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Post by builnacraig on Dec 12, 2010 16:09:02 GMT
Thanks for reply it's very intersting, I don't have an answer however I sometimes think that the pendulum swings too far. Mortality at sea is a separate issue. Using fry as an example it could easily apply to parr or smolts. If you have a +90% fry mortality rate the surviving 10% will be weak because they had a huge struggle to survive in the first instance. In other words the 10% that survive are off to a bad start in life. Could this have a detrimental effect on their survival as parr and then on their survival as smolts etc... In theory the pendulum can't swing too far. The survivors should be the fittest ones rather than compromised by the struggle. Once a fish is able to defend a territory its chances in life increase dramatically and it will thrive in comparison to those trying to eek out an existance on the edges of territories or in poor habitat. True exactly the same principles apply to parr, not so much smolts, but the big mortality occurs in the fry in the first few weeks after emergence from the gravel. Smolts and adults are not subject to the same density dependent pressures as they are not territorial. The behaviour of salmon changes when they smolt, they start to shoal and move downstream en masse. From this point on the survival is expressed in percentage terms so the more that go to sea the better. Space nor competition for food is thought to be a limiting factor in the sea. The 10% survivors have had a lot of competition which doesn't stop at any point in their life, so there is constant weeding out but that selection process will benefit them and the population as a whole. I do a lot of electofishing and the variations in the sizes of the fry and parr between different parts of the river is amazing. In the upper reaches in the good spawning areas the fry and parr can be small (e.g. 18month old parr ave 85mm, fry can be that size at 6 months in the lower reaches) at any given time but there are lots of them so lots of smolts produced. These small 1+ parr go on to become good sized 2+ smolts, or even bigger 3+. This is the natural way of things. In the lower reaches the big fry are now increasingly likely to go to sea a one year old. This means that the smolt production in these areas can increase (more smolts produced annually) although they will be smaller that the 2 & 3 year olds. Size is important to an extent for predator avoidance, as the bigger you get fewer predators can eat you. It is quite easy to produce very large smolts in a hatchery environment from wild stock but size alone offers them little advantage compared to all the other problems they have (e.g. lack of predator avoidance/feeding experience/unnatural growth, etc) BnC
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Post by builnacraig on Dec 12, 2010 16:19:57 GMT
Cant disagree with anything you say, survival of the fittest is key in any widlife scenario. Interested in your theory of of big springers being created as some sort of Frankenstein unplanned experiment. Is there any proof of this having happened? The Lochy quite suddenly produced a fairly high percentage of 30lbs+ fish warranting a separate gallery page. Do you think they are hybrids? Also what do you mean on your last point? Do you think all our rivers now have a diluted gene pool? [/quote] Its not my theory I think John gibb himself said it. It is perfectly plausible, farm fish are selected for growth rate, late maturation and large size, amongst others so if they were to breed with the wild fish, or other escapees, then there is a fair chance of some will follow their pedigree. The surge in big fish from the Lochy in recent years is a new feature isn't it? Genetic sampling should be able to prove or disprove this theory. No, my last point was that there are no Scottish rivers where hatchery derived fish form anything other than a small proportion of the stock. The possible exception could a hydro river like the Conon but here the stocking has always been based on alevins or ova so there is a lot of natural selection going on.
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Post by builnacraig on Dec 12, 2010 17:04:22 GMT
Could this mean in the long term if the rod nos dropped due to hatchery not keping catch levels satisfactory it would end up stopping Iain, Intensive hatchery operations such as smolt stocking should be regarded as the last resort. I'm only aware of four current smolt stocking operations and three of those are in fish farming areas where stock numbers have been decimated. Smolt stocking is expensive and is a high level of management intervention. Ronald Campbell, Tweed senior Biologist, gives a great presentation on fisheries management based on the "attack - defense continuum". Basically what this means is that if things are going well you just need to defend; put up buffer fencing, make sure that the fish stock isn't overexploited. But if things are bad then a greater level of intervention is required, e.g. total catch & release, fishing season restrictions, habitat restoration, stocking etc. It is knowing where you are on that continuum that is key. As I said smolt stocking is expensive. That requires resources, i.e. funds, which means there must be a source of income from somewhere, usually fishery rents. If there is an underlying problem then it is worse as you will have to sustain that expenditure ad finitum. If for any reason the funding reduces then the whole strategy could become non viable and a rethink will be required. The example here is smolt stocking, this is high intervention and high cost. but it could apply to other aspects. Intervention like that has to demonstrate results over a period of time and produce income to succeed.
