Some fish facts...

How big does a fall have to be to stop a fish swimming up it? I've seen footage of salmon leaping imposible falls to get home to spawn.

Cheers

Tom

Salmon are good jumpers, I believe its scientific name Salar salar means leaper. I don't know the maximum height they can jump. I do know that man made weirs are a still significant deterrent to their migration upstream, unless there's a salmon pass, or there's plenty of spates which reduce the effective height of the weir and make it easier to jump.

I don't think that coarse fish are that good at jumping falls.

Some years ago the EA put in a gauging weir on the river Nidd in Yorkshire, and this prevented coarse fish from migrating to spawning areas. I think it has now been removed

Leaping Speeds

The literature pertaining to leaping capabilities by fish is limited, and often uses observed leap heights to back calculate burst swimming velocities attained prior to leaving the water (Aaserude and Orsborn 1986). The equation used to back calculate leap height is usually some form of the simple projectile equation:



where,

HL = leap height

Vo = initial velocity of the fish

g = gravitational acceleration



Aaserude and Orsborn (1996) working with pacific salmonids used burst velocities of short duration to predict leap height and found that they closely matched the range of observed leap heights. Stuart (1962) and Reiser and Peacock (1985) have also stated that leaps use burst speeds of short duration. FishXing uses short duration burst velocities (5 sec burst speeds) to estimate the speed at which fish leave the water when leaping. In FishXing the Maximum Leap Speed is maximum velocity at which a fish exits the water when leaping at the culvert outlet. See the Leaping Calculations section to view the calculations.

Factors Affecting Leaping Success

Besides swimming speed and fall height several other factors appear to affect leaping success, including water velocity, turbulence in the take-off pool, the depth of the take-off pool, the ratio of pool depth to fall height, and where the leap is initiated.

Flow rate may affect the motivation of fish to leap at outfalls and when it does there appears to differences between species and life history stages. Stuart (1962) studying small fish (minnows, and juvenile salmon: 6-15 cm) and Lauritzen (2002) studying kokanee salmon found that passage attempts increased with flow until the flow rate exceeded the swimming capacity of the fish. Conversely, Powers and Orsborn 1985 observed that chum and coho could sometime be stimulated to move upstream by increasing the flow, but they also leaped over outfalls when the flow was reduced to just a trickle.

It seems that different species of fish and life stages may use different leaping techniques, which may lead to differing physical conditions needed to support leaping. Stuart (1962) found that minnows and juvenile salmon initiated their leaps from the surface of the water following a quick body and tail flexion that bent their bodies into a C-shape. These fish also always leaped from the standing wave created by the upwelling of water just downstream from where the falling water stuck the pool surface. On the other hand, Lauritzen (2002) found that adult kokanee salmon initiated their leaps from the bottom of the standing wave with an S-shaped curve of their bodies followed by burst swimming to the surface. These fish also mainly leaped from the standing wave. Aaserude and Orsborn (1986) found that smaller resident trout initiated their leap from the standing wave more frequently than did adult coho or chum salmon. These authors suggest that this difference may be because the upwelling presented a more influential flow condition for trout due to their smaller mass. The depth that is needed in the outfall pool is likely to be related to the leaping technique used.

The turbulence in the outlet pool will influence the fish's ability to jump. As the fish leaps it pushes against the water with its tail. In turbulent water air is entrained in the water column, and instead of the fish?s tail pushing against water it pushes against air. Because air has a much lower density the fish?s tail produces less thrust. In addition, fish seem to use the flow to help direct their leaps, when the water is turbulent their leaping is less directed. Turbulence in the outlet pool is a function of factors such as water velocity, and outlet pool depth in relation to the drop height.

your lucky ....I wrote this this morning

You really need that op completed mate.......and the one on the ol ticker )

true

The only non-member of the salmon family that I have known to leap up falls is the Smallmouth Yellowfish which is a close relative of the barbel.

Cor! blimey Cakey, wot you bin drinkin this weekend? whatever it is I'll have some of that.

Cor! blimey Cakey, wot you bin drinkin this weekend?


Wallpaper PASTE

Over to you then Tom!
Anything else, just ask Cakey...

with a drop of copydex Bob

;-)

Been taking lessons off Wol then Cakey??

"Over to you then Tom!
Anything else, just ask Cakey.."

Why are salmon so much more expensive?

Is it just because they are delicious with a drop of bubbly?

Tom

Is it just because they are delicious with a drop of bubbly?

Fresh Salmon tastes like soil to me, as does Trout. Tinned Salmon on the other hand, with a good dousing of vinegar is quite delicious!






Puts hands defensively over head and waits for tirade from Ron ;-))

Im with you Bob
I love tinned salmon sarnies dripping in vinegar
but the salmon cutlets my wife has taste like cardboard and why they fink I want to eat it raw well...................

and I wont eat trout in any shape or form
give me steamed cod etc and Im happy

found this,made me laugh......................................Whereas you might swan around the Sydney Fish Market complaining about the price of salmon, in the country, you'll discover that not only is salmon expensive, it looks and tastes like the vinyl car seats of a Datsun 120Y.