British Wildlife freshwater report Dr Mark Everard

Freshwater wildlife experienced wildly variable pressures in 2020, from flood to drought. The wettest February and the driest May on record ushered in the longest continuous stretch of high temperatures since the 1960s followed by the wettest day (3rd October) since records began. Covid- 19 lockdown saw late geographic adjustments in abstraction to accommodate a shift from industrial to residential water demand compounding dry weather, some streams drying with occasional needs for rescues. Recruitment of cyprinid species (, the large and family) typically fares well in warm, dry summers. Warmed marginal water with reduced risk of wash-out and abundant food items promotes growth of juveniles, better equipping them to survive autumnal spates. Populations of Chub ( cephalus) and Barbel (Barbus barbus), towards the northern limit of their distribution in Britain, show strong year classes corresponding with prior hot, stable summer weather conditions. A 2018 reclassification1 of the carp and minnow family continues to gain traction amongst biologists, recognising sub-order Cyprinoidei (including the former Cyprinidae) now split into several distinct families based on morphological and genetic differences. British representatives include the revised Cyprinidae (true including Common Carp Cyprinus carpio, Barbel and Crucian Carp Carassius carassius), Leuciscidae ( of Europe, Asia, and North America including Roach rutilus, Abramis brama and Eurasian Minnow phoxinus), Gobionidae (gudgeons including ) and some smaller families including Tincidae (Tench: the sole genus and species Tinca tinca). Crucian Carp have received concerted conservation action over recent years. This generally small cyprinid fish is characteristic of small ponds, studies demonstrating a lack of adverse impacts on pond biota. Crucian remains date back to Roman Britain, though genetic studies suggest a medieval reintroduction; in any event, this fish is long-established in England where it is in decline, as throughout most of its European range. A 2020 study2 assessed populations of Crucian Carp in Norfolk ponds including the success of a decade of introduction/re-introduction efforts, recording a 72% decline in distribution between the 1950s–1980s and the 2010s though pond rehabilitation and restocking has since achieved substantial recovery. Further Crucian conservation initiatives are occurring throughout England. Atlantic Salmon (Salmo salar) populations in 64 principal salmon rivers in England and Wales are increasingly in a critical state. The most recent assessment (2019) categorised 62% ‘at risk’, 33% ‘probably at risk’, 5% ‘probably not at risk’ with none ‘not at risk’3. This in part reflects the legacy of poor spawning in winter 2015/16 resulting from unusually warm conditions and the impact of Storm

1 Tan, M. and Armbruster, J.W. (2018). Phylogenetic classification of extant genera of fishes of the order (Teleostei: Ostariophysi). Zootaxa 4476 (1): 006–039. DOI: https://doi.org/10.11646/zootaxa.4476.1.4. 2 Sayer, C.D., Emson, D., Patmore, I.R., Greaves, H.M., West, W.P., Payne, J., Davies, G.D., Tarkan, A.S., Wiseman, G., Cooper, B., Grapes, T., Cooper, G. and Copp, G.H. (2020). Recovery of the crucian carp Carassius carassius (L.): Approach and early results of an English conservation project. Aquatic Conservation: Marine and Freshwater Ecosystems. DOI: https://doi.org/10.1002/aqc.3422. 3 Environment Agency. (2020). Research and analysis – Salmonid and fisheries statistics for England and Wales 2019. Environment Agency, Bristol. (https://www.gov.uk/government/publications/salmonid-and-freshwater- fisheries-statistics-2019/salmonid-and-fisheries-statistics-for-england-and-wales-2019.)

British Wildlife freshwater fishes report; Page 1 Desmond. But it also reflects increasingly stressful environmental conditions in fresh, transitional and marine waters impacting on salmon, particularly due of climate change, diffuse pollution, habitat quality and barriers to migration. So far in 2020, early reports from a number of fish counters indicate an improvement in returning Atlantic Salmon and Sea Trout numbers on the Test, Itchen, Hampshire Avon and Fowey, which is encouraging, though overall numbers remain historically low and data from the Dorset Frome shows substantial declines in returning adult salmon. The health of Brown Trout (non-migratory Salmo trutta) populations is indicated by Water Framework Directive data, suggesting that nowhere are they reaching predicted status. The (Anguilla anguilla) is assessed as Critically Endangered on the IUCN Red List 4, young eel numbers in British rivers falling by around 90% compared to 40 years ago5. Action to protect eels over the past decade may be helping, with signs of better recruitment in recent years though substantially short of former levels. Research is ongoing to better understand the eel’s fascinating life history, including its oceanic spawning migration.

