Molecular identification of Bathymaster spp. (Bathymasteridae) larvae in the Gulf of Alaska and eastern Bering Sea

Abstract

Information on the phenology and distribution of fish larvae is critical to understanding recruitment dynamics of populations. Larvae of the family Bathymasteridae (ronquils) are an abundant component of the ichthyoplankton community in the eastern North Pacific Ocean and Bering Sea, but cannot be readily identified to the species level using morphological or meristic approaches. We developed a restriction fragment length polymorphism (RFLP) protocol based upon variation in the mitochondrial (COI) gene to identify larvae of three species in the genus Bathymaster: smallmouth ronquil (B. leurolepis), Alaskan ronquil (B. caeruleofasciatus) and searcher (B. signatus). A subsample of larvae from annual ichthyoplankton surveys was screened using the RFLP protocol, and 259 of 260 individuals were correctly identified to species, providing the first data on the seasonal occurrence of early life-history stages in ichthyoplankton surveys for these species. Peak abundance for two species in surveys conducted from 2006 to 2014 occurred in spring. Larvae of smallmouth ronquil were absent from spring surveys and occurred as only 8% of the total numbers collected in later seasons. Our results indicate that larvae of Alaskan ronquil (B. caeruleofasciatus) were more likely to occur at deeper sampling stations (bottom depth > 180 m) in spring, while searcher (B. signatus) larvae were more common at shallower stations (bottom depth ≤ 100 m).