Continuous variation in the pattern of marine v. freshwater foraging in brown trout Salmo trutta L. from Loch Lomond, Scotland

Carbon stable-isotope analysis showed that individual brown trout Salmo trutta in Loch Lomond adopted strategies intermediate to that of freshwater residency or anadromy, suggesting either repeated movement between freshwater and marine environments, or estuarine residency. Carbon stable-isotope (delta C-13) values from Loch Lomond brown trout muscle tissue ranged from those indicative of assimilation of purely freshwater-derived carbon to those reflecting significant utilization of marine-derived carbon. A single isotope, two-source mixing model indicated that, on average, marine C made a 33% contribution to the muscle tissue C of Loch Lomond brown trout. Nitrogen stable isotope, delta N-15, but not delta C-13 was correlated with fork length suggesting that larger fish were feeding at a higher trophic level but that marine feeding was not indicated by larger body size. These results are discussed with reference to migration patterns in other species. (c) 2008 The Authors Journal compilation (c) 2008 The Fisheries Society of the British Isles.

The pitfall with PIT tags: Marking freshwater bivalves for translocation induces short-term behavioural costs

Tagging animals is frequently employed in ecological studies to monitor individual behaviour, for example postrelease survival and dispersal of captive-bred animals used in conservation programmes. While the majority of studies focus on the efficacy of tags in facilitating the relocation and identification of individuals, few assess the direct effects of tagging in biasing animal behaviour. We used an experimental approach with a control to differentiate the effects of handling and tagging captive-bred juvenile freshwater pearl mussels, Margaritifera margaritifera, prior to release into the wild. Marking individuals with passive integrated transponder (PIT) tags significantly decreased their burrowing rate and, therefore, increased the time taken to burrow into the substrate. This effect was contributed to, in part, by the detrimental impacts of handling, which also significantly affected activity, burrowing ability and the time taken for each individual to emerge and start probing the substrate. Disturbance during handling and tagging may lead to indirect mortality after release by increasing the risk of predation or dislodgement during flooding, thereby potentially compromising any conservation strategy contingent on population supplementation or reintroduction. This is the first study to demonstrate that handling and PIT tagging has a detrimental impact on invertebrate behaviour. Moreover, our results provide useful information that will inform freshwater bivalve conservation strategies.

Geophysics and the search of freshwater bodies

Geophysics may assist scent dogs and divers in the search of water bodies for human and animal remains, contraband, weapons and explosives by surveying large areas rapidly and identifying targets or environmental hazards. The most commonly applied methods are described and evaluated for forensic searches. Seismic reflection or refraction and CHIRPS are useful for deep, openwater bodies and identifying large targets, yet limited in streams and ponds. The use of ground penetrating radar (GPR) onwater(WPR) is of limited use in deepwaters (over 20 m) but is advantageous in the search for non-metallic targets in small ditches and ponds. Largemetal or metal-bearing targets can be successfully imaged in deep waters by using towfish magnetometers: in shallow waters such a towfish cannot be used, so a non-metalliferous boat can carry a terrestrial magnetometer. Each device has its uses, depending on the target and location: unknown target make-up (e.g. a homicide victimwith or without a metal object) may be best located using a range ofmethods (the multi-proxy approach), depending on water depth. Geophysics may not definitively find the target, but can provide areas for elimination and detailed search by dogs and divers, saving time and effort.

Evaluation of effective groundwater recharge of freshwater lens in small islands by the combined modeling of geoelectrical data and water heads

In small islands, a freshwater lens can develop due to the recharge induced by rain. Magnitude and spatial distribution of this recharge control the elevation of freshwater and the depth of its interface with salt water. Therefore, the study of lens morphology gives useful information on both the recharge and water uptake due to evapotranspiration by vegetation. Electrical resistivity tomography was applied on a small coral reef island, giving relevant information on the lens structure. Variable density groundwater flow models were then applied to simulate freshwater behavior. Cross validation of the geoelectrical model and the groundwater model showed that recharge exceeds water uptake in dunes with little vegetation, allowing the lens to develop. Conversely, in the low-lying and densely vegetated sectors, where water uptake exceeds recharge, the lens cannot develop and seawater intrusion occurs. This combined modeling method constitutes an original approach to evaluate effective groundwater recharge in such environments.
[Comte, J.-C., O. Banton, J.-L. Join, and G. Cabioch (2010), Evaluation of effective groundwater recharge of freshwater lens in small islands by the combined modeling of geoelectrical data and water heads, Water Resour. Res., 46, W06601, doi:10.1029/2009WR008058.]

