WTT Blog Posts

Low flows and salmonid rivers: an update

Jess Picken was the first to contribute to our new series of guest blogs in which she outlined plans for her PhD. And clearly, she has been busy! She is back with an update already...

To recap on my previous post, numerous studies have reported that low flow reduces the density of salmonids within streams. What is not so well-known is what, or how, other parts of the salmonids’ ecosystem are also affected by low flow. Riverflies and other aquatic macroinvertebrates make up a large proportion of juvenile salmonid diet, which is subsequently reflected in salmonid growth rate, condition and survival. Understanding how the availability of these macroinvertebrates changes with reduced summer flow is important to help conserve fish species of high UK and European importance.

My life at the moment... macroinvertebrates down the microscope!

My experimental study sites are three carrier streams of the River Itchen where complete control of the flow is achieved by sluice gates at the top of each stream. During the summer, the sluice gates were lowered in order to experimentally induce low-flow conditions. Each stream experienced a four-week low-flow treatment, reduced by 90% (Red9), 50% (Red5), or not altered as a control (Cont). Riverfly and macroinvertebrate sampling occurred before (Bef), during (Dur) and after (Aft) each flow treatment (ie following reinstatement of ‘normal’ flow by opening the sluices), and taken to the laboratory for identification. To decipher the results, the codes in parentheses identify each event and where, so for example: Bef*Red9 is a sample taken from the stream before the flow was reduced by 90%

Now... don't panic.... let me walk you through what this plot means!

Picken PhD ordination invertebrate community Itchen

It shows that in the before (Bef*) and (Dur*) samples, macroinvertebrate communities were relatively similar in all flow treatments (Cont/Red9/Red5). We know this because all the Bef* red arrows and all the Dur* red arrows are roughly pointing in the same direction. Black arrows indicate the riverfly and macroinvertebrate species that together make up the whole community.

However, what stands out (to me at least!) is in the after low-flow sampling occasion (Aft*). Aft*Cont is pointing in a markedly different direction to the Aft*Red9 and Aft*Red5. This indicates that following on from re-instatement of normal flow, there was a shift in macroinvertebrate community. Furthermore, the severity of low flow (ie 90% or 50%) treatments are actually remarkably similar. One explanation for this may be that during low-flow, parts of the river bed may become exposed and dry out. Therefore, when flow is reinstated, opportunistic invertebrates may move on to these 'new' patches of stream that would not have become available if low-flow had not occurred. There is one more years’ worth of data to collect and analyse to see if this interesting pattern holds. Watch this space....

Please contact me if you have any questions or comments!

Jessica (j.picken@qmul.ac.uk, or @jesspicken)

Malcolm Greenhalgh's June Blog

In this blog post, WTT Vice President Malcolm Greenhalgh reflects on climate, weather, pollution and sea trout fishing prospects for July. 
Malcolm lives in the north west of England, not dry dustbowl that is the south east !

I am now not only a believer in global climate change, but I am 90% sure that Homo sapiens is probably responsible for the change that has occurred since at least the middle of the 20th century.

During the Industrial Revolution we did alter the climate here in the north of England through the use of coal fires in the Dark Satanic cotton and woollen mills of Lancashire and Yorkshire and in homes and other factories. The effects of the soot laden smoke, with its high acidic nature, resulted in dense smogs in the lowlands and in very acid rainfall in the moorland through to the control of air pollution by Act of Parliament in the 1950s. I once remember cycling home in smog and not being able to see where I was on the road where we lived. I had to get off my bike and walk down the pavement until I recognised our stone gate posts. Visibility was barely five yards. On another occasion I guessed at where I had to turn right in the car and found myself driving up someone’s drive about thirty yards from the avenue into which I wanted to turn right! And in 1969-70, when I was working on the wildlife of the Pennine moorlands that separate Lancashire and Yorkshire, I learned from work done by earlier naturalists in the 19th century that large tracts of Sphagnum bog and its associated special flora, including species like sundew, had been exterminated by the extreme acidity. This loss had resulted in bare peat that had eroded on the flat moorland summits, leading to more violent spates in the rivers fed by these moorland bogs.

Today this sort of pollution is greatly declined and here in northern England conservation organisations are working hard to get the natural moorland flora and its associated bogs back in place. It’s just that the form of pollution has changed and is less visible. And its effects are a general warming-up of the world climates and more extreme weather.

In my book The Ribble, written a decade ago in 2007-2008 and published in 2009, I wrote, of the upper Ribble valley, “In 1969 I was out on the moors on 77 days scattered throughout the year...I experienced snowfall in every month from November to April, and lying snow from November to mid-May.....in 1999 I spent 40 days in the upper dale and saw no sleet or snow falling.” This last winter (2016-7) I recorded snow falling in the head of the Ribble very early morning on the 2nd January, the night of 12th-13th January, on the 9th February (flurries), 28th February but it quickly turned to rain, and on the morning of my 71st birthday, April 25. But in every case it melted within a very few hours. Lying snow is now quite a rare event here in northwest England, causing panic amongst commuters for whom driving in snow is outside their experience.

For extreme weather,  take this June:  we had a heat-wave 17th-21st with perhaps the hottest June day on record, and very heavy rainfall on 5th-7th (with damaging gales), on the 10th and continuously or almost continuously from the 27th to the 30th (it is still raining as I write this on the 30th at 4.53pm).  Outside the heat-wave, my diary records most days having a very cold wind from the NE to NW. Go back to Junes in the 1960s, 1970s and 1980s, these extremes were rarely encountered then.

The consequence is that, throughout the British Isles judging from correspondents, we have had the worst first four months of the trout fishing season since recording began.  
                                               *                                        *                                            *
So much for the bad news; now for the good.

Those of you old enough will remember dear old Hugh Falkus’s two BBC wildlife programmes in the “World About Us” series, Self Portrait of a Happy Man and Salmo the Leaper, made in the 1970s. In those Hugh showed us pools on the Cumberland Esk that held great shoals of sea trout, and through the 1960s and 1970s rivers like the Esk, Lune and Dovey were famed for their vast numbers of sea trout. Then, from about 1980, the number of sea trout declined; I fished the Falkus Esk from 1987-98 and, though I did catch a few sea trout each year there, never saw such big shoals in the pools. This decline was down to a collapse of the Irish Sea herring due to gross overfishing, which was down to the usual EU sea fisheries maladministration. This not only affected the sea trout, but also other fish and sea birds that relied heavily on juvenile herrings (i.e. whitebait) for their food. The Irish Sea cod stocks collapsed (no longer could I go out off the Lancashire coast and catch lots of cod up to the teens and more in weight). And the common tern colonies that I had studies in the late 1960s and 1970s and which then generated well in excess of one young to fledging per pair per summer, a production that resulted in the colonies increasing, collapsed.

