Seasonal and Geographic Variation in Condition of Juvenile Walleye Pollock in the Western Gulf of Alaska

Abstract

AbstractBody length, length‐specific weight, and length‐specific whole‐body energy content (WBEC) of juvenile walleye pollock Theragra chalcogramma were examined for evidence of seasonal and geographic variation. Identifying the impact of winter on these measures of fish condition was of primary concern, but we also sought to determine whether condition varies among different geographic regions. The 2000 year‐class of walleye pollock was sampled in the western Gulf of Alaska during four seasons (the autumn of 2000 and the winter, summer, and autumn of 2001), and the study area was divided into three regions (Kodiak, Semidi, and Shumagin). In each region, length‐specific weight decreased from autumn to winter by up to 17%, subsequently increasing into the summer by 13–20%. Significant seasonal changes in length‐specific WBEC varied by region but reflected the same trends as length‐specific weight. Walleye pollock from the Kodiak region were in better condition than those from other regions, as evidenced by larger lengths in winter (18‐mm difference) and summer, a 5.9% higher length‐specific weight in autumn of 2000, and higher length‐specific WBEC in autumn of 2000 (0.783 kJ/g wet weight, or 18.3%, higher) and in the following winter (0.607 kJ/g, or 14.1%, higher). The poorer condition of juvenile walleye pollock in winter may be widespread through the Gulf of Alaska, but spatial heterogeneity in habitat can also greatly influence the size and condition of juveniles. The impact of such variability on growth and mortality remains uncertain.