Search

Industrial forage fish fisheries may reduce prey availability affecting diet and breeding success of marine predators. However, evidence for fisheries effects on predator demography remains rare, hindering evaluation of their impact on populations. Using 25 years of data on the commercial lesser sandeel fishery in the north-western North Sea, we evaluated the effectiveness of the closure in safeguarding breeding success of four seabird species - black-legged kittiwake, common guillemot, Atlantic puffin and razorbill. We also tested for effects of a scientific fishery in the closed area on breeding success. We quantified how changes in the diet of chicks for the four seabird species were influenced by the abundance of sandeels and the alternative prey species, European sprat, and the potential prey behavioural disturbance effects of sandeel fishing on the prey. Finally, we examined how changes in chick diet and prey abundance have shaped long-term variation in seabird breeding success. The period of fishery operation was associated with a decline in kittiwake breeding success in colonies with foraging ranges overlapping the closed area, from 52 % of young fledged pre-fishery to 23 % during fishery operation. Breeding success increased by approximately 10 % in the period following fishery closure to 2018. We document wide uncertainty around this increase in breeding success, partly driven by variation in the responses of individual colonies. For guillemot, razorbill and puffin we found no evidence for negative effects of the fishery on breeding success, nor for positive effects arising from its closure. We found no evidence for an impact on breeding success of the scientific fishery. The proportion of sandeel in chick diet was positively associated with breeding success in the four species, albeit with only weak evidence for puffin. Fishing effort was associated with a decreased proportion of sandeel in puffin diet, a lower proportion of the sandeel component of the diet consisting of 0-group in kittiwake, razorbill and puffin, and with decreased kittiwake breeding success. Our findings provide quantitative evidence for how forage fish fisheries may impact seabird demography, highlighting the species-specific nature of responses, and the difficulties in teasing apart drivers amongst ongoing environmental change. Time-area fisheries closures show promise as a tool for positively affecting productivity in some seabird species. However, we identify important caveats around its effectiveness for strategic seabird conservation and aspirations of net gain.

Tracking tags have been used to map the distributions of a wide variety of avian species, but few studies have examined whether the use of these devices has impacts on the study animals that may bias the spatial data obtained. As Global Positioning System (GPS) tags small enough for deployment on terns (family: Laridae) have only recently become available, until now tracking of this group has been conducted by following unmanipulated individuals by boat, which offers a means of comparing distributions obtained from GPS‐tracking. We compared the utilization distributions (UDs) of breeding Arctic Terns Sterna paradisaea obtained by GPS‐tracking 10 individuals over 2 weeks, with UDs derived from contemporaneous visual boat tracks from 81 individuals. The 50% and 95% UDs of both methods had high similarity scores, indicating good agreement in the density distributions derived from the two methods. The footprints of the UDs of tagged birds were ~ 75–80% larger, which may reflect an effect of tagging on foraging range or the occasional inability to follow by boat individuals which roamed further from the colony. We also compared the nest attendance and chick provisioning rates of adults that were (1) fitted with a GPS tag and leg‐flag, (2) handled and marked with a leg‐flag but not tagged and (3) fitted with a leg‐flag in a previous year but unhandled in the year of the study. There was some evidence that birds fitted with both a GPS tag and leg‐flag spent slightly less time at the nest compared with unhandled birds and those fitted with a leg‐flag only. Both treatments where birds were fitted with a leg‐flag in the year of the study had similarly lower provisioning rates to those of unhandled control birds > 48 h after handling, suggesting that negative effects on provisioning are due to capture and handling or leg‐flag attachment rather than to GPS tag attachment/loading per se. Overall brood‐provisioning rate was compensated for by the increased effort by the unhandled partner. Our study suggests that despite slight effects of GPS‐tagging on behaviour, the estimates of marine density distribution obtained were very similar to those of unmanipulated birds.

