[benbryant]

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

[Dario]

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. 

Dario

[Rob Brownfield]

Very interesting, but I am going to totally disagree with the lecturer 

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...

[benbryant]

Very interesting, but I am going to totally disagree with the lecturer 

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. 

kind regards

Ben

[Rob Brownfield]

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. 

[Irvine Ross]

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

Irvine

[benbryant]

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

[Tam Greenock]

l have no chance then  l shop online   

[Sandy Nelson]

Very interesting, but I am going to totally disagree with the lecturer 

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?


Ben
I thought it was very interesting
Nice to get a professional angle on things, adds to the various theories we all have as regards the habits of fish

Sandy

[Jim Eddie]

No I can't say I have noticed Brown Trout are more adapted for surface feeding , certaily not the Don troot on Saturday 

Nice post though Ben 

I liked your explanation Irvive   

 

Jim

[Mike Barrio]

Great stuff Ben

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?

Best wishes
Mike

[benbryant]

Great stuff Ben

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?

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

[Irvine Ross]

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?

Unless, of course, you are talking about night feeding sea trout

Irvine

[Rob Brownfield]

Fascinating, Cant say i'd ever noticed this, anyone else?

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.

[Magnus Angus]

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  ) 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