Coastal Cutthroat Trout as Sentinels of Lower Mainland Watershed ...

14excessively warm and too low in dissolved oxygen to support juvenile cutthroat exceptwhere cool tributaries enter as mountain drainages (Slaney and Northcote 2003).Anadromous Cutthroat Only ReachesAnadromous + Resident Cutthroat ReachesResident Cutthroat Only Reaches1000Cutthroat Trout Biomass g/100 sq m90080070060050040030020010000 1 2 3 4 5 6 7 89Average Percent Gradient of ReachFigure 2. Juvenile cutthroat trout standing crops (total biomass per 100 m 2 ) in Region 2stream reaches versus average percent gradient of reach (adapted from Deleeuw andStuart 1982: reach gradients averaged from 0-0, 0-0.5, 0.5-1, 1-3, 3-7 and 7+ m).2.1.2. Spawning and FecunditySpawning typically occurs in mid-winter to spring, but some lake populations spawn inthe fall as documented at Ruby Lake by Wightman and Taylor (1979). Females selectgravel areas with substrates sizes ranging from 5 mm to 50 mm, with spawning sitesfrequently at pool tail-outs with 15-45 cm depth, whereby the pool can be used as escapecover.Fecundity is a function of fork length and thereby repeat spawners have much greaternumbers of eggs than first-time spawners (Table 1). Fecundity (y) is described by y = -935.8 + 5.46x, where x is fork length (mm). Thus, a 30 cm spawner has only about halfthe numbers of eggs as a 40 cm spawner (Figure 3.)The size of first-, second-, and third-time spawners can be compared from Mud Bay andlower Fraser scale collections (from brood fish scales interpreted by R. Ptolemy 1981).Mean size at first spawning was 33.8 cm and ranged from 28 cm to 45 cm (n=11). Meansize at second spawning was 44.5 cm and ranged from 39 to 47 cm (n=10). Third-timespawners averaged 47.7 cm and ranged from 46 to 50.5 cm (n=5). Based on Figure 3,respective fecundities at first-, second- and third-time of spawning are approximately