Conservation Ecology of the Vendace (Coregonus Albula) in Bassenthwaite Lake and Derwent Water, U.K

Ann. Zool. Fennici 41: 155–164 ISSN 0003-455X Helsinki 26 February 2004 © Finnish Zoological and Botanical Publishing Board 2004

Conservation ecology of the vendace (Coregonus albula) in Bassenthwaite Lake and Derwent Water, U.K.

Ian J. Winﬁ eld*, Janice M. Fletcher & J. Ben James

CEH Windermere, The Ferry House, Far Sawrey, Ambleside, Cumbria LA22 0LP, U.K. (*e-mail: [email protected])

Received 3 Oct. 2003, revised version received 8 Apr. 2003, accepted 16 May 2003

Winﬁ eld, I. J., Fletcher, J. M. & James, J. B. 2004: Conservation ecology of the vendace (Core- gonus albula) in Bassenthwaite Lake and Derwent Water, U.K. — Ann. Zool. Fennici 41: 155–164.

Following extinction of two populations in Scotland, the vendace (Coregonus albula) is now found in only two U.K. lakes, i.e. Bassenthwaite Lake and Derwent Water in north-west England. Although the latter remains mesotrophic, the former has under- gone signifi cant eutrophication with associated dissolved oxygen problems and vendace monitoring has shown a declining population status. Additional threats originate from land erosion with subsequent in-lake siltation, and the unconsented introduction of non-native fi sh species including roach (Rutilus rutilus), ruffe (Gymnocephalus cernuus) and dace (Leuciscus leuciscus). The impact of ruffe as a predator of vendace eggs is considered through diet studies during the spawning period. Climate change may also signifi cantly impact local environmental conditions and these threats to the continued local survival of the vendace are assessed and descriptions given of resulting management measures. The latter include phosphorus-stripping, artifi cial spawning substratum, egg incubation in captivity, control of further introductions, and establishment of refuge populations.

Introduction availability of such prey may lead to marked population declines (Auvinen 1988). The vendace (Coregonus albula) is a medium- Within the U.K., vendace populations have sized and typically lacustrine coregonid occur- historically been recorded from four lakes (Mait- ring principally in northern areas of Europe, land 1966a), although the two populations of although it has also been introduced to lakes Castle Loch (54°50Ń, 4°40´W) and Mill Loch further south for fi sheries purposes (Lelek 1987). (55°8Ń, 3°27´W) near Lochmaben in south- Like other members of the genus Coregonus, west Scotland (Fig. 1) are now believed to be it prefers relatively high concentrations of dis- extinct (Maitland & Lyle 1990). The two remain- solved oxygen (Dembinski 1971), low water ing populations occur in Bassenthwaite Lake and temperatures (Hamrin 1986), and spawning areas Derwent Water of the English Lake District in with no or limited fi ne sediments (Wilkonska & north-west England (Fig. 1), which are connected Zuromska 1982). More specifi cally, the vendace by the River Derwent fl owing from the latter to feeds extensively on zooplankton such as Daph- the former over a distance of 5.5 km. Although nia spp. throughout its life cycle and reduced Bassenthwaite Lake (54°39Ń, 3°13´W, altitude 156 Winfi eld et al. • ANN. ZOOL. FENNICI Vol. 41

ated, possibly as a result of gene fl ow from occasional accidental migrants or the relative youth of the lakes (Beaumont et al. 1995). Due to the limited distribution and loss of two populations described above, the vendace is the U.K.’s rarest freshwater fi sh species and is consequently protected under nature conservation legislation. It is also a U.K. Biodiversity Action Plan species. There are thus no current commercial or recreational fi sheries for this species, and indeed the only record of this fi sh being exploited in the U.K. was for the now extinct populations of Lochmaben (Maitland 1966b). The objectives of this paper are to report the historical and current status of the vendace in Bas- senthwaite Lake and Derwent Water, to identify and assess threats to these populations, and to describe conservation measures recently or currently undertaken for this species in the U.K.

