Fishing The Fly Scotland
Index => Main Discussion Area => Topic started by: benbryant on 29/04/2008 at 11:05
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For most of my trout fishing days i have wondered about the complexities and variables that effect the nature and reasoning behind the evening rise. Many of you may know this already, but i was amazed to find in a lecture on vision in fish one of the reasons for the evening rise. I asked my lecturer in depth about the topic "why do trout rise more so in the evening than any other part of the day?" He replied that if the conditions suit, the fish tend to rise for insects on the surface more at this time because of the nature and advantages of their eyes to that of the insects at certain light intensities. In the evening insects are at a slight disadvantage to that of the trout with regards to sight, meaning a delayed reaction, due to the make up of the insect eye. Hence a more prolific rise during evening hours, the darker conditions the more advantage. Many of you would of noticed that on a sunny day there can be less rises at the fishery overall, but i have fished Haddo and as soon as a passing cloud obscures the light, the fish increase in rising. I questioned the Lecturer about this also, and he agreed that there will be an advantage to the fish when this happens.
I found this extremely interesting and it silenced my thoughts somewhat with regards to the notorious evening rise.
Best wishes
Ben
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Thanks Ben, very interesting, and makes me feel better as I alway thought that fish started to rise, once I stop fishing and had my gear packed ready to go home. :oops
Dario
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Very interesting, but I am going to totally disagree with the lecturer :z7
Insects hatch in the evening as they have a far greater chance of survival from predators (plus they have spent the day warming up). It is not just insects, just look around you in the evening...the rabbits are out, the foxes are out, the deer are out, etc etc. The low light levels allow for a greater chance of remaining undetected.
The reason why there is a bigger rise in the evening is simply because there is a bigger hatch of insects! Exactly the same as saying how come you see more people in Tesco than you do in the corner shop..there are more things to chose from so you will see more people competing for more items...hence the evening rise :)
The Brown trout especially is adapted for surface feeding, that is why its eyes are more ontop of its head than say a rainbow. It has also adapted to being able to see shilouettes on the surface in low light because thats when there are more insects in the surface film.
I do not for one instance believe a hatching insect would ever have the ability to see a trout approaching from below, even if it had human sight...coz its eyes are not set in its head so as to be able to see under the water.
Just my opinion though...
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Very interesting, but I am going to totally disagree with the lecturer :z7
Insects hatch in the evening as they have a far greater chance of survival from predators (plus they have spent the day warming up). It is not just insects, just look around you in the evening...the rabbits are out, the foxes are out, the deer are out, etc etc. The low light levels allow for a greater chance of remaining undetected.
The reason why there is a bigger rise in the evening is simply because there is a bigger hatch of insects! Exactly the same as saying how come you see more people in Tesco than you do in the corner shop..there are more things to chose from so you will see more people competing for more items...hence the evening rise :)
The Brown trout especially is adapted for surface feeding, that is why its eyes are more ontop of its head than say a rainbow. It has also adapted to being able to see shilouettes on the surface in low light because thats when there are more insects in the surface film.
I do not for one instance believe a hatching insect would ever have the ability to see a trout approaching from below, even if it had human sight...coz its eyes are not set in its head so as to be able to see under the water.
Just my opinion though...
Hi there,
I like the tesco analogy, however your suggesting that the reason there is more intence activity in the evening is because there is a larger "hatch" and fish are "competing" for more invertebrates. Competition for food usually only occurs in situations where there are limited resources, therefore if there is plentiful food, there would not be such intensity to compete. Trout are very much optimal feeders and if there is a large food source available they will feed optimally for it. In Tesco there is often far greater resources than the corner shop, the prices are somewhat cheaper and i think this is the reason people tend to shop there. :z4
kind regards
Ben
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I will use the Monty Python analogy now ;)
Does not matter how much food is about...if someone offers you that after eight mint you will go for it ;)
What I was trying to say using Tesco was that some folk will flock to a huge supermarket because there is a lot on offer..and so they bulk buy..ie..the trout sees a lot of food..so it stuffs itself silly. :z18
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The flaw with the Tesco analogy is that the superstores are usually a bit of a journey away so it take energy to get there. A better analogy is the village shop and the travelling grocers van.