The UK’s two shad species, Twaite Shad ( fallax) and larger Allis Shad (Alosa alosa), are priorities under the UK Biodiversity Action Plan (BAP). Twaite Shad breed in the rivers Severn, Wye, Usk and Tywi, but the only confirmed breeding of Allis shad is in the River Tamar. Since 2017, numbers of shad returning to the River Severn have been counted at Tewkesbury under the ‘Unlocking the Severn’ project. In 2020, at least 11,678 Twaite Shad returned to the River Severn, a stable number over the last 3 years. There are no population estimates of Allis Shad in the Tamar, though some are thought to persist in the Severn because of high hybridisation rates with Twaite Shad. The Common Sturgeon or Sea Sturgeon (Acipenser sturio), long regarded as an occasional visitor to the UK, is now believed, based on newspaper archives dating back to 1700, to be native, part of a pan-European stock of which some 5-10% of individuals ‘stray’ to new waters to spawn apparently as a tactic to spread distribution. Some adolescent sturgeon from contemporary French and German restoration programmes have appeared off Britain’s South Coast in the last four years, with more projected to follow. The UK Sturgeon Conservation Alliance, formed in 2019, champions this 200 million-year-old ‘living fossil’ as a Pan-European challenge. Though declining since the early 19th century across their estuarine range (North Russia to North West Spain), European (Osmerus eperlanus) are assessed as of Least Concern under the Red List6 but are receiving conservation attention under the UK BAP. Improved water quality in the latter half of the 20th century saw smelt recorded in 36 of the original 52 watercourses in England where they formerly occurred, including the tidal Thames7. The Zoological Society of London has developed a conservation programme focused on estuaries, much-overlooked yet supporting numerous fish species. European Smelt, highly sensitive to pollution, constitute a flagship species in the Thames estuary, which holds one of the largest-known breeding populations of smelt in Britain; recent work confirmed the location of one spawning site and indicated a formerly unknown second spawning site. Alien and invasive fishes continue to cause concern. Topmouth gudgeon (Pseudorasbora parva) can form prolific populations, adversely affecting native fish populations. Under an ongoing eradication programme, Topmouth gudgeon were eliminated from a southern stillwater in early 2020 leaving a

4 https://www.iucnredlist.org/search?query=anguilla%20anguilla&searchType=species 5 ICES. (2018). European eel (Anguilla anguilla) throughout its natural range: ICES Advice on fishing opportunities, catch, and effort. Ecoregions in the Northeast Atlantic. ICES. DOI: https://doi.org/10.17895/ices.pub.4601. 6 https://www.iucnredlist.org/species/15631/4924600. 7 Colclough, S.R. and Coates, S. (2013). A Review of the status of Smelt Osmerus eperlanus (L.) in England and Wales – 2013. Colclough & Coates - SC2 Limited, SC2 Reference: EA/001.

British Wildlife freshwater fishes report; Page 2 handful of remaining UK populations and hope of full eradication. Media reports in 2020 of cichlid species and Silver Dollar Fish (Metynnis argenteus) from Scotland’s River Ness, and of piranha found in a Doncaster lake in 20198 – all tropical South American fishes unable to survive in British waters – are newsworthy highlights amongst many alien species apparently released from aquaria. Releases of alien fishes capable of survival and breeding in British waters pose significant risks. A long-held, often-repeated theory that fish colonise isolated water bodies as eggs attached to weed adhering to the legs of waterfowl continues to be wholly unsupported by evidence. However, a 2020 study9 found that endozoochory (transport within the gut) might play a role. A controlled experiment feeding captive Mallard Ducks (Anas platyrhynchus) with feed including developing eggs of two cyprinids (Common Carp and Prussian Carp Carassius gibelio) retrieved live embryos of both species, surviving beyond hatching, from fresh duck faeces. Dr Mark Everard

8 https://www.bbc.co.uk/news/uk-england-south-yorkshire-47974490. 9 Lovas-Kiss, A., Vincze, O., Löki, V., Pallér-Kapusi, F., Halasi-Kovács, B., Kovács, G., Green, A.J. and Lukács, B.A. (2020). Experimental evidence of dispersal of invasive cyprinid eggs inside migratory waterfowl. Proceedings of the National Academy of Sciences (PNAS), 117(27), pp.15397-15399. DOI: 10.1073/pnas.2004805117.

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