ARCTIC CHAR

Figure 1: A sea each morph, although the differences are resulting in vacant ecological niches (food run char from a Northern best illustrated by viewing a number of the sources and habitat). In lakes, the two Icelandic river, individuals together (Figure 3). most discernible niches are the benthic likely typical environment where invertebrates living of those LIFE HISTORY in and on the lake bottom are the key which initially colonised Planktivores grow rapidly but exhibit a prey item, and the open water or pelagic rivers of the clear limitation in maximum size, never environment where zooplankton are the British Isles exceeding the sizes illustrated and 7 years of main food source. Fish can be considered after the age, whereas piscivores grow slowly but have a third quite different food source. The retreat of the an indeterminate maximum size. The largest ability to effectively exploit these requires last glaciation individual in Figure 3 weighed 2.5kg and particular and quite different attributes was 17+ years old. Benthivores (not shown in the fi sh, in terms of body and mouth in Figure 3) are similar to planktivores with shape and behaviour. Thus, intermediate rapid growth, but a clear limit in maximum morphological forms (including the results size, slightly larger than planktivores. The of hybrids between the different forms) are maximum age recorded for benthivores less effi cient at exploiting these discrete was 11 years. Another striking feature of food resources and are selected against in the piscivorous form is the maturation evolutionary terms. of females at a tiny size, the smallest ripe individual recorded being 74mm, and RANNOCH VERSUS ERICHT containing 18 eggs; a similar individual is The next obvious question is why the shown in Figure 4. presence of two bottom dwelling forms in Loch Rannoch but only one in Loch Ericht? Darwin could have Figure 2: From top to bottom, piscivorous, DIET A strong hypothesis for explaining this benthivorous and planktivorous char forms from The piscivorous form is benthivorous early relates to the physical dimensions of Loch Loch Rannoch. These individuals are of identical length and exemplify the head shape differences on in its life, but switches to feeding on Rannoch, which comprises two basins. characteristic of each form. Piscivorous and fi sh at 16cm. The benthivores were never Catch data indicated that the benthivorous benthivorous are both superfi cially similar in found to contain fi sh, irrespective of size, form only occurred in the small shallow west terms of pale colouration and markings, but preferring instead a diet dominated by basin, whereas the piscivorous form only stayed at home piscivorous individuals have longer heads, larger tiny Pisidium pea mussels, chironomid occurred in the deep east basin. Although eyes and gapes and less rounded snouts than benthovores. Planktivores (bottom) are instantly (midge) larvae, and benthic cladocera (water the constriction between these basins is not Lessons in salmonid speciation and ecology from Scottish char differentiated by their claret colouration, but also fl eas). The planktivorous form consumed suffi cient to physically prevent movement have signifi cantly more slender bodies, smaller predominantly cladocera, but with of the fi sh, catch data in my study and those Dr. David Fraser and became freshwater resident, so too did extensive intra-species diversity. heads and fi ner jaws than the other two forms chironomid larvae also making a signifi cant of other lakes clearly shows that char are all our char, which now reside solely in But, perhaps the most striking contribution at certain times of year. restricted to deeper areas by the competitive provides some insights the deeper lochs, loughs, tarns and lakes, characteristic of Arctic char is their dominance of brown trout in the richer primarily in upland regions. propensity in certain instances to exhibit LOCH ERICHT shallower habitats. Thus, the two bottom into the trout’s often The story from this point forward for multiple races or forms within a single Having largely fi gured out the basic biology living char forms in Rannoch are effectively char is similar to that of non-migratory water body. Studying and identifying such of the Loch Rannoch char, my attention isolated within each basin. The west basin is forgotten cousin, the trout, with populations being isolated in populations was the basis of my Ph.D., then turned to Loch Ericht; its similar relatively shallow, and thus has a relatively waters distinctive in their physical, chemical which fi rmly established my belief in the dimensions to Rannoch and being the productive lake bottom thus selecting for Arctic char. and biological characteristics. Combine need to recognise all salmonids (and indeed next loch upstream in the same catchment a benthivorous specialist, whereas the this with the fact that the founding fi sh fi sh) as not merely individual species, but a made it an obvious comparison site. Field relatively deep west basin has a severely s the grip of the last ice age began to (original invaders) of each lake population group where fi sh from different catchments, sampling immediately yielded char which impoverished bottom fauna, meaning that recede some 