Historical and current status

Information sources

In the absence of current or historical fi sher- Fig. 1. Locations of Lochmaben and the English Lake District, including Bassenthwaite Lake and Derwent ies, this source of information is unavailable Water, in the U.K. Partly redrawn with permission from for the vendace populations of Bassenthwaite Ramsbottom (1976). Lake and Derwent Water. No information at all is available for the pre-1960s period and only three brief studies were subsequently made 69 m, surface area 528 ha, maximum depth 19 m, prior to the 1990s. In the mid 1960s, Maitland mean depth 5 m) and Derwent Water (54°34Ń, (1966a) obtained samples from both lakes, as 3°8´W, altitude 74 m, surface area 535 ha, maxi- did Mubamba (1989) in the mid 1980s, while mum depth 22 m, mean depth 5 m) are physically in the early 1970s Broughton (1972) obtained similar and lie near to each other in the same a sample of vendace from Bassenthwaite Lake catchment, they differ signifi cantly with respect only. Since the early 1990s, the present authors to trophic status (considered further below) have investigated the vendace populations of and fi shery activities. In addition to vendace, both lakes extensively (Winfi eld et al. 1996) and fi sh species native to both lakes include Atlan- currently monitor them by a combination of echo tic salmon (Salmo salar), brown and sea trout sounding and gill netting (Winfi eld et al. 2002a, (Salmo trutta), eel (Anguilla anguilla), minnow Winfi eld et al. 2002b). (Phoxinus phoxinus), perch (Perca fl uviatilis) and pike (Esox lucius) (Winfi eld et al. 1996). At Bassenthwaite Lake, fi shing is largely limited to Bassenthwaite Lake non-game, particularly pike, species but at Der- went Water most activity is focussed on game Based on samples collected in 1965, Maitland angling for brown trout. Genetic investigations (1966a) described the vendace population of Bas- have revealed that the vendace populations of senthwaite Lake as ‘thriving’, i.e. of good status. these two lakes are not signifi cantly differenti- Limited data presented in Broughton (1972) ANN. ZOOL. FENNICI Vol. 41 • Conservation of the vendace (Coregonus albula) in the U.K. 157 from sampling in 1972 also indicated a good dissolved oxygen levels and the siltation of population status, but by 1987 the samplings and spawning grounds. For Bassenthwaite Lake, examinations carried out by Mubamba (1989) examination of fossil diatoms to reconstruct showed that the status had declined to poor as a trophic history over the last 250 years revealed result of inconsistent recruitment. This situation the onset of eutrophication during the 1960s persisted into the early 1990s (Winfi eld et al. (Bennion et al. 2000), and water chemistry and 1996), after which it declined even further with algal data from recent decades have confi rmed continued inconsistent recruitment and conse- this trend (May et al. 2001). Derwent Water, in quently reduced population abundance (Winfi eld contrast, has retained its natural mesotrophic et al. 2002a). conditions (CEH Windermere unpubl. data). Although historical measurements of dissolved oxygen levels are unavailable, profi les Derwent Water from the 1990s (CEH Windermere unpubl. data) show that summer levels may fall to ca. 3 mg l–1 Maitland (1966a) described the vendace popu- in the hypolimnion of both lakes (see Fig. 2), lation of Derwent Water as ‘thriving’ based on which is the level about which vendace distribu- samples taken in 1965. This good status per- tion begins to be impacted (Dembinski 1971). sisted through the 1987 samples of Mubamba Clearly, any further reductions in dissolved (1989) and the early 1990s samples of Winfi eld oxygen levels could have signifi cant adverse et al. (1996), and has continued to the present impacts on the vendace populations. The issue of (Winfi eld et al. 2002a). siltation, which may also have origins unassoci- ated with eutrophication, is considered below. In addition to impacts through oxygen avail- Identifi cation and assessment of ability and deterioration of spawning grounds, threats the observed eutrophication of Bassenthwaite Lake may also impact its vendace population Approach indirectly by shifting potential competitive conditions from those favouring coregonids and Reviews of generic threats facing the conser- salmonids, to those favouring cyprinids (see vation of fi sh communities in the U.K. and Persson 1991). European studies on the vendace by Winfi eld Stimulated in part by concern for the ven- (1992) and Winfi eld et al. (1994), respectively, dace, a nutrient budget constructed for Bas- were used to frame the approach of the present senthwaite Lake in the early 1990s showed that work, augmented by other studies of local the Keswick sewage treatment works upstream environmental conditions and unpublished data of the lake was a major source of phosphorus held by CEH Windermere. This resulted in the and that the introduction of phosphorus-strip- initial identifi cation of four broad threats, i.e. ping would reduce algal populations (May et eutrophication, siltation, species introductions al. 2001). Derwent Water is unaffected by this and climate change, which have subsequently sewage treatment works because it lies upstream been assessed by a combination of fi eld and of its discharge. laboratory studies.

