Tom P. Moorhouse

Evaluating the role of invasive aquatic species as drivers of fine sediment-related river management problems: The case of the signal crayfish (Pacifastacus leniusculus)

Sediment quantity and quality are key considerations in the sustainable management of fluvial systems. Increasing attention is being paid to the role of aquatic biota as geomorphic agents, capable of altering the composition, mobilization and transport of fluvial sediments at various spatiotemporal scales. In this paper invasive species are presented as a special case since: (1) populations may not be constrained by factors characteristic of their native habitats; and (2) they represent a disturbance to which the system may not be resilient. Discussion is centred on the signal crayfish which has rapidly colonized catchments in Europe and Japan, but the hypotheses and models presented provide a framework applicable to other invasive species. This paper explores the mechanisms by which signal crayfish may influence sediment dynamics from the patch scale to the catchment scale. There is potential for signal crayfish to impact significantly on river sediments and morphology as a function of their interactions with river bed and bank material, and with other aquatic organisms, combined with their large body size and aggressive nature, their presence in very high densities, and the lack of effective mitigation strategies. Potential catchment-scale management issues arising from these factors include habitat degradation, mobilization of sediment-associated nutrients and contaminants, and sediment-related flood risks. Further interdisciplinary research is required at the interface between freshwater ecology, fluvial geomorphology and hydraulics, in order to quantify the significance and extent of these impacts. The paper points to the key research agendas that may now emerge.

The Customer Isn't Always Right—Conservation and Animal Welfare Implications of the Increasing Demand for Wildlife Tourism

Tourism accounts for 9% of global GDP and comprises 1.1 billion tourist arrivals per annum. Visits to wildlife tourist attractions (WTAs) may account for 20–40% of global tourism, but no studies have audited the diversity of WTAs and their impacts on the conservation status and welfare of subject animals. We scored these impacts for 24 types of WTA, visited by 3.6–6 million tourists per year, and compared our scores to tourists’ feedback on TripAdvisor. Six WTA types (impacting 1,500–13,000 individual animals) had net positive conservation/welfare impacts, but 14 (120,000–340,000 individuals) had negative conservation impacts and 18 (230,000–550,000 individuals) had negative welfare impacts. Despite these figures only 7.8% of all tourist feedback on these WTAs was negative due to conservation/welfare concerns. We demonstrate that WTAs have substantial negative effects that are unrecognised by the majority of tourists, suggesting an urgent need for tourist education and regulation of WTAs worldwide.

Effects of forage availability on growth and maturation rates in water voles.

1. In populations of small mammals, food supplementation typically results in higher population densities, body weights, growth rates and reproductive rates. However, few studies have demonstrated a relationship between forage levels and demographic rates in wild populations in the absence of supplementation. 2. We examined the association of levels of available forage with individual growth rates and time to sexual maturity in eight re-introduced and three naturally occurring populations of water voles (Arvicola terrestris). 3. Range sizes were smaller at sites with higher population densities. Mean forage availability and individual growth rates covaried with range size at each site. 4. The weight at which water voles became sexually mature was 112 g for females and 115 g for males and did not vary between study sites. Differences in growth rates therefore translated into differences in the time taken to reach maturity between sites. 5. In the re-introduced populations, mean days to maturity varied inversely with mean range length. Females took 7 days (18%, range 40-47 days) longer and males 5 days (13%, range 40-45 days) longer to reach breeding condition at the sites with the shortest mean range lengths. 6. Evidence from this study suggests a possible mechanism by which increased population densities may reduce maturation rates in water voles through a reduction in mean range size, thereby limiting the availability of forage to each individual.

