Brackish water sea trout

bobmiddlepoint

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I would think that, generally, a population of a species has a genetic makeup that reflects the behaviour that selection pressure has pushed them into, rather than having a behaviour that is dictated to them by their genetic makeup. However, time is a factor. Evolution can only act as quickly as the generations and the variations in physical characteristics and behaviour patterns allows.

Col

Yes, no and maybe!
After all there are the big sea trout of Currane in SW Ireland which are far bigger on average than those all the close by surrounding fisheries. The Currane smolts are going into the same seas as all the other local rivers but are the only ones going further and growing bigger.
There are two genetically different strains of "sea trout", one a fast growing short lived (and more inclined to travel) and one a slow growing long lived.
In the same way there is a Ferox gene. This was in part proved in Norway when non ferox trout were stocked into hydro lakes full of charr but failed to feed on them, it just wasn't in them.


I have read that one of the problems for Atlantic salmon is that global warming has pushed their food supply further north faster than their behaviour patterns can keep up with.

Col

And yet this year salmon have returned from the sea in numbers that everyone is telling me are similar to those of twenty or thirty years ago. An odd year with good feeding further south or something Covid lockdown related?
Anyone seen a net marked salmon this year? I've had the returns for over 500 fish come through my hands this year and not one mention of a net marked fish. Makes you think.


Andy
 

sewinbasher

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Yes, no and maybe!
After all there are the big sea trout of Currane in SW Ireland which are far bigger on average than those all the close by surrounding fisheries. The Currane smolts are going into the same seas as all the other local rivers but are the only ones going further and growing bigger.
There are two genetically different strains of "sea trout", one a fast growing short lived (and more inclined to travel) and one a slow growing long lived.
In the same way there is a Ferox gene. This was in part proved in Norway when non ferox trout were stocked into hydro lakes full of charr but failed to feed on them, it just wasn't in them.




And yet this year salmon have returned from the sea in numbers that everyone is telling me are similar to those of twenty or thirty years ago. An odd year with good feeding further south or something Covid lockdown related?
Anyone seen a net marked salmon this year? I've had the returns for over 500 fish come through my hands this year and not one mention of a net marked fish. Makes you think.


Andy
This is really interesting and the clear inference is that the lack of activity by trawlers/netsmen is at least partially responsible for what seems to be a good run of salmon in many rivers. My question is, where would the salmon that might have been netted in previous years have been sold, as presumably there is no quota for a legal catch?
 

Cap'n Fishy

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Yes, no and maybe!

I said generally...

After-all, Darwinian evolution by selection pressure is Darwinian evolution by selection pressure... Could it not be the case that the rivers associated with large sea trout (when neighbouring rivers only give up smaller fish) are selecting for large fish? That is to say it is some aspect of the river environment that is selecting for the larger fish. A river might select for large females that bring a large egg mass/large eggs to the redds? Or large fish in that river are required to evade predation? Or a few large fish offers a better survival strategy over several breeding seasons, compared to many small fish? I'm just making guesses, but if the fish's genetics is dictating its behaviour, then there will be a reason why it got that particular genetic make-up that dictates that particular behaviour.

There are two genetically different strains of "sea trout", one a fast growing short lived (and more inclined to travel) and one a slow growing long lived.

How does this tie in with the fact that there is no strain of 'sea trout', per se - there is only Salmo trutta, a species exhibiting partial anadromy. That is to say that sea trout are simply the individuals in a population that migrate far enough to reach salt water. On the redds, the anadromous individuals and all the other individuals exhibiting the different migration patterns (in that diagram upthread) all meet up. Female sea trout mate with male brown trout. Fluvial–adfluvial can breed with Allacustrine, etc... The ferox type breed 'true to type' by having their marker gene cause a behaviour change - delaying maturity until after changing to a fish diet and growing to a larger size that allows access to spawning burns out of bounds to 'ordinary' browns (so I have read). If a ferox and an ordinary brown meet up on the redds, they will interbreed and produce fertile offspring - they are both Salmo trutta. If any strain wants to breed true to type, it needs a mechanism to separate it from the others with the same genes in the same habitat. Reading that sea trout often run into non-natal rivers seems to suggest they are spreading their genes around and keeping the species a homogeneous mix, rather than trying to produce many isolates?
 