Would you walk five miles to the village shop if they only had one can of beans on the shelf. No, because you would use up more energy walking there than you would get back from eating the beans. Its a better idea to wait at home until the travelling grocer's van comes round to you and then can get all you need.
If there are only a few small insects available and all the rest are hiding under stones then it is more sensible for the trout to stay dozing in its resting lie and save energy. Anyway being out and about in bright daylight leaves it vulnerable to ospreys and cormorants. When the evening rise starts and there is a lot of food available without having to move far, the grocer's van has arrived. Then it makes sense for the trout to eat all it can with the minimum expenditure of energy until it can't eat any more and then go back and doze in the resting lie. If the van is not staying for very long then it has to guzzle all it can in a short space of time. Hence the intense feeding activity during the evening rise.
Get em in quick before closing time :z18
Irvine
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Exactly Irvine,
This is the "optimal foraging theory"
you take as much as you can get while you can get it, we have digressed some what from my original posting, but im enjoying the debate. haha. Often you see birds come back with lots of food in their mouths i.e puffins, they do this because the energy spent travelling and foraging for food is costly so they only way to balance this and make more energy is to take as much as you can find on the trip to make it woth your while.
ben :cool:
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l have no chance then :roll l shop online :z18
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Very interesting, but I am going to totally disagree with the lecturer :z7
:roll
The Brown trout especially is adapted for surface feeding, that is why its eyes are more on top of its head than say a rainbow. It has also adapted to being able to see silhouettes on the surface in low light because thats when there are more insects in the surface film.
Fascinating, Cant say i'd ever noticed this, anyone else? :z6
Ben
I thought it was very interesting :z16
Nice to get a professional angle on things, adds to the various theories we all have as regards the habits of fish :z4 :z4
Sandy
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No I can't say I have noticed Brown Trout are more adapted for surface feeding , certaily not the Don troot on Saturday :roll
Nice post though Ben :z16
I liked your explanation Irvive :z16
:z18
Jim
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Great stuff Ben :z16
Another idea that has often crossed my mind ........ I think fish prefer to feed below the surface most of the time, but perhaps, as dusk comes in and the light fades, it might become more difficult to see your quarry deeper down as less light penetrates the water ......... at which time food on the surface is probably easier to see against the sky? :roll
Best wishes
Mike
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Great stuff Ben :z16
Another idea that has often crossed my mind ........ I think fish prefer to feed below the surface most of the time, but perhaps, as dusk comes in and the light fades, it might become more difficult to see your quarry deeper down as less light penetrates the water ......... at which time food on the surface is probably easier to see against the sky? :roll
Best wishes
Mike
Well Mike that is another very interesting concept, its always more likely that the resaon for the rise is a interaction of many factors rather than one.
And your one most certainly plays a role i would think.
ben
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Another idea that has often crossed my mind ........ I think fish prefer to feed below the surface most of the time, but perhaps, as dusk comes in and the light fades, it might become more difficult to see your quarry deeper down as less light penetrates the water ......... at which time food on the surface is probably easier to see against the sky? :roll
Unless, of course, you are talking about night feeding sea trout :wink
Irvine
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:roll
Fascinating, Cant say i'd ever noticed this, anyone else? :z6
Sandy,
It was the head biologist for the Dee Trust that spent part of his talk talking about this. As Parr, the Brown trout and Salmon have there eyes further towards the top of there head, and with time as they grow, they slowly move round into a more familiier location. Its not hugely noticable but he did have some comparison photos.
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Hi Ben
Interesting mention of Optimal Foraging Theory. Some time back I took part in a discussion of OFT - it certainly helps understanding and predicting predatory behaviour. On the other hand it sort of worries me as a non-scientist that it's almost a dogma, as far as I know there was very little in the way of competition for that theory but there is some.
