The Effects of Logging and Mass Wasting on Juvenile Salmonid Populations in Streams on the Queen Charlotte Islands

Transcription

1 The Effects of Logging and Mass Wasting on Juvenile Salmonid Populations in Streams on the Queen Charlotte Islands Land Management Report NUMBER ISSN NOVEMBER 1992 Ministry of Forests

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3 The Effects of Logging and Mass Wasting on Juvenile Salmonid Populations in Streams on the Queen Charlotte Islands D.B. Tripp and V.A Poulin FISH/FORESTRY INTERACTION PROGRAM Ministry of Forests Research Program 1992

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5 SUMMARY The effects of logging and mass wasting on juvenile coho salmon (Oncorhynchus kisutch), steelhead trout (O. mykiss, formerly Salmo gairdneri), and Dolly Varden char (Salvelinus malma) were assessed in streams on the Queen Charlotte Islands. Fish densities and habitat characteristics of stream reaches were measured during summer and fall. Reaches sampled included undisturbed old-growth forest streams (unlogged), logged streams not directly affected by recent mass wasting (logged), and logged streams directly affected by recent debris torrents and slides (mass wasted). Overwinter survivals and smolt yields in three mass wasted and three non-mass wasted streams (all logged) were also estimated in a downstream spring fish trapping program, after determining the number of fish present in each stream the previous fall. Logged reaches had less undercut bank cover than unlogged reaches, but did not differ significantly from unlogged areas in any other habitat variable measured. Mass wasted stream reaches, in contrast, had even less undercut bank cover, less large organic debris (LOD), fewer pools and glides, and more riffles. They also had shallower pools during summer, a smaller wetted stream width relative to rooted channel width, and less overwinter cover in the form of deep pools with undercut banks and abundant LOD. With one exception, there was no relationship between summer and fall fish densities and any of the habitat parameters measured in this study. The exception was the depth of gravel scour overwinter, which appeared to determine the early summer abundance of coho fry in mass and non-mass wasted streams (all logged). Logged reaches had significantly higher coho fry densities than unlogged or mass wasted reaches in summer and fall. Fish in mass wasted reaches exhibited faster growth rates and attained larger sizes, as long as fry were not trapped in isolated pools when reaches dewatered. In mass wasted streams, a combination of poor egg-to-fry survivals due to excess gravel scour, and poor juvenile overwinter survivals due to overwinter habitat loss, nullified any gains in production attributable to logging. It also nullified the high growth rates and large size achieved by fish in their first year in mass wasted streams. Juvenile overwinter survivals for all species were times higher in non-mass wasted streams than in mass wasted streams; smolt yields were times higher. The overall impacts of mass wasting on juvenile fish, and coho salmon in particular, are serious enough to jeopardize the continued existence of self-sustaining populations in directly affected reaches until stream conditions improve. Four out of 11 mass wasted reaches in 1982 and 2 out of 3 mass wasted reaches in 1984 had effectively no coho fry. Impacts on Dolly Varden and steelhead trout did not appear as serious, though they too showed declines in overwinter survivals and smolt yields. Impacts on other species such as chum and pink salmon were not investigated, though presumably these species would be negatively stressed by increased gravel scour. Fish populations in otherwise normal (logged) reaches downstream of major mass wasting events may also be adversely affected by mass wasting upstream, but the problem requires further study. iii

6 ACKNOWLEDGEMENTS Sincere appreciation is extended to the many individuals who contributed to this study. Special thanks especially to Jeff Cederholm who worked closely with the project in its initial stages and who reviewed a number of preliminary reports. Thanks also to those who reviewed the present manuscript and provided many valuable comments: Al Cowan, Dionys DeLeeuw, Dr. Tom Northcote, Bill Pollard, Charles Scrivener, and Pat Slaney. Ted Harding, with the assistance of Brian Eccles, Dave Davies and Mary Morris, carried out the synoptic survey, while technical assistance for the detailed studies was provided by Ted Bellis, Don Cadden, Charles Rally, and Glen Kendall. The study was undertaken as part of the Fish/Forestry Interaction Program, an interdisciplinary research program funded by the Government of Canada Department of Fisheries and Oceans, British Columbia Ministry of Forests, and British Columbia Ministry of Environment, Lands and Parks. A Government of Canada Fisheries Employment Bridging Assistance Program provided additional field staff in 1982 and iv

7 TABLE OF CONTENTS SUMMARY... iii ACKNOWLEDGEMENTS... iv 1 INTRODUCTION STUDY DESIGN AND STREAM CHARACTERISTICS Study Design Synoptic Survey Stream Characteristics Detailed Study Stream Characteristics METHODS Reach Selection and Habitat Measurements Fish Population Estimates Spring Downstream Trapping Habitat Utilization Data Analysis RESULTS Stream Habitats General Distribution and Abundance of Fish Species Habitat Utilization Effects of Logging and Mass Wasting on Fish Abundance Upstream/Downstream Effects Effects on Coho Growth Effects on Biomass Smolt Yields and Overwinter Survivals Coho Fry Recruitment DISCUSSION Effects of Logging and Mass Wasting on Rearing Habitat Effects on Coho Salmon Logging impacts Mass wasting impacts Downstream effects Effects on Other Species Management Implications Recommendations for Further Study LITERATURE CITED v

