Many will know that Loch Leven is one of the most researched fresh water lochs / lakes in the world with scientific research having been carried out in various forms for almost 200 years. However, it was in the 1960s that a more structured research programme of water quality monitoring on Loch Leven was instigated and is still continued today by the NERC Centre for Ecology & Hydrology (CEH).
More recently, a few years ago, at the instigation of Denise Reed from Scottish Natural Heritage, a new group was set up called the Loch Leven Fish Research Group which meets annually to discuss the fish aspect of the loch. Not before time, I hear you say! In addition to Loch Leven Fisheries and SNH, the group includes members from CEH, Marine Scotland (previously FRS Freshwater Laboratory in Pitlochry) and the River Forth Fisheries Trust.
Since 2008, Ian Winfield of CEH has been conducting annual hydroacoustic surveys of the loch (as well as less frequent gill-netting surveys) in order to try to get a better feel for the fish population of the loch in terms of trends in numbers and sizes of fish. Last week, he produced the following update for us
CEH LOCH LEVEN FISH STATEMENT (6th March)
Since 2008, Loch Leven’s fish community has been assessed periodically by the Centre for Ecology & Hydrology through at least annual hydroacoustic surveys and less frequent scientific gill-netting surveys. All of these activities have been undertaken in close collaboration with Loch Leven Fisheries and other local bodies. Some of this work was presented at the World Fisheries Congress held in Edinburgh during May 2012. Encouragingly, the results show that the fish populations of the loch are responding to recent improvements in catchment management and are generally increasing in abundance. Perch are becoming more diverse in size and, more importantly, the brown trout population dominates the fish community in terms of weight. Individual trout are in excellent condition. Night-time hydroacoustic surveys carried out in August from 2008 to 2012 have shown general increases in the abundances of small- and medium-sized fish, and a particularly sustained increase in the abundance of fish longer than 250 mm (approximately 10 inches). Netting shows the larger fish to be dominated by brown trout.
Trend in small fish numbers in Loch Leven
Trend in medium size fish in Loch Leven
- Trend in large fish in Loch Leven
Trend in overall fish numbers in Loch Leven
Whilst the actual numbers themselves should not be taken literally, the important thing from the fishery’s point of view is that there has been an upward trend in the fish population since 2008/9. This seems to back up anecdotal evidence from anglers who, when conditions were favourable (which alas did not happen too frequently last year), reported brief periods when large numbers of fish were clearly in evidence on the surface covering large areas of the loch.
Encouragingly, Ian Winfield’s fish surveys also indicate a good spread across all age groups. There were a lot of young fish seen last year which augurs well for the future but the number of large fish (classed as 250mm+) also seem to be steadily rising.
Why is the fish population increasing? To be honest, nobody really knows for certain but there are likely to be a number of contributing factors. For example
- The main thrust of CEH research at Loch Leven over the last 40 years has been the monitoring of water quality and they report a sustained /continuing improvement, particularly with regard to the presence of phosphates & nitrates in the loch. This improvement has been most noticable in the last 5 years or so when water quality & clarity reached levels where weed growth etc really started to kick in. Weed growth is now prolific throughout much of the loch to the benefit of the aquatic ecosystem. The fact is that food is now in abundance, as evidenced by the lovely condition of trout being caught.
- There is no doubt that natural recruitment of trout from the burns has recovered enormously over recent years, leading to an increasing supply of young trout making it to the loch. Whilst the last few summers have been disappointing from a weather point of view, the relatively high levels of rainfall have kept plenty of water in the burns which has helped the fry develop. With farmers rarely requiring to extract water to irrigate their crops, there have been few if any cases of burns seeing stretches drying out and affecting the local fish population.
- Changes in agricultural practices have seen the conditions in most burns improve dramatically from a hatching and rearing point of view. Fields are now mostly left with a buffer zone rather than being ploughed right up to the edge. The benefit of this has been that less silt has been washed into to the burns during periods of wet weather, therefore leaving them in much cleaner, more pristine condition.
I am sure there are many other contributory factors as well. And it is not just the brown trout population that appears to be recovering – numbers of perch, pike & stickleback also seem to be on the up too. Generally speaking, therefore, Loch Leven is in pretty good shape and it is a really encouraging story when you consider that it is only 2 decades since Scum Saturday (13th June 1992) when the algal blooms hit national headlines and the loch appeared to be ‘dying’ and in dire trouble. The transformation has been extraordinary.
Finally, a little bit about the angler’s arch enemy, the cormorant. Not surprisingly, we keep a very close eye on numbers here because they undoubtedly caused an enormous amount of damage during the Nineties in particular. The Fishery became involved in an arms race with them where there was only going to be one likely winner – the more we upped the numbers being reared in our ponds for stocking in order to counteract the levels of predation by cormorants, the more they just brought in reinforcements from the Firth of Forth and the North Sea!
At the recent meeting, SNH produced the following charts showing peak and average cormorant numbers on the loch where they do regular counts.
Loch Leven – Peak Cormorant Counts
Loch Leven – Mean Cormorant Counts
These charts show clearly the drop off in cormorant numbers that followed first the cessation of stocking of rainbows and then subsequently the stocking of brownies as well. Over recent years, peak numbers have plateaued at around the 200 level whereas average numbers are just showing signs of gently picking up again from the recent trough.
Looking on the bright side, the gentle upward trend could be taken as a positive. There is no more efficient an angler than the cormorant and they are not going to stay at Loch Leven if there are only meagre pickings to be had. It might be argued that the recent rising trend in average cormorant numbers simply reflects the rising trend in the fish population.
There is another reason why we are not overly concerned at the moment. When stomach contents of cormorants in the past have been analysed by FRS Freshwater Laboratory in Pitlochry (now Marine Scotland), it was found that 90%+ consisted of trout. However, the recovery in the perch & stickleback populations have given the cormorants an alternative quarry and we suspect that the percentage of trout in their diet will have fallen dramatically. Our somewhat unscientific observations of what they have regurgitated etc suggest that perch & stickleback are making up a major part of the diet of younger birds in particular and that it is only the older birds that have developed or retain a taste for trout. We have asked for another scientific survey (from a limited cull) to be carried out in order to build on the 2 previous surveys and it is likely this will go ahead in due course once facilities to analyse the stomach contents are available.
Finally, for sake of completeness when talking about Research, you will fall off your chairs in excitement to learn that Loch Leven has been selected as one of the 26 case studies in a major new research project called OpenNESS which gets underway properly next week in Helsinki and will last 3 years. The Loch Leven Case Study is headed by CEH and the Fishery (Kinross Estate Company) has signed up as a partner and will be involved during the course of the project. Basically they will be looking at how freshwater ecosystems and biodiversity support local services such as fishing, water supply, conservation, tourism, etc., and how competing needs can be balanced. Anyway, we are off now to Helsinki braving -15 C temperatures where hopefully it will all become much clearer!!
OpenNESS – 26 Case Studies
OpenNESS – Loch Leven