Lots of good discussion!
A few thoughts on various things brought up:
• Cormorants are opportunistic feeders… they’ll eat whatever is in abundant supply nearby at the time. The study done over 2 years on the Indiana cormorant colony did not detect any trout/salmon or coded wire tags in cormorant diets, despite sampling during the time period in which smolts were stocked and outmigrating. It was actually one of the driving hypotheses that the researchers were looking at, because they suspected cormorant predation on smolts might be detrimental. But they didn’t find any evidence of it.
o Not saying they don’t eat them if they have the chance but it’s very unlikely they are significantly altering smolt survival rates
o DNR office overlooks harbor/nearshore in Michigan City and it’s rare to see lots of cormorants nearshore at times when smolts are around. Sometimes you'll see
rafts of cormorants offshore out of MC when the alewife are in. Do see terns near the harbor though, they are pretty effective at catching smolts when they are
outmigrating. I wouldn't be surprised if the 100 terns in Michigan City eat more smolts than the cormorant colony does combined. But still - outmigration period is
pretty quick and then the juveniles scatter and are likely not nearly as vulnerable to bird predation in chokepoints like harbor mouths.
• There’s lots of correlation in the ecosystem. A big reason why the cormorant population exploded in recent years is that they’re sight feeders and the water clarity has gone up a ton in the past decade… because of mussels. Which shifted the food web substantially. That shift to clear water and abundant slow and easy food sources (gobies) in addition to alewife, favored cormorant population growth. Over 80% of their diet was goby and alewife in the 2 year study of the EC colony. So like Southshore said, lot of it is correlation rather than causation – it can be very difficult to sort out all the effects
• A couple people brought up discussions from last year’s public meetings, and I think it was summed up pretty accurately – if chinook fall return cannot be improved significantly by trying different things from the limited suite of options available, it doesn’t really make sense to keep wasting the hatchery space, money, and chinook-equivalents of our stocking quota to stock fish that won’t contribute to fishery. I don’t think anybody would argue that?
• With regard to Mike’s question about kings in the St. Joe – yes it’s been 20 years since they were stocked in our waters of St. Joe. Very few make it up that far (less than 300 a year). And even in the Michigan portion, it’s the same story as Indiana tribs – no king fishery that is really worth putting time into fishing.
• Lake trout – I know it’s always contentious but do want to point out that there have been in fact lake trout cuts – about a million fish since the chinook cuts began a few years ago. My *personal opinion* is that those lake trout cuts should probably have been made at the same time as the initial chinook cut, but that’s easy for me to say since I was not working when those decisions were made and have the benefit of hindsight. With increasing natural reproduction on the south end, it’s certainly reasonable for folks to think about reducing or ceasing the remaining southern basin plant
• Wisconsin chinook stocking numbers/port – actually, most of Wisconsin’s stocking numbers per port are fairly similar to other places in the lake. Statistical districts WM4 and WM5, which consistently have the best survival in the lake, typically have less than 75,000 fish per port at their stocking locations (you can look it up at
www.glfc.org/fishstocking/exactsearch.htm). Their biggest stocking is at Strawberry Creek (primary brood weir) and that’s about 150,000 on average. In fact, from 2010-2018, excluding Strawberry Creek, their stocking locations averaged just under 75,000 chinooks per management grid (and some of those are different sites within a grid). Sites of note: Milwaukee averages about 85,000, Kewaunee just under 50,000, Racine 78,000 , and Kenosha also 78,000
o There are a few regions that have great returns (northern Lake Huron, central Wisconsin) and then the south and east regions have very poor returns. It’s almost
certainly driven by environmental food ability for juvenile chinooks. Like Mike said, all the chinooks are stocked about the same size at about the same time of year in
about the same manner, which rules out stocking practices or fish size as a driving force behind the variable survival.
o We’ve asked the USFWS to analyze lakewide coded wire tag returns to see how much of an effect there is related to chinook stocking numbers per site. Early
indications from a few years ago were that there was not much of an effect, but there is more data now so it’s possible there will be a new conclusion. Some
tributaries certainly have more predators and dams, which can definitely be an issue in some localized cases (like the St. Joe). But my gut feeling is that there won’t
be a significant effect of stocking numbers/site, because I don’t think predation is the biggest driving force – as Mike said, all ports have birds, all ports have
nearshore predators, etc. Many of the Wisconsin tributaries are very similar to Indiana’s – fairly small, short, few dams, don’t support huge populations of predatory
fish within the river itself, etc. The only really different variable between them is the environment out in the lake itself, such as substrate/structure, availability of
nutrients/food, etc. We all know adult salmon go where the food is. But juvenile salmon don’t really have the ability to travel hundreds of miles searching for food like
their adult counterparts.
