What are the history and trends of the sizes, distribution, and relative health and diversity of salmonid populations in the Northern Subbasin?
The Northern Subbasin supports populations of Chinook salmon, coho salmon, and steelhead trout;
Using data from two long term data sets for salmonid populations in the SF Eel River Basin (Benbow dam counts occurring from 1938-1976, and Van Arsdale counts from 1933 to the present), trend lines for Chinook salmon, coho salmon, and steelhead trout abundance all show significant decreases throughout the sampling duration. These trends are most likely similar for salmonid populations in Northern Subbasin streams;
Populations of all three salmonids appeared to decline abruptly following the 1955 and 1964 floods;
Current salmonid populations are not only less abundant, but they are less widely distributed than they were historically:
- Historical and anecdotal accounts in 33 Northern Subbasin streams dating back to the late 1930s indicate the presence of presence of Chinook salmon in 12 tributaries (36% of streams sampled), coho salmon in 12 tributaries (36% of streams sampled), and steelhead trout in 20 tributaries (61% of streams sampled) in the Northern Subbasin;
- Current salmonid distribution, based on data collected in 109 streams from a variety of sources (CDFW, USFS, tribal fisheries monitoring, university research, local watershed stewardship programs, and additional fisheries stakeholders) indicate the presence of Chinook salmon in 14 tributaries (13% of sampled streams), coho salmon in 8 tributaries (7% of sampled streams), and steelhead trout in 23 tributaries (21% of sampled streams) in the Northern Subasin;
Historically and currently, Steelhead trout have been found in more tributaries and in areas further upstream than both Chinook and coho salmon. This is due to their preference for habitats that are located farther inland, in smaller streams than Chinook and coho salmon (Moyle et al. 2008), and due to their comparatively superior jumping abilities;
Non-native Sacramento pikeminnow have been documented in most surveys beginning in the late 1990s and are now common in areas of the mainstem SF Eel River and in lower reaches of tributaries. Pikeminnow compete with and prey upon juvenile salmonids, and are adapted to withstand warmer water temperatures than native salmonids.
What are the current salmonid habitat conditions in the Northern Subbasin? How do these conditions compare to desired conditions?
Flow and Water Quality:
Instream flow has been reduced through unpermitted diversion for residential and marijuana cultivation uses. Reduced flow (compared to historical averages) has been documented in Northern Subbasin streams during the late summer and early fall;
Low summer flows result in dry or intermittent reaches on streams, which may be detrimental or stressful to salmonids;
Water quality is reduced by marijuana cultivation operations, particularly in areas where land use is primarily residential (e.g. Salmon Creek). Water quality is compromised in these areas by the input of fertilizers, pesticides, rodenticides, diesel fuel from generators, and sediment from improperly constructed roads, and clearing and construction activities at grow sites;
Water diversion by industrial timber companies for road dust/sediment control has been estimated at 2,000-4,000 gallons/mile/day between May 15th and October 15th. The amount of water used may be substantial at a time when stream flow is already low, particularly in areas with multiple users with high water demand;
Increased turbidity is stressful to salmonids, especially during the rainy winter months. High levels of turbidity occur during salmon and steelhead spawning season.
Excessive sediment in stream channels has resulted in an overall loss of spawning, rearing and feeding habitat for salmonids. High sediment input from natural and anthropogenic sources have resulted in low suitability pool habitat and reduced water quality, and are particularly apparent in the Bull Creek drainage, but are thought to occur throughout the subbasin;
Road density is high (3.3 miles/square mile) in the Northern Subbasin, and is more than twice as high (7 miles/square mile) in the Salmon Creek drainage. Legacy logging roads and new residential road construction are sources of sediment input into streams throughout the subbasin;
Soils in the Northern Subbasin are prone to erosion, and slides and streambank failures contribute fines to the streams;
During the historic flood events of 1955 and 1964, very large quantities of sediment entered Northern Subbasin streams, and this sediment is still moving through the system;
Increased fine-sediment in stream gravel has been linked to decreased fry emergence, decreased juvenile densities, reduced diversity and abundance of invertebrates, loss of winter carrying capacity, and increased predation (Gucinski et al. 2001).