In 1981 commercial fishing for herring was banned in the Irish Sea, another case of closing the door after the horse has bolted. That was 36 years ago, and in the many years since the herring population very, very slowly increased so that in the last two or three years it has come close to its 1970s level. Cod stocks are recovering and from cursory observations of one Ribble ternery this spring it seems that their productivity is on the ‘up’.

Likewise the sea trout. The often torrential rains of 5th to 10th June resulted in some good runs of sea trout and the rains that came on the 27th and have only just cleared up (it is 5.30pm on the 30th June and it has just stopped raining) have brought up the rivers again and sea trout will be heading upstream.

Get out there, for July promises to be a belter for sea trout!

Malcolm Greenhalgh

Here’s one I made earlier….The Hoffer Brook

By Rob Mungovan, WTT Conservation Officer for East Anglia and Central Region

As a new starter my colleagues have been interested to know what projects I’ve already delivered whilst working as a local authority ecologist. I’m able to explain all the usual techniques of channel narrowing and bed raising but one novel approach keeps getting more questions. So the clearest way to explain it is to write it down, and include some pictures. The one below hows the restored brook. 

Hoffer brook 1

The restored (or re-built?) brook. The new bed is suspended over soft silt through the use of grass mesh.

The Hoffer Brook is a small degraded chalk stream in Cambridgeshire that runs for approximately 8km. It suffers from very low flows in its upper reaches but lower down it has a permanent flow. I have known the brook all my life as it forms the parish boundary to the village where I grew up, and I can be certain that there were no trout in it from the late 1980s through to recent years. The reason for the lack of trout was a combination of factors but the main bottleneck seems to have been the almost entire lack of spawning substrate and subsequent fry and parr habitat  - these are the shallow streamy bits which are in stark contrast to the deep slow moving features that the brook exhibits. Water quality of the brook was considered to be high.

The Beds, Cambs and Northants Wildlife Trust, and specifically their Water for Wildlife Officer Ruth Hawksley, have been crucial partners in the delivery of this project. The Wildlife Trust was able to secure funding and oversee the contractual arrangements, while I worked-up the detailed spec and made sure that the final delivery was correct on the ground.

Having played and swum in the brook on many occasions it had always been known that some sections were pretty treacherous and appeared to have no natural bottom or hard bed. This was investigated by a topographical survey and sure enough there were areas that were significantly over-deep. But was this really the work of past over-dredging?

“Not entirely” is the conclusion that I have since come to. Whilst historic dredging may have over-deepened much of the brook, the local topography appeared to be showing a pattern to the deeper sections. What I believed we had encountered was the edge of the chalk escarpment running down to the lower ground. If the land had sunk and sea levels risen what I think we’d found were some areas of ancient silted shallow valleys. There was also another explanation to throw in, that of pingo ponds. This part of Cambridgeshire has a number of post-glacial groundwater-fed ponds still in existence. These ponds formed where an up-welling of ground water froze to form ice lenses which then over thousands of years of freeze and thaw, resulted in round ponds scattered across the landscape. The brook appears to have linked some of these ancient ponds.

Hofffer brook 2

A “bottomless” part of the brook, note the top of the ranging pole. This part is now ~0.5m deep. 

So in terms of restoration, what were we really restoring? The truthful answer is that no-one exactly knows how the brook was more the fifty years ago. Old enclosure maps showed that some of the meanders were being straightened way back. But the hardest, and probably most damaging works came in the mid-1970s when the brook was dug deep and some residents recall it being a mess that simply never recovered to its former state. Older residents of Foxton say how the brook was more open, had a shallow gravelly bed in many places, had a swift flow, and a range of fish species could be seen including brown trout (and to my knowledge they were not stocked). So the usual techniques of channel narrowing, brushwood ledge creation and bed raising all seemed appropriate but how much gravel would be needed? A huge amount. An amount that would have been prohibitively expensive. A new approach was therefore needed.

I’d been thinking this one through for years. I’d toyed with the idea of lining the bed so that the silt could actually become an aid to the project. But how, and with what materials?

One idea had been to use wooden trellises cut down to shape to form a support lattice over the silt. It is known that once wood is in anaerobic silt it hardly degrades but how would we have kept the trellis from tipping as material was placed on it, and what if gaps had formed between the trellis? That could be very dangerous and we could have lost the gravel.

Through brainstorming, Ruth and I (plus my Dad I’ll admit) came up with the approach of using vehicle tracking mesh (Grassform’s grass mesh, light duty) the type that is stretched out over soft ground. The advantage of using the mesh was that it could be cut to the correct width and then be stretched out for a full 30m length (the rolls of mesh came in 2m x 30m lengths).

Hoffer brook 3        Hoffer brook 4

     

 

 

 

 

 

 

 

Threading the rope through the mesh to support it.                                 Sinking the mesh, supported by rope from posts.

 

hoffer brook 5                  hoffer brook 6

 

 

 

 

 

 

 

 

The mesh is flexible so a vegetated margin can be retained as found

 

Hoffer brook 7               Hoffer brook 8

 

 

 

 

 

 

 

 

Note the springs arising from the bed. If a woven mesh was used the natural upwelling could have been interfered with.

Further benefits of the grass mesh were that is could be fixed together using numerous cable ties to make a strong and fail safe join. Then the matting could have 8mm polypropylene rope threaded through the mesh. These lengths of rope were then tied to 100mm chestnut posts that had been driven into the bank at 1m intervals. This effectively allowed the mesh and rope combination to be supported on top of the silt providing a strong but slightly adaptable support onto which we could then re-create a chalk stream. See photos above.

This idea came from those times where you are hitting away at posts only for them to suddenly push through a hard layer to move rapidly into a softer layer. I can envisage times where during the land forming processes of the last ice age there must have been episodes of meltwater which would have moved huge quantities of coarse material and distributed them randomly across the floodplain. In subsequent millennia our rivers have been acting to sort and move this material. I was simply trying to re-create one of the gravel lenses that rests on the softer valley mires.

On to this supporting layer we were able to undertake the usual approach of re-building a small chalk stream. Obviously, we had to take more care when placing the material initially; we couldn’t simply start at one end, we had to layer it all so that the whole mesh was tensioned equally. This was particularly important where we had tried to cut the mesh to accommodate a meander. I will admit that even today the mesh at one point still flexes up.

We did all of this based on sound judgement and a little bit of managed risk taking. We only did the first 45m using this method and were then able to use a more conventional approach, Ideally, I’d have liked to have got more depth of gravel down (we did get ~0.5m in places) but we were restricted by the proximity of a  railway line and its overhead wires; consequently we didn’t get the upper reaches as elevated as we ideally would have. And we never knew how much weight the chestnut posts would support before being pulled out of the soft ground (we were confident of the load-bearing capacity of the rope and mesh).

