Figure 2.--Method of measuring fork length of sockeye smolts by pricking graph paper. Margin of graph paper from headboard is 10 mm. Originally, a drop of clear Karo syrup was used as an adhesive agent for the slides, but the natural mucus from the scales proved to be a better adhesive. Scales were examined to determine growth and age composition that brood year (year egg is fertilized) and the amount of holdover in the lakes could be determined. The scale-reading machine gave an image with variable magnification. Ages were recorded as 1-check (or annulus), 2-check, or 3-check, depending upon the number of annular growth bands shown by the spacing of the circuli, Generally, smolts from Little Kitoi Lake departing in the spring with 1, 2, or 3 checks, and referred to as 1-, 2-, or 3-yr.-old fish, had been spawned about 20, 32, or 44 mo. (months) previously. To compute condition factors, samples of about 30 smolts were taken from Ruth and 1Trade names referred to in this publication do not imply endorsement of commercial products. Little Kitoi Lakes each week during the 1962 migration, transported to the laboratory in 2-1. (liter) polyethylene bags, and measured and weighed individually to the nearest millimeter and the nearest 0.1 g. (gram). Stomachs of fish collected to determine condition factors were examined for food contents with the aid of a dissecting microscope. Organisms were identified to the lowest taxonomic group possible--often determined by the state of digestion of the organisms. Biological Environment No detailed plankton studies were made on Ruth Lake before it was treated in 1955. During the 1955 field season, a few plankton tows were made in various lakes in the Kitoi Bay area. Tows were made at comparable depths for a standard towing time with a 20-mesh Wisconsin net. The plankton was allowed to settle in a 55-cm.3 (cubic centimeter) bottle 10 min. (minutes) for comparison of volumes of plankton. The growth of periphyton was studied in 1956, 1957, and 1958, (Smoker, 1957, 1958, 1960). A different substrate was used each year in an attempt to discover a technique that would best facilitate handling and processing of the substrate and attached growths. During 1956 standard glass microscope slides served as collecting bases; a series of slides was strung together to cover the desired range of depths. In 1957 the microscope slides were replaced by a series of 15.2-cm. glass plates. In 1958 solid glass rods about 1.2 m. long and 12 mm. in diameter were tied end to end and suspended from moored buoys. Each rod had a total area of about 400 cm.2. Each year the substrate was left untouched for 60 days in each lake. This period was selected because tests run during 1956 showed that 60 days were needed for the growth to be great enough to measure. Throughout the 1961 field season, samples of bottom fauna were taken with a 15.2-cm.2 Ekman dredge from shoal and deep areas in Little Kitoi and Ruth Lakes. Shoal samples were from about 1.2 m. depths; deep samples were from the vicinity of maximum depth in each lake--26.8 m. in Little Kitoi Lake and 17.1 m. in Ruth Lake (table 1). The material was preserved in formol alcohol (equal parts of 5 percent Formalin and 70 percent ethyl alcohol) and later was sorted. The organisms were identified and counted, and the wet weight of each sample was recorded (each sample was blotted 1 min. and then weighed on an analytical balance to the nearest milligram). These data were transferred to IBM cards for tabulation and summarization. GROWTH AND SURVIVAL OF SOCKEYE The results of this study encompass several aspects of the life of sockeye in fresh water. The timing of migrations and the apparent effects of lake rehabilitation on survival, Year growth, and condition are considered in the subsections that follow. Migration of Smolts The numbers of all species of downstream migrants taken at the Little Kitoi Lake weir from 1955 to 1963 are shown in table 3. Migrations of sockeye, coho, and Dolly Varden changed little, although they were slightly higher in the later years of the study. Migrations of sticklebacks and sculpins especially decreased sharply throughout the study. This reduction most probably is the result of installation of the weir; no sticklebacks or sculpins have gained access to the lake from salt water since the weir was