Assessing the conservation status of the freshwater pearl mussel in the North of Ireland - Relevance of growth and age characteristics

In order to conserve the freshwater pearl mussel in Ireland, populations that have a high risk of extinction must he identified and given priority for conservation. Growth of freshwater pearl mussels has been found to vary among populations on a wide geographic scale as well as on a local scale. Populations having a high growth constant (k), because of the small size of individuals and their shorter life-span and thus lower reproductive output, may be more likely to become extinct than those which have a low k and hence larger size and greater reproductive output. This study attempts to estimate the growth constant (k) in rivers in Donegal and Northern Ireland based on measuring lire largest shell in each population. Large differences in values of k were found among rivers and these are discussed in relation to catchment bedrock types and the identification of conservation priorities. Appropriate conservation strategies are recommended for Margaritifera margaritifera populations in the north of Ireland.

Towards a strategy for the conservation of the freshwater pearl mussel Margaritifera margaritifera in County Donegal, Ireland

This study attempts to identify the habitat requirements of the pearl mussel Margaritifea margaritifera in County Donegal, in north west Ireland, an area with little urban, industrial or intensive agricultural development. No mussels occur in rivers where calcium and conductivity levels are high or where the substratum is predominantly bedrock or fine sediment but it was not possible to distinguish clearly between mussel and non-mussel sites on the basis of ordination analysis. However, rivers which still support mussels and rivers with historical records of mussels are loosely grouped. Rivers which formerly supported mussels but lack living M. margaritifera appear to have suitable habitat for mussels; pearl fishing is the most likely reason for the extinction of these mussel populations. Where population densities are high, for example in locations on the rivers Eske, Clady and Owenea, conservation may necessitate the establishment of reserves. The prospect for the successful reintroduction of mussels into former mussel rivers such as the Finn and Eany Water, where suitable habitat exists and water quality is high, is very good.

Does the freshwater pearl mussel, Margaritifera margaritifera L., face extinction in Northern Ireland?

1. Until recently the status of Margaritifera margaritifera L. in Northern Ireland was not well documented. This paper presents the results of field surveys conducted in 1990/'91 and in 1996 at over 200 sites covering all major river systems in Northern Ireland. 2.Margaritifera populations in Northern Ireland were recorded at just 20 sites mainly located in the west of the province. Formerly many rivers supported vast numbers of mussels but anecdotal evidence points to periods of major declines in mussel populations since the turn of the century. 3. The absence of mussels smaller than 30 mm in length at most sites suggests very little or no recruitment during the past decade. During the surveys, deteriorating water quality, habitat disturbance and pearl fishing were recorded and are the major causes of the decline of the freshwater pearl mussel in Northern Ireland. 4. Unless the above problems are alleviated in the very near future, M.margaritifera will probably become extinct in Northern Ireland. © 1998 John Wiley & Sons, Ltd.

The current distribution and status of the freshwater pearl mussel Margaritifera margaritifera L. 1758 in north-west Ireland

1.Margaritifera margaritifera populations are declining throughout its range, including Ireland, despite legislation designed to protect freshwater pearl mussels and their habitat. A survey of freshwater 2. pearl mussels was carried out on rivers in County Donegal, north-west Ireland, to determine the current distribution, size and density of M. margaritifera populations, as well as to identify potential threats to mussels there. 3. The survey revealed the freshwater pearl mussel to be widespread, particularly in the western half of the county. However, densities of mussels at most sites are low, with just two sites having mussel densities of over 5?m-2. Furthermore, the species appears to be absent from a number of sites from which it had been previously recorded. 4. According to the literature, there is a long history of pearl fishing in Co. Donegal and neighbouring counties. Evidence from heaps of shells found on the river bed and banks at several sites and recent anecdotal reports from local people suggest pearl fishing is being practised on all rivers investigated during the present study. The main conservation requirements for 5. M. margaritifera populations in Donegal are to maintain water quality at its present high standard and, as pearl fishing appears to be a widespread and immediate threat to the remaining mussel populations, to enforce existing legislation designed to protect M. margaritifera.