original cormorant

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Yes, no and maybe!
After all there are the big sea trout of Currane in SW Ireland which are far bigger on average than those all the close by surrounding fisheries. T

Can I correct that - there WERE big sea trout in Currane. Currane accounted for over 90% of the specimen sea trout recorded in Ireland year after year but no longer. The best explanation for this is salmon farming.
I remember being shown fingerlings in the feeder streams with some shoaling and others adopting solitary stations with the explanation that the shoalers would go to sea. Can't prove it but there were definitely distinct behavior patterns. There used to be a lot of discussion around Currane genetics.
 

easker1

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just an Idea The old poultry growers said it was feeding as much as breeding , the early stages of life must vary from river to river ,some must have better feeding for pre-smolts , so these fish have a head start when running to sea, easker1
 

easker1

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there used to be Tunny in the north sea until the Danes started netting them, as for sand eels don't the danes used them in their powerstations? apart from Bacon what did the Danes ever do for us? easker1
 

bobmiddlepoint

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How does this tie in with the fact that there is no strain of 'sea trout', per se - there is only Salmo trutta, a species exhibiting partial anadromy. That is to say that sea trout are simply the individuals in a population that migrate far enough to reach salt water. On the redds, the anadromous individuals and all the other individuals exhibiting the different migration patterns (in that diagram upthread) all meet up. Female sea trout mate with male brown trout. Fluvial–adfluvial can breed with Allacustrine, etc... The ferox type breed 'true to type' by having their marker gene cause a behaviour change - delaying maturity until after changing to a fish diet and growing to a larger size that allows access to spawning burns out of bounds to 'ordinary' browns (so I have read). If a ferox and an ordinary brown meet up on the redds, they will interbreed and produce fertile offspring - they are both Salmo trutta. If any strain wants to breed true to type, it needs a mechanism to separate it from the others with the same genes in the same habitat. Reading that sea trout often run into non-natal rivers seems to suggest they are spreading their genes around and keeping the species a homogeneous mix, rather than trying to produce many isolates?

I can't remember where I read it but I'm sure I did... there are genetic differences between the "sea trout" (and as you point out this must include the "brown trout") from area to area. Some are predisposed to grow faster but don't live as long. It would seem (to me) that if big fast growers suited the Tweed (or Currane) then they would predominate in those systems and out compete any slow growers.

Why would a sea trout hang around the Wester Ross coast taking 19 years to grow to 12.5lb (as the oldest rod caught sea trout on record did) when it could have popped off elsewhere and grown to 12.5lb in two sea winters? I suggest it was because it was genetically predisposed to muddle about locally and grow slowly while spawning repeatedly whereas the big fast growers are good for only two or three spawning runs.

It's all fascinating stuff and much of it is guess work.

On a slightly related point, I've caught a few Naver sea trout this season and they all have very small tails compared to Uist sea trout (or indeed most Westcountry ones). Have you noticed anything like that with Hope fish?


Andy
 

sewinbasher

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there used to be Tunny in the north sea until the Danes started netting them, as for sand eels don't the danes used them in their powerstations? apart from Bacon what did the Danes ever do for us? easker1
They're now appearing every year in the Western Approaches, Cornwall, West Wales and up the west coast of Ireland. I think that it was the demise of the herring in the mid 20th century that caused their decline in the North Sea.
 
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sewinbasher

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I said generally...

After-all, Darwinian evolution by selection pressure is Darwinian evolution by selection pressure... Could it not be the case that the rivers associated with large sea trout (when neighbouring rivers only give up smaller fish) are selecting for large fish? That is to say it is some aspect of the river environment that is selecting for the larger fish. A river might select for large females that bring a large egg mass/large eggs to the redds? Or large fish in that river are required to evade predation? Or a few large fish offers a better survival strategy over several breeding seasons, compared to many small fish? I'm just making guesses, but if the fish's genetics is dictating its behaviour, then there will be a reason why it got that particular genetic make-up that dictates that particular behaviour.



