Nearshore Habitat Use by Juvenile Chinook Salmon in Lentic ...

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To describe the diet of juvenile Chinook salmon, we followed the procedures of Cortés (1997) and Liao et al. (2001). For each prey group in each sample, we determined the percent weight (%W), percent number (%N), and percent occurrence (%O). A percent index of relative importance (%IRI) was then developed for each prey group: IRI % Oi (% Wi % N i ) and, % IRI IRI i 100n IRI i1 i To help compare the diet between samples, we also calculated Schoener’s diet overlap index (Schoener 1971): Cxy 1 0. 5 p xi p yi where C xy is the index value, p xi is the proportion of food type i used by Chinook salmon at site x and p yi is the proportion of food type i used by Chinook salmon at site y. Researchers commonly use an overlap index level of 0.6 or less to indicate a significant difference in diet (Zaret and Rand 1971; Johnson 1981). Comparisons were made between tributary mouths and lakeshore reference sites, as well as between high and base streamflow conditions at each tributary mouth. A diet breadth index (B; Levins 1968) was also calculated to determine if Chinook salmon utilize a wider variety of prey types at the tributary mouths in comparison to the lake shore: B 1 2 p i where p i is the proportion of the diet represented by food type i. Diet breadth index values range from 1 (no diet breadth: only one prey type in the diet) to infinity. Values less than 2 indicate little diet breadth. Results Catch. —In 2003, beach seine catch rates of juvenile Chinook salmon at tributary mouths and lakeshore sites were extremely variable between sites and between day and night. During the day, we were able to catch Chinook salmon at some tributary mouths but not at lakeshore reference sites. At some lakeshore sites, we could visually observe Chinook salmon but they could easily avoid the beach seine. At tributary mouths, they could be collected more easily, likely because the water was turbid or they retreated to the tributary mouth where they could be easily encircled with the seine. Because of the difficulty of collecting Chinook salmon at most lakeshore sites during the day, we collected Chinook salmon in 2004 at one site in Gene Coulon Park where they were known to be abundant. Nighttime sampling was conducted at a few tributary mouths. Although night sampling was logistically more difficult, it appeared to be less variable than daytime 43
sampling. At night, Chinook salmon were collected at each sampling location; however not enough sampling was conducted to make any meaningful comparison between tributary mouth and lakeshore sites. During high flow conditions, the number of Chinook salmon caught at the mouth of May Creek in 2004 was substantially higher than during base flow conditions. Additionally, nine cutthroat trout (range, 147-190 mm FL) were caught during the high flow event while none were caught during the base flow condition. In contrast to May Creek, more Chinook salmon were caught under base flow conditions than during high flow conditions at the mouth of Taylor Creek (Figure 30). Different types of seine nets were used at Kennydale Creek in 2003 and thus catch rates could not be compared between streamflow conditions. Diet.—In 2003, monthly samples (February to June) were collected at Kennydale Creek and a lakeshore reference site in Gene Coulon Park. Chironomid pupae and adults were the most important prey item for each sample date at both sites (Table 4). Other than chironomid pupae and adults, little else was present in the lakeshore diet for February to May, making up at least 89% of the diet by weight. The same was observed in the April and May diet at the mouth of Kennydale Creek. The March diet sample included a large seed pod that probably offered little nutritional value. If the seed pod is excluded from the analysis, chironomid pupae and adults made of 87% of the diet by weight. The March sample at the mouth of Kennydale Creek was taken during a high flow event yet there was no significant difference in the diet between the lakeshore sample on the same date and between the base flow sample taken in April (Table 5). In February, a large number of springtails (Collembola; 43% of the diet by number and 19% by weight) were present in diet at the tributary mouth but were absent in the lakeshore diet. Springtails are primarily inhabitants of soil and moist vegetation but some species inhabit the neuston of lentic systems (Christiansen 1996). Streams may act as a dispersal mechanism. Because springtails were absent from the lakeshore diet, it indicates Chinook salmon may have been feeding on prey items that originated from the creek watershed. Besides chironomid pupae and adults, the June tributary mouth sample included a large number of emerging mayflies (Caenidae; 38% by weight) and the lakeshore sample included large numbers of chironomid larvae. Number of Chinook . 50 40 30 20 10 High flow Base flow 0 May Creek Taylor Creek FIGURE 30.—Total number of Chinook salmon caught with a beach seine at the mouth of three tributaries of south Lake Washington, 2004. Each bar represents the number caught on one sampling effort; at May Creek three sets were conducted during each flow condition, and four at Taylor Creek. 44
Page 1 and 2:
U.S. Fish and IU.S. Wildlife FishSe
Page 3 and 4: SUMMARY In 2003 and 2004, we contin
Page 5 and 6: An overhanging vegetation/small woo
Page 7 and 8: Table of Contents Page SUMMARY ....
