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Originally Posted By: CJBS2003
Originally Posted By: adirondack pond
Yeah I love that cartoon, I've got a T-shirt with that on it.


Me too!


Sick minds think alike. grin



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I am going to attempt to answer some of the questions on this thread or at least provide some food for thought in understanding the why of prey selectivity.

To be clear there are multiple factors involved and the best we can do is try to understand some of them in context. IMO the factors are biologic/genetic. By that I mean the choice of prey is based on biology and instinct not learned behavior or choice (likes/intelligence). I will do this in parts as one of the studies I have to relocate and copy and paste.

I believe the main factors are predator gape size , energetics and the lake's prey dynamics (statistical probability). Here is some info that should set the stage.


Experimental Analysis of Prey Selection by Largemouth Bass:


Role of Predator Mouth Width and Prey Body Depth

Transactions of the American Fisheries Society

120:500-508, 1991


K. DAVID HAMBRIGHT



Prey-selection behavior of piscivores also influences the vulnerability of prey. Optimal foraging theory postulates that predators maximize the ratio between the benefits gained and the costs incurred in obtaining prey. Obviously, the benefits gained increase as a function of prey size, but cost, in particular that due to handling time, also increases rapidly with prey size (Werner 1974). Hoyle and Keast (1987,1988) demonstrated that, for two piscivores (largemouth bass Micropterus salmoides and grass pickerel Esox americanus), the weight-adjusted handling time for prey of equivalent lengths varied with body shape: it was lowest for shallow-bodied bluntnose minnows Pimephales notatus and tadpoles Rana catesbeiana and higher for deeper-bodied yellow perch Percaflavescens and bluegills Lepomis macrochirus. In addition prey body depth has been shown to influence other cost-related aspects of ingestion by piscivores, such as pursuit time and capture success (Moody et al. 1983; Webb 1986). I here present further evidence that prey body depth in relation to piscivore mouth size is important in determining the sizes of prey selectively consumed by gape-limited piscivores.


Perhaps the most important variable in the selective feeding of piscivores is prey size. Gut analyses show that piscivores are size-selective and that prey size typically increases with piscivore size (Parsons 1971; Knight et al. 1984). Although the upper limit in prey size is constrained by the relationship between piscivore mouth size and prey body depth, piscivores tend to consume prey sizes that are much smaller than the maximum possible (Lawrence 1958; Gfflen et al. 1981). The high occurrence of small prey sizes in piscivore guts is usually assumed to reflect the high relative abundance of these sizes in the prey assemblage (Hoyle and Keast 1987). However, prey size distributions in piscivore guts can be skewed toward sizes smaller than those most abundant in the assemblage, especially when the assemblage is dominated by deep-bodied species such as sunfish, ale wives Alosa pseudoharengus, and gizzard shad (Gillen et al. 1981; Knight et al. 1984).

Using a simple graphical model and census data from a small lake, Hambright et al. (in press) illustrate that this pattern can be explained simply as an interaction between prey body depths available and mouth widths in the piscivore population. If encounters are random, the probability of a particular prey fish encountering a piscivore of mouth width large enough to ingest it decreases as prey body depth increases. As a result, most or all sizes (juveniles to adults) of shallow-bodied species will be highly vulnerable to piscivory. Ingestion of deep-bodied species will be concentrated on the smaller (younger) individuals in the populations, whereas larger adults occupy a size refuge with very low vulnerability to piscivory. In the present study, preference of intermediate and large predators for fathead minnows and pumpkinseeds with similar body depths was equivalent to preference for adult fathead minnows but juvenile pumpkinseeds. Small largemout
bass tended to prefer juveniles of both species This pattern of selection appeared independent of relative prey abundance. Prey were distributed evenly across size-classes (with a few exceptions) at the beginning of each feeding trial, although the distribution of prey sizes changed during the 2-d experiment, resulting in occasional depletion of one or two size-classes. Thus, the preferences observed provide a conservative measure of selection by the largemouth bass. Any tendency for the predators to track the more abundantsize-classes would have directed them toward
the remaining prey (i.e., the larger pumpkinseeds and smaller fathead minnows), thereby potentially reducing the observed preferences.



Last edited by ewest; 02/03/12 09:19 PM.















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Eric, please forgive my intrusion when you're just getting started, something you wrote just begs the question, are you suggesting that LMB choose their prey out of biology/instinct, not by nature of a learned response?

