Activity 1 - Resource Sheet 1

Lake Trout: a Cautionary Tale (Secondary)

Lake trout (Salvelinus namaycush) were once the kings and queens of the Great Lakes fishery.  They are considered, biologically, a keystone species:[1]  remove it, and the whole system may unravel.  And it did.

To begin at the beginning, lake trout can be considered a "glacial" fish, well-adapted to the cold meltwaters pouring off the front of glaciers.

Researcher holds a 25-year-old wild lake trout from Stannard Rock, Central Lake Superior (United States Geological Survey).

During the warmer interglacial periods such as the one we’re in now, lake trout generally retreat to the colder waters of deepwater lakes.  As a result, while lake trout are found across Ontario’s quarter- to half-million lakes, they are actually found in less than 1% of them.  That 1% includes the Great Lakes, where, at the advent of European settlement, they were the dominant predator, dining on lake herring, chubs (deepwater ciscoes), sculpins, sticklebacks, whitefish, smaller lake trout and a range of invertebrates.   They are a large (can easily exceed 23 kg; angling record, Lake Superior, over 28.6 kg.), long-lived (commonly 20-25 yr., up to 60), slow-growing, late-maturing (6-7 yr.) char, a relative of the brook trout. Historically, at least 15-20 different forms of lake trout were recognized by commercial fishermen before sea lamprey invaded.  These fish differed in where they were found, when they spawned, and in their appearance.  They were given such names as blacks, redfins, yellowfins, paper bellies, fats, humpers and sand trout. Today there has been so much interference with wild lake trout as a result of commercial fishing, sea lamprey predation and stocking, that these once recognizable forms are gone, blended into the stocking gene pool or so small and isolated that they are rarely encountered or recognized.  Biologists manage lake trout based on two recognized and generally distinct populations:  siscowet [2] or deepwater lake trout (> 90 metres) and leans or shallow water (< 90 metres), near-shore lake trout.

A lake trout fishery existed in pre-settlement times, and grew with advances in fishing and distribution technologies to a yield of 7.7 million kilograms annually in the Great Lakes.  Superior generally yielded about 2.3 million kilograms each year, Lake Huron somewhat more, during the first half of the 20th Century.  Then the bottom fell out and catches plunged to 10% of original yield in "lucky" Lake Superior and basically nothing in the other Great Lakes.  Why?  There are at least three reasons: 

• Sea lampreys dangling from adult lake trout (United States Geological Survey)

  Fishing pressure.  While yields were relatively steady, fishing pressure was gradually increasing and fishing gear was getting more efficient.  Stock densities were falling, and discrete stocks were being wiped out, some nearshore ones even prior to 1900.  The very adaptations that had proved so successful - late maturation, slow growth and long life, were of little use and some detriment.  Fishing pressure became unsustainable.
• Sea lamprey predation.  These exotics passed through the newly developed Welland Canal and invaded the upper Great Lakes in sequence, peaking in Huron around 1950 and in Superior 5 to 10 years later.  Almost simultaneously, lake trout stocks plunged and lamprey-scarred fish became the rule.  Fortunately for Lake Superior, lamprey control methods were developed before populations were wiped out.  Huron was not so lucky - only two isolated populations of native lake trout survived in Ontario waters.
• Habitat degradation.  Over this same period, the Great Lakes came under pressure from industrial, commercial and residential development.  Dredging, siltation, over-fertilization and toxic pollution added to the lake trout’s burden, particularly affecting the "lean" stocks closer to shore.  These impacts were less in Huron and Superior than in the other Great Lakes, but were, and still are in some cases, locally significant.

By the 1960’s, perhaps the environmental low point in Great Lakes history, the native fish community was in disarray.  Lake trout, lake sturgeon and lake herring populations, as well as some other deepwater fish, had collapsed.  Heavy recreational and commercial fishing and habitat losses had reduced or eliminated stocks of coaster brook trout and other species.  Many small communities on the lake coasts disappeared with the destruction of the fisheries. Deprived of its top predators and beset by increased fishing pressure and an increase in the exotic alewife and smelt, the rest of the fish community began to unravel.  Several chubs may have become extinct. Without significant predation, smelt and particularly alewife populations exploded, then suffered periodic dieoffs, windrows of dead fish on the shore of some Great Lakes a grim reminder of the invisible problems beneath the waves.

