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Croaking Science: Captive Breeding, Conservation and Welfare of Amphibians.

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In general, Froglife does not encourage the keeping of amphibians (or reptiles) in captivity. Unlike the animals which have become used to close contact with people through the long process of domestication (farm animals and those that we treat as pets, or ‘companion animals’), there are no domesticated species of amphibians. We accept that people, especially children, can become fascinated and enthused by keeping newts, frogs or tadpoles, and that this can develop into a life-long interest that may encourage that person to contribute to the cause of wildlife conservation. However, the needs of amphibians are complex, and too often ignorance of these needs can lead to suffering and needless death in captivity. This can be particularly the case for non-native species when we add the traumas of being captured in the wild, international transportation, and being put on display for sale in a pet shop. Captive breeding of non-native species can alleviate some of this stress, but not the lottery of being cared for by enthusiastic but inexperienced keepers. Overall then, it is preferable for people to learn about amphibians from books, the media, wildlife ponds in private gardens and allotments, visits to wildlife sites where they can be encountered in their native habitats….and zoos.

Froglife recognises well-managed zoos (and aquaria) as exceptions to our policy against keeping amphibians in captivity. As well as having a broadly educational role concerning the world’s wildlife, zoos aspire to be an important component of the worldwide effort to conserve biodiversity. Where a species is threatened with extinction in the wild, it may be possible to take a small population into captivity and encourage them to breed, establishing a reserve population which can be used to re-populate the natural habitat when favourable conditions return. This practice is known as ex situ conservation. In this article, I review progress on ex situ conservation of amphibians and ask how well zoos are meeting their welfare needs.

The first Global Amphibian Assessment (Stuart et al., 2004) concluded that amphibians are the most threatened of the vertebrate classes, with about one third of species facing extinction. One response to this finding was the launch in 2007 of the Amphibian Ark (AArk) by a consortium of the IUCN and the World Association of Zoos and Aquaria. Its strategy is to identify threatened species whose survival chances could be improved by an interventionist programme including in-country and out-of-country captive breeding, allied to efforts to mitigate local threats to the species in the wild (Pavajeau et al., 2008). The AArk Newsletter, published quarterly, on open access, provides information on the progress of AArk programmes worldwide.

A major concern is highlighted by a team from Cologne Zoo (Jacken et al., 2020). They surveyed amphibian holdings in 4519 zoos and aquaria. Only about 7% of known amphibian species (=540 species) are currently kept in zoos. The three classes of amphibians are very unevenly represented, with 17.4% of newts and salamanders (=121 species), 6.1% of frogs and toads (=411 species) and only 3.9% of caecilians (= 8 species). Worse still, more than 10% of holdings are just single specimens; breeding success, even when larger populations are kept, is not high; and three quarters of the species kept are not threatened in the wild. Jacken et al. note that their survey did not include a number of good ex situ conservation programmes being run in university departments and museums, but they concluded overall that zoos are not fulfilling the aims of AArk. There can be several explanations for this situation. Although amphibians might seem highly suitable animals for ex situ conservation (for example, they are small, so do not require a lot of space; and they often have high reproductive outputs, with individuals maturing in a short time), in other ways they are highly problematic. For example, they are mostly nocturnal, so active when visitors are absent. Zoos depend for their incomes on paying customers, and need to prioritise species that people like to see. In addition, adult amphibians need live food, mostly insects, and this requires an efficient production facility. The high reproductive output of amphibians can also be a problem: once tadpoles have metamorphosed, how to keep the hundreds, perhaps thousands of offspring when space may be limited? And then there is disease: the high risks to the entire breeding facility from a chytrid outbreak requires a strict biosecure regime, incompatible with visitors (Pessier, 2008).

If AArk is to become successful, it clearly has to do better in encouraging zoos and other wildlife collections to hold more breeding populations of amphibians, prioritising threatened species (as long as a careful assessment concludes that ex situ conservation is an appropriate solution to the threats these species face). However, there is another issue: the psychological welfare of amphibians. There are several manuals of advice on amphibian husbandry, the most authoritative being Poole and Grow’s (2012) resource guide. This deals with food, water, housing, lighting, disease prevention etc. but, like most such guides does not cover behavioural and cognitive aspects of welfare. It has long been recognised that, in captivity, mammals and birds can suffer psychological distress from the lack of stimulation in their environment. This often manifests in the development of repetitive, sometimes self-damaging behaviours known as stereotypies. To avoid these, good zoo-keepers have devised a wide range of husbandry interventions, collectively known as ‘enrichments’, which provide the animals with interests and activities that promote psychological well-being (Young, 2003).

As well as promoting good mental health, enrichments can have another general purpose. Where animals are kept with ex situ conservation in mind, there is a need to prepare them for release into the wild. Enrichments can provide experience of ‘outside’ behaviours such as foraging, predator avoidance and mate-finding, without which survival in the wild is likely to be very brief.

In amphibians (and reptiles), there has been a tendency to believe that their behaviours are so simple and pre-programmed that enrichments are unnecessary. In a rebuttal of Dodd and Seigel’s (1991) critique of ex situ conservation for amphibians, Bloxam and Tonge (1995) wrote that amphibian ‘behaviours are less dependent on learning and environmental experience than those of birds and mammals…It has always seemed apparent to herpetologists that, with their relatively r-selected life history strategies1 and their low levels of behavioural complexity, amphibians should be ideally suited to short or medium-term conservation strategies’. These claims were accompanied by not a single supporting reference. It is worth contrasting these attitudes with work on fish, like amphibians, cold-blooded vertebrates and with a similar level of brain development. Much research, related to improving the welfare of fish in aquaculture, has shown that learning is important and that fish can suffer from pain and distress (Sneddon, 2015; Sloman, 2019). In addition, enrichments can promote the development of life-skills in fish (Salvanes, 2013). If this is the case for fish, why not for amphibians?

The most detailed discussion of enrichment in amphibians is the review by Michaels et al. (2014), subtitled ‘a neglected topic’. In comparison with the hundreds of papers on enrichment in mammals, Michaels et al. found only 14 relevant primary research papers on amphibians, and I have noted only a small number published since 2014. An issue is that ‘enrichment’ is rarely used in the titles, abstracts or key-words of papers related to husbandry in amphibians, whereas it is commonly used in the mammal literature. This in itself indicates that the amphibian research community has not yet taken the concept of enrichment on board. One sign of progress, however, comes from a comparison of the amphibian chapters in the 1999 and 2010 editions of the Universities Federation for Animal Welfare handbook, which recommends good practice for animals kept for use in laboratories. The main laboratory amphibian, since its earlier use in testing for human pregnancies, is still Xenopus laevis. The chapter by Halliday (1999) makes no mention of enrichment, but Tinsley (2010) discusses several aspects of enrichment such as the provision of covers and shelters. In addition to studies on shelters and their behavioural and physiological benefits, Michaels et al. found papers on the benefits of behavioural complexity: ramps, perches and ‘caves’ improved the welfare of bullfrogs. However, papers on the provision of complex habitats for amphibians too rarely investigate which features make a measurable difference in behaviour (for example, McRobert, 2003). In mammals, enrichments which encourage exploration of the enclosure and active foraging for food have been found to have considerable welfare benefits. We tend to think of amphibians as ‘sit-and-wait’ predators, but some species are active foragers. Michaels et al. found a few papers that investigated the welfare effects of varied food delivery techniques. Altering the position of a food dish increased activity levels in dendrobatid frogs, considered as a benefit. This, of course, raises the question: by what criteria do we consider the welfare of a captive amphibian to be improved? The small number of research studies to date means that this key question remains to be fully explored.

