Food quality can be key to the growth and survival of young sockeye salmon

A new study has found that the quality of the food that red-eyed salmon eat during migration is more important to their growth and condition than quantity, highlighting concerns about
the impact of climate change on ocean conditions and salmon.

Researchers from the Institute of Oceans and Fisheries (IOF), the Department of Fisheries and Oceanography (DFO), the University of Toronto, Dalhousie University and the Harkay Institute studied sockeye juveniles from three sites off the coast of British Columbia
.
In 2016 and 2016, the physical condition and nutritional health
of red-eyed juveniles were collected in the northern Georgia Strait, the high-tide mixed Johnstone Strait and the Queen Charlotte Channel, respectively.

Dr Jessica Gazik, a postdoctoral fellow at IOF and first author, said: "We measured fatty acids in sockeye salmon tissue, particularly those stored during starvation that are important for mobilizing energy, such as those faced by these salmon in the Johnstone Strait
.
" "We found that short-term changes in health varied between years, but were independent
of zooplankton biomass, abundance, average size, or species composition.
On the contrary, the quality of zooplankton plays an important role
.
”

Leaving the productive and well-fed areas of the Sound of Georgia to the food-poor environment typical of Johnstone Strait had a huge impact
on the small salmon.
When the larvae entered Johnstone Strait in 2015, they were generally in good physical and nutritional condition and were able to use stored energy resources to successfully cross this less accessible area of prey to reach Queen Charlotte Sound
.
However, when the baby sockfish entered Johnstone Strait in 2016, they were in poor physical and nutritional condition, and when they reached Queen Charlotte Strait, it was difficult to recover
.

"It is clear from our study that the difference in the condition of juvenile salmon over the two-year period was due to changes in the quality of food available to the fish and not any other factor
.
In addition to the analysis of prey abundance, incorporating measurements of food quality is essential to understand changes in fish conditions and survival over many years," said
Dr Garzik.

Dr.
Garzik said understanding how diet affects salmon growth and health early in life could help researchers understand long-term population trends in the species, including their declining
numbers.
Redeye salmon is an iconic species in British Columbia that is commercially and culturally important, but its numbers are dwindling
.

Dr Brian Hunt, senior author and associate professor at the IOF, said the study highlighted how variable the marine conditions faced by juvenile salmon in British Columbia, with migratory salmon experiencing "boom and bust" feeding conditions
.
"Importantly, feeding conditions are inconsistent
from year to year.
They are affected by climate change, and areas that have good feeding conditions in one year may deteriorate the next
.
The more areas that turn to poor feeding conditions, the more difficult it is
for young whales to migrate along the coast and survive their first winter.
”