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Post by weefrankie on Dec 12, 2010 17:47:44 GMT
Brian i understand how complex it is, but from outside and greatley appreciate your input as you understand these things more than most and certainly an awfull lot more than me,who is an observer from the outside with a brain that probably adds 2 and 2 and gets 3 more than others I apreciate its a journey for those envolved and a big hard learning curve, that will impact on Salmon breeding and trying to maintain wild or as near wild stock for many years to come, it is history and science in salmon biology being made And all eyes are spotlighted on them,and to be applauded for doing something How long has the program been going how are the returns survey proving a significant increase or achieving the targets set,to produce stock recovery
Are the sea lice the major factor of the negative impact,I know its mentioned that seals and poachers are mentioned on the lochy site as threats as well When the salmon clear the Linnie etc do they follow the Scottish coast line and pass more farms or do they head out to open water to migrate to there feeding grounds,on there feeding grounds what is happening with them ,is there enough foods whats happening to the fish at sea tagging or radio chipping if funding was avaliable on pre smolt, linked to say satelite tracking,would that show up where fish are being lost at sea,or where nos seem to get lost,or is that far to costly to reduce fish output and invest in tracking, or do fish size and handling make this prohibative,or is suitable technology not yet avaliable where tracing is lost could identify big loss just after farms or certain areas,could catch or trap dead fish are they infested with lice ,or is it another problem
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Post by kingfisher on Dec 12, 2010 18:27:11 GMT
The Lochy quite suddenly produced a fairly high percentage of 30lbs+ fish warranting a separate gallery page. Do you think they are hybrids? Perhaps recent years did no doubt see a rise in big fish, but when I was up in the mid/late eighties, I had a look at the catch returns book kept in the old rod room at Camisky House www.camiskylodge.co.uk/and if I recall correctly there was lots of big fish entered over the years. In fact there was rough cardboard silhouette tyre cuttings adorning the place and one I believe was well over 40, but could possibly be wrong. Also around that time there was a 30+ caught just before we arrived so there was always big fish being caught, perhaps? not as abundant as what is being preceived today. I use the word perceived as they didn't really make much news in those days, just logged in the book for future prosperity.
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Post by builnacraig on Dec 12, 2010 21:47:17 GMT
Wee Frankie, I don't think the technology is there yet to satellite track salmon at sea. Maybe closer inshore where listening stations could be set up for fish tagged with ultrasonic tags but once out in the open sea they are out of reach. The SALSEA research program is investigating the life of salmon at sea. This link shows the results of the Irish netting surveys www.nasco.int/sas/2008_Irish_survey.html . A lot of the fish are caught on the edge of the continental shelf. Quite surprising how small they are.The mean size was 16cm. When we ran the smolt trap on the Ayr the mean size in the river was 13.9cm. They were quite big compared to other rivers but it just shows that they move quickly out to the ocean whilst still quite small. Feeding at sea seems to have been a problem in recent years, e.g. skinny grilse, but survivial on the east coast was obviously good in 2009. A couple years ago I heard a talk which reported that the fish were losing condition on the way back from the feeding grounds. Scale reading showed that they grew well initially but there may have been a lack of feeding in the ocean closer to home. As you can imagine it is a difficult area to research. It took them years to develop nets and to find the areas before they started to catch post smolts at sea. It is vital to know where they go, and when, in order that conservation measures can be put in place if necessary.
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Post by underghillie on Dec 12, 2010 22:01:11 GMT
This has turned into a great thread guys, thanks for the info Brian, some very interesting stuff.