Hoffer brook 9

Work completed. Note that this photo location is the same point as where the 2m ranging pole had previously been pushed entirely into the soft bed. 

 

But most importantly we have been able to restore/re-create a chalk stream habitat where once a spring-fed ditch had run for at least a generation. We’ve now got brown trout, minnow and brook lamprey spawning and attractive beds of water crowfoot and starwort.

To date the work has held up absolutely fine. It has experienced some of the wettest weather in recent times where the open mesh would have had no problem in allowing natural springs to rise from the bed again (which can be a problem where tightly woven membranes are used as liners), the chestnut stakes are still in place (even though some were hit by my old drainage team during their flail cutting operations which took out a couple of pieces of rope). And the new brook looks perfect.

Hoffer brook restored

Photo taken about 14 months after completion. 
The water crowfoot was planted as there was none upstream to colonise this area.

 

Lessons learned:

1.       The use of Grassform’s grass mesh to support aggregate over deep silt can work on small watercourses.

2.       It is not necessary to desilt a channel before undertaking such work (I had instructed a partial desilt simply to remove the dense Phragmites reed growth but the presence of deep silt can be looked upon as an indicator of where the new bed should perhaps be).

3.       Use rope of 8mm thickness or upwards (due to a shortage of materials we did use some finer rope and it did look stretched but has not broken).

4.       The placement of the supporting posts should be a close as can be afforded (this is important as if one support fails there will be others to take the load).

5.       Instead of leaving the chestnut posts slightly proud (where one would have thought a drainage operative would have noticed them!), it would be better to cut them off flush at ground level and then to cover them over with 100mm of soil. That way the posts would have been entirely protected from mechanical destruction, the risk of interference by people and/or degradation by environmental factors.

6.       This approach is not suitable where future watercourse maintenance may necessitate the use of an excavator (this work could be destroyed very easily by one dig and pull of a bucket).

7.       I have no first-hand experience to say if this approach could withstand high velocity flood flows but then you don’t usually get high velocity scouring flows where very deep silt has accumulated for decades. But my gut feeling is probably “yes” as the gravel is effectively protecting the mesh beneath it and as long as the gravel is not lifted then the structure beneath should be fine.

8.       For a greater degree of confidence in the durability of this type of approach some form of metal support post could be used such as a universal beam. A universal beam could be drilled through to create an anchor point for polypropylene rope or even steel cable (we’d decided against scaffold poles as they were too narrow in diameter and were likely to be pulled over when ground conditions became soft).

What makes an apex predator: the ferox trout

I have to admit, the topic of this research really floats my boat (as you may have noticed from the latest Salmo Science Spot)…. I spent several years trying to convince people that perched at the top of the Loch Ness food web was not an elusive plesiosaur but something much, much more sexy. Ferox! So I’m really pleased that the newly doctored Martin Hughes has taken time out to precis his completed PhD, but it does mean I’ll have to review the WTT ferox pages with his new findings.

The brown trout, Salmo trutta, is an incredibly diverse species. Individuals from the same population can adopt completely different life history strategies, which are often given vernacular names. For example, some S. trutta remain in small freshwater streams their entire lives; these are referred to as resident trout. Others migrate into large rivers or lakes to complete their life cycle and retain the name brown trout, but some that migrate into estuarine waters are referred to as slob trout and others that fully migrate into marine waters before returning to natal streams to spawn are called sea trout. One relatively understudied life history is that of ferox trout. ‘Ferox’ which is Latin for ‘Fierce’ is aptly used for these large piscivorous trout which can grow to large size (14kg UK record) and are exceptionally long lived (23 years oldest UK record- reports of 39 years old in Norway). Their impressive growth potential and life span combined with their rarity and near mythical status only adds to the allure to both anglers and scientists alike.

Astonishingly, even in the 21st century we know relatively little about these incredible fish. Genetic studies throughout the 1980s in Ireland only added to the mystery surrounding ferox trout. Pioneering research by Andy Ferguson and his colleagues at Queens University Belfast found some populations of ferox trout were actually part of an ancient lineage of trout, believed to be one of the original lineages that invaded the British Isles after the glaciers retreated approximately 12,000 years ago. This raised interesting questions surrounding the evolutionary history of ferox trout and their taxonomic classification. In 2008, ferox trout were reclassified as Salmo ferox which was recognised by the IUCN. The IUCN however classified Salmo ferox on the Red List of Threatened Species under the category of ‘Data Deficient’ meaning the risk of extinction of ferox trout could not be assessed due to a lack of scientific data. In other words, these potentially vulnerable and genetically distinct fish are not afforded any sort of protection!

I was first introduced to ferox trout during my undergraduate degree at the University of Glasgow and after a meeting with the enthusiastic Alistair Thorne at the Marine Scotland Faskally Laboratory, I was hooked. I based my undergraduate dissertation on ferox trout and working alongside another ferox trout legend, Alan Kettle-White from the Argyll Fisheries Trust (and WTT Trustee), I collected data on ferox trout and brown trout from Loch Awe.

Hughes ferox wild trout trust blog awe

A mirror still Loch Awe in the summer of 2011 (just think of the midges…)

My undergraduate research led directly into a postgraduate degree which was funded by a large EU project called ‘Integrated Aquatic Resource Management Between Ireland, Northern Ireland and Scotland’ or IBIS (http://www.loughs-agency.org/ibis-projects/). As an IBIS PhD student, I was tasked with conducting investigatory research into ferox trout which would inform the scientific community, fishery managers and policy makers. I designed my research to help inform stakeholders on the geographic distribution of ferox trout, gain a greater understanding of their basic underlying biology (including physiology and behaviour), and also investigate differences between brown trout and ferox trout co-habiting the same lake.

Hughes ferox wild trout trust blog

The IBIS project partners the Loughs Agency, Queens University Belfast and Glasgow Univeristy, funded by the European Union.

My first research project on ferox trout distribution was based on an extensive literature review and analysis of angling books going back hundreds of years. After almost 2 years of research, I found 192 lakes in Scotland have evidence of supporting a ferox trout population. I also investigated the environmental characteristics associated with these ferox trout populations and found a strong correlation between lake size, lake depth, and the presence of Arctic charr Salvelinus alpinus.  The strong relationship between ferox trout, habitat size (lake size and depth) and prey species (Arctic charr) are indicative of most apex predator populations. This research was published in the Journal of Fish biology in 2015 and tells us two main things:

  1. Ferox trout populations are relatively rare given the amount of lakes in Scotland they could be found in, and
  2. Ferox trout, where they do exist are most likely fulfilling the role of an apex predator. Given the disproportionate importance that apex predators play in ecosystems globally, ferox trout are likely to be providing an essential ecological service in those lakes.