8 TABLES 1 Synoptic survey study reach characteristics Stream habitat characteristics in the full and reduced sets of unlogged, logged and mass wasted study reaches in the synoptic survey Habitat characteristics of detailed study streams General distribution characteristics, abundance and age composition of juvenile salmonid populations in 1982 synoptic survey reaches on the Queen Charlotte Islands Mean juvenile salmonid densities in the full set of unlogged, logged and mass wasted (logged) stream reaches sampled on the Queen Charlotte Islands in Juvenile coho salmon, Dolly Varden char and steelhead trout densities (number of fish per metre of stream) in the detailed study streams, fall (Sept. 12 Oct. 6, 1983) and summer (July 13 23, 1984) Mean juvenile salmonid densities in the reduced set of unlogged, logged and mass wasted (logged) stream reaches sampled on the Queen Charlotte Islands in Coho fry densities (number of fish per metre of stream) and sample dates in logged stream reaches, with and without mass wasting upstream Mean coho fry fork length, coho fry density, total salmonid density and total salmonid biomass in selected streams on the Queen Charlotte Islands, Annual variation in age composition and fry growth of coho salmon in detailed study streams Salmonid biomass (grams of fish per metre of stream) in unlogged, logged and mass wasted (logged) stream reaches on the Queen Charlotte Islands in Densities, smolt yields and apparent overwinter survivals of juvenile coho salmon, Dolly Varden char and steelhead trout in each detailed study stream, October 1983 July FIGURES 1 Location of synoptic survey ( ) and detailed study streams ( ) on the Queen Charlotte Islands Length frequency distributions of coho salmon, steelhead trout and Dolly Varden char in synoptic survey streams on the Queen Charlotte Islands, Habitat preferences and densities of juvenile salmonids in pools, glides and riffles Seasonal variation in mean fork length for coho salmon juveniles in unlogged, logged and mass wasted stream reaches on the Queen Charlotte Islands, June 9 September 30, Seasonal variation in juvenile coho salmon growth for the 1983 and 1984 year classes in mass and non-mass wasted streams Downstream movements of juvenile coho salmon in mass and non-mass wasted study streams, April 10 June 29, Correlation between mean scour depth and coho fry density (spring outmigrants plus July resident fish combined) in detailed study streams vi

9 1 INTRODUCTION Widespread mass wasting in the form of debris slides, flows and torrents (Varnes 1978) is evident on the sides of virtually every steep watershed on the Queen Charlotte Islands (Gimbarzevsky 1988). When clearly unstable areas such as these are logged, the volume of soil and debris mobilized by mass wasting is increased 34 times over the volume observed in forested areas, while the volume introduced into fish bearing streams is increased 43 times (Rood 1984). Open slope debris slides are the most common type of slope failure events on the Queen Charlotte Islands, but they rarely enter streams and therefore rarely cause immediate damage to fish or fish habitats. Most of the sediment that enters streams directly is transported by debris flows or torrents that can damage fish habitat extensively through excessive stream scouring and the deposition of large quantities of sediment and debris. On the Queen Charlotte Islands, debris torrents in small and medium size streams have the greatest impacts in stream reaches with a gradient less than 7% (Tripp and Poulin 1986a). In these zones, pool depth, pool area, LOD (large organic debris) cover and stable undercut bank area are reduced, while riffle area, channel width and the degree of dewatering that occurs during low flow periods are all increased. Fish overwinter habitat especially in the form of deep pools with abundant LOD cover and stable undercut banks is lost in the mainstem portions of affected streams, a critical factor that may severely limit juvenile survival and smolt yield if protection from high flows is lacking elsewhere. Gravel scouring in spawning areas is also increased (Tripp and Poulin 1986b), which may further limit production if the number of eggs or alevins that survive to emerge from the gravel is too low to fill or seed the available rearing habitat. The effects of debris torrents on juvenile fish survivals and smolt yields in mass wasted streams on the Queen Charlotte Islands have yet to be measured directly. Though the damage caused by torrents in the directly affected reaches of small streams is obviously great, studies on the effects of logging elsewhere indicate that a number of processes can help offset or compensate for declines in the quantity or quality of fish habitat present. Higher intragravel water temperatures during winter, for example, can accelerate fry emergence and extend the growing season, resulting in larger fish in fall with a better chance of surviving the winter (Scrivener and Anderson 1984; Holtby 1988). Increased light in the stream after the surrounding forest is removed may also stimulate fish growth through increased periphyton and macroinvertebrate production (Hawkins et al. 1983; Bisson and Sedell 1984; Murphy et al. 1986). Presumably similar processes occur in streams on the Queen Charlotte Islands, but it is not known whether they are sufficient to offset the damage caused by debris torrents on the scale common in the steeper regions of the Queen Charlotte Islands. The main objective of this study was to assess the effects of mass wasting on the growth, abundance and overwinter survivals of juvenile salmonids in directly affected streams on the Queen Charlotte Islands. Because many mass wasted stream reaches on the Queen Charlotte Islands are also logged, the study also assessed the effects of logging to distinguish the effects of mass wasting. This is the third of three related reports on logging and mass wasting under the Fish/Forestry Interaction Program (Poulin 1984) in British Columbia. The first report described the impacts of mass wasting on juvenile fish rearing habitat (Tripp and Poulin 1986a); the second report described the effects of logging and mass wasting on salmonid spawning habitats and egg-to-fry survivals (Tripp and Poulin 1986b).

