freshwater fish survived in Scotland ... 4 species native to SW Scotland .... industry. ⢠Lochs Grannoch and Dee once regarded as among the best trout fishing ...
Native freshwater fish in SW-Scotland Andy Ferguson Emeritus, School of Biological Sciences, Queen’s University Belfast
‘Freshwater’ fish • Any species that spends at least part of its life cycle in freshwater – Entire life cycle in freshwater – Breed in freshwater & adults feed in the sea – Breed in the sea & adults feed in freshwater
Freshwater fish are often overlooked • Except by anglers, and some species on the fishmonger’s slab, they are rarely seen • However FW fish are an important part of ecosystems – feed on wide range of animals & are food for other fish, birds & mammals • Truly native species • Socially and economically important to local communities and businesses
Freshwater fish • Freshwater ecosystems are increasingly threatened • Freshwater fishes are the most threatened group of vertebrates worldwide – Of c10,000 freshwater fish species, 30% are threatened with extinction (IUCN) – Largely due to human activities
Multiple factors in involved in decline • • • • • • • • • • •
acidification afforestation climate warming decline in food availability decline in water quality diffuse pollution dredging & channelization enrichment habitat damage heavy metal pollution hydroelectric and water offtake dams
• inappropriate stocking • increase in bird & mammal predators • introduction of nonnative species • lack of, or inappropriate, riparian vegetation • over exploitation • pesticides • road and culvert construction • siltation • water abstraction
Impact of last Ice Age • At last ice age maximum (18,000 yrs BP) no freshwater fish survived in Scotland
Postglacial colonisation
• Recolonisation from glacial refuge areas after glaciers retreated (c14,000 – 10,000 years BP) • Several refugia adjacent to Britain & Ireland due to lower sea level
Postglacial colonisation • At end of ice age there was no freshwater connection between Scotland & rest of Europe (cf south of England) • Only species that could live in both the sea and freshwater could colonise naturally • Native species restricted to: salmonid family; smelt; shads; lampreys; eel; (sticklebacks)
Focus on salmonids (Family Salmonidae) • 4 species native to SW Scotland – Vendace – Arctic charr – Atlantic salmon – Brown trout
Adipose fin
Vendace Coregonus albula • Widespread in Scandinavia & Russia • Rarest native fw fish in Britain – formerly only – Derwentwater & Bassenthwaite (R. Derwent) – Castle Loch & Mill Loch (Lochmaben – R. Annan)
Likely colonised from late glacial refuge in Solway area
glacial refuge Glacial refuge?
But why did vendace not colonise other lakes in the Solway area?
Socially important in Lochmaben • 2 clubs formed for vendace fishing & fun • The Scotsman 25 July 1855 – “On Thursday last, at Lochmaben, was held the annual gathering of the St. Magdalene club, whose objects are at set seasons to fish the lochs for vendace and other finny tribes, and socially to masticate the same when cooked. ..a considerable crowd of members and others collected on the shore of Mill Loch. The first haul of the net brought up about 28 dozen vendace, mostly 7” – 8” in length. Meanwhile on the Castlehill were being carried out such pastimes as foot-racing, leaping, wrestling and putting the stone...About five o’clock the outdoor recreations terminated, and the members of St. Magdalene’s adjourned to a dinner at the Commercial Inn, in which vendace formed, as a matter of course, a principal dish.”
Vendace now extinct in Castle & Mill Lochs • No vendace recorded from Castle Loch since 1912 – Enrichment due to new sewage works 1911
• Last vendace from Mill Loch 1970 – Enrichment from surrounding farmland & new housing estate, introduction of non-native bream, lowering of loch level for public access
Refuge conservation populations
• Decline in Cumbria led to vendace being introduced into lochs in SW-Scotland – Loch Skeen (nr Moffat) 1999 (Bassenthwaite) thriving population – Loch Valley (above Loch Trool) 2011 (Derwentwater) status not yet assessed
Arctic charr Salvelinus alpinus
• Widespread in Arctic region circumpolar distribution
Present today in c250 lakes in Britain & Ireland but extinct in c150 lakes (38%) where it was previously known to occur – enrichment, pollution, non-native species, climate warming • Current * Extinct
• Locally, formerly in L. Grannoch (until 1949) and L. Dungeon (until 1952 but possibly present in 1990s & still today?) – now only definitely known from L. Doon – Acidification likely cause of extinction in Grannoch & Dungeon
Loch Doon charr • Now in much reduced numbers but occasional charr still caught by anglers • Conservation refuge populations introduced (1986-90) into Talla & Megget Reservoirs – many charr present in both in 2010
Atlantic salmon Salmo salar • Present in all larger rivers locally • Spawn in tributary rivers – young live there for 1-4 years (typically 2 locally) and migrate to sea as smolts
• Feed around Faroe Islands & W. Greenland – Return after 1 winter (grilse) or 2+ winters (MSW salmon) – latter often in spring ‘Spring Salmon’
• Return with high degree of accuracy to river where born – natal homing – Earth’s magnetic field, currents & smell of home river involved
• Results in each river / tributary having genetically distinct populations with different life history & other characteristics