installed in 1955. The salmonids have not been deterred by the weir because they are able to gain access to an upstream weir section by means of an aluminum Denil-type fish pass and are then passed into the lake by hand. In general, the peak migration from Little Kitoi Lake was 1 to 2 wk. (weeks) earlier for 2-annulus smolts than for l-annulus (table 4, fig. 3). The peak migrations of 1- and 2annulus smolts from Ruth Lake occurred about the same time (table 4, fig. 4). The peak migrations of 1- and 2-check smolts were usually 1 or 2 wk. later from Ruth Lake than from Little Kitoi Lake. The migrations from Little Kitoi Lake tended to peak a few days later as the years progressed, whereas those from Ruth Lake remained fairly consistent (table 4). The single year class of fry released in Midarm Lake departed as 1-check smolts at the same time as the 1-check smolts from Ruth Lake, and as 2-check smolts about the same time as the 2-check smolts from Little Kitoi Lake (table 4). As shown in table 4 and figure 3, the downstream migration from Little Kitoi Lake in 1956 was unusual. The migration of 1-check smolts in 1956 had two separate peaks. The first and major one was almost a month earlier than the average for the other years, whereas the second peak was about 3 wk. later. In the Table 3.--Downstream migrants taken at Little Kitoi Lake weir, 1955-63 Table 4.--Peak periods of migration of l- and 2-annulus sockeye salmon smolts from Little Kitoi, Ruth, and Midarm Lakes, 1955-63 early migration 41,000 of the 50,000 1-check migrants were stunted fish that averaged about 39 mm. fork length. The later group of 1-check migrants had an average length of 61 mm. The cause of this atypical condition (small size of smolts and earlier migration) is not known. The peak of the migration of 2-check smolts in 1956 was also considerably later than average. Smoker (1957), who reported this unusual migration, called attention to the severe winter of 1955-56 and noted that the ice cover was three times as thick as in the previous 2 winters and that the lake had been covered with both ice and snow more than 7 mo. Survival Exact comparisons of estimates of survival among the three study lakes are not possible because the available estimates are based on the egg-to-smolt stage for Little Kitoi Lake and on the fry-to-smolt stage for Ruth and Midarm Lakes. I can, however, make rough comparisons by assuming an arbitrary rate of survival from the egg-to-fry stage for Little Kitoi Lake and calculating a fry-tosmolt survival from the result. In this section. I discuss my estimates of survival in the egg-to-smolt stage in Little Kitoi Lake and the fry-to-smolt stage in Ruth and Midarm Lakes with similar estimates from the literature; I present also my calculations of the fry-to-smolt survival in Little Kitoi Lake when an arbitrary figure is assumed for the egg-to-fry survival. Fry-to-smolt stage, Midarm and Ruth Lakes.--Survival to the smolt stage of fry from the 1955 brood year of Little Kitoi Lake, released in Midarm Lake in 1956 (table 2), was 3.6 percent (table 5)--lower than the survival for Ruth Lake in any year of the study. In Cultus Lake, Foerster (1938a, 1938b) found the average survival to the smolt stage of introduced fry to be 3.24 percent. He attributed the high mortality to predation. Foerster and Ricker (1941) reported a survival of introduced fry of 13.05 percent after partial removal of predator fishes by gill netting, as compared with an average survival of 4.16 percent before gill netting. In Port John Lake, British Columbia, for the 1955 fry that migrated in 1956 and 1957, an estimated fry-tosmolt survival of 80 percent is reported, indicating a low level of predation (Fisheries Research Board of Canada, 1958). Survival to the smolt stage of fry introduced into Ruth Lake ranged from 7.3 to 46.9 percent (table 5, fig. 5). The removal of the resident fish populations probably accounted for these higher figures. Because there is only 1 yr.'s estimate for Midarm Lake, it is not considered further in this discussion. Egg-to-smolt stage, Little Kitoi Lake.