There are chinook salmon populations in Idaho in which an occasional male stays put and matures when only 6 inches long that is, he's able to fertilize eggs at even that diminutive size, says Thomas P. Quinn, University of Washington professor of aquatic and fishery sciences and author of a recently released book, "The Behavior and Ecology of Pacific Salmon and Trout."
Just picture that tiny male under the belly of a 20-pound adult female that's returned to spawn, Quinn says. He's almost as likely to be a "winner" as the full-size males that are releasing their sperm in a competitive frenzy as the female deposits her eggs.
And the tiny male has avoided the harrowing journey taken by most salmon to the ocean and back, bypassing hazards such as dams, sharks and fishermen.
"In some species, all or a fraction of the individuals in some populations do not migrate to sea at all," he says. "These fish sacrifice the growing opportunities at sea for the relative safety of freshwater, and males are more inclined to remain than females. This difference is related to the fact that reproductive success in females is linked to the ability to produce numerous large eggs, hence the need for the female to be of a certain size herself.
"Small males, however, can sometimes fertilize many eggs by sneaking rather than by fighting," Quinn says in the chapter called, "Downstream Migration: To Sea or Not to Sea?" The evidence for this is in the DNA of the resulting offspring.
It should be pointed out that salmon are not "thinking this out" in any cognitive way, that there are some genetic controls at work that scientists don't fully understand, he says.