Activity 1 - Resource 2

A Lake Trout Story (Elementary)

Lake trout were once the kings and queens of the Great Lakes.  They were like a spider at the middle of a web:  remove it, and the whole system may unravel.  And it did.

To begin at the beginning, lake trout live and grow best in very cold water.  When glaciers were near, lake trout were probably found in most Ontario lakes.  During warmer periods, such as the one we're in now, lake trout generally retreat to the colder waters of deepwater lakes.

As a result, lake trout are found in less than 1% of Ontario's quarter- to half-million lakes (about 4000 or so).  But that 1% includes the Great Lakes. 

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

When Europeans first came here, lake trout ruled the Great Lakes,dining on other fish, smaller lake trout and a range of aquatic insects and shrimp.  They are:

• large (can easily top 23 kg, the average weight for a 7 year-old boy; angling record, Lake Superior, over 28.6 kg),
• can live for a long time (commonly 20-25 years, up to 60),
• grow slowly, and mature late for a fish (6-7 years).  

Historically, at least 15-20 different forms or types of lake trout were recognized by commercial fishermen.  These fish differed in where they were found, when they spawned (reproduced), and in how they looked.  They were named blacks, redfins, yellowfins, paper bellies, fats, humpers and sand trout. Today, most of these forms are gone.  Scientists now recognize two forms:  siscowet or deepwater lake trout[3] found deeper than 90 metres, and leans or shallow water (less than 90 metres), near-shore lake trout.

People living near the Great Lakes have always fished for lake trout.  Small amounts caught by scattered tribes grew with increases in population and better ways of catching fish to a yearly catch of 7.7 million kilograms in the Great Lakes.  Lake Superior fishers generally caught 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 the old amounts 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 the total catch stayed about the same, more people were catching fish with better and better equipment.  Lake trout numbers were falling, and some of those different forms were wiped out, some nearshore ones even before 1900.  The very adaptations that had proved so successful – late maturation, slow growth and long life, meant that populations could not quickly bounce back.
• Sea lampreys.  These new, blood-sucking parasites passed through the Welland Canal (going around Niagara Falls) and invaded the upper Great Lakes, peaking in Huron around 1950 and in Superior 5 to 10 years later.  At the same time, lake trout numbers dropped, and most of the trout left had lamprey scars.  For-tunately 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 problems.  Over this same period, the actions of people hurt the Great Lakes.  Digging out ship channels and canals spread mud and silt over the bottom.  Sewage and fertilizers made the wrong kind of plants and animals grow, and toxic pollution poisoned the lake trout, in particular the "lean" stocks closer to shore. 

Alewife Die-off (USGS)

By the 1960s, perhaps the environmental low point in Great Lakes history, the native fish community was in tatters.  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 shallow-water species.  With no fish left to catch, many small communities on the lake coasts disappeared.  Without its top predators the rest of the fish community began to unravel.  Several chubs may have become extinct. With nothing to eat them, smelt and alewife populations[4] would explode and then die off from low temperatures or lack of food, leaving piles of dead fish on the shore of some Great Lakes.
 

Those windrows were also a wake-up call, and people and governments responded.  Lamprey were brought under reasonable control.  Commercial fishing for lake trout was severely limited or closed.  Development issues were, and continue to be, addressed.  A series of water quality agreements greatly reduced pollution.  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 recovery of lakes began, thoughts returned to the former king of the lakes.  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, with fewer problems than any other lake, responded the best. Stocks native to the lake began to reproduce, and increase. Today, wild trout in many parts of the lake are at pre-crash levels. Most of those populations can once again maintain their numbers without help. Only in the eastern part of the lake are numbers below normal, and some fish are still stocked there.

In Lake Huron, lake trout have been increasing in the main part of the lake since 1998, a result of both successful sea lamprey control efforts in the St. Mary's River and new catch limits in U.S. waters. In addition, invasive alewife numbers are down and native lake cisco numbers are up in some locations, and they are better food for lakers. Chinook salmon compete with lake trout for food, and their numbers have also gone down. As a result, 40% of a growing lake trout population sampled by MNR in 2010 were wild fish, not stocked.

In Georgian Bay, remaining wild stocks are increasing near Parry Sound, and stocking stopped in that area in 1997. However, lake trout are declining in other parts of Georgian Bay, particularly in the south, in spite of stocking and other efforts to increase the population. 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.

In Lake Ontario, Lake Trout are not reproducing enough to reduce significant levels of stocking.

So while there has been some success in lake trout rehabilitation, Dave Gonder, an MNR biologist states, "It’s kind of a balancing act right now. We don’t really know what the future holds." The may be many reasons for this, and they may affect one another:

• We may still not know enough to properly address a challenge as complex as bringing back lake trout.
• All those forms of lake trout had evolved for a reason:  the ability to reproduce well in each specific area.  But many of those forms have disappeared forever.  It will take time to find and test forms which may be reasonable replacements.
• People want to fish now.  In trying to meet these needs, we may not be leaving lake trout alone long enough to build up the number of large spawners needed to produce enough fish.
• An unknown number of fish are being illegally netted, adding to the fishing pressure (an estimated 5 times the legal catch in some regions).
• Lake trout originally ruled 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 have to eat the same food - food that is very different than when lake trout was last the boss.
• A lot of people prefer to fish for the introduced sport fish, and there is pressure to stock more of those than lake trout.
• General and regional lake quality may not be good enough yet for healthy populations of lake trout. The lakes continue to change, in part due to invasion by zebra and quagga mussels, which have decreased the quality of historic laker spawning reefs, and reduced the amount of plankton that can be eaten by young lake trout. Another invader, the round goby, eat lake trout eggs and fry.

There is, however, hope for the Great Lakes lake trout. We are getting better at picking successful types, or strains, of fish. 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 looking into the laker's critical first year of life, and why so many die then. The food supply seems to be changing back into the types of fish lake trout like best.

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

Lake trout egg (USFWS)

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 that may be able to hold its own without our help? 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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Footnotes: [3] also called "fat" – more fat makes the fish lighter in water, allowing the trout to more easily move from deeper to shallower water

[4] smelt and alewife are two fish that were introduced by accident to the Great Lakes.