Snakehead ?

Here are the facts the VGIF and other state biologists are getting from population surveys from electroshocking and netting. "Although the VDGIF staff has done less
electro-shock sampling this year than
previously, their catch has gone up
exponentially, more than doubling the
number captured in 2004-2005 combined.
“There has been a big increase in the
Occoquan River system,” Odenkirk said,
and they have been found far upstream.
Larger numbers of fish have been found at
Belle Haven and in Pohick Bay. Substantial
increases have been observed in Oxon
Creek on the Maryland side, as well as in
Mattawoman Creek."
Other studies show that the Snakeheads biomass is indeed increasing in the Potomac and that theyre favorite food is Sunfish and topminnows.

Don't misuse catch per unit effort (CPUE) data. Yearly changes in CPUE usually mean absolutely nothing. If anything, CPUE can read changes over many years or decades using trendlines, but by saying "we caught a bunch more at our sites this year..." you are really just saying that there were more fish caught in that one place at one point in time. I've looked at lots of CPUE charts, and they usually just go up and down at random intervals. Again, over long periods of time they can show something, but when a state biologist says "catches are up/down this year," it should be taken with a grain of salt.

For instance, I just did some standardized electrofishing on a dam the other night. The catches were abysmal. The past couple of years have been great. What will I tell you about the bass populations? Well, they weren't at the dam the other night, most likely. On the flipside, we had a site that was extremely productive compared to other recent years. I'd tell you the same type of thing about that site; there were a lot of fish there that night. On the management side of things, we're going towards looking at age, growth, and mortality of fishes in systems to get better ideas of what populations are doing. It gives you a better idea than "there were a bunch/few fishes in that one place at that one moment."

No, with less effort this year (fewer fish sampled) they're finding a whole lot more snakeheads.

No, with less effort this year (fewer fish sampled) they're finding a whole lot more snakeheads.

I misread the quote... Sleepless nights with screaming babies are making me sloppy. Yeah, there's definitely something to be said for catching large numbers of fish during an invasion.

No, with less effort this year (fewer fish sampled) they're finding a whole lot more snakeheads.

oooh. *also misread the quote*

Soo... *tries to understand* Does that mean that the introduction of snakeheads correlated to increased number of fish?

Im sorry Erica, the article is stating that the populations of Snakehead are increasing in size and area in the Potomoc river basin; some people may argue with this type of statistical data, but I havent heard of any reliable way to estimate populations of invasives without using this data in one way or another. As far as I know from my college biology class bodies of water can only sustain a certain amount of Biomass, if one introduced species is increasing its numbers in that biomass, many times a direct result of that phenomenom is the decrease in the numbers of a different species ex. (Ruffe pop explosion in the great lakes and the decline in numbers of Yellow Perch and emerald shiners).

It would take some convincing to convince me that the biomass in any given body of water is high enough to be anywhere near some potential biomass limit for that body.

It would take some convincing to convince me that the biomass in any given body of water is high enough to be anywhere near some potential biomass limit for that body.

What about temperate estuaries, and salt marshes?

What about temperate estuaries, and salt marshes?

What about an entirely natural eutrophication process, where the productivity of a given lake increases as the lake ages. The biomass productivity increases as a function of prior biomass production. Biomass productivity is then not some set constant but increases as a result of recycling nutrients through many levels. For estuaries and such the nutrient flows through it are far more important, which includes the biota from upstream. The same effect occurs in streams, as a stream with biotic sources restricted to channel flow is especially poor. Healthy streams need the equivalent of estuaries along its borders, harboring various habitats that feed biomass to increase the biomass potential of the stream itself. In some cases it may be restricted to bugs from nearby bushes, but ideally includes various marsh areas with its own biota incrementally feed downstream. The salt marshes and estuaries merely inherits this abundance from a hierarchy of upstream food webs.

If the biomass productivity was merely a matter of raw nutrient content then our effluent problems would be a huge ecological boon. Yet the fact is that for these nutrients to be efficiently used they must pass through a hierarchical food web. Otherwise organisms at the bottom choke out the whole food web just trying to keep up with the nutrient inflow rate, while running short on abiotic resources, like oxygen. The effective limits on biomass is not defined by volume, but by the food web hierarchies that allows the nutrients to be recycled through many levels which each adds to the total potential biomass, which can increase over time as external nutrient sources are incrementally added in a variety of forms.