If so, am I correct in assuming that you are speaking in general terms/generations, and not of specific individuals? We know that fish can become "hook shy", which I consider a learned response, so I'm just wanting to be sure I understand the context behind the statement. I'm looking forward to learning something here, I just don't want to start off with my train of thought already derailed.

Sorry to interrupt.


"Forget pounds and ounces, I'm figuring displacement!"

If we accept that: MBG(+)FGSF(=)HBG(F1)
And we surmise that: BG(>)HBG(F1) while GSF(<)HBG(F1)
Would it hold true that: HBG(F1)(+)AM500(x)q.d.(=)1.5lbGRWT?
PB answer: It depends.
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Don't want to get bogged down in semantics. "Learned" is a catch word here. LMB can become conditioned but do they really learn "ability to think". That shiner tasted good and fit well in my mouth with no fins.

Energetics demands that they max their energy use vs. energy intake. see above "Optimal foraging theory postulates that predators maximize the ratio between the benefits gained and the costs incurred in obtaining prey. " What that means is a LMB is not going to swim around looking for a shiner to eat because it remembers it tasted good before. It is going to eat what gives it the most energy return for the energy expended. That is a genetic/instinct response to a biological function.

Keep in mind the forage population differences. In big open water lakes shiners and shad are the most abundant forage in #s and vol so that is what a LMB is most likely to encounter and thus makes the most energetic sense to eat. But in small waters like ponds the most abundant forage is likely to be BG/sunfish and there it makes the most likely source to be encountered and make the most energetic sense.

A close reading of the study above shows the factors I am referring to - predator gape size , energetics and the lake's prey dynamics (statistical probability).

Studies (I need to relocate)on LMB foraging (sunfish vs. tilapia) show just how well a LMB even from fry size by instinct know what their gape size allows and how accurate they are on strike and swallow ability (no wasted energetic effort). Do they make mistakes - yes but few and far between. The forage fish likewise know this susceptibility instinctively and if they are to big they are not worried about a non capable LMB being around them.

Its instinct not knowledge. More later.
















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Conditioned vs. learned, compared against "the ability to think".

I see what you mean about semantics. This is a very interesting topic, but I hope I can learn to distinguish the differences between the appearance of rudimentary reasoning, and conditioned responses, because right now I'm not sure I can put a fine enough point on my pencil to separate the two.

Good stuff.


"Forget pounds and ounces, I'm figuring displacement!"

If we accept that: MBG(+)FGSF(=)HBG(F1)
And we surmise that: BG(>)HBG(F1) while GSF(<)HBG(F1)
Would it hold true that: HBG(F1)(+)AM500(x)q.d.(=)1.5lbGRWT?
PB answer: It depends.
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I'd say that all predatory will eat first fish they can find in their way. I've seen what can be found in stomach of a pike or perch. Here in Latvia mostly I've found:

1)Perch;

2)Roach (Rutilus Rutilus);

3)Ruffe (Gymnocephalus cernuus)


They all are common fish here. As you can see, perch and ruffe aren't as great pleasure as roach - they got sharp fins everywhere but seems like predators don't care.

By the way we got such fish as stickleback here (3 species actually but 2 of them are quite common - 3 spined stickleback and 9 spined stickleback).



Does it seem to be delicious? Not really... but fish eat them even it's not hard to find much softer fish around.

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Originally Posted By: Omaha
Speaking of people who eat bugs, I did an interview for an article a couple weeks ago with a local Naturalist who used to teach edible insect classes. Her favorite recipe was Cricket Popcorn.



Ken, you were definitely not the only one who thought about eating GSHs from the thread title.

Thread thoroughly hijacked now? grin


That is just thoroughly and completely Yuck!!!

I never go to restaurants either! Who knows what the disgruntled and underpaid employees add to the gravy, getting revenge for their state of affairs, implemented on you. EEEEWWWWWW!!!!

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Not a fan of texture JKB? grin


Grundulis, those stickleback look downright dangerous to eat! Sometimes I wonder how a LMB eats a very round BG and survives.

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We have both the 3 and 9 spined sticklebacks here in the US. The roach is closely related to our golden shiner, so closely they readily hybridize where the roach has been introduced to North America. Your perch and our perch are also extremely closely related, however I am unaware of any European perch being introduced into North America. The ruffe was accidentally introduced into our Great Lakes and is now creating a mess.

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Is the ruffe a sort of goby? Wasn't it a goby that was introduced to the Great Lakes? And I thought the gobies were actually improving the SMB populations?

