Saturday, 12 June 2010

Signs of the times: Spring #20

More comparisons between the British countryside of today and that from 1959-1961 in the paintings of Charles Tunnicliffe in the Ladybird "What to look for..." series of books.

The pleasant'st angling is to see the fish
Cut with her golden oars the silver stream,
And greedily devour the treacherous bait."

William Shakespeare, “Much Ado About Nothing”

(Copyright: Ladybird Books)

Spring picture 22, although a lovely picture in its own right, is a bit simpler to comment on than the previous one, showing a couple of beautiful brown trout rising, taking adult mayflies, with some water crowfoot, the emerging water plant in flower at the foot of the painting.

The mayflies (insects belonging to the order Ephemeroptera) have an interesting life cycle, spending a period (depending on species) of months to 2-3 years as an immature larva in an aquatic phase of its life. Once fully developed, the larva emerges from the water as a winged insect. The mayflies are the only insects to have two adult stages, the “subimago”, which emerges from the final larval stage. This, depending on air temperature, will usually moult within 24 hours, emerging as its second, “imago” stage. The Freshwater Biological Association’s identification key for mayfly larvae clarifies that anglers usually describe the subimago stage as the “dun” and the imago as the “spinner”. The name “Ephemeroptera” comes from the Greek words ephemeros = lasting for a day, and pteron = wing, referring to the brief life of the adult mayflies (also sometimes called “one-day flies”!), which doesn’t have a proper gut system and which has a short life as an adult, evolved only to emerge, mate, lay eggs and then die.

Earlier today, I met Craig Macadam, the Scottish officer for Buglife, the Invertebrate Conservation charity, and he put me on the trail of a study by the Environment Agency (EA) in England, using anglers records of adult mayflies going back many years, sometimes as far as World War Two. Sitting on the bankside for hours at a time, many anglers are very interested in which mayflies are emerging and which the trout are rising to catch and eat, as there is a fine art in making artificial flies that seek to simulate the living flies! So back in 2001, the EA exploited this interest, in some cases lifelong, by collating anglers’ personal records to assess changes in the state of mayflies. An article in the Independent newspaper here, reported that the study identified a significant decline in mayflies in southern England’s chalk streams, particularly in the last 20 years, and ascribes this to the continued increase in pesticides, fertilisers and other chemicals, particularly from intensive agriculture. A more recent (2008) article on the BBC Scotland web pages helpfully reports the general position of mayflies in Scotland, according to Buglife (and Craig), who were trying to recruit volunteer recorders for a survey of mayflies. The article reports that one mayfly species (Ephemera danica, the original “Mayfly”, which emerges when the May or Hawthorn is in flower) is making a comeback in Central Scotland’s rivers, probably due to declining pollution levels. The fortunes of other mayfly species are more mixed; although the water quality of Scotland’s rivers is generally high and has greatly improved over the last 30 years, there are other pressures on invertebrates like mayflies living in the rivers, for example, some northern and upland species are showing changes in their southern ranges in Scotland that are consistent with a warmer climate. You might be interested to look at the website for the River Fly Partnership here, a network of over 60 organisations working to conserve our river fly populations in the UK, including the mayflies.

In the picture, the mayflies are being taken by brown trout (Latin name: Salmo trutta), probably Britain’s most widely distributed and commonest freshwater fish. Lordy, what to write about brown trout? I could write pages (and pages). Many people have written whole books. So, as I don’t simply want to replicate screeds of text from my fish books, I will focus on the main point of this series of posts, a comparison of the status of the features of the pictures compared with when they were painted. Professor Peter Maitland, in his book “Scotland’s Freshwater Fish. Ecology, Conservation & Folklore”, describes the origin of all native brown trout populations in Scotland as all “descended from early post-glacial colonisation by anadromous [sea-going] trout”. Brown trout are found in Scotland wherever water quality is high enough and there are not too many predaceous fish. Populations have also been introduced very widely across Scotland for angling and perhaps for more historical fish production, and many populations are maintained by angling associations and clubs, or by fishery managers, by stocking of farmed or wild brown trout. So, since 1959-1961, it is unlikely that the distribution of brown trout has deteriorated. Indeed, the improvement in the overall quality of our rivers in the past few decades will have allowed the recolonisation of many rivers previously rendered virtually fishless (or at least troutless!) by poor water quality. Stocking and introductions will certainly have increased the distribution, but there is no overall assessment of what this may have done to the many unique, genetically distinct brown trout populations and varieties of form that led historically to an enormous range of local names for brown trout. There is a caveat to this story which relates to the sea trout, a form of brown trout that is born and grows in freshwater then goes to sea (like a salmon) for one or more years before returning to the river to breed. Sea trout have suffered particular problems in recent years but that is a fishy tale for another time.

Finally, the water-crowfoot in the picture could be one of any of a number of related water-plant species, of which Ranunculus aquatilis is probably the commonest (hence, Common Water-crowfoot!). It can cover ponds, streams and ditches in summer. The problem with reporting on how its status compares now with 1959-1961 is that, in 1962, when the original Atlas of British and Irish Flora was published, the differences between a number of water-crowfoot species had not been resolved. It is not really possible, therefore, to say whether any of a number of the water-crowfoot species has increased or declined! Water-crowfoot is not native in most of Scotland’s rivers anyway, but is more likely to be found in southern Scotland, and the River Tweed is particularly important in Scotland for hosting a number of species.


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