The interesting thing about most temperate estuaries is that they don't export as much material as one would think, i.e. there's little "tidal flushing". Material and energy can leave in the form of maturing juvenile fishes and invertebrates that leave the estuary to their adult niches. Most material recycles locally in a marsh rather than move to nearshore environments. So this supports a relatively simple trophic web with high biomass but relatively low diversity, much of the diversity being seasonally produced juveniles.

I did not know that about estuaries nutrients, though I count any living organism leaving as nutrients leaving. I still presume the nutrient inflow is very significant, so this would mean they are remarkably efficient at aggregating nutrients but remarkably inefficient in recycling those nutrients as living biomass, in spite of the high biomass present. In lakes with limited inflows of nutrients the autotrophs convert inorganic molecules to more complex organic compounds that get passed through the food web and strongly recycled so that the total biomass the lake can maintain will increase as the autotrophs produce more raw material from the inflow of simple compounds over time and pass them through the food chain.

I was reading "Restoration and management of lakes and reservoirs" By George Dennis Cooke, about the "top-down bottom-up" model proposed by McQueen et al., which makes a lot of sense and has some good empirical backing. Based on this I looked up the diet of snakehead, which is quiet close to the diet of bass except without the turtles, snakes, and crayfish. Killifish made up the largest numbers in snakehead diets but bluegill made up the largest volume. At first thought the "top-down bottom-up" model indicates the biggest effect of snakeheads to be on planktivores, but a dynamic already exist between bass or piscivores and planktivores, with a multi-year study of Lake St. George, Ontario used as a test case of the model following a winterkill of 72% of the largemouth bass. Hence more likely the biggest effect will be on piscivores like bass, the reduction of which will balance out the planktivore losses to something relatively near null. But this should also have a benefit (log correlated) to non-fish aquatic species, which could benefit other niches. The biggest dangers are probably to somewhat rare species in the same shallow weedy habitats as killifish. Sufficiently large and shallow weedy margins should provide a sanctuary though. Unfortunately the way we often groom the edges of lakes and rivers works against this.

It seems in all cases, regardless of nutrient availability, a huge part of the capacity to carry a high bioload depends on the variability of habitats with plenty of sanctuary regions for different niche biota.

What your writing about (food chain) is true to a certain extent in many circumstances...but this still does not count for the fact that largemouth bass do not have a specialized diet of mainly fish, like the Northern Snakehead, and do not guard their young for as long; another important fact is that local Sunfishes and topminnows in the Potomac basic have had centuries to adapt to predation by Bass whereas the more aggressive Snakehead have been in the Potomac less than 15 yrs. Nutrients have an big affect on Biomass, but from models of what happened to the Sacramento Perch, many Pupfishes and the Emerald Shiner in the Great lakes.....predation and Biomass are connected and not entirely dependent upon nutrient levels in Rivers (the Sacramento), lakes (Lake Superior), and springs (in the Southwest where several Pupfish and native Gambusia went endangered, threatened or extinct due to introductions). Thanks Joe.

Edited by wargreen, 16 April 2011 - 02:23 PM.

Request: I would very much like a reference to the material on "models of what happened to the Sacramento Perch, many Pupfishes and the Emerald Shiner in the Great lakes". This is stuff I am interested in.

Main points:
1) Quote: "...does not count for the fact that largemouth bass do not have a specialized diet of mainly fish..."
Actually I did, which is why I give a likely log benefit to non-fish prey, per the "top-down bottom-up" model and the empirical data supporting it. There is a preexisting counterbalance between piscivores and planktivores, so the notion that planktivores are going to be reduced to numbers under what is required to support the piscivores, including snakeheads, is ecological mumbo jumbo. Hence the losers will likely be predominately piscivores such as bass.

2) Quote: "...local Sunfishes and topminnows in the Potomac basic have had centuries to adapt to predation by Bass..."
I also considered this. For those fish that make up the bulk of existing piscivores diet the balance between predator prey is not likely to significantly change. However, I pointed out the killifish in particular to be in greater danger, though likely others in similar environments should be included, as a direct result of the difference in feeding and predatory habits of the snakehead relative to existing piscivores. This is a direct result of snakeheads in an environment that is not adapted to the presents of snakeheads.

