TOPIC:

dmwarnerusgsglsc.shinyapps.io/AppDraft/

I like data! thanks for posting that Ed.

Thanks for posting Ed.

Dave Warner has been going above and beyond to put his data online for anglers to look at, and producing some great maps

Couple things of note that folks may have noticed already -

young of year of both alewife and bloater have shown small increases in each of the last two years. Likely related to effects of the 2013 stocking cut, as fewer chinooks eased the predation pressure on young alewife.

Unfortunately still high predation pressure on older alewife, and we have not seen a corresponding increase in total alewife biomass. But appear to be holding steady at least. The most concerning thing to me (don't have a pic or diagram at the moment) is that most of the alewife in the lake are young (2015 or 2016 year class). We are down to pretty much only 4 yearclasses right now. Which means our margin for error is VERY slim. If we don't get a couple good yearclasses in the next 2 or 3 years we are going to be in major trouble, because most alewife are only living until 4 years old right now.


Some very good graphical information here that I think sums up the reason why some anglers don't believe what the surveys say:



The scale is hard to see, but on the X-axis it is bottom depth in meters. Basically in 2016, very few alewife were seen deeper than 85 meters (about 275 feet of water).

Basically, all of the alewife now are coastal in their distribution (within 15 miles of shore or so, and inside of 300 feet). This is where 90% of the fishing effort happens, so anglers are absolutely correct when they say they see bait. As it happens though, the surveys are also correct when they are saying biomass has declined, because of that offshore collapse.

Where the disconnect happens I think, is that the offshore alewife have all but disappeared. This happened as the diporiea declined as quagga mussels expanded offshore, and there has been a huge disruption in the offshore lower food web and nutrient cycling

Could you be more specific for everyone when you say "predation" and delineate specifically between lake trout vs chinook? In addition please give us those predation levels by MM and not lakewide? Example....predation of alewife in the southern management units of Lake Michigan are predominantly by Lake Trout and not chinook. That would give everyone a clear and unfiltered look at actual predation breakdown rather than lumping it all together. FYI Chuck Madenjian has the per species per MM isotope data if you need it. Thanks

I'm not sure what you mean by be more specific what I mean by "predation". Predation means the eating of one fish by another in this context. Alewives get eaten by just about everything in the lake. Young of year are especially eaten by the pacific salmonids. Older alewives are eaten by lake trout in addition to pacific salmonids

There is no statistical district-specific consumption estimate in Lake Michigan. Baitfish and predator occurrence are patchy and dynamic from day to day, month to month, year to year. The fish move all over the place so it is rather like Heisenberg's Uncertainty Principle but for fish, if that makes any sense. That's why predation/consumption are measured for the entire lake. There's simply not enough data to provide accurate or precise estimates on such a small scale as a stat district. It would be wonderful to have a few more million-dollar ships and additional crew and the funding to go out and sample a lot more. It would greatly improve our understanding of the lake and our ability to manage it. But we work with the resources available.


The best I can say is there are generally more lake trout in the southern basin compared to the northern. And that generally, lake trout eat more gobies in the southern basin, and more alewife in the northern. And that lake trout diet varies substantially on a seasonal basis; they eat a lot of gobies/sculpins in fall, winter, and early spring, and then switch to more alewife in late spring, summer, and early fall


Isotope data from angler-caught fish says that alewife/smelt comprised 54% of lake trout diet, 85% of chinook diet, 80% of coho diet, 78% of steelhead diet, and 72% of brown trout diet. This is only from one year's collection, and from all angler caught fish (nearshore, from fishing season, etc) so it is somewhat limited, but far and away the most comprehensive diet data we have. It is likely that diet changes somewhat from year to year, based on abundance of prey (e.g. if it is a strong bloater yearclass but poor alewife, they all eat more bloaters, and vice-versa).

Do the alewife consumption percentages seem to be numbers that were expected or these numbers higher than expected? From the few fish I clean and have seen cleaned, there were a large number of perch in the gut. Or is this just a seasonal diet change?

There is district specific information for predator isotope data. When Madenjian and crew pull predators in each district, isotope data is compiled per predator species and recorded per district. DNR types like to mush it all together and give a "lakewide view" so as not to highlight breaking points in the system, such as the one we have here on the southern end of the lake with lake trout predation. Presumably this supports the new "emergency lake trout rule" in Indiana waters. What other emergency could exist other than extremely elevated levels of alewife predation by Lake Trout? The disparity between harvest limit regs between Michigan and Indiana have existed for a while, so using that as reasoning now at this particular time just does not cut it.