The main focus of my research was to investigate underlying biological differences between ferox trout and brown trout. Traditionally this is done using an experimental design called a ‘common garden experiment’. Common garden experiments, as the name suggests, are often used with plants, where plants are raised in a common environment (same temperature, same light exposure, same water availability etc.) so any observed differences between plants are inherited differences and not differences caused by the environment. Essentially you are controlling the external environment at all times. The same can be done for animals raised from birth. However, the logistics and animal husbandry involved makes such an experiment much more complex, and combined with the rarity of ferox trout populations, this was a monumental task. In fact, there were no published records of anyone having collected eggs from spawning ferox trout.

I began my quest for ferox trout eggs in October 2013, in the Highlands around Loch Maree, with the help of Peter Cunningham of the Wester Ross Fisheries Trust. During the following weeks of sampling numerous rivers in the Loch Maree catchment, we caught lots of brown trout but not a single ferox. It turned out to be one of the mildest Octobers on record and the rivers were extremely low. It looked like we might miss our opportunity to catch any spawning ferox trout for another year which would change the planned research considerably.

We identified the river most likely to support spawning ferox trout and waited for the rains to arrive. In early November, the first substantial overnight rainfall was forecast and we assembled a team to be on the river first thing in the morning. Within 2 hours we had captured 3 female ferox trout and a number of males, including a huge male fish which looked like he’d been through the wars, and won! We quickly transported the fish to nearby holding tanks before spawning them to create full sibling groups and hybrid crosses between ferox trout and brown trout.

There is a critical ‘water hardening’ period after fertilisation in which eggs cannot be moved after a 48-hour period or they perish as they become sensitive to movement and light. The water temperature of the eggs also had to be kept cooler than 8 degrees centigrade at all times or I'd risk losing the clutches. After successful fertilisation I stored the precious cargo in flasks surrounded by ice and water in a small blue ford van. With the windows down and AC on I left Wester Ross at 9pm and drove down to the Scottish Centre for Ecology and the Natural Environment (SCENE) on Loch Lomond, wearing two scarfs, a thermal hat and a pair of gloves, wincing at every bump in the road. I arrived at the field station about 3am and began to carefully transport the eggs into specialised temperature-controlled fridges. After an hour of careful negotiation, the final clutch was placed into the temperature control unit.

hughes ferox wild trout trust blog

Ferox trout eggs at a crucial stage of development, the ‘eyed’ stage.

For three months I visited the lab to check the eggs (including Christmas day!) and was ecstatic (relieved) to find they had survived the journey and the embryos were developing well. On the 5th of January 2014, most of the eggs began to hatch and for first time we had juvenile ferox trout in a common garden experiment. Now the real work could begin.

Over the following year all fish were held at the same water temperature and fed the same amount of food allowing me to measure differences in yolk sac size, head shape morphology, metabolism, lipid deposition and mortality rate.

hughes ferox alevins wild trout trust blog

3 day old hatchlings known as alevins. The ferox trout had much larger yolks sacs which is unsurprising as larger females produce larger eggs with larger yolk sacs. What is important, however, is the larger the yolk sac the higher the rate of survival.

Perhaps one of the most interesting experiments we conducted was investigating the dominance behaviour between juvenile brown trout and ferox trout. As juvenile trout form dominance hierarchies in natal streams, with the most dominant individuals enjoying better feeding opportunities, we postulated ferox trout would be more dominant than brown trout. Our reasoning behind this hypothesis was in order to feed on other fish, ferox trout must reach a large size quickly. It is therefore more important for a juvenile ferox trout to reach a large size by acquiring more food than it is for a juvenile brown trout. Our results were staggering! Ferox trout were more dominant than brown trout in 90% of the trials.

hughes ferox

Photograph of fish behaviour footage. On the left is a submissive brown trout juvenile and on the right a light-coloured, dominant ferox juvenile.

Given we had controlled environmental effects and controlled the size of each individual (each fish was matched to within 2mm length of one another), this behaviour is likely inherited from ferox parents. If this behaviour is replicated in the wild, it suggests that juvenile ferox trout may be predetermined to become large piscivorous trout, which supports the evidence provided by Ferguson that ferox trout may be distinct from other brown trout.

The results from the other physiological experiments will be published later this year and therefore cannot be discussed ahead of time. However, more interesting distinctions have been discovered. Like all good research, I have more questions than I started off with and I would like to thank all who have been involved in the research and continue to support the project. If you would like to find out more information, please like the ‘The Ferox Project’ FaceBook page where I will continue to update the progress of the research, follow me on Twitter @DrMartinHughes and watch the full behaviour video behaviour video here (https://www.youtube.com/watch?v=hHBIqHyIe0s&feature=youtu.be)

Martin Hughes (m.hughes.4@research.gla.ac.uk)

 

Related publications

Hughes, M.R., Dodd, J.A., Maitland, P.S. and Adams, C.E., 2016. Lake bathymetry and species occurrence predict the distribution of a lacustrine apex predator. Journal of fish biology.

Hughes, M.R., Van Leeuwen, T.E., Cunningham, P.D. and Adams, C.E., 2016. Parentally acquired differences in resource acquisition ability between brown trout from alternative life history parentage. Ecology of Freshwater Fish.

Malcolm Greenhalgh's May Blog

Malcolm Greenhalgh is a WTT Vice President and contributes the occasional blog post. Here are his thoughts from the end of May. 

At the Wild Trout Trust’s weekend in Derbyshire, of which more anon, everyone from the four corners of our island agreed that this was the coldest spring, and worst spring, for trout fishing that they could recall. Up to the last fortnight May, like the end of March and April, the weather was dominated by strong winds from a direction veering from north-west to east-north-east. As my old friend and mentor that late Jack Norris used to say, “The flies won’t hatch in numbers and the trout won’t rise properly in a wind like this. A cold downstream wind is the kiss of death for dry fly fishing!” (see my little book The Floating Fly for more of dear old Jack). So I saved petrol instead of wasting it by not driving miles to the rivers other than a couple of visits when the weather was not too bad, including an afternoon on the Hodder during the summery heat wave that brought spring, and May, to an end.

The good news is that reports indicate that our rivers have good heads of wild brown trout and grayling. Mick Addison for instance, told me of a visit to the Eden where trout were feeding everywhere on the minutest “little black things” but that he couldn’t catch them even on a size 22 dry fly. Similarly Chris Hosker and Keith Owen visited a lovely beat of the Wharfe on the cold 6th May and found fish everywhere, some of them nice and large, and they caught a few on their nymphs. It was the same on the middle Ribble and upper Hodder.