Designating Marine Protected Areas (MPAs) is seen to be fundamental to future seabird conservation. In accordance with European Union legislation, the UK proposes to extend Special Protection Areas (SPAs) into the offshore zone for seabirds. This study provides the basis of a foraging range extension to the main UK SPA colony of breeding little tern (Sternula albifrons). We applied several established analytical approaches to identify MPAs to multiple data sources including boat-based surveys and individual tracking, alongside a ‘foraging radius’ approach derived from published foraging range. We pooled data from multiple seasons to account for any inter-annual variation in foraging range and distribution. Minimum convex polygon (MCP), kernel density contours and a linked distance cluster method were performed on tracking data, whereas Generalised Additive Models and kernel density estimation were applied to boat-based survey data. The shape and size of the MPAs produced from analyses of the different datasets were broadly similar to each other, generating confidence in the outputs and suggesting that an integrated approach may have widespread applicability. In contrast, generic foraging radii did not produce representative areas, suggesting restricted use as a preliminary scoping tool. Tracking reflected habitat use of birds of known provenance and a simple approach using 100% MCP provided a clearly defined boundary to feed into marine spatial planning that incorporated all important foraging habitats, embraced threats from anthropogenic development and could ‘future-proof’ changes in colony location. Where resources are limited, tracking over multiple seasons may be the most efficacious means of deriving seabird MPAs.

Sheringham Shoal Offshore Wind Farm (OWF), comprised of 88 3.6 MW turbines, was built within foraging range of Sandwich Tern Thalasseus sandvicensis breeding at a European designated site. Boat-based surveys (n = 43) were used to investigate changes in tern abundance within the site and within 0–2 and 2–4 km buffer areas before and throughout the construction of the OWF, over a study period between 2009 and 2012. Visual tracking of individual birds (n = 840) was also undertaken to document any changes in behaviour. This study is amongst the few to detail the response of a breeding seabird to the construction of an OWF. Navigational buoys in the 0–2 km buffer were used extensively by resting and socialising birds, especially early in the breeding season. Visual tracking illustrated avoidance of areas of construction activity and birds surprisingly kept their distance from installed monopiles. Avoidance was strengthened during turbine assembly, with around 30% fewer birds entering the wind farm, relative to the pre-construction baseline. Flight lines of birds that entered the site were generally along the centre of rows between turbines. A focus on transit flight meant that feeding activity was lower in the site than the buffer areas. As the site remained permeable to terns flying to and from foraging grounds further offshore, the overall abundance within the site was not significantly reduced. Although a number of the responses observed were unforeseen by Environmental Impact Assessment, the overall conclusion of only minor adverse effects was upheld. Analysis of further data from the operational site is now planned.

P>1. Quantitative palaeolimnology has traditionally sought to quantify species-environment relationships to use alterations in biological assemblages to reflect past environmental change. Transfer functions have used regression techniques, such as weighted averaging, to define taxon optima and tolerance for a single chemical or biological variable.2. Cladoceran assemblages and their sub-fossil remains in shallow lakes are shaped by a combination of interacting factors. Partial constrained ordination of sub-fossil cladoceran assemblages from 39 shallow lakes (29 in Norfolk, U.K. and 10 in Denmark) indicated that both zooplanktivorous fish (ZF) density and submerged macrophyte abundance significantly influenced community composition. These dual structuring forces precluded the use of a transfer function as one of the key assumptions of this approach was not met, namely that environmental variables apart from the variable being modelled have negligible influence on species distribution or that there is a linear relationship between the two. Separate transfer functions for ZF and macrophyte abundance were developed but had poor performance diagnostics with low bootstrapped r2, high root mean square error of prediction (RMSEP) and large bias.3. To obviate the problem of multiple structuring forces a multivariate regression tree (MRT) was employed, which allows for more than one explanatory variable within a model. The MRT analysis defined six groups with discrete ranges of ZF and macrophyte densities. The technique identified critical values or 'break points' in ZF and macrophyte abundances which result in significant alterations in the sub-fossil cladoceran assemblage. In addition, the MRT groups had different summer mean values for chlorophyll-a, Secchi depth, total phosphorus and nitrate-nitrogen.4. The predictive abilities of the model were assessed by comparing the observed versus predicted MRT group membership. In general group membership was reliably predicted, suggesting sub-fossil cladoceran assemblages reliably reflect ZF and macrophyte density in shallow lakes. For a relatively small number of sites there were differences between the observed and predicted MRT group membership. These failures of prediction may result, at least in part, from the disparity of the time period represented by the environmental data and the surface sediment cladoceran assemblage.

