of females necessary to produce a given number of pups and the recruitment needed to maintain a given level of the female population.

Experimental skins now being processed will make it possible to compare the relative value of sealskins from males and females of various ages. This information, together with information on the mortality of seals of each age, will be used to regulate the kill so as to obtain the maximum monetary value from a year class of seals.

This report summarizes the research data collected on the Pribilof Islands in 1965 and discusses (1) the population dynamics of the seal herd, (2) the reproduction of males and females, and (3) other studies. Forecasts of the kill of male seals in 1966 are given in appendix A.

POPULATION

This section presents information on techniques used to regulate the kills of male and female seals in 1965, and briefly discusses research methods and results having immediate application to studies of fur seal population dynamics.

Males

Male seals of all ages, particularly those age 3 and older, return to the Pribilof Islands each summer. Those from age 1 to about age 9 haul out on areas adjacent to the rookeries. Termed hauling grounds,1 these areas yield the bulk of the commercial harvest of males, of which more than 90 percent is made up of 3- and 4-year-olds. Several thousand males age 9 and older haul out on traditional rookery or breeding grounds where they acquire harems of 1 to 100 females (average 25) each. Information on the number of males of each age killed commercially for their skins, and knowledge of the number of harem and idle (reserve) bulls that return to the Pribilof Islands each summer is needed as a basis for managing the herd.

Commercial kill.--In 1965, male seals were killed daily from 7 July to 9 August on St. Paul Island, and on Mondays, Wednesdays, and Fridays from 7 July to 6 August on St. George Island.

All available subadult males 42.0 inches (106.7 cm.) long or longer (tip of nose to tip of tail), but without manes, were taken on the Pribilof Islands in 1965. A minimum limit of body length allows most 2-year-old males to escape the kill; a maximum limit (indicated by the presence of a mane) allows the recruitment

1 Special terms used in this report are defined in the glossary.

of males age 6 and older into the breeding reserve. Because the mane (long, silvercolored guard hairs on back of the neck and on the shoulders) is not evident until about age 6, use of this secondary sex characteristic permits the killing of nearly all of the available 3-, 4-, and 5-year-old males.

As in previous years, the age classification of males killed in 1965 was based on samples of canine teeth. This information is presented in appendix tables 6, 7, 8, and 9. The trend in the kill of 3- and 4-year-old males is illustrated in figure 1 for St. Paul Island and in figure 2 for St. George Island. Table 1 shows the kill of male seals on the Pribilof Islands for the 1947-63 year classes, table 2 illustrates the dates at which certain kill levels were reached in the years 1954-65, and table 3 shows the cumulative numbers of males killed each year on St. Paul Island 1955-65.

The minimum limit of body length was removed on St. Paul Island 22-26 July 1965 to allow a complete kill of 2-year-old males in the drives. This was the second year of a study designed to determine if the abundance of 2-year-old males on land in late July is related to the kill of 3-year-olds the following year. Age and body length were determined for 20 percent of all males killed during the 5-day period.

In addition to the regular kill and the special kill of 2-year-olds, 854 males larger and older in appearance than those normally taken were killed to test the commercial value of their skins. The ages of 361 males taken 12-21 July ranged from 4 through 8 (80 percent were in ages 5 and 6). Age was not determined for 493 oversize males taken 22 July to 9 August.

Beginning 27 July 1965, collection of canine teeth, recovery of tags, and recording of checkmarks from male seals killed on St. Paul Island was transferred from the killing fields to the byproducts building. Built in 1918 and used until 1961 as a facility for rendering seal carcasses into meal and oil, the byproducts building was converted in 1964 to a plant for grinding and freezing carcasses of seals that have been eviscerated and beheaded. The ground product is used as mink food.

In 1965, carcass-handling facilities were improved by the installation of a constantly moving overhead cable driven at the rate of 6 feet per minute by two electric motors. Attached to the cable at 12-inch intervals were] 360 long-shanked hooks. Each seal carcass was suspended on a hook that passed between the lower jaw bones and up through the mouth (fig. 3). After the carcass was eviscerated, it was washed and cooled as it moved through a series of salt-water sprinklers. About 360 feet beyond the point where the carcass was hung on a hook, a circular blade severed the head and allowed the carcass to drop into a high-speed grinder (fig. 4).