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[Rodney]

Fraser Valley Invasive Species Society is hosting a webinar by biologist Wendy Margetts on invasive smallmouth bass in Cultus Lake. Find out how she is monitoring the population and how you can help. The webinar is at Noon and you can register at:

https://fviss.ca/event/smallmouthbass-cultus-presentation

[Rodney]

Nice short and informative presentation by Wendy. I'll post up the replay when FVISS releases it. Here is an interesting screenshot, the diet components of these smallmouth bass at Cultus Lake from last year's data collection.

[Dave]

Sculpins and crayfish- who knew, lol!  So if they aren't much of a threat to salmonids, why do they need to be eradicated?

[Rodney]

Dave! Sculpin lives matter!

I think the concern is predation on pygmy sculpin, which are endangered. She hasn't been able to differentiate between coastrange and pygmy from the batch they extracted, so can't conclude how many eaten are in fact endangered pygmy.

[Dave]

Right, the legendary Cultus Lake Pygmy sculpin.  Forgot about them ...
I wonder when common sense will factor into some of these policies?

[RalphH]

I think there has been similar prey studies for SMB and LMB  in the states that show they take few salmonids. If there is an issue in the Cultus data it's that they eat similar food items and may compete with trout.

[BNF861]

I didn't see the presentation but an interesting slide in regards to diet composition that's probably quite contrary to the average anglers preconception. Would anyone happen to have a similar analyses of diet composition for cultus pike minnow? I have always heard of how pike minnow (and now bass) prey on salmonoid fry. While this shows possibly a different picture, like Ralph commented it may not be so much that they are actually eating them but may still be out competing them for similar diets.

[wildmanyeah]

How many samples over what period of time?

[Dave]

Would anyone happen to have a similar analyses of diet composition for cultus pike minnow? I have always heard of how pike minnow (and now bass) prey on salmonoid fry.

I spent a lot of time looking at NPM stomachs back in the day.  NPM have a unique digestive system in that food is broken down very quickly, making identification of contents difficult.  Bass may have the same characteristics. Yes, fish bones were common but I never saw an identifiable salmonid.  Sculpins and crayfish were the most common item but that may be because they take longer to digest.  The only for sure time I know of NPM eating sockeye was a night trawl sampling trip where a NPM vomited up several juvenile sockeye.

[RalphH]

from my observations, Pike Minnow have a pronounced tendency to cannibalize smaller members of their species. They also travel in shoals. I have run into cases where larger PMs regurgitated smaller PMs regularly.

If they do tend to puke stomach contents when stressed it may partially explain why you didn't see much in their stomach's Dave.

[CohoJake]

I wonder if it is possible to DNA test their scat, like is done with Orcas and seals, to determine what they have been eating? I also wonder about seasonality - when I have fished for smallmouth, I almost always use a crawfish-imitating plastic grub, but there are definitely periods of time that they seem indifferent to crawfish presentations. When I use a micro-tube, about the size of a salmon fry, I can't keep the juvenile smallmouth away (6-8 inches).  So I guess I'm suggesting that it is worth sampling smallmouth at different life stages, as their prey will vary considerably, as well as taking seasonal samples to see how much their diet varies throughout the year. 

[Dave]

from my observations, Pike Minnow have a pronounced tendency to cannibalize smaller members of their species. They also travel in shoals. I have run into cases where larger PMs regurgitated smaller PMs regularly.

If they do tend to puke stomach contents when stressed it may partially explain why you didn't see much in their stomach's Dave.

That’s a good point Ralph.  As I recall, the stomach of a NPM is like a straight chute from the throat to the anus, making regurgitation an easy operation. One point I found interesting was the chironomid feeding, making the comment from Coho Jake regarding size classes and prey very relevant.

[RalphH]

I've caught PMs on dry flies in Kootenay Lake. Crawford Bay once had a large shoreline population of PMs and they'd rise to the evening mayfly hatches in late spring. Both PMs and SMB are far  more trout like than most give them credit. BTW I have also found crayfish - & quite large ones in the stomachs of cutthroat. In lakes cutthroat switch their feeding strategy as they get past a lb or so in weight focusing more on sizable critters. Same with brown trout unless the waters they are in very rich in insect life.

[clarki]

Nice short and informative presentation by Wendy. I'll post up the replay when FVISS releases it.

Thanks Rod. I'd like to watch the recording. I'm not plugged into this organization and I wasn't aware of the scheduled meeting until your post just a couple hours prior to start. 
     

So if they aren't much of a threat to salmonids, why do they need to be eradicated?

I don't have your fisheries/research background, Dave, but isn't even 4% salmonid when extrapolated over the entire year, and over the entire biomass of bass in the lake, cause for concern?   
I know we can't put the genie back in the bottle, but in my thinking, eradication can be the only desired outcome; there is no acceptable margin of error (predation).

Most of the attention of SMB in Cultus has focussed on sockeye predation, but I find the aggregate 41% diet of crayfish and sculpin to be a little alarming (...yet not unsurprising). Over time, what subtle changes will occur in the lake's ecosystem when we replace crayfish and sculpin biomass with SMB biomass?         

[Dave]

clarki,I think if this 4% was upper Fraser chinook or Thompson steelhead I would agree, but if these salmonids in this Cultus study are indeed sockeye they are hatchery fish put in the lake because the water quality has degraded to the point wild sockeye production is nearly nonexistent.

The reality is Cultus Lake is no longer a suitable lake for spawning or rearing sockeye, and imo the lake should not be managed as such. I don’t think there is enough littoral zone habitat to have a really large SMB population but what is there is making a decent sports fishery , ie two friends caught 5 bass there yesterday, all about a pound.