Im not much of a Biologist myself, but we havent had a severe weather spring like we had most of april in quite some time,and i would think a die off happens every spring ,with or without the weather.
As for the spawn run,the Maumee has been the premier spawn site for Lake Erie for quite some time,and this season was no exception,except for the weather.The river level has been above normal all through the normal spawn temperatures,combined with unrelenting winds out of the east for most of April,those fish that did make it up the river had 7 to 10 foot and higher waves to return to coming out of the river.the usual first stops coming out of the river being 6 to 15ft. depths,i cant imagine swimming through that after a run up a swelled river,romping with the cows and dodging a few thousand snaggers.
Most parasites or biologicals generally need warmer temps that up until recently we havent seen,the river only reaching 59 after 2 85 degree days this past week. And as far as those who did catch in the river,the sizes were quite large,many jack in the 6 to 8 lb. range, which tells me a older,possibly ready to die series of fish returned to this area, 2007 revisited with some nasty weather thrown in.
Just my opine,as i said Im not a scientist, just a fisherman who loves a debate?????