Managing Northern Pike at Lake Davis: A Plan for Y2000

MANAGING NORTHERN PIKE
AT LAKE DAVIS:
A PLAN FOR 2000

SAVE LAKE DAVIS TASK FORCE STEERING COMMITTEE
AND
THE DEPARTMENT OF FISH AND GAME

JANUARY 2000

NOTE TO READER: This document is the product of extensive work by the Steering Committee of the Save Lake Davis Task Force to identify possible strategies for dealing with the Northern Pike problem at Lake Davis. When a management plan is proposed for adoption, the Department and other government agencies as appropriate, will take the steps necessary to comply with the various permitting and environmental review requirements that govern the project.

Director's Foreword

This document, Managing Northern Pike at Lake Davis: A Plan for Y2000, reflects the cooperative efforts of a number of committed individuals from the local community of Portola as well as from city, county and state agencies. The plan that has emerged from this collaboration represents a coming together to meet the challenges posed by a difficult problem -- adequate management and containment of northern pike in Lake Davis.

The California Department of Fish and Game is strongly committed to controlling and containing northern pike at Lake Davis. This effort is a top priority item of the Department and our commitment is steadfast and long-term. Implementation activities will be headquartered at Lake Davis. As part of the Department's commitment, enforcement presence at the lake will be increased and public education efforts will be stepped up. Additional safety measures at the Grizzly Valley Dam will be pursued to preclude the escape of pike.

The Department's overriding consideration is the prevention of the kind of pike population explosion that previously occurred at Lake Davis. This possibility has lead to an exhaustive search of potential long-term solutions to the problem. All of the parties involved in developing a solution to this problem must continue to work together and think "outside the box". We must be ready to take advantage of whatever weaknesses are found in the pike's "armor". Our success hinges on being ready to act together when and if opportunities present themselves.

I want to personally thank everyone who has given his or her time, talent and expertise to this project thus far. We have reached a critical point in our journey towards finding a way to deal with this critical problem. We would not be here if it were not for our joint commitment to work together.

Community Foreward

Managing Northern Pike at Lake Davis: A Plan for Y2000 is a major part of nearly two and a half years of work by a group of local citizens, City of Portola, County of Plumas, and California Departments of Fish and Game, Water Resources, and Health Services. It represents the process of hammering swords into plowshares. The document is the first product that truly represents the cooperation and changes in a group of individuals who began this campaign with conflicting, seemingly insoluble differences. We hope it sets the standard of agency/community cooperation for the future, not only between the Department of Fish and Game and the communities of eastern Plumas County, but for all agencies and communities in the State.

The plan outlines the activities suggested by the widest possible source: An involved and concerned public. Each suggestion, either written or recorded, was reviewed and reviewed again. If it had practical merit which would help reduce, control, eradicate, or prevent further spread of northern pike, the suggestion remains a part of the plan. If the idea had merit, but needed further research or information, it remains in a study mode. If the idea was deemed harmful to drinking water, public health or safety, economic wellbeing of the local area, or was not determined by a team of experts to affect control or eradication of northern pike, it was put on the scrap heap, but not buried. Impractical or unworkable ideas were left out of today's design because time will not stand still, but as history has proved repeatedly, changing conditions provide new opportunities for ideas once thought to be ineffectual or unusable. We need t act quickly against the invader species and with as much force as we can muster, given the limitations we have placed on ourselves to maintain the high standards of our community and State.

As the administration changed in State government, so did the political attitude toward our community. Scientists were no longer isolated from their recommendations, State field workers were no longer fearful of working in an abjectly hostile environment, and most importantly, citizens were asked for their opinions in a truly meaningful way. The plan that follows details the first steps of a determined effort of cooperation to secure our local values and provide for containment of a possibly disastrous invasion of a truly predatory species capable of serious destruction to our own supreme fishery as well as valuable assets downstream. We have learned over the past two and a half years that there is only one tool that will contain, control and eventually eliminate this threat. That tool is the cooperation and support of us all for a single, unified plan.

Our best wishes to Director Hight and his team for their patience and expertise and willingness to listen. Through their responsiveness to our concern, they will truly serve us all.

Managing Northern Pike at Lake Davis: A Plan for Y2000 describes 12 recommended containment and control actions to be implemented during Y2000 as a way to manage the pike problem at Lake Davis. The plan also describes the monitoring program that would be undertaken in order to measure the plan's success and provide opportunities to make informed course corrections should they be needed. While the plan has been designed to be non-technical and readily understood by a broad audience, it does contain selected references in order to provide more detailed background information for those who desire it. Two appendices are also included in the report: the Steering Committee's preliminary feasibility analysis of alternatives, and a brief review of the life history and biology of the northern pike.

The primary strategies outlined in this plan for Y2000 are: 1) To suppress the pike population at Lake Davis; 2) To contain the existing population in Lake Davis and prevent it from spreading into other parts of the state's waterways; and 3) To remove as many pike of all sizes from Lake Davis as possible using a combination of various activities, with implementation concentrated on the spawning season.

In order to control northern pike at Lake Davis and prevent a population explosion, the number of spawning-sized fish should be kept as low as possible and a high percentage of the larval fish produced by successful spawning should be eliminated. These objectives have guided the selection of the control and containment measures recommended in this report. Treatment of the lake with formulated rotenone (rotenone with agents added to aid dispersion) and other chemicals prohibited by Proposition 65 are excluded from this plan at the instruction of the Director of the Department of Fish and Game. The plan instead concentrates on a variety of physical methods, which provide barriers to pike or offer means of destroying pike individually or in groups. Of the physical methods identified for use, a combination of barrier nets, electrofishing and detonation cord (widely used to remove unwanted fish of all sizes by underwater concussion) employed at the right time likely offers the best potential for success.

The primary strategy to suppress and/or remove the pike population in Y2000 relies on an experimental approach that combines a number of different actions concentrated during the spawning season. In addition, a number of other individual physical measures should be used, based on the belief that their cumulative effect would be effective in reaching the plan's management goals for Lake Davis. The plan also calls for increased enforcement, a public education program, and an extensive biological monitoring program.