This article is intended as an introduction to the topic of welfare and enrichment, with a focus on amphibians. In a future article to appear in Froglife’s magazine Natterchat, I will review studies on reptiles.

Note 1: r-selected species generally have many offspring, limited parental care and short lives, as compared to K-selected species with small numbers of offspring, often prolonged parental care and long lives. Actually, some amphibians have complex parental care provision, small offspring numbers and some have long lives. In any case, it is not clear why Bloxam and Tonge feel there is a link between r-selected life histories and suitability for ex situ conservation.

Written by: Roger Downie Trustee, Froglife; Honorary senior lecturer, University of Glasgow

References

Bloxam and Tonge (1995). Amphibians are suitable candidates for breeding-release programmes. Biodiversity and Conservation 4, 636-644.

Dodd and Seigel (1991). Relocation, repatriation and translocation of amphibians and reptiles: are these conservation strategies that work? Herpetologica 47, 336-350.

Halliday (1991). Amphibians. In: Poole, T., editor. UFAW Handbook, 7th edition volume 2. Ps 90-102.

Jacken et al. (2020). Amphibians in zoos: a global approach on distribution patterns of threatened amphibians in zoological collections. International Zoo Yearbook 54, 146-164.

McRobert (2003). Methodologies for the care, maintenance and breeding of tropical poison frogs. Journal of applied animal welfare science 6, 95-102.

Michaels, Downie and Campbell-Palmer (2014). The importance of enrichment for advancing amphibian welfare and conservation goals: a review of a neglected topic. Amphibian and Reptile Conservation 8, 7-23.

Pavajeau et al. (2008). Amphibian Ark and the Year of the Frog campaign. International Zoo Yearbook 42, 24-29.

Pessier (2008). Management of disease as a threat to amphibian conservation. International Zoo Yearbook 42, 30-39.

Poole and Grow, editors (2012). Amphibian Husbandry Resource Guide. Association of Zoos and Aquariums.

Salvanes et al. (2013). Environmental enrichment promotes neural plasticity and cognitive ability in fish. Proceedings of the Royal Society B 280, 1767.

Sloman et al. (2019). Ethical considerations in fish research. Journal of Fish Biology 94, 556-577.

Sneddon (2015). Pain in aquatic animals. Journal of experimental biology 218, 967-976.

Stuart et al. (2004). Status and trends of amphibian declines and extinctions worldwide. Science 306, 1783-1786.

Tinsley (2010). Amphibians, with special reference to Xenopus. In: Hubrecht and Kirkwood, editors. UFAW Handbook 8th edition. Ps 741-760.

Young (2003). Environmental enrichment for captive animals. Blackwell, Oxford.

Acknowledgements

Thanks for feedback on the first draft of this article from Kathy Wormald and Sheila Grundy.

 

 

 

 

Cold Climate Adaptations and Freeze Tolerance in Amphibians and Reptiles

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Amphibians and reptiles are well-known for being ectothermic (cold-blooded). This means that they are unable to internally regulate their body temperature, and instead they rely on their external environment to do so. Consequently, when we think about species like snakes and lizards, we tend to associate them with hot climates, often picturing them basking in the sunshine. Although they do inhabit hot climates, amphibians and reptiles can be found all over the world except for Antarctica. The UK has 14 native species of amphibian and reptile, and a few hardy species can even be found in extreme cold climates such as in the Arctic where temperatures can drop to -45°C. So, how are these species adapted to survive in such extreme conditions?

One important strategy used by amphibians and reptiles is brumation, where they go into a state of dormancy during the cold winter months. They typically brumate in burrows or under log piles, but different species will use a variety of habitats, with some common frogs even brumating in the mud at the bottom of ponds. Although similar to hibernation, the key difference is that brumating animals will emerge for short periods to forage before returning to their state of dormancy, usually on warmer days. All of the native UK species brumate to avoid the coldest weather and conserve energy. Nevertheless, British weather can still be challenging year-round. Common frogs are particularly hardy, and have been found breeding at the highest altitude of any amphibian in the UK at 1,120m in the Scottish Cairngorm Mountains. Higher altitude habitats offer a much shorter window for breeding, so to cope with this, high altitude common frog populations in Scotland have higher growth rates and shorter larval periods compared to low altitude populations (Muir et al. 2014). This ensures metamorphosis is completed before temperatures drop again to maximise chances of survival. On the other hand, some common frog tadpoles will instead delay metamorphosis until the following spring and overwinter as a tadpole rather than a froglet; this may be beneficial in colder temperatures as they will be able to metamorphose at a larger size, improving their chances of survival (Walsh et al., 2008).

 Another UK species which is particularly well-adapted to cold conditions is the leatherback turtle. It often comes as a surprise when people find out that the leatherback turtle is native to the UK, but they are active in our surrounding seas despite the low number of sightings (read more on this here). Leatherbacks have a larger range than other sea turtles and can survive in our cold waters by maintaining a deep body temperature that is 18°C higher than the surrounding water (Frair et al., 1972). They do this through a countercurrent heat exchange process in their flippers (Greer et al., 1973), a process much more commonly associated with mammals and birds than reptiles. Blood vessels in their flippers are closely packed together so that warm blood moving from the core to the extremities passes in close proximity to the cold blood returning from the extremities to the core. Heat hHeateat is transferred into the cold blood and returned to the core, avoiding the extremities where it would be lost to the external environment (Greer et al., 1973). This method of reducing heat loss at the extremities and circulating that heat back into the core of the body is critical for their survival in cold water.

Image Credit: Jack Rawlinson

A very different adaptation is a species’ reproductive strategy, of which there are two key options, oviparity (egg-laying) or viviparity (live-birth). Most reptiles are oviparous as this requires less investment per brood, enabling them to have multiple broods per year. However, reptiles in cold climates are actually more likely to be viviparous because internal development allows the mother to thermoregulate more efficiently, thus improving offspring survival in cold or unpredictable environmental conditions (Tinkle and Gibbons, 1977). Cold temperatures can also reduce the length of the breeding season, making the possibility of multiple broods per year unlikely, and thereby eliminating the benefits of oviparity (Tinkle and Gibbons, 1977). In Scotland, all of the native reptiles are viviparous with one exception; the grass snake. The grass snake is widespread in England and Wales but only found in the far south of Scotland. Could this suggest that being oviparous makes them less suited to the cooler Scottish climate? Interestingly however, there is a population of oviparous lizards, the sand lizard, living on the Scottish island of Coll. They are native to England and not Scotland, but were introduced to Coll in the 70s and are still there today. This may suggest that although viviparity can be beneficial in cold climates, it is not essential.

