NOAA Fisheries —
In 2015, NOAA Fisheries scientists saw the lowest number of pollock larvae in the 30-year history of their Gulf of Alaska spring survey. They also observed the lowest number of juveniles in their late-summer survey, which has occurred since 2000. The low abundance in both surveys coincided with a marine heatwave of record ocean temperatures. Scientist Lauren Rogers and colleagues attribute the absence of larval and juvenile fish to environmental conditions that were not ideal for pollock growth and development during the heatwave.
“Marine ecosystems are complex with lots of connections,” said Rogers. “When you are trying to identify what might be behind a decline in abundance of fish at a particular age, it is often a series of factors that are at play.”
That is exactly what scientists found when looking at young pollock survival in 2015. Their survival was affected by:
- Low-salinity conditions, which affected egg buoyancy and survival
- Low abundance of prey for larval fish
- Poor body condition of young-of-the-year (age-0) juveniles