In a landmark paper published in the journal Nature, researchers have described how fish populations in the Northern Rivers of Alaska are suffering from severe declines, and have identified several key factors that may be causing these losses.
The paper, titled “The state of the Northern Salmon (Carnivora) in Alaska”, examines the salmon population and suggests that the decline is a result of factors beyond humans, such as climate change, a combination of human activity and the loss of native salmon habitat.
In the past 20 years, the average number of salmon spawning in Alaska has declined by roughly 20% and the average annual salmon spawning mortality has decreased by about 30%, according to the study.
The decline is most pronounced in the Upper and Lower North Cascades, where salmon populations are at risk of extinction, and the Lower North Slope, where the population is suffering from rapid declines due to warmer water temperatures and other environmental changes.
The study found that the main factors that contributed to the population declines were the introduction of invasive species, a decrease in the number of mature females, and a reduction in the size of the spawning populations.
“We found that these impacts were much more severe in the Lower Cascade, where populations were losing their main male fish species,” said lead author David S. Tackett, an oceanographer and director of the Institute for Marine and Coastal Sciences at the University of Alaska Fairbanks.
“The males were not reproducing, so there was less sperm than there used to be,” Tacket told Reuters Health.
“That has caused the number and size of spawning females to decrease, which in turn is increasing the risk of mortality.”
The study was the first to compare the mortality rates of different salmon species in the two regions.
It focused on three main salmon species: the Pacific salmon, Arctic salmon and Gulf of Alaska salmon.
“Our findings highlight the importance of looking at a fish’s lifetime mortality to determine the health of a population,” said Tackette.
“We found a clear trend of declines in the survival of Pacific salmon from the 1990s to the 2000s, which is indicative of climate change.
The Arctic salmon has also shown a decline in survival over the same period, but the declines were much less severe.”
The findings suggest that, for the majority of the population, salmon survival is not being affected by the impact of climate or habitat loss.
Tackett’s team studied the mortality of three different species of salmon at different locations in the lower North Ciscades.
They used satellite imagery to record the spawning and mortality rates.
The results showed that the mortality rate of the Pacific Salmon was the highest in the area of the lowest annual salmon mortality, and was higher than in all other locations.
The highest mortality rates were found in the lowland region of the Lower Arctic and Gulf Cascadia, where population numbers are at least 20% lower than the average.
The researchers found that mortality rates in the Arctic were also high, but only because they are more likely to be affected by climate change than in other areas of the world.
In comparison, salmon in the Gulf of Finland and in the North Slopes are faring better, and are in the middle of recovery.
The salmon populations in Alaska and the Northwest Territories have also recovered well, but not as quickly as the populations in other regions.
“There are two important things we can do with these numbers,” Tacksett said.
“First, we need to understand the causes of the declines in salmon populations, because we need a better understanding of the climate change and the impact on salmon that we see in the higher-latitude regions.”
The second point that needs to be addressed is the amount of time that it takes for the mortality to reach zero.
“It’s an ongoing issue.
When the mortality starts to drop, there are some fish that go extinct, and they are not immediately recovered,” he said.”
A population can be recovering in one area for years before it starts to decline, but that may not necessarily be the case for every area of a salmon population.
In Alaska, the number that is recovering in the lowest-lying areas of lower-lying lakes is very low, and it is a bit of a mystery.”
Dr Tacketts believes that, if the salmon populations were to recover, the mortality would be lower, and there would be more salmon spawning.
“I think there is a good chance that we will see some recovery, but we need more data and better understanding,” he added.
The National Oceanic and Atmospheric Administration (NOAA) is also looking at the impact that climate change has on the Northern rivers.
“These declines are not the first time we have seen a dramatic reduction in fish populations across the North Cis-US, and we need answers from the federal government and the states on the impact and the causes,” said Kevin Pyle, an NOAA fisheries biologist.
“There is no single cause for the loss, but there are many factors that