Lake Trout Ecosystems in a Changing Environment - Chapter 3 doc

Krueger Great Lakes Fishery Commission Mark Ebener Great Lakes Fishery Commission Contents The lake trout fishery and its management: 1800–1950s Rehabilitation management: 1950s to prese

chapter three

Rehabilitation of lake trout

in the Great Lakes: past lessons

and future challenges

Charles C Krueger

Great Lakes Fishery Commission

Mark Ebener

Great Lakes Fishery Commission

Contents

The lake trout fishery and its management: 1800–1950s

Rehabilitation management: 1950s to present

Causes for the slow recovery

Status of rehabilitation

Lake Superior

Lake Huron

Lake Michigan

Lake Erie

Lake Ontario

New management approaches

Pulse stocking

Creation of spawning areas

Transplantation of adults

Management lessons and future challenges

Conclusion

Acknowledgments

References

Lake trout Salvelinus namaycush, before colonization by European peoples, were native to

each of the five Great Lakes, occurring throughout Lake Superior, Lake Michigan, Lake Huron, and Lake Ontario, and in the eastern basin of Lake Erie Life history characteristics

of Great Lakes populations span the range for the species For example, spawning typically occurs in the fall, but some populations may spawn as early as August (Hansen et al.,

1995) or even in the spring (Bronte, 1993) Age at first maturity is also highly variable across the lakes For some shallow-water populations in Lake Superior, age at first maturity can be as late as age 9 or beyond, and some individuals may not spawn every year (e.g., Rahrer, 1967; Swanson and Swedburg, 1980) This maturity schedule is comparable to those of some populations from Precambrian Shield lakes (Martin and Olver, 1980) or northern Arctic lakes On the other extreme, lake trout in lakes Erie and Ontario at the southern edge of their native range mature at age 3, and all fish are mature at age 5 or 6 (Cornelius et al., 1995; Elrod et al., 1995) These life history differences can dramatically affect the speed with which populations respond to management actions such as fishery regulations and stocking

The native lake trout of the Great Lakes used a diversity of semiisolated spawning habitats from shallow near-shore reefs to deep offshore shoals to rivers, and this habitat diversity yielded a variety of lake trout forms Aboriginal peoples, Jesuit missionaries,

French voyageurs, commercial fishermen, and naturalists identified several types of lake

trout in the Great Lakes (e.g., Agassiz, 1850; Roosevelt, 1865; Goodier, 1981; Jordan and Evermann, 1911) Three general forms or morphotypes — leans, siscowet, and humpers (also known as bankers) — were recognized based on fat content, morphology, location caught, and spawning condition and timing (Figure 3.1) Within these three forms, several other types were often described (Krueger and Ihssen, 1995) For example, some of the types of lean trout recognized by commercial fishermen were called Mackinaw, yellowfin, redfin, moss, sand, and racer trout (Goodier, 1981; Brown et al., 1981) Whether these lean types all represented significant genetic differentiation is unknown The differences between the deepwater (sicowet) and shallow-water (lean) forms are known to be heritable phenotypic differences, and these differences probably represent important ecological adaptations for the habitats they use Deepwater forms appear to be adapted for rapid vertical migration (Eshenroder et al., 1995a) because adults have high fat content and therefore are nearly neutrally buoyant without gas in their swim bladders (Crawford, 1966; Henderson and Anderson, 2002) This level of differentiation and adaptation within the Great Lakes stands in considerable contrast to the similarity of lake trout within and among small Precambrian Shield lakes (Wilson and Mandrak, Chapter 2, this volume) Unfortunately, the settlement of the Great Lakes basin by Europeans in the 1800s and 1900s threatened the rich diversity of life histories, forms, and adaptations expressed by Great Lakes lake trout This loss also jeopardized use of lake trout as a food and sport fish Lake trout populations declined catastrophically and, in some lakes, were lost because of the stresses caused by commercial fisheries; the construction of canals for shipping; and the timber industry By the late 1950s, native lake trout were gone from Lake Ontario, Lake Erie, and Lake Michigan; nearly gone in Lake Huron; and seriously depleted at most near-shore locations in Lake Superior Finally, when the remaining populations were threatened

by predation from the proliferating non-native sea lamprey Petromyzon marinus,

manage-ment programs began in earnest to protect and rehabilitate lake trout (Hansen, 1999) This chapter reviews the history of the species in the Great Lakes during the past century, describes the progress made toward lake trout rehabilitation, and identifies man-agement lessons and challenges

