Pacific cod or tikhookeanskaya treska (Gadus macrocephalus) in the Chukchi Sea during recent warm years: Distribution by life stage and age-0 diet and condition

Many fish species have moved poleward with ocean warming, and species distribution shifts can occur because of adult fish movement, or juveniles can recruit to new areas. In the Bering Sea, recent studies document a dramatic northward shift in the distribution of Gadus macrocephalus (Pacific cod in English and tikhookeanskaya treska in Russian) during a period of ocean warming, but it is unknown whether the current northward distribution shift continues into the Chukchi Sea. Here, we use catch data from multiple gear types to present larval, age-0, and older Pacific cod distributions from before (2010 and 2012) and during (2017, 2018, and 2019) recent Chukchi Sea warming events. We also report on the habitat, diet, and condition of age-0 Pacific cod, which were present in the eastern Chukchi Sea in recent warm years (2017 and 2019), but were absent in a cold year (2012). We hypothesize that age-0 recruitment to the eastern Chukchi Sea is associated with recent warm temperatures and increased northward transport through the Bering Strait in the spring. Age-0 fish were present in both benthic and pelagic habitats and diets reflected prey resources at these capture locations. Age-1 Pacific cod were observed in the western Chukchi Sea in 2018 and 2019, indicating possible overwinter survival of age-0 fish, although there was little evidence that they survive and/or remain in the Chukchi Sea to age-2. Observed low lipid accumulation in age-0 Pacific cod from the Chukchi Sea suggests juvenile overwinter mortality may be relatively high compared to more boreal regions (e.g. Gulf of Alaska). Adult Pacific cod were also observed in the Chukchi Sea during 2018 and 2019. Although densities in the western Chukchi Sea were very low compared to the Bering Sea, the adults are the first known (to us) records from the Chukchi Sea. The increased presence of multiple age-classes of Pacific cod in the Chukchi Sea suggests poleward shifts in both nursery areas and adult summer habitat beyond the Bering Sea, but the quantity and quality (e.g. summer productivity and over -wintering potential) of these habitats will require continued surveys.

随着海洋变暖，许多鱼类物种向极地迁移，物种分布的变化可能是由于成年鱼的移动，或者幼鱼在新区域的补充。在白令海，近期的研究记录了在海洋变暖期间，大头鳕（英文名Pacific cod，俄文名tikhookeanskaya treska）的分布发生了显著的北移，但目前这种向北的分布变化是否延伸到楚科奇海尚不清楚。在此，我们利用多种渔具类型的捕捞数据，展示了近期楚科奇海变暖事件之前（2010年和2012年）以及期间（2017年、2018年和2019年）太平洋鳕幼鱼、0龄鱼以及年龄更大的鱼的分布情况。我们还报告了0龄太平洋鳕的栖息地、食物和身体状况，在近期温暖年份（2017年和2019年）它们出现在楚科奇海东部，而在寒冷年份（2012年）则未出现。我们假设0龄鱼在楚科奇海东部的补充与近期的温暖温度以及春季通过白令海峡向北的输送量增加有关。0龄鱼在底栖和浮游栖息地均有出现，其食物反映了这些捕获地点的猎物资源。2018年和2019年在楚科奇海西部观察到1龄太平洋鳕，这表明0龄鱼可能越冬存活，但几乎没有证据表明它们能在楚科奇海存活并/或留存到2龄。观察到楚科奇海0龄太平洋鳕的脂质积累较低，这表明与更靠北的地区（例如阿拉斯加湾）相比，幼鱼的越冬死亡率可能相对较高。2018年和2019年在楚科奇海也观察到成年太平洋鳕。尽管与白令海相比，楚科奇海西部的密度非常低，但这些成年鱼是我们所知的楚科奇海的首次记录。楚科奇海中多个年龄组的太平洋鳕数量增加，这表明育幼区和成年夏季栖息地都在白令海之外向极地迁移，但这些栖息地的数量和质量（例如夏季生产力和越冬潜力）还需要持续的调查。