The ecology and invertebrate life of Shetlands many freshwater systems is possibly the least studied area of ecology in Shetland and there are almost certainly new species to find and discoveries to be made for the aspiring naturalist.
Shetland lies in the path of the Gulf Stream and consequently has a mild wet climate , the average temperature difference between the coolest winter month and the warmest summer month is usually not much more than 8 or 9 degrees centigrade. Rain fall is moderate and averages 100-130 cm per year but the relative humidity is very high at 80 - 85 percent. High rainfall and low evaporation coupled with a glacially eroded landscape of mainly impermeable rocks mean that Shetland has at least 500 lochs or bodies of water over 1 hectare and a high percentage of these contain trout.
The geology of Shetland is highly complex with a great variety of rock types all over the islands leading to a great variety of lochs with various levels of productivity however for a variety of reasons the freshwater flora and fauna is relatively uniform.
A dominant feature of Shetland is the wind, and gales occur on average 58 days a year carrying salt spray all over the islands. Consequently most lochs below about 30 feet above sea level are part brackish and lochs below about 300 feet depending on how close they are to the sea are to varying degrees brackish. The salt spray carried by the relentless wind has the effect of blurring the biological distinction between some of the acidic (unproductive) and the nutrient rich productive lochs in terms of the distribution of species that live in them.
PH readings from various surveys of Shetland lochs show PH levels at the low end of scale of around 4 -5 for some of the small lochs and lochan’s that lie on peat land. Readings of around 5-6 for lochs laying on hard impermeable rocks like granite. Depending on underlying geology and water catchment area there are plenty of lochs with a PH over 7 with a few over 8 and 9 that can be considered ecologically productive from an angling point of view. It’s worth noting that even the lochs that have PH below 7 that lay on nutrient poor hard base rock or that are influenced by acidic peat run off can be very good for fishing . Large areas of peat land have given rise to many peaty acidic lochs; however some of these peaty lochs especially if they are shallow and low altitude can be remarkably productive in part because of the effect of salt spray.
There are not many lochs over 700 feet above sea level the highest is at 1220 feet with a large proportion around the 300-350 contours. The few surveys show little altitudinal variation in the flora and fauna but this could be an interesting area of research for aspiring naturalists.
The isolation of Shetland means that some species that are common on mainland Scotland are not present or have a very limited distribution, for example the damsel fly has only been recorded in a few locations in the north mainland and Yell.
There are no coarse fish in Shetland and the six species of fish that live in the freshwater lochs all have a high tolerance for salinity.
Brown Trout, Eel and Three Spined Stickleback are very widely distributed. Arctic Char lives only in the loch of Girlsta. Salmon are less common than they once were but still exist in a few locations, and flounders can also be caught in the lochs that are connected to the sea and are occasionally caught on the fly rod. Stocks of sea trout seem to be making a slight recovery thanks to a heavy restocking programme by the Shetland Anglers Association.
The relentless wind means the water surface is rarely still and the continual wave action hinders the emergence of plants through the water surface meaning that submerged plant species are generally more numerous. Shallow Sheltered bays promote plant growth which in turn acts as trout larders though some such bays are popular nursery areas containing lots a small trout.
It is worth taking note as to what shore takes the brunt of the prevailing wind where plants can find it hard to grow with the knock on effect of creating different habitats for invertebrate species with in the loch. Stone and boulder dwelling species such as shrimp , some species of caddis and stickle back might thrive on the shore that is hammered by the wind however mud loving species such as buzzers and caenis will exist in greater concentrations in sheltered areas.
Wind stirs up particles in the water hindering the depth that the sunlight can penetrate which coupled with peat stain can also hinder or slow down plant growth and general productivity and some lochs become unfishable during periods of high wind and heavy rain because the water becomes very coloured.
Wind also creates strong vertical water movement that almost certainly restricts the thermal stratification that is a characteristic of southern still waters. The bathymetrical survey carried out by Murray and Pullar in 1910 recorded only slight vertical variations in water temperature even in the deepest lochs at the height of summer, how ever explorations with an echo sounder in various deep lochs show a large concentration of (usually non feeding) fish lie at the 22 foot depth contour which is the classic depth of the thermocline, that point where the warm water sits on top of the cold water. These seem to be resting places where the fish feel comfortable and secure because of temperature, light level and protection from predators. These resting areas are not necessarily related to an underwater feature but the feeding areas are never far away. Whether or not the thermocline exists in Shetland lochs could be an interesting area for further study.
The smaller shallow lochs warm up quickest and by mid-May can reach temperatures of over 15 degrees centigrade and in the summer temperatures approaching 20 degrees. The larger deeper lochs warm up more slowly and water temperature generally stays below 10 degrees until the end of May and even in the height of summer seldom reaches 15 degrees.