3) Quote: "...Biomass are connected and not entirely dependent upon nutrient levels..."
Which is precisely the point I have been making. In fact, as I have pointed out, predation is required to maximize biomass production. I included a whole post outlining a simplistic food chain to illustrate this in a hopefully more intuitive manner. So when I later explored the "connection" between biomass production and nutrient levels it was not a claim that nutrient levels define biomass production, but rather efficiency. If you hold the efficiency of all food webs at a constant, which is absolutely not so, only then can biomass production be directly related to nutrient levels. I also explicitly stated that whether the introduction of snakehead resulted in a net gain or loss of biomass capacity is a crap shoot. To say "local environments are not adapted to snakeheads" is simply another way of saying we do not know, i.e., a crap shoot.

When you say "more aggressive Snakehead" what exactly is "more aggressive" suppose to mean? To me it implies attacking their prey with abandon, reducing their prey below necessary levels. Yet what I know about bass puts them at a far more aggressive level than snakeheads in this respect. Snakeheads are tame by comparison. And even if it was so snakeheads still need a certain population of prey to maintain a certain population of snakeheads. The concern is not the prey species in general but those specific species that evolved to habitats that avoided local piscivores but cannot avoid snakeheads as well. If by "more aggressive" you mean attacking people, it is simply not warranted, especially for the snakehead species that have been introduced here. When researcher swim into their guarded nesting sites in the Potomac they hide. The reseachers do not even see them without sitting still and waiting for the snakeheads to think they left. So I cringe at the apparent "monster" mentality these terms imply.

Introductions are a major problem resulting in major losses to local fauna and needs to stop. Yet I would be willing to bet that our own actions resulting in habitat destruction and degradation dwarf the effects of invasive thus far, and often what is blamed on invasives is likely a product of our own destruction of habitats.

Rinne, J.N. 2004. Forest and fi shes: effects of fl ows and foreigners on southwestern native fi shes. Pages 119-124 in G.J.
Scrimgeour, G. Eisler, B. McCulloch, U. Silins and M. Monita. Editors. Forest Land–Fish Conference II – Ecosystem
Stewardship through Collaboration. Proc. Forest-Land-Fish Conf. II, April 26-28, 2004, Edmonton, Alberta.

Foreigners

Changes in fi sh assemblages
The native fi sh fauna of the Southwest is low in
diversity and high in uniqueness and specialization
(Miller 1961, Minckley 1973, Rinne and Minckley
1991). Fewer than 50 species of fi shes naturally occurred
in the waters of the Southwest and only two dozen were
historic inhabitants in the waters of Arizona (Minckley
1973, Rinne and Minckley 1991). By comparison, over
100 species of fi shes have been introduced into Arizona
alone (Rinne 1994) and half have become established
(Rinne 2003a) as self-sustaining populations. Most of
the introductions were for sport fi shing, which naturally
Ecosystem Stewardship Through Collaboration 121
Figure 1. Instantaneous peak discharges in the Verde River, 1974-2002.
Figure 2. Change in relative proportions of natives (light bars) and nonnative (dark bars) in samples in the upper
Verde River, 1994-2003, a period of low, drought fl ows (see Figure 1).
122 Forest Land–Fish Conference II
followed the massive increase in reservoir surface water
acres and habitat (Rinne 2003a). Rinne and Janisch
(1995) reported the extensive coldwater introductions,
and Rinne et al. (1998) the warmwater introductions in
Arizona streams and lakes.
Nonnative, or non-indigenous fi sh introductions
into foreign waters have generally been shown to
have a negative, often dramatic impact (Courtenay and
Stauffer 1984). In the Southwest, increased presence
and abundance of these species is negatively correlated
with native species. In the upper Verde River, in 1994,
nonnative fi shes comprised less than 10% of fi shes
captured (Figure 2). Only a decade later, in 2003, 90%
of the fi shes captured were nonnative species. In the
Gila River, Colorado (Mueller and Marsh 2002) and
Rio Grande rivers similar patterns of increase in nonnative
fi shes is paralleled by an often, dramatic decrease
in native species. Native trout species have declined
dramatically with the introduction on nonnative trout.
Rinne and Minckley (1985) documented the inverse
distributions of the native Apache trout (Oncorhynchus
apache) and introduced rainbow (O. mykiss) and brown
(Salmo trutta) trout. Gila topminnow populations
decrease in presence of the introduced mosquitofi sh
(Gambusia affi nis) (Meffe et al. 1983). Replacement
can come by way of competition, hybridization or direct
predation (Minckley 1983, Rinne 2003a). In summary,
native southwestern fi shes and non-native, predatory or
competitory fi shes generally cannot co-exist (Rinne et
al. in press) in the same reaches of stream. Hydrological
and geomorphological infl uences and interactions can
alter this statement (Rinne 2002).