The lake trout fishery and its management: 1800–1950s

The history of Lake Superior and its lake trout provides a useful case history for the species

in the basin Fishing for lake trout by native aboriginal people around Lake Superior was ongoing when Louis Agassiz and his expedition made their journey to record the natural history along the north shore (Agassiz, 1850) Lake trout were used as a subsistence food fish and were bartered with the members of the expedition The earliest records of

commercial fisheries in Lake Superior are from the 1830s, when the Hudson’s Bay Com-pany and the American Fur ComCom-pany shipped salted fish in barrels from Lake Superior (Bogue, 2000) Seines were used in the earliest days of the commercial fisheries Later, settlers to the region were quick to recognize the value of lake trout as a food fish By

1875, 0.75 million kilograms of lake trout were caught from the lake Efficiency of catching fish increased with technological improvements Pound nets were first used in the 1860s, and steam tugs introduced in the early 1870s (Goodier, 1989) The efficiency of fishing gear further expanded as gas- and diesel-powered fishing tugs were introduced after World War I About 1930, cotton gill nets replaced those made of linen, and in the late 1940s multifilament nylon gill nets replaced cotton (Goodier, 1989; Hansen et al., 1995) When gill net fisheries converted from cotton to multifilament nylon, their nets became much better at catching fish (Pycha, 1962) Between 1913 and 1950, harvest of lake trout averaged 2.0 million kilograms per year (Baldwin et al., 1979) During this same period, sport fishing, though a minor contributor to the total catch, was culturally important at locations such as Duluth, Minnesota, and Munising, Michigan Anglers, while trolling for lake trout, often used copper line to get lures deep Overfishing was clearly evident when fishing effort increased sharply after World War II and yield did not increase, even though

Figure 3.1 Siscowet (top), lean (middle), and humper (bottom) morphotypes are examples of the phenotypic diversity of lake trout from the Great Lakes (Photo courtesy of Gary Cholwek and Seth Moore of the USGS Ashland Biological Station.)

gear efficiency had increased further (Hile et al., 1951; Pycha and King, 1975) Populations

at this point had declined by 50%

While overfishing of Lake Superior and other Great Lakes populations was occurring, the sea lamprey invaded upstream from Lake Ontario The sea lamprey gained access to the upper lakes sometime in the late 1910s by passing around Niagara Falls via the Welland Canal and associated feeder canal, built for the shipping industry (Eshenroder and Burn-ham-Curtis, 1999) Sea lampreys were first recorded in Lake Erie in 1921, in Lake Michigan

in 1936, in Lake Huron in 1937, and in Lake Superior in 1938 (Smith and Tibbles, 1980)

By the 1950s, sea lampreys were very abundant in all the Great Lakes Sea lamprey attached

to lake trout with their circular, suctorial mouth and fed on their blood and other body fluids (Figure 3.2) Lake trout suffered serious mortality from these attacks In Lake Supe-rior, stocks of lake trout were already declining due to overfishing before the sea lamprey invaded; however, the collapse of the stocks was undoubtedly accelerated by the added mortality caused by sea lamprey (e.g., Hile et al., 1951; Coble et al., 1990) Although the exact roles of overfishing and sea lamprey predation in the collapse of lake trout in the other Great Lakes have been a source of debate (Coble et al., 1992; Eshenroder, 1992; Eshenroder et al., 1995b), general agreement exists that both sources of mortality were important in the ultimate demise of the species (Hansen, 1999)

Besides overfishing and sea lamprey predation, other environmental factors may have also played a role in the decline of lake trout Exotic species other than sea lamprey, such

as alewife Alosa pseudoharengus and smelt Osmerus mordax, invaded the Great Lakes, altered

food webs, and replaced native coregonines as a primary forage species for lake trout These species may also have directly controlled natural recruitment of lake trout through competition with, and predation on, juvenile lake trout In addition, a variety of toxic