Incidentally, Chris and Keith stopped off on their way to the Wharfe at Gargrave to support Bradford City AA’s fund raising event for the Wild Trout Trust, who have done some magnificent habitat work on the Aire following the Environmental Agency’s idiotic habitat mismanagement.

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I am now going to speak to the converted, for nitwits don’t read anything, it seems.

I don’t kill wild brown trout, despite the fact that I like to eat trout. Instead I eat top quality rainbow trout, usually by hot smoking them over cherry and hickory and making a pate by whizzing their lovely meat with lemon juice and crème fraiche in the blender. My favourite haunt is Frank Casson’s Barnsfold Water, for the two lakes making up the fishery have great buzzer hatches and the trout raised by Frank and his son Richard are as good to eat as any.

I arrived on the 25th and, having said ‘Hello!’, went to a favourite spot where food accumulates and the trout rise to eat it. Three others were fishing further along the bank and six others scattered elsewhere on the bank of this lake. As I tackled up I noticed that trout were rising.

The leader I use here is 16-feet in length and has two droppers so that I can fish a ‘washing line’ of three flies, each of which matches one of three common foods. Because there was a nice south-westerly breeze, which might bring lots of landbred insects onto the water, I tied my Foam Beetle (size 14) to the top dropper. A fortnight earlier all the trout came to that, and when I came to clean the brace I took home an autopsy revealed lots of tiny black beetles in their stomachs.  Middle dropper was a black Suspender Buzzer (14), one of the greatest inventions of the late John Goddard that matches a midge pupa hanging down from the surface film prior to the adult stage emerging . And on the point I knotted a size 16 black Cul de Canard Midge.

First cast a trout took the CDC Midge, a lovely fat trout with perfect fins and weighing about three pounds. That went in the bag. I cut off the soggy successful fly and knotted on a fresh CDC Midge. I made the second cast of the day and a trout took immediately, again a lovely fish not quite as large as the first. It too went into my bag. The next cast also caught a fish (three in three casts!) as did another about ten minutes later. With finger, wrist and elbow joints giving me pain it was time to stop: playing Frank’s trout really does hurt!

One of the trio fishing further along the bank came over as I discombooberated my tackle.

“What did you get them on?”

“A size 16 CDC dry fly.”

“Never heard of it.” I showed him the four that were drying in my tweed hat. 

“You never caught them on them little flies!” I took the two trout from my bag and spooned them, revealing stomachs nearly packed with tiny black flies and beetles.

“I didn’t think big trout would eat such little things. We thought they would like big things like this.” He showed me a box of reservoir ‘lures’.

“I fish a washing line of three small flies...”

He interrupted: “A what?”

I write magazine articles and have written a few books on flies and fly fishing. Why don’t people read them? Of course, they use the internet. Google ‘Buzzer’ and see the confusing mass of patterns, ideas, ‘rigs’ on offer. But it’s simple: in all real fly fishing you just match what the fish are eating where, in the water, the fish are feeding.

                       *                             *                             *

A special plea. I am primarily a fly fisherman for wild trout and grayling and there are two organisations whose drive is for the protection of these two beautiful species, the Wild Trout Trust and the Grayling Society. I feel privileged to be a vice president of the first and trustee of the second. In spring the WTT has its conference weekend and in autumn the Grayling Soc has theirs. Both are wonderful events, with the Sundays giving members opportunity to fish some of the greatest rivers in Britain. On the Saturdays the presentations are always fascinating and I learn much from them.

But not enough folk who also enjoy fishing for wild trout and grayling are members. They...you (if you are not)...ought to be members, for the rivers and lakes, and the wild trout and grayling that they....you (if you are not)...enjoy, they need your support.

THE WILD TROUT NEED YOU!

THE GRAYLING NEED YOU!

Guest Blog from Malcolm Greenhalgh

Malcolm Greenhalgh is one of the WTT's Vice Presidents and we will be featuring occasional blog posts from him. This one is from April:

For the first time since 1965 I have bought a brown trout and coarse fish England & Wales Rod Licence instead of a salmon and migratory trout licence. The reason is that I can no longer spend hours cast-cast-casting because of arthritis in my right forelimb. A few years ago, when the arthritis began to hinder my fishing, I went to the medic’s who sent me for some X-rays. Then I was summoned to the clinic at Wrightington where a specialist in the condition told me, as he perused the X-rays, “As bad a case of RSI as one can come across! What repetitive job have you done that has caused such damage to all these joints?”

“I do a lot of fly-fishing,” I replied.

“I don’t know much about that. Exactly what do you do when you are fly-fishing?”

I nipped out to the car and returned with the rod that is permanently there, just in case, and I took him through every stage of a single-hand trout cast. As I did so, he pointed out, on the X-rays, the damage done to the ball-and-socket joint of my right shoulder, to the hinge joint of my elbow, and to the several joints in my carpals, metacarpals and phalanges of my wrist and hand. I found the experience fascinating, but was not surprised when the man said, “There’s not much we can do for you other than advise you to do less fly-fishing and offer you painkillers.”

So the heavy double-handed salmon rods were abandoned first; then I ceased travelling to the wilder parts of Scotland and Ireland for the loch/lough fishing and making hundreds of casts every day for up to three weeks solid; and gradually I have restricted myself just to dry fly/emerger fishing, casting to trout (and grayling) that are rising to a hatch. [I did only 20 minutes tenkara with Chris Hosker, caught some grayling, but then had to pack in because my arm was gone.] That doesn’t bother me greatly because I have been fortunate enough to have travelled widely with my fly-rods and caught enough fish to satisfy anybody, plus some biggish ones, like a 37lbs salmon from the Tana, a ferox brown trout that was over 15lbs that had temporarily left its Swedish lake for the outflowing river, and a zonking ‘lake trout’ that is really a char from a Canadian lake. And I have my diaries that recorded all these happy events.

On the 25th of this month I reached the age of 71 years and cannot believe that the 1970s and 1980s, which seem just a few years ago, were three and four decades ago, and that the 1960s are half a century in the past, or 1/21 of the time since the Battle of Hastings! Only this morning I was chatting with our editor Mark Bowler about dear old Hugh Falkus and his sea trouting. I knew Falkus well through the last eleven years of his life (he died aged 78) and I never saw him fishing, other than perhaps having the odd cast. Towards the end of his life I asked that great angler and lovely man, Fred J. Taylor, how much fishing he did: “Well, Malcolm,” he said, “I sometimes pop down to the river in a morning, trot a worm, and if I catch a half pound perch I take it home for lunch! I’ve given up trying to make big bags.”

So even though I am not fishing anywhere near as hard as I did a decade and more ago, I am still fishing.