Tony
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Post by weefrankie on Dec 12, 2010 22:07:45 GMT
Thanks Brian had a quick look will dip into this over the coming evenings Bookmarked,anything else of interest on smolts and migration would be appreciated
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keirstream
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Respect Ma Authorita!!!
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Post by keirstream on Dec 13, 2010 0:51:53 GMT
There is no doubt the Lochy and other North West rivers are having a hard time in general due to fish farms and the passage of smolts has become nearly impossible through the sea lice barrier. It is interesting to note that the Dundonell river having enjoyed the benefit of 4 years fallowing of the Ardessie fish farm in its estuary has enjoyed 2 near record seasons, coming back virtually from the dead. It is principally a sea trout river and fish of up to 6lbs have been recorded over the past 2 seasons. 5 years ago the river was almost devoid of migratory fish. The Gruinard rivers have also seen significant improvement in salmon returns also being influenced by the same farm. There is no doubt that if we can get these farms out of the estuaries the rivers will enjoy a resurgence. Its a great pity our Scottish government give not a jot for wild salmon apart from giving grants to netters.
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Post by weefrankie on Dec 13, 2010 18:23:39 GMT
I was thinking about this as i have heard it said they are looking at constructing large offshore facilities to move away from the coastline,but when i read Bnc's reply about the fish going out as far as the continental shelf is this the answer I can remeber a tv program last year where they had a big sealed cylindrical tube with filtration and tratment facilities linked to so the fish were in a near total confinement envioronment Another question what is the food comparison in putfor a wild salmon and a farmed salmon if diet was say sand eels how many pounds of sand eels to put a pound on a wild salmon,and how many pounds of processed sand eels for a farmed salmon With the decline,and the hopefull upturn in the lochy what does that do to the rateable value of the properties and fishings Surley the owners of properties and fishings could be putting serious pressure on the farms owners or govoerment bodies or is there that much cash generated to the local economy, compared to angling it is not so high on goverment or local goverment agenda
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Post by builnacraig on Dec 13, 2010 19:33:00 GMT
I was thinking about this as i have heard it said they are looking at constructing large offshore facilities to move away from the coastline,but when i read Bnc's reply about the fish going out as far as the continental shelf is this the answer The concentration of larval sea lice will decline in more open water situations, although they could still be a problem. Sea lice larvae stay in the uppe reaches of the water column so imagine a situation with a steady SW wind blowing up loch Linnhe. the lice larvae will be concentrated in very high density at the top end of the loch and the smolts would pick up a lot on the way out. I can remeber a tv program last year where they had a big sealed cylindrical tube with filtration and tratment facilities linked to so the fish were in a near total confinement envioronment Another question what is the food comparison in putfor a wild salmon and a farmed salmon if diet was say sand eels how many pounds of sand eels to put a pound on a wild salmon,and how many pounds of processed sand eels for a farmed salmon I seem to recall that in general predators require to eat ten times the weight on food each time there is a step up the food chain. That principle applies to fish so in the wild a salmon would need to eat 10lb of sandeels to put on 1lb. You can't get a way with from that principle for farmed fish but a lot of the protein now comes from vegetable sources reducing the requirement for fish protein to some extent. With the decline,and the hopefull upturn in the lochy what does that do to the rateable value of the properties and fishings Surley the owners of properties and fishings could be putting serious pressure on the farms owners or govoerment bodies or is there that much cash generated to the local economy, compared to angling it is not so high on goverment or local goverment agenda [/quote] They've been trying to do that for years Iain but it is hard to argue against it now. Just go to Scourie and see what percentage of the local population is employed on the fish farms in that village.
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Post by weefrankie on Dec 13, 2010 20:14:28 GMT
Brian yet again thank you very much, for your answers .
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Post by builnacraig on Dec 13, 2010 20:46:13 GMT
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Post by weefrankie on Dec 13, 2010 20:55:03 GMT
And i thought you were sending me a job application form for working on the fish farms Brian
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Post by kingfisher on Dec 14, 2010 7:33:25 GMT
One picture from our trip this May. This is why we put up with the Lochy to some degree Heaven on earth for me, that area. kf
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