The full report describes 13 different management activities that are recommended for management of the pike problem at Lake Davis. In brief, these activities include:

1. Use of experimental control measures involving the use of net barriers, electrofishing, detonation cord and encircling nets in combination with other management activities. Barrier nets could be used to contain numbers of adult, juvenile and larval pike for removal by electrofishing and by concussion from detonation cord during spring and early summer. This combination appears to provide the greatest potential for controlling pike at Lake Davis;

2. The installation of tributary barriers. Physical barriers could be placed in the tributaries to Lake Davis during spring thaw to prevent spawning and the establishment of stream populations of pike;

3. Blocking spawning areas. At spring thaw, block nets could be used to trap spawning pike in portions of the Lake for elimination;

4. Reducing pike food supplies and stock brown trout as a predator species. The Department could discontinue stocking fingerling trout, a prey source for pike , and plant only larger catchable-sized trout. Brown trout should be included in those plants to increase predation on smaller pike;

5. Encourage pike fishing in ways (including derbies) that do not promote angler interest in pike. Depending on the status of the pike population, the Department may assist the local community in holding organized fishing events to remove pike from Lake Davis;

6. Use drag nets and purse seines (encircling nets). Following spring thaw, various nets can be fished for adult and juvenile pike to additively reduce the pike population;

7. Increase the use of electrofishing, particularly in the spring. Following spring "ice out" and continuing on to fall, electrofishing gear could be used to remove pike from Lake Davis and its tributaries;

8. Use electrofishing to herd pike toward traps and nets. On a monthly basis, an electrofishing boat could be used to drive pike into nets for removal;

9. Take various actions relating to the Dam including: 1) Installation of an upstream containment barrier; 2) Installation of an electric barrier; 3) Modification of the discharge orifice; 4) Maintenance of the lake level to avoid a spill; and 5) Retain the fish grate at the outflow wall. In addition to the fish grate currently used, various devices - electrical barrier, aquatic exclusion system and deep water discharge orifice - could be deployed at the Grizzly Valley Dam to contain northern pike in Lake Davis;

10. Use fyke nets and trap nets. Following "ice out," fyke and trap nets can be set at various locations around Lake Davis to remove pike on an additive basis;

11. Increase enforcement activities. The Department will increase its enforcement efforts to contain pike in Lake Davis and improve its ability to use DNA analysis as a tool of enforcement;

12. Improve public education. The Department will substantially increase its public information efforts to motivate citizens to help contain and control pike in Lake Davis; and

13. Initiative a comprehensive fish monitoring program. Systematic sampling efforts conducted since May 1999 to monitor the pike population at Lake Davis should be repeated in 2000. This would provide an index of abundance of pike and other fish species and measure the success of any control and containment efforts.

The relative effectiveness of the proposed control and containment efforts would be assessed through an extensive monitoring program. The systematic sampling program conducted in 1999 would be replicated in 2000 to provide a numerical index of the number of pike and other fishes and a measure of the success of the program. This information would be gathered through the use of electrofishing, gill nets and box traps.

Looking to the future, those working on the pike problem must continue to employ an adaptive approach that is responsive to changes, new information and new approaches. In the coming months, it is anticipated that the Task Force and Coalition will continue their discussions and work. In addition, the Department and other government agencies plan to take any steps necessary to comply with the various permitting and environment review requirements that govern the project. New information gained through monitoring and other studies at Lake Davis, as well as from new developments in fisheries management, will be folded into the effort.

The Department of Fish and Game plans to continue its collaboration with the community as the plan progresses and the results of the effort are measured.

Introduction

This report -- Managing Northern Pike at Lake Davis: A Plan for Y2000 - outlines a group of actions that together provide recommendations about how to control northern pike at Lake Davis, California. The plan is designed to prevent a pike population explosion and keep the number of spawning-sized fish as low as possible by eliminating the highest possible percentage of larval fish produced by successful spawning. These objectives have guided the selection of the control and containment measures proposed in this report (see Table 1).

The purpose of this document is to record and communicate the results of the cooperative effort undertaken by the Save Lake Davis Task Force Steering Committee working closely with the California Department of Fish and Game to respond to the threat posed by the presence of northern pike (Esox lucius) in Lake Davis.

Lake Davis is located in Plumas County, California, approximately seven miles north of the City of Portola. Lake Davis supports a superb rainbow trout fishery, maintained by a stocking program carried out by the California Department of Fish and Game. The trout fishery is highly valued by the local community and surrounding areas and contributes in a large way to the local tourism economy.

Lake Davis is a reservoir located on Big Grizzly Creek, a tributary to the Middle Fork of the Feather River. Grizzly Valley Dam was constructed by the California Department of Water Resources in 1967 as part of the State Water Project. Three main tributaries feed Lake Davis: Big Grizzly Creek, Freeman Creek, and Cow Creek (see Figure 1).

The Lake is hydrologically connected to the Pacific Ocean via Big Grizzly Creek which drops approximately 800 feet in a distance of five miles to join the Middle Fork Feather River. This stream flows into Lake Oroville, which is a major component of the State Water Project. Water from Lake Oroville flows into the Feather River at the city of Oroville and joins the Sacramento River near Verona. The Sacramento River joins with the San Joaquin River near the town of Antioch to form the Sacramento-San Joaquin Estuary. Estuary water drains through San Pablo and San Francisco bays and enters the Pacific Ocean at the Golden Gate Bridge (see Figure 2).

Portions of Lake Davis, particularly at the northern part of the lake, provide ideal habitat for the survival and reproduction of the northern pike. The task of removing a fish species capable of depositing as many as 9,000 eggs per pound of body weight is a difficult one. The northern pike has already demonstrated its ability to dominate the lake at the expense of a popular trout fishery.

Northern pike, a non-native fish -- highly efficient as a predator on trout and other fish species (see Appendix 2) -- was most likely introduced into Lake Davis sometime in 1994. It is believed the pike were illegally transplanted from unknown sources outside of California or possibly from nearby Frenchman Reservoir, where pike had also been illegally introduced. Beginning in August of 1994, Pike were found repeatedly in Lake Davis by anglers and DFG personnel during sampling operations.

In 1997, after numerous studies, the Department concluded that eradication of the predatory pike was necessary in order to protect the native salmon and steelhead populations found downstream in the Sacramento-San Joaquin river systems and Delta. Meanwhile, in response to what was happening at Lake Davis, the local community began to organize an action group. The Save Lake Davis Committee (originally called Victims of Lake Davis) was formed by a group of local Lake Davis area residents in early 1995. Shortly after its inception, officials from Plumas County and the City of Portola joined the group and became active. Later, the name was changed to Save Lake Davis Coalition to better reflect the makeup of the group.