This movement and seasonal activity of the trout will vary greatly according to the weather for example if we have a mild spring invertebrate activity will be kick started into action earlier with corresponding increased activity from the trout, likewise a cold spring slows everything down.
Early season i.e. March/ April the shallow lochs will warm up quickest making them the best places to fish and weed is less of a problem. Deep lochs are not always at their best this time of year but fish can still be caught in the shallow areas. Fishing in deep water is not generally productive as even though this where a large percentage fish population might be they are unlikely to be actively feeding.
In May Fish start to move off shore into slightly deeper water i.e. 5-8 feet deep. This is the time of year when buzzers start to hatch and fish activity really comes alive and is many anglers favourite month.
By June a percentage of the fish move off shore to graze on the blooms of daphnia, invertebrate life is at its peak and the fish feed heavily. This is the magical days of the simmer dim when the sun hardly dips below the horizon invertebrate and fish activity reaches fever pitch
August can be a challenging month on the lochs as hatches of aquatic insects slow down.
September is a very good month as the trout become aggressive and territorial in preparation for spawning around October. Daddy long legs are at their most abundant this time of year and stickleback feeding reaches a peak.
It can be hard to know where to start when looking at a map of Shetland as there is so much water. The best advice is to pick a loch or area and fish it and be aware that lochs close to each other can be very different in character making for very interesting fishing for the roving angler.
A basic knowledge of the food that trout eat offers a clue to location. Find the food and we find the fish so long as the fish is secure to be there. For example the margins might be teeming with food but unless trout is secure to enter he will only go there under the cover of darkness.
The loch trout is forced to roam and forage because unlike the river trout food will not be bought long by the current. If the food is available in different parts of the loch at different times of day and year the trout has to travel from one location to another in order to survive. It is best to keep on the move till the fish are found, unless you are confident of their presence. Searching the various depths of the loch can also be crucial in locating the fish as some trout food favours different depth contours. For example daphnia moves up and down the water column according to the levels of light, blood worm feeders will be feeding head down grazing the bottom whilst at other times the fish will be looking upwards to pounce on the tasty dung fly that might be blown on the water or to grab the sedge skittering across the surface.
Just because an area is good on one occasion it doesn't mean it will be good on the next. The hot spot will not always be hot, its attraction lies in the production of food and sense of security offered to the trout which will vary according to the conditions. Aquatic creatures favour different environments and hatch at different times so it follows that different areas of loch will have different degrees of popularity with the fish depending on the availability of food. Some places might offer all round fodder ,others are seasonal, some spots work well in the day and others work best at night
In times of feast it seems that every fish will feed, and big hatches can make the trout behave recklessly seeming to be unconcerned at the angler’s presence and like a pack of wolves they out compete each other to get to the food first. In these big hatches of food the trout can become preoccupied with a single food item and close imitation might be essential, however the trout might be locked into the way the food is acting and the fly has to be fished accordingly. In these big hatches trout can sometimes be easy to catch but are more often than not frustratingly difficult to catch.
In times of famine the fish might need persuasion and this when attention grabbing patterns can get a response. Remember that trout do not feed all the time and for large periods of time they dormant and in cold weather they almost shut down all together, but there are usually a few active fish that can be caught which is possibly nature’s way of ensuring survival of the species.
It can be a very good tactic to get to know a few waters very well by spending a seasons on them in all conditions, enabling a picture to be built up of where and when to expect the dominant seasonal food source to be and consequently where the trout will be in any given condition.
The sheer quantity and diversity of lochs in Shetland coupled with the fact that most are set in stunningly beautiful scenery make Shetland a brown trout angler’s paradise.
The following pages many of which are in various states of creative growth and flux offer an over view of some of the key foods that that trout eat and flies used to imitate them. Tight Lines.
Paul Bloomer
References and further reading
Bridget R C - Loch fishing in theory and practice
Coutts J Game fishing in Shetland Highlands and Islands development board Inverness 1967
George D G and Maitland P S: the freshwaters of Shetland physical and morphometric characteristics of lochs institute freshwater biology Edinburgh Freshwater biology (1984). 14 p 95-107
Headley S The Loch Fishers bible
Headley S Trout and Salmon Flies of Scotland
Maitland P S and East K. The freshwater fish fauna of Shetland, the institute of terrestrial ecology Edinburgh. 1976
Murray, J and Pullar, L (1910) Bathymetrical survey of the freshwater lochs of Scotland Edinburgh 1910.
Johnson J L. A Naturalists Shetland 1998
Sandison B – The Trout and Salmon Lochs of Scotland
Shetland Anglers Association - Trout fishing in Shetland 1981 and 1998
Unknown authors - various loch surveys in the records of Shetland biological records centre Lerwick
.
