Impact of predation greater in low water?

[Foxgap239]

Good morning. My buddy and I were up to the Penn's Creek area recently more out of curiosity as to how bad the waters looked seeing the USGS flows and spawning activity than for fishing. But I did fish a brookie stream or two with limited success in anything but the deeper pools. We stopped at the Millheim FH for dinner and refreshments as we know quite a few locals. They know that both of us are avid fly-fisherman and 2 or 3 guys said they were concerned about trout populations as they are seeing much more Eagles, Osprey, etc feasting on trout in the low water flows.

Just wondering what the thoughts are about the importance of this type of predator activity as another impact on the health of our trout populations in exceptionally low flows that we have seen this year.

 

[ryansheehan]

Will the eagles and ospreys advantage tip in ther favor absolutely, will their be a long term negative effect from it, 10,20, 50 years down the road, I don't think so.

 

[SteveG]

I think at spawning predation would be heavy. But with just low water, and since wild fish spook easier in it, it may be a wash.

If the adult population does take a big hit one year, it'll just provide better feeding opportunities (and have reduced cannibalization), of smaller fish. In return, if the population takes a drastic hit, it will affect the predators in turn and reduce their population/health .

 

[Swattie87]

Good to see you FG!

Yeah, agree it'll even out over the long term. Short term, probably more predation of legal+ sized fish (and loss of fish due to the low, warm late Summer flows), but there will be less predation from larger fish and better survival of smaller fish in the coming years. Less big fish means less food short term for the Ospreys and Eagles...they may move elsewhere is search of food. Cycle repeats itself.

I suspect Browns are more resistant to avian predation than Brookies or Bows too. Browns tend to hide under rocks and things more during daylight and low water conditions.

 

[troutbert]

Eagles and osprey are protected, so there's not much that can be done about that.

Mergansers can be hunted, though, I think.

The warm water temps and resultant low oxygen levels probably cause more mortality than predators during droughts.

And Penns Cr can get very warm during droughts. I didn't take temps on Penns during this drought, but in a past drought I took a temp of 86F between Cherry Run and Weikert, and a guy who lived there said he took a temp of 87F that year.

The answer to that is good forested riparian buffers along the entire length of Penns Creek and all of its tribs.

I think this is the main thing that would help Penns Creek maintain its wild trout populations during droughts.

Another thing might be trying to improve the physical habitat (holding water) in some of the tribs, because when Penns gets warm, trout will move up into cooler tribs.

How well they do up in those tribs can depend a lot on whether there is good holding water (pools and cover) or not.

If the tribs are mostly flat and shallow, then their value as refuge areas isn't so great.

Cherry Run and Poe Creek for example. There is some holding water, but there is also a lot of very shallow water. Because of impacts from the roads closely paralleling those streams, probably.

 

[phiendWMD]

What happens when you feed the geese? Instead of moving on after exhausting the local food sources, they set up camp.

I wonder if something similar occurs with animals that prey on fish. If you artificially inflate the population with fish that are easier to catch than wild fish, which do you think an eagle or heron is going to target? Then concentrate even more of those dumber stockees due to low water and it seems like a buffet to me. I'm sure most of us have heard of birds raiding hatcheries.
What happens when the stockees are harder to catch due to lower numbers caused by predators picking them, after the predators are habituated to that food source?

Nature has a way of balancing itself. Unfortunately man thinks he can do better. Often the best of intentions turn bad.

 

[PocketWater]

PFBC can just stock more rainbows in there.

 

[sarce]

I came across this report a while ago, it's old but I think it has some great insight into how trout (brook trout in this case) are impacted by drought. It touches on predators briefly and as many of you stated, predators find the fishing a little easier in low water.

Shenandoah Drought - Brookies

Also note the comments about water temperature...brook trout in this study survived water temperatures up to 83 degrees.

 

[SteveG]

Poe Creek, being top release, is probably useless during a drought during any remotely warm weather.

 

[Swattie87]

Good read sarce.

Watersnakes...didn't expect that but it makes sense on those small streams. Easier for an eagle or osprey to hunt on bigger water like Penns I imagine.

