Systematics, variation, distribution, and biology of rockfishes of the subgenus Sebastomus : (Pisces, Scorpaenidae, Sebastes)

Abstract

Author(s): Chen, Lo-Chai | Abstract: Following Matsubara, Sebastodes is synonymized with Sebastes.The form known as S. helvomaculatits found in southern California is distinguished from that species and described as S. simulator, n. sp. S. rhodochloris (Jordan and Gilbert) is synonymized with S. helvomaculatus Ayres, and the form called S. rhodochloris by Phillips is described as S. ensifer, n. sp. S. eos of authors is a complex and a new species, S. rosenblatti, is described. In addition, three other new species, S. noting, S. lentiginossus and S. exsul, are described. Full description is given to each of the seven remaining species of the subgenus Sebastomus. Forms occurring in the southern hemisphere are all referred to as S. capensis. On the basis of similarities in meristics, body configuration, and color patterns, relationships among species of Sebastomus are discussed.Meristic numbers in species of Sebastomus are found to be constant ontogenetically and geographically. Vertebral counts tend to be higher in northern species of Sebastes than in southern ones. Variability of meristic numbers is discussed, using the coefficient of variation as a criterion.Allometry and its significance in taxonomy is discussed. Morphometric characters in speciea of Sebastomus are found to vary geographically. Both slopes and intercepts of the allometric regressions are equally susceptible to variation. There seems to be a correlation between growth rate and body form within a population.Distributional data for all eastern North Pacific species of Sebastes are presented, with 34 new range records. Species of Sebastes are concentrated in the area from 34 to 38°N. As many as 50 species may occur in the same latitudinal range. There seems to have been a barrier near the latitude of San Francisco. A hypothesis involving differentiation following crossing of this barrier can explain the observed pattern of species distribution.Growth of Sebastes umbrosus is studied in detail, using otoliths for age determination. Growth data back-calculated from otolith measurements are compared with those from average lengths of age groups and the discrepancy is discussed. This species can attain an age of 17 but mortality seems to increase after age 7. A Bertalanffy curve describes growth of this species well. Lee's Phenomenon is demonstrated and is explained as result of size-dependent mortality. No compensatory growth is detected and there is no correlation between early and subsequent growth. Fish that grew fast in early years, however, continue to be larger. There is no difference in growth rate between sexes. Individuals from Tanner Bank seem to grow more slowly than those from La Jolla.Growth data of S. rosaoeus, S. ensifer, S. chlorostictus, and S. dallii are also presented, and, along with those of S. umbrosus are compared with those of other species of Sebastes.Individuals of small species of Sebastomus such as umbrosus and ensifer may reach sexual maturity at age 3, whereas those of large species such as constellatus, chlorostictus, and rosenblatti generally do not mature until 10 years old or older. Species of Sebastomus spawn from February to July. Young of the year have been found to settle to the bottom starting from October.