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Some South Esk salmon numbers

Tuesday, September 25th, 2012

These bulletin blogs represent news about Finavon and the South Esk, and my views as a riparian owner. They are not the views of any other organisation, nor are they designed to promote the interests of any individual or organisation other than Finavon Castle Water and factors affecting the fishery. Tony Andrews

In the light of the publication of 2011 catch statistics for all Scottish salmon districts, it may be useful to revisit my blog of last summer when, based on calculations of smolt production and ICES/NASCO returning adult fish percentages, I concluded that the annual run of salmon and grilse into the South Esk is about 10,000.

What did the nets catch in the September 2012 extension period? The item of news that should interest anyone who knows the South Esk is the number of salmon and grilse caught by Usan Fisheries Ltd during the two week extension of the netting season into September. This “two weeks” was actually eighteen tides, and the total catch was 272, of which the main part was grilse. I have good reason to believe that my source is reliable. TA

In 2011 I wrote;

“While there’s no room for complacency, it is very encouraging that in 2011 there are good numbers of spring fish in the river. Of course one swallow doesn’t make a summer, but it is also true that the 2010 run of spring salmon indicated a reasonable return of adult salmon, despite the poor rod catches resulting from low water yet again. The evidence therefore suggests that there appears to be a surplus of spring salmon year-on-year. By “surplus” I mean an escapement of fish to spawn that allows the regeneration of numbers of adult fish well above the minimum number required for sustaining stocks to return to the river between the start of the season and the end of May each year. That for me is the meaning of the term ‘sustainable’.

Ken Whelan fishing Pheasantry in May 2010 (above)

We don’t know how many salmon and grilse run the South Esk. It is a pity that the Esk Board has not devoted some of its considerable resources to a proper assessment of South Esk stocks, and continues to make management decisions on the current guesswork basis. We only have rod catch statistics to tell us what the trends are. But I will hazard a guess that the five-year average of returning adults, based on 60% of Usan net catches and the declared rod catch, plus our own observations, is somewhere around 10,000 fish. That figure has not yet been challenged and reflects more the general ignorance of the numbers and structure of South Esk stocks than it does on the actual numbers of fish”.

I based that speculative figure on 1,500 MSW fish up to 31 May, 3,000 MSW salmon and grilse in June, July and August and 5,500 MSW salmon and grilse from 1 September until spawning time (ie including salmon that enter the river after the close season on 31/10).

Since these figures were not challenged, and in fact a number of scientists commented that the method of reaching them was logical and consistent with experience from other rivers, I think it is fair to quote them again here. Based on those figures I wrote the following:

Average number of South Esk salmon and grilse killed by mixed stocks nets = c. 2,500*

Total number of salmon and grilse returning to the River = c. 10,000*

Total number of spawning females, allowing for 20% in-river losses = c.4,000

Average weight of spawning hen salmon = c. 8 lbs

Average number of eggs deposited by each hen fish = 4,500

Total number of eggs deposited in South Esk catchment (4,500 X 4,000) = c.18 million

Number of smolts produced annually by S.Esk (say 1% of total deposited eggs) = c.180,000*

Assume smolts returning as grilse is about 8% and of MSW fish about 5% (average 6.5%)

6.5% of 180,000 = c. 11,700 salmon and grilse arriving off the Angus coast (PFA) prior to nets exploitation.

Looking at those figures now, I really don’t see much need to change them. Perhaps I would reduce the return average from 6.5% to 6% to reflect the downturn in grilse numbers, and the proportion of fish caught at Usan and attributed to the South Esk more like 40% than 60%, but I think that those are the only adjustments neccessary.

In the context of those (admittedly speculative) figures I was interested to see the 2011 catch statistics published by Marine Scotland last week for salmon and grilse caught in the South Esk District. These returns include net and rod fisheries of fish killed and fished caught and released by rods. Nets of course kill everything they catch.