Alewife Die-off (USGS)

Those windrows were also a wake-up call, and people and governments responded.  Lamprey were brought under reasonable control.  Commercial harvest of lake trout was severely limited or closed.  Development issues were, and continue to be, addressed.  A series of bi-national Great Lakes Water Quality Agreements began in 1972, greatly reducing the point-source discharge of pollutants into the lakes.   The waters began to clear.  Pacific salmon, brought in to control smelt and alewife, did just that, and provided a thriving sport fishery, to boot.

Once the lakes were stabilized and recovery more than a faint hope, thoughts returned to the once keystone species.  Now, said fisheries managers, is the time to bring back the lake trout.

More than 180 million stocked fish later, results are, to say the least, mixed.  Superior, impacted the least, responded the best.  Stocks native to the lake responded, and reproduced.  Today, wild stocks in many parts of the lake are at 90% of pre-crash levels, and in two areas those levels are exceeded.  Most of those populations are once again self-sustaining.  Only in the southeast are higher than normal harvests limiting recovery, and their commercial quotas have recently been reduced.

The other Great Lakes are another story.  After years of significant effort, there is little reproduction of "wild" fish.  The reasons for this are likely many, and to some degree synergistic:

• Stocking is an evolving science, and at the time, we just didn’t know enough to properly address a problem as complex as lake trout restoration.
• All those discrete lake trout stocks had evolved for a reason:  reproductive success of lake trout in each area.  The fish were in effect "tailor-made", but many of those stocks have disappeared forever.  It will take time to find  and test stocks which may be reasonable replacements.
• People want fish, and fishing opportunities, now.  In responding to these desires, we may not be giving lake trout the opportunity to accumulate the necessary "critical mass" of large spawners.
• An undetermined amount of fish are being illegally netted, adding to the fishing pressure (an estimated 5 times the legal catch in some regions).
• Lake trout evolved and achieved success in fairly simple biological systems with no direct competitors.  They are being reintroduced into lakes now teeming with other large, exotic predators:  Chinook and coho salmon, brown and rainbow trout.  While lakers do not directly compete with these fish for spawning habitat, they all use the same forage base - one that has been altered significantly since the lake trout was dominant.
• A lot of people prefer to fish for the introduced sport fish, and there is pressure to use scarce stocking resources to maintain those fisheries.
• General and regional lake conditions may not yet have returned to a level of quality where overall reproductive success is assured.
  

There is, however, hope for the lake trout in Huron and elsewhere.  Stocking issues are better understood.  Particular genetic strains are now being assessed for reproductive success.  Younger fish are being released on historic, mid-lake, rock rubble spawning shoals in the hope that they will "imprint" on them and return to spawn.  Particular areas are being made into refuges, safe from all fishing, to allow uninterrupted recovery.  Researchers are delving into the laker’s critical first year of life, and why mortality is so high then.  The forage base seems to be evolving back into the native, deepwater herring/chub complex lake trout are best adapted to.

Lake trout eggs are placed on astroturf and bundled into crates for placement on natural spawning reefs (USFWS)

Along the Huron portion of the GLHC,  remnant wild stocks in Iroquois Bay, just east of the North Channel, and in Parry Sound are showing progress.  In fact, about half of the Parry Sound stock is now wild, and stocking was discontinued in that area in 1997.  Increased efforts have begun in controlling lamprey in the St. Mary’s River, the last major source of sea lamprey in the Lakes and just upstream of the North Channel.  Initial assessments of results are positive, and may open the door to further lake trout restoration along the coast.  However, these trout must spawn along rock rubble, nearshore banks, and these areas are sensitive to local impacts.  Additional efforts to curb these impacts may be required before wild reproduction succeeds.

Lake trout egg (USGS).

The final questions may be:  Why lake trout?  Are they really that important?  Is it enough that they were once there, and are now not because of our actions?  Is it enough that they may be the only large predator with the potential for self-sustainability?  Is it even sensible to "restore" a species to its original habitat if neither the fish nor the habitat are "original"?  The answers may determine whether the social and political will is there to complete the task.

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[1] Species whose ecosystem impacts are large, and greater than would be expected from abundance or total biomass; removal changes ecosystem structure and often reduces biodiversity.

[2] also called "fat" -- fat helps regulate buoyancy, allowing the trout to easily move up or down