(Published in Spring 2018)
Or, in other words, can our coho and Chinook salmon in Lakes Michigan and Huron adapt to a new forage base?
And, can they change from being pelagic predators, feeding in open water at mid-depth to foraging on the bottom?
To review how we got to this point, the quagga mussels caused the plankton levels to decrease enough to cause the alewives to crash in Lake Huron a number of years ago.
A similar crash in Lake Michigan is approaching but it has taken longer for that to happen.
The reasons are likely the greater depth of Lake Michigan and that there are more nutrients feeding into Lake Michigan. The additional nutrient load is partly due to the fact that many more people live in its vast watershed.
Based on reports from anglers and charter boat captains last fall the numbers of salmon were down in Lake Michigan but there were a fair number of large salmon, a seeming enigma. The scarcity of plankton has reduced the alewife numbers to record or near record lows.
Coho and, especially, Chinook salmon are very dependent on alewives in their diet.
These fish prefer to feed up in the water column, they are what biologists call pelagic predators and the pelagic zone is also where you find alewives, filter-feeding on plankton.
The round goby, another invasive species, is turning out to be good for the food chain in that this species is feasting on the mussels. Just think about what the lakes would be like if most of their bio-energy was tied up in the mussels. We would have an ultra-clear but very sterile Lake Michigan.
The good news is that lake trout, steelhead, brown trout, and, even, whitefish are feeding heavily on the mussel eating gobies.
This essentially gets the nutrients back into the food chain. And, as has been reported in these pages, another positive for this change in the forage base is that gobies are in one way, better food for salmonids.
Alewives have an enzyme, thiaminase, which breaks down an important nutrient, thiamine, for these fish. Gobies do not have the same level of this enzyme. Thiamine is a fairly critical element in their diet and the lack of it was considered to be having a major negative impact on the natural reproduction of lake trout. The evidence is obvious in that lake trout are reproducing well in Lake Huron and their natural reproduction is rapidly increasing in Lake Michigan.
In addition to not being as available to all the predators in Lake Michigan, the other negative to gobies is that the trout and salmon grow faster when eating alewives.
This probably has something to do with the fact that alewives have a higher fat content. And it appears that a portion of the salmon population found concentrations of the remaining alewives in 2017 and took advantage. But the value of the gobies getting the mussels back into the food chain can’t be overstated.
While lake trout are doing very well and have become the mainstay of the northern Lake Huron fishery, most big lake anglers don’t want to give up their silver fish.
Some think the answer might be to just plant more steelhead.
That is a lot easier said than done. It is much easier to raise Chinook to smolt size than steelhead. Another possibility might be to open up additional cold water river miles for steelhead to spawn in via dam removals and ladders or other fish passages or devices.
We are going to get a boost in natural reproduction soon with the removal of the dam on the Dowagiac River near Niles and possibly with the removal of the dams on the Boardman (if they elect to pass steelhead upstream). This will open many miles of mainstream and cold-water tributaries where the steelhead can spawn.
More steelhead will help but I think it is too soon to give up on the salmon.
Acoustic surveys show that the survival of the 2015 year class of alewives was fairly good as was the hatch of the 2016 year class. We had two mild winters in a row but last year was a strange but overall, probably an average winter so we shall see. But, only if these young alewives can find enough to eat. We must also remember that these year classes are still among the weakest recorded.
Perhaps the better hope for reasonably good salmon fishing in the future will be the ability of these fish to adapt to the new forage base.
We are already seeing signs that coho salmon are focusing in on gobies. In northern Lake Huron, some Chinook were caught that had gobies in their stomachs too. We old-timers remember when the Tule Chinook strain from Oregon was first introduced they all tended to turn dark before entering the rivers in late September. These fish were almost ready to spawn. Then natural selection took over in our northern Lake Michigan tributaries where early returning salmon seemed to have a competitive advantage. It didn’t take many generations before we had wild, silver Chinook returning in July and August, still many weeks away from spawning.
Both wild Chinook and coho have also been able to adapt to the pressure that a closed weir on the Little Manistee put on them.
The weir is usually closed in August and not opened until the end of October. This has resulted in the development of an early run of silvery wild Chinook in early July.