Here are the 2011 salmon and grilse catch returns for the South Esk District

Salmon killed = 5,646

Grilse killed = 1,203

salmon caught & released = 518

Grilse caught & released = 85

Total South Esk District catch = 7,452 salmon & grilse

If we take the figures for the South Esk District nets (the only legal nets being those belonging to Usan Fisheries Ltd) we see that:

In May 2,307 salmon were killed: average weight 4.13 Kgs

In June 1337 were killed: average weight 4.26 Kgs

In July 1053 were killed: average weight 4.2 Kgs

In August 746 were killed: average weight 4.36 Kgs

The consistent average weight of fish throughout the season (about 9lbs) suggests that there was a predominance of MSW fish throughout the season, expressed either as some very large MSW salmon offset by the lower average weights of grilse, or (more likely) a reflection of very low numbers of grilse, which would typically average 2 Kgs.

The figure that stands out in the 2011 season is the large number of 2,307 salmon killed in May. There are a number of aspects relative to this figure that are worth comment:

1. The value of 2.307 of prime spring salmon is very high. One may assume a per fish value of £150 to £200, giving a gross income to Usan Fisheries Ltd for May month of £300,000 plus. No wonder the Usan business doesn’t want May removed from the netting season, as has already happened in February, March and April.

2. If the 2012 radio tracking data are used to indicate how many of these May fish were bound for the South Esk, we might assume, from the proportion of recorded tagged salmon in the South Esk, that 40% of those 2,307 salmon killed in May 2011 were South Esk fish.

3. Upper proprietors observed that there was a prolific run of spring salmon in 2011. Usan’s May return confirms that the spring run continued to be strong into May. Based on Usan’s May catch return we might assume that about 900 of those fish were of South Esk origin. That figure tallies with my guess that an average of 1,500 salmon enter the South Esk before the end of May.

4. Catch returns from Cortachy & Downie Park, Inshewan and Finavon indicate that there were good numbers of MSW salmon in the South Esk from March onwards, and of course with no netting taking place in March and April, these salmon had free access to the river. Moreover, none of the rod-caught salmon in those two months was killed. Spawning escapement in 2011, even with the 900 fish killed in May by Usan nets, was clearly significant.

It is important that the Marine Scotland radio tracking project fulfills its purpose, which is to find out where early running South Esk salmon spawn. The project has nothing to do with stock assessment beyond that single purpose, although people (such as I!) will inevitably extrapolate from the data to support their arguments. We need to have a health warning on such methodology because the data coming from the MS project are not fit for any purpose other than demonstrating where some spring fish go in the South Esk catchment.

Posted in History, River Report, Salmon | Comments Off on Some South Esk salmon numbers

Thinking about the Lemno Burn

Monday, September 17th, 2012

The structure of a river catchment is one of the factors that determines the breakdown of the river’s stock of salmon – and maybe sea trout – into distinct populations. The shape of the catchment, altitude, gradient, topographical features (such as waterfalls), geology and chemical characteristics of its water, define a river’s migratory salmonids in terms of run timings and the predisposition of its salmon to return as grilse or multi sea-winter salmon, as well as variations in behaviour of sea trout. In big rivers, like the Tay or Dee, that may seem an obvious statement, but for a little river, such as the South Esk, we may overlook the importance of its smaller tributaries, and the role they play in the evolution of the characteristics of the stock of the whole river catchment.

The Lemno Burn just upstream of its confluence with the South Esk at Finavon. The photograph above was taken during a cleaning up operation by volunteers in April 2012, which involved moving tons of rubbish from the burn, whose gravel bed was covered by a thick blanket of gooey silt, up to 2′ 0″deep in places.

The Lemno Burn is a much abused drain for agricultural run-off and chemical enrichment from the intensively farmed Vale of Strathmore. There is anecdotal, but I think reliable, evidence that the Lemno was once an important spawning burn. Farmers upstream of Battledykes, through whose land the King’s Burn flows, tell of dead salmon kelts washed up on the banks of the burn after winter floods. As far as I am aware, there has not been any redd or official juvenile count in the King’s Burn in recent years. My guess is that it still supports a stock of salmon and trout, albeit a diminished one.

The photo above shows how the artificially wide channel and silting up of the burn has slowed the current and reduced scouring, even in a spate. By getting the water moving again we hope to reveal the good quality gravels beneath the silt and encourage fish to use the burn again.

