Dive performance in a small-bodied, semi-aquatic mammal in the wild

Aquatic foraging is a fundamental component of the behavior of a number of small mammals, yet comprehensive observations of diving are often difficult to obtain under natural circumstances. Semiaquatic mammals, having evolved to exploit prey in both aquatic and terrestrial environments, are generally not as well adapted for diving (or for life in the water) as are fully aquatic species. Because dive ability also tends to increase with body size, small, semiaquatic mammals are presumed to have fairly limited dive ability. Nevertheless, diving plays an important role in food acquisition for many such species. We used time–depth recorders (TDRs) to measure and describe the dive performance of 9 female and 5 male free-living American mink (Neovison vison; body mass approximately 1 kg) on lowland rivers in the southern United Kingdom. We recorded dives up to 2.96 m deep (maximum depth X ¯ 5 1.82 m) and up to 57.9 s in duration (maximum duration X ¯ 5 37.2 s). Dive duration was approximately 40% of that predicted by allometry for all air-breathing diving vertebrates (as might be expected for a small, semiaquatic animal) but was twice as long as previously measured for mink in captivity. Mink performed up to 189 dives per day (X ¯ 5 35.7 dives/day), mostly during daylight, and spent a maximum of 38.4 minutes diving per day (X ¯ 5 7.6 min/day). Some individuals maintained particularly high diving rates over the coldest months, suggesting that the benefits of aquatic foraging in winter outweigh the costs of heat loss. We observed a number of very shallow dives (depth approximately 0.3 m) of particularly long duration (up to 30 s). The function of these dives is currently unknown, but possibilities include searching for prey, travelling, or avoidance of threats. There is only 1 other study of which we are aware that presents detailed measurements of dive performance in a small, shallow-diving, semiaquatic mammal.Fil: Harrington, Lauren. University of Oxford; Reino UnidoFil: Hays, Graeme C.. Swansea University; Reino UnidoFil: Fasola, Laura. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Austral de Investigaciones Científicas; ArgentinaFil: Harrington, Andrew L.. University of Oxford; Reino UnidoFil: Righton, David. No especifíca;Fil: Macdonald, David W.. University of Oxford; Reino Unid

Practical implementation of ecosystem monitoring for the ecosystem approach to management

1. The implementation of the ecosystem approach means there is a need to monitor an increased range of environmental conditions and ecological components in the marine environment. Many existing monitoring surveys have successfully added tasks or components to an existing monitoring programme while maintaining consistency of time series. This approach is not practical when the immediate data need for a wide range of ecosystem components requires substantial changes to the programme or when collections of different ecological components have conflicting requirements. 2. We propose a more integrated approach aimed at not only assessing change, but simultaneously delivering evidence of the underlying reasons for observed changes. Using principles developed from observational and modelling efforts in the Barents Sea and the wider literature, we distil the essential characteristics an integrated monitoring programme must exhibit. We demonstrate how such an integrated programme can offer substantial operational efficiencies compared to a coordinated approach. 3. Integrated monitoring based on ecosystem processes has significant advantages over the coordinated approach that uses ecosystem states independently and focuses on maximizing precision of each indicator. While integration is needed to address current policy requirements, changes to monitoring risk time-series consistency. However, we explain how such risks can be minimized while at the same time establishing a framework that allows the incorporation of important information from other less flexible data sources to be used in the assessment. 4. Policy implications. Process-based integrated monitoring is essential for the ecosystem approach. The focus on ecosystem processes provides the essential elements for future proof efficient management: (i) It provides both unbiased status estimates for reporting requirements and describes the causes of state change. (ii) It minimizes risks to historic time series while coping with changing ecological conditions. (iii) It quantifies ecosystem processes and provides the means to test hypotheses on how different processes interact. (iv) It uses all available information efficiently when used in conjunction with integrated assessments. (v) It is effective due to its adaptability to meet future policy demands and ecosystem requirements while using data in the most efficient manner given these demands

A Review of the Tools Used for Marine Monitoring in the UK: Combining Historic and Contemporary Methods with Modeling and Socioeconomics to Fulfill Legislative Needs and Scientific Ambitions

Marine environmental monitoring is undertaken to provide evidence that environmental management targets are being met. Moreover, monitoring also provides context to marine science and over the last century has allowed development of a critical scientific understanding of the marine environment and the impacts that humans are having on it. The seas around the UK are currently monitored by targeted, impact-driven, programmes (e.g., fishery or pollution based monitoring) often using traditional techniques, many of which have not changed significantly since the early 1900s. The advent of a new wave of automated technology, in combination with changing political and economic circumstances, means that there is currently a strong drive to move toward a more refined, efficient, and effective way of monitoring. We describe the policy and scientific rationale for monitoring our seas, alongside a comprehensive description of the types of equipment and methodology currently used and the technologies that are likely to be used in the future. We contextualize the way new technologies and methodologies may impact monitoring and discuss how whole ecosystems models can give an integrated, comprehensive approach to impact assessment. Furthermore, we discuss how an understanding of the value of each data point is crucial to assess the true costs and benefits to society of a marine monitoring programme

