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Andrew Trites and Villy Christensen, both professors at the University of British Columbia Fisheries Centre, made the comparison to the Agatha Christie whodunit as they testified Wednesday at the Cohen Commission of Inquiry into the Decline of Sockeye Salmon in the Fraser River.
Led by B.C. Supreme Court Justice Bruce Cohen, the commission has been given more than two years and a $25-million budget to figure out why sockeye salmon stocks have been in decline for the past two decades, and why only about one million fish returned to spawn in 2009, when 10 million were expected.
As part of the inquiry, Judge Cohen has assigned teams of scientists to look at 12 different issues, examining everything from climate change to sport fishing to determine the impact on salmon.
In a report on predation, Dr. Trites and Dr. Christensen tried to find which, among the myriad predators that feast on salmon, could have been responsible for killing so many sockeye as to decimate the population.
They came up with a long list of suspects and then narrowed it down to the six most fearsome killers: salmon sharks (220 kilograms and so aggressive they sometimes bump fishing boats), blue sharks (triangular teeth with finely serrated edges), daggertooths (the name says it all), sablefish (black cod with gaping mouths), lamprey (jawless fish that suck blood) and the common murre (a bird that dives 60 metres deep and can swim faster than a fish).
"It's six," Dr. Christensen said of the top suspect list. "We could have made it eight or 10. ... It's subjective. Salmon shark is at the top of the list. For the rest, it's hard to say [how to rank them]. We found evidence for all of these six, that they might have considerable impact."
In their report, the two science investigators say they are unable to point the finger at any one suspect, because so many factors are at work. They compared their dilemma to the one faced by the detective Hercule Poirot, who finds a passenger has been murdered while the Orient Express is speeding across Europe.
"The murderer had to be on board," states the report. "M. Poirot interviewed everyone on the train, but there was no 'usual suspect,' no smoking gun and no butler. Rather, it seemed that all of the passengers (save M. Poirot) had a motive and an opportunity. That made for a difficult case - who did it?"
The scientists concluded the mysteries on the Fraser River and on the Orient Express had the same answer: "All the suspects played a role and all are guilty."
They state that while all the predators feed on sockeye salmon, none of them does so exclusively, and none to such an extent that it could explain the population collapse. And predation alone, even by all the suspects combined, cannot fully explain the long downward trend of the sockeye population or the sudden collapse in 2009, they say.
"For the Fraser River sockeye, it may well be that the declining survival trend over the last decades was caused by a combination of effects, and not by any single one," they write. "If predation had been the smoking gun in the disappearance of Fraser River sockeye salmon, it should have been smelled by now."
Dr. Trites and Dr. Christensen said the study was hampered by a shortage of up-to-date data and they called for more research on what happens to Fraser River sockeye after they leave fresh water and enter the ocean.
Dr. Christensen said the last major ocean research projects on salmon were undertaken in the 1950s and 1970s, and a new effort, using modern technology, is warranted.
Perhaps it might even solve the mystery of what killed all the salmon.
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