Figure 3.2 Sea lamprey colonized the Great Lakes by using shipping canals to pass by barriers such

as Niagara Falls

substances, specifically organochlorine compounds, can become concentrated in lake trout eggs, fry, and the environment These compounds reduce the hatching success of lake trout in the laboratory, but under natural conditions the relationship between toxic sub-stances and lake trout mortality remains unclear (Zint et al., 1995) Quarrying operations may have destroyed spawning habitat in some areas During the late 1800s and early 1900s, a fleet of 45 schooners quarried cobble for more than 40 years from Lake Ontario along 100 km of shoreline between Burlington and Whitby (Whillans, 1979) The timber industry also may have affected some near-shore populations Sawmills deposited large amounts of woody debris and sawdust in the lakes (Lawrie and Rahrer, 1973; Bogue, 2000) This organic debris may have covered some near-shore spawning reefs Logging drives downriver may have affected river-spawning lake trout Dams associated with hydroelectric development such as on the Montreal River, a tributary to eastern Lake Superior, must also have contributed to the decline in river-spawning lake trout

What happened by 1960? Natural reproduction failed to sustain lake trout populations

in Lake Ontario, Lake Erie, and Lake Michigan Wild lake trout were eliminated from these systems In Lake Huron only two small populations remained, one in Parry Sound and the other in Iroquois Bay, both located on the eastern shore of the lake (Berst and Spangler, 1973; Reid et al., 2001) Near-shore populations in Lake Superior were decimated, although remnants of a few populations, such as the one adjacent to Gull Island Shoal, persisted (Schram et al., 1995) Offshore lake trout in Lake Superior were comparatively unaffected, especially the humper and deepwater siscowet forms, which continued to support limited fisheries through the 1960s and 1970s (Peck et al., 1974) Distance offshore and deep water may have provided some protection to these fish from commercial fisheries and sea lamprey predation The sequence of the collapse of lake trout stocks in the upper lakes was Lake Huron first, Lake Michigan next, and Lake Superior last (see review in Hansen, 1999) Another important commercial species in the upper Great Lakes, lake

whitefish Coregonus clupeaformis also declined to their lowest point in the late 1950 and

early 1960s because of the effects of sea lampreys, other non-native species, and overfish-ing By 1960, the lake trout and whitefish fisheries of the Great Lakes were devastated

Rehabilitation management: 1950s to present

As lake trout populations declined precipitously through the 1950s in the Great Lakes, the governments in Canada and the United States embarked on a program of fishery rehabilitation focused on lake trout that has continued to the present The two federal governments undertook many of the early management actions used to restore the lake trout and whitefish fisheries of the Great Lakes For example, though the states have authority for fishery management, essentially the U.S Bureau of Commercial Fisheries managed U.S waters during the 1950s and early 1960s as a result of an absence of state interest Over time, however, the lake trout rehabilitation program shifted toward, and has been sustained by, the eight Great Lakes states, the Province of Ontario, and the U.S aboriginal tribal authorities In 1955, the two federal governments formed the international Great Lakes Fishery Commission for the purpose of developing a program of sea lamprey control, conducting fishery research, and promoting coordinated management (Figure 3.3) The commission explicitly adopted lake trout population rehabilitation as one of its goals and has always encouraged fishery management agencies to restore lake trout populations (Great Lakes Fishery Commission, 2001)

A variety of management actions have been implemented since the late 1950s to rehabilitate the fisheries and overcome the obstacles faced by lake trout in the Great Lakes Approximately 330 million yearling and fingerling lake trout were released into the Great Lakes from 1950 to 2001, primarily into near-shore areas (Table 3.1) In Lake Superior,

117 million lake trout were stocked, and of these 86% were yearlings Lake trout fishing was closed in 1962 in Lake Superior and restricted in the other lakes during the early years of the rehabilitation program

To reduce sea lamprey predation, selective lamprey toxicants (lampricides) were used

to kill sea lamprey larvae in streams The first stream treatments began experimentally in Lake Superior in 1958, and routine applications were extended to the upper Great Lakes shortly thereafter (Smith and Tibbles, 1980) Sea lamprey control measures were imple-mented later in Lake Ontario (1971) and in Lake Erie (1986) A suite of techniques is now used to control the lamprey, including lampricides, adult trapping, the release of sterile males, and the placement of barriers to block access to spawning streams Beginning in

1966, management activities were coordinated through lake committees organized by the Great Lakes Fishery Commission These committees included a representative from each fishery management authority on a lake The lake committees developed lake trout man-agement plans and helped to coordinate manman-agement actions such as stocking and fishery regulations within each Great Lake

