No abstract

The Pacific walrus (Odobenus rosmarus divergens) population is an important ecological and economic resource of the Bering Sea region. We describe population change, beginning with a low in 1950, through a high in about 1980, and ending in 1989. Estimates of abundance for the years after 1989 were not attempted due to the lack of harvest data and other population parameters. Selective hunting practices resulted in biased data regarding population composition and reproductive performance. Rates of reproduction had to be estimated from ovarian data, which indicated a dramatic drop in the 1980s. High harvests in the 1980s likely contributed to a decline in the population, but uncertainties as to accuracy of population estimates and other data raise reasonable doubts, especially with respect to the number of males, for which the most recent (1985) population estimate suggests a sharp decline. Past population estimates were revised upwards to compensate for walruses underwater and not seen in aerial surveys. The weaknesses in the available data make it clear that effective management of the population will require many improvements in collection of data regarding harvests, population structure, reproduction, and population trend.

The Pacific walrus population has been depleted and subsequently allowed to recover three times in the past 150 yr. As we see it, the population has been made to fluctuate like an r‐selected species, rather than being maintained at a high, stable level, as befits a K‐selected species. The latest depletion began in the 1930s but was not recognized until 25 yr later, by which time the population had been reduced by at least half. Without benefit of communication, the U.S.S.R. and the State of Alaska put similar protective measures into place by 1960, and in the next two decades the walrus population recovered again, at least doubling in size. By 1980, it already was showing density‐dependent signs of having approached or reached the carrying capacity of its environment. As productivity and calf survival declined sharply in the late 1970s and early 1980s the catches more than doubled. We believe that the combined effects of natural curtailment and human intervention may be bringing the population down again rather rapidly. With the present, crude monitoring methods, delayed management responses, and poor international communications, however, the downward trend may not be acknowledged for at least another decade, by which time the unilateral Soviet and American corrective measures are likely to be too much, too late. Walrus management needs to be based less on response to immediate crisis and more on long term prediction than it has been in the past. Because the U.S.A. and U.S.S.R. are trying to manage the same walrus population, without sufficient communication or consensus and sometimes to opposite ends, an international joint management program needs to be implemented.

No abstract

1986. Metabolic and hormonal correlates of molting and regeneration of pelage in Alaskan harbor and spotted seals (Phoca vitulina and Phoca largha). Can. J . Zool. 64: 1086-1094. Cellular, hormonal, and metabolic changes during annual molts and regeneration of the pelage were studied in two harbor and five spotted seals of different ages. Seals were maintained in an appropriate photoperiod and monitored biweekly to monthly by measuring their serum cortisol, thyroxine, and triiodothyronine and their standardized resting metabolic rate. Concurrently, external signs of their molt (shedding of hair) were recorded, and samples of skin were collected from the midback for histological determination of the duration of the regenerative phase of the pelage cycle. Timing of the molts coincided with those of free-ranging seals in the natural environment. The overall duration of the period of shedding and regeneration, from first descent of the hair bulbs on the face and flippers to full emergence of new hair on the back, was estimated as 120-170 days. During the period of descent of the hair bulbs and initial growth of new hair on the back, the resting metabolic rate declined an average of 18.6% below premolt values, generally reaching its minimum when shedding of the old hair and rapid growth of new hair began. Serum cortisol generally reached a maximum just before or during the main shedding of hair from the torso, then decreased abruptly to its premolt level or lower during the main period of rapid growth of new hair. Although corticosteroids appear to inhibit protein anabolism, they favor fat catabolism and may in this way help to maintain the slow growth of new hair before and during the first part of the molt. Serum concentrations of thyroid hormones declined to minima early in the molt, then increased to maxima toward the end, when growth of new hair was most rapid. ASHWELL-ERICKSON, S., F. H. FAY, R. ELSNER et D. WARTZOK. 1986. Metabolic and hormonal correlates of molting and regeneration of pelage in Alaskan harbor and spotted seals (Phoca vitdina and Phoca largha). Can. J . Zool. 64: 1086-1094. Les changements cellulaires, hormonaux et mktaboliques au cours de la rnue annuelle et du renouvellement du pelage ont fait l'objet d'une Ctude chez des phoques, deux P. vitulina et cinq P. larghu de diffkrents iiges. Les phoques Ctaient gardCs dans un environnement B photophiode appropriCe et des manipulations, a raison de deux par semaine a une par mois, permettaient de mesurer leurs concentrations de cortisol, de thyroxine et de triiodothyronine sCriques et d'Cvaluer leur taux de mCtabolisme au reps.En mCme temps, les manifestations externes de la rnue (perte de poils), Ctaient notkes et des Cchantillons de peau sur le milieu du dos Ctaient prClevCs pour permettre 1'Cvaluation histologique de la durCe de la phase de renouvellement du pelage. La @ride de la rnue coincidait avec celle de phoques libres en nature. La dude totale de la pCriode de perte de poils et de la p6riode de renouvellement du pelagem, c'est-a-dire du pr...