In recent years the Ribble and lower reaches of the Hodder have seen fabulous hatches of grannom. On one visit to the Ribble at Gisburn I found a corner sheltered from the wind, watched a lovely lot of grannom egg-laying and had three nice brown trout, one at 16”. On a second I could find nowhere out of the icy breeze, saw a few grannom when the wind dropped, but saw only two trout rising and managed to catch one. My fly: Elk hair caddis minus body hackle; it’s dead easy to tie...a body of dubbed brown fur and a wing of bleached elk tied low over the body.

I also visited LFFA’s water on the upper Hodder, after Andy Ralph sent me an enthusiastic email extolling the virtues of its fly hatches. It was so cold that I saw not one other idiot on the entire beat. There, large dark olives were the chief fly hatching, but again in very tiny flurries. But most interesting was a trickle of iron blue duns. Donkey’s years ago I used to see good hatches of IBDs on the Aire, Ribble as far downstream as Mitton, middle Lune and Eden. I have seen fewer in recent years. On the chalk streams IBDs were the fly they all raged about when there was a cold wind blowing in spring, and here it was on a cold spring day. I saw some grayling rising in one lovely pool (I try not to catch them when they are out of season as they don’t ‘count’ and it is illegal to cast to a grayling deliberately when they are out of season). Then I saw two fish rising that I thought were not grayling: one was, a lovely fish in the order of 13-14” length, and the other was a brown trout of about 10”. They took a size 16 dry Iron Blue Dun that is one of about a dozen I tied probably 20 years ago and that have been in the box since then, neglected.

One evening I was booked to give a talk to Catterall Gardeners’ Association on growing great salads (like Oliver Edwards, I grow lots of fruit and vegetables). Getting there for 7pm would have involved the M6 motorway around Preston at rush hour. Instead I drove in the early afternoon to Barnsfold Water, which is only a short country lane drive to Catterall village. Bright sunshine and a chilly easterly did not bode well, but I fished my dry buzzers and emergers hard for a couple of hours until the old arm told me to stop. So I de-tackled, sat in the sun and ate a banana and an orange. As I did so, the wind dropped, the temperature rose, buzzers hatched and two other fly-fishers had two and three nice rainbow trout in about 15 minutes. Then the wind returned, the hatch ceased, the trout went down, and I headed off to talk about a huge range of salad crops that you can grow easily, including a leaf mix called Hertie Gerty’s Frilly Mix.

Tight lines

Malcolm Greenhalgh

The riparian invasion: salmonid friend or foe?

'Tis the season to bash balsam - if you don't know how to, check out the definitive guide from WTT chum, Theo Pike, for guidance! Timely then for a new blog focussing on invasive plants. Alex Seeney from the Centre for River Ecosystem Science (CRESS) at the University of Stirling, is battling with balsam and knotweed from a more academic angle, and below gives an overview of some his research to date. This valuable work is supported by Scottish Natural Heritage.

Some of the most diverse and complex habitat types in aquatic systems are found at the interface between terrestrial and aquatic communities – the riparian zone. These diverse, dynamic systems provide an ecologically important buffer between land and water, and as such they are of particular importance to the health and quality of the waterways they border.

knotweed invasive species INNS riparian river Seeney trout

The dynamic nature of riparian zones increases their susceptibility to invasion, particularly by non-native flora, which use river networks like blood vessels around the human body, spreading through river corridors and using these systems for both short and long distance dispersal. Invasion of the riparian zone by non-native flora is commonly perceived as a negative occurrence and has a sizeable economic impact, with an estimated £5.6 million spent in 2010 to control riparian Japanese knotweed (Fallopia japonica) in Great Britain.

It is also important to consider how these plants may affect salmonid fish, especially considering the high economic value of salmonids to angling and the status of the Atlantic salmon (Salmo salar) as a protected species in the UK. My aim is to tease apart the effects of invasive riparian plants from a range of environmental factors that affect salmonids, quantifying not only the direction, but also the size of these effects. In doing so, we might take a step towards justifying the large amount of funding that is currently being provided to treat these plants. Monitoring both aquatic and terrestrial invertebrate communities is also important, as both provide essential food sources for salmonids residing in streams and rivers. Changes in the physical and chemical composition of riparian plants may affect both invertebrate groups, altering the type and volume of these food sources entering the aquatic food web.

Whilst searching for field sites for my PhD project in early 2015, the height and depth of the previous year’s invasive plant stands were easy to see. The stands were often wider than the small tributary streams they bordered and as such, tracking the spread of these plants along river corridors is quite a simple process. However, relating the presence of invasive plant stands to hydrological processes and furthermore, to critically important terrestrial and aquatic invertebrate food sources, is more difficult. In order to help me achieve this, a range of samples have been collected over a 2 year fieldwork period during 2015-16.

Alex Seeney PhD fieldwork salmonid trout habitat invasive species river riparian

Field sites were selected based on suitable habitat for adult salmonid spawning and juvenile survival. Sites were located on small tributary streams, and were chosen in communication with fisheries trusts to ensure populations of Atlantic salmon and brown trout (Salmo trutta) in tandem with established stands of Himalayan balsam (Impatiens glandulifera) and Japanese knotweed. A pair of uninvaded control sites were located upstream from a pair of invaded treatment sites on each waterbody, giving a total of 24 sites across 6 rivers. Treatment sites were chosen under the criteria that invasive plant coverage must exceed a minimum of 50% (based on a visual assessment).

In order to monitor physical changes at sites, thalweg profiles (showing the main flow of the river) and cross-sectional riverbed profiles were recorded each year, in tandem with pebble counts to monitor changes in grain size diversity and distribution. Full depletion electrofishing surveys were carried out during summer 2015 and 2016, covering a minimum of 100m2 where possible at all sites. Weights and fork lengths were recorded for all Atlantic salmon and brown trout, and a small number at each site were anaesthetised and a gastric lavage (stomach flushing) was performed to assess diet composition. This procedure was regulated under Home Office licence (Home Office Project Licence PPL 70/8673).

invertebrate riverfly monitoring seeney trout INNS invasive species balsampitfall invertebrate INNS seeney trout

A full range of terrestrial (Malaise and pitfall traps) and aquatic (Surber and drift nets) invertebrate samples were taken during the summer of 2016 to assess the terrestrial and aquatic communities present at each site. These samples will be used to show how the abundance and diversity of both aquatic and terrestrial invertebrate communities (and therefore the availability of prey items for salmonids) differs between invaded and uninvaded sites. Furthermore, vegetation surveys were carried out at all sites during the summer of 2016, which will allow invasive coverage to be expressed on a continuous (as opposed to binary) scale.

The range of samples collected over the past 2 years provides an exciting opportunity to investigate how invasive riparian plants may be affecting juvenile salmonids on a fine scale. Stomach contents and invertebrate samples from both years will be used to assess how different salmonid age classes are utilising the available habitat and food sources between invaded and uninvaded sites. I also plan to use electivity indices to look for evidence of any preferential feeding habits, giving an insight into the effects of invasive riparian plants on species and age-specific groups of juvenile salmonids.