Silt, sewage, pollution and utrification have severely damaged the habitat for spawning and juvenile salmon and sea trout once provided by this South Esk tributary. Despite the degraded condition of the habitat in some parts of the Lemno, electro fishing the middle and upper reaches by Marine Scotland scientists has revealed some very large parr, especially in the area of the confluence with the King’s Burn at Battledykes. There is no record of whether these fish were salmon or trout, or whether there is a mixture of the two. If we can restore the Lemno to a level that can support a diversity of aquatic life, it is likely that the burn will once again make a valuable contribution to the recruitment of salmon and sea trout.

Blocked by trees and accumulated rubbish, and full of the detritus of years of neglect and a thick ‘porridge’ of silt, the Lemno Burn is far from the ideal environment one would look for in an important tributary of the South Esk. But even in the photo above we can see the potential for restoration with the healthy flow and substrate of good quality gravel and cobble. If we can reduce the tree canopy to let the light in, we should have more phyto and zoo life in the burn, which should lead to providing the food necessary for healthy juvenile fish abundance.

Another photo (above) of the degraded channel of the Lemno Burn in its lower reaches. The accumulation of feet of glutinous silt at this point ensures no salmon or sea trout could spawn in this part of the burn.

If you walk up the Lemno Burn from its confluence with the South Esk at Finavon’s Red Brae Pool, the first thing that strikes you is the unnatural width of the channel downstream of the A90 dual carriageway. The channel is indeed an artificial one, because it was the lade of the roundstone dyke at Tannadice which was removed in 1946. Prior to that time the Lemno Burn joined up with the lade which provided water power for the mill on the Finavon Estate. When the water from the main river was diverted into the lade by a sluice on the south end of the dyke it combined with the water from the Lemno to make a sizeable stream. In low water the effect of the diversion was to discourage fish from running, with the result that they would gather in large shoals in the pools immediately above and below the Red Brae.

The last mile of the Lemno Burn, between the A90 and where the burn joins the South Esk, is a heavily wooded section. Over the years the tree canopy has spread out and removed all direct light from the sun. The photo above shows how the burn now looks after a major tree thinning operation in the winter of 2011/12.

In this summer’s blogs I have commented on the importance of one of these smaller tributaries – the Rottal Burn – and the rather surprising lack of our knowledge about its role in contributing to recruitment of juvenile salmon and sea trout prior to the start of the restoration project. It would I think have been useful to have had a baseline from which we could measure the effects of the project on populations of migratory fish using the burn. The lack of that baseline means that we may have to resort to guessing, which, for those of us who take an interest in the South Esk, is all too familiar a situation!

While the Rottal Burn is an upper catchment tributary and, as such, a natural destination for early running salmon – producing mainly S3 smolts (but maybe some S4s amongst them), the Lemno Burn is a middle catchment tributary. The Lemno Burn’s confluence with the main river at the Red Brae Pool on Milton Beat of Finavon Castle Water is about 15Kms from the tide at Bridge of Dun. The ‘plateau’, which I described in the previous blog, where there is about 500 metres of gentle gradient between two much steeper gradients, seems to be at about the right distance from the tide for migrating fish to rest. Spawning fish arriving at the mouth of the Lemno in the late summer and autumn may have used the burn to gain access to the King’s Burn at Battledykes. One of the radio receivers used in the tracking project is currently sited on the Lemno Burn. It will be interesting to see if any spring salmon use this burn.

The Lemno Burn may be more like the Pow Burn, which is the lowest of the South Esk’s tributaries and provides habitat mainly for sea trout, or like the tributaries of the upper catchment catering for the needs of salmon, or both species. It will be interesting to find out; and the best place to start is to clean up the lower reaches and improve conditions for spawning and juveniles further upstream. Work in progress.

TA 20 September 2012

Posted in Habitat improvements, History, River Report, Salmon, Sea Trout | Comments Off on Thinking about the Lemno Burn

Tributaries: The Lemno Burn

Monday, March 5th, 2012

After reading Bill Menzie’s report of 1957 I came away with the conviction that the South Esk’s tributaries are of more importance than I had thought to the capability of the river to regenerate its distinct populations of salmon and sea trout. This function applies as much to the catchment’s low ground burns as it does to those in the upper catchment. This is not to suggest that the main stem of the South Esk, especially downstream of its confluence with the Prosen, does not play a vital role in providing spawning habitat for summer and backend fish, and juvenile habitat for parr that have moved out of their native tributaries, as well as well as parr born in the main stem of the river. It is worth remembering that Menzies wrote his report at a time of strong runs of spring salmon and summer sea trout.