The number of amphibians and reptiles that thrive in the British weather is undoubtedly impressive, but even more remarkable is the array of hardy species which survive extreme cold-climates such as the Arctic. For any species this would be a challenge, and for most ectotherms freezing temperatures are lethal – the fluids within their cells freeze and form ice crystals which can then rupture (Storey and Storey, 1988). However, there are two fundamental strategies used by cold-climate ectotherms to combat this; freeze avoidance (supercooling) and freeze tolerance. Freeze avoidance is where cell fluids remain liquid despite reaching freezing temperatures, while freeze tolerance is where an individual is able to survive freezing to an extent by restricting freezing to extracellular areas (Storey and Storey, 1988). These processes typically rely on the production of a cyroprotectant, a substance which reduces the freezing point of water and can be used to prevent freezing overall (freeze avoidance) or in cells and key organs (freeze tolerance). Different substances can act as cryoprotectants in amphibians and reptiles, with some common ones including glycerol, glucose and taurine. Cyroprotectants are also used in medicine, for example when donor organs are preserved through cooling, cyroprotectants are often used to prevent cell freezing and rupture.

One species which uses these strategies is the wood frog, the only frog known to live in the Arctic Circle. They can tolerate being frozen at -3°C for two weeks, with up to 70% of their body water freezing (Costanzo et al., 1993). They use glucose as a cyroprotectant, which they produce in high quantities in key organs to prevent ice formation (Costanzo et al., 1993). This restricts freezing to less important parts of the body where it is less likely to cause damage. Red-sided garter snakes in Canada use a similar strategy and can survive at -2.5°C with up to 40% of their body water freezing, using taurine as their cryoprotectant (Churchill and Storey, 2011). Unlike wood frogs they have a much shorter period of tolerance, with only a 50% chance of survival after 10 hours of freezing (Churchill and Storey, 2011). This may suggest that this is not a strategy that is used regularly, but instead an adaptation to survive short periods of frost in the autumn or spring soon before/after brumation.

Although species like the wood frog and red-sided garter snake are incredibly hardy, there is one species which can out-do them all; the Siberian newt. Temperatures in Siberia can reach as low as -45°C and it seems impossible that much life could thrive here, yet the Siberian newt does. Incredibly, it can survive being frozen to -35°C for 45 days, or -50°C for 3 days (Berman et al., 2016). It is not entirely clear how this remarkable species survives such hostile temperatures, but it seems likely that they produce a cryoprotectant to protect their cells and key organs from freezing, although it is not known what this cyroprotectant might be. 

 Amphibians and reptiles are ectothermic, and consequently are often associated with hot climates. In reality, they can be found in a huge variety of habitats and climates and have an array of behavioural and physiological adaptations which enable them to live and thrive in even some of the coldest parts of the world. Adaptations such as brumation, viviparous reproduction, and efficient heat transfer systems are just a few of the things that can help amphibians and reptiles survive in cold or variable climates. Remarkably, in the coldest regions, species use even more extreme adaptations of freeze avoidance and freeze tolerance in order to stay alive. The ability of some species to tolerate being frozen at extreme temperatures for extended periods tells an incredible story of survival and adaptation, and reminds us never to underestimate the brilliance of amphibians and reptiles.

Written by Mirran Trimble

References:

  1. Muir A.P., Biek R., Thomas R., Mable B.K., 2014. Local adaptation with high gene flow: temperature parameters drive adaptation to altitude in the common frog (Rana tomporaria). Molecular Ecology. 23, 561-574.
  2. Walsh P.T., Downie J.R., Monaghan P., 2008. Larval overwintering: plasticity in the timing of life-history events in the common frog. Journal of Zoology. 276, 394-401.
  3. Frair W., Ackman R., Mrosovsky N., 1972. Body temperature of Dermochelys coriacea: Warm turtle from cold water. 177, 791-793.
  4. Greer A., Lazell J., Wright R., 1973. Anatomical Evidence for a Counter-Current Heat Exchanger in the Leatherback Turtle (Dermochelys coriacea). 244, 181.
  5. Tinkle D.W., Gibbons J.W., 1977. The Distribution and Evolution of Viviparity in Reptiles. Miscellaneous Publications Museum of Zoology. 154.
  6. Storey K.B., Storey J.M., 1988. Freeze tolerance in animals. Physiological reviews. 68(1), 27-84.
  7. Costanzo J.P., Lee R.E., Lortz P.H., 1993. Glucose concentration regulates freeze tolerance in the wood frog Rana sylvatica. Journal of Experimental Biology. 181, 245-255.
  8. Churchill T.A., Storey K.B., 2011. Freezing Survival of the Garter Snake Thamnophis sirtalis parietalis. Canadian Journal of Zoology. 70(1), 99-105.
  9. Berman D.I., Meshcheryakova E.N., Bulakhova N.A., 2016. Extreme Negative Temperatures and Body Mass Loss in the Siberian Salamander (Salamandrella keyserlingii, Amphibia, Hynobiidae). Doklady Biological Sciences. 468, 137-141

Ponds Against Climate Change

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From Antarctica to the tropics, ponds are widespread habitats found in nearly all terrestrial biomes (Jeffries, 2016). Research estimates that there are 304 million natural lakes and ponds worldwide, covering a total area of approximately 4.2 million km2 (Downing et al., 2006). This article will focus on ponds: according to limnologists, the difference between ponds and lakes is that ponds are shallow enough that plants could grow across the entire surface meaning that it has a photic zone where sun can reach the bottom. By contrast, lakes have an aphotic zone meaning there are sections deep enough that sunlight cannot reach the bottom. Ponds are biodiversity hotspots for both aquatic and terrestrial species, providing habitat for rare specialists such as fairy and tadpole shrimp. Not only are they vital for these species, but they are also vital in managing landscapes from threats such as flooding and climate change. It is known that aquatic ecosystems have a large role in managing greenhouse gases, with oceans among the most well-known of carbon sinks. However, with lakes and ponds covering such a vast expanse of area, is it possible that they are the climate’s unsung heroes?

Carbon sinks are reservoirs that absorb and store atmospheric carbon through physical and biological processes. One study concludes that ponds may be more active in nearly all of these processes than large lakes, marine ecosystems and terrestrial ecosystems (Downing, 2010). Carbon burial rates between ponds can vary depending on composition. Ponds are not ubiquitous, thus the effectiveness of carbon sequestration varies per site depending on factors such as substrate type and vegetation. Gilbert et al., (2014) found that permanent and naturally vegetated ponds were the most efficient at sequestering carbon dioxide, particularly those dominated by thick moss swards and aquatic grasses. These form a thick, moist blanket when the pond dries out, minimising the release of stored carbon into the atmosphere. The least efficient ponds were temporary, shallow arable ponds which lacked vegetation and were regularly disturbed. When discussing the value of ponds in carbon sequestration, it may be unhelpful to group all ponds together as their importance can vary considerably based on their composition. Furthermore, it is important to note that ponds can serve a variety of purposes. Whilst ponds capturing excess fertilisers and pesticides are useful in the fight against climate change, they may not make good wildlife ponds or facilitate biodiversity.