Coho took the other option and stayed in the lake until November and then ran the river. The result was a strong run of wild fish that were significantly larger than the average coho.
A good fishing buddy of mine “complained” about the numerous double figure cohos hampering his November steelhead fishing last fall, “they kept beating the steelhead to his lures.”
It is also important to note that Chinook do feed on bottom-dwelling fish in the ocean. Anglers fishing in the Pacific Ocean near Alaska often catch Chinook salmon with scratches on their gill plates from rubbing against rocks.
Sand lance, a very slender forage fish that lives on the bottom and can quickly dive/burrow into the cracks and crevices of the rocky substrate, are found in the stomachs of these salmon. So I am thinking that when necessity calls, our salmon will adapt and find a way to add round gobies to their diet.
Many of us tend to forget how tough the transition to the lake is for salmon and steelhead smolts.
While our fish don’t have to make the adjustment to saltwater, they do have to find food and avoid being eaten. Finding food has become much tougher because of the lower levels of plankton. Zooplankton are relatively small critters but they are very important in the diet of the young salmon.
Predators abound at the river mouths of the tributaries because the rivers carry nutrients and are almost always warmer than the Lakes in the spring. Smelt are also attracting predators as they make their spawning runs. Alewives spawn in the lake and later than the smelt but they also move closer to shore.
And, since our adult salmon, steelhead, and brown trout are also looking for food as the lake warms they have no problem becoming cannibals.
Cormorants and other fishing eating birds are also arriving from their southern sojourn further putting stress on these young fish.
Wild smolts will likely be able to make the transition more easily than planted smolts. They have spent their whole life dodging predators and finding food while hatchery smolts have been fed and protected from predators. This is another reason we should place special value on our wild fish. Now that the salmon are mass marked, it might be time to consider releasing a major portion of the wild salmon we catch in the Big Lakes.
This year we had a cold spring followed by a rapid warm-up in May.
A mild spring can be good news or bad news. Chinook smolts often migrate to the beach at night and during low light periods to feed on insects and other terrestrial food items. This activity will cease when the water at the shoreline gets too warm. This migration pattern may explain why Wisconsin seems to be having a bit better smolt survival as with the prevailing west to east wind pattern; their nearshore water is often cooler than Michigan’s. Cold water is up-welled on their side of the lake and warm surface water is piled up on Michigan shoreline.
On the other hand, a warm spring promotes an earlier thermal stratification of lake.
We are all familiar with the thermocline, a narrow zone of water where the water temperature drops rapidly from the warm surface zone (epilimnion) to the cold deep layer (hypolimnion). Plankton, both phytoplankton and the zooplankton that feed on phytoplankton migrate vertically on a daily basis. When the lake thermally stratifies the thermocline acts as a barrier to the vertical migration of plankton. We end up with a concentration of plankton and the fish that feed on the plankton at the thermocline.
Modern sonar (graphs) can detect this concentration.
The thermocline also concentrates the salmon and trout we are after since they can find food and a comfortable temperature in this band.
When much of the plankton is “trapped” in the thermocline, there is less of it for the mussels to ingest. So an early and prolonged stratification of the lake is good news for the forage base and the salmon and trout that prey on these small fish.
The quagga mussels currently have the trophic levels of Lake Michigan out of balance, especially as far as we anglers are concerned. But this angler thinks that this is somewhat temporary.
The mussels have exploded in numbers but are already starting to stabilize and even decline in some parts of the lake. Soon their population will decline further and reach some sort of balance.
We will probably never see salmon populations like they were in the banner years but as an ever-optimistic angler, I believe they will adapt and return to numbers that will provide a decent fishery.
Early 2018 Lake Fishing
The fishing for salmon, both coho and Chinook, was very good in southern Lake Michigan this spring. The fish were plentiful and their condition was good, indicating that the salmon were finding ample prey.
The not so good news is that this good salmon fishing did not extend to the northern half of the lake.
However, while salmon were relatively scarce, northern Lake Michigan anglers did enjoy excellent fishing for lake trout. Anglers also reported that they observed good numbers of baitfish and that some larger alewives were found in the stomachs of their catch.
Maybe we are starting to see a leveling off or decreasing effect of the mussels on the plankton and the beginning of an alewife rebound.
Let us hope so, time will tell.
- written by Jim Bedford