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Originally Posted By: Omaha
Not a fan of texture JKB? grin


Grundulis, those stickleback look downright dangerous to eat! Sometimes I wonder how a LMB eats a very round BG and survives.


Just remembering and reminiscing about my high school days working in a restaurant.

I was a breakfast cook at a place called the Texan Restaurant. Nothing Texan about it except for the FAKE Longhorns out by the road. (figure that one out)

Anyway, I had decided to quit one day, and Petrousk (cute gal, just a nickname) Influenced me with just a bit evil on my certain departure.

We used this colorless and odorless liquid extract to make our Famous Texan Chili (need a roll eyes, combining with puke icon)

To get back, Nobody liked Mel "AT ALL", Not even the customers!

The colorless/odorless liquid played a major role in the mornings events when Mel took a bite out of his OE eggs.

No way to escape that kinda pain!!! That must of hurt for someone not suspecting!

And I got a Standing Ovation, not only by my coworkers, but by the customers themselves! I went into the audience and took a few bow's to rub it in, and was promptly fired when Mel finally caught his breath.

Funny thing is, Mel got fired a week later, and I got called back with a "no thank you" response from me.

We all know Mel, don't we! laugh laugh laugh

Thinking about this gives me a big kick, and 30+ years later, I would do it all over again! The look on Mel's face that morning was priceless!!! and I'll never forget it grin

Me, a bad boy whistle No comment! smirk

A bit off topic, eh!


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Sticklebacks are small creatures. 9 spined stickleback usually is even smaller than in picture but 3 spined stickleback can be as large as smallest finger. They aren't big and despite their "needles", they get eaten by predators.
These fish spawn in special "nests" and protect them. I guess that their look help them to defend these nests against more peaceful fish but I doubt that a pike would care about that smile

Omaha, I really don't know what is that goby you are talking about so I won't be helpful in this case.
About ruffe and Great Lakes... Lets look at the Wikipedia (http://en.wikipedia.org/wiki/Ruffe):
It has been introduced into the Great Lakes of North America, reportedly with unfortunate results
.
Seems like you are right. I haven't heard about this case but it sounds interesting and I'm willing to read more. But somehow I don't understand how it can do so great impact on environment...

Average fish size is very small and predators like to eat it. What can it do? It eats fish eggs and thet's the worst thing I can imagine.

ADDED:
I read quickly and article:
http://www.great-lakes.net/envt/flora-fauna/invasive/ruffe.html

Nothing much has been said there but one phrase sounds silly:

Ruffe rarely grow bigger than 5 inches, although the sharp spines on their gill covers, dorsal and anal fins make them difficult for larger fish to eat.

Seems like writer hasn't seen this fish and doesn't know much about them. As I said above - predators eat perch and ruffe much and seems like they don't care about their fins. Large pike can eat really large perch and it would eat very large ruffe if there were any (they don't reach such size). Their fins don't differ much.

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Yep, seems like the ruffe and goby are two different fish entirely. Sounds like they had a similar impact on the Great Lakes though. I'm sure Travis will weigh in with more knowledge of the subject, but from what I've ready the goby was introduced in the 80s. They're aggressive little boogers that like to eat eggs as well. But I guess smallies love them and that aspect of the fisheries has thrived since then.

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Ruffe are closely related to our yellow perch and walleye. In the same family. Except they only get about 8" and multiple like rabbits...

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The following should add some more info wrt my post above. Its all about energetics and conditions relative to optimal foraging theory. Those are based on instincts that come through genetics and enhanced by conditioning.

From

Transactions of the4rnerican Fisheries Society 114:725-731, 1985

Effects of Cover and Prey Size on Preferences of Juvenile
Largemouth Bass for Blue Tilapias and Bluegills in Tanks
HAROLD L. SCHRAMM, JR. &
ALEXANDER V. ZALE

Abstract
The effects of vegetative cover and relative size of prey were tested on the forage preference of
juvenile largemouth bass Micropterus salmoides offered blue tilapias Tilapia aurea and bluegills
Lepomis macrochirus in laboratory electivity experiments. When offered forage at or near the
maximum consumable size in tanks without vegetative cover, largemouth bass preferred bluegills,
but consumed blue tilapias in the presence of vegetation. When offered forage smaller than the
maximum consumable size in tanks without vegetation, largemouth bass selected blue tilapias.
Differences between the forage species in body morphology and effective use of protective cover
apparently caused the changes in prey selection .