This diversity of ponds is reflected in the range of carbon sequestration rates found across the literature. One study found that small ponds sequester 79-247g of organic carbon per square meter annually, a rate 20-30 times higher than woodlands, grasslands and other habitat types (Taylor et al., 2019). Céréghino et al., (2014) suggested that some 500m2 ponds may even be capable of sequestering up to 1000kg of carbon per year, as much as a car would produce in that time. Although ponds only take up 0.0006% of land area in the UK, a tiny proportion compared to the 36% of grasslands (Carey et al., 2008), their high rates of carbon burial suggest that their overall contribution is significant – even when compared to much larger habitats. Thus their role in tackling climate change should not be overlooked.

Biological processes carried out by aquatic vegetation are pivotal in carbon sequestration in ponds. Photosynthesis contributes to the sequestration of carbon dioxide by turning it into oxygen and biomass. One kilogram of algae uses an average of 1.87 kilograms of carbon dioxide a day (Anguselvi et al., 2019). Algae in ponds also contribute to reducing additional greenhouse gases such as nitrous oxide (N2O). Nitrogen is a key component in chlorophyll and thus used in farm fertiliser. Excess nitrogen could react with oxygen in the air to become N2O. The presence of algae in farm ponds to capture this excess can prevent this reaction from occuring and limit emission of the greenhouse gas. A study has found that two thirds of farm ponds act as N2O sinks (Webb et al., 2019), making them an important contributor to combating climate change, particularly as N2O traps heat at 300x the rate of CO2. 

Ponds play an important role in mitigating climate change, however, there is evidence to suggest that they can also act as carbon sources. Does this offset their sequestering benefits? Take for instance, permafrost thaw ponds. Permafrost thaw ponds in northern regions can be particularly prominent sources of carbon. As permafrosts thaw, vast amounts of carbon dioxide and methane are released, resulting in the formation of small ponds which become carbon emission hotspots (Kuhn, 2018). Although they are releasing carbon, it is not the pond itself creating these gases. Global warming is causing the permafrosts to thaw out and release the stored carbon. Although the ponds facilitate the emissions, it is perhaps misleading to label them as a carbon source in these instances. 

Large habitats such as oceans and woodlands are well-known for their role in reducing greenhouse gasses and mitigating the effects of climate change, but ponds may play an equally important and largely underappreciated role. Ponds are also a fantastic tool against climate change because they give people a way in which to take action. People can easily create ponds in their own gardens and community spaces, and in this way play a part in reducing greenhouse gas emissions and contribute to the global fight against climate change.

Written by Mirran Trimble & Emily Robinson

 

References

Anguselvi, V., Masto, RE., Mukherjee, A., & Singh, PK. (2019) CO2  Capture for industries by algae, Algae, Yee Keung Wong, IntechOpen, DOI: 10.5772/intechopen.81800. Available from: https://www.intechopen.com/books/algae/co-sub-2-sub-capture-for-industries-by-algae

Carey, PD., Wallis, S., Chamberlain, PM., et al. (2008) Countryside Survey: UK results from 2007. Swindon, UK: Natural Environment Research Council.

Céréghino, R., Boix, D., Cauchie, HM., et al. (2014) The ecological role of ponds in a changing world. Hydrobiologia. 723, 1–6.

Downing, JA. (2010) Emerging global role of small lakes and ponds: little things mean a lot. Limnetica. 29(1), 9-24.

Downing, JA., Prairie, YT., Cole, et al. (2006) The global abundance and size distribution of lakes, ponds, and impoundments. American Society of Limnology and Oceanography. 51(5), 2388-2397.

Gilbert, PJ., Taylor, S., Cooke, DA., et al. (2014) Variations in sediment organic carbon among different types of small natural ponds along Druridge Bay, Northumberland, UK. Inland Waters. 4(1), 57-64.

Jeffries, MJ. (2016) Flood, drought and the inter-annual variation to the number and size of ponds and small wetlands in an English lowland landscape over three years of weather extremes. Hydrobiologia. 768, 255–272.

Kuhn, M., Lundin, EJ., Giesler, R., et al. (2018) Emissions from thaw ponds largely offset the carbon sink of northern permafrost wetlands. Scientific Reports. 8, 9535.

Taylor, S., Gilbert, PJ., Cooke, DA., et al. (2019) High carbon burial rates by small ponds in the landscape. Frontiers in Ecology and the Environment. 17(1), 25-31.

Webb, JR., Hayes, NM., Simpson, GL. et al. (2019) Widespread nitrous oxide undersaturation in farm waterbodies creates an unexpected greenhouse gas sink. PNAS. 116(20), 9814-9819.

 

Should we count marine turtles as members of the British fauna?

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In August 2020, the media outlet Wales On-line reported that a five-foot long marine turtle had surfaced beside a small fishing boat off the north coast and swum alongside it for an extended period before diving out of sight. The excited boat owner said that he had fished those waters for over 20 years, and never seen a turtle before. Was this an exceptional sighting? The fisherman was certainly lucky. Over the last century or so, the average number of leatherback turtles (the species observed) seen in British waters each year is around 15. However, this is bound to be a vast underestimate of the turtle numbers actually present in British waters. This is due to them being incredibly difficult to locate as they rarely emerge from the depths to breath, nor do they nest on British beaches; so the chances of actually spotting one in the huge expanses of our coastal waters are very slim.

Botterell et al. (2020) have published an analysis of marine turtle sightings, strandings (usually found dead washed up on shore) and captures (by-catch in fishing nets) since 1910. Of 1997 records, 84% are of leatherbacks; 12% of loggerheads, and 3% of Kemp’s ridleys. The remaining 13 records concern tiny numbers of three more species. Until 1980, records were small in number for all species, with substantial increases from the 1990s onwards. Mapping of the records shows that most are predominantly from the western side, including the English Channel, all around Ireland and north to the Orkneys and Shetlands. Leatherbacks and loggerheads have been recorded at all times of the year, with peaks in June-October (leatherbacks) and November-March (loggerheads). Kemp’s ridleys have only been seen from October-February. Measurements on body size, mostly from strandings and captures, suggest that most leatherbacks in British waters are adults, while loggerheads and Kemp’s ridleys are juveniles.

Although they may seem like an exotic species, these data clearly show that we should regard leatherback turtles as normal members of the migratory fauna that inhabits our surrounding seas. Adult leatherbacks manage this by generating enough heat that their body temperature is above ambient, allowing them to remain active in the cold waters of the North Atlantic; even juveniles can raise their body temperature above cold water temperatures by activity and reduction of heat loss (Bostrom et al., 2010).  For loggerheads and Kemp’s ridleys, the majority of records in British waters are strandings of juveniles in winter: these are most likely animals cold-stunned as water temperature declines. What is unknown is the number which venture into our waters, but manage to travel south and survive.

