Lake Trout Rehabilitation in the Great Lakes: an Evolutionary, Ecological, and Ethical Perspective

J. Great Lakes Res. 21 (Supplement 1):518-529 Internal. Assoc. Great Lakes Res., 1995

Lake Trout Rehabilitation in the Great Lakes: an Evolutionary, Ecological, and Ethical Perspective Randy L. Eshenroder,l E. J. Crossman,2 Gary K. Meffe,3 Charles H. Olver,4 and Edwin P. PisterS 'Great Lakes Fishery Commission, 2100 Commonwealth Blvd., Suite 209 . Ann Arbor, Michigan 48105-1563 2Royal Ontario Museum, 100 Queens Park, Toronto, Ontario M5S 2C6 3University of Georgia's Savannah River Ecology Laboratory, Drawer E Aiken, South Carolina 29802 40ntario Ministry ofNatural Resources, Box 9000, Huntsville, Ontario POA 1KO 5Desert Fishes Council, P. O. Box 337, Bishop, California 93515

ABSTRACT. We reviewed key features of the evolutionary biology of lake trout (Salvelinus namaycush) and their significance for rehabilitation programs in the Great Lakes. Despite repeated translocation by glacial advances during the Ice Age (the Pleistocene) that eliminated most populations, lake trout have genetic diversity comparable with other North American salmonines. Various embryological and adult features suggest lake trout had a long reproductive history in lakes, although river spawning may be a primitive feature of the species and may have been important in glacial refugia. Observations that hatchery-reared lake trout select mostly mainland shoals for spawning in the Great Lakes are interpreted by us to be a result of evolution in smaller lakes where the main source of spawning gravels is shoreline erosion. We hypothesize that longevity in lake trout (a record among chars) may have evolved because of a near absence of predation on adults in contrast to predation on juveniles that survived less well, in part, because of cannibalism. Longevity, a physiological ability to colonize the coldest of waters during deglaciation, and an ecological role as a dominant piscivore in unperturbed systems all indicate that lake trout should fare best under conditions of low adult mortality and high biomass. Although the Great Lakes fish community is enriched compared with when lake trout populations were abundant or with where lake trout evolved, the species has the potential to suppress other fishes to its benefit. We provide ecological and ethical reasons why lake trout rehabilitation should be a priority for the Great Lakes: lake trout are particularly suited for the deepwater food chain, they are the only salmonine (among those currently stocked in the lakes) that have the potential to become self-sustaining at their current levels of abundance, and emphasis on stocked exotics reflects adherence to a scientifically obsolete philosophy of "wise use" that ignores evolutionary-ecological relationships. For fishery management, we recommend greater use of genetic diversity and of life stages capable of being imprinted, maintenance of high adult survivorship and biomass, and expanded communication with a wider array of clients. We also advocate lines of research that will test our management recommendations, including assessing the implications of attempting to keep the Great Lakes fish community in an early stage of succession. INDEX WORDS:

Lake trout, phylogeny, rehabilitation, evolution, ethics.

FEATURES OF LAKE TROUT EVOLUTIONARY BIOLOGY

INTRODUCTION Our objective was to consider how knowledge about the evolutionary biology of lake trout (Salvelinus namaycush) can be applied to the rehabilitation of this species in the Great Lakes. Our approach is organized as follows: 1) a synthesis of relevant features of lake trout evolutionary biology; 2) a discussion of ecological and ethical concepts relevant to rehabilitation; and 3) recommendations for management and research.

Diversity Behnke (1980) considered the lake trout to be a taxonomically stable species exhibiting little morphological variation throughout its geographical range except in the Great Lakes. He believed that they evolved as a highly specialized, deepwater, lacustrine predator, probably in

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Lake Trout Evolutionary Biology response to feeding on coregonines. Lake trout can be considered primitive in that they lack certain behaviors associated with advanced salmonines: they are not agonistic or territorial (Noakes et ai. 1989), they do not construct redds, and adults are capable of more than one spawning. Because its closest living relatives (S. fontinaZis and S. ieucomaenis) are river spawners (Benhke 1980, Savvaitova 1980, Cavender 1984, Volobuev et ai. 1985, Gudkov 1992), river spawning may be another primitive feature of the species. The evolutionary biology of lake trout was shaped strongly by glaciation. Repeated glacial advances created much of the lake habitat now characteristic of the species. If speciation in North American SaiveZinus occurred near the start of the Ice Age as suggested by Behnke (1980), lake trout may have spent a great part of their history in river refugia. Lakes are presently scarce in the Atlantic and Mississippi refugia where lake trout from the Great Lakes area survived the most recent glacial advance, the Wisconsinan (Underhill 1986, Ihssen et al. 1988, Mandrak and Crossman 1992). Much of the diversity within the species, including deepwater forms that probably evolved in the Great Lakes in interglacials before the present epoch, was presumably lost during each glacial advance, because lakes were much less common in the refugia than in the present range of lake trout (Mandrak and Crossman 1992). Richmond and Fullerton (1986), in an extensive review of Quaternary glaciation in North America, identified 11 major advances of the Laurentide ice sheet beginning in the late Pliocene. A first glacial maximum was dated at 2.1 million years B.P. (Before Present), and the last readvance of the Green Bay and Superior lobe areas ended approximately 10,000 years B.P. Thus, the process of colonization and retreat has probably been the norm for lake trout for over 2 million years. High genetic diversity might not be expected in a lacustrine species repeatedly forced into riverine environments by glaciation. For example, Bernatchez and Dodson (1991) reported an extreme loss of mtDNA for Mississippian (refugia) lake whitefish (Coregonus clupeaformis), the most common lineage in the present whitefish range, due to glacial-induced translocation. However, the post-Wisconsinan recolonization of the Great Lakes by lake trout, which was marked by evolution of deepwater forms (Behnke 1980) including humpers (Rahrer 1965) and siscowets (Saiveiinus namaycush siscowet) (Eschmeyer and Phillips 1965), suggests otherwise. This ecological evidence of diversity is consistent with genetic data that confirm the genetic differences among forms and among populations (Krueger and Ihssen 1995). Ihssen et ai. (1988) and Krueger et al. (1989) reported that of the total variation in lake trout, 14-21 % was due to differences between stocks, which was similar to that reported for non-anadromous salmonines (Reisenbichler et al. 1992). The genetic data support Behnke's (1980) observation