I would welcome any questions or comments, and hope to provide an update in the coming months once the bulk of these samples have been processed – over 50,000 invertebrate samples identified so far!

Alex (alex.seeney@stir.ac.uk or @AlexSeeney)

Can watercress farming directly impact fish communities in chalk streams?

Asa White gets to call wading around in the Bourne Rivulet work! Our research interests in chalk streams have some parallels. While I am curious as to how a colourless, odourless gas (methane) contributes to the fuelling of their food webs, Asa is trying to understand how an equally invisible chemical is affecting invertebrate and fish life. Here, he outlines his research plans and offers up the experience of electric fishing - read on! 

Watercress is native to the chalk streams of southern England, and has been harvested for millennia. In the early 19th century, the advent of the railway made commercial production viable for the first time. A growing London market supplied by trains (the famous ‘Watercress Line’ being one) led to an explosion in the number of watercress farms throughout the south of England. Historically, watercress was grown in gravel beds irrigated by water diverted from chalk streams, but hygiene concerns now oblige growers to irrigate their beds using fresh water abstracted from boreholes. In both instances, the water used to irrigate the beds is discharged into adjacent chalk streams. 

Today, much watercress farming is highly mechanised, with modern practices allowing for year-round production. A number of large-scale modern watercress farms now house washing and packing facilities for the watercress farmed onsite in addition to imported salad leaves. Abstracted water is used to rinse the crop prior to packing, with the spent water returned to the chalk stream. Typically it is first filtered through screens and channelled into settlement ponds or through watercress beds to reduce sediment load before discharge. While sediment is often effectively treated, there is growing concern that the mechanical abrasion of watercress and other salad leaves during the washing process - and to a lesser extent during the harvesting of watercress - induces the release of phenethyl isothiocyanate (PEITC) into the receiving water course.

Watercress possesses the glucosinolate-myronase system; regarded as the classic defence against herbivorous organisms. Damage to watercress tissue initiates the synthesis of PEITC, the compound which gives watercress its hot peppery taste. While pleasing to many human consumers, myself included, PEITC has unsurprisingly been shown to be toxic to a number of aquatic and terrestrial invertebrates. A number of surveys by the Environment Agency have demonstrated altered invertebrate communities downstream of watercress farm outflows. Some expected taxa were found to be absent, along with a significant depletion in a staple year-round component of salmonid diets, Gammarus shrimp. While the impact on invertebrates has been documented, until now the effect of watercress farming on fish populations hasn’t received attention.

Asa White PhD research Brighton watercress salmonid

My research at the University of Brighton comprises three main elements. Firstly, using electric fishing surveys around three watercress farms over two years, I am ascertaining whether discharges are having a population-level impact on fish communities. Secondly, at the same sites, I am surveying habitat suitability for salmonids in terms of the physical habitat and prey species abundances. Lastly, I am running laboratory ecotoxicology experiments to study the effects of PEITC on fish. The aim of the research is understand what effect, if any, watercress farming is having on fish populations. Should a negative impact be uncovered, then mitigation strategies to lessen the impacts could be developed to ensure that fish populations in chalk stream headwaters flourish. 

It is well-known that early life stages of fish are particularly sensitive to pollutants. With salmonids and bullhead spawning in the upper reaches of chalk streams where watercress farming typically occurs, there is a very real potential for developing embryos to be exposed to PEITC. To assess the impact of PEITC exposure, I am running a series of ecotoxicology experiments on fish eggs in the laboratory.  Brown trout are the main focus due to their high value within chalk stream ecosystems, but I have plans to experiment with grayling and at least one cyprinid species.  Last October I exposed brown trout eggs to a range of PEITC concentrations throughout embryonic development. I am currently repeating the experiments using photoperiod eggs obtained this March that I am expecting to hatch around the end of April. If the results from the first experiment are accurately replicated, then I have a very strong dataset for publication. Watch this space!    

My study sites are located around three watercress farms and include sites immediately upstream and downstream of discharges at each farm for direct comparison. To investigate the downstream extent of perturbations caused by discharges, each farm has two further sites, one approximately 500m and another between 1km and 1.5km downstream.  One of the farms is on The Bourne Rivulet, a tributary of The Test in Hampshire, and is owned by VItacress Salads Ltd, a company which has generously part-funded the research through the Vitacress Conservation Trust. This reach boasts a very well-regarded wild trout fishery made famous by Harry Plunket Greene in his 1924 book on fly fishing Where the Bright Waters Meet. A further two farms in Dorset complete the sites; one on the River Frome and the other on the River Crane, a tributary of the River Stour. Both of these farms are located on SSSI perennial chalk river headwaters. So far I have surveyed these sites during spring and autumn in 2016, and I will return to survey them again this year.

The electric fishing at each site is carried out over 100m runs using a standard three run depletion method.  The catch is identified to species level and the standard length and weight of each individual recorded before being returned to the river unharmed. It is important to tease out whether any differences in trout numbers seen downstream of watercress farm discharges are related to the discharge or merely a function of the prevailing conditions such as substrate type, hydrology, plant cover, geographic location etc. I’m addressing this by using detailed habitat surveys fed into HABSCORE software. HABSCORE outputs an estimate of expected salmonid abundances for the given physical habitat, which can then be compared to the actual abundances found during electric fishing.

Using standard three minute kick and sweep sampling, the invertebrate fauna is being surveyed to see if the abundance of suitable prey species for fish is present. In addition, I am using biotic indices to assess whether the invertebrate assemblages indicate that the sites are impacted by pollution. Should fish populations be found to be altered below watercress farm discharges, we can then begin to ask ‘are differences in expected fish populations driven by changes in prey availability, lack of suitable habitat or a direct effect of PEITC in discharge water – or a combination of these factors?’

So far I have enjoyed data collection in the field for two seasons, and have been very fortunate to have been blessed with fine weather. The main catch from these chalk streams is naturally brown trout and bullhead with the occasional eel. However, the downstream site on the Frome has proved to hold a diverse range of species. I pulled out a magnificent grayling on my last visit, along with pike, stone loach, minnow, perch and brook lamprey. One of the joys of electric fishing is one never really knows what one is going to find, and if it is in the run, it will come to you! My survey work would be impossible without the help of volunteers. Students from the Aquaculture and Fisheries department at Sparsholt College inevitably turn out to be real gems, bringing with them lots of experience. However, I always train any volunteer who hasn’t had electric fishing experience and they soon get the hang of it. I’m always on the lookout for volunteers, so if any readers of this blog would like to try their hand at electric fishing and habitat surveying, I would be delighted to hear from you!  