Siltation Eutrophication The presence of large amounts of fi ne sediments The adverse effects of advanced eutrophication was observed in the late 1990s by underwater on coregonids are now well known from many video inspections of all known vendace spawn- case histories throughout Europe, e.g. Wilkonska ing grounds in Bassenthwaite Lake but not and Zuromska (1982), with the two primary Derwent Water (Winfi eld et al. 1998a), although impacting mechanisms being low hypolimnetic subsequent chemical analysis has shown that 158 Winfi eld et al. • ANN. ZOOL. FENNICI Vol. 41

Bassenthwaite Lake Derwent Water T (°C)/DO (mg l–1) T (°C)/DO (mg l–1) 0 5 10 15 20 0 5 10 15 20 0 0 5 5 10 July 10

Depth (m) 15 Depth (m) 15 20 20 T (°C)/DO (mg l–1) T (°C)/DO (mg l–1) 0 5 10 15 20 0 5 10 15 20 0 0 Fig. 2. Summer temperature 5 5 (T) and dissolved oxygen 10 August 10 (DO) proﬁ les of Bassen- thwaite Lake and Derwent

Depth (m) 15 Depth (m) 15 Water from 1992 which are 20 20 illustrative of those of the T (°C)/DO (mg l–1) T (°C)/DO (mg l–1) 1990s as a whole (CEH 0 5 10 15 20 0 5 10 15 20 Windermere unpubl. data). 0 0 Profi les at the former lake were taken on 13 Jul. 1992, 5 5 24 Aug. 1992 and 21 Sep. 10 September 10 1992, while those at Der- went Water were taken on 9 Depth (m) Depth (m) 15 15 Jul. 1992, 20 Aug. 1992 and 20 20 14 Sep. 1992. this material is largely inorganic and appears This particular threat to the vendace populations to be the result of erosion in the lake’s catch- was raised in 1986 for Bassenthwaite Lake by ment (CEH Windermere unpubl. data). Similar the lake’s fi rst record of roach (Rutilus rutilus) investigations at Blelham Tarn in another catch- discovered during sampling of its deep-water ment of the English Lake District have shown area (Mubamba 1989), to which vendace are increased sedimentation to be attributable to restricted outside the spawning period. Equiva- surface soil erosion, largely as a direct response lent sampling of Derwent Water did not record to increased pressure from sheep (Ovis aries) this species (Mubamba 1989). The competitive grazing (van der Post et al. 1997). Whatever abilities of roach for zooplanktonic prey (Pers- its origins, the presence of this material in Bas- son 1991) gave rise to concern over its possible senthwaite Lake makes successful vendace egg impact on the vendace of Bassenthwaite Lake. incubation extremely unlikely. Furthermore, the existence of the connecting River Derwent between this lake and Derwent Water, with no signifi cant obstacles to fi sh Species introductions migration, also meant that this and other fi sh species could colonise the latter lake by a short The introduction of new fi sh species is widely riverine migration. considered to be one of the greatest threats to Initial full assessments of the fi sh communi- aquatic biodiversity conservation on a global ties of both lakes, including both deep water basis, with introduced species potentially acting and shallow water sampling locations, were as predators, competitors or environmental undertaken in the early 1990s as described by degraders (Winfi eld 1992). U.K. lakes are par- Winfi eld et al. (1996). From the mid 1990s, more ticularly susceptible to this threat because their extensive sampling involving echo sounding and fi sh communities are naturally species-poor as a gill netting has been continued to monitor the result of the last glaciation ca. 10 000 years B.P. fi sh communities as described by Winfi eld et al. ANN. ZOOL. FENNICI Vol. 41 • Conservation of the vendace (Coregonus albula) in the U.K. 159

Fig. 3. Species compositions by numbers of the deep-water ﬁ sh communities at Bassenthwaite Lake (total sample size 927 individuals) and Der- went Water (total sample size 1354 individuals) between 1987 and 2001. Regular monitoring by survey gill net has only been undertaken at Bas- senthwaite Lake since 1995 and at Derwent Water since 1997, but results from earlier gill net surveys in 1987 (data from Mubamba (1989)) and 1991 at both lakes and at Derwent Water in 1995 are also shown. For consistency, species lists have been retained from those of the entire lake communities given in Win- ﬁ eld et al. (2002b).

