Table 2. Results of tracking antarctic fur sealsto their foraging areas near Seal Island, Antarctica,

from 14 to 22 February 1991NOTE: Maximum distance away from Seal Island is indicated. Compassbearing from Seal Island to the last position observed is also noted.

MaximumIdentificationTracking timesElapsed distance

time(in kilo-numberStart trackEnd track (in hours) meters) Bearing

790a14 Feb: 1849 15 Feb: 073012.723340849b15 Feb: 2015 l7 Feb: 042832.249036810a17 Feb: 2057 l9 Feb: 072534.541330750b19 Feb: 0002 19 Feb: 07197.314011830b19 Feb: 0417 19 Feb: 13389.314086790a19 Feb: 2000 20 Feb: 122316.436319957 a20 Feb: 2226 21 Feb: 085010.418341770b21 Feb: 2052 22 Feb: 06009.935030

that patches of krill were present throughout the area; feedingtrips of fur seals during this period were shorter (1-3 days)than in January. This pattern suggests that predator foragingareas may change within seasons in direct response to preydistribution and abundance.

The authors thank all of their colleagues at Seal Island andaboard the Kaiyo Maru, Alcazar, and Surveyor for sharing theirthoughts and ideas in stimulating discussions. Special thanksare extended to D. Croll, P. Eberhardt, M. Goebel, T Ichii, H.Ishii, A. Mujica, and M. Naganobu. We are grateful to theofficers and crews of the three ships for providing excellentlogistic support and for helping to make our field experienceso enjoyable. This research was supported by the NationalOceanic and Atmospheric Administration as part of its AMLRprogram.

a Complete track of feeding trip.b Partial track of feeding trip.

References

relatively few krill or other prey species were detected by acous-tic or net sampling; penguin and fur seal feeding locations werewell offshore and fur seals were making rather long (5-9 days)trips to sea. In February, acoustic and net sampling revealed

Bengtson, J.L., P. Boveng, and RE Hewitt. 1990. Fur seal and penguinforaging areas near Seal Island. In AERG staff (Eds.) AMLR 1989190Field Season Report (Administrative Report LJ-90-11). La Jolla, Calif.:Southwest Fisheries Center, National Marine Fisheries Service.

AMLR program:Reproductive performance

of chinstrap penguinson Seal Island,

South Shetland Islands,Antarctica

DONALD A. CROLL, JOHN K. JANSEN, and JOHN L. BENGTSON

National Marine Mammal LaboratoryAlaska Fisheries Science Center

National Marine Fisheries ServiceNational Oceanic and Atmospheric Administration

Seattle, Washington 98115

Seabirds have been identified as potentially important mon-itors of offshore prey resources (Boersma 1976; Crawford andShelton 1978; Anderson and Cress 1984; Cairns 1987; Williamsand Croxall 1990). As part of the Commission for the Conser-vation of Antarctic Marine Living Resources (CCAMLR) Eco-system Monitoring Program (CEMP), chinstrap penguins (Py-goscelis antarctica), macaroni penguins (Eudyptes chrysolophus),and cape petrels (Daption capensis) have been studied since 1987at Seal Island, South Shetland Islands (60°59.2'S 55°23.1'W).The reproductive performance, demography, and behavior ofthese species are monitored annually in an effort to understand

the relationships of these predators to prey and other environ-mental conditions.

The goals of the 1990-1991 field season on Seal Island (4December 1990 to 11 March 1991) were to• monitor the breeding success, chick growth, fledgling size,

reproductive chronology, foraging behavior, diet, abun-dance, survival, and recruitment of chinstrap and macaronipenguins,

• investigate the diving behavior of chinstrap penguins to as-sess changes in foraging behavior and effort as the breedingseason progressed,

• assess the reproductive success of cape petrels,• evaluate the potential effects of electronic instruments on the

behavior of penguins, and• measure the energetic cost of reproduction as chinstrap pen-

guins incubate, guard, and creche their chicks.We report here some of the results of reproductive factors

measured for chinstrap penguins during the 1990-1991 breed-ing season on Seal Island, and compare these results with ob-servations from previous years.

We estimated chick production by censusing creched chin-strap chicks present in nine geographically discrete coloniesundisturbed by other activities (table 1), and we assessed themean reproductive success of individual nests and nestingchronology by monitoring the number of incubated eggs orbrooded chicks until the chicks at individually identified nestsin two colonies (of 124 and 113 nests each) had creched (table2). Hatching peaked on 24 December 1989 and 29 December1990 and fledging began on 3 February 1990 and 13 February1991 in the 1989-1990 and 1990-1991 austral summers.

218 ANTARCTIC JOURNAL

4.5

4.0

3.5

3.0

ZY 2.5

oo 2.0a

1.5

1.0

0.5

0.0

Table 1. Number of chinstrap penguin chicksraised to creche in selected colonies

on Seal Island, South Shetland Islands, Antarctica,from austral summer 1987-1988 through austral summer 1990-1991

YearColony1987-19881988-19891989-19901990-1991

21128998753

245330 15

31316278354221

32792712850

331777618274

42133102241146

5164496028

5412613514786

66211142288203

Total1,2879381,488866

We monitored the growth rates of chinstrap penguin chicksby weighing a sample of chicks every 5 days from a colony ofapproximately 2,000 nests (colony 4). In 1987-1988 and 1988-1989, samples of 30 randomly selected chicks were weighed. In1989-1990 and 1990-1991, during the guard stage, samples ofat least 50 chicks (contained in at least 30 nests) were measured.After creching, a total of 75 chicks was measured each samplingperiod. Chinstrap penguin chick weights peaked prior to fledg-ing (figure, table 2), as reported at other sites (Volkman andTrivelpiece 1980; Taylor 1985). Following the initiation of chin-strap penguin fledging, daily samples of fledglings preparingto depart from the beach were weighed until the completion offledging (table 2).