Riparian Condition/Water Temperature:
Canopy density met or exceeded target values in most surveyed streams in the Northern Subbasin, and values increased over time (using habitat typing data collected during two time periods: 1990-1999, and 2000-2010);
In the 1990s, 55% of the stream length surveyed had canopy densities below 50% and only 19% met target values of 80% or greater. Coniferous canopy cover was relatively low (< 50%) in most streams, especially those creeks that are located outside the boundaries of Humboldt Redwoods State Park. The largest streams in the subbasin, Bull Creek and Salmon Creek, had the lowest coniferous canopy percentages (less than 10%);
In the early 2000s, there was no stream length with less than 50% canopy density, and 51% of surveyed stream length met target values of 80% or greater;
Canopy density suitability was in the highest category in most Northern Subbasin streams in the early 2000s. Suitability was in the lowest category on select reaches of Bull and Salmon creeks, and the second lowest suitability category in very limited areas of Butte, Elk, and Canoe creeks;
The average percent of coniferous vegetation increased and percent open canopy decreased in most streams over time. An exception to this pattern was Elk Creek and its unnamed tributary, which showed significant decreases in coniferous canopy coverage and increases in deciduous cover due to significant timber harvest activity in recent years;
Water temperature data collected by HCRCD (between 1996-2003), and ERRP (in 2012) indicated poor (≥66ºF) conditions at 16 sites, fair (63-65˚F) conditions at 7 sites, and good conditions (50-62˚F) at 7 locations in Northern Subbasin streams. There was one site where lethal (≥75ºF) conditions were recorded, in the mainstem SF Eel River near Miranda;
Bouma-Gregson recorded average daily temperatures above lethal levels (≥75˚F) on 27 days between July and August 2013 in the mainstem SF Eel River at Phillipsville.
None of the surveyed streams met target values for pool depth, and the percent of stream length surveyed that was primary pool habitat was less than 10% in all stream order categories during both habitat sampling periods;
Quality pool structure is lacking in Northern Subbasin streams; the average mean pool shelter rating was 43.0 in the 1990s and 49.4 using habitat data collected between 2000 and 2010. These values are well below the target pool shelter value of 100 for salmonids, although they increased slightly over time;
Boulders were the dominant shelter type, followed by LWD, in Northern Subbasin streams in all subbasin reaches during both time periods;
Pool riffle ratios were below optimal ratios (1:1) in any Northern Subbasin streams, but the percentage of pool habitat relative to riffle habitat increased slightly in recent years (2000-2010) compared to percentages recorded on surveys in the 1990s.
Cobble embeddedness conditions improved in most Northern Subbasin streams over time, with average embeddedness values of 7.8% for data collected in the 1990s and 33.4% for data collected between 2000 and 2010. Although embeddedness values increased, they were still below target values (>50% category 1) during both time periods;
The percent of pool tails surveyed in cobble embeddedness category 1 nearly tripled between the 1990s and early 2000s. The percent of pool tails in category 2 stayed nearly the same, and the percent of pool tails in embeddedness category 3 was reduced by more than 50% between the two time periods. Only categories 1 and 2 are suitable for salmonid spawning;
Low substrate embeddedness suitability for salmonids in Northern Subbasin streams is due to extensive sediment input from highly erosive soils, active landslides, roads, and historical flood events.
Salmonid habitat conditions were generally rated as medium potential refugia, meaning that habitat is degraded or fragmented and salmonids are present but reduced in density and age class representation. Habitat may improve with modified management practices and restoration efforts;
Only Squaw Creek was rated as high quality salmonid habitat in this subbasin. It is the only creek with relatively undisturbed habitat, with conditions necessary to support species diversity and natural production;
Bull Creek was rated as high potential refugia habitat. This watershed currently has diminished but good quality habitat, and may become high quality refugia habitat with current natural resource management practices;
Cuneo, South Fork Cuneo, Salmon, Fish, and Ohman Creeks were all rated low quality. These watersheds have few salmonids and highly impaired riparian and instream habitat. Current conditions and management practices have modified the natural environment extensively, and major changes are required to improve habitat conditions.
