May 20, 2014

Young Mallards Eat Dead ‘First-Flush’ Coho Smolts on Byrne Creek

Unfortunately we had yet another "first-flush" kill of juvenile coho smolts on the creek in SE Burnaby, BC, over the last day. Whenever we release hatchery coho smolts, we're always on edge, hoping there is no rain for a week or so following. That's because the first rain after release that washes all the crap off our roads and into the creek tends to kills a significant proportion of the newly released fish. Indigenous coho and trout appear to survive just fine, so it seems to be an acclimatization issue with a certain proportion of the hatchery fish. Today I counted 40 dead smolts following yesterday's shower. That's not bad -- in previous years we've enumerated as many as 400-500 morts. This year's batch had six days to acclimatize and start moving downstream before the first flush of accumulated pollutants such as gas, oil, antifreeze, brake-lining dust, pesticides, and whatever other toxins that make it onto our urban streets.

I should point out that I also saw lots of live fish ranging from fry to smolts, so they are likely coho and cutthroat trout that hatch and and are resident in the creek.

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On happier note, in contrast to the dead "first-flush" coho juveniles, I was pleased to see that the mom mallard and ducklings that have been hanging around the Byrne Creek habitat seem to be doing well. She still has six ducklings, and they're getting to be of a size where predation is gradually becoming less of a worry. I dunno about the little ones, but I wouldn't be surprised if Mom hasn't scarfed a good feeding of dead coho smolts. Yes, I've seen mallards eat dead smolts before.

byrne_creek_mallard_babes_20140520

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And then, as I was going through my photos, I noticed something dangling from a duckling's mouth. I did a massive crop on the photo, and yep, even the ducklings are scarfing the dead coho yearlings!

byrne_creek_mallard_baby_eats_coho_20140520

Posted by Paul at May 20, 2014 02:32 PM