10 2 STUDY DESIGN AND STREAM CHARACTERISTICS 2.1 Study Design To assess the effects of mass wasting on juvenile fish, the densities of coho salmon (Oncorhynchus kisutch), steelhead trout (O. mykiss, formerly Salmo gairdneri), and Dolly Varden char (Salvelinus malma) were first measured in a synoptic survey of 33 stream reaches in 29 small and medium sized streams on the Queen Charlotte Islands (Figure 1). This project was followed by a second, more detailed study on overwinter survivals in six streams previously sampled in the synoptic survey. In the synoptic survey, three types of stream reaches were compared: undisturbed old-growth forest streams (unlogged), logged streams not directly affected by recent mass wasting (logged), and logged streams directly affected by recent debris torrents and slides (mass wasted). In the detailed study, only logged streams with a range of mass wasting conditions were compared. The synoptic survey portion of the study was conducted in 1982, during which all 33 stream reaches were sampled once for fish and habitat in summer (June 15 August 23), and 27 were sampled again for fish in fall (September 1 30). Streams in the overwinter survival study were sampled in , once in fall (September 12 October 5, 1983) to determine the number of fish present before winter, once in spring (April 16 June 29, 1984) to enumerate smolts and fry migrating downstream, and again in summer (July 13 22, 1984) to measure habitat and estimate the number of fish present after downstream movements had ceased. 2.2 Synoptic Survey Stream Characteristics The location, drainage area, gradient characteristics and dimensions of each study reach in the synoptic survey portion of the study are presented in Table 1, together with a brief description of the logging and mass wasting conditions within and above each reach. Study streams were first to third order (Strahler 1957) gravel and cobble bedded streams, 17 of which were located within the Queen Charlotte Ranges and 12 in the Skidegate Plateau (Figure 1, inset). Average drainage area of the study streams was 10.5 km 2 (range km 2 ); average drainage area of the study reaches was 8.4 km 2 (range km 2 ). Average channel gradient of the study reaches was 2.4% (range %), average length 530 m (range m), and average width 22.5 m (range m). Most study reaches started at the mouth of the stream. Some, however, were 5 9 km upstream. Average distance upstream was 760 m (range m). Almost all the study reaches contained juvenile coho salmon and Dolly Varden; about two-thirds also contained steelhead trout. Most of the reaches are used for spawning by chum salmon (O. keta), and about a third, mainly the larger third order streams, are used by pink salmon (O. gorbuscha). None of the streams are used by sockeye (O. nerka) or chinook (O. tshawytscha) salmon, and only two (Phantom and Sachs creeks) had cutthroat trout (O. clarki, formerly Salmo clarki). The latter appeared to be resident populations, inasmuch as they were restricted in their distribution to the headwaters of each stream, well upstream of the study reaches. Sculpins (Cottus aleuticus and C. asper) were common but were not included in the analysis. Unlogged study reaches (N = 11) were all in old-growth forests of hemlock, cedar and Sitka spruce, and, with the exception of three reaches (Cache 1 and 2, Phantom 1; Table 1), unlogged reaches were also unlogged upstream. Cache Creek had the upper one-third of its drainage logged 1 7 years before the study, but no obvious effects of the logging showed in the study reaches downstream. Phantom Creek, in contrast, had several active gravel deposits within the study reach, which may have been started by a recent slide out of a logged area 800 m upstream. Phantom Creek and three other unlogged reaches also had recent (<4 years old) debris torrents in unlogged areas upstream (Table 1). Located within m of the study reach, two of the torrents (Windy Bay Creek tributary and Government Creek) may have indirectly influenced fish populations in the study reach downstream. The other two torrents (in Phantom Creek and Matheson Side Creek) were km upstream of the study reaches. 2