How does this tie in with the fact that there is no strain of 'sea trout', per se - there is only Salmo trutta, a species exhibiting partial anadromy. That is to say that sea trout are simply the individuals in a population that migrate far enough to reach salt water. On the redds, the anadromous individuals and all the other individuals exhibiting the different migration patterns (in that diagram upthread) all meet up. Female sea trout mate with male brown trout. Fluvial–adfluvial can breed with Allacustrine, etc... The ferox type breed 'true to type' by having their marker gene cause a behaviour change - delaying maturity until after changing to a fish diet and growing to a larger size that allows access to spawning burns out of bounds to 'ordinary' browns (so I have read). If a ferox and an ordinary brown meet up on the redds, they will interbreed and produce fertile offspring - they are both Salmo trutta. If any strain wants to breed true to type, it needs a mechanism to separate it from the others with the same genes in the same habitat. Reading that sea trout often run into non-natal rivers seems to suggest they are spreading their genes around and keeping the species a homogeneous mix, rather than trying to produce many isolates?
The scientists support the idea of fast growing and slower growing strains. Many Welsh rivers have exceptionally large sea trout, the Irish "specimen" weight is 6lb and it was rare that a non Currane fish reached this weight but on at least six Welsh rivers a 6lb sea trout is unexceptional.
 

Cap'n Fishy

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I suggest it was because it was genetically predisposed to muddle about locally and grow slowly while spawning repeatedly whereas the big fast growers are good for only two or three spawning runs.

For sure it will be genetically best-suited to the river system it and its ancestors were born in. Whatever its life strategy, in terms of growth rate, longevity, spawning cycles, etc... it will be whatever is best for where it is, while those with different strategies will be best suited to their river systems. (However, this is always subject to being diluted by fish breeding in non-natal rivers!)

On a slightly related point, I've caught a few Naver sea trout this season and they all have very small tails compared to Uist sea trout (or indeed most Westcountry ones). Have you noticed anything like that with Hope fish?

Not noticed Hope fish being any different from other sea trout.

This is a Loch Naver fish, caught last week by a friend...



Looks fairly normal???

I think some sea trout tend to have very small heads and tails, because of them growing very fast. This is a Hope sea trout, I would say of normal proportions...

Hope4-6Aug20_0324.jpg


This is a Hope finnock...

Hope2019_9538.jpg


The distance between the snout and the back of the eye/end of maxilla and the distance from the end of the body to the fork of the tail is about equal for both fish. However, in the sea trout that distance is about 1/12 of the overall length of the fish, while in the finnock it about 1/15.

Finnock faster-growing than the sea trout?

(I tried to do the exercise on the Naver fish, but it falls down a bit, because it looks like it is a cock fish, with a long jaw. The head measurement is 1/7 the overall length. The tail is about 1/12 though - like the Hope sea trout.)
 

ohanzee

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This is really interesting and the clear inference is that the lack of activity by trawlers/netsmen is at least partially responsible for what seems to be a good run of salmon in many rivers. My question is, where would the salmon that might have been netted in previous years have been sold, as presumably there is no quota for a legal catch?

Northumberland seafood offer wild salmon online, although currently not.....from the website...

''Fortunately in Northumberland we have two of the best Salmon rivers in England – the Tyne and the Tweed. Whilst remaining the salmon’s friend from a conservation point of view our inshore fishermen do bring home some of the wildest, tastiest salmon during the season. However we do recommend wild salmon as a delicacy and would like to highlight its high conservation risk before purchase''
 

sewinbasher

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For sure it will be genetically best-suited to the river system it and its ancestors were born in. Whatever its life strategy, in terms of growth rate, longevity, spawning cycles, etc... it will be whatever is best for where it is, while those with different strategies will be best suited to their river systems. (However, this is always subject to being diluted by fish breeding in non-natal rivers!)



Not noticed Hope fish being any different from other sea trout.

This is a Loch Naver fish, caught last week by a friend...



Looks fairly normal???