In that discussion we touched on the idea of saticficing - which has gained some theoretical ground in other areas of decision theory. (Attractive because its based on a Scots word :z4) It seemed to some of us, me included, that idea might better explain why trout as predators hunt sometimes and specifically seem to hunt more aggressively when prey is in short supply - why they don't simply lie dormant until times of abundance - why stunted wee male fish spawn with large lush females. We were thinking of the small males who get by in highland streams, feeding opportunistically, while some of their chums and a disproportionate percentage of females find richer feeding. Point being those small male fish are mature fish, fit for breeding but their very limited supply of food means they are only a few inches long.
http://cas.bellarmine.edu/tietjen/Ecology/role_of_satisficing_in_foraging_.htm
http://www.blackwell-synergy.com/doi/abs/10.1111/j.1365-2656.2007.01237.x?journalCode=jae
The second of those is just an abstract but the last summary point is really interesting:
The results of this model do not agree with previous observations of lumpfish behaviour, and thus it appears that juvenile lumpfish do not try to maximize their net energetic gain. Instead, our data suggest that juvenile lumpfish forage in a manner that reduces activity and conserves space in their limited aerobic scope. This behavioural flexibility is of great benefit to this species, as it allows young individuals to divert energy towards growth as opposed to activity. In a broader context, our results support previous speculation that ectotherms often forage in a manner that maintains a minimum prey encounter rate, but does not necessarily maximize net energy gain.
Magnus
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Hi all,
been following this with interest.
Ectotherm - Cold-blooded’ animal such as a lizard, that relies on external warmth (ultimately from the Sun) to raise its body temperature so that it can become active. To cool the body, ectotherms seek out a cooler environment. From Google.
Probably true to say that most animals ,inc, fish will adopt a range of behavioural strategies dependent on a range of environmental stimuli. How's that , should be in politics , eh ? :z4
Paul.
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Hi Magnus,
I havn't yet had a chance to look at those links, you mention trout in highland streams so im taking it they are wild browns or sea trout? I have done most of my research on stillwater rainbows but to an extent salmonids all expose the same features. Like any species its vital to complete the life cycle and ensure reproduction. Trout need to feed in order to provide energy for both growth and reproduction, don't overlook reproduction it is very very costly in energy terms, competition (aggressive that is) for food supply takes place beacuse there is a lacking of food, they probably do this because they have no idea when the next feed will become available so its important to compete for limited resources also.
If i digress slightly to the marine environment, the cod stocks of the North sea are over exploited and near total depletion. maturation in cod had gone from 7yrs of age to 3 or 4 yrs presently. this is due mainly to a combination of overfishing and water temperature changes. In a nut shell these cod are putting all of there energy in to reproduction and their gonads. Hence the cod are very low in weights and small overall. This may be reflected somewhat in trout?
As for the behaviour of Rainbow trout in Mikes Loch, thats a whole different kettle of fish and something i would love to research more on, as the Triploid trout operate very differently.
Kind regards,
Ben
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because they have no idea when the next feed will become available
The implication being a trout living in richer water has an idea where their next meal will be?
Is it just me or is that an image of a fairly bright, cognitively well endowed, trout? Those guys are planning for their future?
I can think of a few politicians with more limited "behavioural strategies". (eg Gordon Brown)
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My head is spinning.
I had trouble penetrating the language of the first reference on saticfising and found it all a bit too broad brush and general. I can't see how you can compare the hunting strategy of e.g. a cheetah who has had to learn from its mother over a long period and has a reliable long term memory. It will know from several year's experience that the wildebeast will come when the rains come.
An more primitive animal like a trout has its hunting behaviour hard wired from birth and its long term memory is probably a lot more limited. It's response to stimulii like hunger will involve much less reasoning and more instinct. Because its ability to adapt will be limited then the inherited hunting behaviour will have to be a general strategy that covers most circumstances adequately but cannot cover each circumstance optimally. So I don't see how the lack of optimal foraging behaviour in trout proves or disproves anybody's theory.
Anyway why can't the smug s@ds who wrote the paper on saticfising write in clear English like the authors of the paper on lumpfish ???
Moan over :wink
Irvine
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Hi Irvine
Moan away, as Ben, Paul and others can tell you that's how science is written - try some medical articles or a little philosophy (preferably German) is you want a real headache.
