Very few records extend back in time, but there is at least one historic record that can help us understand conditions in the past. The Alaska Department of Fish and Game has been preserving scales from herring sampled since the 1970s. By reading the scales like tree rings, it is possible to examine the changes in growth over time.
From the archive, sixty scales are selected each year for each of three ages of fish (four, five, and six). The sixty scales from each age group is split so half are from males and half from females. Pictures are taken of the scales and the image is examined to ensure the scale is of sufficient quality to age and measure. The annual growth increments are measured using image analysis software. The measured growth rates are then regressed against various environmental factors to determine what may influence growth.
What we will learn
By looking at historic growth rates we will be able to understand the factors that affect growth and how growth relates to recruitment. This provides a means to extend the work on herring condition back in time. The scales are also to be analyzed to determine if the age at first spawn can be discovered and if herring spawn every year.