This is the section of the Lemno Burn immediately upstream of the Red Brae confluence. The banks have recently been cleared of unthinned woodland that prevented light getting to the bed of the burn. Woody obstructions have also been removed from the bed of the stream, along with overhanging bankside vegetation. For the first time in at least 20 years the burn is now flowing freely which should start to clean its gravels and encourage increased spawning.

The Lemno Burn is an important middle-river tributary of the South Esk which enters the River about 1000 yards downstream of the A90 bridge at Finavon. The Lemno flows through an intensively farmed section of the Vale of Strathmore where repeated unauthorised dredging over the years has been normal land management practice. The most recent of these dredging incidents took place in 2010/11 after considerable pressure was exerted by a farmer on SEPA officials who, apparently disregarding the SAC status of the S Esk and its tributaries, and in contravention of the letter and the spirit of the Controlled Activity Regulations, allowed a dredging operation on nearly a kilometre of the burn upstream of Bogindollo. The straightening of this already damaged water course smacks of the abuse of the Rottal Burn in Glen Clova. If you add the diffuse pollution from fertilisers and pesticides to the point pollution from roads run-off and slurry pits to the catalogue of abuse that the Lemno represents, it is not surprising that it is a poor performer spawning and juvenile-wise.

The Lemno a bit further upstream from the picture above. This section of the Lemno Burn used to include the lade from Tannadice Dam, which was demolished in 1946. The artificially wide channel has never had a chance to close up because of the lack of bank growth and consequent protection from erosion. This picture was taken immediately after the remedial forestry work was completed. A good spate should clear out the bed of the stream and start the long process of moving the silt and cleaning the gravels.

But how bad a performer is the Lemno? At present I don’t have the details (but I am working on that). Suffice to say that electro fishing of the Lemno up to Bogindollo reveals some salmon fry but very few parr, and those that were caught were (I quote an MSS scientist) “gigantic”. We can assume they have feasted well on fry. One of the problems of the burn in terms of juvenile salmon habitat is that there is very little riffle because of the woody dams holding back the water in a series of deep and slow moving pools, ideal for predators, including large parr. That problem may now be solved in the bottom section (downstream of the A90) after the remedial work completed in March 2012.

It is worthwhile comparing the shapes of the catchments of the North and South Esks. In the case of the former, the line drawn around the river’s watershed produces a shape not unlike a chestnut tree, with a short trunk and tributaries spreading widely as the full foliage of a mature chesnut tree does. The South Esk’s watershed shape by contrast looks more like a poplar tree with its long trunk and relatively few small branches. The confluence with the Prosen (or to continue the tree analogy, the fork in the poplar), the South Esk’s main tributary, is located in the upper third of the river catchment, some 28 miles from the sea. The shape of the North Esk’s catchment is similar to that of Tweed, where good-sized tributaries flow through fertile and relatively low ground glens to form a chestnut tree shaped catchment. In terms of the ‘wetted area’ available as nursery habitat, Tweed and North Esk provide better facilities for young salmon than the South Esk, and that is reflected in their relative abundance of salmon.

Until about ten years ago sea trout were the South Esk’s dominant species. It may well be the case that the trend of fewer spring salmon and the increase in autumn salmon has displaced sea trout from their spawning and juvenile areas. Certainly, the ratio of salmon to sea trout has changed noticeably in the last few years. In the longer term, species identification and genetics should help us understand whether this thesis is defensible.

As Menzies points out, the tributaries of the South Esk and Prosen are crucial in regenerating salmon and sea trout. The fact that the South Esk depends so heavily on its tributaries, and that there are so few of them, means that we need to value every yard of every tributary, from Pow Burn to Noran, Melgund, Lemno, White Burn, Carity, Moy and all the other tributaries above the Meetings. We should pay attention to the detail of managing these precious streams and of monitoring their outputs of parr/pre-smolts. That means more measuring – boring, but essential groundwork of accurate and effective fishery management.

TA 5/3/2012

Posted in History, River Report | Comments Off on Tributaries: The Lemno Burn

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Some South Esk salmon numbers

Thinking about the Lemno Burn

Tributaries: The Lemno Burn

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