Marine turtles display what are known as cosmopolitan ranges, meaning that they are near-ubiquitous in waters globally. This has led to their incorporation into indigenous cultures around the world, with their size and habits having led to mythological status in many places. In an ecological context, the extensive migrations they undertake between foraging and nesting grounds (which often span entire oceans) are important for connecting ecosystems globally. The three species commonly found in British waters have distinct breeding and foraging grounds, with much information recently derived from satellite tracking of tagged adult females following capture at nesting sites (Fossette et al., 2014). For example, Atlantic leatherbacks consist of two separate populations. South Atlantic turtles breed either along the coast of Brazil or of West Africa, especially Gabon. Foraging takes them across the ocean and southwards, but not into the North Atlantic. The North Atlantic population breeds on the beaches of southern Florida, the islands of the Caribbean and the Guianas. They forage east and north, as far as British waters, as we have seen. Adult females return to nesting beaches every 2-4 years and lay up to 7 clutches, each 60 – 110 eggs, over several months.

Female leatherback turtle nesting on a beach in Tobago.

The males wait near the approaches to the beaches and attempt to mate with any females that turn up; however, they do not come onto land and instead spend their entire lives at sea. Leatherback females show moderately high nesting site fidelity, with all their nests in a season being laid on the same beach which they were born on or ones in close proximity. Hatchlings disperse into the sea and travel east towards open ocean to develop into juveniles. Kemp’s ridleys nest in the Caribbean, nearly all on one 16- mile Mexican beach; juveniles extend across the North Atlantic. Loggerheads are highly cosmopolitan with three distinct Atlantic populations. In the West Atlantic, they nest on beaches as far north as New Jersey and south to Parana in Brazil. Juveniles forage very widely. The Gulf Stream (also called the North Atlantic Gyre) was thought to be the primary determinant of juvenile distribution, as it carries developing individuals into east Atlantic waters. However, active dispersal has been recently documented in loggerhead, green and Kemp’s ridley turtles which suggests a more selective use of habitat than previously thought (Mansfield et al., 2014).

Sources of nutrition are a key determinant of marine turtle distribution. In other words, they go where the food is. The abundance of jellyfish in eastern Atlantic waters brings adult turtles, including loggerhead and Kemp ridley’s, but especially leatherbacks to UK and Irish coasts. As well as helping to predict the position of leatherbacks, the presence of jellyfish affects the depth at which the turtles swim. Jellyfish display a diurnal pattern of vertical migration, following their plankton prey up and down the water column. Plankton move to the water’s surface at night, when they are less visible to potential predators, and are closely followed by the jellyfish and, in turn, the turtles. Leatherbacks are so committed to pursuing their translucent prey that one intrepid individual was found swimming over 1000 metres underneath the surface during a foraging mission. This feat put leatherbacks into the top three diving animals on the planet alongside beaked whales and sperm whales. Their dedication to pursuing cnidarians was also shown by a 12,000 mile foraging journey from Indonesia to the US, which shows the determination present in their feeding habits.

It is these same feeding habits that have become a source of harm in recent times. Ingestion of marine litter, especially plastic bags, is a leading cause of turtle mortality. Particularly affected are leatherback turtles, due to their specialised diet of jellyfish which closely resemble partially degraded plastic bags hanging in the water column. One study analysed historical autopsy records spanning 123 years (1885-2007) and found plastic to be present in the digestive tracts of 34% of the dissected turtles (Mrosovsky et al., 2009). Plastic ingestion has a range of detrimental consequences, including reduced nutritional intake and asphyxiation.

There is a considerable worldwide effort to conserve marine turtle populations. One measure of this is the regularly updated IUCN Red List.  Since the 1980s, there has been a large reduction in leatherback numbers which has led to a ‘vulnerable’ classification by the IUCN. However, there are subpopulations that are doing even worse, such as those of the northwest Atlantic subpopulation who were reclassified from Least Concern to Endangered in 2019. Another case was a subpopulation based in the South China Sea that produced 10,000 yearly nests on the beaches of Malaysia. However, from the 1960s the population dwindled to the point where only two nests were laid in 2008, both of which were infertile (WWF, on-line). This decrease in numbers was partly made worse by misled conservation efforts, which collected and artificially incubated eggs at excessive temperatures, scrambling the sex determination process. As in many other reptile species, sex is determined by the temperature of incubation of the eggs. This shows the need for in depth research when developing conservation measures to deal with anthropogenic threats.

There is a wide range of barriers to the recovery of turtle numbers, with pressures both natural and anthropogenic. Among the natural threats faced by marine turtles is the impact of climate change on temperature-dependent sex determination, which disrupts reproduction and has knock-on effects on population demographics and dynamics. Another prominent challenge to successful reproduction is the predation of eggs and juveniles, which make for easy pickings for a diverse array of coastal predators.

A group of black vultures patrol a nesting beach looking for hatchlings to prey on.

Conservation efforts and scientific surveys are often based around these issues, when the turtles are onshore and accessible for data collection. Studies focused on the reproductive stage of turtle life are very valuable to the implementation of management strategies and can provide a range of insights into their life histories. The Exploration Society operating out of the University of Glasgow has run many research projects along these lines, based in the Caribbean islands of Trinidad and Tobago. These studies have contributed analyses of egg temperatures, tagging efforts to track distribution and last year uncovered a novel female behaviour for nest protection: after burying the eggs, females create a ‘decoy trail’ aimed at misleading predators over the location of the nest (Burns et al., 2020). All of these contributions are helpful to maintaining healthy populations of turtles, but there is still a large gap in the knowledge of turtle life out in the open ocean.

Leatherback hatchlings burst from a concealed nest, heading to the sea to begin their life of roaming the oceans of the world.

Marine turtles spend most of their lives navigating the oceans, across a massive geographic range and at various depths. This makes them pretty tough to track throughout their development from hatchling to mature adult, and even between nesting events. However, as we have seen, the use of satellite tracking has revealed much about adult migrations. In addition to this, the missing pieces of the puzzle can be cleared up with the help of sighting and stranding data collected from coastlines within their range, which can be acquired through citizen science projects and compiled into databases to map distributions at different stages of development. Stranded carcasses can also be inspected to gain an insight into the causes of death, and the larger scale threats to their survival. For example, carcasses with scars on their shells can show the impact of high densities of fishing vessels. The number of sightings can also be used as an indicator of population trends, as was shown by Botterell et al. (2020), summarised above. Tracking sightings and strandings off the British and Irish coasts, the study was able to attribute dips in numbers to major environmental events such as the Deepwater Horizon oil spill in 2010 and link population increases to successful conservation programmes. This shows that despite the challenges facing this fascinating group of reptiles, we can make use of the full range of analysis tools available to more fully understand their life history; from hatching through juvenile to nesting adult. From this, effective conservation strategies can be developed to protect marine turtles throughout their cosmopolitan range.

References

Bostrom, B.L. et al. (2010). Behaviour and physiology: the thermal strategy of leatherback turtles. PLoS ONE 5(11), e13925.

Botterell, Z.R.L. et al. (2020). Long-term insights into marine turtle sightings, strandings and captures around the UK and Ireland (1910-2018). Journal of the Marine Biological Association of the United Kingdom 100, 869-877.

