Effects of Habitat Manipulation on Coldwater Fisheries and Salmonids

Effects of Habitat Manipulation on Coldwater Fisheries and Salmonids

Matthew S. Varner

West Virginia University

Wildlife and Fisheries Department

Morgantown, WV 26505

EFFECTS OF HABITAT MANIPULATION ON COLDWATER FISHERIES AND SALMONIDS

MATTHEW S. VARNER

Wildlife and Fisheries Department, West Virginia University, West Virginia 26505 USA

Abstract. Stream and river restoration projects for salmonid population enhancement have been conducted for nearly 70 years. These projects have stemmed from the increases of negative impacts on water systems causing large declines in salmonid populations. Salmonids are susceptible to increases in water pollution, sedimentation, water temperature, and various forms of habitat loss. The intolerance of salmonids to negative habitat changes have caused a great interest in the protection of critical habitat, creation of new habitat, and the lessening of impacts on water systems. To preserve salmonids, watersheds must be protected and projects to restore impacted watersheds need to be developed. A popular method for enhancing streams is by manipulating habitat to better suit salmonids. This method can greatly benefit salmonid populations if done correctly. Prevention of negative habitat impacts and increased positive habitat manipulations need to be utilized to continue the survival of salmonids in the future.

Key Words: anadromous; salmonid; habitat; habitat manipulation

:INTRODUCTION

Trout are barometers of stream health…where they thrive, the water runs clean, cold, and oxygen rich (Newman 1996). Coldwater fisheries support a range of fish families and species. The salmonid family is divided into three subfamilies: Coregoninae, Thymallinae, and Salmoninae (Jenkins and Burkhead 2000). Of these subfamilies the Salmoninae group will be the focus of this paper. This subfamily contains brown trout (Salmo trutta), brook trout (Salvelinus fontilanis), rainbow trout (Onchorhynchus mykiss), cutthroat trout (Salmo clarki), Atlantic salmon(Salmo salar ), and others. Throughout this paper I will refer to them under the general title of salmonids. High interest in salmonid research is due to their mystique as sport fish combined with their value in commercial fisheries and aquaculture (Moyle and Cech 2000). Salmon and trout require cold water of high quality, preferably flowing through relatively undisturbed watersheds (Moyle and Cech 2000). Increasingly, such habitats aren’t available. Due to hatchery restocking programs, salmonid populations have been able to continue despite massive habitat impacts (Moyle and Cech 2000). Some impacts facing salmonids include: habitat loss, sedimentation, urban runoff, agricultural runoff, loss of canopy cover, increases in water temperature, stream bank degradation, acid precipitation, and acid mine drainage. Negative and positive habitat manipulations will be the focus of this paper. Negative manipulations are often simply the loss of habitat by urban sprawl, timber practices, and agriculture. Positive habitat manipulations are generally the result of well-designed restoration efforts.

By first examining the salmonid life history and effects of habitat manipulations at various stages, I will establish the need for stream restoration. Secondly, I’ll probe the forms of habitat manipulation, its contributors, and the individual effect each aspect has on salmonids. Lastly, I will summarize efforts being conducted and the monetary values associated with them.

