Forage Fish Surveys
The Herring Research and Monitoring program is conducting aerial surveys during June and July for forage fish in Prince William Sound. The focus of the June surveys is a systematic count of age-1 herring schools throughout PWS. The entire coastline is surveyed over an eight day period with observation of herring and other forage fish schools logged. Observations of whales and numbers of sea lions at haul outs are also recorded. With half of the June surveys completed, the initial observation is that the number of age-1 herring schools is low, but the number of age-2 schools is above normal. This is consistent with a large 2012 brood year class moving up. Those fish are expected to join the spawning stock beginning in April 2015.
The July surveys will use a different approach in that a series of grid blocks have been identified for surveying in a design similar to that used for moose surveys. The Gulf Watch Alaska forage fish project will also be validating the aerial observations to confirm the species identification and provide acoustic estimates of the school volume. The use of acoustics and aerial survey approaches are complementary. The aerial surveys cover more area, but only detect fish when they are schooled near the surface. The acoustics can’t go as many places, but can detect fish that don’t school or are deeper than can be observed from the plane.
It is normal to get large changes in the number of age-1 herring schools between years. Over the past years the number of schools observed in June ranged from just over one hundred to over two thousand. By surveying the age-1 herring schools we hope to be able to predict future recruitment to the spawning stock. The complete survey of forage fish provides a glimpse into this important link in the ecosystem.
Aerial view of herring school