Intensive removal of signal crayfish (Pacifastacus leniusculus) from rivers increases numbers and taxon richness of macroinvertebrate species

Invasive species are a major cause of species extinction in freshwater ecosystems, and crayfish species are particularly pervasive. The invasive American signal crayfish Pacifastacus leniusculus has impacts over a range of trophic levels, but particularly on benthic aquatic macroinvertebrates. Our study examined the effect on the macroinvertebrate community of removal trapping of signal crayfish from UK rivers. Crayfish were intensively trapped and removed from two tributaries of the River Thames to test the hypothesis that lowering signal crayfish densities would result in increases in macroinvertebrate numbers and taxon richness. We removed 6181 crayfish over four sessions, resulting in crayfish densities that decreased toward the center of the removal sections. Conversely in control sections (where crayfish were trapped and returned), crayfish density increased toward the center of the section. Macroinvertebrate numbers and taxon richness were inversely correlated with crayfish densities. Multivariate analysis of the abundance of each taxon yielded similar results and indicated that crayfish removals had positive impacts on macroinvertebrate numbers and taxon richness but did not alter the composition of the wider macroinvertebrate community. Synthesis and applications: Our results demonstrate that non-eradication-oriented crayfish removal programmes may lead to increases in the total number of macroinvertebrates living in the benthos. This represents the first evidence that removing signal crayfish from riparian systems, at intensities feasible during control attempts or commercial crayfishing, may be beneficial for a range of sympatric aquatic macroinvertebrates.

Measuring animal welfare within a reintroduction: an assessment of different indices of stress in water voles Arvicola amphibius.

Reintroductions are an increasingly common conservation restoration tool; however, little attention has hitherto been given to different methods for monitoring the stress encountered by reintroduced individuals. We compared ten potential measures of stress within four different categories (neuroendocrine, cell function, body condition and immune system function) as proxies for animal welfare in water voles being reintroduced to the Upper Thames region, Oxfordshire, UK. Captive-bred voles were assessed pre-release, and each month post-release for up to five months. Wild-born voles were captured in the field and assessed from two months post-release. Plasma corticosteroid, hydration and body condition of captive-bred voles differed between their pre-release measures and both their first (“short-term”) recapture, and their final recapture (“long-term” release), however only body condition and immunocompetence measured using the Nitroblue Tetrazolium (NBT) test were significantly different post-release between the first and last recaptures. Captive-bred animals had lower fat reserves, higher weight/length ratios and better immunocompetence (NBT) than did wild-born voles. Captive-bred males had higher ectoparasite burdens compared to wild-born males and, as reintroduction site quality decreased, became less hydrated. These observations indicate that some methods can identify changes in the stress response in individuals, highlighting areas of risk in a reintroduction programme. In addition, a single measure may not provide a full picture of the stress experienced; instead, a combination of measures of different physiological systems may give a more complete indication of stress during the reintroduction process. We highlight the need to monitor stress in reintroductions using measures from different physiological systems to inform on possible animal welfare improvements and thus the overall success rate of reintroductions.

Daily energy expenditure in the face of predation : hedgehog energetics in rural landscapes

ABSTRACT Failure to balance daily energy expenditure (DEE) with energy intake can have an impact on survival and reproduction, and therefore on the persistence of populations. Here we study the DEE of the European hedgehog (Erinaceus europaeus), which is declining in the UK. We hypothesise that there is a gradient of suitable habitat for hedgehogs in rural areas, which is a result of fewer food resources, a higher risk from predation by badgers (Meles meles) and colder ambient temperatures, as distance to the nearest building increases. We used the doubly labelled water method to obtain 44 measurements of DEE from hedgehogs on four predominately arable sites, to determine the energetic costs associated with proximity to buildings, on sites with and without badgers. The mean±s.e.m. DEE was 508.9±34.8 kJ day−1. DEE increased the further a hedgehog was from buildings during the study, possibly as they ranged larger distances on arable land, supporting the hypothesis that hedgehogs select villages owing to the lower energy demands in comparison to arable farmland. Hedgehogs had an approximately 30% lower DEE on sites with badgers. We speculate that on badger-occupied sites, hedgehogs may restrict movement and foraging in response to a threat from predation and thus have reduced DEE. Therefore, hedgehogs may also seek refuge in villages where the perceived threat of predation is lower and foraging is unrestricted. In a broader context, we demonstrate that individual differences in DEE can aid in understanding habitat selection in a patchily distributed species. Highlighted Article: European hedgehogs are declining in Britain, particularly on arable land; badger presence and habitat use impact on hedgehogs’ energy expenditure, explaining hedgehog distribution in rural areas.