We use age distributions of sea otters (Enhydra lutris) found dead on beaches of western Prince William Sound, Alaska, between 1976 and 1998 in conjunction with time-varying demographic models to test for lingering effects from the 1989 Exxon Valdez oil spill. Our results show that sea otters in this area had decreased survival rates in the years following the spill and that the effects of the spill on annual survival increased rather than dissipated for older animals. Otters born after the 1989 spill were affected less than those alive in March 1989, but do show continuing negative effects through 1998. Population-wide effects of the spill appear to have slowly dissipated through time, due largely to the loss of cohorts alive during the spill. Our results demonstrate that the difficult-to-detect long-term impacts of environmental disasters may still be highly significant and can be rigorously analyzed by using a combination of population data, modeling techniques, and statistical analyses.

: Several important aspects of reproduction in the female sea otter, such as gestation, pupping frequency, period of pup dependency, and annual pupping rate, were unclear when this study was begun. We present data from 75 tagged adult females that indicate gestation is variable, but on average is about 6 months, the length of pup dependency is 6 mo, thus the pupping interval is usually 12–13 mo. Most females breed for the first time in their fifth year of life. About 85–90% of adult females pup in a given year.

Sea otters in Prince William Sound. Alaska, were spatially segregated into predominantly (97%) male areas at the front of the expanding population and breeding areas with fewer (up to 33%) males. From 1975 to 1984 we captured and marked 267 otters with tags and (or) radio transmitters and investigated their reproductive strategies, social relationships, and patterns of sexual segregation. Mating occurred year-round, but peaked in September and October. Females first bred at 4 years of age and were capable of pupping annually; they generally separated from their pup before mating. Males established breeding territories that enabled prolonged precopulatory interactions that may have prompted female–pup separation and post-copulatory interactions that precluded females from mating with other males. Male mating success was related to age, weight, territory quality, and the length of time they maintained their territory. After the breeding season, territorial males returned to male areas where food was more abundant. Young, dispersing males also entered male areas and remained there until attaining breeding age. In male areas, otters commonly rested in groups of >50 individuals. Gregariousness promoted social interactions and likely enhanced food finding and (historically) predator protection. As food diminished, males moved into adjacent, unoccupied regions; females then occupied former male areas.

Two oiling experiments were conducted from 1977–1979 on sea otters Enhydra lutris in Prince William Sound, Alaska. In the first experiment, four captured otters were fitted with radio-transmitters and released following contamination of their pelage with 25 cc of Prudoe Bay crude oil; a fifth individual was oiled and cleaned with detergent prior to being released. For all experimental animals activity increased dramatically during the first week following treatment; this effect was accentuated in the otter cleaned with detergent. Most of the increase in activity corresponded to increased grooming, whereas the feeding pattern (as measured by dive time analysis) did not change. It appeared that all experimental otters survived the first experiment, probably because only a small portion of the pelage was treated, and because food resources in the study area were abundant. In the second experiment we observed behavioural reactions of two otters in an above-ground swimming pool which was partly covered with crude oil. Both otters spent very little time on the oiled side of the pool (less than 1 minute per hour), but occasionally surfaced in it for brief periods and eventually became contaminated. One of these individuals was not cleaned and died within 24 h of first encounter with the oil; the other was cleaned and released with a radio-transmitter that failed shortly afterwards.

