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Cap'n Fishy

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Sea trout runs aren't "regenerating" over much of the west coast because they are being hammered by lice from fish farms.

I can think of several places that even in my fishing lifetime have seen a collapse and return of sea trout runs over ten years or so. Several East Devon rivers went from mediocre to excellent to dire and back to just about OK for no obvious (to me or anyone else) reason. South Uist sea trout runs went from pretty good to as near as makes no difference totally failed over a few years. Then from nowhere they suddenly returned one year in numbers way above those that were around when I first went there.

It seems to me the pattern is almost always the same. For some reason the finnock (whitling/peal/herling) numbers suddenly drop one year but the mature fish are still there in good numbers. The next year the finnock are still missing and naturally the mature fish start to thin out, the 2lb'ers go missing but the big ones are still there. The year after there are still no finnock to speak of and now you are starting to see less and less mature fish (they are dying off naturally and not being replaced by last years finnock). And so it goes on until all you are left with is a few old big mature fish. Then just as you are about to throw the towel in one year out of the blue the finnock reappear in great numbers. Thereafter the stocks rebuild and everyone is happy until the finnock vanish again! Obviously this doesn't happen everywhere but it a pattern I've seen enough times first hand and also looking back through the record books of some West County fishing hotels (when such things still existed!).

What causes these cycles? I don't know but it does show that sea trout runs are quite capable of "regenerating" from a very low base very quickly if the conditions suit them.


Andy

We often refer to 'sea trout stocks', but when you look at how the species operates, there is no such thing as 'sea trout stocks'. Sea trout are the fish we associate with the 'furthest outpost' of the migration of a population of Salmo trutta. In any year the proportion of the population that are sent to the furthest outpost is subject to many influences - genetic, and environmental. So, it is prone to large fluctuations when these influences are in a state of flux. That could be why you can get these boom and bust years out of seemingly nowhere... ??? :unsure:

The only 'stock' is the entire parent population of Salmo trutta. It is up to them how many sea trout they choose to give us in any year... Just a thought... :)
 

Cap'n Fishy

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Another thing about that paper - it didn't even entertain the notion of whether anadromous trout and potamodromous trout might try to avoid each other on the spawning redds. Mature trout are mature trout, regardless of how far they have migrated before getting to the redds. End of! (y)
 

easker1

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loch Maree problem is that there is now a huge head of minnows thanks to the Drop minnow men from some of the surrounding lochs,so the current residents don' have the hunger imperative to run to sea, the minnows are right up in the Kinlochewe river, In the Falklands the fish stocked in the river there are still known as sea run Browns,,easker1
 

easker1

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It's a bit like asking whether folk who have been to Spain on their holidays interbreed with folk who stayed in Arbroath.
wow Col you have way of cutting to the chase, but then I don't know any one from Arbroath or their sexual Proclivity, but obviously you seem to, easker1
 

ohanzee

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Salmon and trout are different species. It is in their interests to try to breed only with their own type.

You are trying to separate brown trout from sea trout. Surely there is no need, nor even desire, to separate brown trout from sea trout? They are a single species that modulates the migration patterns of its members to suit the situation at any given time. There is no need for the different types of migrant to avoid each other when it comes to breeding. Surely it makes much more sense for the purpose of maintaining the plasticity of the migration pattern if everyone is free to breed with everyone else? In addition, the fact that many systems have a large sex bias - up to 6 female sea trout to one male - makes if clear that the female sea trout are breeding with the male river trout.

I'm not trying to separate them nor making a case for either, I'm just pointing out that the sperm and ovarian fluid interaction is a mechanism that prevents the sperm making it to fertilisation, if returning sea trout and resident brown trout don't have the same sperm and ovarian fluid interaction then the nip in's are not fertilising.
 

Cap'n Fishy

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loch Maree problem is that there is now a huge head of minnows thanks to the Drop minnow men from some of the surrounding lochs,so the current residents don' have the hunger imperative to run to sea, the minnows are right up in the Kinlochewe river.

