Highlights
The Fraser River has warmed by nearly 2ºC since the 1950s, with the last 20 years being some of the warmest on record. High river temperatures have been associated with the high mortality.
Sockeye salmon have been in decline since the early 1990s. Contributing to this has been massive migration mortalities where between 40 and 95 per cent of some salmon populations have died en route to spawning.
The researchers suggest some sockeye salmon populations are more susceptible to warming river temperatures than others. Chilko sockeye salmon, which get their name from the lake and river near where they spawn, may be more resilient to warming temperatures, while other populations, like Weaver sockeye salmon, which get their name from the creek where they spawn, appear especially susceptible.
The researchers found that the optimal water temperature for the fish matched the historical river temperatures encountered by each population on their migration routes. The optimal temperature for each population was determined by measuring each fish’s swimming performance, metabolic and heart rates.
In water temperatures above their optimal temperature, the salmon’s swimming ability declined. “We propose that this is due to a collapse of the cardiovascular system,” says Eliason.
“Currently, the Fraser River’s peak river temperatures during the summer months exceeds the optimal temperatures for every population we examined and temperatures are near lethal for some populations.”
To measure the swimming ability of the salmon populations, Eliason and her colleagues monitored the metabolic and heart rates of adult salmon from each of the eight populations as they ran them through a “fish treadmill” – a tunnel capable of producing varying water speeds and temperatures.
The source article Some populations of Fraser River salmon more likely to survive climate change: study was published March 31, 2011 by Physorg.com .
Sounds alarming, but what about genetic pool’s diversity of those populations after massive deaths ? That is the relevant consideration whenever there’s any increase in temperature, cause fishes are highly plastic animals and since populations don’t drop below any threshold there’s no consensus about sustainability of these populations yet.
In fact the biggest concern is the overfishing and degradation of fish habitats.