When offered forage at or near the maximum
consumable size in tanks without vegetative cover,
largemouth bass consumed more bluegills than
blue tilapias in 11 of 12 trials (Table 1). When
offered forage of the same relative size in tanks
with vegetation, largemouth bass consumed more
blue tilapias than bluegills in all 8 trials (Table
1). In trials with forage smaller than the maximum
consumable size in tanks without vegetation,
largemouth bass consumed more blue tilapias
than bluegills in 8 of 10 trials (Table 1).
Selection was significantly different from random
in all three cases.



In the absence of vegetative cover, juvenile
largemouth bass consumed blue tilapias rather
than bluegills when both species were smaller
than the maximum consumable size, but reversed
their preference when prey were at or near
the maximum consumable limit. We suggesthis
reversal is consistent with optimal-foraging theory
(Schoener 1971; Pyke et al. 1977). Within
each of these trials, body depths of both forage
species were equivalent and interspecific differences
in total lengths were relatively small or
absent (Table 1). However, blue tilapias consistently
weighed more than bluegills of equivalent
body depth or length. This difference in depthor
length-specific weight was attributable to the
more robust morphology of blue tilapia; blue tilapias
are conspicuously thicker bodied and have
a greater girth than bluegills of equivalent length
or body depth. When offered easily ingestable
forage, well below the maximum consumable size,
largemouth bass selected the heavier, and therefore
more energetically valuable, prey item
(blue
tilapia). Conversely, when offered forage at or
near the maximum consumable size, for which
handling costs are high (Werner 1974), largemouth
bass selected the more laterally compressed
prey (bluegill). Thinner-bodied prey may
be ingested more efficiently because of reduced
girth or defensive struggle capabilities, or may
have been selected simply because largemouth
bass perceived them to be smaller, despite their
body depth. Largemouth bass prefer forage
smaller than the maximum consumable size
(Tarrant 1960; Wright 1970; Shaftand and Pestrak
1984).
Because the largemouth bass in experiment 3
(forage smaller than the maximum consumable
size) were larger than the largemouth bass in experiment
1 (forage at or near the maximum consumable
limit), differences in predator size may
have affected prey selection. However, both
groups of largemouth bass were of a size considered
to be predominantly piscivorous (Carlander
1977) and no relationship between predator size
and prey selection within each experiment was
evident (Table 1). We consider relative prey size
to be a more likely explanation of the observed
reversal in prey selection.

The presence of vegetative cover caused a profound
shift in the diet of largemouth bass offered
blue tilapia and bluegills of maximum consumable
size; bluegills were consumed in trials in
open tanks but largemouth bass selected blue
tilapia when vegetation was present. Glass (1971)
and Savino and Stein (1982) found reduced predation
success by largemouth bass on bluegills
at high densities of simulated aquatic vegetation.
Young bluegills typically occupy vegetation
(Stuntz 1975; Werner et al. 1977) and, hence,
reduce the risk of predation (Werner et al. 1977;
Cooper and Crowder 1979; Stein 1979; Savino
and Stein 1982; Werner et al. 1983). Habitat use
by young blue tilapias is not known but small
individuals of other tilapias occupy vegetated
habitats in native African lakes (Lowe-Mc-
Connell 1959; Jackson 1961; Donnelly 1969;
Bruton and Boltt 1975), apparently in response
to predatory pressures (Lowe-McConnell 1959;
Jackson 1961). We have collected young blue
tilapias in dense beds of eelgrass Vallisneria
americana in Lake George, Florida, and Hulon
and Williams (1985) collected young blue tilapias
in littoral habitats in Lake Tohopekaliga,
Florida. However, our casual observations of blue
tilapias in aquaria indicate they are not as inclined
to enter cover when frightened as bluegills.
The increased consumption of blue tilapias by
largemouth bass in the vegetated tanks suggest
that blue tilapias did not use vegetative cover to
escape predation as effectively as bluegills.
Our findings indicate habitat characteristics
may affect relative use of blue tilapia by largemouth
bass. Furthermore, the consumption of
blue tilapia may affect the predator-prey dynamics
of other forage species. High densities and
stunting of bluegills are commonly attributed to
reduced vulnerability to predation by piscivores
when aquatic vegetation is abundant. Juvenile
largemouth bass selectively foraging on blue tilapias
when vegetation is present may further
reduce predation on bluegills. Shaftand et al.
(1983) found an increase in the abundance of
small bluegills in a vegetated lake containing
largemouth bass and an expanding population of
blue tilapias.



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