During the 1960s, lake trout survived, and the abundance of subadults and adults increased in the upper three Great Lakes (Superior, Huron, and Michigan) in response to sea lamprey control, regulation of fishery harvests, and stocking Most of these lake trout were hatchery-origin fish, the survivors of past stockings Similar increases in lake trout abundance occurred in Lake Ontario in the late 1970s and in Lake Erie in the late 1980s and early 1990s

Unfortunately, rehabilitation management became increasingly complicated in the mid-1960s because new sport fisheries began, particularly in Lake Huron, Lake Michigan,

and Lake Ontario, and were focused on catching non-native Pacific salmon (Oncorhynchus

sp.) (Bence and Smith, 1999; Kocik and Jones, 1999) Alewives had become enormously abundant and were experiencing massive die-offs that fouled beaches and clogged the water-intake pipes of cities Salmon were stocked initially to control these fish and to create new sport fisheries Salmon stocking was successful, and the fisheries that resulted pro-vided an economic stimulus for coastal communities after the loss of the commercial fishing

Figure 3.3 The convention between Canada and the United States that formed the Great Lakes Fishery Commission was fully ratified in 1955

Table 3.1 Number of Fingerling and Yearling Lake Trout Stocked into the Great Lakes, 1950–2001

industry Little contribution to the salmon fisheries came from natural recruitment, and the fisheries were dependent on stocking

In the decades that followed, mortality of adult hatchery-origin lake trout increased

to levels at which too few fish survived to either their first or second spawning Angling effort, in general, increased in the Great Lakes because of the salmon fisheries, and anglers often caught lake trout State and provincial agencies, in most cases, allowed anglers to keep hatchery-origin lake trout even though these fish had been stocked for rehabilitation purposes Lake trout were harvested as by-catch in the salmon fisheries, but sometimes lake trout were targeted by anglers Gill-net fisheries grew as aboriginal peoples exercised treaty rights in some U.S waters These fisheries harvested substantial numbers of lake trout incidental to targeting lake whitefish (Brown et al., 1999; Hansen, 1999) Also, sea lamprey in the 1960s and 1970s expanded into new spawning habitats because water quality improved as a result of new environmental laws and policies such as the Great Lakes Water Quality Agreement (e.g., Peshtigo River, Moore and Lychwick, 1980) In spite

of these new challenges, large, abundant stocks of hatchery-origin lake trout became established in several localized areas of the Great Lakes Surprisingly, little reproduction and natural recruitment was observed in any of the lakes other than Lake Superior The lack of natural recruitment in the Great Lakes stands in sharp contrast to the frequent establishment of naturally reproducing populations after stocking lake trout into the small inland lakes of the Province of Ontario (Evans and Olver, 1995) and suitable western lakes such as Yellowstone Lake (Kaeding et al., 1996) Why then was there so little successful reproduction in the Great Lakes?

Causes of the slow recovery

Several hypotheses have been offered to explain why lake trout rehabilitation has been slow in the Great Lakes (Eshenroder et al., 1984, 1999; Selgeby et al., 1995), and some of these are described below Among the explanations proposed, empirical data support them all, but none accounts fully for the slow recovery For example, one cause proposed for the slow recovery is that too few fish survive to spawning age after stocking, and thus natural reproduction is so low as not to be detectable or capable of sustaining a population Although lake trout at some locations have had difficulty attaining spawning age because

of excessive fishing and sea lamprey mortality, at many other locations catch rates of spawning-age lake trout in gill nets have been comparable to, or exceeded, those observed for wild populations in Lake Superior (Krueger et al., 1986; Elrod et al., 1995; Hansen, 1999)

Another hypothesis is that lake trout do not reproduce successfully because they cannot find spawning grounds or mates because of the absence of proper cues (olfactory homing or pheromones) Hatchery-origin lake trout have spawned over inappropriate substrates at some locations Moreover, stocking often has occurred at locations where little spawning habitat exists in the immediate vicinity However, hatchery-origin lake trout are also known to locate and readily spawn over clean natural substrate that has been deposited along the shoreline, such as in Tawas Bay, Lake Huron (Foster and Kennedy, 1995), as well as over natural reef substrate such as at Stony Island reef in Lake Ontario (Perkins and Krueger, 1995)