Burns, T.J. et al. (2020). Buried treasure- marine turtles do not ‘disguise’ or ‘camouflage’ their nests but avoid them and create a decoy trail. Royal Society Open Science 7, 200327.

Fossette, S. et al. (2014). Pan-Atlantic analysis of the overlap of a highly migratory species, the leatherback turtle, with pelagic long-line fisheries. Proceedings of the Royal Society B 281, 20133065.

Mrosovsky, N. et al. (2009) Leatherback turtles: The menace of plastic. Marine Pollution Bulletin 58, 287-289.

Mansfield, K.L. et al. (2014) First satellite tracks of neonate sea turtles redefine the ‘lost years’ oceanic niche. Proceedings of the Royal Society B: Biological Sciences 281, 20133039.

WWF on-line. Search at https://www.wwf.org.my/?25625/Marine-Turtles-Malaysias-National-Heritage

Cameron Boyle, Roger Downie and Jack Rawlinson

Photos generously provided by Jack Rawlinson

University of Glasgow

The effect of the climate crisis on UK reptile populations

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Back in 2018 we discussed some of the impacts of climate change on amphibians worldwide (Froglife 2018). Since then, climate change has continued to accelerate, with global average temperatures in 2020 more than 1oC warmer relative to pre-industrial levels. The 2015 Paris Agreement has not, so far, caused nations to reduce their emissions anywhere near fast enough (Global Carbon Project 2020). The extent of future warming is projected to reach somewhere between 2 – 4oC or above, dependent upon a range of scenarios (IPCC 2014). The magnitude and speed of this change is unprecedented, and the impacts upon wildlife are already being seen.

We know that wildlife and their habitats – collectively termed the ‘biosphere’ – are in a fine, dynamic and interconnected balance. Unpicking the exact drivers of population changes is not straightforward, because they themselves are interacting in complex ways. What’s clear is that climate change is an additional stress factor for wildlife worldwide, on top of (and often accelerating) habitat loss and fragmentation, pollution and the impact of invasive species. In the UK climate change is predicted to cause hotter, drier summers and warmer, wetter winters. There will be greater extremes of weather, as well as sea level rise (Met Office 2019).

So how might the UK’s terrestrial reptiles be affected by climate change?
To begin to answer this, we can consider the direct effects of climate change on reptile physiology and behaviour, and indirect impacts from changing trophic interactions (populations of predators and prey), and from changes to reptile habitats (Le Galliard et al. 2012).

UK reptiles are more or less at the northernmost edge of the range for their species, although the adder, common lizard and slow worm have Scandinavian populations at higher latitudes. These three species are viviparous, meaning embryos develop within the body of the adult and born live. The smooth snake is ovoviviparous, which can be described as a more primitive form of viviparity, where the eggs develop within the mothers body. Sand lizards and grass snake are oviparous, meaning they lay their eggs externally, and embryos are therefore more reliant on environmental factors for their development. 

All UK reptiles however, have cousins residing in the warmer southerly climes of Iberia and Central Europe and the Balkans. So, we could assume that warmer climate here will improve survival in existing reptile populations, while enabling a northward shift of their distributions. Unfortunately, the reality is not that simple. Dunford and Berry (2012) modelled UK reptile population changes under low and high emissions scenarios for 2050 and 2080. Grass snakes appeared to be the only species consistently predicted to shift northward while maintaining the majority of their present distribution (see Cathrine, 2014 for tantalising evidence of Scottish grass snake populations), while slow worms showed a mixed northward shift with a contraction of southern populations. For all other species modelling predicted widespread population decline, greater under a higher emissions scenario (Dunford and Berry 2012).

Being ectothermic, reptiles are highly sensitive to their environment, with a tight bell curve describing their optimal climatic conditions (Le Galliard et al. 2012). Temperature and rainfall strongly influence reptile behaviour, and a changing climate has great potential to create mismatches – for example if temperature and rainfall is suboptimal either for reptiles or their prey species, especially at key points in the year such as hibernation emergence. Climate change is already affecting reptile prey populations and will continue to do so. For example Ewald et al. (2015) identified numerous invertebrate groups demonstrating sensitivity to extreme climate events over the last four decades. These trends must be considered alongside the ongoing impact of other pressures, particularly pesticide use (van Klink et al. 2020), all of which creates a complex picture. Climate impacts will vary between species groups and depend upon other biogeographical factors, meaning that impacts will not be the same everywhere for a given species.

In the UK, warming should increase reptile growth and maturation rates, due to longer periods of activity. Milder winters will likely reduce hibernation lengths for our reptiles. Earlier spring emergence, and activity extending further into the autumn and winter months would likely bring reproduction forward in the year, as gestation and incubation length is generally shorter in warmer climates. Larger body sizes in warmer climates may result in greater reproductive success (Le Galliard et al. 2012). Warm temperatures also enable a greater number of number of broods per year, observed in slow worms (Smith 1990), and common lizards (Bestion et al. 2015). However, life cycle changes may have additional impacts on population demographics and survival. Bestion et al. (2015) created experimental common lizard populations in climate-controlled chambers, with populations either subject to current average temperatures or those matching IPCC predictions for the coming century. Warming increased growth rates, brought reproduction forward, and resulted in a higher number of broods per season. However, this life cycle acceleration was coupled with a reduction in adult survival rates. Of several possible causes, the authors proposed the most likely to be greater metabolic requirements for larger individuals, with warmer temperatures increasing energetic requirements which could not be met fully by increased foraging, particularly when warm weather restricted their activity.

Our fragmented UK landscape creates major barriers for all wildlife. Reptile species are generally philopatric (tending to return to or remain near the same particular area), and so are especially sensitive to habitat loss, with populations often centred around relatively small habitat pockets or managed reserves. So even if a warmer climate could result in populations expanding northward, whether this will occur in reality depends on whether there are routes and habitats for them to do so. Araujo et al. (2006) simulated climate change driven UK reptile population dynamics under assumptions of unlimited and zero dispersal ability. Unlimited dispersal resulted in population expansion, with some local extinctions in southerly locations. Zero dispersal resulted in population contractions for all UK species, indicating climate change driven population collapse. This demonstrates the importance of considering all factors influencing population viability and dispersal in combination with climate change pressures.

Adders are usually reliant on specific habitat patches and are highly sensitive to habitat destruction and hibernation area disturbance due to their low recolonization abilities, even relative to other reptile species. On a local level, given typically small population sizes and low mobility, climate change driven habitat quality declines could result in local extinctions particularly as they may not have suitable adjacent habitat, nor the inclination to move (Gleed-Owen and Langham 2012). Although McInerny (2018) indicates that implementing appropriate mitigation can enable adder populations to persist alongside human modifications to local habitats, the adders ongoing decline nationwide is concerning (Baker et al. 2002, Gardner et al. 2019), which even a low emissions climate change scenario is likely to exacerbate (Dunford and Berry 2012).