DISCUSSION

Most species of salmonids are anadromous or are derived from anadromous forms. Nonanadromous forms have evolved from anadromous fish populations, which over time have become trapped above new barriers or otherwise find it evolutionarily advantageous not to go to sea (Moyle and Cech 2000). While anadromy is not a universal feature of the salmonids, most species do undertake spawning migrations and possess a series of distinctive life-history stages (Moyle and Cech 2000). The age at which fish reach sexual maturity varies; Schlosser (1990) noted that in headwater streams species generally mature by age 2. Once salmonids reach sexual maturity reproductive patterns can vary within species. Jenkins and Burkhead (1993) note that salmonid reproductive patterns range from egg scattering to nest building to stereo-typed ritual. They also noted that most salmonids exhibit a pre-spawning movement toward upstream reaches. One possible reason for headwater spawning by salmonids relates to substrate size. Another reason may be that headwater areas have low current velocity, therefore the spring flows would have less scouring ability on the nest and also lower sedimentation. Another possible reason may be that fry have increased survival rates in headwater areas due to the decreased number of aquatic predators. Nevertheless, salmonids migrate to upstream areas and spawn once a suitable site is located. Salmonids prefer to spawn in gravel substrates with current downwelling , which allows for the removal of waste and maintenance of high oxygen levels within the redd. Salmonids also require low sediment conditions, since they are susceptible to suffocation. Thus areas utilized for spawning occur at the head of riffles or at the tail of a pool. Incubation periods vary depending on temperature, but typically range from 1-2 months in their southern range and up to 9 months in their northern range (Jenkins and Burkhead 1993). Once hatched, fry utilize channel edges as nursery areas (Johnson et al. 1994). Bisson et al. (1982) stated that fish require different physical habitats, spatial heterogeneity and the connectivity of habitat patches for the completion of their life cycles. Schlosser (1995) showed that fish require refugia from unfavorable conditions or predators, spawning habitat, and feeding habitats with optimum growth conditions. These habitat linkages consist of a variety of water depths, velocities, and forms of cover and are a result of a watershed’s climate, geology, and vegetation (Hunter 1991). Climate dictates the amount and distribution of precipitation in a watershed, which at length affect the runoff entered into a river. The geology of a basin determines what shape and flow patterns a stream will experience. Vegetation is dependent upon both the geology of an area and its climate (Hunter 1991). Vegetation allows runoff to slow and absorb into the soil, thus lessening sedimentation into streams. Beasley (1985) stated soil erosion and sedimentation rates are low in areas of dense vegetation (<2% bare soil). Darby (1999) noted that vegetation also strengthens bank materials by buttressing and root reinforcement. Gravity and friction are the main factors in a stream flow’s velocity. Gravity causes water velocities to increase whereas friction in the streambed acts to resist flow. A stream’s gradient, physical habitat composition, vegetation, curvature, and flow obstructions all influence flow, which in turn influence habitat (Hunter 1991). Energy sources and water quality also influence habitat (Orth 1993). Orth noted that “habitat for fish is a place--or for migratory fishes, a set of places--in which a fish , a fish population, or a fish assemblage can find the physical and chemical features needed for life, such as suitable water quality, migration routes, spawning grounds, feeding sites, resting sites, and shelter from enemies and adverse weather” (Orth 1993). Hunter (1991) stated that in-stream habitat is made up of many components, which include pools, riffles, complexes, cover via aquatic vegetation, woody debris, undercut banks, overhanging vegetation, water temperature, and discharge. In a study conducted by Kershner, he noted that most age classes of rainbow trout utilize lateral scour pools, which occur when flow veers against a channel bank. Kershner also noted that the fry utilized all available forms of habitat, especially the riffle and step/run regions (Hunter 1991). Woody debris, especially large woody debris(LWD), plays an important role in trout habitat and survival. LWD creates increased total cover, pool volume, mean depth, and percentage of fine substrate (Gowan and Fausch 1996). Merritt and Cummings distinguished that woody debris “…provides a significant portion of stable habitat for insects”, which is the major energy source for salmonids (Merritt and Cummings 2000).

Cover signifies an important aspect of a trout’s life. Cover yields security and visual isolation, which is critical to the survival of young salmonids (Hunter 1991). In a study conducted by M. Gary Wickham (1967), he observed albino brook trout and cover utilization. He noted that the brook trout spent 94% of their time utilizing cover provided by large boulders, LWD, and turbulent surface waters (Hunter 1991). In a study on the advantages of fish in shade, Helfman (1981) showed that fish utilize overhead cover( i.e. undercut banks, LWD, vegetation) since the sunlit viewer has impeded vision of a shade veiled target and a sunlit viewer has a raised contrast perception threshold and therefore has difficulty responding to a shaded target. This alludes to the necessity of cover to trout not only for protection from avian predators, but also aquatic predators. Adult brown trout, which are commonly piscivores, were shown by Young (1995) to select bank-associated habitats. Young also showed that the brown trout preferred overhead cover when selecting habitat. Kershner et al. (1997) noted that in Colorado River cutthroat trout (Onchorhynchus clarki pleuriticus) the population of adults was 2.5 times greater in areas with undercut banks. Thus the utilization of overhead cover may correlate with the trout’s ability to ambush prey. It may also provide the necessary cover for a trout to mature and survive in the aquatic biota.

