The Burrishoole system has a run of both grilse or 1 sea-winter (1SW) and 2 sea-winter (2SW) or spring salmon. There is only a small spring fish component in the Burrishoole stock, normally <10% of the total run. It has not exceeded 100 fish since the early 1960s. Reasons for this decline were early season drift netting of L. Furnace (ceased in 1965), the Greenland Fishery from 1962 to date and UDN from 1967 to the mid 1970s.
On the Burrishoole system, grilse first appear in late May with the peak of the run in July. Escapement to the system is primarily influenced by the success of the drift net fishery which has exploited from 60% to 80%+ of the stock.
Since 1970, the unique trapping facility in place on the Burrishoole system has allowed a complete census of all descending smolts and ascending adults. From the trap counts and the rod catch at Burrishoole it is possible to calculate;
- spawning escapment
- survival between generations
- survival from ova to smolt
- survival from smolt to adult
- survival to kelt (spawner fish)
- survival from kelt to second spawner exploitation rates by rod fishing.