Seven hundred and eight sea otters (Enhydra lutris) captured in Alaska were translocated from 1965 to 1972 in efforts to reestablish this species in parts of its range from which it was extirpated during the fur hunting period in the 18th and 19th centuries. In Alaska, 467 sea otters were translocated to several locations from 1965 to 1969. During the period 1969-72, 89 sea otters were translocated to British Columbia; 59 otters were released in Washington in 1969-70. During 1970-71, 93 sea otters were released in Oregon. Results of surveys of translocated populations are: (1) at the Pribilofs no reproduction was observed and few, if any, otters now remain there; (2) the southeastern Alaskan population is established; 479 otters were counted in 1975; (3) 70 otters, including some pups, were observed in 1977 in British Columbia; (4) 36 otters, including 1 pup, were observed in Washington in 1981; and (5) reproduction was observed in Oregon, and a high count in 1973 indicated 23 otters, but in 1981 only 1 was found. It is expected that this colony will disappear. WILDL. SOC. BULL. 10:100-107 Intensive exploitation of sea otters began soon after the discovery of the Commander Islands by Vitus Bering in 1741 and continued for the next 170 years (Kenyon 1969). During this period sea otters were eliminated from much of their original range, which extended from the northern islands of Japan to the central Pacific coast of Baja California. Remnant populations survived only on the Kamchatka coast; in the Kuril, Aleutian, and Commander Islands of the north Pacific; in the Queen Charlotte Islands of British Columbia; near Point Sur, California; and near Cedros Island and San Benitos Island, Mexico. The Mexican and British Columbian populations disappeared by 1919 and 1929, respectively (Ken-

The ages of 249 territorial male fur seals taken on St. Paul Island, Alaska, ranged from 7-17 years; the majority were aged 9-11 years. The ages of 156 males that died from natural causes were similar to the 249 killed. An annual mortality of 0.38 was estimated from the distribution of ages among these 405 adult males. An important cause of death is believed to be fighting. Few males under 10 years of age are successful in holding a breeding territory. Fifty percent of the territories on which males were killed were reoccupied within 24 hours, most replacements probably coming from the water rather than the land. Commercial use of young males could probably be increased without adversely affecting the productivity of the herd. The primary objective of current research on fur seals (Callorhinus ursinus) of the Pribilof Islands, Alaska, is to determine the level at which the breeding population will yield the maximum number of salable skins. Fur seals of the eastern North Pacific Ocean spend the greater part of their lives on the high seas, returning to the Pribilof Islands of St. Paul, St. George, and Sea Lion Rock in summer to bear their young and to breed. Here, the Bureau of Commercial Fisheries of the U. S. Department of the Interior supervises the annual harvest of 2to 5year-old males. Females are taken only in years when recruitment of this sex exceeds the number needed to maintain the population at the desired level. The number of males killed depends on the number of seals available on traditional hauling grounds during the period of harvesting. The degree to which a year class of males is utilized can be regulated by varying the length of the killing season, by imposing minimum and maximum limits on the size of seals taken, or by other means of varying harvest effort. The large number of mature males on the hauling grounds probably indicates that optimal use has not been achieved. Accurate estimates of the recruitment needed to maintain the population of adult males at a selected level have not been possible because the mortality was not known. Considerably more information is necessary before the optimum level for maximum production will be known. This paper presents information on the annual mortality rate of adult males as derived from the age composition of 249 territorial males killed on two areas of Northeast Point Rookery (St. Paul Island), two areas of Sivutch Rookery (Sea Lion Rock), and 156 adult males that died from natural causes on St. Paul Island beaches, in the summer of 1965. Also included is information on the rate at which animals killed were replaced. Territorial males are physically mature animals that haul out on the fur seal rookeries of the Pribilof Islands where they vigorously defend territories from late May to early August. Pregnant females returning to the rookeries accumulate in the territories, forming harems of various sizes. Not all of the territorial males acquire harems. As a group, however, they are essentially the only males active in breeding. The following biologists of the Marine Mammal Biological Laboratory assisted in collecting the data and determining ages: C. Fiscus, H. Kajimura, A. Roppel, and V. Scheffer.

It is well known that usual tag-sample estimates are valid if it can be assumed that the sampling process is random with respect to the presence or absence of the tag. This may occur because of natural processes or it may be the result of deliberate design of the experiment either in the tagging phase or in sampling, or in both. Procedures of this type, which have been applied to estimate the population of young Pribilof fur seals, are discussed. Particular consideration is given to variance estimates, comparisons of sample size, and methods of determining the randomness of allocation of the tags.