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  1. #1

    Default Magnetic North Pole and salmon

    I recently watched a program which showed the actual magnetic north pole positions over the last 100 years. It is moving at a very fast rate and has moved almost as much in 20 years as it had in the previous 100 years and is heading to Siberia. We keep on being told that Atlantic salmon use this magnetic field to navigate to feeding grounds and back to their rivers of birth. I also read recently that salmon have been found to have low deposit of iron in their heads to aid this navigation. Could this magnetic shift be playing havoc with the Atlantic salmon ? Could they be getting "Lost at Sea" ???? Could this explain the low numbers of the salmon numbers on English & lower Scottish rivers As the film states. Maybe there is and maybe not but thought i would throw it out there and see what our forum members could come up with as there is a few clever chaps on here , Maybe even a few graphs to aid the thread !!!!!

    Also add in the recent news that the 2010's has been the hottest temperatures recorded and was it the hottest sea temperatures also ?
    Last edited by ArchieL; 03-12-2019 at 05:32 PM. Reason: Adding text.

  2. #2
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    Have a look at The Annual Miracle for an outline of dual-frequency magnetic navigation in salmon. Then we'll be better placed to start the debate.

  3. #3

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    There is much documentation of past magnetic pole shifts on this planet. The north pole moves south and the south pole moves north til they swap positions for another 10,000 to 12,000 years. Seems to be accompanied with an ice age and many planetary weather anomalies. Very interesting.

  4. #4

    Default

    Excellent blog post Michael, would i be correct in surmising that if the young smolt leaves its river of birth then they get the magnetic map of the area then use this on the way back ? It is honestly a mine field of information. One thing i think about when reading your blog and other information is could the outgoing smolts be homing in to a magnetic line which has shifted over time and could this be taking the fish a longer route ? Or into the path of new predators which were never encountered previously ? It is a very interesting subject and one which is going to trundle on for many years before we get answers. Regarding the smolt tracking in the North Sea , lets remember that Britain could not find U-Boats in the North Sea without first getting hands on an Enigma decoder machine. Look at the size of a U-Boat compared to a small smolt.

  5. #5
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    There could be something in that ArchieL,the AST where telling us that last year personally I don't buy it I have been saying for a long time they have been going missing in our rivers and not even making the sea,now they are doing smolt tracking the scientists are finding it out for themselves it's just a shame they were not listening to the ghillies,boatmen and anglers years ago who were blaming the predators in the river.

  6. #6

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    Without a doubt Phil.b there are far too many young salmon & sea trout being lost in the rivers and burns to predation. I keep saying it that i never seen these cormorants or mergansers 15-20 years ago where i fished. Now it feels like they are taunting me no matter where i go fishing. I honestly do not know how we try to understand their migratory routes or anything about this journey as it would cost millions and like i quoted about the U boats it is too big an area to try and track a few hundred smolts. I am not one for thinking that after you catch a smolt then open its gut to implant an acoustic tag then release it that it would be feeling too hot and up for the challenge of making it out to sea anyway.

    But getting back to this magnetic guidance system do we think it is now letting them down due to the amount it has moved in the last 20 years and that it will slow down again and the fish numbers will start to return, Or are we ever going to even see a run like what we got in 2010 ever again ??

  7. #7
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    Quote Originally Posted by ArchieL View Post
    Excellent blog post Michael, would i be correct in surmising that if the young smolt leaves its river of birth then they get the magnetic map of the area then use this on the way back ? It is honestly a mine field of information. One thing i think about when reading your blog and other information is could the outgoing smolts be homing in to a magnetic line which has shifted over time and could this be taking the fish a longer route ? Or into the path of new predators which were never encountered previously ? It is a very interesting subject and one which is going to trundle on for many years before we get answers. Regarding the smolt tracking in the North Sea , lets remember that Britain could not find U-Boats in the North Sea without first getting hands on an Enigma decoder machine. Look at the size of a U-Boat compared to a small smolt.
    Thank you, I'm glad you enjoyed reading about what is by any standard a fascinating topic. My hypothesis is that, like the Monarch butterfly, the salmon is born with an inherited map embedded in its cellular structure, and that local magnetic features (as distinct from whole earth magnetic effects) form part of that map.