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that, although lake trout are taxonomically stable throughout their range, enough genetic differentiation has occurred in ecological, physiological, and life-history traits to allow adaptation by the species to a wide range of environments. Smith (1972) noted that lake trout was the only predator in the Great Lakes that occupied an entire lake from shore to shore and top to bottom. Examples of phenotypic differentiation in lake trout include: 1) maximum adult sizes of 281 g in a Rocky Mountain stunted population (Donald and Alger 1986) and 28,600 g in Lake Superior (Eschmeyer 1957)-two orders of magnitude difference; 2) a 16-fold difference in longevity between offspring of two geographically proximate populations (Plosila 1977); 3) habitation of depths to 426 m in Great Bear Lake (Martin and Olver 1980), which exceeds the 407-m maximum depth of Lake Superior; 4) success as either planktivores or piscivores (Martin and Olver 1980); 5) spawning in both lakes and rivers (Scott and Crossman 1973); and 6) a wide range of spawning times-June to January (Martin and Olver 1980, Goodier 1981) and April (Bronte 1993). Ryder et ai. (1981) have questioned whether the phenotypic diversity expressed by lake trout (and ciscoes) in the Great Lakes represented evolution of distinct genotypes. They postulated that the various forms of lake trout represented phenotypic not genotypic stocks, because of the short period since deglaciation. However, Eschmeyer and Phillips (1965) reported a genetic basis for fat content in lean lake trout and siscowets from Lake Superior (siscowets were twice as fat). Both forms bred true on the same diet in a hatchery and hybrid crosses had intermediate fat contents. The fat content in humpers, a third variety researched, continued to increase at advanced body sizes in comparison to leans, and one sample of the Green Lake strain of lake trout, a population originated in part from deepwater shoals in Lake Michigan, had a fat content similar to that of siscowets of the same size. These experiments on fat content are of particular ecological interest because high fat levels may be an adaptation to reduce energetic requirements associated with buoyancy regulation in vertically migrating fish (Alexander 1993). Eschmeyer and Phillips (1965) originally thought that the variations in fat content among lake trout genotypes might be related to different amounts of oily ciscoes (Coregonus spp.) in their diets, but, more recently, researchers have reported that the deepwater planktivore community in the Great Lakes migrates vertically at night (Janssen and Brandt 1980, Brandt et ai. 1991, Argyle 1992). The genetic differences in fat content among lake trout phenotypes may, therefore, have an ecological basis in reducing the energetic costs of feeding on deepwater ciscoes when they migrate from the bottom at night. The largest siscowets researched by Eschmeyer and Phillips had a muscle fat content (48% wet weight) that probably made them neutrally buoyant without a swim bladder (Alexander 1993).

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Other research indicates that phenotypic differences among lake trout are heritable. Successive generations of the Green Lake strain of lake trout spawned later (in November instead of October) than did other strains reared in the same hatchery (Krueger et al. 1983). Elrod and Schneider (1987) reported that planted lake trout from a shallow lake (mean depth < 13 m) in Manitoba inhabited shallower water in Lake Ontario than did lake trout strains from deeper lakes reared in the same hatchery. Eshenroder et al. (1995b) found that Seneca Lake-strain lake trout survived ·44 times better than did two other strains in matched-planting experiments in Lake Huron. Sea lamprey (Petromyzon marinus) predation was the major source of mortality on the Lake Huron lake trout. The concept outlined by Ryder et al. (1981), that rapid phenotypic adaptability of lake trout and ciscoes allowed them to proliferate in the Great Lakes after deglaciation, is logical, but their idea that phenotypic isolation did not result in new genotypes is less plausible. The evidence for distinct genotypes among the lake trout strains used in the Great Lakes is reasonably strong. Ryder et al. (1981) only cited one Great Lakes study (Smith 1964) to support their concept of phenotypic plasticity. They suggested that Smith (1964) reported that the loss of top piscivores led directly to introgression among the cisco species in Lake Michigan-an event consistent with their idea that piscivores were responsible for isolation of the cisco phenotypes. Smith stated, however,that the extreme scarcity of several cisco species coupled with the extreme abundance of another cisco species created conditions favorable for hybridization. Scarcity of the cisco species was caused by over-fishing and sea lamprey predation, not by loss of the piscivores. This issue of phenotypic versus genotypic stocks of lake trout remains uncertain, but the essential point of agreement is that the lake trout is an adaptable species. Spawning and Homing