12,000 years ago, one would have differed in their genetic rivers, lakes or even within the same water visually clearly comprised two different other fi sh are the main prey opportunity. Aof the fi rst arrivals in our rivers was and phenotypic characteristics, and you are likely to be inherently different, and thus forms (Figure 5). Subsequent quantitative These differences are maintained and the Arctic char, Salvelinus alpinus which, have all the ingredients for evolutionary need to be managed as such. shape analysis confi rmed two discrete shape further reinforced in Loch Rannoch by each having resided in waters on the periphery diversifi cation amongst char populations. My study capitalised on earlier work of Figure 3: Three piscivorous char (top) and three forms, with dietary analysis determining form utilising a different spawning habitat. of the great ice sheets, strayed into rivers Although both trout and char have been Ross Gardiner, Andy Walker, Ron Greer, planktivourous char (bottom) illustrating the that the pale form was a piscivore, whereas The benthivorous form spawns in the mouth newly emerged from the retreating ice. similarly subject to such processes, char Colin Adams and others in exploring the growth potential of the two morphs the coloured form was a zooplanktivore. As of the River Gaur, the main infl owing river These pioneering individuals progressively differ from trout in the sheer extent to which multiple forms of Arctic char in Loch with Loch Rannoch, the piscivorous form entering the west basin. The planktivorous colonised our freshwaters and form the they have diversifi ed (and before I upset Rannoch in Perthshire. Initial studies grew relatively slowly but lived longer and form (which occurs in both basins) spawns basis of the approximately 340 British Isles the readership, I speak as one who is fully by these co-workers indicated two forms attained greater ultimate sizes than the in the shallow stony wave washed zone (1-3m populations of this reclusive but magical signed up to the huge value of variability in of char within Rannoch but subsequent planktivorous form. depth), with some evidence existing that the cousin of Salmo trutta. Those fi rst colonisers trout populations!). The result is char which work by myself, Colin Adams and Felicity piscivorous form spawns at greater depths. were anadromous sea farers, akin to present differ from lake to lake, often strikingly in Huntingford using shape, diet and length- HOW DID THESE DIFFERENT day sea trout, as can still be encountered in terms of their size, life history, shape, diet, at-age analysis indicated three forms: a deep CHAR FORMS ARISE? NURTURE VERSUS NATURE? Iceland, Greenland, northern Norway and colouration and behaviour. This diversity was water, bottom-dwelling, piscivorous (fi sh- The question of how such multiple Despite the apparently striking differences North America (Figure 1), and essentially recognised (although not fully understood) eating) form, an open water, planktivorous co-occurring forms of a single species arise observed within a single water body, anywhere North of 65 degrees latitude, the by the earliest biologists, with fi fteen char form (feeding on mid-water invertebrates) and persist is one that has generated a great these have been demonstrated to be of threshold for sea run char. In the same way species being named in the British isles and a deep water, benthivorous form (feeding many scientifi c papers; a key hypothesis environmental rather than genetic origin. that many of our post glacial colonising sea originally. Modern classifi cation now largely on bottom-dwelling invertebrates). Figure Figure 4: An example of a small sexually mature is they occur where there is the absence In these scenarios individuals from a single trout populations gave up their wanderlust regards them as a single species, with 2 shows three similarly sized individuals of female char of the piscivorous form of competition from other fi sh species, gene pool specialise on different habitats

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and prey (typically benthic and pelagic) early on in life, and this specialisation results in two different forms. So, is this the case with the Rannoch char? Common rearing experiments (Adams Figure 5: The and Huntingford, 2002) demonstrated that two forms of although much of the shape differences char from Loch Ericht. The top between wild planktivorous and two fi sh are benthivorous char disappeared when reared piscivorous form, together, indicating a strong environmental whereas the component, differences did remain, bottom three are indicating inherent genetic differences. planktivorous The authors concluded that this did not undermine the hypothesis that the different Although this is likely to have been an affected by climate change, and in this Rannoch forms comprised three non- to be an isolated individual, it highlights respect Lochs Rannoch and Ericht are interbreeding gene pools which were at an that such populations are one discarded or well placed. Waters at the other end of the early stage of the speciation process. released bucketful of livebait away from climate sensitivity spectrum may fare less potential catastrophe. well, particularly when