Atlantic herring spawn in summer-fall in the western Gulf of Maine. However, the actual timing of spawning can vary by several weeks from one year to the next. Spawning time can be predicted by periodically monitoring the development of ripening ovaries. This information is then used to implement spawning area closures.
Samples of herring are collected from the commercial fishery and processed to record individual length and GSI (Gonadal Somatic Index) of maturing females
Given that larger herring spawn earlier, yet all sizes reach a similar max GSI, each fish is standardized to a 30cm herring (GSI30)
Once 3 samples have been processed showing a significant increase in GSI30, the forecasted date when the GSI threshold (23) will be reached is shown
If there is insufficient data (< 3 samples) to forecast a closure date, a default closure date will apply, depending on the area:
A closure will be announced within 5 days of either a forecasted or default closure date
Once closed, an area will remain closed for 6 weeks
If additional samples show greater than 25% of fish in spawning condition once an area re-opens, the area will re-close for an additional 2 weeks
For complete details of the spawning closure system, see Addendum II to Amendment 3 to the Interstate Fishery Management Plan for Atlantic Herring