By 1997, northern pike were found in great abundance at Lake Davis, at the expense of the trout population and the local businesses dependent on the trout fishery. Pike lived up to their reputation of being a large, voracious and fast-growing predator fish that can readily destroy other fisheries. By 1997, the trout population at Lake Davis was dramatically reduced and was mostly made up of a limited number of fish seventeen inches long and larger. The economic impact to the local economy was substantial.

In October 1997, the Department chemically treated the lake in an effort to eradicate the pike. In July of 1998, the Department began restocking Lake Davis with over a million trout including hundreds of trophy sized rainbow trout to rebuild the recreational trout fishery.

In May 1999, pike were rediscovered in Lake Davis. Subsequent monitoring efforts have shown that there now exists an established, reproducing population. It is not known if pike survived the chemical treatment or were reintroduced. Although at this time the pike population appears to be relatively small, based on previous growth rates, the population must be suppressed before it grows too large to control.

On May 31, 1999, Department Director Robert Hight visited Lake Davis and surrounding communities to meet with Coalition leaders and discuss the problem. Director Hight suggested a Task Force be formed to explore and develop a solution to the pike problem. A Task Force was formed comprised of the Portola City Administrator, the Mayor, a representative of the County Board of Supervisors, the chairs of the Coalition and Fisheries groups, two local business people and various Department personnel. The Task Force was broken down into two groups; the Steering Committee, consisting of the entire group, meets in Portola twice a month; and the Oversight Committee, consisting of the Portola City Administrator, the County Supervisor, Coalition Chair, and key Department personnel meets in Sacramento as needed. The plan development process utilizing these two groups has proven itself effective at promoting the flow of information between the public, the Coalition and Steering Committee and the other agencies involved in the project.

The Task Force, including the Department of Fish and Game, has been working together steadily since its inception in spring of 1999 to develop recommendations for a proper course of action. During this period, citizens of the Portola and Lake Davis area and Department staff have been doing extensive research on Northern Pike, fishery management, and methods of eradicating nuisance fish species. Numerous biologists, engineers, and other technical experts from California as well as from out-of-state have been consulted and departmental scientists have continued to do an extensive search of scientific and trade publications.

At the August 5, 1999, Coalition Meeting in Portola, the public at large was asked for suggestions to provide possible northern pike control measures. All the ideas, from the public as well as proposals from pike experts and the Save Lake Davis Task Force Steering Committee, including Department biologists, were compiled into an initial list of approximately 40 options. This list was provided to the Steering Committee on October 28, 1999, and to the public at the Coalition Meeting on November 3, 1999. The list was originally organized into three major categories; biological methods, physical methods and chemical methods. Treatment of the lake with formulated rotenone (rotenone with agents added to aid dispersion) and other chemicals prohibited by Proposition 65 were excluded from the list at the instruction of the Director.

During December 1999 the Steering Committee analyzed each of the proposed options as documented in Appendix (1), "Feasibility of Alternatives for the Control of Northern Pike in Lake Davis". The alternatives at this point were grouped into three categories 1) options that should be implemented 2) options needing further information or evaluation and 3) options not recommended for implementation.

As a result of this process, 13 specific action alternatives have been identified and are presented as recommendations in this plan. Together they form a proposal for the coming year's work for dealing with northern pike at Lake Davis. Entitled Managing Northern Pike at Lake Davis: A Plan for Y2000, this document is designed to record and communicate the collaborative efforts the local community and the Department have accomplished thus far.

Risk to Lake Davis Trout Fishery and the Local Economy

Lake Davis currently supports an exceptional rainbow trout fishery. The reestablishment of a northern pike population in Lake Davis poses a threat to this fishery. Pike are a top of the food web predator and prefer prey species that are high in fat content and relatively free of spiny fin rays. As such, the rainbow trout is a preferred prey species for pike at Lake Davis.

In 1997 when the pike population dominated Lake Davis, this predator had effectively consumed all trout less than 17 inches in length. It is estimated that pike have the ability to consume trout approximately 1/3 to 1/2 their own body length. As the length of an individual pike increases, it may have the potential to consume trout upwards of 17 to 20 inches. Such large pike could essentially eliminate trout from Lake Davis or leave an extremely low population of rainbow trout.

In the presence of a pike-dominated fishery at Lake Davis, it would not be in the best interest of the people of the State for the Department to continue stocking trout at the Lake. Nor would it be possible for the California Fish and Game Commission's trout planting guidelines to be met.

In addition to trout, other fish species are available to the pike at Lake Davis. These species consist of golden shiners, pumpkinseeds, sunfishes and brown bullheads, as well as a small population of brown trout. As has been documented in other states, pike would prey on these species and could decrease the prey fish populations to a point where pike would become stunted by reduced food sources. The pike could continue to survive, preying on any remaining fish species as well as the invertebrate species of the lake.

A pike population explosion similar to the one that occurred from 1994 to 1997 at Lake Davis would dramatically decrease the number of trout available to anglers. Trout anglers would likely shift their fishing activities from Lake Davis to trout waters elsewhere. The financial impacts to the local economy, which is heavily dependent on anglers visiting Lake Davis and the area, could be considerable. While many local businesses would be affected, hardest hit would be those businesses directly dependent on trout anglers. The local economy and the Lake Davis trout fishery go hand in hand. Maintaining a healthy trout fishery is a primary goal.

Risk to California's Fisheries

The existence of northern pike in Lake Davis creates the danger of pike establishing reproductively viable populations in other areas of the State. Lake Davis' connection to the Sacramento-San Joaquin Delta/San Francisco Bay Estuary makes the possibility of downstream movement of pike an issue of considerable concern (see Figure 2). Escape of pike into the creek below the reservoir could be accomplished either by spillage during or following a major storm event or by withdrawal from the reservoir through one of the dam outlets. Illegal relocation of pike to downstream areas is another possibility.

