Sea Lamprey Abundance Research Articles

Effects of Improved Water Quality and Stream Treatment Rotation on Sea Lamprey Abundance: Implications for Lake Trout Rehabilitation in the Great Lakes

Efforts over the past 25 years to improve water quality in the Great Lakes basin may be counteracting progress toward lake trout rehabilitation that has been made possible by sea lamprey control. Improved water quality in streams has been linked to increased amounts of suitable sea lamprey spawning and ammocoete habitat leading to increased sea lamprey production. To assess the impact of improved water quality on sea lamprey production, we simulated transformer (young adult stage) production in a model stream assuming 50%, 75%, and 100% habitat availability. We also assessed the effect of lengthening the lampricide treatment cycle in streams; a proposed solution to inadequate funding of the sea lamprey control program. Increasing habitat availability dramatically increased the number of transformers produced in the stream; for example, doubling the available sea lamprey habitat resulted in a 2.5 fold increase in sea lamprey production. In addition, we found that the combined effects of improved water quality and lengthened lampricide treatment rotation caused transformer production to increase at a faster rate than either factor acting alone. Increased sea lamprey production directly impacts lake trout mortality and retards efforts toward achievement of lake trout rehabilitation goals. To counteract the improvement of sea lamprey habitat in tributaries, sea lamprey control efforts must be increased in order to enable lake trout rehabilitation to succeed.

Joint nesting in the acorn woodpecker

Control of invasive sea lamprey in the Great Lakes with a selective pesticide (lampricide) that targeted larval sea lamprey began in the late 1950's and continues to be one of the main methods for control. Although the Great Lakes Fishery Commission, which was formed with the mandate of controlling sea lamprey, often expresses the success of the sea lamprey control program in terms of percent reduction from lake-wide pre-lampricide control adult sea lamprey abundances, there remains a large amount of uncertainty surrounding these estimates. In this study, we gathered historical data on adult sea lamprey captures from trapping efforts from the mid-1950's through the late 1970's to better understand pre-control abundance. We used this information to estimate lake-wide population abundances of adult sea lamprey using a weighted linear regression that includes environmental and lampricide treatment predictor variables. We varied trapping efficiency for early trapping data to evaluate the uncertainty in abundance estimates. Pre-control adult sea lamprey abundances in all lakes were much greater than current population sizes, but estimates were quite sensitive to trapping efficiency. In Lake Superior, declines in abundance aligned with increases in control efforts, but in other lakes, declines were occurring prior to the onset of lampricide application, perhaps because of a loss of prey. We suggest that previous estimates of pre-control adult sea lamprey abundance may have been underestimated unless trapping efficiency was greater than what is currently achieved in the basin.

Sea Lamprey (Petromyzon marinus) Control — Where to From Here? Report of the SLIS Control Theory Task Force

Sea lamprey (Petromyzon marinus) control with selective toxicants has reduced sea lamprey abundance in the Great Lakes to levels which permit survival of desirable fish species, but development of alternate and supplemental control methods is essential since chemicals cannot be used indefinitely. The Task Force addressed hypotheses which relate to regulation of sea lamprey numbers during different life history stages and why sea lampreys appear to affect fish stocks differently in various bodies of water. Examination of the information about the various factors that control sea lamprey abundance, both natural and man-made, permitted the Task Force to develop several hypotheses and to indicate areas where additional emphasis or research could produce new or supplementary control methods. Efforts to develop an integrated program of sea lamprey control should be accelerated by development of present promising areas as well as expansion in new directions. Sea lampreys when compared with teleosts exhibit many features of a prototype vertebrate and some unique specializations. Physiological, biochemical, or behavioral differences between lampreys and teleosts may be exploitable for developing control techniques specific to sea lampreys.Key words: sea lamprey, Great Lakes, population control, barrier dams, integrated pest management, buffer species, physiology, teleosts

Role of Physical Barriers in the Control of Sea Lamprey (Petromyzon marinus)

Mechanical and electromechanical barriers played a significant role in the initial attempts to control sea lamprey (Petromyzon marinus) populations in the upper Great Lakes. More recently electromechanical weirs have been used to assess the relative abundance of spawning-run sea lampreys in Lake Superior. Development of an integrated control approach to sea lamprey control has stimulated an ongoing research program to define structural and/or velocity criteria that can be used to design barrier dams that block spawning runs of sea lamprey.Key words: sea lamprey, Petromyzon marinus; physical barriers, burst swimming speed, barrier dam criteria

Changes in Mortality of Lake Trout (Salvelinus namaycush) in Relation to Increased Sea Lamprey (Petromyzon marinus) Abundance in Green Bay, 1974–78

Increased sea lamprey (Petromyzon marinus) abundance in Green Bay during 1977 is documented utilizing sea lamprey counts and lake trout (Salvelinus namaycush) wounding as methods of measurement. Since lake trout rehabilitation began in 1965, sea lamprey predation has been consistently higher in Green Bay and Northern Lake Michigan than other areas of the lake. It appears that increased sea lamprey predation in Green Bay, above the former high levels, resulted in decreased abundance and increased mortality of lake trout. The increase in lampreys is related to the colonization of the Peshtigo River, Marinette County, Wisconsin.Key words: Green Bay, sea lamprey increases, Peshtigo River, lake trout, increased mortality