Amazing how well they can flourish in the right conditions though, and how they can recover so quickly to reach the natural carrying capacity of the stream.

 

[k-bob]

I also like the article sarce linked, interesting mention of watersnakes consuming stranded small stream VA brookies in a severe drought...

brookies in pools separated by dry stretches in a drought might be easy prey for watersnakes, herons, etc ... a lot of us ave done small stream fishing in northern PA... I wonder if you guys have the same experience: I dont see watersnakes on tiny brookies UNTs and tribs in northern PA ... I see those guys round ponds and lakes everywhere, and sometimes somewhat bigger trout streams a bit further south... maybe the watersnake population on small streams is higher in VA, where that study was done?

maybe I am just spacing out, but I cant recall seeing a watersnake on a very small mountain-UNT-type stream in NEPA?

If VA versus PA has more watersnakes on tiny mountain streams, I am OK with that... they'd just be one more thing to watch out for..

 

[Swattie87]

Bob - I see way more NWS on streams in southern PA too. Sometimes even on smaller streams. Saw a large one on a small Brownie stream in York Co. recently.

Can't say I've ever seen one on a small stream up north though. Or if I did, it didnt register. Most of my on the stream herp encounters up there have involved the ones with rattles on their tail! :-o

 

[wildtrout2]

k-bob wrote:
maybe I am just spacing out, but I cant recall seeing a watersnake on a very small mountain-UNT-type stream in NEPA?

Neither have I. I haven't even seen one on larger freestone streams in NC. As Swattie mentioned, I've only ever seen rattler snakes, but that's a good thing.

 

[sarce]

The first time I ever explored a native brookie stream, I came across a water snake eating a 9" brookie. This was in SEPA.

Last year in very low water the same thing happened on one of the VA streams mentioned in that report. This time the snake was trying to eat a 10" brookie.

Water snakes are very common even if not always seen, and they are very effective predators and can hunt in the undercuts where birds can't reach. It could be true that there are less of them farther north or at higher elevations, VA streams are pretty high up but also warmer.

I've also watched a snapping turtle grab an adult brown trout when it swam past the wrong undercut. Lots of animals out there that have a taste for trout!

 

[k-bob]

Fwiw, I think watersnakes may just be more common in tiny mountain tribs as you get further south... for ex, I remember seeing them on small mtn streams in western MD, and that's still north of Shenandoah.

 

[salvelinusfontinalis]

I've seen water snakes eat brookies in sepa. Like the rest I've never noticed them doing this in the northern tier.
Interesting topic.

 

[salmonoid]

I have scared the crap out of, or had the crap scared out of me, by water snakes on numerous small streams in SE PA. They are in the northern tier as well, ran into several on Kettle last year. One piece of angling research from the 1940s lamented the prevalence of water snakes on tributaries to Kettle Creek.

 

[bearfisherman]

Have seen lots of NWS in Elk County, mostly tribs to the Clarion. And lots on the Clarion itself.

Have also noticed the affection they have for habitat improvement devices, mostly notably mud sills and log frame deflectors.

 

[k-bob]

here's a guess at why I don't see too many northern water snakes when fishing small infertile NEPA brookie tribs. the staple diet of the NWS is minnows, not trout, even if they sometimes do get trout: "gamefish are not their staple, smaller fish like minnows are their standard."

http://www.fishandboat.com/Resource/AmphibiansandReptiles/Documents/04northern.pdf

some good tiny NEPA brookie tribs can be so infertile/ acidic that they don't have many minnows. (minnows have small mouths, and can't survive on the larger terrestrials that keep the brookies going in infertile streams with few aquatic insects.)

see the bio report below, first three tribs w/ only brookies and no minnows or other fish species are "mountain UNT-type" class a brookie tribs.

https://www.fish.state.pa.us/images/fisheries/afm/2006/5x10_23lehigh_tribs.htm

I am probably fishing these infertile trib types with fewer minnows, so maybe fewer NWS...

 

[fisherboy3]

Fish can get away from eagles and ospreys. Real problem on the streams I fish has been the blue herons. There has been days where ive seen 4-5 herons on one stream. They are slow moving, quiet, and have a fast attack. They put a hurting on the smaller, younger fish.