Contrasting the maturation, growth, spatial distribution and vulnerability to environmental warming of Hippoglossoides robustus (Bering flounder) with H. elassodon (flathead sole) in the eastern Bering Sea

Abstract

Two similar appearing congeners, Hippoglossoides robustus (Bering flounder) and H. elassodon (flathead sole), inhabit the Bering Sea and are harvested together during the commercial fishery. In order to establish more precise overfishing limits, the annual spawning biomass must be estimated. Spawning biomass is modelled using the best estimate of the age and length at which 50% of the stock is expected to reach maturity (A 50, L 50). The major objective of this study was to establish the first maturity estimates for Bering flounder. Females matured at a similar age for Bering flounder (A 50, 9 years) and flathead sole (A 50, 10 years). However, the body length at which females matured was significantly smaller for Bering flounder (L 50, 238 mm) compared to flathead sole (L 50, 320 mm). The difference in the length-at-maturity was probably caused by growth differences, which significantly differed between species. The distribution and spawning locations of both species in the eastern Bering Sea survey area was related to the prevailing seawater temperatures and Bering flounder occurred in significantly colder water than flathead sole. The association between cold and the distribution of Bering flounder suggests that this species may be particularly vulnerable to periods of extended sea warming.