Start Paddling:
I'd say your characterization of more alewife, but younger alewife is a pretty good concise summary of the lakewide situation right now.
edit: it's not letting it start at the specified time, go to 59:23 into the presentation to see the image I am referencing
This is the start of a presentation about the 2021 state of Lake Michigan preyfish from the USGS forage fish expert Dave Warner (he runs the acoustic survey). It's a good presentation, if you have the time and interest to watch the whole thing I really recommend it.
Note that almost all the fish captured are age 0, age 1, or age 2. A few Age 3s, and very few older than that. But, there are some. A few years ago IIRC they didn't even catch any older than 3 at all. Period.
Alewife are not sexually mature until Age 2 at earliest. The survey used to get a lot more fish in the Age 4, 5, 6, 7, and even a few 8 year old fish. This is (errr...was) a good thing because an 8 year old alewife had at least 5, probably 6 spawning opportunities over the course of their lifetime
Whereas if all fish are dying (read: eaten) by Age 3 or maybe 4, that is maybe 2 spawning opportunities for each fish. Much less of a stable situation. If an alewife spawns once or twice in its lifetime before it dies, and if either one of those years happens to be poor conditions for larval survival, that entire yearclass of alewife contributed very little to the future bait population. That is the dire situation the lake was in 6-8 years ago. 2 bust yearclasses in a row could sink the lake. Thankfully we avoided that, it was a close call. The extremely poor alewife spawns of 2013 and 2014 produced some really lean years.
(go to 56:52 to see the graph)
Note the right graph - bad spawns in 2013 and 2014. We were really on the edge. But recently, we had a pretty poor yearclass of alewife in 2019 and it didn't sink the fishery - likely in large part because by reducing predation pressure leading to alewife living longer than they were a few years ago, we've built some resilience into the system
It's sort of like having a savings account. If you are living paycheck to paycheck (not enough "savings" of older alewife), one unexpected bill (a bad alewife spawn in this analogy) will put you in debt.
But if you have a robust savings account (older alewife) you can weather a couple unexpected expenses without getting in bad financial straits
I would say that we're seeing lots of encouraging signs (more bait, larger bait, more yearclasses) but we're not to the point yet where we feel very confident that we have a robust situation that will persist even if there are some big bumps in the road ahead
One final thought - note that when the acoustic survey is performed (August) 1 year old alewife were about 100-140 millimeters (4 to 5.5 inches). And then pretty much anything 2 years or older is in that 140 mm to 200 mm range (5.5 to 8 inches) size class. There is considerable overlap, and outside of being confident that a <2.5 inch alewife is Age 0,
you cannot tell an alewife age from the length due to the fast growth and substantial overlap in length at age. So, while seeing larger bait is certainly a great sign (they're finding enough to eat, growing well, have more calories per individual etc) , it also doesn't mean they are older fish.