Water temperature is a critical factor in accessing salmonid habitat. Trout growth is maximized at various temperatures depending upon individual species (Moyle and Cech 2000). Brook trout prefer temperatures around 5-19 C, brown trout 12-20 C, and rainbow trout 12-19 C ( Jenkins and Berkhead 1993). Temperature is effected by ground water, surface exposure to solar radiation, and volume of water being heated (Schlosser 1990). Brown and Krygier (1970) determined that canopy cover is the principle factor in elevated stream temperatures. Platts and Nelson (1989) indicated that thermal inputs and salmonid biomass are directly correlated. Therefore, streams that are shielded from increased solar inputs often have increased trout biomass.

Anthropogenic forces have decreased salmonid habitat in much of their range. A few of these forces include logging practices, agriculture, dam mitigation, and urban sprawl. Generally these practices impact one or more aspects of in-stream cover. For instance, early logging practices often used explosives to remove obstructions in stream channels to permit the floatation of trees downstream to sawmills. They also dammed streams to accumulate enough water to float logs downstream to sawmills. After enough water had been amassed the dam was blown up, which caused a massive amount of water, debris, and logs to flow downstream thereby devastating the stream channel in its path (Hunter 1991).

Agricultural practices are common factors in the loss of salmonid habitat. Naiman and Rogers (1997) noted “…large animals can significantly modify the structure (channel geomorphology, vegetative characteristics, and biodiversity) and function (productivity, connectivity, and resistance and resilience to disturbance) of river corridors. Further, Naiman and Rogers (1997) noted that it might have long-term ecosystem-level consequences. The consequences of modified structure and function of water systems include increased sediment loads, which inhibit salmonid spawning success and increased temperatures, which can cause salmonid die-offs. In addition, agricultural practices also contribute runoff via irrigation ditches, which not only increase sediment input but also increase nutrient loads in streams. These increased nutrient amounts can lead to increases in algae blooms. These blooms can cause anoxic conditions via respiration and organic breakdown, thus contributing to the occurrence of fish kills in all salmonid life stages. Excessive algae blooms can also lead to decreased stream visibility, thereby inhibiting the ability of salmonids to capture prey.

“Urbanization” occurs when an area’s land cover and hydrology are fundamentally altered by humans and further occupied in large numbers (Moses and Morris 1998). Areas covered by roads, rooftops, etc. can cause massive amounts of runoff which lead to increased sedimentation, peak flows, and channel straightening. These problems further lead to flooding in the spring and very low velocities in the summer months, due to the lack of groundwater recharge through impervious structures (Moses and Morris 1998). Another effect of urbanization is the construction of hydroelectric dams. Today, many of these dams have become out-dated and serve only to block fish migrations, thus they have deleterious effects on anadromous fish stocks (Orth 1996). All of these habitat influences negatively affect salmonids, yet many habitat manipulations have positive effects on salmonid populations.