Various studies reviewed by Martin and Olver (1980) suggest lake trout have, at least, some homing behavior. Arctic char (Salvelinus alpinus), a closely related species capable of spawning in lakes, shows homing behavior, and imprinting is presumed to occur (Nordeng 1977). Noakes et al. (1989) argued that species whose young spend considerable time in spawning beds would be selected for an ability to locate and use the best spawning sites. In salmonines, this strategy could have been accomplished most simply by return of adults to their natal streams. In the Great Lakes, where spawning habitats can be regionally scarce (Eshenroder et al. 1995a), homing ability becomes much more important for lake trout. One interpretation of these studies is that lake trout could not have been as successful as they were in the Great Lakes without a precise homing mechanism. Rearing young lake trout in hatcheries during a time in their life cycle when they would presumably be imprinting on spawning grounds has been identified as a possi-

ble impediment to reestablishing lake trout in the Great Lakes (Foster 1984). This practice may be especially detrimental to a shoal spawner like lake trout in contrast with the effect on introduced Oncorhynchus species, which reproduce in suitable Great Lakes tributaries (Emery 1985). Lake trout spawning habitats in the Great Lakes are spatially heterogeneous and selection of suitable sites by lake trout may be a more challenging task than is choosing suitable spawning riffles after anadromous salmonines select a particular stream. In terms of homing ability, lake trout stocked in the Great Lakes as advanced juveniles are, in effect, strays. Behavior associated with spawning-site selection could be random, a process potentially adaptive for anadromous salmonines because some of the strays select suitable streams and extend colonization. If site selection is random for strays, stocked lake trout might be expected to appear in abundance on many of the historically used shoals, including those offshore, but they do not. The weak ability of hatchery lake trout to concentrate on known historical sites indicates that they are not pre-adapted for spawning-site selection in large water bodies. Whether stocked in the Great Lakes or inland lakes, hatchery lake trout behave similarly-they spawn mostly along mainland and, to a lesser extent, island shorelines in shallow water (Eshenroder et al. 1995a,b; Gunn 1995; Schreiner et al. 1995). This behavior is adaptive in inland lakes where most of the spawning habitat is derived from shoreline erosion. This observation is consistent with an understanding that lake trout evolved before the Pleistocene (Behnke 1972, 1984), that is, before the Great Lakes were formed (Dorr and Eschman 1970). Much of the shoreline spawning habitat used by stocked lake trout in the Great Lakes may be unsuitable for egg incubation because of excessive water turbulence and erosion (Eshenroder et al. 1995b). The success of lake trout in the Great Lakes may be attributed both to the long time for colonization and low water levels that occurred about 9,500 B.P. (Hough 1963). This temporary dewatering, following the Lake Algonquin (high water) stage, made what subsequently became submerged shoals into islands whose shorelines were presumably more attractive to colonizing lake trout. Slowly rising water levels then provided time for lake trout spawning on island shorelines to evolve into deep-spawning populations. Deglaciation and the associated fluctuating water levels, therefore, abetted lake trout colonization, which otherwise was inhibited because, unlike the exotic anadromous salmonines that are fundamentally adapted to reproduce in suitable tributaries regardless of mainstream size, lake trout exhibit spawning behavior that is adaptive for smaller lakes where they probably evolved. An alternative explanation for selection of shallowwater spawning sites among hatchery-reared fish in the Great Lakes may be that some kind of conditioning to shallow-water results from rearing in raceways. A number of the offshore shoals stocked in Lake Huron, how-

Lake Trout Evolutionary Biology ever, were small islands (one supported a lighthouse) and catches of lake trout spawners were as low on these as they were on nearby submerged shoals (Eshenroder et aJ. 1995a). The abundance of hatchery spawners on mainland spawning sites, therefore, cannot be attributed to a simple preference for shallow water or the offshore, emergent shoals in Lake Huron should have yielded more spawners in assessments. Hatchery-conditioning effects may play some role in spawning-site selection by hatchery lake trout but these effects may be hard to elucidate because of involvement of more than one factor (Foster 1984). For instance, if shallow water and pheromones were involved together as conditioning effects, lake trout might be attracted to the mainland because it is shallow and a richer source of chemical cues. Although lake trout probably evolved from a fluvial ancestor (Savvaitova 1980, Cavender 1984) and are capable of spawning in rivers, several features suggest they have a long history in lakes. Balon (1980, 1984) identified unique ontogenetic features of lake trout, that in comparison with its congener (S. fontinalis), can be considered adaptations to lake spawning: large size of the perivitelline space and oil globules, delayed calcification of the skeleton, and delayed onset of negative phototaxis. He relates the first two adaptations to buoyancy regulation and the third to prevention of premature descent to deep water. Because stocked lake trout appear in many Great Lakes tributaries in the late summer and fall, anadromy in the native populations is of considerable interest. Milner (1874), however, stated that lake trout did not ascend U.S. Great Lakes rivers to spawn, and anadromy in Canadian waters was reported only recently (Loftus 1958). We identify a mechanism that may account for anadromy in native populations of lake trout in the Great Lakes. This mechanism is based on the idea that the riffles used by lake trout were formerly lake shoals that these fish continued to use when lake levels receded. Two geological features of the region in northeastern Lake Superior where lake trout did spawn in rivers could convert lake trout spawning shoals to spawning riffles. First, this area is one of two regions, the other being northeast Georgian Bay, of maximum isostatic rebound since the last high (Nipissing stage) lake levels of about 4,000 years B.P. Since that time, northeastern Lake Superior shorelines rose about 23 m (Larsen 1994). Second, rivers in the uplifted area are of high gradient, as evidenced by extensive falls and the coarse gravel and boulder deposits used by lake trout as spawning beds (Loftus 1958). Steep gradients also favor short ascents by lake trout, which required deep water either in Lake Superior or in lagoons, for concealment during daylight hours of the spawning period (Loftus 1958). High gradient streams without documented spawning populations of lake trout are plentiful in southwestern Lake Superior, but because the outlet of Lake Superior is rebounding faster than is this area, the lower sections of these