http://www.biologica...s/9215_5491.pdf article of the gila chub http://www.audubongu...ced_fishes.html audobon society atricle on non-natives,http://www.jstor.org/pss/3671390 article from the 80s on introductions in Southwest.http://www.desertmuseum.org/programs/invasive_Aquatic.html tells about the correlations between introductions and threatened species,http://www.fws.gov/southwest/es/arizona/Documents/RecoveryPlans/DesertPupfishRecoveryPlan.pdf article on one pupfish and the introductions that threaten it. Mywan this is a short and abbreviated reading list just on the Southwest and endangered fish due in part to introductions. I will post more on the Sacramento Perch and Emerald shiner. Thanks Joe.

Ecological Effects of Non-native Fish Species in Low Elevation Streams of the Central Valley, California
Marchetti, M

Dissertation Abstracts International Part B: Science and Engineering [Diss. Abst. Int. Pt. B - Sci. & Eng.], Oct 1999, vol. 60, no. 4, 1400

Three separate studies are described which examine the effects of non-native fish species on Central Valley California streams. The first is an experimental study of competition between a California native centrarchid, the Sacramento perch (Archoplites interruptus) and an ubiquitous non-native, the bluegill (Lepomis macrochirus). The experiments indicate that (1) Sacramento perch gain less weight and show reduced growth when placed with bluegill, (2) Sacramento perch demonstrate less aggressive behavior than bluegill, (3) Sacramento perch shift their habitat use in the presence of bluegill. Overall the results imply that Sacramento perch and bluegill exhibit interspecific competition. The second work is an investigation into the larval ecology of stream fish in Putah Creek, a Central Valley stream. Native larvae occurred both earlier in the year and in higher abundance than introduced species. Both native larvae and overall numbers of larvae were more abundant at the upstream site. Larval fish abundance was not a good indicator of juvenile abundance at the same sites later in the year. The two methods of collection utilized tended to select for different species. At both locations larval fish were collected in significantly greater numbers at night. It is suggested that the difference between the sites is due to habitat changes resulting from an upstream dam that has created a refuge for native taxa.




http://www.csuchico....chetti 1999.pdf article on a study showing how Bluegill are more aggressive than Sacramento Perch, can outcompete the Perch and take over feeding and spawning sites,http://www.nanfa.org/articles/acsacperch.shtml excellent article in our own AC on the Sacramento Perch. This was just a few on the Sacramento Perch, next Ill post on the Emerald shiner.

Environmental Biology of Fishes
Volume 5, Number 3, 225-233, DOI: 10.1007/BF00005356
Alewife, rainbow smelt and native fishes in Lake Michigan: competition or predation?
Larry B. Crowder

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no accessJournal Article

Food and habitat partitioning between young-of-year alewives and rainbow smelt in southeastern Lake Ontario

Timothy P. Urban and Stephen B. Brandt

Environmental Biology of Fishes, 1993, Volume 36, Number 4, Pages 359-372

Several native fish species in Lake Michigan became rare or locally extinct during the increase of rainbow smelt (1930s) and alewife (1950s–1960s). These particular native species have pelagic eggs or larvae which were large relative to the zooplankton and which co-occurred with feeding alewife, smelt or both. Alewife, smelt and most of the other planktivores in the lake probably consumed eggs, and at least alewife and smelt are known to consume larvae. For each species, I comment on the probable role of predation on early life history stages in their decline. Several species which currently co-exist with alewife and smelt have shown large scale declines during the increase of the exotics. Recruitment declines were often dramatic and the probability of predation on these species during their early life history is evaluated.

