Herring schools can extend for miles and be deep enough that they cannot be seen from the air. By using acoustics, we can estimate the biomass of these schools. The acoustic estimate is then provided to the age-structure-analysis model to help constrain the model output. The Prince William Sound Science Center has annually conducted surveys of the spawning biomass using hydroacoustic techniques.
Surveys are conducted using a towed hydroacoustic sensor. Schools are located during the day, often by using the presence of whales. The surveys are conducted at night when the school is further off the bottom. The acoustic return, known as echograms, are analyzed to determine the biomass of fish observed.
This project provides the data required to estimate the herring population in Prince William Sound. The observations are provided to all of the other projects for use in their analysis. It is only by collecting the information included in this project that we can determine the status of herring recovery. Last spring acoustic surveys took place in Port Gravina, Hawkins Island near Canoe Pass and in bays along the northeast end of Montague Island. Echograms from these surveys are currently being analyzed but preliminary results showed small number of aggregated schools in Port Gravina, and only small, isolated schools near Canoe Pass on Hawkins Island and bays in the northeast region of Montague Island.