Shetland lies in the path of the Gulf Stream and consequently has a mild wet climate , the average temperature difference between the coolest winter month and the warmest summer month is usually not much more than 8 or 9 degrees centigrade. Rain fall is moderate and averages 100-130 cm per year but the relative humidity is very high at 80 - 85 percent. High rainfall and low evaporation coupled with a glacially eroded landscape of mainly impermeable rocks mean that Shetland has at least 500 lochs or bodies of water over 1 hectare and a high percentage of these contain trout.
The geology of Shetland is highly complex with a great variety of rock types all over the islands leading to a great variety of lochs with various levels of productivity however for a variety of reasons the freshwater flora and fauna is relatively uniform.
A dominant feature of Shetland is the wind, and gales occur on average 58 days a year carrying salt spray all over the islands. Consequently most lochs below about 30 feet above sea level are part brackish and lochs below about 300 feet depending on how close they are to the sea are to varying degrees brackish. The salt spray carried by the relentless wind has the effect of blurring the biological distinction between some of the acidic (unproductive) and the nutrient rich productive lochs in terms of the distribution of species that live in them.
PH readings from various surveys of Shetland lochs show PH levels at the low end of scale of around 4 -5 for some of the small lochs and lochan’s that lie on peat land. Readings of around 5-6 for lochs laying on hard impermeable rocks like granite. Depending on underlying geology and water catchment area there are plenty of lochs with a PH over 7 with a few over 8 and 9 that can be considered ecologically productive from an angling point of view. It’s worth noting that even the lochs that have PH below 7 that lay on nutrient poor hard base rock or that are influenced by acidic peat run off can be very good for fishing . Large areas of peat land have given rise to many peaty acidic lochs; however some of these peaty lochs especially if they are shallow and low altitude can be remarkably productive in part because of the effect of salt spray.
There are not many lochs over 700 feet above sea level the highest is at 1220 feet with a large proportion around the 300-350 contours. The few surveys show little altitudinal variation in the flora and fauna but this could be an interesting area of research for aspiring naturalists.
The isolation of Shetland means that some species that are common on mainland Scotland are not present or have a very limited distribution, for example the damsel fly has only been recorded in a few locations in the north mainland and Yell.
There are no coarse fish in Shetland and the six species of fish that live in the freshwater lochs all have a high tolerance for salinity.
Brown Trout, Eel and Three Spined Stickleback are very widely distributed. Arctic Char lives only in the loch of Girlsta. Salmon are less common than they once were but still exist in a few locations, and flounders can also be caught in the lochs that are connected to the sea and are occasionally caught on the fly rod. Stocks of sea trout seem to be making a slight recovery thanks to a heavy restocking programme by the Shetland Anglers Association.
The relentless wind means the water surface is rarely still and the continual wave action hinders the emergence of plants through the water surface meaning that submerged plant species are generally more numerous. Shallow Sheltered bays promote plant growth which in turn acts as trout larders though some such bays are popular nursery areas containing lots a small trout.
It is worth taking note as to what shore takes the brunt of the prevailing wind where plants can find it hard to grow with the knock on effect of creating different habitats for invertebrate species with in the loch. Stone and boulder dwelling species such as shrimp , some species of caddis and stickle back might thrive on the shore that is hammered by the wind however mud loving species such as buzzers and caenis will exist in greater concentrations in sheltered areas.
Wind stirs up particles in the water hindering the depth that the sunlight can penetrate which coupled with peat stain can also hinder or slow down plant growth and general productivity and some lochs become unfishable during periods of high wind and heavy rain because the water becomes very coloured.
Wind also creates strong vertical water movement that almost certainly restricts the thermal stratification that is a characteristic of southern still waters. The bathymetrical survey carried out by Murray and Pullar in 1910 recorded only slight vertical variations in water temperature even in the deepest lochs at the height of summer, how ever explorations with an echo sounder in various deep lochs show a large concentration of (usually non feeding) fish lie at the 22 foot depth contour which is the classic depth of the thermocline, that point where the warm water sits on top of the cold water. These seem to be resting places where the fish feel comfortable and secure because of temperature, light level and protection from predators. These resting areas are not necessarily related to an underwater feature but the feeding areas are never far away. Whether or not the thermocline exists in Shetland lochs could be an interesting area for further study.
The smaller shallow lochs warm up quickest and by mid-May can reach temperatures of over 15 degrees centigrade and in the summer temperatures approaching 20 degrees. The larger deeper lochs warm up more slowly and water temperature generally stays below 10 degrees until the end of May and even in the height of summer seldom reaches 15 degrees.
