The Gerrard Rainbow Trout spawner counts.
gerrardA data.frame:
The year of the spawner count (int).
The peak count (int).
The total number of fish days (int).
The total number of fish removed prior to spawning.
The total escapement can be estimated by multiplying the peak count by 3.08 or by dividing the total number of fish days by the residence time (currently) assumed to be 11.9 days.