Loch Leven Pre Season Update

With the start of the new season on Loch Leven today, not surprisingly anticipation is rising.  A number of very hardy anglers have ventured out and it will be interesting to see if they have any early success – the cold, bright conditions at the time of writing this are perhaps not as ideal as they could be!

Last month, we held what has hopefully now become an annual Loch Leven Fish Research Meeting.  Although it sounds a bit dry, the meeting was extremely useful and informative.  Particular thanks must go to SNH, and in particular Denise Reed, for again organising the session and for all those from various organisations who attended.  The Centre for Ecology & Hydrology (CEH) again sent a strong team consisting of Linda May (water quality), Dave Carss (cormorants) and Ian Winfield (trout & perch).  It was also nice to have Joanna Girvan present, representing the River Forth Fisheries Trust.

2014 Season Catch Returns

Let’s start with the most important thing – feedback on the 2014 season.  Those who have fished Loch Leven over the last couple of seasons will quite probably have been asked to fill out a Catch Return Card.  Now that the practice of catch & release has become the general norm, the accurate recording of catches has become much more difficult now that few trout are being brought back to the Pier and weighed in.  With Loch Leven being one of the sites of a big EC funded project called OpenNESS, we have agreed to try to provide them with more accurate data on fish catches and boat turns – our Catch Cards therefore are very important and we are extremely grateful to all of you anglers who have taken the time to fill them in over the last 2 seasons and we hope that you will do so again this year.

Example Catch Survey Card

Example Catch Survey Card

We have just received feedback on the initial analysis of the 2014 cards from Ian Winfield and his team at CEH and it is interesting to see how the results for 2014 compare with 2013 which was the first year in which we ran the scheme

2014 Season 2013 Season
Cards Completed

529

428

Fishing Hours Covered

2,594.25

2,649.5

Total Brown Trout Caught 1,635

1,310

–          Retained

287 (17.6%)

358 (27.3%)

–          Released

1,348 (82.4%)

952 (72.7%)

Catch per Unit Effort      (per boat hour)

0.63 trout

0.494 trout

As you can see, there was a good increase in the number of cards completed and submitted (thank you again!) although interestingly the number of fishing hours they actually cover is little changed.  The number of trout recorded on the cards as being caught showed an encouraging increase and it is interesting to see that the percentage released back into the loch rose by almost 10% to over 82%.  As a fishery, we offer no guidance to anglers about catch & release because we are very happy for anglers to take trout home ‘for the pot’ – that said though, we are extremely appreciative of those of you who carefully release trout back into the loch after catching them!

The important figure though is the CPUE (Catch per Unit of Effort) which gives perhaps the best indication of how the loch is fishing.  The CPUE measures the number of trout caught per hour a boat is out on the loch.  in 2013, boats were catching a trout about every 2 hours (0.494 trout per hour). Last year, the catch returns would suggest it was 1.25 fish every 2 hours (0.63 trout per hour).

The chart below tries to put that into some sort of historical context, illustrating the data from 1975 – 2003 when reasonably accurate catch returns were recorded (and before catch & release took off and rendered the Fishery’s statistics meaningless).

 

Historical Catch Rates on Loch Leven

Historical Catch Rates on Loch Leven

  • The left hand scale shows the number of fish per boat boat per hour fished.
  • The solid black line plotted represents brown trout
  • The dotted black line plotted represents rainbow trout
  • The bold red horizontal line shows the 0.63 trout caught per boat per hour fished in 2004 (dotted red line shows equivalent 2013 figure)
  • The bold orange line is less meaningful, merely representing the number of brown trout kept (as opposed to released) per boat per hour fished in 2014 (dotted orange line shows the equivalent 2013 figure).

At first glance, the 2014 result of 0.63 trout caught per boat per hour fished looks really positive.  Not only was it nicely ahead of 2013 but it appears to be better than any year since 1975 when we started keeping this data. However, there is an element of trying to compare apples & pears here – the 1975 to 2002 data reflects fish actually weighed in at the Pier before catch & release became popular whereas the 2013 & 2014 figures are derived from anglers’ returns which predominantly include those caught and then released.

Although the 2014 result looks encouraging, one needs to input a further degree of caution. Not every boat took out and completed a card and those that did had an inevitable bias towards local regular anglers who were happy to help in the survey.  Local knowledge has always been an enormous advantage at Loch Leven and therefore the catch ratio of 0.63 is almost certainly higher than it would have been if every boat in every session had completed a catch survey card.

Click on the following link if you would like to read the full Preliminary Report from Ian Winfield (CEH):  Preliminary analysis of 2014 LL catch returns

 

Loch Leven Fish Population

Although, looking back through last season’s weekly (?!) fishing reports,  the fishing was at times reported as being pretty difficult, anglers were reporting seeing plenty of fish even if they were proving hard to tempt to the fly.  Young fish in particular appeared in huge numbers on various occasions which was hugely encouraging, even if they are frustrating for anglers.  Our feeling is that the trout population is pretty healthy at the moment both in terms of numbers, spread across age groups and their condition.