If pike escape across Grizzly Valley Dam (which separates Lake Davis from Big Grizzly Creek) they can move to the Middle Fork Feather River. In the Middle Fork, the trek would be arduous for invading pike because of the numerous cataracts and waterfalls, but some could eventually reach Lake Oroville. Although unlikely, the fish could reproduce in Lake Oroville. While Oroville Dam may slow the further spread of pike, pike could eventually escape into the lower Feather River. Once the fish reach the lower Feather River there are no physical impediments to their movement into the Sacramento-San Joaquin Delta. The lower Feather River, the Sacramento River, and the Delta are relatively low gradient (flat) and have ideal habitat for pike.

Anecdotal evidence indicates that solitary pike may have already moved into Lake Oroville and the Delta. This makes containment/eradication more urgent. If pike have escaped downstream, these strays may still be too isolated from each other and spawning habitat to form a viable reproducing population. That is, they may live out their lives without finding partners and reproducing. The predacious and voracious nature of the northern pike may necessitate large territories that exclude other predatory fish, such as other pike, temporarily keeping reproduction from occurring. However, the risk of a viable population becoming established increases with the escape of more strays.

While there are no guarantees that pike will become established in the Delta if not eradicated, the worst-case scenario must be considered and addressed. As previously noted, the pike is a voracious predator. Top predators such as the pike prey upon salmon and native minnows and can seriously and negatively alter ecosystems. The Central Valley fisheries are sufficiently imperiled without additional predation pressure from northern pike. Already depressed stocks of salmon, native and wild trout, striped bass, and other anadromous, resident and native stocks would be jeopardized by predation and increased competition.

A successful pike invasion of the Delta could jeopardize the State's multi-million dollar commercial salmon fishery. The salmon resource of the Central Valley is of particular importance to the State's economy. Estimates of California coastal community and state personal income impacts of the troll (commercial) and recreational ocean salmon fishery for major port areas averaged $20,700,000 for commercial and $19,800,000 for recreational for the years 1989-1998 (Pacific Fishery Management Council, 1999).

Sensitive fish species such as the endangered winter-run chinook salmon, threatened spring-run chinook salmon, threatened delta smelt, and Sacramento splittail could be adversely impacted by the further spread of the northern pike. If pike were to invade the Delta this could lead to future listings of threatened and endangered species and increase the possibility of extinctions.

While most attention has been given to the possibility of escape of northern pike into the Delta, there is also the cause for concern if there are illegal introductions of pike into other water bodies in the State. As yet there are no known reproductively viable populations in other State waters. However, if pike are moved to other lakes that have spawning habitat and temperatures appropriate for reproductive success, pike could not only decimate native and sport fish populations but also impact the diversity of other aquatic life. In smaller water bodies, fewer pike would be needed for successful reproduction. If pike become established, sport fishing opportunities in other lakes could be threatened, and other communities could face loss of tourism income.

Proposed Containment and Control Actions for 2000

In order to control northern pike at Lake Davis and prevent a population explosion similar to the one experienced at the lake from 1994 to 1997, the number of spawning-sized fish must be kept as low as possible and a high percent of the larval fish produced by successful spawning must be eliminated. These objectives must guide the selection of the control and containment measures to be employed. Of the physical methods identified for use, the combination of barrier nets, electrofishing and detonation cord employed at the right time appears to offer the best potential for success.

It was thought by the Steering Committee that Mosquito Slough (see Figure 1) was an ideal location to install a barrier net to partition northern pike off from the main body of the lake. Of the 197 northern pike taken during the 1999 electrofishing surveys around Lake Davis, 181 fish were taken in the Mosquito Slough area. Commencing November 3, 1999, the Department increased its electrofishing efforts in Mosquito Slough to remove fish that might spawn in the spring and to determine if northern pike were concentrated in the area. From November 3 to November 23, ninety-one fish were collected in the Mosquito Slough area, including a 27-inch fish.

On December 2, a barrier net was placed across the mouth of Mosquito Slough to contain as many pike as possible while they were concentrated in this area. Areas directly upstream of Mosquito Slough, including Big Grizzly Creek and the flood plain likely to be covered with water from spring run-off, contain prime pike spawning habitat. Mosquito Slough contains excellent nursery habitat for larval pike. Both areas were separated from the lake by the barrier net.

The Mosquito Slough net barrier, about 200 yards long and 20 feet in depth, was installed primarily to isolate the highest known concentration of pike in the lake (one additional barrier net may have to be installed upstream if the spring run-off breaches the peninsula in a low area). The immediate benefits of this action include: 1) the separation of pike from the primary food source of trout; 2) the establishment of conditions for pike to feed on pike in a confined area; and 3) the creation of conditions for removal of the contained pike and a substantial number of any offspring produced.

The Mosquito Slough barrier net has established the conditions under which a considerable number of adult, juvenile and larval pike could be removed from the lake. Prior to spring spawning, some pike will be eaten by other pike. Pike are expected to spawn upstream of Mosquito Slough in Grizzly Creek and on its flood plain inundated by spring run-off. This area provides ideal spawning habitat for pike. Fish may spawn prior to spring thaw but typically spawn following the thaw. Spring thaw at Lake Davis is typically mid to late-March. Spawning activity may range in length from a few days to a month (Franklin and Smith 1963). Depending on water temperature, eggs will typically hatch in April (see Appendix 2 for northern pike life history information).

The product of spring spawning will be larval pike (small pike after hatching from the egg). Larval pike may emigrate (move out) from spawning grounds to nursery areas as small as 3/4 inch total length but some may not emigrate until they reach two inches total length or more (Morrow and Miller). It is thought that most of these small fish will move from the Big Grizzly Creek spawning areas downstream to the nursery areas of Mosquito Slough. Movements of these young-of-the-year fish will likely be in pulses, coinciding with spawning times. As a matter of reference, the Department collected a young-of-the-year pike on June 22, 1999, that measured 3.5 inches total length (Dennis P. Lee, Senior Fisheries Biologist, California Dept. Fish and Game, personal communication).

Prior to larval emigration, an additional net with a finer mesh could be installed adjacent to the existing net. This net may not be necessary in that larval pike will likely remain in the protective cover of the vegetation in the Mosquito Slough area, less vulnerable to predation.

Pike become aggressive and cannibalistic at very small sizes (Hunt and Carbine 1951, Giles et al. 1986, Wright and Giles 1987). Adult pike remaining in the containment area can be expected to feed on larval pike.