This palaeolimnological study investigates recent changes in the biological structure of an English shallow lake (Upton Great Broad, Norfolk). By focusing on the historical occurrence of submerged macrophytes, particularly the rare UK species, Najas marina L. (Holly-leaved Naiad), we address a management question that frequently arises for shallow lakes, namely whether to undertake sediment removal to increase water depth and/or restore conservation value. Macro-remains of aquatic macrophytes and molluscs were analysed in two littoral sediment cores and combined with other historical ecological data covering the last 100 years. Before around 1900, the lake had Chara meadows (including at least three species) and an associated species-rich community of Mollusca. Between around 1900-1970 a period of high angiosperm diversity is suggested with a reduction of Characeae and the development of patches of water-lily (particularly Nymphaea alba L.) and fen swamp in the open water. Then, after around 1970, our data indicate a rapid shift towards Najas-dominance coupled with a decrease in the seasonal length of the plant-covered period. The expansion of Najas was clearly associated with, and may even be dependent upon, a highly unusual fluid, green sediment formation that developed at the site from around the same time. Thus, despite the loss of an earlier more diverse vegetation and associated fauna, we suggest that best practice conservation may be allow natural site development and not to undertake active management such as sediment removal which might threaten the status of Najas. Our conclusion could only have been arrived at through the long-term ecological perspective that a palaeolimnological approach provides.

To assess the similarity, not only in community structure, but also in the factors that shape cladoceran assemblages, we analysed the contemporary zooplankton populations and their sub-fossil remains in 39 shallow UK and Danish lakes. Contemporary zooplankton populations sampled from both the lake edge and the open water in August were compared with surficial sediment assemblages. The sedimentary assemblage data combined counts of both ephippial and chitinous remains in order to provide some representation of Daphnia and Ceriodaphnia. A relatively large volume of sediment (>5 cm3) was analysed for ephippial remains so as to include those species best represented by the larger ephippia. Ephippia were identified to species level in the case of Daphnia magna, and to species aggregates for other groups such as Daphnia hyalina agg., Daphnia pulex agg. and Ceriodaphnia spp. In accordance with previous work several species found in contemporary samples (copepods and the cladocerans Polyphemus pediculus, Scapholeberis mucronata and Diaphanosoma brachyurum) were absent from the surface sediments. There were extensive supporting environmental data sets for the 39 sites. It was therefore possible to determine the factors which influenced assemblage composition for the two datasets by a combination of constrained ordination, in this case redundancy analysis (RDA), partial RDA and Procrustes rotation. The same two factors, zooplanktivorous fish density and submerged macrophyte abundance, were not only the main structuring forces for both data sets, but also explained very similar amounts of the variation in the different assemblages. Thus, we conclude that the living communities and their sedimentary remains reflect the environment they are shaped by in broadly similar ways. Calibration of sub-fossil cladoceran assemblages against modern environmental data to reconstruct environmental change can, therefore, validly employ principles elucidated by contemporary studies to determine the most appropriate modelling technique.

The shallow lakes of Eastern England have been subject to intense anthropogenic pressures including nutrient enrichment and fish stocking. We sought to determine the relationships between fish community structure and other ecosystem characteristics in 28 of these lakes through classification of fish species into piscivorous, zooplanktivorous and benthivorous feeding guilds according to the literature. Canonical correspondence analysis produced clear associations between fish and ecosystem characteristics that generally agreed with other theoretical (e.g. the alternative stable states hypothesis) and empirical studies, but with some important differences. There was a striking lack of relationships between nutrients and other variables, indicating the importance of top-down rather than bottom-up processes as a structuring force in the generally eutrophic study lakes. The presence of submerged (and shoreline) vegetation was associated with a diverse assemblage of apparently co-existing piscivorous (principally pike Esox lucius) and zooplanktivorous species. Perch Perca fluviatilis, a significant predator in other studies, was unimportant and argued to be limited by water quality in the extremely shallow lakes. In contrast, the benthivorous fish guild (principally carp Cyprinus carpio, bream Abramis brama and tench Tinca tinca) essentially represented the inverse of the potential pelagic associations between piscivores/zooplanktivores and vegetation. The introduction of large benthivores to many study lakes could have precipitated a loss of submerged vegetation through direct uprooting during foraging, with the effect of simplifying the fish community being most acute where littoral vegetation was limited by other anthropogenic factors. It is implied that attempts to promote or restore submerged vegetation in these lakes would best target benthivorous species.