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The dual pressures of habitat loss and climate change are even more apparent for our two most limited reptiles, the sand lizard and the smooth snake. Sand lizards can be found on lowland heath as well as coastal sand dunes. Smooth snakes are only known to be present on lowland heath in the south of England. Populations are generally isolated with little capacity for dispersal, creating a barrier to adaptation to changing conditions. Climate change could threaten habitat quality, for example increased frequency of heavy rainfall events could destroy sand lizard nests and reduce juvenile survival rates (Edgar and Bird 2006), while increased fire prevalence and sea level rise could destroy important habitat features. Dunford and Berry (2012) paint a particularly dire picture for the sand lizard, as its reliance upon highly specific landscape features such as south facing slopes and complex habitat mosaics makes the species highly sensitive to habitat loss. A small population of sand lizards has persisted on the Scottish Isle of Coll, since their introduction for research in the 1970s. Comparing the climate change resilience of this northern and relatively isolated population with that of other UK populations will be an interesting topic for study over the next few decades.

Heathland habitats are one of our most heavily impacted by urbanisation in the UK. Although direct loss through land-use change is now controlled by planning and environmental legislation, development in surrounding areas continues to increase pressure on remaining isolated heathland patches, through increased fire risk, predation by domestic animals and disturbance (Hayhow et al. 2019). Fagundez (2013) describes further pressures facing heathlands under climate change, including fires, and shifts in vegetation composition. We are used to a static conservation model for our heaths. As climate change progresses, the ideal climatic conditions for heath will likely expand in Britain (Thomas et al. 1999), and Loidi et al. (2010) point out that extensive lowland heaths throughout southern Europe support a greater diversity of reptiles than we see here. However, whether habitats will be able to expand is an entirely human choice (Coll et al. 2016, Hayhow et al. 2019).

All of the pressures we have presented here are anthropogenic in origin, born from human choices, and our expectations of how we can and should manage the land and its resources. The enormity of shifting these practices cannot be underestimated, but at least it is within our abilities to do it!

Written by Zak Mather-Gratton 

References
Araújo, M.B., Thuiller, W. and Pearson, R.G., 2006. Climate warming and the decline of amphibians and reptiles in Europe. Journal of biogeography, 33(10), pp.1712-1728.

Baker, J., Suckling, J. and Carey, R., 2002. Status of the adder Vipera berus and the slow-worm Anguis fragilis in England. English Nature.

Bestion, E., Teyssier, A., Richard, M., Clobert, J. and Cote, J., 2015. Live fast, die young: experimental evidence of population extinction risk due to climate change. PLoS Biol, 13(10), p.e1002281.

Cathrine, C., 2014. Grass Snakes (Natrix natrix) in Scotland. Glasgow Naturalist, 26(Part 1), pp.36-40.

Coll, J., Bourke, D., Hodd, R.L., Skeffington, M.S., Gormally, M. and Sweeney, J., 2016. Projected climate change impacts on upland heaths in Ireland. Climate Research, 69(2), pp.177-191.

Dunford, R.W. and Berry, P.M., 2012. Climate change modelling of English amphibians and reptiles: Report to Amphibian and Reptile Conservation Trust (ARC-Trust).

Edgar, P. and Bird, D.R., 2006. Action plan for the conservation of the Sand Lizard (Lacerta agilis) in Northwest Europe. Document T-PVS/Inf (2006), 18.

Ewald, J.A., Wheatley, C.J., Aebischer, N.J., Moreby, S.J., Duffield, S.J., Crick, H.Q. and Morecroft, M.B., 2015. Influences of extreme weather, climate and pesticide use on invertebrates in cereal fields over 42 years. Global Change Biology, 21(11), pp.3931-3950.

Fagúndez, J., 2013. Heathlands confronting global change: drivers of biodiversity loss from past to future scenarios. Annals of Botany, 111(2), pp.151-172.

Froglife 2018. Amphibians and Climate Change. Croaking Science
Gardner, E., Julian, A., Monk, C. and Baker, J., 2019. Make the adder count: population trends from a citizen science survey of UK adders. Herpetological Journal, 29, pp.57-70.

Gleed-Owen, C. and Langham, S., 2012. The Adder Status Project–a conservation condition assessment of the adder (Vipera berus) in England, with recommendations for future monitoring and conservation policy.

Report to Amphibian and Reptile Conservation. ARC, Bournemouth, UK.
Global Carbon Project. 2020. Carbon budget and trends 2020. [www.globalcarbonproject.org/carbonbudget] published on 11 December 2020

Hayhow, D.B., Eaton, M.A., Stanbury, A.J., Burns, F., Kirby, W.B., Bailey, N., Beckmann, B., Bedford, J., Boersch-Supan, P.H., Coomber, F. and Dennis, E.B., 2019. State of nature 2019.

IPCC, 2014: Climate Change 2014: Synthesis Report. Contribution of Working Groups I, II and III to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change [Core Writing Team, R.K. Pachauri and L.A. Meyer (eds.)]. IPCC, Geneva, Switzerland, 151 pp.

van Klink, R., Bowler, D.E., Gongalsky, K.B., Swengel, A.B., Gentile, A. and Chase, J.M., 2020. Meta-analysis reveals declines in terrestrial but increases in freshwater insect abundances. Science, 368(6489), pp.417-420.

Le Galliard, J.F., Massot, M., Baron, J.P. and Clobert, J., 2012. Ecological effects of climate change on European reptiles. Wildlife conservation in a changing climate, pp.179-203.

Loidi, J., Biurrun, I., Campos, J.A., García‐Mijangos, I. and Herrera, M., 2010. A biogeographical analysis of the European Atlantic lowland heathlands. Journal of Vegetation Science, 21(5), pp.832-842.

McInerny, C.J., 2019. The study and conservation of adders in Scotland. The Glasgow Naturalist Volume 27, p.67.

Met Office, 2019. UK climate projections: Headline findings.
Smith, N.D., 1990. The ecology of the slow-worm (Anguis fragilis L.) in southern England. Doctoral dissertation, University of Southampton.

Thomas, J.A., Rose, R.J., Clarke, R.T., Thomas, C.D. and Webb, N.R., 1999. Intraspecific variation in habitat availability among ectothermic animals near their climatic limits and their centres of range. Functional Ecology, 13, pp.55-64.

Does the reintroduction of beavers help amphibian (and reptile) populations?

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After centuries of exploitation for their fur, flesh and secretions, Eurasian beavers (Castor fiber) were extinct over much of their range, with only a few relic populations totaling about 1200 individuals by the start of the 20th Century. In Britain, they were extinct by the 16th Century. On mainland Europe, recognition of the ecosystem services beavers provide led to many countries adopting reintroduction programmes: for example, from 1922 in Sweden; 1966 in Bavaria; 1988 in Romania. Thompson et al. (2021) have evaluated the costs (to landowners) and very substantial ecosystem services provided by beaver presence, mainly in habitat and biodiversity enhancement, and in greenhouse gas sequestration. Through protection measures and reintroduction efforts, beavers have now recovered across most of their former range, with recent population estimates of 1.5 million individuals (Halley et al., 2021). Initially, Britain was resistant to beaver reintroduction, mainly because of the concerns of major landowners and forestry interests; however, more recently several high-profile projects have come into being.

