Age, growth, and reproduction of the roughskin skate, Dipturus trachyderma, from the southeastern Pacific

Abstract

AbstractLicandeo, R., Cerna, F., and Céspedes, R. 2007. Age, growth, and reproduction of the roughskin skate, Dipturus trachyderma, from the southeastern Pacific. ICES Journal of Marine Science, 64: 141–148. Age, growth, and reproductive parameters of the roughskin skate, Dipturus trachyderma, in the southeastern Pacific are reported. Age was estimated by counting the growth rings of thin sections of vertebral centra from 201 fish (61–253 cm total length, LT). No systematic ageing bias was observed, and the precision of growth ring counts indicated a high level of reproducibility. Marginal increment analysis supported the hypothesis of annual deposition of growth rings, which form during winter. The oldest female and male were 26 and 25 y, respectively. Von Bertalanffy parameters for combined sexes based on length-at-age data were L∞=257.7 cm LT, K=0.081 y−1 and t0=–1.363 y. Skates from the southernmost areas attained a larger mean size than those from more northern areas, and females reached a larger adult size than males. Males began the maturation process at ∼186 cm LT, indicated by the abrupt enlargement of the claspers. Developed oviducal glands, uteri, and ovaries indicated that females began to mature at 200 cm LT. The length and age at which 50% of the population matured were 215 cm LT and 17 y for females and 195 cm LT and 15 y for males. The youngest mature female and male D. trachyderma were 15 and 13 y, respectively. The ovarian fecundity ranged from 28 to 68 follicles. Females carrying egg cases were found in March and July. Dipturus trachyderma is slow-growing, long-lived, attains large size, matures late, and has low fecundity, life history characteristics that make it highly susceptible to exploitation.