11 FIGURE 1. Location of synoptic survey ( ) and detailed study streams ( ) on the Queen Charlotte Islands. 3

12 TABLE 1. Synoptic survey study reach characteristics. Reach no. Period Basin Distance a Reach Channel % Period Grad. b upper area upstream length width Basin reach (%) reaches (km 2 ) (m) (m) (m) logged logged logged Remarks Unlogged Reaches Cache Unlogged H Cache Unlogged H Government Unlogged Unlogged Headwaters torrented pre-1940, 1972, 1978 Hangover Unlogged Unlogged Large 155-year-old rock slide upstream Inskip Unlogged Unlogged Old slides upstream (undated) Marshall Unlogged Unlogged Matheson Head Unlogged Unlogged Matheson Side Unlogged Unlogged Headwaters torrented Phantom Unlogged H Headwaters torrented 1979; slides in logged areas Salmon Unlogged Unlogged Windy Bay Trib Unlogged Unlogged Headwaters torrented Logged Reaches Landrick A36 H78-82 Peel Road H50 s H50 s Piper A55 H summer flood damage extensive Sachs pre 56 H74-82 Headwaters torrented 1974 Sachs ND pre 56 H74-82 Headwaters torrented 1974 Schomar H65-67 H70-76 Torrented upstream 1979; study area impacted 1984 Talunkwan A45 H69-73 Torrented upstream Tarundl H64 H64-82 Tarundl H72-78 H m debris jam at end of reach Thurston A,S39-48 H68-75 Torrented upstream Riley H74 H77-80 Torrented upstream Mass Wasted Reaches Bonanza H80-82 Unlogged 1982 torrent deposition zone; channel aggraded Macmillan H46 H76-82 Torrented Mosquito Trib H60 s H60 s Banks eroded, channel wide and heavily aggraded Mountain S58 H65-67 Banks eroded, channel wide and heavily aggraded Riley H74 H77-80 Torrented ; extensive aggradation Riley Trib H74 Unlogged Banks eroded; channel torrent-like Saltspring H65 Unlogged Torrented , , Shelley H72 H73 Torrented Southbay H60 H61-80 Torrented , 1983; new LOD added 1982 Southbay H61-67 H61-80 Torrented , 1983 Two Torrent H65-66 H65-66 Torrented a Distance from stream mouth to start of reach. b A = A-frame logging; S = skidder logging; H = highlead logging. Logged study reaches (N = 11) had a range of logging histories dating back between 4 and 46 years. Five reaches were A-frame or skidder-logged before the mid-1950 s; the rest were highlead-logged from the late 1950 s to the present. All logged reaches were more recently logged upstream with highlead systems. Average age after logging within each study reach was 24 years, while the average age since the start and end of logging upstream was 10 and 5 years, respectively. Two reaches (Riley 1 and Tarundl 2) had narrow buffer strips left alongside them after they were logged, but only one reach (Tarundl 2) had some of these trees still standing during the survey. Because dense stands of red alder dominated the riparian zone of all logged reaches, those reaches with no mass wasting were usually heavily shaded during summer. Four reaches also had recent (<4 year old) debris torrents that stopped an average of 550 m (range m) above the study reach. Eight of the 11 mass wasted stream reaches selected for study had been directly affected by one or more debris torrents within the past 3 4 years; 3 others had been affected by a combination of torrents, slides and accelerated bank erosion over the past 3 24 years (Roberts and Church 1986). All mass wasted reaches were in previously logged areas, and all except three were logged upstream. Average age since the end of logging in each reach was 16 years, and average age since logging started and stopped upstream was 12 and 6 years, respectively. As for logged streams, dense stands of red alder dominated the 4

13 riparian zone of each study reach; however, unlike logged streams, most of the alder was too young and too far back from the wetted channel to provide much shade during summer. 2.3 Detailed Study Stream Characteristics The synoptic survey streams selected for further study on juvenile overwinter survivals in (Macmillan, Piper, Saltspring, Schomar, Southbay Dump and Tarundl creeks) were first and second order streams in the Skidegate Inlet Skidegate Channel region between Moresby and Graham islands (Figure 1). Schomar Creek was a tributary of the Deena River; the others all flowed into the ocean. In Tarundl Creek, the study reach started 1.6 km upstream of the mouth and extended 600 m farther upstream to the base of a large debris jam, above which there were no coho salmon. In the rest of the streams, the study reaches started at the mouth and extended as far upstream as there were coho. None of the streams, therefore, had any coho that could move down into the study reaches, and only Schomar and Tarundl creeks had coho that could move up into the study reach. Reach length ranged from 475 to 870 m, while channel width ranged from 7.7 to 41.9 m. Wetted width ranged from 2.6 to 7.1 m, channel gradient from 2.1 to 4.0 %, and drainage area from 4.0 to 9.6 km 2. All six detailed study reaches were logged and, with the exception of Saltspring Creek, this logging extended upstream (Table 1). Macmillan Creek (torrented in 1979) and Saltspring Creek (torrented in 1979 with successive failures in 1982 and 1983) were considered to be the most seriously disturbed streams. Southbay Dump Creek was also torrented in 1979, but because new LOD was re-introduced in the upper 315 m of the study reach in 1982 (Tripp 1986), it was considered to be less disturbed than Macmillan or Saltspring creeks. Although much of the new LOD added to Southbay Dump Creek was eventually buried or dislodged by another torrent in August 1983, approximately 110 m of good stream habitat with new LOD remained more or less intact in this study. Piper Creek and Tarundl Creek had no major debris torrents within or upstream of the study reach, and they were therefore considered the least affected streams in the study. Schomar Creek was similarly unaffected when the study began, but it had a major debris torrent jam immediately above the study reach, which broke open during the study and inundated the study reach with large quantities of gravel on at least two occasions. A small tributary stream in the creek, where fish could escape conditions in the main channel, was also damaged during the study when a 5-m section of road 235 m upstream washed out and spilled downstream. Because none of the other streams had any tributaries or off-channel habitat that fish could inhabit overwinter, survivals in all six streams are considered to be fairly representative of conditions in the main channel. 5

