Population parameters of ringed seals ( Phoca hispida Schreber, 1775) in the Svalbard area

• Published in: Canadian Journal of Zoology
• Main Authors: Lydersen, Christian, Gjertz, Ian
• Format: Article in Journal/Newspaper
• Language: English
• Published: Canadian Science Publishing 1987
• Subjects: Svalbard; Phoca hispida; ringed seal
• Online Access: http://dx.doi.org/10.1139/z87-162; http://www.nrcresearchpress.com/doi/pdf/10.1139/z87-162

Samples were taken from 284 ringed seals (Phoca hispida) in the Svalbard area during April–July 1981 and March–April 1982. The age of 283 seals was determined by reading annuli in the cementum of the canine teeth. The mean age of the males was 11.3 years, and of the females, 14.9 years. Females were found to be significantly older than males. The mean length of sexually mature ringed seals was 128.9 cm for both sexes. The mean weight of adult males and females was 53.5 and 61.4 kg, respectively. Females were found to be significantly heavier than males. The sex ratio was 47.8% males and 52.2% females. Studies of microscopic sections of testis and epididymis from ringed seal males showed that 63, 75, and 80% of 5-, 6-, and 7-year-old animals, respectively, were sexually mature. The weights of testis and epididymis, diameters of tubuli, and the size of testis all showed a marked increase in the 5-year age-class. Macroscopic sections of ovaries from ringed seal females showed that 20, 60, and 80% of 3-, 4-, and 5-year-old animals, respectively, were sexually mature. The size of the ovaries showed a marked increase in the 5-year age-class. The ovulation rate of ringed seals from Svalbard was calculated to be 0.91.