Barriers and other concerns:
Both natural (landslides, gradient, and LDA) and anthropogenic (partial and total culvert) barriers were mapped using information from stream inventories, field reconnaissance, and the CalFish Passage Assessment Database;
Most culvert barriers, both total and partial, were located at road crossings along the mainstem SF Eel River, where Highway 101 and smaller roads leading into individual basins cross tributary streams. Two partial culvert barriers were located in the Bull Creek drainage, where the Mattole Road crosses Cow and Harper Creeks;
Five landslide barriers were identified in upper Bull Creek: one each in Cuneo, NF Cuneo, and SF Cuneo Creeks, and two in the Panther Creek drainage. Habitat restoration and evaluation, assessment, and planning projects have been completed at many of these sites to reduce sediment input and stabilize stream banks;
Three LDA barriers were identified in the Bull Creek drainage, in Albee, Harper, and Cow Creeks;
Gradient barriers, mostly waterfalls, were identified in Northern Subbasin streams if they occurred in areas other than natural ends of anadromy in headwater areas. These barriers may be partial (a barrier to certain species or life stages), total, or temporal (only a barrier at certain times of the year), and some form of gradient barrier was identified in most streams in the subbasin.
What are the impacts of geologic, vegetative, fluvial, and other natural processes on watershed and stream conditions?
Natural erosion rates in the Northern Subbasin are high due to:
- All rock types in the SF Eel River Basin are considered lithologically soft, prone to erosion, and sensitive to land use. The major rock type underlying the Northern Subbasin is sandstone of the Yager Terrane, which is made up of moderately erodible fine-grained marine sediments;
- The relatively unstable geology of the subbasin results in many shallow landslides or debris flows, and streams are affected by sediment deposits from steep slopes in tributaries, mainly in upstream areas such as Cuneo Creek in the Bull Creek drainage;
- The Northern Subbasin is located in one of the most seismically active regions in North America, and fault movement can result in uplift or subsidence of the local landscape, increasing the potential for erosion or deposition;
Floods periodically occur due to high winter precipitation levels and high runoff rates;
During the rainy season, heavily silted water flows from steep upstream terrain, downstream to lower reaches, increasing turbidity and sediment levels throughout Subbasin streams;
The predominant vegetation type is mixed conifer and hardwood forest, covering 55% of the Subbasin area. The average percent deciduous canopy was greater than coniferous canopy in surveyed streams, but the percent coniferous canopy increased between the late 1990s (18%) and early 2000s (30%).
How has land use affected these natural processes?
Changes in basin due to land use:
Most (52%) of the land in the Northern Subbasin is owned by the CA State Parks; acquisition occurred between 1920s and 1970s, and the Humboldt Redwoods State Park now includes all of the land in the Bull and Canoe Creek drainages. Historically, timber harvest was the primary land use in these watersheds. Since the Park acquired the property, management actions have prioritized forest habitat preservation and fisheries habitat management;
In the Salmon Creek drainage, the primary land use is residential, and there has been a substantial increase in the number of marijuana cultivation operations in this watershed. In 2012, there were 567 grows (281 outdoor and 286 indoor) identified in this drainage alone, with an estimated 18 million gallons of water per growing season required to support these operations (Easthouse 2013). Water sources include direct diversion from streams, groundwater wells, and storage tanks, but little is known regarding how much water is supplied by each source;
Sediment input from land use activities, primarily roads and timber harvest, is particularly problematic in this subbasin due to highly erodible soils and active landslides.