(2002b), where combined data from the deep Assessments of the likely impacts of the and shallow areas of each lake are presented. In above introductions on the vendace popula- addition to confi rming the increase of the Bas- tions have been made by a combination of diet senthwaite Lake roach population discovered by and distribution studies of young and adult life Mubamba (1989), this work also produced the stages, in the context of roach as a potential fi rst records of ruffe (Gymnocephalus cernuus) in competitor and ruffe as a potential predator of Bassenthwaite Lake and roach in Derwent Water vendace eggs (Winfi eld & Durie 2004). While in 1991 (Winfi eld et al. 1996), and dace (Leucis- it was concluded that there was no evidence that cus leuciscus) in the former lake in 1996 and in roach posed a threat in either lake, a conclusion the latter lake in 1999 (Winfi eld et al. 2002b). subsequently supported by an independent study Subsequently, ruffe have also been recorded in of roach and vendace in Sweden (Beier 2001), Derwent Water in 2001 (Winfi eld et al. 2002a). there remains concern over the impact of ruffe. Species compositions by numbers of the deep- Vendace eggs were absent from the diet of this water fi sh communities of both lakes during percid in the vendace spawning period of 1995 this period began with a strong domination by (Winfi eld et al. 1998b), but were subsequently vendace, but fi nished with Bassenthwaite Lake found in varying amounts in the corresponding dominated by introduced ruffe and roach (Fig. 3). periods of 1996 and 2001 (Fig. 4). The diet of Dace have remained a minor component of the ruffe in Derwent Water has not yet been exam- deep-water fi sh communities in both lakes. ined. Finally, the introduced dace have remained 160 Winfi eld et al. • ANN. ZOOL. FENNICI Vol. 41

temperature itself and, for example, a study of growth in non-coregonid species in North America has shown the importance of associated changes in the timing of lake stratifi cation (King et al. 1999). For coregonids, which generically share a requirement for relatively low temperatures and high dissolved oxygen levels, global warming may present the additional complica- tion of causing mortalities through suffocation as predicted for the whitefi sh (Coregonus lavaretus) in Lake Constance, Europe (Trippel et al. 1991). In both Bassenthwaite Lake and Derwent Water, temperature and dissolved oxygen conditions (Fig. 2) are already periodically near the toler- ance limits of vendace and so any further deterioration could have catastrophic consequences. Assessment of the threat posed by climate change to the conservation of vendace in the English Lake District is currently being undertaken by modelling temperature and dissolved oxygen profi les in relation to local weather conditions, including wind speed and its effects on stratifi cation, and thus calculating the lake volume inhabitable by vendace (V. A. Bell pers. comm.). This approach will ultimately allow hindcasting of temperature and oxygen profi les Fig. 4. Diet composition (by numbers of prey) of prior to the 1990s when their routine monitor- ruffe on a vendace spawning ground on three dates ing began, and by coupling the model to climate in the spawning periods of 1996 (total sample size 10 individuals, size range 45 to 124 mm) and 2001 (total change models the approach will also allow the sample size 46 individuals, size range 68 to 104 mm) forecasting of future impacts under various sce- at Bassenthwaite Lake. Note that although the three narios of environmental change. prey types Aerial insect, Bivalvia and Gammarus were present in the diet on some occasions, they never com- prised more than 1% of the diet composition. Conservation measures at relatively low abundance in both lakes, so Approach it is unlikely that they pose a serious threat to vendace even though they have been shown to Identifying, recommending and applying appro- predate coregonid larvae in the laboratory (Shi- priate and feasible conservation measures for the robokov 1992). vendace of Bassenthwaite Lake and Derwent Water are inherently complex tasks and involve a wide range of stakeholders. Much of the sci- Climate change ence underpinning this management has been performed and reported by the authors under The biology of aquatic poikilothermic animals contract to various local and national regula- is greatly affected by variations in water tem- tory bodies, with the aim of conserving the two perature, and so changes associated with climate vendace populations in their natural habitats. change have a great potential to infl uence the However, the precarious status of the vendace ecology of many lacustrine fi sh species. Such in Bassenthwaite Lake has also forced additional effects are not simply directly attributable to and less preferred measures. ANN. ZOOL. FENNICI Vol. 41 • Conservation of the vendace (Coregonus albula) in the U.K. 161