A third proposed cause is that lake trout gametes are infertile because of toxic chemical contamination and a thiamine nutritional deficiency Toxic substances such as organochlo-rines and their effects on gamete viability have been suspected of being one of the causes

of lake trout reproductive failure (Zint et al., 1995) A serious disease known as early mortality syndrome (EMS) also occurs in adult lake trout from the Great Lakes, apparently because of consumption of alewives, which are non-native (Fitzsimons et al., 1998) If lake

trout feed heavily on alewives, adult females become thiamine deficient and their eggs are not viable However, Brown et al (1998) reported that not all females captured from Lake Ontario produced families that showed this syndrome Also, lake trout gametes collected from Lake Ontario in the 1980s from hatchery-origin adults were propagated successfully in hatcheries More than a million fish from this source were stocked back into the lake (Elrod et al., 1995)

A fourth cause is that the wrong genetic types of lake trout were stocked, and these fish were maladapted for survival and reproduction The shallow-water, lean morphotype has been the only form of lake trout stocked into the Great Lakes during the past 50 years, and this form may be poorly adapted for colonizing the extensive offshore or deepwater habitats (Krueger and Ihssen, 1995) Nevertheless, some sources such as the Superior strain originating from the Apostle Islands region of Lake Superior and the Seneca strain from the Finger Lakes region are known to successfully reproduce at some locations (e.g., Grewe

et al., 1994)

A fifth cause is that predation on lake trout eggs and fry by non-native and/or native species inhibits natural recruitment For example, predation by the non-native alewife on lake trout fry has been implicated in preventing natural recruitment at some near-shore locations (Figure 3.4; Johnson and VanAmberg, 1995; Krueger et al., 1995a) This source of mortality, however, would be comparatively unimportant at offshore locations such as the midlake reef in Lake Michigan or Six Fathom Bank in Lake Huron or in Lake Superior and Lake Erie, where alewife abundance is apparently minimal

Although evidence exists to support each of these hypotheses, no single one explains the general lack of natural reproduction by lake trout Probably, varying combinations of each plus other causes account for the slow recovery of lake trout in the Great Lakes

Status of rehabilitation

Lake Superior

Lake trout were declared rehabilitated along most of the Lake Superior shoreline in 1996 (Schreiner and Schram, 1997) Wild lake trout have continued to increase in abundance since that time and may be more abundant now than at any time during the last century

in many areas of the lake (Wilberg et al., 2003) Substantial natural reproduction has been

Figure 3.4 Alewives invaded and colonized Lake Ontario around 1870

noted at most locations in the lake Population recovery was first noted at areas where remnant stocks were present, such as at Gull Island Shoal (Swanson and Swedburg, 1980), Isle Royale, and Standard Rock, and recruitment, presumably from hatchery-origin lake trout, was noted later in areas where wild lake trout were absent (Figure 3.5; Hansen et al., 1995) Recovery at one location, Devils Island Shoal, was aided by the stocking of fertilized eggs in artificial-turf incubators (Bronte et al., 2002) Rehabilitation has been slowest along the Minnesota shoreline Abundant and widely distributed spawning habitat, remnant stocks, effective harvest regulation, and few non-native species such as the alewife prob-ably all contributed to the success in Lake Superior Supplemental stocking is no longer required at most locations Sea lampreys continue to cause lake trout mortality, and control efforts must be maintained to protect the wild populations Abundance of the siscowet or deepwater form appears high and may be increasing (Bronte, C.R., U.S Fish and Wildlife Service, personal communication, 2003)

Lake Huron

Natural reproduction of lake trout has been detected at several sites in Lake Huron; but,

at only one site, Parry Sound in Ontario waters, has a self-sustaining population been established (Reid et al., 2001) The success at Parry Sound appears to be caused by reduced fishing mortality because of restrictive angling regulations, successful sea lamprey control, and the establishment of a refuge A remnant population of wild lake trout was also present in Parry Sound and may have speeded the recovery Naturally reproduced lake trout have also been caught from an artificial reef in Tawas Bay (Foster and Kennedy, 1995) and from natural sites in South Bay (Anderson and Collins, 1995), Thunder Bay

Figure 3.5 Relative abundance of wild and hatchery lake trout caught in gill net surveys in U.S waters of Lake Superior and of all lake trout caught in waters <70 m deep in Canadian waters,

1950–1999 (Data from C.R Bronte, U.S Fish and Wildlife Service.)

Canadian Waters

0 10 20 30 40 50 60 70 80

Year

U S Waters

0 10 20 30 40 50 60 70

Year

Wild Hatchery