Researchers have found a more accurate way to predict the size of sockeye salmon runs in the Fraser River, which could help officials make better decisions about how many fish to allocate to commercial, First Nations and recreational fisheries.
Scientists at the Scripps Institution of Oceanography in California found their new method was more accurate than most preseason forecasts of Fraser River sockeye runs from the past 58 years.
In 2014, they predicted the dominant sockeye salmon run would contain between 4.5 and 9.1 million fish, while the Fisheries and Oceans Canada forecast predicted a much broader range of 6.9 to 20 million. The actual run weighed in at about 8.8 million fish.
"What we were trying to do is show that there are alternatives to the traditional way of making fisheries models," said Hao Ye, the study's main author. "You can actually get better forecasts than the traditional models, and you don't lose anything in the process."
The technique, called empirical dynamic modelling, uses environmental data to improve run-size predictions. For instance, warmer ocean temperatures are known to lower salmon survival before they spawn.
Current forecasts for a given year are based largely on the number of spawning females from four years earlier, because sockeye salmon typically return to their native rivers and lakes to spawn when they are four years old. Simplistic assumptions are usually made about environmental factors such as water temperature, Mr. Ye said.
In reality, those environmental variables affect salmon in very complex ways, he said. For example, warmer ocean water is more damaging to fish populations when they are already smaller than average.
The strength of this new technique is that it includes all that variation in its forecasts, according to George Sugihara, a lead researcher on the project.
"Traditionally, the model assumes that the species doesn't really exist in a broader ecosystem," he said.
"This modelling approach allows the data to speak for themselves."
Dr. Sugihara said he hopes the technique will be adopted by fisheries managers to help the salmon industry plan ahead.
Sue Grant, a scientist with Fisheries and Oceans Canada who co-authored the study, said in a press release that the department "welcomes opportunities to examine alternative approaches which might improve the forecast of salmon returns in B.C."
Others disagree about the impact this technique could have. Mike Lapointe is the chief biologist with the Pacific Salmon Commission, the body that determines salmon allocations for the Fraser River each year. He said inaccurate preseason estimates are corrected when the salmon actually start to run.
"Decisions made by the Fraser River Panel of the Pacific Salmon Commission … are based primarily on very intensive 'in-season' assessments conducted by my staff each summer as the fish return," he wrote in an e-mail.
Aaron Hill, executive director of the Watershed Watch Salmon Society, was also uncertain about the implications, though for a different reason. He said the Pacific Salmon Commission's decisions are too strongly influenced by the salmon industry, a problem that better science won't fix.
"The panel is heavily dominated by fishermen," he said. "They often adopt run sizes that are higher than what the scientists recommend. The main problems in our fisheries management are not going to be addressed by better math."
But Mr. Ye believes the new technique could have broader implications for the industry and for conservation. For one thing, he said, the method provides accurate forecasts two years in advance.
"Having the information sooner can be valuable," he said. "Commercial fishermen will be able to better allocate resources."
He also said that models linking salmon abundance to environmental factors can help predict how the populations will respond to climate change.
"We can get a reasonable idea of how salmon returns may look decades in advance," he said.
Mr. Ye said the technique could be used to predict run sizes for other fisheries as well, in the Fraser River and beyond.