Possible effects seen in stream conditions:
Instream habitat conditions for salmonids are thought to be poor:
Low summer flows are exacerbated by diversions, which result in dry or intermittent reaches on streams, which are stressful to salmonids;
In addition to low flows, water quality (temperature, pollution, turbidity) decreases in areas with high instream diversion and input of fertilizers, chemicals, sediment, and waste from grow operations, resulting in decreased habitat suitability for salmonids;
Excessive sediment in stream channels has resulted in an overall loss of spawning, rearing, and feeding habitat for salmonids. Sediment input from both natural and anthropogenic sources are high, with correspondingly high turbidity levels which are stressful for salmonids. Substrate embeddedness values were high in most surveyed reaches, but have shown significant improvement over time;
None of the surveyed streams met target values for pool depth or pool shelter;
Boulders were the dominant shelter type in pools, followed by LWD. Average percent shelter from LWD was less than 5% for both sampling periods;
Pool:riffle ratios were well below optimal (1:1) ratios
Erosion related to timber harvest on unstable soils is a concern:
Industrial timber harvest occurred in most areas in the subbasin prior to the 1960s, when the CA State Park system purchased the last of the land in the northern part of the subbasin (including almost all of the Bull Creek drainage). Landslides are abundant in upper Bull Creek, and large amounts of sediment are constantly entering streams from natural sources. Historically, additional sediment entered the streams from timber harvest and related activities such as road building;
Timber harvest, while less of an issue than in the past, still occurred in the headwaters of all of the creeks (located outside the State Park boundary) in this subbasin from 1991 to 2013. Erosion related to timber harvest is a concern throughout the subbasin due to highly erosive soils, active tectonics contributing to unstable slopes, and heavy rains received during winter months;
Timber harvest impacts were magnified by the 1955 and 1964 floods, and sediment pulses from historic land use practices and floods are still moving through Northern Subbasin streams;
Based upon these conditions trends, and relationships, are there elements that could be considered to be limiting factors for salmonid production?
Based on available information for this subbasin, it appears that salmonid populations are limited by:
Low summer flows;
High summer water temperatures;
High levels of fine sediments in streams;
Loss of habitat area and complexity, particularly primary pool habitat and pool shelter;
Competition with and predation pressure from Sacramento pikeminnow.
What watershed and habitat improvement activities would most likely lead toward more desirable conditions in a timely, cost effective manner?
Restoration activities that will create additional pool habitat and scour existing shallow pools, while reducing input from surrounding hillsides, are highly recommended throughout this subbasin;
More than half of all habitat recommendations targeted instream habitat, including pool and cover categories. Most other recommendations targeted riparian habitat/water temperatures (canopy and temperature) and erosion/sediment (related to streambanks and roads);
Ensure that water diversions used for domestic or irrigation purposes bypass sufficient flows to maintain all needs of fishery resources;
Identify areas where marijuana cultivation is occurring and quantify environmental effects at sites, including illegal diversions (especially during low flow times), input of pesticides and other pollutants, and sediment loading from these practices. Enforce existing and developing environmental regulations;
Support ongoing efforts by timber harvest review agencies to quantify water usage by industrial timber companies for road dust abatement, and support actions designed to encourage efficient use of water;
Carefully modify log debris accumulations in tributaries over time, with attention paid to resultant downstream sediment loading;
Conduct an upslope erosion inventory in order to identify and map stream bank and road-related sediment sources. Sites should be prioritized and improved;
Stabilize eroding stream banks with appropriately designed structures and vegetation;
Increase depth, area or shelter complexity in pools, by adding LWD or combinations of boulders and LWD. This must be done where banks are stable, or in conjunction with stream bank armor to prevent erosion;
Consider replanting of native species, like willow, alder, redwood and Douglas fir in areas with little or no native vegetation, or in areas with non-native vegetation;
Consider thinning hardwoods to increase growth of conifers where riparian forest is strongly dominated by hardwoods and shade canopy will not be adversely affected;
Monitor streams near land development activities and existing rural residential areas for turbidity, pollution, and drainage issues;
Conduct biological sampling to determine salmonid usage and populations, including but not limited to the continuation of current CDFW redd counts and establishment and operation of a life cycle monitoring station within the SF Eel River Basin;
Consistently collect water quality data, including temperature, dissolved oxygen, and water chemistry throughout the year for several years in order to accurately characterize conditions;
Regular use of prescribed fire could reduce fuels so that catastrophic fires are less likely to occur. The CA State Parks system already has a prescribed burning program in place in the northern part of the subbasin;
Support programs and organizations such as SRF and ERRP that develop studies to monitor the flow, temperature, diversion, and water quality of streams throughout the subbasin, particularly in developed areas.