Conservation measures addressing the threat 5 December 1998, but on their subsequent inspec- of climate change are obviously a general environ- tion only 15 days later they had become heavily mental issue and have aspects far beyond the man- silt-laden and thus inhospitable to vendace eggs. agement of the U.K. vendace populations. Conse- The frequent resuspension of exogenous fi ne quently, they are not considered further here. sediments currently presents an insurmountable problem for the successful incubation of vendace eggs in Bassenthwaite Lake. Moreover, like Eutrophication eutrophication, this is likely to remain a problem for at least a considerable number of years. Following the identifi cation of Keswick sewage treatment works as a major contributor to the phosphorus budget of Bassenthwaite Lake, Egg incubation in captivity phosphorus-stripping was introduced during 1994 and 1995 (May et al. 2001). Improve- If vendace eggs cannot currently be incubated ment towards mesotrophic conditions has sub- successfully in Bassenthwaite Lake over at least sequently been limited, with little impact on the next few years due to siltation on all known dissolved oxygen conditions (CEH Windermere spawning grounds, then a potential emergency unpubl. data). This slow progress is partly the measure is to bypass these conditions by strip- result of the phosphorus-stripping process being ping fi sh and incubating their eggs in captivity overwhelmed by high water volumes during before returning the resulting young to the lake. periods of high rainfall, and partly due to internal Although such capture and husbandry presented loading in the lake sediments (Reynolds & Win- no technical problems in the late 1990s (see Lyle fi eld 2002). Eutrophication is thus being actively et al. 1999), attempts to catch appropriate brood- addressed, but is unlikely to show signifi cant stock in 2000 and 2001 were unsuccessful due improvement in the immediate future with to very low population abundance of vendace respect to vendace habitat requirements. (Winfi eld & Fletcher 2002).

