Loch Leven Research Update 2014

Those of you who follow this blog regularly may remember that last year we did a blog post detailing all the various forms of research that is going on at Loch Leven covering water quality, the fish population, cormorant numbers etc.

Rather than regurgitating much of that again this year, it might be worth quickly looking back at what we wrote then (click here to see the 2013 Loch Leven Research Update) and then we can concentrate on bringing you up to date on what has happened in the last year since then.

Fish Population Survey

Loch Leven Survey Sites

Loch Leven Survey Sites

A big chunk of last year’s update explained how the Centre for Ecology & Hydrology (CEH) have been studying fish numbers in Loch Leven since October 2007.  They carried out gill-net surveys in 2008 and 2011 and are planning a further gill-net survey this year to continue the sequence.  In addition, since October 2007, they have carried out annual hydroacoustic studies every autumn.

Loch Leven is not ideal for hydroacoustic surveys because much of it is shallow and is often windy.  CEH therefore adopt a very conservative approach to fish numbers and fish sizes.  The chart below though summarises their hydroacoustic results including last autumn’s survey.

Loch Leven Fish Population (all sizes from 40mm upwards)

Loch Leven Fish Population (all sizes from 40mm upwards)

What the survey suggests is that, last autumn, they found just under 900 fish per hectare which measured 40mm or more in size. Although these will predominantly be brown trout, it will also include pike & perch as the hydroacoustic equipment does not differentiate between species. CEH quite reasonably tells us not to place undue weight on the absolute numbers (ie 900 fish per hectare) but they are pretty confident about the trend which suggests the fish population has doubled since 2011 and quadrupled since 2009!!

The vast majority of this apparent growth in the total fish population has been in juvenile fish measuring 40 – 99mm (ie up to 4 inches).  Whilst this is not much use to you as anglers (indeed small fish can be a nuisance), it is hugely encouraging from the point of view of the future of Loch Leven as a wild brown trout fishery. It backs up anecdotal evidence that the loch’s various feeder streams are once again producing considerable numbers of young trout.

[Incidentally, we would like to pass on a huge thank you to Ian Winfield from CEH who has overseen all these fish surveys at Loch Leven but also to all the rest of the CEH team (Dr Linda May, Laurence Carvalho, Helen Woods et al) who are massive supporters of Loch Leven and continue their invaluable water quality analyses.]

But it is not all about small trout. Memorably, last May saw Alan Campbell smash the record for the heaviest fish ever caught on Loch Leven (11 lbs 5 3/8 ozs) which had stood for over 100 years. And with this season barely underway, Craig Dickson has already caught a lovely specimen estimated at up to 5 lbs. In the past, we have received comments wondering what all the excitement was about with a brown trout measuring just 11 lbs (let alone 5 lbs). The fact is that Loch Leven is a wild brown trout fishery where the average fish landed since records began back in the 1880s (over 2 million weighed in) has weighed slightly under 1 pound! For us here at Loch Leven, a 5 pounder is a great fish; an 11 pounder is something one can usually only dream about!

Catch Survey Cards

The last 10 – 15 years has seen a dramatic, and laudable, increase in the catch & release by anglers but this has meant that the Fishery’s catch data, which historically had almost exclusively captured landed and weighed in,  had become almost meaningless as it did not record those fish being released.

A new initiative was therefore launched last year as part of the big EC funded OpenNESS project to provide much more accurate data on fish being caught on Loch Leven.  Based on the catch log books used by Ian Winfield of CEH at Lake Windermere, we introduced Catch Survey Cards to be completed by anglers last season.

Catch Survey Card

Anglers were asked to take these cards before setting out and then recording every fish they caught in the boat, whether kept or released.  They were asked to measure every fish caught using the measure in every boat, the weight of each fish where practical (however the size alone was sufficient) and which part of the Loch it was caught in.

A huge thanks to all those of you who took these Catch Survey Cards out with you and filled them in as you fished on the loch.  Ian Winfield and his team from CEH are in the process of studying the data from these cards but the initial statistics are as follows:

  • 428 catch cards were completed and returned (including nil returns)
  • catch cards covered the period 21st April – 29th September 2013
  • they covered a total of 2,649.5 fishing hours
  • fish were caught in over 150 different locations on the loch
  • a total of 1,310 trout were caught of which 952 (72.7%) were returned and 358 (27.3%) kept. In addition, 4 perch and 37 pike were recorded as caught!
  • out of the total 1,310 brown trout caught, individual records of length and/or weight were reported for 1,179 brown trout and included individuals between 110 mm and 770 mm in length and between 4 oz (113 g) and 11 lb 5 oz (5,132 g) in weight.