I think some sea trout tend to have very small heads and tails, because of them growing very fast. This is a Hope sea trout, I would say of normal proportions...

Hope4-6Aug20_0324.jpg


This is a Hope finnock...

Hope2019_9538.jpg


The distance between the snout and the back of the eye/end of maxilla and the distance from the end of the body to the fork of the tail is about equal for both fish. However, in the sea trout that distance is about 1/12 of the overall length of the fish, while in the finnock it about 1/15.

Finnock faster-growing than the sea trout?

(I tried to do the exercise on the Naver fish, but it falls down a bit, because it looks like it is a cock fish, with a long jaw. The head measurement is 1/7 the overall length. The tail is about 1/12 though - like the Hope sea trout.)
I'm a bit confused, I thought a finnock was a yearling sea trout.
 

Cap'n Fishy

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The scientists support the idea of fast growing and slower growing strains. Many Welsh rivers have exceptionally large sea trout, the Irish "specimen" weight is 6lb and it was rare that a non Currane fish reached this weight but on at least six Welsh rivers a 6lb sea trout is unexceptional.

Do they really mean 'strain' in the biological sense here? :unsure: From Wiki...

"In biology, a strain is a genetic variant, a subtype or a culture within a biological species. Strains are often seen as inherently artificial concepts, characterized by a specific intent for genetic isolation.[1] This is most easily observed in microbiology where strains are derived from a single cell colony and are typically quarantined by the physical constraints of a Petri dish. Strains are also commonly referred to within virology, botany, and with rodents used in experimental studies."

It's possible for a population of trout with geographical isolation to develop into a recognisable isolate, such as a population of river trout above an impassable falls, or an inland lake with no access to other river systems or the sea. It's also possible to have a population breed true to type thanks to a recognised behavioural difference allowing sympatric speciation, such as with ferox (or the thousands of species of cichlid in Lake Malawi).

Every river system will have some minor genetic differences in its gene pool from those of other river systems, and may have recognisably different populations within the same river system, however these would not qualify as biological 'strains'. As sea trout are interbreeding with non-anadromous, riverine trout and are often breeding in non-natal rivers, it seems the brown trout is doing its best to establish separate gene pools, but sea trout are doing their best to keep the whole species homogeneous? :unsure:

Col
 

sewinbasher

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Northumberland seafood offer wild salmon online, although currently not.....from the website...

''Fortunately in Northumberland we have two of the best Salmon rivers in England – the Tyne and the Tweed. Whilst remaining the salmon’s friend from a conservation point of view our inshore fishermen do bring home some of the wildest, tastiest salmon during the season. However we do recommend wild salmon as a delicacy and would like to highlight its high conservation risk before purchase''
I accept that this covers the NE but what about all the rivers flowing SW or West and the Irish rivers with very limited estuarial netting?
 

ohanzee

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I accept that this covers the NE but what about all the rivers flowing SW or West and the Irish rivers with very limited estuarial netting?

I'm still looking, but you are right, the market for wild salmon is strangely invisible.
 

JohnH

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Quick fyi everyone, a very similar text to the one Sewinbasher referred to in post #41, by Professor Andy Ferguson about what drives brown trout migration whether to sea, estuary or large lake, loch or lough, is in the October issue of Fly Fishing & Fly Tying...
 

Cap'n Fishy

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Sorry, I was confused by the apparent comparison of the growth rate of essentially a sea trout with a sea trout. I understand now!

Aye, it was to see if it could be shown that the faster-growing a fish is, the smaller its head and tail are, as a proportion of overall body length. I often see finnock that look like they pile on the flesh at a much faster rate than their bigger, older relatives.

I tried the same exercise with typical South Uist sea trout and finnock...

Finnock...

Uist2016_7957.jpg


Proportions different for head and tail - head measurement longer than tail. Head = 1/11 body length. Tail = 1/13 body length. So, roughly similar to the Hope sea trout.

Sea trout...

3658.jpg


Again, head length longer than tail. Head = 1/9 body length. Tail = 1/13. Not sure if any of this is proving anything? :unsure:

Col
 

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