Latitudinal variation in the growth and condition of Juvenile flatfishes in the Bering Sea

Abstract

The Bering Sea spans a wide latitudinal range, connecting with the temperate North Pacific Ocean to the south and the arctic Chukchi Sea to the north. Climate change has rapidly and significantly altered Bering Sea ecosystem dynamics. The biomass of predominantly boreal marine species have increased in the subarctic northern Bering Sea following recent record-high water temperatures across the shelf. Among those species are two commercially-important flatfishes: yellowfin sole (Limanda aspera; YFS) and northern rock sole (Lepidopsetta polyxystra; NRS). In this study, the Bering Sea was divided latitudinally into three areas – north, central, and south – to assess the implications of a northward shift or expansion of juvenile flatfish habitat on production potential. The growth, diet, and condition of juveniles were compared among areas from 2016 to 2018. Summer bottom temperatures in the Bering Sea in 2016 and 2018 were anomalously warm, but 2017 temperatures were closer to the 2010–2018 average. Prey availability does not appear to be a limiting habitat factor across the Bering Sea. Juveniles of both species grow faster in length and to greater length-at age in the south. The morphometric-based condition of juvenile YFS appears to be better in the northern Bering Sea, while that of juvenile NRS also improves towards the north. Condition increased from 2016 to 2017, but then decreased slightly from 2017 to 2018. Although the results suggest larger size and faster growth of juveniles are associated with warmer bottom temperatures, there is also indication that growth and condition of juvenile flatfish may not continue to increase if current high temperatures persist in their habitat. Exploratory habitat models show that the condition of juvenile YFS may be negatively influenced by temperature. Negative effects on growth and energy storage may set in as the upper thermal physiological tolerance of each species is approached. The critical temperature maxima for each species is unknown, but it may be lower for the cold-adapted YFS than for NRS, implying that YFS may be less buffered against effects of climate warming.