13. FISH POPULATIONS 13.1 Standing stocks.

The relative abundance of fish in the various lakes was determined by setting standard gangs of gillnets according to a consistent field procedure (see earlier Methods section). The results of this test-netting program, which was conducted during the summer and autumn visits, are summarized in Table 10 and Fig. 21. Fish taken by netting were also used in the derivation of various other population parameters (see below). All the lakes harbor rainbow trout (Salmo gairdneri); this is by far the most common sport fish in the Okanagan headwaters. In addition, Hydraulic and Headwaters Lake No. 1 have fine scaled sucker (Catostomus catostomus), and Hydraulic Lake also has a species of dace, tentatively identified as Rhinichthyes osculus. These "coarse " fish species made up 96 % and 73 % of the gillnet catch (by numbers) from Hydraulic and Headwaters Lakes respectively. The amounts of rainbow trout taken in the gillnets varied greatly among these lakes. Catches show some correlation with other productivity indices, but other factors are also intimately involved. Lambly Lake yielded the highest catches (48 trout, weighing 7.6 kilograms, per net) ; this is clearly the richest lake of the series investigated. Fish Hawk Lake, TABLE 10. Summary of standard gang gillnet catches from 11 selected headwater lakes in th