Fertilizers boost declining B.C. fish populations
FRY GROW UP TO 95-PER-CENT BIGGER IN STREAMS TREATED WITH NUTRIENTS, FISHERIES BIOLOGISTS SAY
By RANDY SHORE
YOUNG STEELHEAD AND SALMON GREW DRAMATICALLY IN STREAMS SEEDED WITH SACKS OF SLOW-RELEASE FERTILIZER, A METHOD THAT SHOWS REAL PROMISE TO HELP REBUILD COLLAPSED SPAWNING POPULATIONS, ACCORDING TO B.C. BIOLOGISTS.
Photograph by: Ric Ernst, PNG files
VANCOUVER – Young steelhead and salmon grew dramatically in streams seeded with sacks of slow-release fertilizer, a method that shows real promise to help rebuild collapsed spawning populations, according to B.C. biologists.
The method has proven effective at improving steelhead growth and survival in Vancouver Island streams in programs dating back to 1989.
Steelhead fry in treated areas are typically about 95-per-cent larger than those in untreated streams, while coho fry are about 40-per-cent bigger. Fish counts in the Keogh River found a 50-per-cent increase in the number of coho that survived the freshwater stage of life.
Fisheries biologists are using fertilizers to replace the nutrients that would be added to the stream naturally by the rotting carcasses of fish that die after spawning, said Kevin Pellett of the B.C. Conservation Foundation. Enhancement programs are operating in 15 watersheds and 28 rivers on the Island and southwestern B.C.
When spawners fail to return, die and rot due to overfishing or ecological conditions, the entire food chain of the stream, from algae and insects to fish fry, goes into decline.
The fertilizers are designed to stimulate growth of certain algaes that in turn cause the populations of insects such as mayfly and stonefly to thrive. Juvenile salmon and steelhead fry feed on those insects.