mature male sockeye
The hooked jaw andred colorationare both signs of maturity in male sockeyes, which battle competitors for gravid females.
Photo (c) Jeremy Sarrow and Dave White
female sockeye excavates spawning pit

The female sockeye excavates her spawning pit for egg deposition while a male protects it from invaders and wiats for her cue to release his milt.
Photo (c) Jeremy Sarrow and Dave White

newly hatched sockeye salmonA newly hatched sockeye salmon spends 2-3 weeks in the alevin stage growing and absorbing its yolk sac.
Photo (c) Jeremy Sarrow and Dave White

Sockeye Speciation

Unlike viruses and bacteria, advanced organisms like fish take thousands of years to speciate, or evolve into new species. Or so we thought. Scientists are discovering that species may evolve about ten times faster than previously assumed.

Geographic barriers such as mountains or rivers sometimes prevent otherwise compatible populations from mating, which can eventually lead to two separate species, unable to interbreed. Other times, the barriers are not so obvious, as separate groups of a population adapt to different local environmental conditions. Some time later, these "specialized" populations may be distinct enough to be considered two different species.

Either scenario was thought to take many hundreds of generations, but Andrew Hendry of the University of Massachusetts, studying sockeye salmon (Oncorhynchus nerka) introduced into a lake in Washington State, has found otherwise.

The population of salmon has become noticeably split within a mere 13 generations, or about 60 years. One group lays its eggs on the lake's beaches; the other adapted to river breeding. River-adapted males have slimmer bodies, making swimming upstream easier, and females of the river group are larger and able to dig deeper nests. The study has shed new light on the effects of adaptation to habitat diversity.