The most significant factor behind the return to health of the Fishery has got to have been the huge improvement in water quality over the last two decades. The sustained decline in the levels of phosphates & nitrates found in the loch over the period is perhaps best illustrated by the dramatic recovery in macrophytes (aquatic plants) in the loch.  Improved water clarity has resulted in weed banks growing at depths last seen almost a century ago. Not only that but there is a much greater variety of macrophytes being recorded – back in August 2014, Iain Gunn of SNH reported that they had recorded more varieties (20) at Loch Leven in a single year since 1910!

The only cautionary note was expressed by Dr Linda May  (CEH) who noted that 2014 had seen a small upward tick in what was a strong downward trend in phosphate levels in the loch.  They will be keeping a close eye on whether this was a blip due to weather conditions or whether the improving trend is showing signs of leveling off.  As luck would have it, CEH are due to carry out one of their 5 yearly Loch Leven Catchment Area phosphate & nitrate loading surveys starting imminently (results due in August 2016) and this should give us a much better idea.

Returning to the fish population, CEH (Ian Winfield & team) having been carrying out annual acoustic surveys of the fish population since 2007.  In 2008 & 2011, his team carried out gill net surveys at 3 sites on the loch and, keeping up the 3 year programme, they did so again last year.  What they found was very interesting.

CEH - 2014 Gill Net Summary Results

CEH – 2014 Gill Net Summary Results

The number of brown trout caught continues to increase.  However, Ian Winfield pointed out that there are indications particularly from the acoustic surveys that the trout population is now dispersed much more evenly around the loch than was the case a few years ago, quite probably because the improved habitat means that food sources are much more widely spread.

The perch population findings are equally interesting.  In 2011, there was a big spike in the young perch population (50-60 mm).  As you can see from the diagram below, 3 years later in 2014, there is a much more even spread across the size bands.  There appear to be far fewer smaller perch but many more larger ones (which will be predating on the small ones!).

CEH _ Loch Leven Perch Population

CEH _ Loch Leven Perch Population

Ian Winfield commented that these results showed an extremely positive trend for perch and exactly the sort of text book profile that they would expect from improving water quality.  There were also indications that Pike numbers were growing and Stickleback are now being seen in huge numbers.  All in all, it seemed very positive.

Loch Leven Catchment Area

The condition and performance of the many feeder streams in the Loch Leven Catchment area is obviously of paramount importance to a wild brown trout fishery such as ours.  The days of rearing hundreds of thousands of young trout from eggs in the fish ponds at Tarhill on the north shore to stock the loch are disappearing into the distant past.  The trout population of the loch is now totally reliant on recruiting juveniles from the various feeder streams every year.

Willie & Michael monitor the various feeder streams throughout the year but there is obviously particular attention paid every autumn as the adult trout run the burns to breed. This year, gratifyingly, they observed healthy numbers of brood stock in all of the burns and this was backed up by the Redd counts.  The run starting in the first week of September and lasting right through until the first week in November.  The water conditions during the spawning season were very good – consistent spates without too much flood.

In the past, there have been periodic studies of juvenile trout in the burns and their tributaries.  Back in 1994, Ross Gardiner of FRS Pitlochry (now part of Marine Scotland) carried out an extensive survey of juvenile trout populations at 18 sites within the catchment area using electro-netting as a means of counting the fish population at those sites.  He then carried out a smaller scale study in 2009 when 8 of the original sites were revisited and electro-netted again. His summary findings made interesting reading

‘Given the relatively small size of the catchment supporting the population of trout in the loch, the burns have to be very productive. 8 of the previous 18 sites from 1994 were re-visited. Comparative photos showed that in some sample sites the channel characteristics had changed, with bank-side cover becoming slightly less, but others were very similar. The slightly later time of year could account for some of the differences.

 

There were generally higher densities in 1994 than 2009 and fish were slightly bigger in 2009. This may be due to the cover being slightly less and therefore fish may have moved off.  Other reasons may be that the number of ascending brood stock is less. In at least one case, the drop in densities may be at least partly due to a large stocking effort in the mid-90’s at a particular site, stocking no longer takes place on the catchment. [What Ross Gardiner is referring to here is that, back in the 1980s & 1990s, there were only so many young brownies that the fishery could grow on in the fish rearing ponds at Tarhill.  Any excess fry were released into the higher reaches of burns and their tributaries in the catchment area. He was pointing out that, in at least one of his survey sites, counts might have been boosted by this stocking of surplus fry.  This practice had long stopped by 2009].

