The Effects of Ocean Acidification on the Growth Rate of Early Life Stage Walleye Pollock, T. chalcogramma

Ocean acidification has become a concern over the past decade, largely due to the uncertainty of how organisms and ecosystems will be affected. The Bering Sea supports a number of commercially important fisheries and is expected to be one of the regions most affected by ocean acidification. Previous work on tropical fishes has found that ocean acidification does not negatively affect growth rate; however, little work has been done to determine the effects on cold water fishes. The purpose of this study was to determine how the early life stages of walleye pollock, Theragra chalcogramma, may respond to decreases in ocean pH. Five batches of walleye pollock eggs were obtained from laboratory broodstocks and incubated across a range of pH treatments (7.2, 7.6, 7.9, and 8.05). Standard length, body depth, eye diameter, and yolk area of newly hatched larvae were measured from digital photographs taken under magnification. Accounting for differences in hatch time, size at hatch (length and depth) was slightly higher in the intermediate pH treatments and lowest in the 7.2 pH treatment. In a separate experiment, juvenile walleye pollock will be reared for 8 weeks across the same range of pH treatments and growth rates determined through biweekly measurements (in length and mass). Results to date on older juvenile walleye pollock, as well as other marine fish species, suggests that early life stage development is not significantly influenced by ocean acidification.