Summary The total length (TL) at sexual maturity by sex, fecundity characteristics, and some population aspects (size structures and sexual proportions) are presented for the yellownose skate, Dipturus chilensis, in the eastern South Pacific Ocean. Samples were taken between January 2003 and August 2004 from three zones (principal fishing grounds for the species) in Chile’s southern channels (41°30′S–55°10′S). TL at which 50% of the individuals reach maturity was significantly different by sex, with females estimated to mature at 103.9 cm and males at 89.7 cm. The average estimated fecundity was 23.4 (SD 6.4) ova per female. We report on the relationships of clasper lengths and oviducal gland widths with TL and the stages of maturity. Length compositions were statistically different by sex in the same zone (P < 0.05) and between zones for combined sexes (P < 0.05). The proportion of females increased when these reached the TL at which 50% attained maturity, becoming highly available to the fishing gear, possibly in relation to the reproductive strategy. Finally, the results yielded valuable knowledge about population responses to exploitation through fishing.

Doryteuthis gahi is a small squid species that has a wide distribution in South America. This species is characterized by coastal and benthic spawning, and its ontogenetic vertical migration is associated with upwelling zones, features that may restrict its dispersal potential. It has also been proposed that populations of these neritic squid are structured by the influence of local processes which act as barriers to gene flow. Based on this background, we evaluate the geographical structure of genetic diversity in D. gahi along its distribution in the south-eastern Pacific Ocean. We used 116 COI mtDNA sequences of squid collected from different sites in Peru and Chile and calculated genetic diversity, the population structure index Fst, and performed analysis of spatial molecular variance and exact tests to detect differences among localities. To infer demographic history we carried out tests of neutrality and Bayesian skyline analysis. Although there was little molecular divergence between Peru and Chile, we detected a significant genetic differentiation of D. gahi along its geographical distribution. Squid from Chile showed higher genetic diversity than those of Peru and the results of the demographic inference analysis suggest that the population of Peru is experiencing or experienced in the recent past demographic expansion, a pattern that was not found in Chile. We think that the current genetic patterns are consequences of northward migrations in the glaciation periods and posterior re-colonization of southern Chile in the deglacial period.

Licandeo, 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.

No abstract

No abstract