Over The Horizon

Salmon Under Spotlight

Could a genetically distinct salmon population, or sub-species, evolve in New Zealand rivers?

That's the question JUNIPEX, the Joint University of Washington/NIWA Salmon Population Experiment has sought to answer. ["Studying Sacramento Salmon", Nov 1996]

Chinook, or quinnat salmon were introduced to New Zealand between 1901 and 1905. They had been taken from the Sacramento River in California. JUNIPEX scientists wondered whether differences between stocks in different New Zealand rivers might arise from genetics rather than from environmental factors such as temperature, availability of food, and their effects on growth rate, size and condition.

Martin Unwin, the project leader at NIWA (the National Institute of Water and Atmospheric Research) says results to date provide strong evidence that differences between distinct New Zealand chinook populations are at least partially under genetic control.

"These differences are most apparent when the fish mature as adults, and show up in a suite of life history traits including migration timing, maturation timing, reproductive output and marine survival," Unwin says.

"For example, salmon from the Waitaki River consistently matured later than Rakaia salmon, even when reared under identical conditions."

A better understanding of how salmon have adapted to the New Zealand environment may ultimately allow researchers to develop models for forecasting variation in annual run size.

The results are also valuable for the salmon industry, who need to know more about genetic variation between populations to maximise potential benefits from their breeding programmes. Unwin says that for NIWA's US collaborators, the results are beginning to challenge long-held beliefs about the rate at which salmon populations evolve, and have already started to attract attention from other researchers.

"Evolution is a fundamental characteristic of living things, and underpins virtually all modern biology," he says.

"By virtue of its geographic isolation, New Zealand provides a unique laboratory for studying evolutionary processes," he adds. "By allowing us to study these processes over a time scale of less than 100 years -- in contrast to the thousands or millions of years spanned by the fossil record -- JUNIPEX is giving us new insights into evolutionary change over the scale of a human lifetime."