14 3 METHODS 3.1 Reach Selection and Habitat Measurements Prospective study reaches in each stream in the synoptic survey were selected in the following manner. Since the entire length of each reach had to be accessible to anadromous salmonids, a preliminary survey of each stream was first conducted to see how far juvenile coho salmon extended upstream. Stream gradients were then measured with hand-held levels in the accessible portion of each stream to locate all main LOD steps, sediment wedges and basin gradient breaks. Bank-full channel widths were measured every 50 m. The stream was then divided into reaches that had a more or less constant gradient, the same level of access to anadromous fish, and a similar valley shape. Final selection of study reaches was based on reaches that also had the same logging and mass wasting condition throughout. Methods used to quantify juvenile fish rearing habitat in each study reach are described in detail by Tripp and Poulin (1986a). Length, width and maximum depth were recorded for each pool, glide and riffle in the study reach during the summer low flow period, along with the amount of rooted undercut bank and LOD cover present. Additional information collected from detailed study reaches included the specific types of pools present as defined by Heifetz et al. (1986) and the agent responsible for the formation of each pool (e.g., stream banks, LOD, boulders, bedrock). To determine the proportion of each habitat type present in both surveys, the area of each habitat type was summed and divided by total wetted area. 3.2 Fish Population Estimates Population size in the synoptic survey portion of the study was estimated with a removal method. Typically, two pools, a glide and a riffle (or two pools and two riffles if glides were rare) were individually enclosed with fine mesh seine nets and fished intensively for two successive and equal passes, using both electroshockers and pole seines in pools and glides. Electroshockers only were used in riffles. Numbers of fish in each habitat unit were then estimated by species and age group (fry = age o + fish; parr = age 1 + and older fish) according to Seber and LeCren (1967), and averaged by habitat type. Densities in each habitat type were in turn multiplied by the proportion of the study reach occupied by that habitat, and summed to obtain average density over the whole study reach. In this way, fish densities for each study reach were weighted according to the amount of different habitat present, to provide a better comparison between streams at different stage heights and with widely varying portions of pool, glide and riffle habitat. Where glides were not sampled, glide densities were assumed to be of the same magnitude, relative to pools and riffles, as in reaches where all three habitat types were sampled. Fish numbers in the detailed survey portion of the study were estimated with a single census markrecapture method. In fall, numbers were estimated for each habitat unit over the whole study reach in each stream. The following summer, when fish movements downstream had ceased, the estimates were repeated over the whole study reach in Macmillan, Saltspring and Southbay Dump creeks, and in three subsections that together represented half of each study reach in Piper Creek, Schomar Creek and Tarundl Creek. Throughout the estimates, stop nets were placed at the top and bottom ends of each reach or reach subsection. Fish were therefore prevented from moving in or out of the enclosed areas during the estimate, although they were free to move between habitat units (pools, glides, riffles) within the enclosed areas. Fish were collected with electroshockers and minnow seines, marked with an adipose fin clip, and redistributed according to the number initially captured in each habitat unit. Fish were resampled hours later and the number of fish present estimated according to Chapman (1951, in Ricker 1975). Where the number of recaptures in any one habitat unit was too small (i.e., <3) for an accurate estimate, results were pooled for an estimate of overall density in each habitat type. Where the number of recaptures in each habitat type was too low for an estimate, results were pooled again for an estimate of overall density in the study reach. In both the synoptic and detailed surveys, we regularly considered data only for coho salmon fry, coho salmon parr, Dolly Varden parr and steelhead parr. Because of their small size and reclusive habits, reliable estimates were rarely obtained for sculpins or Dolly Varden fry and they had to be excluded from analysis. Steelhead fry were also difficult to capture in the early summer (June) of 1982, so they were only considered in the 1982 fall (September) and 1984 summer (July) estimates. 6

15 Fish captured during sampling were measured to the nearest millimetre fork length and designated as fry (o + fish) or parr (1 + and older fish) on the basis of their length frequency distributions (all species) and scale age-length relationships (coho and steelhead) in each reach type. Mean weights were estimated from length-weight relationships derived separately from subsamples of fry and parr of each species that had been preserved in dilute (1%) formalin and weighed within 24 hours to the nearest 0.1 g. 3.3 Spring Downstream Trapping To estimate apparent overwinter survivals for each species, we compared the number of fish present in each reach the previous fall (fry and parr) with the number of fish captured moving downstream in the spring, plus the number of fish (parr only) still left in the stream after all spring downstream movements had ceased. To enumerate smolts and fry moving downstream in the spring, temporary weir and trap facilities were installed at the lower end of each study reach. Separate m panels covered with 6.4 mm galvanized wire mesh were nailed and wired together into V-shaped patterns pointing downstream. These guided fish into baffled live-boxes via a m long wooden trough. The trough was covered with black plastic mesh and pinned to the weir with a 0.4 m long steel rod (1.25-cm rebar) passed horizontally through the trough and the end of each panel at the apex of the V. Wire mesh extending 25 cm past one side of each panel overlapped the next panel and prevented fish from escaping through seams in the weir. Extra mesh dug into the substrate on the bottom of each panel prevented fish from moving under the weir. Each wing of the weir was also buried into a steep bank to keep fish from moving around the weir; a 1 m wide strip of heavy plastic film on the bottom of the weir prevented scouring downstream. The entire structure was supported with steel rods driven into the substrate behind the panels, with ropes tied from the tops of each steel rod to trees upstream. Weirs were operated for 40- to 80-day periods, between April 10 May 6 and June 11 29, Depending on the weather and flow conditions, each trap was checked daily for emigrant fish, and the essential data (species, age, fork lengths, marks) were recorded before fish were released downstream. Previous studies indicate that weirs of this type in small streams are very efficient at capturing downstream migrating smolts over widely varying flow conditions (Tripp and McCart 1983; Tripp 1986). In this study, however, floods and excessive bedload movements prevented trapping for 3 10 days (avg. 6 days) in each study stream during storms in late May. Since May was a critical period for emigrant coho smolts, the estimates obtained on smolt yield and overwinter survival in the detailed study streams are minimum estimates only. 3.4 Habitat Utilization To examine habitat use by fish in the synoptic survey portion of the study, overall densities of each species were compared in pools, glides and riffles of each reach type. Habitat preferences by fish in the detailed study streams were quantified by relating the fraction of the population found in each particular type of habitat in fall (September 1983) and summer (July 1984) to the relative abundance of that habitat within each study reach. The relationship is based on the electivity index of Ivlev (1961) as follows (from Bisson et al. 1982): U i = (D i - D t ) D 2 t where: U i = utilization of habitat type i; D i = fish density in habitat type i; D t = overall fish density in the study, all habitat types combined. Values of this coefficient (U i ) theoretically range from -1, indicating total non-use of a habitat type, to positive infinity as more and more fish in the population reside in the preferred habitat. A value of 0 indicates that the habitat is neither preferred nor avoided. 7