http://www.glsc.usgs...h_invasive_fish graff showing growth of Ruffe biomass in relation to emerald shiners, The Usgs, Epa, and the states of Minnesota and Wisconsin have even more info available online on the relationship between the exotic Ruffe and native emerald shiner; Mywan I agree with you 100% that the greatest factor in causing our natives to become threatened, endangered and extirpated is habitat destruction and degradation.....but unfortunately due to the population growth of humans and pure economics, I do not believe we will be able to stop our effects on the enviroment (although I for one wish we would). Exotic introductions are a major problem in many areas where we have natives that could be susceptible to extirpation, and it is my belief that it would be cheaper and more reasonable for governments to pass laws enabling us (and of course themselves to enforce by their agencies) to fight the spread of non-natives than to reverse the incredible damage to the habitat of our rivers,lakes and streams. I do believe that we should try to preserve the natural habitat and fight the introduction of non-natives at the same time; and to even "ark" certain species for reintroduction and possible hobbiest use in the future. You havent touched upon the problem of introduced diseases with non-natives, or lack of natural enemies (were still trying to figure out how best to catch Snakeheads in the Potomac on a rod and reel). I agree that LMB's will be on the losing end in a fight for its ecological niche with Snakehead, but I also believe that Snakehead are a more efficient piscavore and will have a greater affect on topminnows and Lepomis,Enneacanthus,Acantharchus,Ambloplites and Elassoma fishes, not to mention the damage it could have on darters, sculpins and Sleepers. Snakehead are more aggressive defenders of territory to protect their young, they do so in pairs and much more aggressively than bass, and will kill any fish that cross into the school of their young or nesting site, even if its too big to eat whereas Bass will diplay first to drive the other fish away before attacking; as far as people go I dont believe Snakehead will go around "hunting" for swimmers to eat.....but I would much rather get accidentally bitten by a LMB than a Northern Snakehead (and I would much rather fish for LMBs also). Lakes and rivers go through cycles which control to a large part how big their available biomass is very true, but the lake still has only so much oxygen, food or space for the fish to live in at any given point, and not all fish can simply adapt in enough time to life in the Ocean or rivers and streams if they are outcompeted by other species before becoming extirpated. Mywan if you have any studies that have scientific evidence to the contrary that disapprove of biomass and population viability theory, please show me......I am always open to changing my opinions on the basis of hard facts. Thanks again, Joe.

Edited by wargreen, 17 April 2011 - 03:22 PM.

Rinne, J.N. 2004. Forest and fi shes: effects of fl ows and foreigners on southwestern native fi shes. Pages 119-124 in G.J.
Scrimgeour, G. Eisler, B. McCulloch, U. Silins and M. Monita. Editors. Forest Land–Fish Conference II – Ecosystem
Stewardship through Collaboration. Proc. Forest-Land-Fish Conf. II, April 26-28, 2004, Edmonton, Alberta.

Foreigners
Changes in fish assemblages
[...]

The entire article this (clipped) quote came from can be found here:
http://www.chiltonra...rest_fishes.pdf

The actual source was indeed informative, but the article explicitly illustrates how this is not strictly an invasives issue. In fact the strongest impact described was hydrology, where most of these native fish are artificially restricted to isolated spring heads and runs. So not only are these native fish extensively restricted in their habitat by dams and diversions, but when instantaneous peak discharges hit their highs, more closely corresponding to the yearly variances before hydrological alterations, the natives out-compete the non-natives by 4 to 1. Check the graph on the source. Yet the low flow years imposed by theses hydrological alterations has the non-natives out-competing natives by 4 to 1.

So this begs the question, is the competitive difficulties these native species are having the result of non-native species or the result of a non-native habitat? Just because the habitat is in the same location as their native habitat was does not make it their native habitat. You can honestly say it is the combination of both, but comparatively that is essentially a pedantic claim. Almost like putting a riffle fish in a swamp and blaming its death on the cayman that eat it.