-Survival rates for potential egg deposition to the smolt stage in Little Kitoi Lake ranged from 2.0 to 8.5 percent (table 5) and are comparable to figures obtained during certain other investigations. For instance, Holmes (1934) estimated a survival of 1 percent from egg to smolt in Karluk Lake. In three separate studies in Cultus Lake, Foerster estimated egg-to-smolt survivals of 1.13 percent (1934), 2.5 percent (1936), and 1.80 percent (1938a). Brett and McConnell (1950) estimated an eggto-smolt survival of 0.4 to 1.1 percent for sockeye in Lakelse Lake. Over a 7-yr. period in the Lakelse Lake system, the average survival from egg to smolt was 1.4 percent (Fisheries Research Board of Canada, 1956). Over a 6-yr. period in the Babine Lake system of the Skeena River area, British Columbia, the survival from egg to smolt was 0.49 to 2.49 percent (Fisheries Research Board of 10 5 O 20 15 10 5 O 10 1957 1958 5 O 10 0505 15 O 505 15 10 O 1959 1960 1961 JULY 5-91 Figure 3.--Timing of migrations of 1- and 2-annulus sockeye salmon smolts from Little Kitoi Lake, 1955-63. Data grouped by 5-day periods. Canada, 1957). In 1957, the egg-to-smolt survival in the Babine Lake system was 6.1 percent (Fisheries Research Board of Canada, 1958). Fry-to-smolt stage, Little Kitoi Lake, assuming 30-percent egg-to-fry survival.--The fry-to-smolt survival that would result in 5-DAY TIME PERIODS Figure 4.--Timing of migrations of 1- and 2-annulus sockeye salmon smolts from Ruth Lake, 1957-62. Data grouped by 5-day periods. Little Kitoi Lake, if the average egg-to-fry survival is arbitrarily assumed to be 30 percent, is shown in table 6. It is highly probable that the average egg-to-fry survival could be even higher than 30 percent, which would reduce the figures on fry-to-smolt survival correspondingly. Although most studies in other areas have generally demonstrated less than 10 percent survival from egg to fry, these studies have been on stream-spawning populations. Little Kitoi Lake sockeye spawn almost entirely on lake beach sites. Data on potential egg-to-fry survival in natural beach spawning sockeye populations are not available, primarily because beach spawning areas are difficult to sample. The most comparable data are those of Quistorff (1962 and personal communication) in which survival at the Baker Lake artificial spawning beach averaged about 65 percent over a 4-yr. period. This survival in a beach incubation situation indicates that the 30-percent egg-to-fry survival assumed for Little Kitoi Lake may be conservative. Table 5.--Number of migrants and percentage survival by age groups of sockeye smolts in migrations from Little Kitoi, Ruth, and Midarm Lakes, 1954-59 brood years 1 Based on average number of eggs per female. Estimated on basis of a 30-percent survival from egg to fry; see table 6 and later discussion for details. 60 LITTLE KITOI LAKE 50 ןויויד POTENTIAL EGG-TO-SMOLT SURVIVAL (PERCENT) The fry-to-smolt survival in Little Kitoi Lake would have ranged from a low of 5 percent for the 1961 brood year to a high of 28 percent for the 1957 brood year (table 6). For the same brood years 1955-59, the assumed unweighted average fry-to-smolt survival for Little Kitoi Lake would be 14 percent. This is considerably less than the actual unweighted average fry-to-smolt survival in Ruth Lake of 24 percent. If the assumed egg-to-fry survival in Little Kitoi Lake was actually greater than 30 percent, then the fry-to-smolt survival would be less than 14 percent, and Ruth Lake would appear to have provided an even greater survival for rearing juvenile sockeye. 50 40 30 30 20 10 MM 1954 1955 1956 1957 1958 1959 50 30 20 FRY-TO-SMOLT SURVIVAL (PERCENT) Figure 5.--Magnitude of migrations and percentage survival of sockeye salmon to smolt stage by brood year, Little Kitoi and Ruth Lakes, 1954-59. Relation of Population Density to Survival Survival to the smolt stage of fry planted in Ruth Lake was considerably lower in 1959 and 1960 (1958 and 1959 brood years) than in earlier years (table 5). The plant of only 50,000 in 1959 resulted in the lowest survival (as well as the greatest percentage of holdover) throughout the study. The environment may have had an adverse effect on this particular plant, or the relatively large number of fingerlings in the lake from the plant of 110,000 fry in 1958 may have depressed the survival of the 1959 plant. The relatively low survival of the heavy 1960 stocking (425,000 fry) may have been the result of overstocking, but this relation cannot be proved because of the still lower survival of the 1958 plant. |