16 3.5 Data Analysis For most of this report, juvenile densities are expressed as numbers of fish per metre of stream length, to facilitate comparisons between the same study reaches sampled at different times and stage heights, and between different study reaches with different drainage areas or sediment budgets. The exception is where data on juvenile densities in pools, riffles and glides were compared, in which case densities are expressed as numbers of fish per square metre to compensate for differences in the shape of each habitat type. In both cases, confidence limits about the arithmetic means are based on values transformed to log (x+1). For the synoptic survey streams, differences in habitat and the number of each species of fish in the different reach types were analysed with a full data set and a reduced data set. The full data set included all study reaches sampled, regardless of logging or mass wasting conditions upstream. Thus some unlogged study reaches had logging or mass wasting upstream, and some logged streams (no mass wasting) had mass wasting upstream. To eliminate the possible downstream effects of logging or recent mass wasting upstream, a reduced data set was also analysed which included only those stream reaches with the same conditions upstream as instream. Sample sizes for each data set in summer and fall are as follows: Reach Type Summer Fall Full data set (N) Unlogged 11 7 Logged 11 9 Mass wasted Reduced data set (N) Unlogged 5 4 Logged 7 7 Mass wasted 8 8 Non-parametric statistics were used to analyse much of the data on fish abundance in the different reach types, (1) because the error involved in estimating fish density for a whole study reach as described above was not determined, and (2) because not all the data could be normalized with standard transformations. Streams where the total absence of a species was clearly unrelated to the quality of the rearing habitat available were especially troublesome. The Mann-Whitney U-test was used to compare abundance and percent survival overwinter in two different stream types, while a Sign test was used to compare percent declines in abundance. Where abundance or preferences in more than two habitat or reach types were compared, a Kruskal-Wallis analysis of variance test was used to test for differences, with additional U-tests whenever Kruskal-Wallis tests indicated a significant (P<0.05) difference. Differences between the habitat characteristics of unlogged, logged and mass wasted reaches in the synoptic survey were tested with analysis of variance (ANOVA) tests, followed by Tukey s HSD tests on pairs of means where significant differences were indicated by analysis of variance. Other possible relationships between the habitat variables and fish abundance data were explored in a Pearson correlation matrix, but then discontinued when probability values (Bonferroni adjusted) indicated no significant correlations between fish numbers and the habitat parameters measured. Other analyses included a least squares regression analysis to compare the number of recently emerged coho fry (including downstream migrants), in each detailed study stream in spring 1983, with the amount of gravel scour recorded the same year in the same streams (data from Tripp and Poulin 1986b). Regression tests were also used to compare coho fry fork length and fish standing crop in the synoptic survey, to see if coho fry growth may have been affected by density dependent factors. To reduce the variability caused by differences in sampling times, the data were adjusted to August 30, which was approximately 1 week after the last stream was sampled in the first sampling period (June 15 August 23) and 1 day before the first stream was sampled in the second sampling period (August 31 September 30). To adjust fork lengths and fish densities to August 30, apparent instantaneous growth (G) and mortality (Z) 8