affected by factors WHAT DO GENETIC STUDIES Surprisingly, despite the clear value of such as eutrophication, and the acute and TELL US? multiple co-occurring char forms from a irreversible effects of the introduction of Although the studies described above scientifi c, conservation and educational novel fi sh species. provide clear evidence that three perspective, none of the sites where they Compounding these threats, translocation reproductively and ecologically discrete exist receives statutory protection; these to other waters as a mitigation option does forms exist, genetic studies further reinforce include not just Lochs Rannoch and Ericht, not lend itself to co–occurring forms of char. this. However, arguably the greatest but also more recent discoveries in Lochs Remember that these forms are products of additional benefi t of genetics is in further Awe, Tay and Doine. The inadequacy the particular environmental conditions of elucidating hypotheses for how the char of this situation was thrown into sharp the lake in which they reside, and fi nding arose. Early work on Loch Rannoch char focus in recent years when a planning or replicating these in an alternative water undertaken by Sheila Hartley and developed submission for a multi-million pound body would likely be impossible. In an by Eric Verspoor and colleagues more golf and leisure development including economic and policy climate where there is recently suggests that the two deepwater within lake development was submitted for often an assumption that any development forms originated from a single post glacial the south shore of Loch Rannoch. Many or impacts can be mitigated by spending invading race, which diverged into a parties opposed the development, including money in such ways, it is worth highlighting piscivorous and benthivorous form within Scottish Natural Heritage, although no case where this is not the case. Loch Rannoch due to the two basin profi le, was able to be made in terms of the char, due I hope that readers will indulge this whereas the planktivorous form derives from to the loch not being statutorily protected in deviation from WTT’s troutier focus, but a separate post glacial invading race. This terms of its char. in doing so I believe char provide us with two invading race hypothesis may explain One saving grace is the inclusion of Arctic an insight to the same processes which take why we do not perhaps have more waters char on the UK Biodiversity Action Plan place throughout salmonid fi sh, including with multiple char forms. It may be that list which does at least provide an element Salmo trutta, and which should continue to a combination of within-lake conditions of recognition of its conservation value at a be the focus of research and conservation needs to coincide with two or more invading general level. efforts. The biodiversity of our salmonids char races. However, if we consider that is still far from fully documented, and invading races were adapted for sea going PROGNOSIS FOR CHAR we can only conserve what we know and and might have been broadly similar in So what of the prospects for a fi sh whose understand; there is not one Salmo trutta, shape it is clear that most of the signifi cant name indicates that it might not be best one Salmo salar nor one Salvelinus alpinus, divergence in shape, life history and ecology able to cope with a warming world? Well, there are many, many. has taken place within Lochs Rannoch and fi rst let me challenge some preconceptions. Ericht – and in the last 12,000 years since It is often said that char are an “ice age Dr. David Fraser is Principal Aquatic Ecologist deglaciation. relic”. This is somewhat of a nonsensical at APEM Ltd. (www.apemltd.co.uk) term, as all of our current fauna is the THREATS result of colonisation of previous glaciated References Despite Loch Rannoch and similar sites areas and char are no different in this I. J. Winfi eld, J. Hateley, J. M. Fletcher, being remote and removed from signifi cant respect from our non-migratory brown J. B. James, C. W. Bean, P. Clabburn (2010) development pressure, it would be naive to trout populations; indeed it may be that Population trends of Arctic char (Salvelinus assume threats don’t exist. The introduction the term “Arctic” in the name does the fi sh alpinus) in the UK: assessing the evidence for a of invasive non-native species (and I include disservice by suggesting an exotic origin. widespread decline in response to climate change. here species native to the UK but not to the Nonetheless, recent analysis of a limited Hydrobiologia, 650, Issue 1, pp 55-65. water body concerned) is surely one of the number of UK populations suggests recent Adams, C. E. and Huntingford, F. A (2002) most acute threats to rare fi sh communities. decline (Winfi eld et al., 2009) partly due Inherited differences in head allometry in During my studies my catches included to climate change. Char populations of polymorphic Arctic char from Loch Rannoch, a crucian carp, which appeared to have the largest, deepest lakes and those at the Scotland. Journal of Fish Biology, 60, Issue 3, been introduced via pike angling live bait. greatest altitude are likely to be the least pp515-520.

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