pressure

[MikeT]

This is all wonderful and fascinating stuff, and relevant too- I am interested that we can improve our chances of catching fish through scientific study of their behaviour. However, I still feel that we are largely practicing pseudo-science here. We grope around in the dark.

 

Take the main issue of this thread (of whether fish feeding behaviour is influenced by change in atmospheric pressure). There is plenty of anecdotal evidence (Budgie) that this is the case. There are hypotheses, to a greater or lesser extent plausible, of the mechanism of this. However, what we cannot know is how significant these effects are. We can only speculate. This is not true science, and may not be reliable.

 

I mean, take Budgie’s experience above, where he found the fish came onto the feed immediately before he found rise in atmospheric pressure. Well, I would suggest that this alone does not prove anything. There could have been many dozens of other factors which induced the fish to feed at that moment- both coincidental and relative- such as water chemistry, temperature, light levels, humidity, change in predator behaviour, angler movement, gaseous partial pressures and saturation, overflying birds, alignment of the planets, etc., etc., etc.

 

We all agree that the propensity for fish to feed is governed by so many different things. Indeed, what we don’t know would probably amaze us! The scientific problem we face is proving that one single factor has a certain effect, in isolation of the others. This may be possible in an experimental lab (and it seems there has been some good research), but this would not necessarily relate to conditions in nature.

 

This is what I meant by the matter being greater than the sum of its’ parts. We might perhaps study every single factor influencing fish feeding behaviour, and yet never fully understand the complex inter-relations of these factors. I have long suspected that fish are affected by combinations of different effects, and it is unreliable to imagine that something as simple as a single factor is solely responsible for their behaviour.

 

Fish are natural things, and sensitive to natural effects. Being highly evolved and complex, we can be certain that their behaviour is profoundly complicated. This, for me as a scientist, is wonderful, since it fills me with awe at the beauty and unpredictability of nature. Without wishing to sound too tree-huggish, I think we should enjoy the fact that fish behaviour is mostly mysterious and unfathomable- rather than try to reduce it to pseudo-scientific rationality.

 

I love the fact that I cannot rely on the Metcheck forecast for catchability! If I could, I reckon I should soon become bored with the predictability of fishing.

[Steve Walker]

Fish are natural things, and sensitive to natural effects. Being highly evolved and complex, we can be certain that their behaviour is profoundly complicated. This, for me as a scientist, is wonderful, since it fills me with awe at the beauty and unpredictability of nature. Without wishing to sound too tree-huggish, I think we should enjoy the fact that fish behaviour is mostly mysterious and unfathomable- rather than try to reduce it to pseudo-scientific rationality.

 

I found the ethology lectures at university had a similar effect on me; it felt like reducing animal behaviour to black boxes of inputs and outputs evolved to optimise fitness. Too dry. When I thought of animal behaviour, I thought of the behaviour of individual creatures. I couldn't relate the theory to, say, my pet dog. The theory, of course, is to do with emergent properties. A dog is not (for example) trying to forage optimally to obtain the maximum energy consumed for energy expended, he's trying to get the fridge door open because he can smell the left over roast. But dogs in general are "hardwired" to behave in that way because it works. To my mind the theory is undoubtedly correct, but it deals with generalities and probabilities and is less concerned with individual "hows" than with population "whys". We can say that change x in the environment is followed by a y% increase in behaviour z in the fish and that there's less than a 5% chance that our observations are coincidence. That does not necessarily translate to "that barbel there in front of me", "that cloud scudding in from the West" and "my bait sat there on the bottom".

 

Despite that, I think that you can play the probabilities, and if you are aware of a correlation between an environmental variable and behaviour which makes fish easier to catch, you would be unwise not to.

[johng]

Steve W,

 

I'm sure that fish can detect small changes in TOTAL pressure (of which atmosperic pressure is a tiny part), but as with your diver they use this information to monitor and regulate the depth at which they swim. They can't use the SAME information for weather forecasting.

 

Over a long period of time on several of these message boards I have noticed that the proposition that they can detect changes in atmospheric pressure has become the received wisdom. I feel as though I have stumbled into a meeting of the flat earth society

 

Regards

 

 

John

 

 

. The point of mentioning the diver is that changes in air pressure are just as detectable under water as they are at the surface. Whether fish can detect them is another matter.

[Steve Walker]

I'm sure that fish can detect small changes in TOTAL pressure (of which atmosperic pressure is a tiny part), but as with your diver they use this information to monitor and regulate the depth at which they swim. They can't use the SAME information for weather forecasting.

 

In the absence of much evidence either way, I would be unwilling to reject either hypothesis.

 

Actually, we have four hypotheses:

 

H0: Fish cannot sense total pressure.H1: Fish can sense total pressure.	H1.0 Fish cannot detect changes in atmospheric pressure	H1.1 Fish can detect changes in atmospheric pressure

 

I'm actually using "fish" to mean "certain fish", since any ability to do this may not be common to all species.

 

I have seen two papers which seem to support H1.1, neither of which I would consider enough to be conclusive. We have the example of the weather loach which appears to support H1.1. There is so much anecdotal evidence that the weather loach responds in this way that it has come to be an orthodoxy repeated in textbooks, but I can't find any original research to test this.

 

So, I am not willing to rule any of those out. I don't accept the argument that H1.1 is somehow physically impossible because variation in atmospheric pressure is such a small component of variation in total pressure because of the counter-example of the perception of light intensity in humans. We can still tell a bright day from a cloudy day even though the variations in light intensity between indoors and outdoors, sun and shade are greater than the variations between dull and bright.

 

What experimental evidence do you have to reject H1.0?

Edited October 18, 2006 by Steve Walker

[MikeT]

Humans can tell a bright day from a cloudy day because we have the function to do this. The mechanism of our visual sensitivity is certainly understood scentifically, and it is easily demonstrable. It is conjecture to uphold a hypothesis (H1.1) that fish have the function to detect atmospheric pressure change, and equal conjecture to ophold its antihypothesis (H1.0), without certain scientific knowledge. But it seems perfectly reasonable to hypothesise on either until we have the data.

 

Anyone fancy a PhD project?

[Steve Walker]

Anyone fancy a PhD project?

 

Been there, done that, bought the disillusionment

 

Putting the weather loach question to bed would make a good honours project for an undergrad though.

[ColinW]

I can detect pressure changes less than one billionth of atmospheric pressure, fortunately for me I can only do this over a limited frequency range! Who is to say whether a fish's pressure sensors have the same limitations? I would imagine that the ability to predict bad weather would be useful to creatures evolving in the sea. Just because we have lost that ability (if we ever had it) doesn't mean the same goes for fish.

[MikeT]

I can detect pressure changes less than one billionth of atmospheric pressure

 

WOW!!!

 

How?

[Steve Walker]

WOW!!!

 

How?

 

Cochlear hair cells, I should think.

[johng]

Steve, I think scientific evidence is needed to prove H1.0 rather than the other way round. There is no obvious means by which fish can sense AP and, it seems, no published scientific findings that support the hypothesis.

 

You might just as well ask me to prove that they are not picking up the shipping forecast on long wave

 

Regards

 

John

 

What experimental evidence do you have to reject H1.0?