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A Tweed Fisheries Biologist’s Week – Monday 10th May.

Monday May 10th: On traps again this week, but nothing much happening on the burn traps, the water levels are very low. It is this sort of situation that gives us information on how environmental conditions affect young fish – and therefore affect the strength of their year class when they become large enough for anglers. Up till this year, the trap at Tweedsmuir has reliably produced good numbers of migrants in March, April and May – but this year hardly anything. Will they come at all without higher water ? Will they get so desperate that they will move regardless of water level ? If not, what will happen in the burn if there is a whole extra year class of fish that stays put, using food and space that would otherwise have supported younger fish? Some of the burns along the Yarrow Valley are already dried out on their valley-bottom stretchs, where their water sinks into gravel, though still running well on the hillsides on bedrock. No smolts will get out of such burns this year therefore, without a spate. Downloaded the automatic listening station at Philiphaugh, more fish arrived there. Also found one fish had passed Mertoun, but the bulk of the tagged smolts are either still in the Yarrow or piling up at the cauld at Philiphaugh, in the deep water there. Is this something that only happens in dry years? If we are lucky, next Spring will be wet and we can see the contrast. Timing is very important for smolts as they have to adjust their physiology from living in fresh water where their body fluids are more concentrated than the water in which they live, to salt water, where it is the reverse. It is reckoned that there is about one week in which they are in the right physiological state to make this transition – so what happens if low flows delay their passage downstream ?

Tuesday 11th May: A reasonable count in the Yarrow smolt trap – being off a larger channel, this is less affected by water levels. Carlin tag some larger Sea-trout smolts – this is the old-fashioned way of tagging fish, an ordinary external tag, nothing electronic. Download the acoustic listening station at Melrose and find a couple of fish recorded there.

Wednesday 12th May: On traps again. Am checking each smolt for signs of damage by predators and recording the numbers & types of damage found but today came across a form of damage I'd not seen before: very obvious, U-shaped, marks on both of  a smolt's flanks that looked just like another fish had seized it in its jaws –  from below. The predatory fish didn't look to be very much larger than the smolt itself – if the marks showed the full extent of its jaws. It could be, though, that it was a much larger fish that only caught the smolt in the tip of its jaws, which is how it escaped. No puncture marks, which is what you would expect from the big teeth of a Pike in the loch though. Check some of the Yarrow with the mobile acoustic tracking device, but find nothing.

Thursday 13th May: Checking the smolts in the Yarrow trap found another example of a U-shaped bite from below. More Sea-trout smolts tagged & kept overnight. Six migrants in the trap at Tweedsmuir, the biggest daily total so far, but very different from other years, when there should have been several hundred in May as well as in April. Smolts started on the Gala though, and should be able to tag there soon. It's curious that the smolts should be “sticking” at the Philiphaugh Cauld but not in any of the natural pools in the Yarrow. If they were looking for some deeper water in which to rest or delay their migration while the water is low, why aren't there any holed up in the other pools? It will be interesting to see if the same thing happens on the Gala, where the impoundment behind the Skinwork's Cauld is smaller, but relatively just as prominent a feature.

Friday 14th May: Weekly meeting in the morning, then out to do traps. A bigger catch than for the last few days at the Yarrow trap. Released the acoustic tagged fish from yesterday in amongst them