Yes it is broad brush because it's a discussion of how a theory is used across the board. OFT is used to study the behaviour of all animals. The idea is that all successful, "fit" foraging animals in the evolutionary sense, including predators, are fit because they do it optimally - they balance cost against reward for maximum benefit. I guess it's better to say their behaviour is aimed at that as an ideal - individual trout don't get out a pocket calorie counter and work out the ratio of energy burned for calories consumed.
"A more primitive animal" - hmm! Depends how you set up the hierarchy. There's evidence that fish learn - anecdotally, try a fly a fish has refused, sometimes works sometimes spooks the fish. I seem to recall reading something about a tropical fish where the young learned form older fish. I know there is a paper or two out there about the difference between fish raised in a plain un-stimulating tank and fish raised in a more varied tank or in the wild - see the link below.
As theories, instinct and reason seem like the alternatives but they leave a lot of gaps. OFT was/is widely used to study observed behaviour, I guess the idea is that there is no need to mess around worrying about reason or instinct, nature or nurture, if you can see the results of decisions. In that sense it seems to me like a powerful scientific tool.
I feel satisficing is a more subtle tool. Paul mentioned that "...fish will adopt a range of behavioural strategies dependent on a range of environmental stimuli..." intuitively that seems right to me - as a species it would make sense. With all the eggs in one basket, a natural event like a drought doesn't just wipe out the run for that year it eliminates all the salmon native to a river.
Just out of interest see if this reads easily - check the account of hatchery fish and how they deal with risky situations.
http://beheco.oxfordjournals.org/cgi/content/full/15/2/192
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Interesting theory sharing gent's but I'm from the uneducated masses - Is it OK if I just put on a dry fly and hope something takes it? :z4
p.s anyone got a dictionary that I can borrow? :z6
Iain
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Ian
You have got to admit that some of us are prepared to work harder on our excuses for failing to catch anything. “My fly selection was based on the optimal foraging behaviour concept when the fish were in fact satisficing today” See how well that goes down with your mates in the pub. :grin
Magnus
No moans about the English in the hatchery fish paper. It is a model of clarity and is based on science. I am beginning to suspect the debate about optimal foraging vs satisficing is more philosophical than scientific. I haven’t had the time to read much of the literature on this subject but it strikes me there is a big element of how you choose to interpret the data rather than any clear cut evidence. If some poor animal under observation tries to follow his genetic programming and do some optimal foraging but circumstances means it fails to achieve it in practice then the observer could choose to conclude that it must have been satisficing instead. On the other he could conclude that “incorrect assumptions were made about the constraints on the forager”. Optimal foraging behaviour strikes me as a sound idea but expecting animals to achieve it in practice is a bit unrealistic.
I am still to be persuaded that trout are not “a more primitive animal” than say a cheetah. Their brain is certainly a lot smaller. They are also abandoned by their parents at egg laying so all the foraging behaviour needed to support them through their early life needs to be carried on their genes. Their need to learn from their parents is none existent so it is safe to assume their capacity to learn is much lower than a “higher” predator like a cheetah. I’m not claiming it does not exist, just that it must have significant limits. Sophisticated hunters work together cooperatively. Has anyone observed trout doing that? Will your fish that refused the fly today refuse it again next week?
I don’t think that instinct and reason are opposites at all. I’m suggesting that reasoning modifies instinct. Instinct says there is food, so chase. Reasoning, and several instances of being walloped round the ear by mum, says I am too far away so I had better creep closer until I am within catching distance.
I agree with Paul "...fish will adopt a range of behavioural strategies dependent on a range of environmental stimuli..." It doesn’t really matter what label we put on their behaviour. The important thing is to know that if they are hungry and there is food about they are probably going to be feeding.
Then if I can’t catch them it’s because I’m a poor hunter. :cry
Irvine
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Hi Irvine
I am beginning to suspect the debate about optimal foraging vs satisficing is more philosophical than scientific.
Yes it is a philosophical debate, one the scientific community is having.
Irvine these theories are being applied to all sort of decision making by the guys who analyze business or voting patterns or animal behaviour (since businesses and voting is animal behaviour) They could delve into imponderables like what an individual was taught when his her mum taught him by (conditioned his behaviour by...another theory, operant conditioning) clouting him around the lug and speculate on genetic tendencies - or you can look at situations and behaviours of groups and populations. The theory model you choose determines how you approach the study - extremely hard if not impossible to start a study without a hypothesis or theory of some sort. You might well use optimal theory, that tends to be our gut reaction - that decision makers always try to make the most out of... IMHO, that fails to account for a good deal of the actions and decisions that are made. More recently there's been a lot of work on other models including satisficing, where the idea is that to be fit an agent needs to make good enough decisions.
