One of the unrecognized causes of depletion of salmon and steelhead stocks is caused by what I have named "Sudden lethal toxic discharges syndrome" from municpal storm water drains which is caused by three principal factors: Increased urbanization, vechile traffic and prolonged periods of no preciptation. 170 hectres of urban pavement annually produces approximatly one metric ton of phospates, nitrates, heavy metals and carceogins.
During a prolonged dry spell the volume of these road toxins builds up. Rains comes, floats it off and down the storm drains into the local water bodies. If tide and time are right it kills off large amount of 'bait fish' eggs which are deposited on the gravel, rocks etc. just below the low tide mark. Smolt fishing, sea runs etc. arrieve to find their principal nutriment unavailable. In most areas water quality of creeks, rivers entering lagoons etc. is only measured twice a year and misses this sudden toxic discharge. (And why they predication rates of returns are frequently inexplicably not correct)
Vancouver, Canada for example, has 1750 storm drains draining directly into the Frazer River. The 'toxic flush' takes about four hours to wash several tons of toxins into the river.
Canada's Dept of Ocean and Fisheries is unaware of and does not monitor for this factor.
For severial years this massive area of pavement recieved heavy rains at a critical period in the smolt and returning salmon cycle.
In the UK one fly club recently discovered after years of trying to increase fish numbers and size, and having tried everything from stocking, shorter season, catch limits and gear restrictions, that the real culprit was a new overpass built nearby. When dry spells ended and washed the toxins into the drains it killed off the aquatic insect life and the fish were severly under nourhished. Correcting the problem with organic filters improved the fishery in short order.
Settlement tanks are not particular helpful as they do can not remove the toxins but they can inhibit, under certain conditions, the sudden entry of volume of the lethal dischare.
Breast cancer and storm drain discharges have been recognized as connected in Kingston, Ont, which has the second highest rate of breast cancer in North America, after Manhantan Island in New York state. Both these communities are down stream from literally tens of thousands of storm drains from up river sources.
Four years of trying to get this information out which I first noticed when fishing a lagoon at the end of long dry spell has hardly dented those employed or charged with monitoring and maintaining water quality. I have had some success in Victoria, BC, which is the first place to instal a storm drain filter system, however the principal salmon and steelhead rivers in BC still recieve these unrecognized lethal toxic discharges and usually at critical mirgration times.
Campbell River town drains two storm drains directly onto spawning salmon! They have refused to discuss the problem and I am having to pay for the water testing myself. Last year, during the Chinook run (what there was off it) the discharge from the storm drains was as black as oil.
Help get the word out. Its not a hard problem to fix but its a hard thing to get those in charge to pay attention to anything not in the manual. Example:
I was told by the Environmental Officer at a BC university after presenting the information,
"It can't be a problem or we would be testing for it".