Siltation Species introductions

The problem of siltation on vendace spawning In contrast to the above threats, species introduc- grounds in Bassenthwaite Lake undoubtedly tions are an issue in both Bassenthwaite Lake has a eutrophication-induced component, but and Derwent Water. In addition to now being it is apparently dominated by processes begin- present in both lakes, it is highly probable that ning elsewhere in the catchment. As a result, populations of roach, ruffe and dace have also its management is both complex and diffi cult. established in the connecting River Derwent. Moreover, even if the source or sources in the However, with respect to the vendace, only the catchment were to be identifi ed and rectifi ed, it ruffe has been concluded to pose a signifi cant would probably take a considerable time period threat under current circumstances. before natural fl ushing removed those problem Although similar introductions of ruffe else- sediments already in the lake. where in the U.K., mainland Europe and North In view of the severity of the siltation prob- America have been recognised as a threat to lem with respect to incubating vendace eggs, an coregonid populations for many years (Winfi eld assessment of the feasibility of introducing clean et al. 1998c), intensive attempts to fi nd appropri- artifi cial spawning substratum was made during ate biological, chemical or molecular control the vendace spawning season of 1998 (Winfi eld measures have been unsuccessful (Gunderson 1999). Mats of a type of plastic grass that had et al. 1998). Moreover, for the specifi c case of previously been successfully used as an incuba- Bassenthwaite Lake the observed spatial overlap tion substratum for whitefi sh eggs (Winfi eld et al. between ruffe and vendace in the deep-water 2002c) were introduced on a spawning ground on areas (Fig. 3) means that any physical removal 162 Winfi eld et al. • ANN. ZOOL. FENNICI Vol. 41 method such as trawling or gill netting would ments of vendace. The remaining four sites were produce a signifi cant and counter-productive evaluated by fi eld visits including the sampling lethal bycatch of vendace. of their fi sh communities, but none was found Control of the introduced ruffe populations to be ideal. Consequently, refuge populations in Bassenthwaite Lake and Derwent Water is of vendace have not yet been established in thus impractical, but the threat of species intro- England. ductions still needs to be addressed on a more However, attempts have been made to generic level by preventing the introduction of reintroduce vendace to Scotland using donor further potentially problematical species. There material from Bassenthwaite Lake and Derwent is strong evidence that such introductions, along Water by stripping adults during three spawn- with some to other water bodies of the English ing seasons from 1996 to 1998 and incubating Lake District, are attributable to discarded or the resulting eggs in captivity. As the original escaped live-bait used by anglers during recrea- vendace localities of Castle Loch and Mill tional angling for pike (Winfi eld & Durie 2004). Loch remain environmentally unsuitable, after Consequently, the Environment Agency, the appropriate evaluation and consultation newly- relevant regulatory body, proposed a change to hatched larvae from Bassenthwaite Lake have local fi sheries byelaws to ban the use or posses- been introduced to Loch Skeen (55°26Ń, sion with intended use of any dead or alive fresh- 3°18´W) and those from Derwent Water to Daer water fi sh, salmonids or eel as bait in 14 named Reservoir (55°21Ń, 3°37´W) (Lyle et al. 1999). lakes of the English Lake District, including The outcomes of these introductions have yet to Bassenthwaite Lake and Derwent Water (Win- be determined. fi eld & Durie 2004). This proposal successfully passed through an extensive public consultation phase and has subsequently been approved by Closing remarks the Department of the Environment, Food and Rural Affairs with effect from 26 July 2002. The degrees of threats to the conservation of vendace in Bassenthwaite Lake and Derwent Water diverged dramatically in the latter years of Refuge populations the previous century following the development of eutrophication and sedimentation issues at All of the above measures share the aim of con- the former lake, and its more developed history serving the last two U.K. vendace populations in of introduced species. Prospects for the local their natural habitats of Bassenthwaite Lake and survival of vendace in Bassenthwaite Lake may Derwent Water. However, given the poor status now be poor, although they may be marginally of vendace in the former lake and the low prob- enhanced by the possible occasional natural ability of an improvement in local environmental input of individuals from the more robust and conditions in the near future, the establishment of less threatened population of Derwent Water by refuge populations has also been given attention. passage along the connecting River Derwent. In order to avoid the generation of new con- Under these circumstances, there is now an even servation problems at the recipient site, introduc- greater reason to ensure that the vendace populations to establish refuge populations are rightly tion of the latter lake, which is now the last con- subject to the same conditions and safeguards as sistently recruiting such population in the U.K., those required for fi sheries purposes. A feasibil- is not itself placed under additional threats. ity study was consequently undertaken on 87 In a country that draws extensively on its potential recipient sites in or near the English natural resources, and not always in a sustainable Lake District (Lyle & Winfi eld 1999). During a way, mapping such ideals from theory to practice desk study, 34 sites were eliminated on the above is not an easy task. The successful conservation grounds as they or their catchments contained of the vendace in the U.K., and indeed equiva- other rare fi sh species, while another 49 sites lent actions with other species elsewhere, must were concluded not to meet the habitat require- ensure that scientifi c understanding is fi rmly con- ANN. ZOOL. FENNICI Vol. 41 • Conservation of the vendace (Coregonus albula) in the U.K. 163 nected to environmental policy and management. 24: 165–169. In order to achieve this, the onus is on fi sh ecolo- Hamrin, S. F. 1986: Vertical distribution and habitat par- titioning between different size classes of vendace, gists to devote effort to make the move towards Coregonus albula in thermally stratifi ed lakes. — Can. their managerial colleagues, even if achievement J. Fish. Aquat. Sci. 43: 1617–1625. metrics currently commonly used in science do King, J. R., Shuter, B. J. & Zimmerman, A. P. 1999: not recognise such activities (Meffe 2002). Even Empirical links between thermal habitat, fi sh growth, when such objective information has been suc- and climate change. — Trans. Am. Fish. Soc. 128: 656–665. cessfully inoculated into the managerial domain, Lelek, A. 1987: The freshwater fi shes of Europe. Volume 9. fi sh ecologists still have a vital role to play in Threatened fi shes of Europe. — AULA-Verlag, Wies- securing appropriate decisions by harnessing baden. public opinion through increased awareness and Lyle, A. A., Maitland, P. S. & Winfi eld, I. 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