At the most opportune times, when fish are concentrated in the containment area, various methods can be used to kill pike of all ages. Detonation cord is a commonly used method in fisheries management to create underwater explosions and is easily installed (see Feasibility of Alternatives in Appendix 1). Detonation cord has been widely used elsewhere to remove unwanted fish of all sizes, including larval forms. Other removal methods including electrofishing and netting can also be attempted in the containment area.

Detonation cord is the most effective tool readily available for the direct take of large numbers of northern pike. Fish can be effectively killed by concussion which produces a pressure wave in the water. The distance fish can be killed is determined by the size of the explosive and distance the pressure wave travels in water. Because of the extensive shallow water northern pike habitat at Lake Davis, numerous explosive charges over a large area might have to be set to be effective.

Barrier nets would be placed at the mouths of Freeman and Cow creeks and possibly other areas immediately after the spring thaw. These nets would be used in a manner similar to the use of the Mosquito Slough barrier.

Following the rediscovery of northern pike at Lake Davis in May 1999, the Department conducted a systematic sampling program to establish a baseline information on the distribution and abundance of pike at the lake. These procedures should be repeated in 2000 to provide an index of relative abundance and distribution of pike.

The Department may propose to utilize the 2000 monitoring program, mostly electrofishing, to escalate removal of pike from Lake Davis. When individual fish or "pockets" of fish are located by the electrofishing surveys around the lake, the specific areas would be identified for removal actions. When water depths permit, encircling nets would be placed around these areas and fish so contained would be removed by additional electrofishing or by the use of detonation cord.

Physical barriers should be placed in each tributary that may be accessible to northern pike for spawning and establishing stream populations. Each stream needs to be surveyed to identify the most appropriate location to install upstream barriers to migrating adult northern pike. In at least three streams these locations will likely be at culverts located on the east side of the western perimeter road. These culverts typically create an abrupt hydraulic drop between six to 12 inches. These locations can be retrofitted with small temporary structures (such as those used by the Department to prevent white bass migrations in the Tulare Lake Basin) constructed of perforated plate and other materials to create hydraulic conditions that would prevent northern pike from swimming or jumping upstream. In situations, such as the lower reaches of upper Big Grizzly Creek other types of barriers may need to be deployed, since no abrupt hydraulic changes occur. Such designs would be similar to those used by the Department to screen juvenile salmonids in anadromous streams. If screening or modifying hydraulics is not an option, attempts could be made to use temporary electrical barriers that are generator driven or are solar powered.

Subsequent to installation of each barrier, the upstream reaches should be routinely sampled (by electroshocking) to ensure that no pike has ascended. Should pike be found upstream the barrier would be modified and intensified electroshocking would be conducted until pike are removed or reduced significantly in number.

Design and prefabrication should begin as early as possible. Installation and final retrofit for the smaller streams should begin as soon as snow and ice clear (mid-March 2000). For the larger and lower gradient streams installation could take several weeks beginning in late March. Depending on runoff conditions, however, installation in these larger streams could take even longer or may not be possible with conventional methods.

Portions of Lake Davis known to be possible spawning areas for northern pike should be partitioned from the main body of the lake using block nets. As soon as adult spawners have entered these areas, block nets would be placed behind them and fish passage kept to a minimum or completely eliminated. Pike that spawn or attempt to spawn in these areas would then be subjected to reduction methods, such as those described in the section of this plan entitled Experimental Control Measures.

At present, the Department believes that a significant portion of the northern pike population in Lake Davis is in Mosquito Slough (mouth of upper Big Grizzly Creek). In December 1999 the Department placed a block net in hopes that most of that population was confined to a smaller area. In other areas of the north and western shoreline many similar areas exist that could be blocked to contain spawning northern pike. At a minimum four additional areas could be blocked with nets. These areas include the mouths to Freeman and Cow creeks and two other unnamed bays on the western shore.

Block nets would be placed as soon as each area begins to thaw. Northern pike may begin entering shallow margins of the lake at the onset of spring thaw. As soon as each area is safely accessible by boat a block net would be installed.

The objectives of these proposed alternatives are to maximize the recruitment and harvest of planted trout while minimizing the potential for predation on planted trout by northern pike and to increase the potential for larger more predacious trout to prey on or out-compete northern pike.

The existing trout stocking allotment for Lake Davis for the year 2000 is 1 million fingerling and 20,000 catchable rainbow trout. Fingerling trout are, however, very vulnerable to northern pike predation and should not be stocked in order to reduce the food supply for pike. Only the largest sizes of trout that are available in Department hatcheries should be stocked at Lake Davis. The equivalent of 1 million fingerlings, by weight, would be replaced by catchable and larger size rainbow trout. Department hatchery managers should be alerted as to the trout stocking needs and should modify fish production to accommodate these needs. Because catchable trout take longer to grow than fingerlings, trout plants may need to be spread over an extended period of time.

Brown trout are effective predators. At the request of members of the Steering Committee, the Department should stock additional brown trout in the hope that these fish would prey on and compete directly with northern pike.

It is not anticipated that pike in Lake Davis, during the calendar year 2000, will be of sufficient size or numbers to provide reasonable opportunities for organized fishing events. It is expected that fishermen may make random catches of pike when fishing for trout. Anglers making such catches are required to comply with the regulations found in Section 5.51 of the California Sport Fishing Regulations booklet. Anglers must 1) immediately kill the fish by removing the head, 2) maintain the fish head and body in a refrigerated or frozen condition; and 3) notify the Department of Fish and Game within 24 hours by calling the Department's CalTip telephone number 1-888-DFG-CALTIP.

If various sampling methods indicate that the size and numbers of pike present in the lake would provide a reasonable opportunity for an angler to catch a pike, the Department should work with the local community to consider organizing a "Special Fishing Event" to assist in the removal of pike from Lake Davis.

Rewards and bounties have been used as part of efforts to reduce a particular fish species. A reward has been offered for the capture of Columbia River pike minnow for a number of years and during the 1997 season, over 100,000 fish were harvested. In spite of these harvest numbers, however, the species has not been eliminated from the system. Encouraging the take of northern pike or offering a reward or bounty for their capture may encourage distribution of northern pike to other waters in California.