Their brain is certainly a lot smaller.
Yes and...? This is not about levels of intelligence or the ability to speak, its about making appropriate decisions. Trout and cheetah are both successful species, they're not in competition with one another so I doubt there is any meaningful sense in which either could function in the others environment. If we want to say a cheetah, has a larger brain and is more like a human, fine - lets see Mike or Hamish survive as a cheetah, or like a trout for that matter :grin
I’m suggesting that reasoning modifies instinct. Instinct says there is food, so chase.
Yep that would seem to be the typical answer and I think it's what fly fishing depends on. Dig deeper and you find things like nociception - where a fish will react to noxious stimuli by avoidance - where one 'instinct' is in conflict with another. In an analogous situation we might claim to use reason to judge the risk against the reward, to decide when a threat is too great, or the reward is so necessary the risk is acceptable. It can be pretty complicated for humans, can lead to 'cognitive dissonance' or simply not bothering to vote :grin
How do trout do that? How do trout weigh up the calories which might be expended against the calories which might be gained? OFT says they do exactly that, and that it's a critical decision, a matter of life and death, not just a matter of choosing which inept politician to vote for.
Sorry if this stuff bores anyone - it intrigues me.
Magnus
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Hi All,
"Sorry if this stuff bores anyone - it intrigues me."
Me too. Sad eh ?
Do trout possess the grey matter to make complex trophic calculations and act on them .
Clearly they do not.
However, I agree with you Magnus that it is right (essential ?) to challenge established scientific ideas and theories albeit we,ve got to be very careful not to anthropomorphise here .
Do fish , not just trout, possess “instincts” which allow them to survive ? Clearly they do.
Do fish respond in a manner beneficial to their survival most of the time ? Clearly , yes, they do, else the population does not survive.
OFT may therefore be something which is one of these nebulous “instincts” .
That might sound strange from a biologist !!
As you will know there are other examples in the animal world of optimal "instinctive" behaviours or strategies , in foraging/feeding, migration, reproduction, etc. etc.
I agree too it is interesting to ponder and wonder why that fish took our fly and not the “same” one presented in an “identical” fashion by another angler.
What instincts/learned behaviours/ genotypes/phenotypes (?!) /triggers/ competition/ etc. etc. etc. have brought about this potentially fatal situation?
Particularly worthy of study when you consider the 2% of anglers catching 80% of the fish scenario.
I don’t think I would want to know though. :z4
Thank goodness for the unpredictability ,
Good thread though .
Cheers,
Paul.
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Hi Paul
Yeah sad :z4 I'm in no position to challenge scientific orthodoxy, thats the job of scientists. But we can all comment from outside and try to get to grips with some of the issues. For example from a meta-theory pov the interesting thing about peer-review is that it resists change.
Do fish , not just trout, possess “instincts” which allow them to survive ? Clearly they do.
Do fish respond in a manner beneficial to their survival most of the time ? Clearly , yes, they do, else the population does not survive.
OFT may therefore be something which is one of these nebulous “instincts” .
That might sound strange from a biologist !!
If you call on the idea of natural selection then there is automatically a sense of optimization - insects which hatch at inappropriate times die out, they are unfit in that sense, the populations we see tend to hatch when their chances of successfully reproducing are best. As far as I know emergence is down to environmental cues? Similarly changes in the environment lead to significant population changes, eg siltation favours some species (eg buzzers) and makes life harder, sometimes impossible, for other insects (eg mayflies.)
Instincts in the sense of 'fixed action plans' are the product of evolution, of natural selection - hunting behaviour seems to be a good example of FAPs in a lot of animals, eg dogs and cats certainly, trout and other fish as far as I know, I'd be very surprised if it isn't. Those behaviours (FAPs) can be pretty complex, courtship dances and the like. They require no big rational effort, it's a complex reaction released by an external stimulus or combination of stimuli - fish sees red bus fish tries to attack red bus :grin (you know the classic example.)