Changes in Biological Characteristics of the Sea Lamprey (Petromyzon marinus) as Related to Lamprey Abundance, Prey Abundance, and Sea Lamprey Control

Biological characteristics of adult sea lampreys, Petromyzon marinus, in the Great Lakes changed in response to lamprey and prey abundance and the chemical control program. Sea lampreys collected as early as 1947, through 1978, from southern Lake Superior, northwestern Lake Michigan, the Ocqueoc River and Canadian shore of Lake Huron, and the Humber River of Lake Ontario were analyzed. Generally, abundance of sea lampreys peaked in each lake before the chemical control program began. The annual mean lengths and weights were relatively low when lampreys were abundant and increased as the numbers were reduced by the control efforts. As an indication of the change in sea lamprey weight per unit change in length, annual log10 weight on log10 length equations were solved at the arbitrary length of 410 mm. The values were plotted against years for each lake and interpreted with respect to chemical treatment periods. All slopes were negative before the control period and positive thereafter. Sea lamprey lengths and weights were low when fish stocks in the Great Lakes were near depletion. As salmonids again became abundant through stocking, lampreys grew larger. In Lake Superior, where detailed records on lake trout abundance have been available since 1959, a significant relation exists between the changes in the sea lamprey estimated weight values at 410 mm and in lake trout abundance (P < 0.01). Male sea lampreys were the dominant sex when populations of the parasite were high. A shift to a preponderance of females occurred as lamprey abundance declined.Key words: Petromyzon marinus, Salvelinus namaycush, abundance, sex ratio, weight–length relationship, chemical control

Predatory-Phase Sea Lampreys (Petromyzon marinus) in the Great Lakes

Incidentally caught predatory-phase sea lampreys were obtained from the commercial fisheries of the Laurentian Great Lakes, together with related catch data, in return for a reward offered to fishermen. Catches of sea lampreys per unit of fishing effort in Lake Superior generally paralleled other indices of sea lamprey abundance. Recently metamorphosed sea lampreys tended to appear early in the season in deepwater fisheries, typically those directed toward cisco (Coregonus spp.), whereas older specimens were taken more often in gear set at shallower depths during summer and fall. The proportion of male sea lampreys in the collections decreased annually between spring and fall, due apparently to a shoreward movement of the males. Large lake trout (Salvelinus namaycush) appeared to be the preferred prey of the sea lamprey. From studies of the stomach contents, sea lamprey feeding activity appeared to reach a peak in late summer or early fall, thereafter declining until the cessation of feeding in early spring. Growth rate reached a maximum in late summer or early fall. Greatest length was attained between January and March, after which a decrease in length was observed. Predatory-phase sea lampreys remained concentrated near the mouths of their parent streams if sufficient numbers of prey were present. Their distribution in the Great Lakes was related to the location of prey.Key words: sea lamprey, predation, Great Lakes fishery

Lake Trout (Salvelinus namaycush) and Sea Lamprey (Petromyzon marinus) Populations in Lake Michigan, 1971–78

Lake trout (Salvelinus namaycush) was exterminated in Lake Michigan by the mid-1950s as a result of the combined effects of an intensive fishery and predation by the sea lamprey (Petromyzon marinus). The widespread application of lampricide in tributary streams had greatly reduced the abundance of lampreys by the early 1960s, and a program to restore self-sustaining populations of lake trout through stocking of yearlings and fingerlings was initiated in 1965. Although the hatchery-reared fish spawned widely in Lake Michigan each year after 1970, no progeny were observed except in an isolated area in Grand Traverse Bay. During 1971–78, sea lamprey abundance was generally greater in Wisconsin than in other parts of the lake. However, the rate of occurrence of sea lamprey wounds on lake trout dropped dramatically there in 1978 after the Peshtigo River, a tributary to Green Bay, was treated with lampricide. Application of Lake Michigan wounding rates to a regression model relating mortality to lamprey wounding developed from Lake Superior data, yielded lamprey-induced mortality estimates in 1977 of 5% in Michigan plus Indiana (combined) and 31% in Wisconsin; corresponding estimates for 1978 were 5 and 15%.Key words: lake trout, sea lamprey predation, abundance, Lake Michigan

Growth of Lake Trout in Lake Superior before the Maximum Abundance of Sea Lampreys

The growth in length of lake trout (Salvelinus namaycush) from the inshore water of Lake Superior in 1953 increased with age from the 3rd to 9th year, and was nearly constant from the 9th to the 12th year. Growth was greatest in the 1st year (4.0 inches) and least in the 2nd and 3rd years (2.3 inches). Between the 4th and 9th years the increments increased from 2.6 to 3.5 inches. Growth was calculated from a curvilinear body-scale relation. Intraseasonal growth in length extended from late April until well after October; most growth was in late summer and fall. The younger fish started growth earlier, and some mature fish did not increase in length until after the October spawning. Lake trout reached the minimum legal weight (1.5 pounds) in the 7th year of life and the average size taken in the commercial fishery (about 3 pounds) in the 8th year. The annual increase in weight in the 8th year of life was over 64%. Fish used in this study grew more slowly than those from Lakes Michigan and Huron taken during the period when sea lamprey abundance was increasing, but at about the same rate as lake trout of Lake Michigan before the sea lamprey appeared.