Gill and trammel nets should be fished in potential spawning areas to capture larger spawning pike. These nets should be set as soon after "ice out" as possible. The nets need to be placed perpendicularly to the shoreline to entrap any pike moving into or out of the spawning areas. They would be fished 24 hours a day and checked on a daily basis. All fish captured need to be identified to species, measured, and all northern pike retained for life history studies. Catch rates would be expressed as number of fish per hour of net fished. Fish species, other than pike, captured in these nets should be released if the biologist in charge determines that there is a reasonable chance for the fish to survive. Fish which are dead or would not survive should be disposed of accordingly. This would require an appropriate disposal location for the fish carcasses. Past experience has indicated large numbers of trout were ensnared in this type net and survivability of the trout was minimal. To minimize this impact on the trout, gill and trammel net use should be limited to times when the pike will be concentrated, i.e. during spring spawn.

Project personnel should use beach seines in areas that are determined to be habitat for larval and young-of-the-year pike and relatively free of impediments such as rock, stumps and heavily vegetated areas. Typically, these types of areas consist of very shallow gradient bottoms found in the back end of coves. Areas to be sampled would be from a point where the water depth is approximately two meters deep into the shoreline. All fish collected would be identified to species, measured and released. All pike should be retained for life history studies. Catch rates would be expressed in number of fish per seine haul. Beach seining must be concentrated during the late spring and early summer prior to the heavy growth of aquatic vegetation. During periods of heavy aquatic vegetative growth (summer and fall), this method would become less effective, due to the lifting and rolling of the lead line by the vegetation, and would be a limited tool for sampling and collecting pike.

Project personnel should use various types of electrofishing equipment to collect northern pike from Lake Davis and its tributaries. Electrofishing should be concentrated in the near shore areas where pike were collected during the summer and fall of 1999. Data would be recorded for the following parameters: time expended electrofishing; numbers and species of fish captured; subsample of lengths and weights of fish captured (all northern pike would be measured and weighed); location of sampling site, water and air temperature; type of habitat sampled; and any other data deemed pertinent. Fish other than pike would be released back into the water.

Electrofishing should commence in the spring of 2000 as soon after "ice out" as possible, weather permitting, and continue throughout the summer and fall until the lake or tributaries freeze over. Electrofishing would not be conducted during inclement weather (high winds causing white caps on the lake or during rain storms). Sampling of Lake Davis should be done using a boat, while sampling of Grizzly, Freeman and Cow creeks, and other tributaries should be conducted using a back pack electrofisher.

Boat electrofishing would require a minimum crew of three persons (boat operator and two netters). Use of the tote barge would require a minimum crew of five persons (barge operator, two electrofisher operators and two netters). The back pack electroshocker would require a minimum of three persons (operator and two netters).

Boat electrofishing during the spring spawning period should be concentrated in Mosquito Slough and the Freeman Creek area of Lake Davis. Electrofishing effort should be directed to areas within 100 meters of shore in water less than three meters deep and containing vegetation. In addition to these areas, random sampling would be conducted along all shoreline areas of the lake, using the above parameters to determine the sampling area. If pike are discovered in other areas, electrofishing crews would schedule increased sampling in the area. Electrofishing would be conducted during both daylight and evening hours, with concentrated effort being performed during time frames proving to be most productive in capturing northern pike. Weather permitting, electrofishing would be conducted during the spring spawning period at least two days per week. All fish captured would be identified to species and measured, with northern pike being retained for life history studies. Catch rates would be expressed in numbers of fish captured per 1,000 seconds of electrofishing time.

Sampling of Grizzly Creek, Freeman Creek, and Cow Creek should also be initiated in the spring when flows subside to a point that allows safe access for personnel and when northern pike are most susceptible. Electrofishing would be conducted during daylight hours. Sampling frequency during the spring spawning run would be one or two days per week. The tote barge would be used in areas where the tributaries are too deep to allow for wading and use of the back pack shocker. All fish other than pike would be identified to species, measured, and released. All pike would be retained for life history studies. Catch rates would be expressed in numbers of fish per 1,000 seconds of electrofishing effort.

During the summer and fall months, boat electrofishing should continue on a weekly basis with sampling being conducted a minimum of one day per week. Areas where pike are found would receive concentrated efforts with other areas of the lake being randomly sampled to determine the presence or absence of pike.

Electrofisher sampling of upstream tributaries should be conducted on a bi-weekly basis throughout the summer and fall months. In addition, the Grizzly Creek out flow below the dam would be sampled at least once every month during the summer and fall to determine whether or not any pike have escaped from Lake Davis.

The electrofishing boat can be used in an attempt to herd pike into gills nets placed in strategic locations. This procedure would be used in areas where waters to be sampled can be completely blocked off by the gill net. This method would be used once per month. All fish other than pike captured would be identified to species, measured and released if it is determined there is a reasonable chance for their survival. Pike would be retained for life history studies. Capture rates would be expressed in number of fish per 1,000 seconds of electrofishing.

The objective of this action item is to prevent or minimize the escape of northern pike over and/or through the dam.

Several methods are being considered that could potentially prevent migration of northern pike out of Lake Davis. Each of these could be used singly or in combination to achieve containment. These efforts would be used in conjunction with the Department of Water Resources (DWR) efforts (at the request of the Department) to manage lake levels to minimize and/or prevent uncontrolled spills. Uncontrolled spills could allow movement of pike into downstream reaches.

In 1997, a grate structure was installed on the outlet structure by DWR, at the request of the Department, to radically dissipate water in an attempt to kill any pike that enter the outlet structure. Except during repairs and maintenance to the dam, this structure has been operational. This device will continue to be deployed indefinitely.

Electrical barriers are generally used to divert fish into an area or to prevent them from going into an area. In an attempt to kill any pike that may pass through the outlet structure or fish grate, an electrocution device could be experimentally deployed by the Department of Water Resources. Offsite testing to determine the effectiveness of the device should be conducted prior to application to Grizzly Dam. Smith Root Incorporated, the only company having the necessary expertise in this area, can be contracted to conduct the testing in late spring of 2000. If the test results are satisfactory, retrofit of the dam could begin that summer.