Those types of stereotypical behaviours don't include the agent thinking about it, considering the costs and benefits, making trophic calculations - they don't actually require much in the way of reasoning rational thought at all.
I've no argument with that scheme of things but there needs to be a place in that for some sort of unpredictability and plasticity.
Hopefully its 20%/80% of anglers or we're really buggered :z4
Magnus
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Joining this one late but an interesting post, especially after a few glasses of wine!
My theory on this is pretty simple, like myself (I'll say it before Sandy puts in a cheap shot!) :z4 :z4 Fish don't have eyelids and therefore will probably have a lower tolerance to bright ligh, especially if cross bred with a gremlin. Therefore, the best time to be near the surface of the water, where most light penetrates, is when there is little light, ie. evening or overcast days. Also, on overcast days there is usually more moisture in the air leading to insects wings taking longer to dry so they can't take off. There are obviously exceptions, if they are hungry the fish may pput up with some discomfort to eat. It is like going for a beer or 8 and knowing it is going to hurt when the better half gets hold of you.
Magnus, let's keep the words simple for us simple folk!
Mike
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I've always run under a similar perception to Mr Livingstone
An equally simple individual :z4
I would add, moist air tends to be denser so hampers insects trying to fly, have you noticed how when there is rain in the air the insects fly much lower, yet when it is dry they fly higher, House martins and Bats etc are good indicators of where in the air the insects are.
Might have something to do with Air pressure too, but i'm not a meteorologist, To me high pressure air is something to ignite :grin or give you a lift :z7
As for the rest of it, great stuff to read, If we can recognise when things are likely to happen, due to certain circumstances then we approach the situation with more confidence and will therefore catch more fish anyway, so too much knowledge is not necessarily a bad thing. Bruichladdich 'Rocks' however is great for aiding the understanding of many words you do not know :wink
Sandy
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Going back to the initial post http://www.biolbull.org/cgi/reprint/21/5/265.pdf is interesting because its a study of phototaxis (ie physical reaction to light) in nymphs. The type of nymph in that study automatically (instinctively) move away from light, ie they are negatively phototactic. The bit I like is where the biologists get creative. They guess that light causes chemical changes in the nymph's skin and eye so they dope the water with chemicals and find they can reverse the effect, so insects which had swum away or into shade then seek brighter light.
Hi Mike - which words cause problems, I'll try to be clear.
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Those behaviours (FAPs) can be pretty complex, courtship dances and the like. They require no big rational effort, it's a complex reaction released by an external stimulus or combination of stimuli - fish sees red bus fish tries to attack red bus :grin (you know the classic example.)
Those types of stereotypical behaviours don't include the agent thinking about it, considering the costs and benefits, making trophic calculations - they don't actually require much in the way of reasoning rational thought at all.
I've no argument with that scheme of things but there needs to be a place in that for some sort of unpredictability and plasticity.
Magnus
I’m beginning think there is big hole in my understanding of the optimal foraging concept. I have been under the impression that an animal like a trout simply follows a set of inherited reactions to a range of stimuli which results in the animal following something close to an optimal foraging strategy. Not because it has consciously chosen to do so but because evolution has selected for the animals whose inherited set of reactions best suit the environment it occupies. As Paul says it’s a nebulous instinct.
If I understand you correctly, you appear to be saying that the concept implies some level of conscious thought or realisation of the concept by the animal. That I find difficult to cope with.
And OK the cheetah was a poor comparison with a trout. I should have use the killer whale instead. ;D
Irvine
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Hi Irvine
It could equally be my understanding of OFT that's at fault. Like most of these things, depending on who you read the same terms mean different things.
Not because it has consciously chosen to do so but because evolution has selected for the animals whose inherited set of reactions best suit the environment it occupies. As Paul says it’s a nebulous instinct.
The idea of a "fixed action plan" is an automatic, unthought, innate behavior, an instinctive behaviour released by environmental stimuli which must be carried through to its conclusion. Nothing nebulous about it. Fitness for an eco-niche means the total of decisions an organism takes, the actions it makes, must keep it alive and well and be sufficient to allow it to mature and breed. Nothing that nebulous there either.
