Lower Susq R smallies: re Dave Weaver's question

[Mike]

Dave Weaver inquired in another thread about Lower Susquehanna smallmouth bass (York Haven to Pequea) and their compensatory responses to high fingerling mortality since 2005. Smallmouth bass had been growing at a rate that was at least for the time being a year ahead of the growth that used to occur prior to the fingerling mortality problems and reductions in small to moderate size SMB that began soon thereafter. Additionally, SMB survival has improved. Good growth=fat fish=good winter survival. The improved growth rates were noted by 2008 and increased survival was speculated upon then and later confirmed (well before the no-kill regs went into effect), most likely due to limited competition for the large forage base, which now included rusty crayfish on top of the already abundant minnows and gizzard shad. We first reported the rapid and accelerated growth rates at the Susquehanna SMB symposium that Dave attended in about 2008 or 2009. The fall, 2013 electrofishing sample at the fixed night electrofishing sites that have been sampled for decades (Accomac, Long Level, Safe Harbor tail-race to Pequea) showed that SMB abundance had greatly recovered despite continued high rates of fingerling disease incidence. It remains to be seen whether that is what is found in 2014 sampling, or was a 2013 anomaly, but the 2013 abundance indices were very encouraging and suggest that fishing should be good in 2014. Reports of Susquehanna R SMB sampling results have periodically appeared on the PFBC web page's biologists' reports in Areas 3, 4, 6, and 7, depending upon the year.

Note to C&R trout advocates: Compensatory survival also occurs in wild trout populations and that is why the limited harvest of the type that occurs in Pa's unstocked wild trout streams is of little population concern in that renewable resource.

 

[Fishidiot]

Thanks Mike - good stuff.

I think it should come as no surprise that individual, adult SMBs, are showing good growth rates in the lower Susky these days (except maybe to those who continue to believe the river is "dead").
As anyone who fishes it knows - if they have bothered to pay attention - the river is very thick with forage, both macros and small fishes. I'm amazed at the number of aquatic insects I see when I roll rocks there. The bass are fat (mostly) and there are many of them in large sizes >15 inches. Ditto for the lower Juniata.
I'm pleased to see better numbers of adult SMBs in the lower Susky last year.....but am still concerned about YOY. Hopefully, the better showing of adult SMBs in that section of river will gradually result in some better numbers of younger fish in the future. Here's hoping for stable water levels this year in May/June. We still need to see more younger fish IMO. At least the picture is looking better rather than worse.

In any event, the increased growth rate being connected to Rusty crays is of particular interest. With this species (and I think some other exotic crayfish) present, the overall number of crayfish in the river is just stunning. The PFBC biologist (Lieb I believe is his name) has shown that there can be up to 18 crays per square foot of bottom. Anyone who has waded the lower Susky in the evening just before dark knows this isn't an exaggeration. How many are native vs exotic, I don't know but I'm sure the high density suggest predominately exotics(?). I see this in local WW creeks in both the Susky and Potomac watersheds as well. The number of crayfish is just off the charts! (Note: not everywhere, but in many localized areas.)
There have been some studies on SMBs in tanks that reveal that they prefer to prey on smaller crays with smaller claws and often avoid bigger ones with big claws. The Rusties and the Allegheny Crayfish tend to get very big very fast and have large claws. Nevertheless, there must be so many of them that the bass can just feast on whatever size they would prefer. With fewer bass and so many more crayfish (in addition to all the other forage), it's no wonder that section of river has seen better than average growth rates.

 

[geebee]

Aren't crayfish explosions blamed for decreasing YOY Pops though ? Through predation of eggs and swim ups ?

 

[Fishidiot]

geebee wrote:
Aren't crayfish explosions blamed for decreasing YOY Pops though ? Through predation of eggs and swim ups ?

Exotic crayfish can certainly have negative impacts on native flora/fauna...but I think the main concern at this stage is their impact on other native species of crayfish. They can certainly impact plant growth and may have some impact on spawning/YOY as well. I wouldn't attribute the bass crash in the lower Susky to crayfish as Rusties and other exotics widespread in PA now and the bass problems have been limited to the lower Susky.
Perhaps for bass in the lower Susky, there's a net gain with all the crayfish somewhat similar to the situation with gobies in Erie: initial concern about ecological impact...but a new and very good food source for SMBs(?). (However, I'm not suggesting that the affect is as pronounced as the gobie situation.)

Mike,
You refer to "compensatory responses" in lower Susky bass as linked to reduced population (if I'm following) and this seems to imply that the SMB population is demonstrating faster growth following a natural and logical adaptation to fewer overall numbers of fish. Is this correct? If so, one would surmise that these higher growth rates are not being seen in areas upriver such as the West and North Branches as these upriver areas - although they have all the new crayfish - did not see bass population drops.
In other words, is the growth spurt a result of fewer bass; or a result of more food; or a combination of both? With all the crayfish, there might be demonstrable (albeit smaller) increases in bass growth upriver or in other rivers with similar forage. Is there statistically significant evidence of better growth elsewhere?

 

[Mike]

You are correct regarding my comments: the increased bass growth and survival is most likely directly related to the reduced density of bass. I would expect growth for most size classes to slow to normal rates as the bass population increases, but that may not be the case for young fish if reproductive success continues to be depressed. Young bass that survive may still display rapid growth due to lack of competition at small sizes. As for the crayfish contributing to the rapid growth with their extra high densities, that is pure speculation (educated guess) on my part, given their densities. The river bass were full of crayfish prior to the rusty introduction, and are full of them now. As for upriver locations, I have not heard of increased growth there. I would expect improved growth in the middle Susq R, but I did not get that feeling from Kris Kuhn, the AFM. Survival has improved, however. As for farther upstream, I have not had that conversation with those AFM's, but I would be surprised if growth rates have changed. On the West Branch, growth may be faster in areas that have not reached the river's carrying capacity for bass as of yet, but that comment is based on ecological theory or principles, not on any observations from the AFM.