removed from the breeding colonies. Segre-gation by age in this population has previously been noted on asmall scale in late summer (Stirling 1969). Transects showed

Figure 2. Sue Braun and Ward Testa prepare a glue-on pelage trans-mitter for a weaned Weddell seal pup in Erebus Bay.

substantial concentrations of 1-3 year old seals near the edge offast ice. We suspect that conditions in this area are quite dif -ferent from those further from open water where adults aremore common, and such factors as predation by killer whales orprey availability may affect survival of these two segments of thepopulation differently. The possible social basis of this segrega-tion is being studied. Also, the incorporation of weaned pupsinto the subadult population in late summer is being studied bymeans of radio-telemetry (see figures 1 and 2).

This research was supported by National Science Foundationgrant DPP 80-20097.

References

Calhaem, I., and D. A. Christoffel. 1969. Some observations of thefeeding habits of a Weddell seal, and measurements of its prey,Dissostichus mawsoni, at McMurdo Sound, Antarctica. New ZealandJournal of Marine and Freshwater Research, 3(2),181-190.

Dearborn, J. H. 1965. Food of Weddell seals at McMurdo Sound, Ant-arctic. Journal of Mammalogy, 46,37-43.

DeMaster, D. P. 1978. Estimation and analysis of factors that control apopulation of Weddell seals (Letonychotes u'eddelli) in McMurdo Sound,Antarctica. Unpublished doctoral thesis, University of Minnesota.

Siniff, D. B., D. P. DeMaster, R. J . Hofman, and L. L. Eberhardt. 1977.An analysis of the dynamics of a Weddell seal population. EcologicalMonographs, 47(3), 319-335.

Stirling, I. 1969. Ecology of the Weddell seal in McMurdo Sound,Antarctica. Ecology, 50(4),573-586.

1983 REVIEW 215