Bound to be a factor - and fits right in with everything in that Ferguson paper. Similarish situation on Loch Shiel, if they were to get rid of the salmon farms in the area. While the lice have been killing the sea trout, and the population has adjusted to staying at home, the smolt cages on the loch have resulted in a biological bloom that has produced a vast increase in stickleback numbers... so now the stay at home trout have a good reason to stay at home. Never used to associate Loch Shiel with large brown trout, but now it produces double-figure fish! Not had one myself, but had a 6 lb 4 oz and an 8 lb 12 oz. If they got rid of the salmon farms, then what is the incentive for the trout to run the gauntlet of going to sea, compared to the relative safety of staying at home? (Unless they also remove the smolt cages.)

In the Falklands the fish stocked in the river there are still known as sea run Browns,,easker1

Of course they are - that is the correct name for them. We really ought to call our fish sea-run browns, not sea trout. 😜
 

Cap'n Fishy

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I'm not trying to separate them nor making a case for either, I'm just pointing out that the sperm and ovarian fluid interaction is a mechanism that prevents the sperm making it to fertilisation, if returning sea trout and resident brown trout don't have the same sperm and ovarian fluid interaction then the nip in's are not fertilising.

You are trying to separate them. You are clearly trying to look for ways to keep brown trout 'brown', and sea trout 'sea'. Give it up!

The sperm and ovarian fluid thing is relevant to cross species hybridisation. I have seen nothing to suggest it has any relevance to the migration of Salmo trutta. If you want to propose it, you will need to cite some papers that support it.

And, end of the day, your claim about nip-ins doesn't even hold true. I looked up the whole sperm/ovarian fluid thing, and it's all marginal differences, even between different species, never mind within a species!!!

Honestly, you're flogging a dead horse there...
 

ohanzee

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You are trying to separate them. You are clearly trying to look for ways to keep brown trout 'brown', and sea trout 'sea'. Give it up!

The sperm and ovarian fluid thing is relevant to cross species hybridisation. I have seen nothing to suggest it has any relevance to the migration of Salmo trutta. If you want to propose it, you will need to cite some papers that support it.

And, end of the day, your claim about nip-ins doesn't even hold true. I looked up the whole sperm/ovarian fluid thing, and it's all marginal differences, even between different species, never mind within a species!!!

Honestly, you're flogging a dead horse there...

You suggesting I want to separate sea trout and brown is a straw man, its inconsequential to my point.

Research on ovarian fluids is unlocking a few mysteries and is a thing, sea going trout evolved a similar spawning cycle as salmon, males returning to fertilise, what my point opens up can equally support sea and brown trout as one fish, and in doing so could explain why there is a decline.

The reason male sea trout exist is to pass on a set of strong genes to enable future sea trout to survive, if the sperm/ovarian fluid thing holds good and is the same you have random fertilisation, not the best way to pass on successful survival genes and a possible reason for natural decline.

On the other hand if the sperm/ovarian fluid is different as it is in salmon, you have a biological mechanism that choses sperm to benefit survival.

I don't know which, and I have no baggage in either, but I know which one makes biological sense and partly supports what we see.
 

Cap'n Fishy

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You suggesting I want to separate sea trout and brown is a straw man, its inconsequential to my point.

Research on ovarian fluids is unlocking a few mysteries and is a thing, sea going trout evolved a similar spawning cycle as salmon, males returning to fertilise, what my point opens up can equally support sea and brown trout as one fish, and in doing so could explain why there is a decline.

The reason male sea trout exist is to pass on a set of strong genes to enable future sea trout to survive, if the sperm/ovarian fluid thing holds good and is the same you have random fertilisation, not the best way to pass on successful survival genes and a possible reason for natural decline.