17 rates between the first and second sampling periods were calculated and the rates used to interpolate between the two sampling periods. The formulae used to calculate growth and mortality rates G and Z were as follows: G = lnl 2 - lnl 1 t Z = - (ln N 2 - ln N 1 ) t where: L 1 and L 2 = average fork length of coho fry in each study reach in the first and second sampling periods, respectively; N 1 and N 2 = fish densities in the first and second sampling periods; t = proportion of the year sampled between the first and second sampling periods. 4 RESULTS 4.1 Stream Habitats Logged and mass wasted study reaches in the synoptic survey had a significantly (P<0.05, ANOVA) greater portion of their drainage basin logged (37 and 30%, respectively) than did unlogged reaches (7%). The reaches were otherwise similar in length, width, gradient and drainage area (Table 2). Distance upstream from the mouth to each study reach also did not differ significantly, although it was highly variable. While most study reaches started within 275 m of the stream mouth, one logged reach (Riley Creek) and two mass wasted reaches (Bonanza and Riley creeks) were located km upstream. When the latter three reaches were deleted from the data, mean distance upstream from the mouth to the start of each reach in each reach type was more similar 210 m in unlogged reaches, 271 m in logged reaches, and 163 m in mass wasted reaches. Mass wasting substantially reduced the amount of summer rearing habitat available in directly affected reaches (Table 2). Compared to unlogged stream reaches, mass wasted reaches had significantly less pool/glide habitat, shallower pools, less LOD cover, and less stable (i.e., rooted) undercut bank cover (P<0.05). Compared to unlogged or logged reaches, mass wasted streams also had significantly smaller wetted stream widths relative to total channel width because of lateral channel movements, bank erosion and dewatering at major sediment deposits. Reducing the data to eliminate reaches with different logging or mass wasting conditions upstream did not change the overall pattern appreciably, although the smaller sample sizes meant fewer significant differences. Mass wasted stream reaches in the reduced data set still showed significantly less surface flow, shallower pools and less LOD cover than in logged or unlogged reaches, but differences in pool/riffle area and stable undercut bank cover were no longer significant. The habitat characteristics of logged reaches tended to be either very similar to those of unlogged reaches (e.g., pool/riffle areas, the ratio of wetted width to channel width) or intermediate between unlogged and mass wasted reaches (e.g. LOD cover, undercut bank area, net pool depth). Few of the differences were statistically significant (P<0.05). Logged reaches had less undercut bank area than did unlogged reaches (P<0.05, full data set only), but otherwise did not differ significantly from the latter in any other stream habitat variable measured. Similarly, the only significant difference between logged and mass wasted reaches was that wetted stream width relative to channel width in logged streams was twice the wetted width in mass wasted streams (full and reduced data sets). 9

18 TABLE 2. Stream habitat characteristics in the full and reduced sets of unlogged, logged and mass wasted study reaches in the synoptic survey. Values are means ± 95% confidence limits. Significant differences among reach types (P<0.05, ANOVA) are denoted with an asterisk. Habitat Reach type variable Unlogged Logged Mass wasted P Full data set Sample size Stream length (km) 4.8 ± ± ± Reach basin area (km 2 ) 8.0 ± ± ± Reach basin area logged (%) 6.7 ± ± ± * Reach distance upstream (m) ± ± ± Reach length (m) ± ± ± Gradient (%) 2.4 ± ± ± Wetted width (m) 8.2 ± ± ± Bankfull width (m) 24.1 ± ± ± Wetted width/bankfull width 0.4 ± ± ± * Pool, glide area (%) 65.8 ± ± ± * Riffle area (%) 34.2 ± ± ± * LOD cover (%) 11.8 ± ± ± * Undercut bank cover (%) 3.3 ± ± ± * Net pool depth (cm) 58.0 ± ± ± * Reduced data set Sample size Stream length (km) 5.6 ± ± ± Reach basin area (km2) 10.6 ± ± ± Reach basin area logged (%) 0.0 ± ± ± * Reach distance upstream (m) 50.0 ± ± ± Reach length (m) ± ± ± Gradient (%) 2.1 ± ± ± Wetted width (m) 11.6 ± ± ± * Bankfull width (m) 31.0 ± ± ± Wetted width/bankfull width 0.4 ± ± ± * Pool, glide area (%) 63.4 ± ± ± Riffle area (%) 36.6 ± ± ± LOD cover (%) 10.0 ± ± ± * Undercut bank cover (%) 1.9 ± ± ± Net pool depth (cm) 69.4 ± ± ± * Results of the habitat surveys in the detailed stream reaches (Table 3) were similar to those of the synoptic survey. As in the synoptic survey, mass wasted streams in the detailed survey had wider rooted widths and narrower wetted widths (P<0.05) than did non-mass wasted streams. They also had significantly smaller and shallower pools, less total pool/glide area, and more riffle area. Total wetted area during low flows was therefore only 14% of total channel area in mass wasted streams, compared to 38% in nonmass wasted streams (P<0.05). The differences were not related to differences in drainage area or stream gradient. They were, however, consistent with the bank erosion, channel shifts and dewatering observed in mass wasted streams wherever large quantities of sediment had inundated the channel. In the detailed stream survey, non-mass wasted streams had, on average, twice the number of LOD pieces per metre of stream that mass wasted streams had (0.45 vs pieces per metre, P<0.05). They also had twice the LOD coverage in planview, although in this case the differences were not signficant because the differences in the species composition of the riparian zones greatly increased the variability in the length and diameter of the LOD present. The riparian zone along the first 500 m of the study reach in Piper Creek, for example, was A-frame logged in the 1950 s which effectively removed all of the instream debris. The latter was replaced by small, short pieces of debris from the red alder which now completely dominates the riparian zone. Conifer logs that were longer and thicker than the alder debris in Piper Creek dominated the LOD in the rest of the streams. Of these, Tarundl Creek had the largest average debris pieces which were derived mainly from the adjacent buffer strip. Debris in the other creeks came mainly from the 10