Page 9 and 10: List of Figures Figure Page FIGURE
Page 11 and 12: FIGURE 37.—Water column depth (m)
Page 13 and 14: The major tributary to Lake Washing
Page 15 and 16: Fry emerge from their redds from Ja
Page 17 and 18: FIGURE 2.—Location of index sites
Page 19 and 20: most dates (Figure 4). Unlike 2002,
Page 21 and 22: Chinook/m 2 1 0.8 0.6 0.4 0.2 0 Wes
Page 23 and 24: 0.3 Mercer Island Chinook/m 2 0.2 0
Page 25 and 26: particularly valuable. Shoreline im
Page 27 and 28: FIGURE 8.—Map of south Lake Washi
Page 29 and 30: FIGURE 10—Map of south Lake Washi
Page 31 and 32: # of marked Chinook 40 30 20 10 0 A
Page 33 and 34: CHAPTER 3. RESTORATION SITES Introd
Page 35 and 36: Beer Sheva Park.—At Beer Sheva Pa
Page 37 and 38: Results Seward Park, 2003.—In 200
Page 39 and 40: 4 3.5 Chinook/100 m 3 2.5 2 1.5 1 0
Page 41 and 42: Martha Washington Park, 2003.—In
Page 43 and 44: 120 Chinook/100 m 100 80 60 40 20 s
Page 45 and 46: snorkeling and scuba diving were co
Page 47 and 48: Water column depth (m) . 0.80 0.60
Page 49 and 50: CHAPTER 5. FEEDING AT TRIBUTARY MOU
Page 51 and 52: FIGURE 28.—Location of four south
Page 53: FIGURE 29.—Photos of sites used t
Page 57 and 58: TABLE 5.—Diet overlap indices (C)
Page 59 and 60: TABLE 7.—Diet overlap indices (C)
Page 61 and 62: TABLE 10.—Diet composition of juv
Page 63 and 64: The lack of a large difference betw
Page 65 and 66: CHAPTER 6. USE OF NONNATAL TRIBUTAR
Page 67 and 68: shallow to snorkel were surveyed th
Page 69 and 70: Number of Chinook ff 700 600 500 40
Page 71 and 72: column depth used by Chinook salmon
Page 73 and 74: Chinook / m . 5 4 3 2 1 2003 - upst
Page 75 and 76: TABLE 13.—Diet overlap index (C)
Page 77 and 78: (P. Castle, WDFW, unpublished data)
Page 79 and 80: FIGURE 41.—Placement of Scotch br
Page 81 and 82: FIGURE 43.—Photo of a group of ju
Page 83 and 84: CHAPTER 8. LAKE QUINAULT SURVEYS In
Page 85 and 86: FIGURE 45.—Photos of large woody
Page 87 and 88: Similar to April surveys, the nears
Page 89 and 90: Chinook / 100m . 500 400 300 200 10
Page 91 and 92: Tabor and Wurtsbaugh (1991) conclud
Page 93 and 94: FIGURE 48.—Location of south Lake
Page 95 and 96: FIGURE 49.—Conducting visual obse
Page 97 and 98: FIGURE 52.—Photo of a group of ju
Page 99 and 100: ACKNOWLEDGMENTS We wish to thank He
Page 101 and 102: workshop, Shoreline, Washington, No
Page 103 and 104: Paron, D.G., and E. Nelson. 2001. S
Page 105 and 106:
Werner, E.E., and D.J. Hall. 1988.
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Nearshore Habitat Use by Juvenile Chinook Salmon in Lentic ...

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