Toxins in Coastal Waters: Will Surf Smelt and Other Forage Fish Survive?

Surf smelt are a forage fish--small fish that are prey for larger fish--native to the Salish Sea. They are a source of food for fish such as salmon and tuna and they act as important indicators of ecosystem health. Surf smelt spend their early life stages in shallow coastal waters where diatoms are also abundant. Diatoms are single-celled algae that release toxins called polyunsaturated aldehydes (PUAs) when they are broken down. The goal of this study was to test the effects of PUAs on the growth and development of surf smelt to determine possible causes of any future fluctuations in surf smelt populations. First, we took fertilized surf smelt eggs and divided them into two control groups and five treatment groups of increasing PUA concentrations. Then, we measured the mortality rate of embryos, as well as the body length and eye area of larval surf smelt post-hatch. We found that surf smelt embryos had greater mortality rates when exposed to high concentrations of PUAs, and larvae had reduced body length and eye size. These overall findings indicate that the early life stages of surf smelt are negatively affected by PUAs, suggesting that other forage fish, which are akin to surf smelt, will likely experience similar effects. Increased PUA concentrations in coastal waters will likely decrease forage fish populations and cause detrimental cascading effects throughout the Salish Sea food webs.