Hydroacoustic (sonar) techniques are an incredibly useful tool for assessing fish populations and habitat. Since 1993, the Science Center has conducted adult herring surveys in Prince William Sound utilizing these techniques. Juvenile herring surveys were initiated in 2006. These surveys increase our understanding of habitat utilization and abundance of juvenile herring, especially age-0. By conducting pre and post winter surveys we also get an estimate of the juvenile mortality during the critical first winter.
During this project Dick Thorne and Michele Buckhorn of the Prince William Sound Science Center conduct acoustic surveys three times a year (August, November and March) throughout Prince William Sound. The August surveys provide an assessment of summertime abundance and location of age-0 herring, before their shifting to overwintering locations. Pre-winter surveys (November) and post-winter surveys (March) in up to ten different bays provide information on distribution and overwinter mortality. Surveying is conducted during the night, when herring are known to come near the surface, which makes them more accessible to hydroacoustic methods. The survey emphasis is placed on the heads of the bays, since juvenile herring are typically located in these shallower waters. Direct capture of juvenile herring is used to confirm the species and size of fish observed by the acoustics.
This study will document the changes of biomass from fall to spring, complementing other studies that propose to examine overwinter mortality – a possible factor effecting herring recruitment. These surveys will also provide a better understanding of where juvenile herring are located and describe their preferred habitat. The extensive coverage of Prince William Sound bays and inlets will help determine potential sites for herring supplementation efforts.