Positive habitat manipulations include stream bank stabilization, log drop structures, small dams, deflectors, cover structures, and stream fences (Hunter 1991). Wu et al. (2000) showed that stream banks with stable vegetation increased amounts of trout per square mile compared to those with low amounts of vegetation. They also showed that with large vegetation increases on sparsely vegetated banks, trout populations increased 40-60%. Stream bank stabilization can range from the addition of rip-rap or brush bundles to tree planting (Hunter 1991). Soil bioengineering methods, which utilize living plant materials, can also be used in stream bank stabilization projects (Akridge, et al. 1999). Thus utilizing native plant species that thrive along streams, salmonids are able to benefit in many ways. Akridge et al. (1999) noted that native “stream bank” species develop deep roots, which help hold the stream bank in place, thereby limiting sedimentation. They also found that stream bank vegetation offers water cooling shade to a stream and its foliage slows precipitation runoff, thus reducing stress on the stream bank and reducing thermal inputs. Log drop structures are built to mimic the function and structure of LWD. Log drop structures help increase total cover, pool volume, mean depth, and the percentage of fine substrate (Gowan and Fausch 1996). During a study on long-term demographic responses of trout populations to habitat manipulation in Colorado streams, Gowan and Fausch (1996) observed that in the areas supplemented with log drop structures the number of adult trout and overall trout biomass increased. Gowan and Fausch (1996) also noted that immigration was the primary factor in adult trout increases in the treatment areas, since once a trout encountered a newly formed pool it tended to remain there. Another method utilized in habitat restoration is the use of deflectors. Deflectors are used to force the stream into a more meandering pattern and to create pools (Hunter 1991). Gowan and Fausch (1996) noted that current deflectors reduce wetted area and fine sediment and concentrate flow. White and Brynildson (1967) noted that deflectors are the best all around devices for restoring or enhancing low-gradient stream channels. They also noted two important guidelines for deflector implementation: 1) the deflector should direct the current, not block it; and 2) deflectors shouldn’t have any projections, which may cause debris accumulation, and should be built of a low profile. Dams built of a low profile are also used in stream enhancement projects. They function much like log drop structures creating increased pool habitat, reduced velocity, and resting areas. Two types of dams commonly used are wedge dams and K-dams. Two logs connected at the ends forming a “V” shape create wedge dams. The apex of the “V” is then placed in the stream facing upcurrent and butts of the logs are secured into the bed. The structure is reinforced with gravel, rebar, and other rip-rap, thereby creating a deep scour pool down stream of the apex. The K-dam is similar to a wedge dam and log drop structure, but it requires more extensive excavation and is more prone to wash outs (Hunter 1991). Small dams are often very useful in habitat formation, but large dams can be very harmful to anadromous fish. To counteract the effects of large dams, fishways are constructed to help link fish with critical spawning ground. Fishways downstream aren’t as successful as upstream fishways. The downstream fishways cause a 10% mortality rate in young-of-the-year (YOY) salmonids and >50% mortality in adults which utilize the passage through the dam (Orth 1993). To help decrease fish mortality, diversion screens and tunnel lighting to guide the fish are installed within fishways, yet efforts have yielded little improvement in mortality rates. Oftentimes when YOY fish pass through the dam they are released in a downstream pool only to be quickly consumed by predatory fish. To inhibit the increased mortality resulting from predation, the Bonneville Dam on the Columbia River has installed a bypass flume system that releases fish in various outputs stationed below the dam. Overall, this system is predicted to increase juvenile survival 8-18% (Helwig et al. 1999). Yet, the best solution for blocked migration routes of salmonids is to remove barriers, which impede their movements. Many organizations are working to remove dams that are no longer in use, especially those found within watersheds with anadromous populations. Another aspect of useful habitat modifications is a streamside fence, which prevent livestock from damaging the streambed and bank vegetation. Many forms of fencing can be utilized such as barbed wire, split rail, and electric fencing; barbed wire being the most commonly utilized method. Livestock watering-accesses should have bank and streambed reinforcement via railroad ties or another planking material and flood gates to prevent down/upstream movements of the livestock. Placement of rip-rap above and below the planking helps stabilize the structure, thus preventing washouts during high water events (Hunter 1991). Another method for habitat enhancement is the use of cover structures, such as trees, large boulders, and root wads. The cover structures can be placed in streams to create salmonid habitat (Hunter 1991). These “natural” structures also serve as habitat for macroinvertebrates and are aesthetically pleasing. Taking trees and placing them into a streambed by driving the sharpened limbs into the substrate create “Porcupines”. The remaining limbs stick up to collect substrate and debris (Owens 1994). Trout Unlimited groups often implement these structures, which serve to not only provide cover but they also help restore a streams meander.