I'm not sure where you got the information on the Delta smelt population Tom, because I found different numbers.
A June 6, 2016 article in the Sacramento Bee regarding the 2016 U.S. Fish & Wildlife's release of the spring trawling surveys that track adult Delta smelt found "handfuls" of smelt across the areas they are know to spawn, leading biologists to estimate the population likely to be 13,000 smelt. The survey began in 2002, estimating the smelt population about 600,000 (597,000 posted) to the current low in 2016 of 13,000 fish. By the way, Delta smelt's life span is only one year.
The article did say Dr. Peter Moyle, a UC Davis biologist who has studied the Sacramento/San Joaquin Delta fish species for almost fourty years, said the smelt were the most numerous species in Delta when he began his work, numbering in the millions.....