Thing is there's a difference between those, behaviour is to do with specifics, it answers a proximate question. The sort of thing might be 'Does a fish choose a mate and if they do how do they choose?" or 'What causes an insect to hatch or delay hatching?"
There's a difference in type between those questions and things like "Why does natural selection favour insects hatching that way? In what way fish are who don't select an individual mate more fit?" - so-called ultimate questions. (No the answer isn't 42 :z4)
If you ask "How does this insect forage? (find and handle food)" and answer "They forage optimally." Then I think you're asking a question of the proximate type and getting an answer to the other type of question. When I ask how a trout finds and handles food when it hunts, I want to know how it locates it, what factors cause or allow it to perceive that thing as prey and behave in an appropriate manner. If the answer to that is "They do it optimally." how useful is that? At worst it's redundant since all behaviour by a successful animal is optimal in some sense. At best, in that situation, acting optimally seems to imply trout has some superior knowledge of prey density in its immediate area, or even that it knows which bugs will be hatching in droves tomorrow.
"Optimal models often make precise predictions, e.g. switch to less preferred food when preferred food fall below set rate. In practice animals will sample less preferred option even at higher rates. Again modification to original model make it possible to predict partial preference." quoted from an online piece.
Optimal models predict trout hunting in the here and now will fully and optimally exploit an abundant hatch - reduce the time needed for encountering, identifying and handling prey to a minimum - in short they gorge on the most abundant bugs. The reality is they don't become absolutely fixated on the most abundant hatch. Trout also 'sample' other bugs.
In my fishing experience, when trout are feeding hard on an abundance of one prey its often a very good tactic to offer something that looks nothing like the caenis of mayfly or buzzers or.... The way I understand that, optimal applies to why they do what they do. Trout food varies a lot through the season, its in the best interests of their fitness that they sample other prey. That means how they behave may appear sub-optimal - they waste time and energy nailing a daddy when there are thousands of buzzers in the water. But optimal in the ultimate sense that they can switch their attention to other prey with a minimum of adjustment.
Incidentally if you think about how trout 'in the zone', gorging on an abundant hatch, behave and how they recognize prey it has interesting implications for us. In my experience and in the experience of many other anglers I know, fish feeding hard are more difficult to spook, far less 'wary' far easier to approach. They appear to identify their prey using a minimum of cues, patterns can be more general, things like size and simple encounter may be the deciding factors. Far less shilly-shally, if they meet it they eat it or ignore it. Takes tend to be calm, they just suck it in and look for the next.
Magnus
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Hi Irvine
It could equally be my understanding of OFT that's at fault. Like most of these things, depending on who you read the same terms mean different things.
Magnus
You have obvious read and thought about this is in some depth so I doubt if the hazy understanding is on your side. Have you got a PhD in behavioural ecology that you're not telling us about?
I think most aspects of animal behaviour are a bit fuzzy (especially with humans) so the more they try to refine the concept and the accuracy of their predictions, the more the scientists tie themselves in knots, as in your example:
In my fishing experience, when trout are feeding hard on an abundance of one prey its often a very good tactic to offer something that looks nothing like the caenis of mayfly or buzzers or.... The way I understand that, optimal applies to why they do what they do. Trout food varies a lot through the season, its in the best interests of their fitness that they sample other prey. That means how they behave may appear sub-optimal - they waste time and energy nailing a daddy when there are thousands of buzzers in the water. But optimal in the ultimate sense that they can switch their attention to other prey with a minimum of adjustment.
Yes I have noticed that too but I just put it down to the fuzzyness of the model, or should I say my assumption that the model had to be a bit fuzzy.
In my experience and in the experience of many other anglers I know, fish feeding hard are more difficult to spook, far less 'wary' far easier to approach. They appear to identify their prey using a minimum of cues, patterns can be more general, things like size and simple encounter may be the deciding factors. Far less shilly-shally, if they meet it they eat it or ignore it. Takes tend to be calm, they just suck it in and look for the next.
Yes indeed! If only it would happen a bit more often, especially on a Saturday when I can get to the river.
Irvine