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streams have been submerged since the Nipissing highwater stage (Larsen 1994). The role of uplift in the development of river-spawning lake trout populations and Milner's (1874) observation of no spawning in U.S. waters are less plausible if such populations were fished-out before they could be documented. Milner, however, surveyed commercial fishermen in 1872 and 1873, who would seemingly have known about lake trout spawning at the time of the first permanent fishery settlements on the upper lakes, which began, for instance, only 40 years earlier in Lake Huron (Eshenroder et aJ. 1995a). Smith (1972) stated, however, that river-run lake trout and coregonines were common in the 1800s and that the largest populations disappeared in the early 1900s. The coregonine runs are well documented in reports of the U.S. Commission of Fish and Fisheries, but records for lake trout are lacking. The first take of lake trout eggs by the Commission was from northern Lake Huron in 1882, and these were shipped to a hatchery already established to culture whitefish that spawned in the Detroit River (Clark 1884). Even if lake trout were spawning in more rivers than were documented, as suggested by Smith, their prevalence was seemingly low. At Milner's time the only competing salmonine, except in Lake Ontario, was the brook trout. The success of the river-spawning salmonines introduced in the Great Lakes after many streams were dammed or otherwise despoiled raises a profound question; why were river-spawning lake trout apparently not widespread when rivers were yet pristine and large-bodied competing salmonines were absent? The good success with which lake trout have been introduced into Ontario inland lakes (Hitchins and Samis 1986, Evans and Olver 1995) is consistent with our interpretation of the evolutionary biology of spawning-site selection of lake trout. Stocking experience in the Great Lakes is also consistent. One way to encourage spawning in deeper water is to stock remote offshore, submerged reefs where distance and depth discourage migration inshore. Resident fish (those that do not migrate) on these reefs would presumably move into shallow water to spawn as they do near the mainland and islands, but because no shoreline habitat exists, deep-water spawning occurs on the tops of the reefs. This process is occurring on the Six Fathom Bank in Lake Huron, which is 60 km from the mainland and isolated by deep water (Eshenroder et af. 1995a). Conversely, lake trout spawners emigrated from an offshore reef (Reynolds Reef) stocked in northern Lake Huron that was within 20 km of the mainland (Eshenroder et aJ. 1995a). How distance and depth interact to discourage migration is unclear, but the mainland could be considered to be within the home range of lake trout stocked on Reynolds Reef, which is part of the lake's littoral zone. These observations from Lake Huron indicate why insights about evolutionary biology are important in developing programs for reestablishment of lake trout. The stocking strategy for the rehabilitation

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program in the Great Lakes was based on assumptions about how re-introduced lake trout would select spawning habitats, and when performance did not meet expectations, the patience of program managers was sorely tested (Eshenroder et ai. 1984). An understanding of how behavior for spawning-site selection might have evolved in inland lakes and how lake trout recolonizing the Great Lakes adapted to an environment of this scale is essential for developing effective stocking strategies.

Longevity Because longevity is such a salient feature of lake trout, we discuss its evolution and its significance for reestablishment of self-sustaining populations in the Great Lakes. Lake trout are the longest-lived char (Behnke 1980). They commonly reach ages of 20-25 yr and some northern populations have been aged from otoliths in excess of 60 yr (Martin and Olver 1980). Longevity in lake trout and its correlate, late maturation, are an extreme among North American trout and salmon. The exceptional longevity of this species (for a salmonine) may represent a trade-off in reproductive costs. The migration of other North American salmonines to special spawning habitats and burial of eggs could be viewed as forms of parental investment that carry large energetic and survival costs in relation to further reproductive effort (Winemiller and Rose 1992). An absence of extensive spawning migration and redd construction in lake trout may diminish the costs of reproduction, allowing for greater longevity. Their absence would also reduce the risk of adult mortality during spawning. Selection for increased longevity in lake trout could have occurred in glacial refugia. We assume that longevity evolved in lake trout because its closest living relatives, S. fontinaiis and S. ieucomaenis (Behnke 1980, Savvaitova 1980, Cavender 1984, Volobuev et ai. 1985, Gudkov 1992) are short lived, and their ancestor may have been diadromous, migrating between the sea and freshwater (Savvaitova 1980), a reproductive strategy associated with shorter life spans in salmonines (Stearley 1992). If refugia were rivers draining glaciers and lake trout were adapted for reproduction in lakes, a harsh physical environment (e.g., flooding) could have made reproductive success infrequent in lake trout. In this environment, longevity is favored as a means of increasing the probability that an adult will experience a year favorable for successful reproduction. Winemiller and Rose (1992) suggest that such an environment would also favor a reduction in maternal investment, another characteristic of lake trout discussed previously. Balon (1980), however, did not include lake trout with salmonines (graylings and landlocked salmons) having small eggs, a characteristic that would, were it in lake trout, be additional evidence of selection in an environment with large interannual variation (Winemiller and Rose 1992). If selection for longevity occurred mainly in lakes (during interglacials), an environment with relatively