Calculations of catch-per-unit-effort over the entire fishing season produced figures of 0.494 fish per boat per hour fished for brown trout caught and 0.135 fish per boat per hour fished for brown trout retained. So, on average throughout the season, each boat (regardless of the number of anglers in the boat) appears to have caught 1 fish every two hours or so.

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).

  • 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 dotted horizontal line shows the 0.494 trout caught per boat per hour fished
  • The bold dotted orange line is less meaningful, merely representing the number of brown trout kept (as opposed to released) per boat per hour fished.

Historical Catch rates

 

At first glance, the 2013 result of 0.494 trout caught per boat per hour fished looks really positive.  The only year since 1975 to achieve a higher catch ratio of brown trout was 1989 when the ratio hit 0.6.  If the catches of brown trout & rainbow trout were combined, then the catch ratios of 1993 & 1999 would also have been slightly higher than last year.

Although the 2013 result is very encouraging, one needs to input a 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 0.494 is almost certainly higher than it would have been if every boat in every session had completed a catch survey card.

Nevertheless, the 428 cards representing 2,649.5 fishing hours is felt to be a meaningful sample.  The survey is being repeated this year when hopefully we can have nearer 1,000 cards submitted.  CEH have also added a request for anglers in the boats with catch survey cards to put in the first part of their post code (ie KY13 ) so that they can track what distances anglers have travelled to come to Loch Leven – we hope that little extra info won’t put people off completing the cards!

If you would like to hear more about what CEH have learnt from last year’s Catch Card Survey and indeed their water quality monitoring results, we are proposing to hold a Loch Leven Anglers meeting next month to which everyone is cordially invited.

LOCH LEVEN ANGLERS MEETING

at 6.30PM on THURSDAY 15th MAY

BOATHOUSE BISTRO, KINROSS

ALL WELCOME 

The CEH team led will make presentations on both the fish population and catch surveys as well as water quality results.  However, much of the meeting will be more of an informal discussion as CEH and Loch Leven Fisheries seek feedback from anglers on all aspects of fishing on Loch Leven.  The results and feedback will obviously form a key part of the ongoing OpenNESS project.  The bar will be open and we will be providing eats.  We hope lots of you will come along to what should be a very interesting evening.

Cormorants on Loch Leven

Finally, we cannot end without giving everyone an update on cormorant numbers at Loch Leven as they are always at the very top of anglers’ hate lists.  SNH continue to do regular counts of cormorants and their latest updated results including 2013 are shown in the 2 charts below, the first showing the peak numbers and the second showing the average count during the year.

Peak Cormorant Numbers

Peak Cormorant Numbers

Annual Average Cormorant Numbers

Annual Average Cormorant Numbers

The results indicate a steady state for the last two years.  Every cormorant is one too many but these sort of counts (average 142 up to the end of Jan 2014) are probably sustainable on a loch the size of Loch Leven.  It is perhaps slightly surprising that the increasing fish population from the CEH hydroacoustic surveys is not showing through in increased cormorant numbers as yet but it would be no surprise if there started to be a greater correlation between the two surveys if the fish population continues to increase.

We continue to press SNH for permission to conduct a further study on the feeding habits of cormorants on Loch Leven.  Obviously this would require a limited cull of cormorants in order that their stomach contents can be analysed.  Previous studies along these lines were made by what is now Marine Scotland (previously FRS Pitlochry) in, from memory, about 1991 and 2001. A further study is arguably now due but has as yet not been sanctioned by SNH.

In 2001,  for example, we were still actively stocking both brown trout & rainbow trout and FRS found that 85% of the cormorants’ diet (by mass) comprised trout with Perch & Sticklebacks accounting for 7% each. FRS estimated that the cormorants were consuming 81,000 brown trout (range 42,000 – 128,000) and 5,000 rainbow trout (range 1,000 – 12,000) during the 7 month period from Sep 1998 – Mar 1999. These projections by FRS were fairly staggering figures when you bear in mind that anglers were catching on average 6,000 brownies and 13,000 rainbows on average each year between 1996 & 2000.

Currently, both peak and average cormorant counts on Loch Leven are just under half what they were back in 1991.  Also, our suspicion is that the 85% figure for the percentage of the cormorant diet will have dropped sharply due to the recovery in perch & stickleback numbers which have resulted from the greatly improved water quality.  Nevertheless, it would be nice to know whether a proper scientific analysis of the current cormorant diet would back up this hypothesis – hopefully SNH will come round to supporting a limited cull for research purposes because it would undoubtedly improve our knowledge.

If you are interested in reading the actual summary findings of the 2001 FRS Loch Leven Cormorant Study, click on the link below

FRS Cormorant Survey 2001

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