what are differences in old and new methods? Also, I don't seem to recall lake trout being super abundant in the mid '90s. Maybe they were, but I just didn't fish for them back then. Memory fades.....
Note how the model of the old one had a flat abundance for the past few years? It's because it wasn't updated during that time and was basically frozen in time. Disclaimer because I am not a modeler, but I have seen a presentation by one of the researchers leading the effort. The old model was for the treaty waters, since it was mandated as part of the Consent Decree. And it was extrapolated to the rest of the lake, which obviously was a known faulty assumption but best that could be done given the existing model. Hence the lake committee pushing for this updated model. The new model breaks the lake up into a bunch of different zones, which is really important since lake trout stocking, survival and natural reproduction is much more variable by zone than most other salmonids, and most importantly they also don't move nearly as much as other salmonids. You don't need to break up a chinook model by zone since they roam around the entire lake and are almost entirely mixed in their population, regardless of stocking location or wild reproduction location. In contrast, with limited lake trout movement, there are zones of the lake which much higher wild reproduction and those fish are almost entirely confined to a regional area. In any case, the new model includes more and better information about all of the areas of the lake, and I believe also incorporates a lot of much higher quality information from the mass marking program (wild fish, movement, survival, etc). Overdue and really going to be useful in management moving forward. There's a significant push toward updating all the models, which is a big task and takes a lot of expertise, new info, and time/money. Steelhead is the next big one IMO. There are a lot of steelhead and a decent amount are wild fish, so important to get that updated. Unfortunately the covid lockdown is really badly timed as there are going to be significant challenges with the steelhead mass marking program as a result. I hope it resolves quickly so it's not a huge setback.
I'm not sure what caused that huge spike in the late 80s and early 90s, it is a significant divergence between the models, which is unusual so far back in time, since almost all the fish around back then are long dead. Usually when a model is updated with recent info, any divergence you see is in the more contemporary time period, not from 30 years ago. Again, not being involved I'm not sure, but the only significant event I can think of happening during that approximate time frame would be BKD. Possible that anglers switching to targeting lake trout with the decline of chinook during the 90s lead to the model overestimating lake trout based on that factor, especially if more information specific to the southern basin was included in the new model. The high harvest of lakers in the mid-90s could possibly have led the model to assume that lake trout abundance must have significantly increased a few years prior, to produce all the 5-10 year old fish that would have been harvested in the mid-90s. But that would be a great question for the team that put the model together.