low interannual variation, it may have been caused by a substantial predation-induced survival differential between juveniles and adults. Selection pressures that lengthen life decrease the value of offspring and increase the value of adults (Steams 1992). Over its geographical range, the lake trout is associated with a simple fish community, in which adults are virtually immune from predation (Martin and Olver 1980). Juveniles, however, are commonly vulnerable to burbot (Lata iota), fish-eating birds (notably loons, Cavia spp.), and adult lake trout (Evans and Willox 1991). Johnson (1972, 1994) theorized that adult lake trout in unperturbed lakes suppressed recruitment of their juveniles. Under such conditions of low or no exploitation, most of the lake trout biomass is in large, old fish. Adult anadromous salmonines, unlike adult lake trout, are exposed to a variety of fish and mammalian predators throughout their life. This exposure reduces selection for long-lived adults, and, instead, favors early maturation. Regardless of whether longevity in lake trout was a response to highly variable reproductive success in refugia environments or was an adaptation to low adult mortality during interglacials, the resulting life-history trade-off of reduced (for a salmonine) juvenile investment has implications for fishing, because lake trout fecundity remains low. That is, lake trout have two of the three characteristics (longevity and reduced juvenile investment, Winemiller and Rose 1992) associated with large pelagic species that are resilient to fishing, but unlike the fecundity of these species, the fecundity of lake trout is lowprobably because of phylogenetic constraints (salmonines have large eggs). The ability of lake trout to compensate for fishing mortality is, therefore, limited. Johnson (1972) was concerned that fishing in inland lakes could remove adult lake trout and destroy a balance between adults and juveniles. Overfishing of lake trout was evident or suspected in the Great Lakes at various times since the late 1800s (Hile et ai. 1951, Lawrie and Rahrer 1972, Hartman 1973, Coble et at. 1990, Eshenroder 1992), and the lake trout fisheries were essentially unrestrained since before the turn of the century. Although lake trout yield for the Great Lakes was steady for a long time (Baldwin et ai. 1979), Brown et ai. (1981) and Eshenroder et ai. (1995a) showed that some populations became extinct during this period of apparent stability. Intense fishing and predation by sea lampreys represented a profound change for lake trout. These processes are contrary to the selection regime under which lake trout evolved, and, if unrestrained, could prevent their rehabilitation in the Great Lakes.

Community-Level Features Behnke (1972) believed that the absence of other salmonine species was an important factor in the speciation process that produced brook trout and lake trout. Lake trout communities are relatively simple, and Arctic-lake communities are very simple. Martin and Olver

Lake Trout Evolutionary Biology (1980) listed only 19 fish species found in lake trout lakes, excluding the Great Lakes, and of these only one piscivore, the burbot, shares similar habitat. Carl et al. (1990) found that the highest density of lake trout occurred in small lakes with few or no other fish species present. In these lakes the presence of fish predators was found to negatively affect lake trout abundance. Lake trout are thought to have been early invaders of proglacial (melt water) lakes, which also would have had simple fish communities (Martin and Olver 1980). Evans and Olver (1995) argued that lake trout would have been among the first colonists to reinvade following deglaciation. Balon (1980) noted, in a discussion on lake trout ontogeny, that chars are the freshwater fish most capable of living in the coldest of waters. Thus, the fish communities in the proglacial lakes fronting the Laurentide Glacier were species-poor compared to the present Great Lakes. The fact that lake trout evolved and proliferated in simple fish communities raises important questions about their welfare in the Great Lakes. These large water masses provide a southern range extension for lake trout and a northern range extension for many temperate-zone fish. Also, being large, well connected, and widely settled by humans, the Great Lakes are subjected to considerable pressure for introductions of other biota. The consequences of introductions for a species that evolved in a simple fish community became evident when the sea lamprey invaded the upper Great Lakes (Smith and Tibbles 1980). Here, a life-history strategy of large size entailing late maturity made lake trout vulnerable because of intense size-selective mortality. Mills et al. (1993) listed 25 introduced fish species in the Great Lakes, several of which may be detrimental to lake trout. Krueger et ai. (1995) observed alewife (Alosa pseudoharengus) predation on lake trout fry in Lake Ontario. The alewife, an introduced fish, is widely distributed in the Great Lakes (Smith 1972) and may suppress recruitment of lake trout by feeding on their fry when they emerge in spring. Unlike the alewife, the native pelagic planktivore, the lake herring (Coregonis artedi), concentrates for spawning in late autumn when lake trout eggs are in rocky substrates protected from predation. Pacific salmon, successfully introduced in the 1960s, have diets similar (especially chinook salmon, Oncorhynchus tshawytscha) to that of lake trout (Brandt 1986, Jude et al. 1987, Conner et al. 1993). In a preliminary study applying bioenergetic models to Minnesota waters of Lake Superior, Negus (1992) estimated that introduced salmonines and lake trout were consuming more planktivores than were produced. Lake trout ration in these simulations, which did not account for migration of salmonines into or out of the study area, appeared to be at a minimum where further reductions resulted in only enough energy for maintenance. Lake trout and chinook salmon also appear to interact on spawning shoals in the North Channel, Lake Huron. Powell and Miller