In Scotland, serious discussion of the issue began in the 1990s, and the national conservation agency Scottish Natural Heritage (SNH, now NatureScot) suggested a trial reintroduction in 2000. The Government rejected this proposal, but a change of Government and more discussion led to a new proposal, which got the go ahead in 2008. The plan was for a trial reintroduction at a well-contained site in Knapdale Forest, Argyll, to be managed by the Scottish Wildlife Trust in collaboration with the Royal Scottish Zoological Society, and to be monitored independently by researchers commissioned by SNH. The Scottish Beaver Trial began in 2009, when 17 wild beavers from Telemark, Norway, were quarantined for six months in Devon, then released in May 2009 at three freshwater lochs in Knapdale. The trial continued until 2014 (Jones and Campbell-Palmer, 2014). SNH chose the monitoring topics: these included beaver ecology, otters, fish, woodland habitat and dragonflies, but NOT amphibians or reptiles (nor did they agree to permit independent study of the effects on herpetofauna). However, another population existed, formed from accidental escapes or releases in Tayside and these animals were unprotected from landowners who objected to their presence. The Tayside population generated more conflict with some landowners, especially in prime agricultural land where the damming of drainage ditches can lead to impacts on arable farming. After consideration of the data generated through the Scottish Beaver Trial, general public support and consultation with various interest groups and land management sectors, the Scottish Government agreed in November 2016 that the beavers could remain in Scotland. Going on further in May 2019 the Government granted legal protection for all beavers living in the wild (although landowners may still apply for a licence to have animals removed if they can show they are causing damage that cannot be mitigated via alternative means).

In England, the Devon Wildlife Trust received a Government licence in 2014 for a five-year study of the beaver population (origins unclear) already living in the catchment of the River Otter. The study report (Brazier et al., 2020) resulted in DEFRA’s agreeing that the population, now 15 family groups, can stay. As with the Scottish trial, herpetofauna were not a focus of the study. Nevertheless, the study concluded that the ‘effect of beaver engineering and feeding has delivered significant ecological benefits with new areas of wetland habitat created and managed, with documented benefits for amphibians, wildfowl and water-voles’. Although no regular monitoring of amphibians was carried out, in an area where beavers had constructed 13 dams along a 180 metre stretch of stream, counts of common frogspawn had increased from 10 in 2011 to 681 in 2017.

Although we lack studies on the impacts of beaver activities on amphibians in Britain, Dalbeck et al. (2020) have recently reviewed ten papers based on work in six central and eastern European countries (Switzerland, Germany, Lithuania, Denmark, Russia and Poland); they could find no reports so far from southern, western or northern Europe. They focussed on beaver impacts on streams and rivers, rather than on lakes. As is well known, beavers create dams using the logs and branches they cut down, producing ponds with low flow rates. Their tree-felling activities have several effects on local habitats: opening gaps in the forest canopy allows more light to reach the forest floor and water surface, raising temperatures and promoting primary productivity; a great quantity of rotting wood is produced and this promotes invertebrate diversity and habitat complexity. All these effects are potentially beneficial to amphibians. However, river ponds are good habitats for many species of fish, generally not considered helpful to amphibians because they consume eggs and prey on larvae. Indeed, in the UK, we do not regard streams as good amphibian habitat in general, unlike the situation in North America, where many species, especially urodeles, are primarily stream dwellers.

Central Europe supports 19 species of amphibian (six urodeles and 13 anurans). Dalbeck et al. (2020) categorised these into four groups, according to their habitat preferences: forest (6 spp.), open country (5), ubiquitous (4) and pioneers (3). All 19 species were reported from beaver ponds at least occasionally, but only forest and ubiquitous species were found frequently in such ponds. Two pioneer species (green and natterjack toads) and great crested newts were rarely found in beaver ponds. From the UK viewpoint, it is interesting that our two species of greatest conservation concern, great crested newts and natterjack toads, may not benefit significantly from beaver reintroductions. None of the reviewed studies included before and after data, but one of the German reports did compare the amphibian fauna of beaver ponds (mean 4.1 species +/-1.4 SD) with that of nearby beaver-free floodplain ponds (1.2+/-1.3) indicating a significant enhancement in the beaver ponds. Some of the studies compared the fauna of beaver ponds in headwater, small sized streams with those in wider rivers. Species richness was highest in small stream ponds, with a maximum of eight species found in a single German pond.

Sadly, the UK has a much less rich amphibian fauna than central Europe. Nevertheless, the reviewed results indicate that the habitat engineering work performed by beavers should have a positive impact on some of our species. It is, therefore, time that some relevant studies be carried out in Scotland and Devon. With beavers now having been active in Britain for some years, it should be possible to design studies that compare beaver-affected areas to similar areas that are beaver- free.

What about reptiles? The habitat changes wrought by beavers ought to be beneficial for them too, especially the creation of sunlit gaps in the forest, where animals can bask, and the habitat complexity generated producing refuges and hibernacula, and promoting invertebrate diversity. Dalbeck et al. (2020) do not report on impacts on reptiles, nor are they considered in the two British project reports. In the USA, there have been a few reports (e.g. Metts et al., 2001; Russell et al., 1999) on the impacts of beavers on reptiles (and amphibians), but they are not directly applicable to Europe since they concern a different species of beaver (C. canadensis) and a very different reptile fauna. Nevertheless, Metts et al. concluded that ‘disturbances resulting from beaver-created wetlands increase regional abundance and diversity of herpetofauna’. Another topic for research as beavers come back to Britain?

References

Brazier, R.E. et al. (2020). River Otter Beavers Trial: science and evidence report. University of Exeter, Devon Wildlife Trust and others. Available online.

Dalbeck, L., Hachtel, M. and Campbell-Palmer, R. (2020). A review of the influence of beaver Castor fiber on amphibian assemblages in the floodplains of European temperate streams and rivers. Herpetological Journal 30, 135-146.

Halley, D. J., Saveljev, A. P. and Rosell, F. (2021). Population and distribution of beavers Castor fiber and Castor canadensis in Eurasia. Mammal Review 51, ISSN 0305-1838

Jones, S. and Campbell-Palmer, R. (2014). The Scottish Beaver Trial: the story of Britain’s first licensed release into the wild. Final Report. Scottish Wildlife trust and the Royal Zoological Society of Scotland. Available online.

Metts, B.S. (2001). Evaluation of herpetofaunal communities on upland streams and beaver-impounded streams in the upper piedmont of South Ca

Russell, K.R. et al. (1999). Amphibian and reptile communities associated with beavers (Castor canadensis) ponds and unimpounded streams in the piedmont of South Carolina. Journal of Freshwater Ecology 14, 149-158.

Thompson, S. et al. (2021). Ecosystem services provided by beavers Castor spp. Mammal Review 51 (published on-line).

 Roger Downie, University of Glasgow and Froglife Trustee

Roisin Campbell-Palmer, Independent Beaver Ecologist, Associate of University of Exeter