Sediment, temperature, pool habitat, escape and ambush cover, and substrate embeddedness in the estuary are thought to be outside of supportive levels for salmonids in the estuary

Predation upon depressed fish populations by birds and mammals in the estuary;

Excessive extraction of water during low flow periods;

Artificial fish passage barriers exist at some road crossings of streams;

Abandoned roads, new road construction, and road maintenance issues related to landsliding and sediment input to streams;

High water temperatures;

Pollutant spills, such as some recent bulk diesel spills into tributaries;

Herbicides used on industrial timberlands;

Location and conduct of timber harvest operations;

Sub-division development and construction;

Low stream habitat diversity and complexity;

Low stream shade canopy cover;

Large woody debris recruitment to streams;

Absence of salmonid information, low fish densities, or absences of fish;

Access for agency personnel to private land for field studies.

Findings Related to Issues

What are the history and trends of the sizes, distribution, and relative health and diversity of salmonid populations in the Mattole Basin?

Historical accounts and stream surveys conducted in the 1960s by CDFG indicate that the Mattole Basin historically supported relatively robust populations of Chinook salmon, coho salmon, and steelhead trout. Fishery surveys have been conducted on many tributaries throughout the Mattole Basin in the last ten years. These biological stream surveys indicate the presence of Chinook salmon and steelhead trout in all five Mattole subbasins and the presence of coho salmon in the Eastern, Southern, and Western Subbasins. Coho salmon also utilize the Estuary Subbasin on their migrations; however, in limited surveys conducted in the Northern Subbasin since the 1980s, coho salmon have not been detected. No studies have been conducted to estimate subbasin or tributary specific population levels of coho salmon or Chinook salmon. However, a nine-year intensive study of three tributaries within the Northern Subbasin indicated stable age classes of steelhead trout. Intensive studies of the Estuary Subbasin have shown depressed populations of over-summering Chinook salmon and steelhead trout, and no coho have been detected. Mattole Basin-wide population estimates indicate depressed meta-populations of Chinook and coho salmon. A metapopulation is a “regional (Mattole Basin) population consisting of semi-isolated local (stream/subbasin) populations” (Levins 1970).

What are the current salmonid habitat conditions in the Mattole Basin? How do these conditions compare to desired conditions?

Instream sedimentation in several stream reaches throughout the basin may be approaching or exceeding levels considered unsuitable for salmonid populations. Currently, the estuary is very shallow and lacks channel complexity. Erosion/sediment reduction is the top recommendation category for the Eastern and Estuary subbasins;

Riparian/Water Temperature
High summer water temperatures in many surveyed tributaries are deleterious to summer rearing salmonid populations in the Estuary, Northern, Eastern, and Western Subbasins. Riparian/water temperature improvements is the top recommendation category in the Northern Subbasin;

Instream Habitat
In general, pool habitat, escape and ambush cover, and water depth are unsuitable for salmonids in many mainstem and tributary stream reaches in the Mattole Basin. In the Southern Subbasin summer flow is inadequate or non-existent in many reaches. Large woody debris recruitment potential is poor in the Northern, Eastern, and Western subbasins. Instream habitat improvement is the top recommendation category in the Southern and Western subbasins;

Available data from sampled streams suggest that suitable, high quality spawning gravel for salmonids is limited in some streams in all subbasins;

Refugia Areas
Salmonid habitat conditions in the Mattole Basin are generally best in the Southern and Western Subbasins, mixed in the Eastern Subbasin, and worst in the Estuary and Northern subbasins.

This table summarizes subbasin salmonid refugia conditions in the Mattole Basin:

Subbasin salmonid refugia conditions
Ratings in this table are done on a sliding scale from best to worst. Subbasin refugia ratings are aggregated from their tributary ratings.

What are the relationships of geologic, vegetative, and fluvial processes to natural events and land use history?

