"We know that fish farms raise sea lice levels, and we know that sea lice kill fish," said the study's lead author Martin Krkosek, a Ph.D. student at the University of Alberta Centre for Mathematical Biology. "This is the first study to combine field surveys, experiments and mathematical modeling in one system to estimate the total impact of the farms."
The primary sea lice hosts are adult salmon. Under natural conditions, the adults are far offshore when the juveniles are migrating out to sea. Fish farms put adult salmon in net pens along the migration routes. The result is a cloud of sea lice through which the juveniles must migrate. "It takes only one or two sea lice to kill a juvenile pink or chum salmon," said Krkosek. "The juveniles are so vulnerable because they are so small ?only one to two inches long."
"We often worry about wildlife making humans sick, but here is a case where humans are making wildlife sick," said study co-author Dr. Mark Lewis, a mathematician and biologist at the University of Alberta.
The study found an increasing number of salmon were killed over the migration season, from 9 per cent in early spring when the sea lice population was low to 95 per cent in late spring when the sea lice population was higher.
"Everyone knows that only a small fraction of juvenile salmon survive to return as adults," said Lewis. "The fish-farm sea lice are reducing that fraction even more."
The research was conducted by a team of biologists and mathematicians working in coastal British Columbia. "We counted sea lice on more than 14 thousand juvenile salmon migrating past fi
Source:University of Alberta