• Much reduced numbers compared to past • River Dee one of the best salmon rivers in 19th and early 20th Centuries
• Many other factors involved in decline both in the river & at sea
• Marine survival c30% cf 20 years ago – Increasing sea temperature & changing currents affecting food availability – also competition – Parasites eg sea lice from salmon farms – Interbreeding with escaped farm salmon – Increase in predators at sea
• Marine Scotland Regulations on salmon exploitation since 2016 – No coastal /estuary netting (haaf net exception) – Category 3 rivers catch and release only by anglers (c70% of Scottish rivers in 2018) eg Fleet, Bladnoch, Annan, Dee (Cats 1&2 – some catch)
Brown trout Salmo trutta • Economic importance of tourist and recreational trout angling – Salmon & trout anglers spend c£110 million each year in Scotland (Scottish executive 2004)
• UK Biodiversity Action Plan priority species – Although overall as a ‘species’ it is not endangered, individual populations / ecotypes are & some are IUCN red-listed as endangered / vulnerable, etc
• Scientific interest – Has become model species for studying fish population genetics and life history diversity
current native trout distribution
©Schöffmann 2013
Very high variability / diversity • The adjectives that best describe brown trout are ‘variable’ / ‘diverse’ • Brown trout is one of the most genetically & phenotypically variable vertebrate ‘species’ • While this makes it scientifically very interesting, it present a challenge for management and conservation relative to more uniform species eg Atlantic salmon
Brown trout Salmo trutta
Galloway hill lochs – not more than 10 miles apart
Trout life history variation • River resident staying within general area where born – eg where good adult feeding in spawning tributaries or impassable barrier (eg waterfall) preventing upstream return • Lake resident where entire life cycle is spent in lake & spawning takes place within lakes – Within lake spawning probably more common than currently recognised
Migratory trout 1. Migration from spawning tributary to main stem of river (fluvial potamodromous) 2. Migration from spawning river to lake (adfluvial potamodromous) – Numerically commonest LH in Scotland and most important for angling – c30,000 lochs
3. Migration from spawning river to sea (sea trout – anadromous)
Both nature (genetics) and nurture (environment) determine life history & indeed most other characteristics (as for ourselves)
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All can be present in one river system with a lake Adfluvial lake trout spawning
Lake trout feeding
Resident lake trout spawning Lake trout outlet spawning Sea trout feeding
Fluvial trout feeding
Fluvial trout spawning
waterfall
River resident trout spawning & feeding
Sea trout spawning Estuary ‘slob’ trout feeding
One species or many? • Many local common names referring to particular geographical types / ecotypes etc • Breac, spotted trout, speckled trout, ferox, gillaroo, sonaghen (an), dollaghen (an), salmon-trout, buddagh, croneen, white trout, bull trout, slob trout, lake trout, harvester • Some argue for multiple species – 19th C - 50+ species – Early 20th C - 1 species – 2017 - 47 species named
Much genetic diversity • Irrespective of whether we recognise one or many species, there is considerable genetic diversity within & among trout populations as seen from colour variation, variation in life history, molecular genetic analyses, etc • As with other organisms important to conserve the genetic biodiversity represented by the various populations – not just the species
Brown trout are present in many lochs and rivers in SW-Scotland
• Region of considerable interest to anglers since early 19thC – still economically important part of tourist industry
• Lochs Grannoch and Dee once regarded as among the best trout fishing lochs in Scotland • Downstream parts of rivers provided prime sea trout angling – reduced by dams eg Dee • Trout numbers adversely impacted by acidification especially latter part 20thC
Acid precipitation • Sulphur & nitrogen oxides produced from burning fossil fuels – with water give acids • Galloway worst affected region in Britain – Granitic rocks over-laid by peat – little buffering – High rainfall – 2m+ – Prevailing winds
• Diatom studies of lake sediments showed acidification mid 19thC+ industrial revolution
pH scale – logarithmic so 1 unit = X10
History of acidification • First Galloway loch affected – Enoch – pH decreased from 5.4 in 1840 to 4.4 in 1982 – Late 19th century reports of ‘tailless’ trout – Due to abnormal development under acid conditions (not abrasion on sharp sand!) – Mid 19thC accounts of “baskets of four or five dozen nice trout” – Enoch trout extinct by 1920s (possibly as early as 1883)
Impact of acidification • Low pH & associated elevated levels of metals eg aluminium impact salmonids by: – Failure of eggs to hatch – Increased mortality especially fry & smolts – Skeletal & fin deformities
% of deformed trout in samples taken from lochs of different pH values. Data from Campbell & Maitland survey 1984 of 34 lochs in Scotland – mostly Galloway
1978-79 & 1984 FFL surveys • In addition to Enoch, no trout caught in Lochs Valley, Neldricken, Narroch and Fleet - all known to contain trout in the 1950s • Low numbers in many other lochs • Angling reports indicated reduced / no catches
Changes in acidity • The acidity increased rapidly from 1950 - 1970 with the pH falling in several lochs to