The number of chinstrap penguin chicks raised to crechingon Seal Island in 1990-1991 was lower than in the previous 3

Table 2. Peak chick size and reproductive successof chinstrap penguins at Seal Island,South Shetland Islands, Antarctica,

from austral summer 1987-1988 through austral summer 1990-1991NOTE: Peak weights (in kilograms) indicate maximum age prior to fledg-ing at colony number 4. Fledging weights were obtained from chicks onthe beach preparing to their departure to sea. Reproductive success wascalculated as the number of chicks raised to creche of the nests thatsuccessfully hatched eggs (chicks/nest). The number of creched chicksof the nests that successfully raised chicks to creche (chicks per activenest) at colonies number 4 and 25. Values in parentheses representstandard deviations and sample sizes.

Evaluation Yearparameter 1987-1988 1988-19891989-19901990-1991

Peak3.763.923.403.30weight(0.38, n=30) (0.40, n=30) (0.60, n=75) (0.42, n=75)Fledging3.273.253.002.90weight(0.28, n=49) (0.37, n=87) (0.40, n=141) (0.30, n=254)Chicks per

nest1.62_a 1.201.35Chick peractive nest1.751.481.451.45

a Data unavailable.

01020304050

Date (Julian)

Growth of chinstrap penguin chicks at colony number 4 on SealIsland, South Shetland Islands, Antarctica, in 1989-1990 and 1990-1991. Error bars represent ± 1 standard deviation. (kg denotes kilo-gram.)

years (table 1). Reduced chick production may have resultedfrom a number of possibilities:• a decline in prey availability prior to breeding (resulting in

fewer birds attempting to breed),• a decline in prey availability during breeding (resulting in a

higher nest failure rate during the early incubation periodprior to the field team's arrival),

• both of these factors, or• other factors such as weather or ice conditions.A comparison of data between 1989-1990 and 1990-1991 pro-vides some clues about the possible timing of these interannualdifferences in environmental conditions. Although fewer chickswere produced overall in 1990-1991, the reproductive successof individual nests was similar to that observed in 1989-1990,indicating that the lower chick production resulted from fewerbirds attempting to breed or more nests being lost between egglaying and hatching (or both) rather than an increased mortalityof chicks during the chick rearing period. Although chinstrappenguin chick growth rates were similar in 1990-1991 and 1989-1990, the timing of chick growth was temporally shifted, dueto the later hatching dates in 1990-1991. This shift providesfurther inferential evidence that environmental conditions wereless optimal some time either prior to or during the early stagesof reproduction.

Chinstrap fledgling weights were similar in 1989-1990 and1990-1991, but lower than in the previous 2 years. Chinstrappenguins are capable of raising two chicks: because prey avail-ability varies from one year to the next, energy may be investedin two chicks of lower body mass at fledging or one chick ofhigher body mass at fledging. Bost and Jouventin (1991) havefound that gentoo penguin (Pygosce/is papua) chick survival pernest during is higher during "good" years, and the mean fledg-ing weight is lighter. A similar situation may have occurred onSeal Island. Food availability may have been sufficient duringchick rearing in 1989-1990 and 1990-1991 to permit individualnests to raise more chicks of lower body mass. Conditions priorto chick rearing in 1990-1991, however, may have led to a fewernumber of nests surviving to the chick rearing stage, leadingto the overall reduction in chick production in 1990-1991 inspite of the high chick survival to creching.

We thank Harriet R. Huber, Steven D. Osmek, Michael E.Goebel, and Peter Boveng for their energetic assistance with

1991 REVIEW 219

the field work at Seal Island. We also thank the officers andcrews of the National Oceanic and Atmospheric Administration(NOAA) Ship Surveyor and the MN Society Explorer for provid-ing outstanding logistical support. This research was sup-ported by the (NOAA) as part of its Antarctic Marine LivingResources (AMLR) Program.

References

Anderson, D.W, and E Cress. 1984. Brown pelicans and the anchovyfishery off southern California. In D.N. Nettleship, G.A. Sanger, andPE Springer (Eds.), Marine birds: their feeding ecology and coininericalfisheries relationships. Special Publication, Canadian Wildlife Service.

Boersma, PD. 1976. Breeding patterns of Galapagos penguins as anindicator of oceanographic conditions. Science, 200, 1481-1483.

Bost, C.A., and P. Jouventin. 1991. The breeding performance of thegentoo penguin Pygoscelis papua at the northern edge of its range.Ibis, 133, 14-25.

Cairns, D.K. 1987 Seabirds and indicators of marine food supplies.Biological Oceanography, 5, 261-271.

Crawford, R.J.M., and PA. Shelton. 1978. Pelagic fish and seabirdinterrelationships off the coasts of south west and South Africa.Biological Conservation, 26, 227-238.

Taylor, J . 1985. Ontogeny of thermoregulation and energy metabolismin pygoscelid penguin chicks. Journal of Comparative Physiology, 155,615-627.

Williams, T.D., and J.P. Croxall. 1990. Is chick fledging weight a goodindex of food availability in seabird populations? Oikos, 59, 414-416.

Volkman, N.J., and W.Z. Trivelpiece. 1980. Growth in pygoscelid pen-guin chicks. Journal of Zoology, 191, 521-530.

220 ANTARCTIC JOURNAL