The Lake Superior Committee in 1990 established the following specific targets for sea lamprey populations in their Fish Community Objectives:
Achieve a 50% reduction in parasitic-phase sea lamprey abundance by 2000, and a 90% reduction in parasitic-phase sea lamprey abundance by 2010.
Based on estimates of the damage caused by the parasitic-phase population in the mid-1980s, these reductions were established to reflect the need for enhanced control on Lake Superior, with full recognition of the need for further evaluation of the costs of suppressing lamprey to these levels.
This sea lamprey target was developed to support the following objective for the community of lake trout and other salmonids.
Achieve a sustained annual yield of 4 million pounds of lake trout from naturally reproducing stocks, and an unspecified yield of other salmonid predators, while maintaining a predator/prey balance which allows normal growth of lake trout.
Naturally reproducing stocks of lake trout can only be maintained with a total annual mortality of less than 45%. Reaching this objective for total mortality requires a combination of regulation of fishery exploitation and control of sea lamprey abundance.
The Service maintains an extensive network of assessment traps for spawning-phase sea lampreys in index streams of the south shore of Lake Superior and annually estimates populations east and west of the Keweenaw Peninsula (Fig 2). Populations east of the Peninsula generally remained stable during 1987-93, declined substantially in 1994, but increased again in 1995. Populations to the west generally have declined during 1989-95. The program achieved the sea lamprey target for Lake Superior (50% decline by 2000) in 1994 when compared to the 1986-90 average of 42,500 (13,700 in 1994). In 1995, the estimated population increased to 24,100 which is a decline of 43% of the 1986-90 average. At present, the program is slightly above the target for sea lamprey abundance.
Figure 2: Estimated number of spawning sea lampreys in U.S. waters (west and east of Keweenaw Peninsula) of Lake Superior 1986-1995.
The Lake Michigan Committee established the following specific objective for sea lamprey populations in their Fish Community Objectives in 1995:
Suppress the sea lamprey population to allow the achievement of other fish-community objectives.
In general, treatment of Lake Michigan tributaries over the past 25 years has provided sufficient control of sea lampreys yet recent increases in lamprey wounding rates on lake trout in northern waters of the lake is a concern.
The sea lamprey objective was developed to support the other fish community objectives for Lake Michigan, specifically those for lake trout and other salmonines.
Establish a diverse salmonine community capable of sustaining an annual harvest of 2.7 to 6.8 million kilograms (6 to 15 million pounds), of which 20-25% is lake trout. Establish self-sustaining lake trout populations.
Control of sea lamprey populations and fishery exploitation will be necessary to meet these objectives. The lake-wide management plan specifies four different areas: refuges, primary, secondary, and deferred rehabilitation zones in order to focus lake trout rehabilitation to the areas where the chances of success are best. The primary zones and refuges where priority should be given to reducing mortality caused by sea lampreys include the mid-northern region of the lake, the mid-lake reef zone, and an offshore reef area in the southwest portion of the lake.
The Service annually has operated an assessment network for spawning-phase sea lampreys on 11-13 streams in Lake Michigan, and we present this information as total catch in all other rivers and estimated spawning population in the Manistique River, 1986-95 (Fig. 3). This index shows the population in the lake has been relatively stable during the time period, but our assessments also show lampreys are more abundant in the northern part of the lake than in the south.
Figure 3: Number of spawning-phase sea lampreys captured in assessment traps in an annual average of 12 streams (range, 11-13) in Lake Michigan, 1986-1995, and estimated population of spawning lampreys in the Manistique River, 1986-1995.
The Lake Huron Committee (1993) has established a specific objective for sea lamprey abundance as part of its Fish Community Objectives:
Reduce sea lamprey abundance to allow the achievement of other fish community objectives; obtain a 75% reduction in parasitic sea lamprey by the year 2000 and a 90% reduction by the year 2010 from present levels.
The progress toward this objective will be monitored by the abundance of spawning sea lampreys in four index streams in northern Lake Huron: the Thessalon, St. Marys, Cheboygan and Ocqueoc rivers.
This sea lamprey target is in support of the objectives for the other species groups in the fish community including, for example, the Salmonine community objective to:
Establish a diverse salmonine community which can sustain an annual harvest of 5.3 million pounds, with lake trout the dominant species and anadromous species also having a prominent place.
To attain and maintain a self-sustaining lake trout population capable of supporting 3-4 million pounds of this overall yield objective the total annual mortality should not exceed 45%. The plan calls for management of exploitation and control of lampreys to reach this objective. The lake-wide management plan identifies refuges and special rehabilitation zones in which rehabilitation is most likely to succeed. These priority zones are distributed throughout the lake, including the northern section and the North Channel. The plan states these areas should be priority areas for the suppression of lampreys and control of fishery exploitation.