So what is the exact isotope data for lake trout vs chinook in Indiana waters specifically with regards to alewife consumption on a year round basis? Not angler data, USGS data. We have seen this data, have you?

You cannot honestly state that "generally" lake trout eat more gobies in Indiana waters and more Alewife in northern waters without having specific district isotope data. How else would you come to that conclusion other than just by guessing?

I realize this is putting you on the spot, but there is so much data being compiled by well funded and highly educated sporstmen advocate groups based upon data collected by Madenjian and Warner that absolutely and unequivocally point the finger of alewife decimation directly at the jaws of lake trout in the southern basin. Surely you know that between 70-80% of a Lake trouts diet in the southern basin is alewife. Madenjians own words...

So back to the original assessment, to broadly stroke the brush of "predation" is disingenuous at best. Lets be more specific here and delineate between Lake Trout and Chinook so sportsmen can see the actual truths of "predation" by predator species in the region of the lake of which matters to them.

I think you're conflating consumption estimates (how MUCH is consumed by total predators) with the isotope data (WHAT is being eaten). Those are different pieces of information. Yes, there is regional specific isotope data. No, there are not regional specific consumption estimates.

I also think you are confusing agencies here... the isotope data is coming from the Mass Marking folks at USFWS. These data are coming primarily from angler-caught fish collected by USFWS headhunters.


Managers are not "hiding" breaks in the system by lumping things together at a larger scale; they simply understand statistics and know that you cannot draw reliable information from very low sample sizes. They also realize there is a lot of complexity, and as much as it is nice to make things simple and black and white, it's just not realistic. For example, there are biases in all types of sampling. The isotope data is primarily coming from angler-caught fish. That leads to biases in location (most angler effort is within 15 miles of shore, anglers more likely to fish near suspended bait balls, and most effort happens April-August, and more likely to catch hungry fish rather than full fish). In contrast, diet studies from fisheries-independent data (primarily spring gill netting) also have biases. They're catching almost all bottom-oriented fish, during a narrow window of time. So although they catch all fish (not just hungry ones), there are other issues. Neither paints a complete picture all on their own.

Like I said before, I wish we had a lot more sampling effort and a lot more data. We'd like nothing more than to have a better and more robust picture of what is going on. Do you think we enjoy spending half our public interaction time talking about data gaps and dealing with conspiracy theories? We are working hard to put a TON of information out there, so it irks me when we are accused of hiding things. I take it personally, in fact. The simple fact is that the ecosystem is complex and our understanding of it is limited, and there is a lot of uncertainty involved with ANY fisheries management.


The "emergency rule" is just the name of the rule making process used outside the normal rule-making timeline. Since the rule making process takes foreeeever, we use temporary rules to fill the gap. We use the emergency rule process all the time to pass regulations as temporary rule while the permanent rule is in the (time consuming) process of being made. We just thought it would be helpful to have the new bag limit regulation in place for the start of the fishing season, rather than starting in the middle of the season when the permanent rule is approved. Just common sense, we think. Sorry, no conspiracy here.

The lake trout regs were primarily changed because anglers requested it. In particular, we've been having discussions with several Indiana charter captains for some time now about the disparity between Michigan and Indiana regs being a pain, especially since they are straddling the state line a lot of the time when fishing. This is mostly a social regulation rather than a biological one. Frankly, if it were passed with the intention of reducing the lake trout population, it would be a pretty worthless attempt at doing so, given that the limited amount of additional harvest that would occur inside of Indiana waters.

And as Steelie Don astutely pointed out, prey consumption often varies by year, because nature is variable.

A lot of predators ate young of year yellow perch since there was a massive 2015 yearclass of perch. That has not happened in a long time. If there is a big bloater yearclass, predators will eat them. Lake trout in particular are very opportunistic. Alewife distribution is very patchy; sometimes they are all on the Wisconsin shoreline (last and the Michigan coast has very little bait (like last summer). Other times they are in different places for a significant portion of time. If you only take a snapshot based on part of a single year, you are getting a very incomplete picture. More data in each year and across years is what you need to start telling the whole story. It's a very difficult (read: generally inappropriate) to extrapolate a single piece of information and apply across space and time and assume it's not changing or not variable.