Behaviour of stocked and naturally recruited European eels during migration

One objection to the stocking of translocated eels as a management measure for the European eel Anguilla anguilla L. is that these eels may lack the ability to find their way back to the spawning area in the Sargasso Sea because the translocation will confuse their imprinted navigation. We undertook a series of tagging experiments using satellite tags, data storage tags and acoustic tags to test the hypothesis that eels translocated 1200 km from the UK to Sweden differed in their ability to migrate compared to naturally recruited eels. Eels to be tagged were caught in 2 locations, one with a record of eel stocking for more than 20 yr and with a series of barriers to upstream migration and another in a river with only natural immigration and without barriers to upstream migration. In the first year, the naturally recruited and stocked eels were released in a fjord where the initial escapement behaviour could be monitored by acoustic tagging in addition to using archival tags to track the subsequent marine migration. In the second year, eels were tagged with archival or satellite tags and released on the open coast, and only their marine migration was investigated. Eels were tracked more than 2000 km along a route that, after leaving the Skagerrak, followed the Norwegian Trench to the Norwegian Sea, turned south and west along the Faroe-Shetland channel before emerging into the Atlantic Ocean, and then continued west. There were no statistically significant differences in estuarine or oceanic behaviour regarding route, swimming speed and preferred swimming depth between stocked and naturally recruited eels. These results provide the first empirical evidence of a Nordic migration route and do not support the hypothesis that a sequential imprinting of the route during immigration is necessary for adequate orientation or behaviour during the adult spawning migration.</p

Mapping silver eel migration routes in the North Sea

Recent developments in tracking technology resulted in the mapping of various marine spawning migration routes of the European eel (Anguilla anguilla). However, migration routes in the North Sea have rarely been studied, despite many large European rivers and hence potential eel growing habitat discharge into the North Sea. In this study, we present the most comprehensive map to date with migration routes by silver European eels in the North Sea and document for the first time successful eel migration through the English Channel. Migration tracks were reconstructed for 42 eels tagged in Belgium and 12 in Germany. Additionally, some eels moved up north to exit the North Sea over the British Isles, confirming the existence of two different routes, even for eels exiting from a single river catchment. Furthermore, we observed a wide range in migration speeds (6.8-45.2 km day(-1)). We hypothesize that these are likely attributed to water currents, with eels migrating through the English Channel being significantly faster than eels migrating northward

First tracking of the oceanic spawning migrations of Australasian short-finned eels (Anguilla australis)

Anguillid eel populations have declined dramatically over the last 50 years in many regions of the world, and numerous species are now under threat. A critical life-history phase is migration from freshwater to distant oceans, culminating in a single life-time spawning event. For many anguillids, especially those in the southern hemisphere, mystery still shrouds their oceanic spawning migrations. We investigated the oceanic spawning migrations of the Australasian short-finned eel (Anguilla australis) using pop-up satellite archival tags. Eels were collected from river estuaries (38 degrees 5,142 degrees E) in south-eastern temperate Australia. In 2019,16 eels were tracked for up to about 5 months, similar to 2620 km from release, and as far north as the tropical Coral Sea (22 degrees 5,155 degrees E) off the north-east coast of Australia. Eels from southern Australia appeared to access deep water off the Australian coast via two main routes: (i) directly east via Bass Strait, or (ii) south-east around Tasmania, which is the shortest route to deep water. Tagged eels exhibited strong diel vertical migrations, alternating between the warm euphotic zone (similar to 100-300 m, 15-20 degrees C) at night and the mesopelagic zone (similar to 700-900 m, 6-8 degrees C) during the day. Marine predators, probably lamnid sharks, tuna, or marine mammals, ended many eel migrations (at least similar to 30%), largely before the eels had left the Australian continental shelf. The long and risky marine migrations of Australasian eels highlight the need for better information on the processes contributing to eel mortality throughout the life cycle, including the impacts of future changes to oceanic currents, predator abundance and direct anthropogenic disturbances

Vertical movements of North Sea Cod

Various air-breathing marine vertebrates such as seals, turtles and seabirds show distinct patterns of diving behaviour. For fish, the distinction between different vertical behaviours is often less clear-cut, as there are no surface intervals to differentiate between dives. Using data from acoustic tags (n = 23) and archival depth recorders attached to cod Gadus morhua (n = 92) in the southern North Sea, we developed a quantitative method of classifying vertical movements in order to facilitate an objective comparison of the behaviour of different individuals. This method expands the utilisation of data from data storage tags, with the potential for a better understanding of fish behaviour and enhanced individual based behaviour for improved ecosystem modelling. We found that cod were closely associated with the seabed for 90% of the time, although they showed distinct seasonal and spatial patterns in behaviour. For example, cod tagged in the southern North Sea exhibited high rates of vertical movement in spring and autumn that were probably associated with migration, while the vertical movements of resident cod in other areas were much less extensive and were probably related to foraging or spawning behaviours. The full reasons underlying spatial and temporal behavioural plasticity by cod in the North Sea warrant further investigation