19 debris torrents or debris jams above each study reach. As described earlier, large conifer logs were also added to Southbay Dump Creek. Orientation of the debris relative to stream flows did not differ significantly between the mass and nonmass wasted detailed study streams (all logged). Average debris orientation was diagonal in all streams except Southbay Dump Creek, where the extra debris added to the creek was placed at right angles to the stream flow. Position relative to the stream surface, on the other hand, did differ significantly (P<0.05) as shown by the differences in deflection values. In mass wasted streams, the debris tended to be perched above the water surface, on bouldery substrates in riffles or where new pools were scoured out underneath small debris jams. Instream cover characteristics were highly variable. Mass wasted streams had about half the deep water cover (5.3 vs. 10.7% of wetted stream area) and total overwinter cover (6.6 vs. 14.5%) present in nonmass wasted streams. The differences were not significant (P = 0.10), but they were suggestive. There were no significant differences between LOD cover, undercut bank cover or rock cover in the two stream types, nor were there any differences in the total amount of cover. TABLE 3. Habitat characteristics of detailed study streams Habitat variable Mass wasted streams Non-mass wasted streams Macmillan Saltspring Southbay Schomar Piper Tarundl Reach characteristics Drainage area (km 2 ) Length (m) Rooted width (m) Wetted width (m) Gradient (%) Surface substrate characteristics % fines (<5 mm) % gravel (5 63 mm) % larges (>63 mm) D Pool characteristics Total pool area (%) Average pool area (m 2 ) LOD pool area (%) No. pools / 100 m Net pool depth (cm) LOD characteristics No. pieces/m Average length (m) Average diameter (m) Orientation a Deflection b Instream cover characteristics LOD (%) Deep water (%) Undercut banks (%) Rock (%) Total (%) Total winter cover (%) c a Average position of each LOD piece relative to stream flows: 1 = parallel; 2 = diagonal; 3 = perpendicular. b Average position of each LOD piece relative to the stream surface: 1 = over; 2 = in/out; 3 = submerged. c The sum of the instream LOD, deep water, rock and undercut bank cover in LOD controlled pools. 11

20 4.2 General Distribution and Abundance of Fish Species Coho salmon were present in all but one of the synoptic survey reaches sampled in Only Macmillan Creek (mass wasted) lacked coho in 1982, although they were present in 1983 and Two other reaches contained coho parr but no fry (Shelley Creek and Riley Creek tributary), while another one (upper Southbay Dump Creek) had coho fry in fall but none in the summer. Dolly Varden, the next most widespread species, were present in 82% (N = 27) of the study reaches; steelhead trout were present in 67% (N = 22) of the study reaches. There were no significant differences in overall mean basin area, distance upstream or reach gradient between the three species (Table 4). Dolly Varden, nevertheless, appeared to use steeper reaches than did either coho or steelhead. The average maximum stream gradient recorded for Dolly Varden in streams without any obvious barriers to upstream migrating fish was significantly higher (10.9%, P<0.05, Mann- Whitney U-tests) than the maximum gradient recorded for coho (7.0%) or steelhead (6.0%). No streams with a basin area <5 km 2 contained juvenile steelhead (unless it was part of a larger basin). It thus appears that coho and Dolly Varden are also capable of using smaller streams. Coho salmon was the most common species in the study area. Overall, juvenile coho densities in summer (unlogged, logged and mass wasted reaches combined) averaged 7.04 fish per metre, which represented 93.6% of all salmonids present (excluding Dolly Varden and steelhead fry), and 1.90 fish per metre in fall, or 57.4% of all salmonids present (including steelhead fry, Table 4). Dolly Varden densities rarely exceeded 0.2 fish per metre at any time and thus they were relatively uncommon in the streams examined, but widely distributed. Steelhead numbers were intermediate, averaging 0.33 fish per metre in summer when only parr were considered, increasing to 1.32 fish per metre after fry had completed emergence. TABLE 4. General distribution characteristics, abundance and age composition of juvenile salmonid populations in 1982 synoptic survey reaches on the Queen Charlotte Islands. Numbers in brackets are 95% confidence limits. Population characteristics Fish species Coho salmon Dolly Varden Steelhead trout Distribution % of reaches Reach gradient (%) 2.5 ( ) 2.7 ( ) 2.1 ( ) Maximum gradient (%) 7.0 ( ) 10.9 ( ) 6.0 ( ) Mean basin area (km 2 ) 8.4 ( ) 6.9 ( ) 10.5 ( ) Smallest basin (km 2 ) a Abundance Summer density (n/m) 7.04 ( ) 0.17 ( ) 0.33 ( ) Fall density (n/m) 1.90 ( ) 0.10 ( ) 1.32 ( ) Age structure Summer (% fry) 94.1 ( ) ND b ND Fall (% fry) 94.1 ( ) ND 82.5 ( ) a Smallest basin that flows into the ocean (i.e., not part of a larger basin). b No data; fry estimates unreliable or emergence incomplete. Most of the juvenile coho salmon and steelhead trout sampled were fry. Coho fry accounted for 94% of the coho present in both summer and fall; steelhead fry accounted for 83% of that species in fall samples. Coho parr were almost exclusively 1 + fish, while steelhead parr ranged from 1 + to 4 + fish. On the basis of their length-frequency distribution (Figure 2), at least four age classes (excluding fry) of Dolly Varden were also present. The latter included both parr and adult stages, many of which (parr and adults) were sea run fish that had evidently moved into the streams in fall. 12