March 05, 2010

Sample Density of Fish Killed in Byrne Creek

Sometimes it takes death to reveal how much life there is.

Would you believe that on average there was a dead fish less than every 2 meters along a sampled section of Byrne Creek the morning after someone poured a toxin down a street drain in the upper watershed on March 4, 2010? Most people never see fish in the creek - it takes patience, stealth, and knowing where to look to spot them when they are alive. My wife and I counted 231 dead trout, coho smolts (yearlings) and coho fry (this spring's babies) in an approximately 400-meter section of the creek. For those interested, here's the breakdown:

182 - Small cutthroat trout (say less than 15cm)
20  - Medium cutthroat trout (say 15-20cm)
1   - Large cutthroat trout (over 20cm)
Total 203 cutthroat trout

16 small-to-medium dead fish visible inside the culvert, too dark to ID
1 - large trout, very dark, no cutthroat markings on chin, near footbridge

8  - Coho smolts
3  - Coho fry
Total 11 coho salmon

Grand total dead fish in that stretch: 231

And that's likely lower than the actual number due to several factors: dead fish get wedged under rocks and drop deep in pools, the tiny fry are difficult to spot at all and we know that before the kill there were schools of dozens in the area sampled. In addition, opportunistic predation starts almost immediately after the toxin is quickly flushed down the creek: we found several fish partially eaten, and only strings of guts and bits of flesh too small to ID here and there.

The coho were found around T518 to T516 (lower end of the lower ravine). The coho fry were found in the vicinity of T517 where we photographed live ones a few days ago... See the entry below "Video of 2010 Salmon Fry in Byrne Creek."


The above photo shows dead fish ranging from coho fry at the bottom left,
a coho smolt a the bottom right, and an adult trout above. There was a
surprise to come, as you'll see in the next photo. . .


The big trout had a fry in its mouth. It's not hard to imagine what
happened - it spotted a little fish in distress from the chemical,
thought it an easy meal, and then before it could even finish
swallowing its target, the bigger fish also died.

Posted by Paul at March 5, 2010 09:10 PM