7. On certain rookeries where pups were counted in both seasons, 16,241 being found in 1896 and 14,318 in 1897, or, applying a count adopted by Professor Thompson, 14,743 in the latter year, there is evident a decrease of nine to twelve per cent within the twelvemonth in question. The count of pups is the most trustworthy measure of numerical variation in the herd. The counts of harems, and especially of cows present, are much inferior in value. The latter counts, however, point in the same direction. The harems on all the rookeries were counted in both seasons. In 1896 there were 4,932; in 1897 there were 4,418, a decrease of 10.41 per cent. The cows actually present on certain rookeries at the height of the season were counted in both seasons. Where 10,198 were found in 1896, 7,307 were found in 1897, a decrease of 28.34 per cent. The important element in these special counts, undertaken with a view to determining the relative condition of the breeding herd for the two seasons, is the count of pups. All other classes of rookery population fluctuate from day to day, but the pups remain constantly on shore and near to the place of birth for the first six weeks of their lives, and it is merely a matter of patience and skill in counting them. Such a count on any rookery is an absolute record of the number of breeding females which has visited it for the season in question. The minimum figure of nine per cent adopted by Professor Thompson is based upon a recount of a single rookery made by himself under conditions less favorable for accuracy than in the case of the official counts, which give the larger figure of twelve per cent, and which were made jointly by representatives of both commissions. 8. It is not easy to apply the various counts in the form of a general average to all the rookeries of the islands. We recognize that a notable decrease has been suffered by the herd during the twelvemonth 1896 to 1897, without attempting, save by setting the above numbers on record, to ascribe to the decrease more precise figures.