Especially if we're talking about North America, you're talking about a severely altered ecosystem with many former common species like chestnuts and passenger pigeons gone, and massive alteration of land and water by humans. Many of the invasives are good at taking advantage of disturbed habitats and shredded community ecosystems, you don't have to invoke any heavy theory to describe this.

The entire article this (clipped) quote came from can be found here:
http://www.chiltonra...rest_fishes.pdf

The actual source was indeed informative, but the article explicitly illustrates how this is not strictly an invasives issue. In fact the strongest impact described was hydrology, where most of these native fish are artificially restricted to isolated spring heads and runs. So not only are these native fish extensively restricted in their habitat by dams and diversions, but when instantaneous peak discharges hit their highs, more closely corresponding to the yearly variances before hydrological alterations, the natives out-compete the non-natives by 4 to 1. Check the graph on the source. Yet the low flow years imposed by theses hydrological alterations has the non-natives out-competing natives by 4 to 1.

So this begs the question, is the competitive difficulties these native species are having the result of non-native species or the result of a non-native habitat? Just because the habitat is in the same location as their native habitat was does not make it their native habitat. You can honestly say it is the combination of both, but comparatively that is essentially a pedantic claim. Almost like putting a riffle fish in a swamp and blaming its death on the cayman that eat it.

Indeed Mywan, I read the whole article including the summary, where they state that they believe hydrology has more of an impact than non-natives (they never once stated that non-natives do not contribute to the decline of natives in the Southwest); although I believe like I've stated previously that habitat degradation and hydrology do have a role in many instances, I believe that many natives live in a degraded habitat without being extirpated (too many examples to cite), and that many that are close to being extirpated now are being pushed over the brink due to exotics. I dont believe that there are many bodies of water left in the lower 48 states that haven't had one form of habitat degradation or another. It depends on how much the habitat was altered and which exotics were introduced, and which natives were the ones being on the losing end of the population equation (on whether hydrology was the main reason). Once again I would like to see the evidence that the Pupfish , Emerald shiner and Sacramento Perch would have been doomed to threatened status, or at least have the drastic population reductions in many areas without the introduction of non-natives.....I havent seen any yet. I do believe that changes in Hydrology would most definately affect populations; but all three of these fish are are very adaptable to fluctuations in hydrology and had weathered many natural changes in hydrology in their long histories in their native habitats. The Sacramento river (which I used to live by) used to change drastically with long years of droughts or flooding, Sacramento Perch used to be abundant in the river where bluegill and LMBs now thrive and can handle waters more alkaline than most fish; most pupfish's can handle extremes in temperatures, salinity, and ph; and Emerald shiners have a very large range from the arctic to the gulf, from lakes to rivers to streams. I have to admit I got a chuckle out of you calling the facts of both habitat destruction, and the introduction of non-natives a comparative "pedantic claim" in the population models shown; Mywan I would gladly own up to being "pedantic", more than I would "assumptive".
Many species have disappeared from habitat destruction...thats well documented; but I also believe that many have also disappeared from the introduction of non-natives. I believe its more like putting a Caiman in with the Greenthroat darter (riffle fish)in Texas and accurately stating the Caiman shouldnt be in the middle of the Lone Star state eating the native darters (stinkin Caimans!), no one can positively tell me the Caiman wouldnt be munching on the darter if their wasnt a dam up the creek; but I can positively tell you that the dam didnt put the Caiman in central Texas.....people did!

Edited by wargreen, 19 April 2011 - 08:39 PM.

I believe its more like putting a Caiman in with the Greenthroat darter (riffle fish)in Texas and accurately stating the Caiman shouldnt be in the middle of the Lone Star state eating the native darters (stinkin Caimans!), no one can positively tell me the Caiman wouldnt be munching on the darter if their wasnt a dam up the creek; but I can positively tell you that the dam didnt put the Caiman in central Texas.....people did!

The irony of that statement is that the biggest threat to Greenthroats is habitat degradation...

That being said, I have a policy of shooting all caimans I encounter on sight. American Alligators, however, always get a pass.

That being said, I have a policy of shooting all caimans I encounter on sight. American Alligators, however, always get a pass.

Lol, the only Caimans Ive ever seen were when I was stationed in Panama, I didnt like them there, and I sure wouldnt like them here!