This movement and seasonal activity of the trout will vary greatly according to the weather for example if we have a mild spring invertebrate activity will be kick started into action earlier with corresponding increased activity from the trout, likewise a cold spring slows everything down.
Early season i.e. March/ April the shallow lochs will warm up quickest making them the best places to fish and weed is less of a problem. Deep lochs are not always at their best this time of year but fish can still be caught in the shallow areas. Fishing in deep water is not generally productive as even though this where a large percentage fish population might be they are unlikely to be actively feeding.
In May Fish start to move off shore into slightly deeper water i.e. 5-8 feet deep. This is the time of year when buzzers start to hatch and fish activity really comes alive and is many anglers favourite month.
By June a percentage of the fish move off shore to graze on the blooms of daphnia, invertebrate life is at its peak and the fish feed heavily. This is the magical days of the simmer dim when the sun hardly dips below the horizon invertebrate and fish activity reaches fever pitch
August can be a challenging month on the lochs as hatches of aquatic insects slow down.
September is a very good month as the trout become aggressive and territorial in preparation for spawning around October. Daddy long legs are at their most abundant this time of year and stickleback feeding reaches a peak.
It can be hard to know where to start when looking at a map of Shetland as there is so much water. The best advice is to pick a loch or area and fish it and be aware that lochs close to each other can be very different in character making for very interesting fishing for the roving angler.
A basic knowledge of the food that trout eat offers a clue to location. Find the food and we find the fish so long as the fish is secure to be there. For example the margins might be teeming with food but unless trout is secure to enter he will only go there under the cover of darkness.
The loch trout is forced to roam and forage because unlike the river trout food will not be bought long by the current. If the food is available in different parts of the loch at different times of day and year the trout has to travel from one location to another in order to survive. It is best to keep on the move till the fish are found, unless you are confident of their presence. Searching the various depths of the loch can also be crucial in locating the fish as some trout food favours different depth contours. For example daphnia moves up and down the water column according to the levels of light, blood worm feeders will be feeding head down grazing the bottom whilst at other times the fish will be looking upwards to pounce on the tasty dung fly that might be blown on the water or to grab the sedge skittering across the surface.
Just because an area is good on one occasion it doesn't mean it will be good on the next. The hot spot will not always be hot, its attraction lies in the production of food and sense of security offered to the trout which will vary according to the conditions. Aquatic creatures favour different environments and hatch at different times so it follows that different areas of loch will have different degrees of popularity with the fish depending on the availability of food. Some places might offer all round fodder ,others are seasonal, some spots work well in the day and others work best at night
In times of feast it seems that every fish will feed, and big hatches can make the trout behave recklessly seeming to be unconcerned at the angler’s presence and like a pack of wolves they out compete each other to get to the food first. In these big hatches of food the trout can become preoccupied with a single food item and close imitation might be essential, however the trout might be locked into the way the food is acting and the fly has to be fished accordingly. In these big hatches trout can sometimes be easy to catch but are more often than not frustratingly difficult to catch.
In times of famine the fish might need persuasion and this when attention grabbing patterns can get a response. Remember that trout do not feed all the time and for large periods of time they dormant and in cold weather they almost shut down all together, but there are usually a few active fish that can be caught which is possibly nature’s way of ensuring survival of the species.
It can be a very good tactic to get to know a few waters very well by spending a seasons on them in all conditions, enabling a picture to be built up of where and when to expect the dominant seasonal food source to be and consequently where the trout will be in any given condition.
The sheer quantity and diversity of lochs in Shetland coupled with the fact that most are set in stunningly beautiful scenery make Shetland a brown trout angler’s paradise.
The following pages many of which are in various states of creative growth and flux offer an over view of some of the key foods that that trout eat and flies used to imitate them. Tight Lines.
Paul Bloomer
References and further reading
Bridget R C - Loch fishing in theory and practice
Coutts J Game fishing in Shetland Highlands and Islands development board Inverness 1967
George D G and Maitland P S: the freshwaters of Shetland physical and morphometric characteristics of lochs institute freshwater biology Edinburgh Freshwater biology (1984). 14 p 95-107
Headley S The Loch Fishers bible
Headley S Trout and Salmon Flies of Scotland
Maitland P S and East K. The freshwater fish fauna of Shetland, the institute of terrestrial ecology Edinburgh. 1976
Murray, J and Pullar, L (1910) Bathymetrical survey of the freshwater lochs of Scotland Edinburgh 1910.
Johnson J L. A Naturalists Shetland 1998
Sandison B – The Trout and Salmon Lochs of Scotland
Shetland Anglers Association - Trout fishing in Shetland 1981 and 1998
Unknown authors - various loch surveys in the records of Shetland biological records centre Lerwick
.