New technology is available to "filter out" pike before they approach the outlet and/or spillway. "Gunderboom" is the trade name for a material that allows water to pass while preventing fish passage. A "Gunderboom" is a patented, full-water-depth filter curtain comprised of treated polypropylene/polyester fabric suspended by flotation billets on the water surface and secured in place with anchoring systems. This system is custom designed and deployed to provide the passage of large volumes of water while excluding fish, fish larvae and fish eggs. This system could be employed at the dam spillway or as a blocking or barrier device.

Most fish, including pike, typically live in the upper levels of the lake where food and oxygen are plentiful. Therefore, discharging water from the deepest portions of the water column is desirable to prevent escape of northern pike. There are three outlets to Grizzly Dam each at varying levels from shallow to deep. A retrofit of the intakes to each of these outlets could be done to maintain a constant draft of water from only the deepest location. Initial examination of the dam schematics by the Department's senior hydraulic engineer indicates that such a retrofit could be done. The Department should work closely with DWR engineers to seek the most effective design and safe installation.

Trap nets have been effective in collecting adult pike early in the season when they are moving into the shallows to spawn. Trap nets should be placed in strategic locations as soon after "ice out" as possible and in locations where pike would be moving to or from the spawning grounds. The nets would have the leads placed against the shoreline and the net would be set perpendicularly to the shoreline. The nets would be used mainly in Mosquito Slough and the Freeman Creek area. They would be fished 24 hours per day and require checking on a weekly basis. Trap nets should be fished throughout the spring until such time it is determined that they are no longer catching pike. All fish would be identified to species, measured, and released back into the water. Pike would be retained for life history studies. Capture rates would be expressed in number of fish per trap net day (trap net day defined as one 24 hour period).

Fyke nets should be placed in Grizzly Creek and Freeman Creek as soon as flows subside to the point where placement of the nets is feasible. Numbers of nets to be placed in each tributary would be governed by the width and depth of the tributary. The fyke nets would be fished 24 hours per day during the spring and summer months. All fish except pike captured in the fyke nets would be identified to species, measured, and released back into the water. Pike would be retained for life history studies. Capture rates would be expressed as number of fish per fyke net day (fyke net day defined as one 24-hour period).

The absolute containment of northern pike to Lake Davis by means of enforcement personnel only is a difficult undertaking. Northern pike can be moved by individuals around patrol schedules, under the cover of darkness or released in tributaries leading to numerous lakes within Plumas County. The most effective means of combating the spread of northern pike by individuals is through public education. Public education would enhance compliance. In addition, a greater awareness of the illegal movement of northern pike would generate leads and assist investigative efforts. The following is a four component enforcement plan to best address the containment of northern pike, and to develop the capability to identify the source of an illegal pike introduction.

Daily patrols of eastern Plumas, Sierra and Nevada counties have been implemented and will continue. This patrol effort consists of uniformed personnel patrolling Hallelujah Junction Agricultural Station and the following lakes and reservoirs: Davis, Frenchmen, Stampede, Boca, Jackson Meadows, Gold Lakes, Antelope, Donner, Almanor, Bucks, Prosser and Butt. Officers will distribute pamphlets regarding the illegality of transporting live northern pike and inspect all boat live wells. The public will be educated on what to look for relative to the movement of northern pike and asked to report any suspicious activity.

Continue Investigative Efforts into the Identification and Apprehension of
Those Responsible for the Illegal Movement and Introduction of Northern Pike

The Department will continue to follow up leads and conduct investigations. Leads are generated from investigations, information gathered in the field by Department personnel and reports from the general public. The investigative team is working closely with other agencies and is assisting the wildlife forensic laboratory with the DNA sampling of northern pike. The development of a forensic grade DNA genetic system is essential to establishing unequivocal evidence. Such forensic capability can be used to identify the source of northern pike at Lake Davis before and after the 1997 treatment. This forensic tool can be utilized in the court system against any persons caught planting pike or against persons thought responsible for such planting. The use of a forensic grade DNA genetic system gives the Department the capability to identify fish possessed by violators and to identify the planting site or planting source. Also, if northern pike are found in California waters other than Lake Davis, their origin can be established.

Reward for Information Leading to the Arrest and Conviction for the
Unlawful Movement or Introduction of Northern Pike

The establishment of a sizeable monetary reward for information leading to the arrest and conviction of the person(s) responsible for the introduction of northern pike into Lake Davis would be helpful. Effective publicizing of the reward may lead to information needed to arrest the perpetrator(s). The current reward has not generated any productive leads but a larger monetary incentive may prove fruitful. The reward may be advertised in many ways including: brochures, bill boards, newspapers, public service announcements and discussion at public meetings.

Efforts to keep the public fully informed on all Lake Davis/pike activity through the media, the Department Internet web page, and other educational outreach methods will be an important part of the Lake strategy. The public will be informed on Department and Steering Committee activities through town hall meetings, workshops, news releases and news conferences, prompt responses to media inquiries, extensive web page information, and by maintaining regular office hours in Portola. Informing the public of recreational opportunities at Lake Davis will also be a high priority. The Department will work with Plumas County, the City of Portola, local businesses and citizens in this regard, utilizing the publication of brochures, news releases, and sponsoring special events, such as fishing derbies as vehicles of communication and partnership.

In addition, the Department is increasing its efforts to educate the public on the illegality and severe penalties (fines up to $50,000 and six months in jail) associated with transplanting detrimental species like northern pike into the State's lakes and waterways. With the concurrence of the Plumas National Forest, signs outlining the penalties associated with moving pike will be posted at all boat ramps and other access points. Also, a brochure covering this subject is being prepared for distribution to the public at many locations including sporting goods stores and at border inspection stations.

1999 Monitoring of Northern Pike at Lake Davis

The Department initiated a program to monitor the fishery of Lake Davis after northern pike were reported in the lake in May, 1999. Monitoring included sampling by electrofishing, gill nets, and box traps in the sizable areas of the lake. Sampling efforts were directed at the north and northwest areas of the lake, and tributary streams. The study design of this sampling focused on the ability to replicate the efforts in 2000 and obtain meaningful data on the status of the northern pike population and the status of other fishes. Repeating the same systematic sampling regimen of 1999 in 2000 would provide a meaningful approximation of the northern pike population, develop indexes of abundance of pike and other fish species and provide pike life history information. Most importantly, a comparison of data systematically collected over time would provide a measure of the success of the proposed control and containment measures.