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(1990) suspected that shoal-spawning chinook salmon were attacking spawning lake trout-the chinook salmon were much larger than the lake trout-which subsequently showed evidence of unusual wounds. This behavior was observed again and confirmed by the authors. It is of special concern because the lake trout involved are from one of only two native stocks remaining in Lake Huron (Berst and Spangler 1973). Evans and Olver (1995) discussed how lake trout, once established, exert predatory control over potential predators of its eggs, alevins, and juveniles. Johnson (1994) theorized that lake trout are an ecologically dominant species (in unperturbed lakes) that exerts control over other species in a successional process ending in reduced species richness. In his definition, dominant species were those least controlled in their abundance by other species. Likewise, Christie et ai. (1987) argued that the rate of rehabilitation of natural fish communities in the Great Lakes is very sensitive to the longevity of lake trout, a species whose biomass acts to dampen the sensitivity of the community to perturbations, whether natural or man-induced. Evans et al. (1987) also recognized that long-lived piscivores with large body sizes, in effect, store periodic reproductive success that contributes to the stability of the community that they dominate. Application of these concepts to the rehabilitation of lake trout in the Great Lakes suggests that prospects for successful reproduction would be improved if the biomass of older adults were largerlarge enough to achieve dominance. This idea is consistent with experience in Lake Superior where lake trout, mostly from stocking, were the dominant top-predator during the early phase of rehabilitation. Rainbow smelt (Osrnerus rnordax), an exotic prey species, declined sharply under these conditions (Hansen 1994). Fish diseases may prove to be a major result of interaction between lake trout and introduced Oncorhynchus spp. Oncorhynchus were stocked in the upper lakes without regard to suppression of bacterial kidney disease (BKD), which now is associated with severe chinook mortalities in Lake Michigan (Johnson and Hnath 1991). Unlike Oncorhynchus, lake trout are propagated from captive broodstocks managed for disease control. BKD pathogens have proliferated in Lake Michigan, and transmission to lake trout has occurred. Pathologists on the Great Lakes Fish Disease Control Committee report that 100% of the lake trout sampled from Lake Michigan test positive for BKD. ECOLOGICAL AND ETHICAL CONCEPTS FOR REHABILITATION Ecological Concepts

Why lake trout and why self-sustainability? Do lake trout have adaptations that make them especially productive in comparison with the introduced salmonines: brown trout (Sairno trutta), chinook, coho (Oncorhynchus kisutch), and steelhead (0. rnykiss)? Smith

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(1972) implied that the lake trout was facultative for depth, but the introduced salmonines are considered to be pelagic obligates. This ability enables lake trout to structure and transfer energy in both benthic and pelagic food webs. The benthic food web in the oligotrophic Great Lakes is especially important for fish production because two macroinvertebrates, Mysis relicta and Diporeia spp., make up the greatest biomass of large, highenergy particles for planktivores (Sprules et ai. 1991) and for juvenile lake trout. The significance of"the two macroinvertebrates is evident in the adaptive radiation of fishes stimulated by opportunities following deglaciation. Only deepwater forms evolved: five species of deepwater ciscoes (Coregonus spp.) (Smith and Todd 1984) and a deepwater lake trout form, the siscowet. The single remaining deepwater cisco in Lake Michigan, the bloater (Coregonus hoyi), migrates vertically at night (Argyle 1992) apparently to feed on Mysis which also migrates (Beeton 1960). Although the bloater in Lake Michigan has probably introgressed with other shallow-water and deepwater ciscoes (Smith 1964, Todd and Stedman 1989), vertical migration appears to have been a general characteristic of deepwater ciscoes in the Great Lakes. Wells and Beeton (1963) reported that Mysis was more important in adult bloater diets in Lake Michigan with increasing depth, and most of their specimens began life before introgression occurred in Lake Michigan (Smith 1964). The Mysis food web involving deepwater ciscoes was probably historically important because the extinct species of deepwater ciscoes were larger-bodied than the bloater and occupied deeper water (Smith 1964) where Mysis should have been even more important in their diet (Reynolds and DeGraeve 1972). Radiation of only deepwater forms and the magnitude of the resulting food web (bloaters dominate planktivore biomass in Lake Michigan, Sprules et al. 1991) indicates that vertical migration is a key feature of the ecosystem. Oncorhynchus are not successful predators on Mysis introduced in other North American lakes (Martinez and Bergersen 1989). Those authors believe that the absence of co-evolution and dependence on sight feeding results in Oncorhynchus not being able to locate Mysis when they migrate to pelagic waters at night. Mysis and the associated deepwater ciscoes would be available to sight-feeding Oncorhynchus during the day, but chinook salmon, the salmonine most desired by anglers, has not shown an ability for hypolimnetic foraging in the Great Lakes, even though it has been taken below depths of 110 m in the Pacific Ocean (Healey 1991). Tody and Tanner (1966) did not justify Oncorhynchus introductions because of a perception that lake trout were genetically impoverished. They wanted to suppress alewives with species that had outstanding angling qualities. Twenty-five years later, exotic planktivores (mainly rainbow smelt) and Oncorhynchus have declined substantially in Lake Superior, and lake trout have recovered to where introduced salmonines now make up less

