I don't believe science has a good explanation, but I think the fundamental reason is that the natural mortality level stayed very high. For more than a decade we would go out to do our surveys. We'd see young fish produced each year but in fairly small numbers. The next year, when they were one year old, there would be a lot fewer; at two years old, there would be a lot fewer. They didn't survive beyond age six. The level of mortality for more than a decade was so high that it was simply eliminating very quickly what was produced each year. None of them was surviving much beyond age six or seven.
On September 21st, 2016. See this statement in context.