Many seabirds travel widely to exploit variably distributed prey resources, utilizing even profitable patches only briefly as prey become available. Assessing the relative importance of areas occupied by wind farms relies on sufficient survey effort to increase the probability of detection and later assessment to an acceptable level. Conventional techniques suffer from high sampling costs and infrequent sampling of patches within larger areas. Remote techniques, which continuously sample habitat, may offer a solution although sufficient coverage may be difficult to achieve. In this paper, we outline experiences of the use of radio telemetry on LittleTerns Sterna albifrons at their most important UK breeding site, the Great Yarmouth North Denes Special Protection Area (SPA), in relation to a 30 turbine offshore wind farm on Scroby Sands, which encroaches to 2 km from the North Denes colony. Little Terns had not been radio-tagged previously in the UK, and the technical difficulties of tagging and subsequently following a small (55 g) diving seabird limited data collection. However, comparative data from 2 years (2003 and 2004), in which the abundance of the terns’ preferred prey varied greatly, revealed striking differences in activity and foraging patterns, which changed the perception of the scope of the birds. With an active nest, birds occupied a range of < 6.3 km2 with a range span of up to 4.6 km. In comparison, failed birds ranged widely, occupying ranges up to 52 km2 and travelling up to 27 km in a single foraging bout. As birds were recorded from 2 to 3 km offshore, the wind farm is within range of birds from the breeding colony at North Denes, although only a small proportion of foraging time was spent at such distance in the years of study. The potential value of radio (and satellite) telemetry in illustrating habitat use, perhaps to set precautionary distance limits for wind farms as well as defining actual use of particular areas including for collision risk assessment is discussed.

The restoration of river environments has been of growing importance to river management and planning in the UK. The extension of ecological restoration to floodplains as well as river channels is more complex, partly because of the range of stakeholders and the diversity of relevant management institutions. This paper draws on a qualitative survey of river managers in the UK to identify institutional factors relevant to the success or failure of floodplain restoration projects.

We discuss two contrasting discourses of environmental management for the management of rivers and floodplain environments in the United Kingdom. Through the 1990s a long-established flood defence discourse gave way to a new discourse of river and floodplain restoration. We draw on qualitative interviews with river managers to set out these discourses, and consider the engagement between them. We consider particularly the way in which flood defence engineers have resisted and gradually been won over to aspects of the new restoration discourse, and the role of champions in that discourse transition.

1. Piscivores (annual stocking of 1000 individuals ha -1 of 0+ pike and a single stocking of 30 kg ha -1 of large 20-30 cm perch) were stocked in seven consecutive years in a shallow eutrophic lake in Denmark. The stocking programme aimed at changing food-web structure by reducing zooplanktivorous and benthivorous fish, with resultant effects on lower trophic levels and ultimately water quality. 2. The fish community and water quality parameters (Secchi depth, concentrations of total phosphorus, chlorophyll a and suspended solids) were monitored between 1996 and 2000 and relationships were evaluated between predatory fish and potential prey and between zooplanktivorous or benthivorous fish and water quality parameters. In addition, potential consumption of piscivorous fishes was calculated. 3. The density of fish feeding on larger zooplankton or benthos (roach >15 cm, crucian carp >15 cm) declined distinctly during the study period. This effect was attributed to predation by large (>50 cm) pike. Based on scale readings, we cautiously suggest that the stocking of 0+ pike boosted the adult pike population to produce an unexpected impact in later years. Conversely, no direct impact of stocked 0+ pike was detected on 0+ roach. 4. A major decline in the recruitment strength of 0+ roach was observed in 2000. A combination of (i) the indirect effect of large pike preying on adult roach, with negative effect on roach reproduction and (ii) the direct predation effect of 0+ pike and/or 1+ and 2+ perch recruited in the lake, provides the most likely explanation of this phenomenon. 5. A marked increase in Secchi depth in 2000 and declining trends in suspended solids, chlorophyll-a and total phosphorus concentrations were observed. These changes may also be attributable to changes in the fish community, although the relationships were not straightforward. 6. This 7-year study indicates that piscivorous fish may be a significant structuring force in shallow eutrophic lakes, suggesting that stocking piscivores can increase predation pressure on cyprinids. However, the general lack of impact of 0+ pike points to the need of refining current stocking practices in several countries across Europe.