It was confirmed that the brown trout densities are still high for the UK. Anecdotal information from KEC suggested that there were bigger numbers of ascending brood stock last year than for a number of years.

 Other issues arising in the discussion of the findings were: might brown trout stay in the stream with the proportion dropping back to the loch becoming reduced? Flow is critical to the density of juveniles; are there density dependent effects on age of maturity? Fishermen are finding a wide range of age classes in the loch. In the 1960s there was a distinct smolt run but there is no recent information on what proportion of trout recruited to the loch is as fish which have undergone smoltification.’

Last year, we were very grateful to the River Forth Fisheries Trust for offering to again survey juvenile trout population in the catchment area now that this type of activity is no longer carried out by Marine Scotland.  Dr Joanna Girvan and her team surveyed 8 upstream sites within the catchment area, 5 of which corresponded to original sites surveyed in 1994 by Ross Gardiner.

Catchment Area Survey Sites (1994 & 2014)

Catchment Area Survey Sites (1994 & 2014)

Whereas Ross Gardiner reported in 2009 that counts had fallen from 1994 levels (albeit the fish appeared slightly bigger), Dr Joanna Girvan’s findings were overall positive – counts were either similar or higher than in 1994 (and therefore more so than in 2009) in the 5 corresponding sites.  She went on to point out that the comparisons between the 2 sets of data if anything understate the 2014 results because she only electro-netted each site once. Back in 1994, Ross Gardiner had electro-netted each site several times in quick succession to ensure they got a full count and that none were escaping.

Comparing fry densities (0+ year old)

Comparing fry densities (0+ year old)

Comparing parr densities (1+ Year old)

Comparing parr densities (1+ Year old)

We are very grateful to Dr Joanna Girvan and the River Forth Fisheries Trust for undertaking this study and she is hopeful that she will have the time and resources to be able to repeat these surveys every few years going forward.

Cormorants

Willie always insists that mention is made of the cormorants on Loch Leven in our pre season reports.  Neil Mitchell of SNH gave us the 2014 cormorant count details which showed a continuing gradual increase in average numbers.  If you happen to be a ‘glass half full’ type of person, you can take encouragement from this.  Cormorants are extremely efficient predators and they would not be here on Loch Leven if there was little for them to catch.  Might their slowly rising headcount indicate a growing fish population?

Most anglers understandably cannot find any silver lining in cormorant numbers because of the huge damage they can do to fish populations.  Here at Loch Leven, we suspect the damage to the trout population is actually being reduced by the continuing recovery in perch, pike and stickleback populations mentioned earlier which will help satisfy the cormorants hunger.  Many of you will have seen Michael’s recent post on our Facebook page:

‘Don’t say I’m not honest and cover all aspects of what goes on. Working on the loch today and came across about 100 cormorants feeding in the Hole ‘o’ Inch. They all got up. However, as quite often happens the more heavily laden with fish birds regurgitate what’s in there throat. Two cormorants had a pike each plus around 50 to 100 sticklebacks. Not what I was expecting. Hopefully good news for the trout. Fingers crossed the other 300 cormorants are eating the same. Both pike were about one pound.’

What the cormorants were eating!

What the cormorants were eating!

Unfortunately, gone are the days when we could reduce the numbers of cormorants on Loch Leven by shooting an agreed quota.  We have tried for a licence but have to accept facts that we are not going to be given one due to Loch Leven’s status as a National Nature Reserve amongst other things.  We are having to cheer on the Sea Eagles who have been seen harrying the cormorants on the loch – go, boys, go! Looking further ahead, we are exploring in collaboration with SNH the possibility of carrying out in the near future a controlled cull of a number of cormorants to enable a scientific analysis of their stomach contents to ascertain changes to their diet.  The signs are reasonably hopeful if resources can be made available to analyse the stomach contents.

FRS Pitlochry carried out cormorant diet surveys back in 1991 and then 2001 (click here to see the FRS Cormorant Survey 2001).  As mentioned earlier, our suspicion is that the proportion of the cormorant diet made up by trout could well have fallen sharply from the 85-90% found in the earlier surveys – but it would be fascinating to see if that were actually the case.

The new 2015 Season

Our season on Loch Leven has just begun today with a number of intrepid anglers out in boats.  As always at the start of the season in March, there is the usual anticipation about what the forthcoming season will bring.  Water clarity throughout the winter months has been in the main very good.  Huge shoals of stickleback have been seen pretty much all over the loch all winter, providing ample food supplies for fish and birds.

Tight Lines to one and all and we hope you have a cracking season wherever you are fishing!

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One Response to Loch Leven Pre Season Update

  1. Brian Stewart says:

    Hi Willie / Michael,

    Many thanks for this – very informative and positive.

    Best regards, Brian

    Sent from my iPad

    >

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