than 10% of the lakewide catch of salmonines (Hansen 1994). Exotic planktivores (both alewives and rainbow smelt) are declining in the other Great Lakes as well (Brown et ai. 1987, Henderson and Nepszy 1989, Jones et ai. 1993), and with them the prospects for wide-scale salmon ranching. The difference between the events in Lake Superior and in the other lakes may well only be a matter of time. We accept that lake trout possess superior characteristics for foraging in the Great Lakes - why need they be wild? There are many well-understood, germane arguments about the inappropriate use of artificial propagation. They include costs of artificial propagation, problems with disease suppression, and, for the Great Lakes, the logistics of culturing a complex of deepwater and shallow-water forms and of dispersing them throughout the lakes. Perhaps more important are issues related to genetic diversity and how species persist in changing environments. Fish, like all organisms, are biological entities adapted by natural selection. Hatcheries interfere with this process (Waples 1991) and address only the symptoms of stock declines-not the causes (Meffe 1992, 1995). The recent collapse of chinook salmon in Lake Michigan (Johnson and Hnath 1991) is but one example of the difficulty of maintaining fitness in hatchery fish. Other examples are a newly discovered lethal virus that plagued lake trout hatcheries in the upper Great Lakes in the late 1980s (McAllister and Herman 1989) and the resurfacing of whirling disease in 1994 in Great Lakes fish hatcheries after it had been dormant since a costly outbreak in Michigan in 1968 (Yoder 1972). Ethical Concepts

The Great Lakes contained, until the 1940s and 1950s, the largest complex of wild char in the world. Ethical considerations emerge about the rights of one human generation to determine whether too much has already been invested in their restoration or whether lake trout are to be replaced with, or jeopardized by, introduced salmonines. Because the Great Lakes drain to the Atlantic Ocean, the ethics of causing the establishment of Oncorhynchus downstream where they may not be wanted is also an issue. Dumont et al. (1988) appropriately questioned the propriety of these introductions made without the consent of the Province of Quebec or other potentially affected jurisdictions. Questions of ethics or values are overshadowed by concerns about commodity production and economics. "The result has been that the economic manifestation of recreation, rather than its ethical aspect, is subverting the resource agency's mandate to manage for a conservation ethic" (G.R. Spangler, pers. comm., U. of Minnesota, 1987). Primary concern with commodity production constitutes a philosophy of "wise use," developed by G. Pinchot, that was subsequently recognized by Leopold (1949) as being based on an obsolete, pre-ecological scientific paradigm (Callicott 1991). This paradigm did not

Lake Trout Evolutionary Biology recognize evolutionary or ecological relations among species and their environments. Nevertheless, the wise use philosophy persists in part because decision-makers perceive production and its importance in an industrial economy to be a model for nature (Lichatowich 1993) rather than nature being a model for a good economy. Nature does not function like an industry (Lichatowich 1993), and resource agencies must contend with deeprooted social concerns because their programs are, in fact, a search for values (Scarnecchia 1988). These ethical values do not change with shifts in societal and economic interests (Pister 1995). Pister (1995) illustrated that although people cherish fish because of attributes that evolved in them millions of years ago, their horizon is short-sighted. Should an attempt be made to restore lake trout to an original condition or should they be rehabilitated to a lesser state? This is an important question, but the notion that pristine conditions cannot be completely recreated has been rationalized to justify an indefinite need for introduced piscivores and even preservation of exotic planktivores. The direct beneficiaries of alternative management programs are, however, not particularly concerned about ethical (and ecological) ideas and exert enormous pressure for fish community configurations whose sustainability is questionable. Fears of alewife scarcity in Lake Ontario prompted cuts in stocking rates of lake trout and two of five other (stocked) salmonines. In Lake Michigan, alewife scarcity was suspected as a cause of the catastrophic chinook salmon mortalities, yet stocking levels have hardly changed. The risks to native forms from BKD were discounted by the enormous pressure to maintain the fishery. These examples support Eshenroder's (1989) prediction that as artificial systems destabilize, managers will be pressured to take even more risky actions. Managers have resisted the worst of the solutions proposed by their clients, but years of communicating purpose based on commodity production has had its effect. An entrenched belief that nature has only instrumental value is still prevalent. We believe that long-term solutions to fish-stock recovery in the Great Lakes require an evolutionary-ethical foundation as originally defined by Aldo Leopold. Ethically sound programs are inevitably biologically sound and enduring (Pister 1995). An ethical approach will also require collaboration with other groups presently excluded from policy making, e.g., environmental managers and their clientele. Other solutions lack a scientific rationale and values that can be widely accepted. RECOMMENDATIONS FOR MANAGEMENT AND RESEARCH What we ought to be doing is recognizing these changes [lake trout losses since settlement] and engineering a fish that can live in the lakes. -Detroit Free Press, 25 February 1994