Geologic units within the basin can be grouped into one of three bedrock terrains (hard, moderate, and soft) and one for Quaternary alluvial units. Larger landslides are more prevalent in soft terrain and are typically earthflows, while smaller slides, typically debris slides, are more prevalent in hard and moderate terrains;

Weak geologic materials, steep slopes, high rainfall, and strong earthquakes common to the basin result in high rates of natural landsliding and surface erosion, particularly in soft terrain. These natural processes can be exacerbated by human land use within the basin. About one half of the basin is considered to have a high to very high landslide potential;

In general, the subbasins can be ranked in terms of relative impacts with geologically unstable areas linked to adverse stream effects. The Northern Subbasin has the largest proportion of geologically unstable (soft) terrain, which is linked to the highest amount of historically active landslides, gullies, and stream features indicative of excess sediment production, transport, and storage. The Southern Subbasin has the lowest proportion of geologically unstable terrain, historically active landslides, gullies, and stream features indicative of excess sediment production and transport. The Eastern and Western Subbasins are intermediate between these two extremes due to the variability in the proportion of soft terrain and steep slopes;

Source and transport reaches of the blue line streams as depicted on NCWAP stream network maps, were identified primarily in bedrock terrains, while response (depositional) reaches were identified in the Quaternary (alluvial) unit reaches. Features indicative of excess sediment production, transport, and storage have decreased throughout most of the basin in the period between 1984 and 2000. The reduction in these features was greatest in the hard terrain. The distribution of these features in bedrock terrains suggests that portions of the areas interpreted as having a high to very high landslide potential are also the sources of sediment that has been delivered to streams;

Human activities such as timberland conversion to grasslands and brush, grazing, timber harvest, and road construction and use, have interacted with natural geologic instability to increase sediment production above naturally high background levels. Historic timber harvesting and streamside road construction reduced riparian canopy and increased direct sediment inputs and water temperature. Overall, the current landscape is comprised of smaller diameter forest stands than in pre-European times. Decades of fire suppression have created dense forest stands and brush-lands leading to the designation of Mattole Basin population centers as high wildfire threat areas.

How has land use affected these natural processes?

Land use, including road construction and use, timber harvesting, and grazing, have added excess sediment to the fluvial system. Many of the effects from these activities are spatially and temporally removed from their upland sources. Excess sediment remains in the Mattole mainstem despite decades of low timber harvesting activity;

Currently, roads are a major land use contributor of sediment (CDF, 2002). Large storms or other catastrophic events combined with poor road location and construction practices have the potential to deliver large and adverse amounts of sediment into stream systems;

Water extraction for agriculture, road maintenance, and residential use has the direct effect of reducing the amount of available habitat for fish;

Large woody debris recruitment potential is limited by the low percentage of near-stream forest stands containing trees in large diameter classes;

Grazing is widespread on privately owned grasslands and has shifted to cattle from sheep since the enactment of predation protection measures. Stock impacts to streams are not widespread, but watercourse exclusionary fencing is limited.

Based upon these conditions trends, and relationships, are there elements that could be considered to be limiting factors for salmon and steelhead production?

Based on available information for the Mattole Basin, the NCWAP team believes that salmonid populations are currently being limited by:

Impacted estuarine conditions;

General basin-wide lack of habitat complexity;

High instream sediment levels;

High summer water temperatures;

Reduced basin-wide coho and Chinook meta-populations.


Flow and Water Quality Improvement Activities:

Discourage unnecessary and wasteful use of water during summer low flow periods to improve stream surface flows and fish habitat, especially in the Southern Subbasin;

Increase the use of water storage and catchments systems that collect rainwater in the winter for use in the drier summer season;

Support local efforts to educate landowners about water storage and catchments systems, and find ways to support and subsidize development of these systems;

Support and expand ongoing local efforts that monitor summer water and air temperatures on a continuous 24-hour basis to detect long-range trends and short-term effects on the aquatic/riparian community;

Support efforts to determine the role of sediment in the mainstem Mattole River in elevated estuarine water temperatures.