The Service and Department have trapped an average of 12 streams during 1986-95 to monitor abundance of sea lampreys in northern Lake Huron. During this period, lamprey abundance generally increased during 1986-93 but declined in 1994-95 (Fig. 4). These trap catches represent an excessive number of sea lampreys in Lake Huron and the data is further substantiated by similar patterns in indices of parasitic sea lamprey abundance and fish wounding. We suggest that without continued substantive action to manage the presently uncontrolled population of larvae in the St. Marys River we will fail to make progress in achieving sea lamprey objectives for lake trout rehabilitation in Lake Huron.
Figure 4: Number of spawning-phase sea lampreys captured in assessment traps in an annual average of 12 streams (range, 10-16) in Lake Huron, 1986-1995, and estimated population of spawning lampreys in the Cheboygan, St. Marys and Thessalon rivers, 1986-1995 (population in Thessalon not estimated in 1988 and 1991).
The Lake Erie Committee is currently developing Fish Community Goals and Objectives for the lake. The Committee is considering the previous management plans and will define objectives for the eastern basin salmonid community. The current draft in development recognizes the need for continuing control but does not set specific objectives for sea lamprey.
A specific management plan for sea lampreys in Lake Erie was developed prior to the implementation of stream treatments in 1986. The plan defined an "experimental program" of control to reduce sea lamprey populations to levels where wounding on lake trout would be less than 5%, assessment trap catches of lamprey would be less than 10% of pre-treatment levels, and nest densities would be less than 2 nests per km of spawning habitat. By 1989 the first 2 of these objectives had been met in the eastern basin of Lake Erie. Based on the success of the experimental control program, in 1992 the Great Lakes Fishery Commission declared the control program on Lake Erie to be an ongoing program like the stream treatment programs in the other lakes.
The lake trout management plan for rehabilitation of self-sustaining stocks in the eastern basin of Lake Erie prescribed a maximum annual mortality rate of less than 40% be achieved to permit the establishment and maintenance of suitable stock of spawning adults. Mortality would be controlled through management of fishery exploitation and continued suppression of sea lampreys.
The Service and Department annually have trapped spawning-phase sea lampreys in an average of 6 tributaries since 1986 and estimated the number of spawning lampreys in Cattaraugus Creek during 1991-95 (Fig. 5). Current catches are significantly less than those prior to the start of lampricide management (first round of treatments conducted in 1986/87 and showed effect in spawner population by 1989) but are greater than 10% of pretreatment catches. Since lake trout wounding remains at less than 5%, we are achieving sea lamprey objectives in the lake.
Figure 5: Number of spawning-phase sea lampreys captured in assessment traps in an annual average of 6 streams (range, 3-8) in Lake Erie, 1986-1995, and estimated population of spawning lampreys in Cattaraugus Creek, 1991-1995.
The Lake Ontario Committee (1988) in the Lake Ontario Fish Community Objectives supported continuing sea lamprey control and defined a specific objective for lampreys in terms of mortality to lake trout:
Limit the size of the sea lamprey population to a level that will not cause mortality in excess of 90,000 lake trout annually.
This specific objective was developed to support the productive salmonine community including a lake trout population that shows significant reproduction in the near term.
The Lake Ontario Committee has revised its Lake Ontario Lake Trout Rehabilitation Plan from the original plan developed in 1983. The goal of the plan is to rehabilitate a self-sustaining population of lake trout as defined in the Fish Community Objectives. The plan includes the fundamental premise that continued control of sea lamprey induced mortality is necessary for lake trout rehabilitation. The plan includes a specific objective for sea lampreys of:
Controlling sea lamprey so that fresh wounding rates (A1) of lake trout larger than 431 mm is less than 2 marks/100 fish.
This specific objective is meant to maintain the annual survival rate of 60% or greater in order to maintain a target adult spawning stock of 0.5 to 1.0 million adults of multiple year classes. Along with sea lamprey mortality, angler, and commercial exploitation also shall be controlled so that annual harvest does not exceed 120,000 fish in the near term.
The Service and Department annually have operated traps in an average of 15 index streams for spawning-phase sea lampreys in Lake Ontario since 1986. During that period, spawning catches have remained relatively stable, ranging from about 4,000 to 8,000 annually (Fig. 6). Lake wide wounding rates average about 2 marks/100 fish, with annual survival between 50-70%. As well, lake trout deaths from sea lampreys were about 30,000. Thus, the control program is achieving the current sea lamprey objectives for Lake Ontario.
Figure 6: Number of spawning-phase sea lampreys captured in assessment traps in an annual average of 15 streams (range, 13-16) in Ontario, 1986-1995, and estimated population of spawning lampreys in the Black and Humber rivers, and Duffin, Port Britain, and Shelter Valley creeks, 1992-1995.
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