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Nature has provided a fish, the lake trout, that, as evidenced by its history, can flourish in the Great Lakes. Its evolutionary biology provides insights that, applied to management, can improve the prospects for its rehabilitation in each lake. First, considering strategies relevant at an organismal level, the stocking programs in each lake are only using a fraction of the genetic diversity catalogued by Krueger and Ihssen (1995) for the Great Lakes region. Other undescribed sources of diversity may exist in lakes that were separated from the Great Lakes during the last high-water (Nipissing) stage, which ended about 4000 B.P. The genetic integrity of these sources should be protected. Deep-water forms of lake trout from Lake Superior should be incorporated into stocking programs in Lakes Michigan and Huron where they are now extinct (Brown et al. 1981, Eshenroder et al. 1995a). The evolution of much of the former diversity within lake trout in the Great Lakes, the deepwater forms, was probably facilitated by changing lake levels. The geological process probably responsible for the diversity obviously cannot be reemployed, but better use should be made of the existing diversity. The evolution of spawning behavior also has implications for management at the organismal level. Lake trout stocked at the yearling stage are essentially colonists or strays with a predilection in the Great Lakes for spawning in shallow water along shore1ines-a trait associated, we believe, with inland-lake ancestry. Managers are already attempting to circumvent this problem by stocking remote reefs with yearlings (Eshenroder et al. 1995a, Holey et al. 1995) and by stocking embryonic life stages that have the potential to imprint to historically used spawning sites (Holey et al. 1995). Although the very remote reefs are already being stocked with yearlings in Lake Michigan and Huron, use of deepwater strains of lake trout on these sites is also recommended. The current program of stocking embryonic life stages is small in relation to the potential benefits. We recommend an expanded program of stocking lake trout on historically used reefs at a life stage when they can imprint. At the population level, the foremost concern for management is increasing natural recruitment by reducing mortality on adult lake trout. This can be accomplished by concentrating stocking in the best habitats and by minimizing adult mortality from fishing and sea lampreys. Eshenroder et al. (1995a) showed that the use of a majority of the spawning habitat in Lake Huron's main basin is deferred for lake trout stocking to allow liberal commercial-fishing regulations. We recommend a reconsideration of policies that defer using vast amounts of habitat for rehabilitation. The sea lamprey-control program should also be expanded and harvests of lake trout should be regulated to keep total mortality below 50%, a figure linked by Healey (1978) to lake trout population declines. The status of lake trout in the Great Lakes fish community is largely determined by fishery management and

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efforts to suppress sea lampreys. Lake trout evolved as a dominant piscivore capable of shaping the remaining community (Ryder et ai. 1981, Christie et ai. 1987, Evans et ai. 1987, Johnson 1994). The enriched fish fauna in the Great Lakes is detrimental to lake trout rehabilitation. If lake trout have the potential to alter the community to their benefit, which appears probable (Hansen 1994), they should be managed to be dominant in Lakes Michigan, Huron, and Ontario as they are in Lake Superior (Busiahn 1990). This recommendation means deemphasizing Oncorhynchus stocking, preventing new introductions, and returning, as much as possible, to the original fish community. Most of our preceding recommendations have social ramifications that entail a major challenge for implementation. We suggest two approaches. One involves public education about ecological rationales for native species and self-sustaining fisheries. The other involves widening the stakeholder base in the policy-making process. Because fishery management agencies around the Great Lakes have traditionally emphasized commodity-production values, direct users, anglers and commercial fishermen, have become almost exclusive clients. This emphasis should be changed. A wide majority (87%) of fishery and environmental managers working on the Great Lakes support lake trout rehabilitation (Knuth et at. 1995). We recommend that the Great Lakes Fishery Commission support and coordinate a public-education effort. Research is needed to support our recommended management strategies for lake trout. Genetic research such as undertaken on lake trout in Lake Ontario by Grewe et ai. (1993) is required to monitor strain performance as well as to identify new strains for potential use in the Great Lakes. Stocking of early life stages should be done experimentally with a goal of assessing when imprinting occurs. The population dynamics of adult lake trout have been extensively researched in the Great Lakes; not as well researched was the linkage between adult populations, their use of spawning habitat, and factors limiting recruitment. At the community level, trophic relations as expressed by species succession and dominance (Ryder et ai. 1981, Christie et ai. 1987, Evans et at. 1987, Johnson 1994) are of particular interest. Can the oligotrophic Great Lakes be kept in an early successional stage dominated by exotic planktivores and Oncorhynchus? If lake trout are managed as a minor species among the piscivores, will burbot assume the ecological role of lake trout? If lake trout are the dominant piscivore, could a restructured community be more sustainable and provide more fishing opportunities than an exotic planktivoreOncorhynchus community? These questions relate to the future of salmonines in the Great Lakes and should provide a central focus for ecological-research programs. Additional social research as started by Knuth et at. (1995) is also recommended. Assessment of stakeholder values and an understanding of how such values change

are needed to support programs of public education about the Great Lakes ecosystem and its indigenous species.

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