帮忙看一句话的意思，谢谢！

It can be inferred from the passage that the occasional failure of some salmon to return to their natal（出生的） streams in order to spawn provides a mechanism by which

这是一个题目，

尤其帮忙详细解释一下这个mechanism，谢谢

  Yet high rates of straying can be problematic because misdirected fish may interbreed with the existing stock to such a degree that any local adaptations that are present become diluted.

这句话也帮忙看看尤其后半句，谢谢！