On the other hand if the sperm/ovarian fluid is different as it is in salmon, you have a biological mechanism that choses sperm to benefit survival.

I don't know which, and I have no baggage in either, but I know which one makes biological sense and partly supports what we see.

Just read that Ferguson paper...
 

ohanzee

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Just read that Ferguson paper...

I have, I'm not aware of challenging his theories on genetic divergence, I'm talking about the mechanisms that make this possible.

There is a line in one of his 'Genetics of sea trout' that I had to dig for there, 'it does not mean there is no genetic basis to anadromy, a point that has been misinterpreted by some authors'

This misinterpretation has led many to cite Ferguson and extrapolate that he supports a nice tidy all one trout theory, which is not quite the whole story, even in the paper you are telling me to read.

Anyway, I have added my bit, I'll leave you to it.
 
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bobmiddlepoint

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We often refer to 'sea trout stocks', but when you look at how the species operates, there is no such thing as 'sea trout stocks'. Sea trout are the fish we associate with the 'furthest outpost' of the migration of a population of Salmo trutta. In any year the proportion of the population that are sent to the furthest outpost is subject to many influences - genetic, and environmental. So, it is prone to large fluctuations when these influences are in a state of flux. That could be why you can get these boom and bust years out of seemingly nowhere... ??? :unsure:

The only 'stock' is the entire parent population of Salmo trutta. It is up to them how many sea trout they choose to give us in any year... Just a thought... :)

Yes I’d go along with something to do with population densities and environmental pressures causing a sudden switch from one strategy to the other. As you say the whole thing in a state of flux.

I just can’t buy the idea that there is anything keeping sea trout and brown trout separate. There are even cases of sea trout smolts occurring upstream of impassable falls where no adult sea trout has ever been seen. I had several myself in Otterhead lakes at (funnily enough) the head of the river Otter in Devon. These lakes (reservoirs) have dams that no fish could ever get over but they hold a good population of small wild trout. The urge to go to sea is still there and some still smolt although none can ever come back. These fish have only been isolated for 150 years but those above natural falls might have been cut off from sea for thousands of years yet still turn out some sea going fish. It’s all part of the population survival strategy. If some disaster befalls the stream above the falls (disease, massive flood, ice age) there are still a few out to sea that can seek out a new home and keep the genes going.

Andy
 

Cap'n Fishy

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I have, I'm not aware of challenging his theories on genetic divergence, I'm talking about the mechanisms that make this possible.

There is a line in one of his 'Genetics of sea trout' that I had to dig for there, 'it does not mean there is no genetic basis to anadromy, a point that has been misinterpreted by some authors'

This misinterpretation has led many to cite Ferguson and extrapolate that he supports a nice tidy all one trout theory, which is not quite the whole story, even in the paper you are telling me to read.

Anyway, I have added my bit, I'll leave you to it.

If you've read it, why are you worried about ovarian fluid?
 

Cap'n Fishy

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I thought you knew something of biology? Ferguson did a paper on genes, where do you think sperm/ovarian fluid comes into that?

What role do you think ovarian fluid plays in the migration patterns of Salmo trutta?

The Ferguson paper makes no mention of ovarian fluid.

You suggest it as a means to keep potamodromous trout from interbreeding with anadromous trout. It is abundantly clear that potamodromous trout breed freely with anadromous trout.
 

ohanzee

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As you say, Ferguson doesn't mention sperm/ovarian fluid, another straw man.

And like I say a similar sperm/ovarian fluid situation in both returning sea trout and resident trout equally offers a perspective on genetic differences well within all trout being just trout, it was you that chose to assume otherwise.
 

Cap'n Fishy

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As you say, Ferguson doesn't mention sperm/ovarian fluid, another straw man.

And like I say a similar sperm/ovarian fluid situation in both returning sea trout and resident trout equally offers a perspective on genetic differences well within all trout being just trout, it was you that chose to assume otherwise.

Now, who could argue with that?

 

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