    If you look at the mapping of magnetic features in the earth's crust - largely induced by tectonic pressure - especially to the east and north of Scotland, you will see that there are some clearly defined paths that would lead smolts pretty directly to the primary feeding grounds (and home again). These local features don't change or move with shifts in the position of magnetic north, which is a whole earth phenomenon. If these do indeed play an important role in migratory navigation, they don't vary so the routes remain broadly consistent.

    Tracking anything underwater is a technical challenge, especially when, like a smolt, it isn't magnetic, doesn't emit any form of radiation and is very small. That's the reason for using tags, which are becoming progressively smaller and more capable. Nevertheless there is still the open question of whether the tag changes smolt behaviour and thereby renders it more vulnerable to predation or death.

    Predation of smolts at sea is a matter of random variable (luck) and combinations of very big numbers (water volume) and very small ones (smolts). Unless a batch of smolts get unlucky, attrition at sea is comparatively low per unit of time: they are indeed micro-needles in an enormous watery haystack and even the most accomplished predators will have difficulty finding them - even if they were hunting them specifically, which they don't. In comparison, while migrating downriver, a substantial proportion of a smolt cohort may get eaten in the space of a couple of weeks.

    The disciplines of operational analysis tell us that attrition is directly related to density. For that reason 98% of salmon die where they are most densely concentrated - within 200 metres of their place of birth. The 2% that survive to be smolts are most concentrated when migrating down-river and at the salt water boundary (where they are also disorientated and consequently vulnerable): lots get eaten, others die during the transition process. Compared to that two-stage massacre, the numbers that die in the open ocean are tiny, until they return to find a big pod of dolphins and enough seals to sustain the world's population of Orcas for a century waiting for them at the Scottish coast, when concentration returns to haunt them.
    Last edited by MCXFisher; 04-12-2019 at 05:52 PM.

  8. #8
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    Its not just the predators. Its the trace chemicals cities etc. These may make them sterile or smaller. Agriculture pesticides creates less food in the river, thus leaving the smolts smaller. Also Smolts leaving at S1 instead of S2 makes a big difference. Smaller smolts are far easier prey, be that FEBs, trout, bass mackerel etc.

    Cheers

    Mows

  9. #9

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    Im certainly in agreement, for us to concentrate on in river and estuary .
    My big concern is the water.
    As has been mentioned, FEB, Seals etc take masses, but how many thousands do we lose down to toxic water. Each farm the river passes, use the water as a dump, then we got every town sewage works pumping in gunk. Then we got our roads, and plastic residue washing in.
    I would like see Water monitors every few miles down each river. All the millions being spent, and we dont even know what is in the water, and what effects it has.

  10. #10
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    Quote Originally Posted by phil.b View Post
    There could be something in that ArchieL,the AST where telling us that last year personally I don't buy it I have been saying for a long time they have been going missing in our rivers and not even making the sea,now they are doing smolt tracking the scientists are finding it out for themselves it's just a shame they were not listening to the ghillies,boatmen and anglers years ago who were blaming the predators in the river.
    ++++++++++++++

    For more years than I care to remember I have advocated against wasting money on full time river based biologists. Sure, they can do electro surveys and tell us juvenile densities over a river catchment. But you can hire someone part time at a fraction of the cost or else, as the L.L.A.I.A. have done, sponsor a post graduate student for a year as a basis for their research element. Very commendable indeed.
    Even I have a certificate that states I am qualified to carry out this work after a week's course at the Agricultural College at Dumfries. So, it's far from science of the rocket variety.
    Point is, instead, I have consistently advocated the use of the huge amount of knowledge contained within the ranks of the river professionals, the ghillies, boatmen and beat managers.
    There is quite often an obvious barrier between biologists and professionals because the biologists know fine that they would easily get caught out so tend to ignore a ghillie's advice.
    When we only put 2% or less of our parr production to sea it is blindingly obvious, regardless of how the marketing is couched, that the problem lies squarely where the professionals have been screaming for action for years, but here we are, throwing millions at scientist's sea jollies with always inconclusive results needing more funding.
    And yet 98% mortality is within touching distance of our riverbanks.
    I just don't get it.
    Respect My Authorita!!

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