Spawn Surveys


Spawn Surveys


Herring gather to spawn in large numbers. This provides an opportunity to get information on the biomass of the spawning stock and age composition. This information is then fed into the age-structure-analysis (ASA) model to estimate the return for the next year. Aerial surveys have been conducted each spring since 1972.


Aerial surveys are used to measure the miles of spawn, estimate biomass, and map congregations of birds and mammals. Information we gather is recorded on an electronic tablet and photographs taken for confirmation of the distribution of spawn. Fish are collected using a seine or cast nets. The fish are frozen and later analyzed to determine age, weight, length, and sexual maturity. Fish are also provided to the herring disease and maturity projects. The length-weight information used by the acoustic survey project. One of the main measurements collected from these aerial surveys is known as mile-days of spawn. Each day an aerial survey is conducted the miles of spawn observed is recorded. At the end of the survey season, the number of miles of spawn observed on each individual survey are added together to get the measurement. In other words, mile-days spawn is the measure of spawn observed each spring.

What we are learning

This project provides the data required to estimate the herring population in Prince William Sound. The observations we make 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. In 2018 twelve aerial surveys were conducted. The number of surveys conducted was down from previous years due to poor weather conditions. During these surveys spawning events were limited to Canoe Pass and Port Gravina culminating in 4.52 miles-days of active spawn milt. This number represents an all-time low for Prince William Sound.