Asa White (A.White2@brighton.ac.uk)

Little weirs and little fishes

Jeroen Tummers has been wrestling with more holistic fish passage solutions during the course of his PhD with Dr Martyn Lucas at Durham University (Martyn gave us a few comments about this project on a previous WTT Blog). But below, we hear from Jeroen himself, about his valuable contribution.  

One of the most important components in restoring impacted river systems, given their linear nature, is to reconnect habitat patches separated by obstacles to free movement. Fishes rely on free access to habitat upstream, and downstream, in a river system to spawn, for feeding, or for finding refuge. Since the presence of these three functional habitat types can change both spatially and temporally, it is important that free access is retained.

But movement between these habitats can be severely hindered by man-made in-stream structures. It is generally agreed that high-head structures like dams have a profound effect on the survival and sustainability of fish assemblages. However, what about low-head structures? Each individual low-head structure might have a lower impact but as they are much more abundant, their combined fragmentation effect may be even greater. How much more abundant these low-head obstructions are compared to high-head ones is not well known, but this is currently being analysed across Europe for the AMBER project (Adaptive Management of Barriers in European Rivers), which I currently work on. Driven by national and international legislation, such as the EU Water Framework Directive (WFD), obstructed surface waters must be reconnected so that fishes may move freely up and down the river.

Jeroen tummers phd wtt blog

 

 

 

 

 

 

 

 

An example of a formerly fragmented river system is the River Deerness, which I studied during my PhD, and which was failing WFD classification for fish because of a lack of connectivity. At the start of my studies, eight obstacles to fish movement were present in the catchment, of which - over the course of two years - six were either completely removed or modified by provision of a fishway, to facilitate both up- and downstream fish passage. The aims of my study were to evaluate how effective these different solutions were for mitigating river habitat fragmentation for a range of fish species and age groups.

I used a combination of approaches, including capture-mark-recapture of a wide range of fish age groups: for smaller individuals a Visible Implant Elastomer (VIE) was used as mark; larger fish were tagged with a Passive Integrated Transponder (PIT), allowing individual recognition in following recapture surveys. This was conducted in 20m zones directly up- and downstream of each obstruction, before and after its removal or modification. For young-of-the-year (YOY) fish, VIE markings were site, zone and survey session specific, allowing for in-depth analysis of spatial behaviour of very young fish in the context of habitat fragmentation, an approach rarely used before.

Results showed quantitative, medium-term evidence of increased dispersal of smaller, more sedentary species (e.g. European bullhead, Cottus perifretum) as well as of larger, more mobile fishes (e.g. brown trout, Salmo trutta) past each of the restored sites, but not at the two unmodified control structures. It is worth highlighting that YOY trout showed increased upstream as well as downstream dispersal rate over modified or removed structures relative to unmodified control sites as well, with similar good quality habitat available at all sites. Young trout suffer from competition for food and space in a population which reaches carrying capacity, a situation which may be exacerbated close to a barrier. My results demonstrate that as soon as a reach is reconnected by barrier removal or modification, these young fish can disperse up- and downstream to areas of lower density with less competition. 

The study is innovative because it combines multiple approaches to evaluate the effectiveness of a range of fish passage solutions, in both up- and downstream direction, in a fragmented system for fishes with poor and good swimming capacity (bullhead and brown trout, respectively) following a before/after intervention method. It also shows that conventional techniques used to evaluate a given fish passage solution, such as sporadic semi-quantitative electric fishing surveys downstream and upstream of a (modified or removed) obstruction, may not be very effective. We have published part of this work in the journal, Science of the Total Environment, available here.

It is hoped that in years to come, in addition to an increase in abundance and area of occurrence of species already present in the Deerness, Atlantic salmon (Salmo salar) may also return to spawn, as habitat suitable for redds is available throughout much of the middle and upper Deerness. Salmon has been almost absent in the last few decades in the greater Wear catchment, but is now on the increase in the main river. So hopefully, this work will help river managers like the Wear Rivers Trust to make better informed decisions on how to deal with obstructions on fragmented systems.

Jeroen (j.s.tummers@durham.ac.uk)

Land and lake interconnectedness

On a day-to-day basis, most of my time as WTT Research & Conservation Officer is devoted to river habitats, but in my academic role at the Lancaster Environment Centre, lakes are a long-standing focus of my aquatic ecology research. A Natural Environment Research Council grant allowed a colleague from Cambridge and I to convene a workshop with scientists from Canada, the USA and Sweden, with common interests in how lake food webs may be fuelled by subsidies from the land. The output from that meeting is a recently published synthesis based upon data from ~150 northern lakes. Most of the planet's freshwater lakes and rivers that we associate with various ecosystem services, like fisheries and water supply, are found in the northern hemisphere, a region that is changing rapidly in response to human activity intertwined with shifting climatic trends.

The classical view of lake food webs is that of algae produced via photosynthesis forming the food base for zooplankton (such as water fleas or Daphnia) that is then munched by fish. We do not contest this because algae are typically a very high quality diet, and many lakes contain plentiful algae. However, in lakes that do not contain adequate supplies of such a resource, or during winter when it is less available or completely unavailable, then organic matter from the land, derived from the breakdown of terrestrial plants, can still be used via intermediary bacteria. And this situation is more common than you might imagine.

Our team used stable isotope techniques as natural ‘tracers’ of diet and analysed over 550 zooplankton samples from lakes across a range of conditions from the boreal zone to the sub-tropics. In half of the zooplankton samples, these tiny animals comprised at least 42% terrestrially-derived material. In some instances, terrestrial food sources accounted for up to 83% of total zooplankton biomass.

By concurrently investigating how physical characteristics of the land draining into lakes influenced the observed terrestrial subsidies in the lake food webs, we could identify certain key determinants. Differences in tree cover, vegetation density, soil carbon concentrations, lake area, and lake perimeter can all potentially impact upon the amount of terrestrial matter available to aquatic life.

These widespread findings further highlight the interconnectedness of ecosystems. But they also convey an important message for those tasked with conserving and managing freshwater resources. We must understand how landscape changes, such as forest clearing or reinstatement, or agricultural practices, impact upon lakes that they adjoin or are linked to via river networks.

What does this mean for trout? Well, trout are renowned for their ability to maintain higher populations than we might expect for a given stretch of river or area of lake. That is because they can and do readily tap into food resources from ‘outside’ of the waterbody, i.e. daddy long-legs or heather flies, worms, even cicadas, mice and lemmings. However, if some of their ‘aquatic’ food is already heavily subsidised by terrestrial matter, then it is even more important for us to consider sensitive land management beyond a riparian buffer strip.

The full article for those that are brave, is available open access here: http://advances.sciencemag.org/content/3/3/e1601765

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