The lake was sampled by boat electrofishing on 20 days/nights from June 22 through November 23, 1999. A total of 134,697 seconds of electrofisher pulsator output were recorded and 3,803 fish captured and identified (Table 2). Included in this sample were 197 northern pike. An additional two northern pike were captured by boat electrofishing as part of media electrofishing demonstrations.

Experimental control efforts using stationary multiple-mesh gill nets and electrofishing boats in a combined effort on September 9 and 10, 1999, resulted in three juvenile pike and 33 rainbow trout captured in the nets.

Box trap nets were fished in the Mosquito Slough area from June 23 through October 21, 1999 and 316 fish were captured including juvenile northern pike, pumpkinseed sunfish, golden shiners, brown bullheads, and rainbow trout (Table 3).

Five streams tributary to Lake Davis were also sampled using backpack electrofishers. Electrofishing crews captured 35 juvenile northern pike from Freeman and Big Grizzly creeks during the period June 23 through September 15, 1999 (Table 4).

2000 Monitoring of Northern Pike at Lake Davis

Davis Lake should be monitored during 2000 in a manner similar to monitoring during 1999 to continue to approximate the northern pike population, develop indexes of abundance and collect northern pike for life history information. Davis Lake should be electrofished in a random stratified manner every other week for two consecutive nights using a minimum of one electrofishing boat with one operator and at least one netter. Effort should be directed to areas within 100 meters of shore, water less than three meters deep, and with aquatic vegetation. All fish captured would be identified to species, measured, and all northern pike retained for age and growth studies, and electrofisher pulsator output recorded. A minimum of three separate electrofishing efforts would be conducted each sampling day/night. Electrofishing effort would be documented and catch rates expressed as fish per 1,000 seconds of electrofishing effort. All northern pike captured would be retained for age and growth analysis, food habits and life history studies. Data would be summarized to provide information on northern pike locations.

Box traps should be continually fished in near shore areas of Mosquito Slough and other identified areas to capture northern pike. Traps would be serviced weekly and all fish captured identified to species, measured, and all northern pike retained for life history studies. Catch rates would be expressed as number of fish captured per trap day. All northern pike captured would be retained for age and growth analysis and life history studies.

Multiple mesh monofilament gills nets should be fished a minimum of 48 hours every-other-week as soon after "ice out" as possible at identified sites where appropriate and feasible. All fish captured would be identified to species, measured. Catch rates would be expressed as number of fish captured per net hour. All northern pike retained for age and growth and life history studies.

Near shore areas and tributaries of Lake Davis should be sampled with seines, nets and electrofishers as appropriate to collect northern pike eggs and larvae. Surveys would be conducted weekly immediately following ice-out and in both the lake and tributaries. Location and habitat information (i.e. substrate, vegetative cover and type, water depth, water flow, and temperature) would be recorded for future analysis. All northern pike retained for age and growth and life history studies.

Major tributaries should be sampled during periods of low flow when fish are vulnerable to back-pack electrofishers. Information on location of capture and electrofishing effort would be recorded and expressed and catch rates per 1,000 seconds of pulsator output. All northern pike collected would be retained for life history and age and growth studies.

In addition to the fish populations monitoring, angler catches and satisfaction would be measured using standard fishery techniques (i.e. creel and angler surveys) on a monthly basis beginning with the spring fishing season and continuing until angling activity is discontinued in the fall. Surveys would be conducted in a manner comparable to surveys conducted in 1999. Angler catch composition and rates would be compared to 1999 rates.

Collected data would be entered into project databases for analysis, and summarized and reported in annual reports.

References

Franklin, D.R. and L.L. Smith, Jr. 1963. Early Life History of Northern Pike, Esox lucius L., with special reference to the factors influencing the numerical strength of year classes. Trans. Am. Fish. Soc. 92:91-110.

Giles, N., Wright, R.M. and Nord, M. E. 1986. Cannibalism in pike fry, Esox lucius L.: some experiments with fry densities. Journal of Fish Biology 29:107-113.

Hunt B. P., and W. F. Carbine 1951. Food of young pike, Esox lucius L., and associated fishes in Peterson's ditches Houghton Lake Michigan. Transactions of the American Fisheries Society 80:67-83.

Morrow, J. V. Jr. and G. L. Miller. Size of Larval Northern Pike Emigrating from Spawning Wetlands. (Reprint. Source unknown).

Pacific Fishery Management Council. 1999. Review of 1998 Ocean Salmon Fisheries. Table IV-18.

Wright R. M. and N. Giles 1987. The survival, growth and diet of pike fry, Esox lucius L., stocked at different densities in experimental ponds. Journal of Fish Biology 30:617-629.

Members of the Steering Committee to The Save Lake Davis Task Force
Plumas County Fran Roudebush, Steering Committee Chair City of Portola John Larrieu, City Mayor (2000) Bill Powers, City Mayor (1999) Jim Murphy, City Administrator (Former Steering Committee Chair) Save Lake Davis Coalition Leonard Marsh, Chair Colleen Marsh, E. Plumas Fisheries Mgmt. Comm.	California Department of Fish and Game Diana Jacobs, Science Advisor Ron Pelzman, Project Manager Nick Villa, Environmental Specialist IV Ivan Paulsen, Senior Fisheries Biologist California Department of Water Resources Ralph Hinton, Chief, Water Management Branch Ralph Howell, Water Services Supervisor Local Businesses Saralyn Bensinger, Grizzly Resort and Store Jerry Dollard, Dollard's Sierra Market

Other Scientists Providing Pike Expertise Douglas Krieger, Colorado Division of Wildlife Rod Pierce, Minnesota Dept. of Natural Resources David Rutz, Alaska Dept. of Fish and Game Ned Horner, Idaho Dept. of Fish and Game Terry Margenau, Wisconsin Dept. of Natural Resources Tina Carlsen, Lawrence Livermore National Lab David Rice, Lawrence Livermore National Lab	California Department of Fish and Game Advisory Staff Banky Curtis, Regional Manager Gene Fleming, Chief, Fisheries Programs Branch Greg Laret, Deputy Regional Manager Joe Milton, Staff Counsel Dennis Lee, Senior Fisheries Biologist Susan Ellis, Environmental Specialist IV Robert Snyder, Fisheries Habitat Supervisor Lori Powers, Scientific Aide Gregory Slusser, Scientific Aide