Estimating mean age at sexual maturity in the crabeater seal ( Lobodon carcinophagus)

• Published in: Canadian Journal of Fisheries and Aquatic Sciences
• Main Authors: Hårding, Karin C., Härkönen, Tero
• Format: Article in Journal/Newspaper
• Language: English
• Published: Canadian Science Publishing 1995
• Subjects: Crabeater Seal; Crabeater Seals; Lobodon carcinophagus
• Online Access: http://dx.doi.org/10.1139/f95-827; http://www.nrcresearchpress.com/doi/pdf/10.1139/f95-827

Mean age at sexual maturity (ASM) in crabeater seals (Lobodon carcinophagus) was estimated according to two different methods. Samples were from 1964, 1977, and 1989. Using the first method, the estimated ASM in 1989 was 6.57 ± 0.82 years, which was considerably older than reported earlier. This estimate is the only one existing for crabeater seals that can be used to compare populations and species. The first method was based on the maturity rate at age. Behavioural segregation of mature and immature seals could give skewed maturity rates in samples. Because the 1964 and the 1977 samples were collected during a season when segregated behaviour was expected (breeding season), results from these years were not comparable with the 1989 estimate (collected during moult). The second method does not produce absolute values of ASM, but the estimates could be used as indices of ASM within a specific population. There was a statistically significant increase in the ASM index in 1989 (4.93 ± 0.57), compared with 1964 (3.75 ± 0.31) and 1977 (3.80 ± 0.44). This is a strong indication of a true increase in ASM in crabeater seals. Recommendations are made to improve future procedures for studying reproductive status in seals.