Trout Unlimited recently published a piece on the importance of genetic diversity in wild steelheads that you might find interesting.  Some life histories survive better in certain conditions and years than others and different life histories tend to use different parts of a watershed at different times. Ultimately then, diversity helps reduce annual variability in run sizes and improves the resilience of the population as a whole.

You can click on Diversity to read the article.

Wild steelhead diversity is key to long-term survival