Modelling Eurasian Beaver Foraging Habitat and Dam Suitability, for Predicting the Location and Number of Dams Throughout Catchments in Great Britain

Eurasian beaver (Castor fiber) populations are expanding across Europe. Depending on location, beaver dams bring multiple benefits and/or require management. Using nationally available data, we developed: a Beaver Forage Index (BFI), identifying beaver foraging habitat, and a Beaver Dam Capacity (BDC) model, classifying suitability of river reaches for dam construction, to estimate location and number of dams at catchment scales. Models were executed across three catchments, in Great Britain (GB), containing beaver. An area of 6747 km2 was analysed for BFI and 16,739 km of stream for BDC. Field surveys identified 258 km of channel containing beaver activity and 89 dams, providing data to test predictions. Models were evaluated using a categorical binomial Bayesian framework to calculate probability of foraging and dam construction. BFI and BDC models successfully categorised the use of reaches for foraging and damming, with higher scoring reaches being preferred. Highest scoring categories were ca. 31 and 79 times more likely to be used than the lowest for foraging and damming respectively. Zero-inflated negative binomial regression showed that modelled dam capacity was significantly related (p = 0.01) to observed damming and was used to predict numbers of dams that may occur. Estimated densities of dams, averaged across each catchment, ranged from 0.4 to 1.6 dams/km, though local densities may be up to 30 dams/km. These models provide fundamental information describing the distribution of beaver foraging habitat, where dams may be constructed and how many may occur. This supports the development of policy and management concerning the reintroduction and recolonisation of beaver

Echinococcus multilocularis Detection in Live Eurasian Beavers (Castor fiber) Using a Combination of Laparoscopy and Abdominal Ultrasound under Field Conditions

Echinococcus multilocularis is an important pathogenic zoonotic parasite of health concern, though absent in the United Kingdom. Eurasian beavers (Castor fiber) may act as a rare intermediate host, and so unscreened wild caught individuals may pose a potential risk of introducing this parasite to disease-free countries through translocation programs. There is currently no single definitive ante-mortem diagnostic test in intermediate hosts. An effective non-lethal diagnostic, feasible under field condition would be helpful to minimise parasite establishment risk, where indiscriminate culling is to be avoided. This study screened live beavers (captive, n = 18 or wild-trapped in Scotland, n = 12) and beaver cadavers (wild Scotland, n = 4 or Bavaria, n = 11), for the presence of E. multilocularis. Ultrasonography in combination with minimally invasive surgical examination of the abdomen by laparoscopy was viable under field conditions for real-time evaluation in beavers. Laparoscopy alone does not allow the operator to visualize the parenchyma of organs such as the liver, or inside the lumen of the gastrointestinal tract, hence the advantage of its combination with abdominal ultrasonography. All live beavers and Scottish cadavers were largely unremarkable in their haematology and serum biochemistry with no values suspicious for liver pathology or potentially indicative of E. multilocularis infection. This correlated well with ultrasound, laparoscopy, and immunoblotting, which were unremarkable in these individuals. Two wild Bavarian individuals were suspected E. multilocularis positive at post-mortem, through the presence of hepatic cysts. Sensitivity and specificity of a combination of laparoscopy and abdominal ultrasonography in the detection of parasitic liver cyst lesions was 100% in the subset of cadavers (95%Confidence Intervals 34.24-100%, and 86.7-100% respectively). For abdominal ultrasonography alone sensitivity was only 50% (95%CI 9.5-90.6%), with specificity being 100% (95%CI 79.2-100%). For laparoscopy alone sensitivity was 100% (95% CI 34.2-100%), with specificity also being 100% (95% CI 77.2-100%). Further immunoblotting, PCR and histopathological examination revealed one individual positive for E. multilocularis, whilst the other individual was positive for Taenia martis

Beaver genetic surveillance in Britain

Founder genetic composition can affect reintroduction success, especially as the number of animals released tends to be small and therefore less genetically diverse than their source populations. Numerous translocations and reinforcements of beavers, Castor fiber, have occurred with little regard to geographic and/or genetic origin. Beaver reintroduction to Britain has been haphazard and currently disjointed populations of varying status exist – from sanctioned wild releases, unlicensed populations and naturalistic enclosed projects. This study investigated the genetic composition of two originally unofficially released beaver populations in Britain - Tayside, east Scotland, and River Otter, Devon, to provide data to support decision on their future management. From both wild populations (n = 34Tayside, n = 9Devon) all were confirmed as Eurasian beaver. The vast majority, origin was likely assignable to Germany and the mixed founder population of Bavaria. Eighty-two percent of the Tayside individuals examined at 275 loci were at least as closely related as first cousins, with pairwise estimates of relatedness at 26 loci indicated that the Devon beavers were more closely related on average. So far there is no evidence to suggest that beavers are failing to adapt to the British environment despite their reduced genetic founder based, however attention to genetic augmentation and longer-term management of genetic diversity should be factored into comprehensive restoration plans for the species across Britain. Many recent reintroductions are relying on serial founder events from an already limited founder base and that is counter to best practice in reintroduction planning

Laparoscopic view of <i>E. multilocularis</i> cyst.

<p>Laparoscopic view of <i>E</i>. <i>multilocularis</i> infection in the liver of a beaver cadaver.</p

Post laparoscopic investigation incision site.

<p>View of incision site on closing following laparoscopic insertion, yellow stain marks represent iodine solution as fur wetted to aid ultrasound examination.</p

Histological presentation <i>Taenia martis</i>.

<p>Histological presentation of 3mm wide hepatic cyst, consistent with <i>Taenia martis</i> in PCR analysis. Section A: The cyst is lined by a band of thick fibrous tissue, and contains an intraluminal, 2mm wide metazoan organism. Section B (inset of Section A): This organism does not possess a coelomic cavity and features a protoscolex (arrow), and three suckers (arrowheads). H&E stain.</p

Sonogram of <i>E</i>. <i>multilocularis</i> cyst.

<p>Ultrasound image of <i>E</i>. <i>multilocularis</i> cyst in the liver of the same beaver cadaver as <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0130842#pone.0130842.g004" target="_blank">Fig 4</a>.</p

Normal laparoscopic image.

<p>Laparoscopic image of normal abdominal organs in an anaesthetised beaver.</p

Normal sonogram.

<p>Ultrasound image of normal abdominal organs in an anaesthetised beaver.</p

Beaver category with screening method employed.

<p>Frequency of individual tests for the detection of cysts and <i>Echinococcus multilocularis</i> associated hepatic lesions.</p><p><i>na</i> = not examined</p><p>* also tested for haematology and serum biochemistry</p><p>Beaver category with screening method employed.</p