Erosion and Sediment Delivery Reduction Activities:

Reduce sediment deposition to the estuary by supporting a basin-wide road and erosion assessment/control program such as the Mattole Restoration Council’s Good Roads, Clear Creeks effort. Continue to conduct and implement road and erosion assessments such as the ongoing efforts in the Dry and Westlund planning watersheds in the Eastern Subbasin. Expand road assessment efforts because of the potential for further sediment delivery from active and abandoned roads, many of which are in close proximity to stream channels, especially in the Bridge and Thompson planning watersheds in the Southern Subbasin;

Establish monitoring stations and train local personnel to track in-channel sediment and aggraded reaches throughout the basin and especially in the North Fork Mattole and the Upper North Fork Mattole rivers, Mattole Canyon, Blue Slide, Squaw, Honeydew, and Bear creeks;

Consider the nature and extent of naturally occurring unstable geologic terrain, landslides and landslide potential (especially Categories 4 and 5, page 89) when planning potential projects in the subbasin;

At stream bank erosion sites, encourage cooperative efforts to reduce sediment yield to streams. CGS mapping indicates eroding banks are not a significant basin wide issue, but may be of localized importance. They occur in isolated, relatively short reaches distributed throughout the Mattole Basin;

Based on the high incidence of unstable slopes in the Northern Subbasin, any future sub-division development proposals should be based on an existing county-imposed forty acre minimum parcel sub-division ordinances;

Encourage the use of appropriate Best Management Practices for all land use and development activities to minimize erosion and sediment delivery to streams. For example, low impact yarding systems should be used in timber harvest operations on steep and unstable slopes to reduce soil compaction, surface disturbance, and resultant sediment yield.

Riparian and Habitat Improvement Activities:

Where current canopy is inadequate and site conditions, including geology, are appropriate, initiate tree planting and other vegetation management to hasten the development of denser and more extensive riparian canopy, especially in the Northern Subbasin;

Landowners and managers in the Northern and Western subbasins should work to add more large organic debris and shelter structures to streams in order to improve channel structure, channel function, habitat complexity, and habitat diversity for salmonids;

Ensure that stream reaches with high quality habitat in the Mattole Basin are protected from degradation. This is especially important in the Southern Subbasin. The best stream conditions as evaluated by the stream reach EMDS were found in the South Fork of Vanauken Creek, Mill Creek - at Mattole river-mile 56.2 (RM 56.2), Stanley Creek, Thompson Creek, Yew Creek, and Lost Man Creek Tributary in the Southern Subbasin, and in Harrow Creek in the Eastern Subbasin. Refugia investigation criteria, which include biological parameters, indicated Bear Creek was the best stream evaluated in the Mattole Basin.

Supplemental Fish Rescue and Rearing Activities:

Since 1982 a successful cooperative salmonid rearing facility in the Mattole Basin headwaters has been operated by the Mattole Salmon Group (MSG) and CDFG. They also operate a Chinook juvenile out-migrant rescue rearing program near the estuary, which released 2,400 coded-wire-tagged Chinook sub-yearlings in October 2002. These programs should be continued as needed to supplement wild populations while the improvements from long-term watershed and stream restoration efforts develop;

Initiate a systematic program to monitor the effectiveness of fish rescue and rearing activities, and determine the need for the continuance of cooperative, supplemental fish rearing efforts;

Update as scheduled the MSG/CDFG five-year plan that provides guidance to the cooperative rearing and rescue projects. Base the periodic plan updates on the findings of the effectiveness monitoring program and best available science.

Education, Research, and Monitoring Activities:

Utilize Humboldt State University studies conducted in the early 1990s as baseline information to periodically monitor trends in estuarine conditions and fish production;

Encourage ongoing stream inventories and fishery surveys of tributaries throughout the Mattole Basin, especially in the Northern Subbasin;

In order to protect privacy while developing data, the possibility of training local landowners to survey their own streams and to conduct salmonid population status surveys throughout the basin would be advisable;

Further study to investigate the affects to water quality from timberland herbicide use is recommended;

Follow the procedures and guidelines outlined by NCRWQCB to protect water quality from ground applications of pesticides;

Encourage appropriate chemical transportation and storage practices as well as early spill reporting and clean-up procedures;

Conduct training as needed and desired to assist landowners, managers, consultants, and other interested parties in the construction and appropriate application of landslide occurrence and potential maps from GIS analysis.