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Location: Essexville, MI./Saginaw Bay. | Probably not what you thought the post was about, but includes some great explanations and knowledge shared about why our Saginaw Bays Perch populations are down. On my fishing board a discussion by Many of the "Old Boys" who grew up having great fishing for perch, blames the resurgence of our walleyes for their demise. This E-mail from my DNR biologist buddy explains it nicely and sheds light on the ecological dynamics at work in virtually any other body of water as well. Enjoy.
Just got this E-mail: Some of it confirmed my thoughts on the subject, but some of it also dis-proved and shed new light on what I simply assumed. I welcome the DNR's science and years of knowledge involved in collecting the Saginaw Bays history, as well as it's obvious conclusions.
Dan:
In a nut shell its like this:
From the 1940s until 1993 we had lots of yellow perch reproduction in the bay (or at least enough) that it created good fishing. If anything we had so many their growth rates were slow, even stunted. In 1993/94 zebra mussels invaded and perch recruitment (reproduction) declined. The exact mechanism wasn’t clear but there was less yellow perch coming up in the system. This helped improve growth rates but meant fewer perch. Still perch numbers were good enough that we enjoyed decent fishing. The alewives collapsed in 2003/04 (and remain scarce ever since). What does alewives have to do with it you might ask? Two things: In the absence of alewives Percids (perch and walleye) reproduction exploded. We’ve all seen the effects of that on walleye (now recovered), but what about perch? Turns out we know from our fall survey that yellow perch are reproducing like crazy (we see scads of age-0s or ‘young-of-the-year’) in September (with our trawl sampling), but we don’t see hardly any age-1+ (yearling and older). We hypothesize that the alewives were buffering the predation on perch. Meaning predators were eating alewives (especially YOY alewives that used the bay as a nursery grounds for their first year of life). So alewives were a “double-edged sword” for yellow perch. They affected their reproduction (depressed it) but also buffered them from predation. In the absence of alewives we get super reproduction of perch but very poor survival.
It’s not only the walleye that are eating perch. All the predators we examine in the September survey are feeding on yellow perch, but there are more walleyes than any other predator so we tend to think of them most as the ‘culprits’. By now you should be asking: “wait a minute, we historically had both abundant walleyes and yellow perch, even before alewives invaded back in the 1950s, so how come it’s an ‘either/or’ situation today?”. Our hypothesis is that historically cisco (lake herring) buffered predation on young perch from walleye (and other predators). Cisco and alewives are trophically very similar (both pelagic planktivores that both used the bay for spawning and nursery grounds). The key difference is that cisco didn’t have the same suppressive or deleterious effect on perch reproduction that alewives do. We believe this is because cisco are fall spawners (alewives are spring spawners). We believe the main mechanism that alewives affect perch reproduction is by feeding on their emerging fry in the spring. Percid fry hatch off just about exactly the same time that huge numbers of adult alewives entered the bay (to spawn). With cisco, our walleye and perch fry were already grown up to a fingering size that was too large to be eaten when cisco entered the bay (for fall spawning).
So there is lots of good things going on in the bay (in the absence of alewives) but there are still some things ecologically broken. We suspect it is this important historically linkage between the main basin of the lake (producing and bringing in huge numbers of pelagic planktivores to the bay for spawning). Historically that was cisco. Alewives drove out the cisco in the 1950s. Hurt Percid reproduction but still provided the same buffer. Now that alewives are gone and cisco have not returned, we get good reproduction but lack the predation buffer. The solution isn’t to hope for alewives to return, but to hope for the native cisco to return. Sadly so far they have not (even in the absence of alewives). That’s a whole-nother story as to why or what could be done about it.
The commercial guys are in the same boat as the sport angler. Both yellow perch fisheries are way down in numbers. The good news is that we have been seeing more gizzard shad reproduction in recent years and sometimes they can buffer predation on perch. We’ve seen the predator diet (walleye included) become more diverse in recent years. We’re hoping that translates into better perch survival. Some would like to address the problem by reducing walleye numbers. For me at least, that seems backward or only addressing a symptom not the true cause. I’d rather see cisco recovery promoted if we could somehow. BTW; there was a diet study on cormorants in the bay this past year (2013). Analysis is still continuing but it appears that the cormorant diet is nearly 100% gobys (very little perch). While any perch consumption by cormorants contributes to the overall poor survival of them, I don’t think they are a big factor number wise.
Meanwhile we still get reports occasionally about great perch fishing. I think those are mostly occasions when perch are concentrated (like for spawning or first and last ice, schooled up somehow). So there is still good perch fishing but much less predictable and consistent under the current situation.
Edited by walleye express 12/10/2013 12:36 PM
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Perch Versus Walleyes.