— This study investigated interactions between zooplanktivores (roach and perch) and piscivorcs (pike and large perch) in experimental ponds (16 m2) with open water habitat and three densities of natural macrophytes. Fish habitat selection was determined both day and night and was supported by daytime observations to study anti-predator behavioural patterns. Diel migration out from among macrophytes was seen in the absence of predators, particularly for roach, which changed from 13% of individuals being in open water during the day to 90% at night. The risk of predation from piscivores influenced the habitat selection of the zooplanktivores. Roach seemed to be the most vulnerable to predation from pike and selected the open water (90-92%) during daylight hours, but kept a 1-m distance from the macrophytes edge. The presence of pike thus reduced the use of macrophytes by roach, which in turn may improve macrophytes and the edge area as a refuge for zooplankton. Pike appeared to have less impact on the gross habitat selection of O+ perch, which were associated with the macrophytes (58–89%), though they were still vulnerable to predation. Adult perch, which was a generally less effective predator than pike, showed subdued behavior, concealing them selves in the macrophytes most of the time. No effect of the simultaneous presence of two predator species was found.

In Mexico, as in many other subtropical and tropical countries, there has been a recent trend towards stocking non-native carp (Cyprinus carpio) in lakes and ponds as a source of food in rural areas. However, the results of a study in a series of small(1–8 ha.), shallow (

The current state of biomanipulation was the subject of muchdiscussion at Shallow Lakes ‘95. This led to a workshop focusing onthe factors influencing the establishment of macrophytes and themechanisms responsible for their stability followingbiomanipulation. The purpose of the current paper is to distilcurrent knowledge on biomanipulation in shallow lakes gleaned fromdiscussions at the conference and recent literature.Biomanipulation should be used in the theoretical context of twoaltemative stable equilibria, as the extreme perturbation requiredto move from a phytoplankton dominated state to one dominated bymacrophytes. Understanding the nature of the factors and mechanismsresponsible for turbid water, is critical if biomanipulation is tobe appropriate. We suggest that with sufficient information,particular components of the fish community may be targeted andprecise figures for removal, designed to exceed critical thresholdvalues, may be set. Without this knowledge, a ‘play-safe’ strategyshould be adopted and at least 75% of the fish removed. Stockingwith piscivores may be a useful additional measure to fish removal.The principal objective of biomanipulation in shallow lakes is togenerate a period of clear water of sufficient length to allowmacrophytes to establish. To this aim, as well as for technicalreasons, biomanipulation is best undertaken in winter and earlyspring to generate clear water as early as possible in the season.In the cases where grazing is important, this coincides with thespring peak of Daphnia spp. Biomanipulation may have to berepeated if macrophytes do not colonise effectively within thefirst season. The factors responsible for the lag in response ofmacrophytes in some cases and the potential mechanisms contributingto the maintenance of clear water in macrophyte beds are discussed.From empirical data sets from many lakes, both a relative increasein the piscivorous fish stock and a reduction in nutrient levelsare thought to be important in stabilising the system in thelong-term. Whether biomanipulation may lead to alternativeequilibria (i.e. high diversity macrophyte communities withpiscivorous fish at high P) is unknown. Further study ofexceptional cases, theoretical modelling and development andanalysis of more long-term (>10 years) case histories isrecommended.

Fractional or point-abundance sample (PAS) electric fishing was compared with conventional electric fishing within stop-nets in several shallow, structurally complex, lowland lakes. The two methods tended to sample the fish community in different ways. PAS provided significantly higher total population estimates, partly as a result of the higher estimates for the dominant small fish (e.g. 0 + perch, Perca fluviatilis L.). Fish hidden by cover (macrophytes, branches, etc.) or substrate, such as eels Anguilla anguilla (L.) and ruffe Gymnocephalus cernuus (L.), were also sampled at a higher rate and for eel, this led to considerable variation in biomass estimates between the two methods. It is argued that PAS, rather than electric fishing within stop-nets, provided more accurate estimates of fish population parameters and that PAS had several distinct advantages when used for qualitative and quantitative stock assessment, particularly in shallow lakes dominated by emergent and submerged vegetation.

The activity patterns and habitat selection of tench in a shallow eutrophic lake were determined by radio telemetry. Environmental variables, including prey availability, depth and vegetational composition were quantified in order to explain observed patterns of distribution. Tench were generally only active at night, foraging on benthic animal prey, particularly chironomid larvae. Feeding fish clearly selected for particular locations although only weak associations with depth and densities of preferred prey were found. In addition, it appears that fish spent a considerable time searching for prey and travelling relatively large distances in the process, with the result that only relatively few prey were ingested during the course of a night. During daylight, fish were almost completely inactive, resting together in favoured locations and displaying a strong association for the littoral emergent vascular plant, Typha angustifolia. This may be because Typha usually grows in relatively deep water and forms stands of relatively widely spaced stems, thus allowing such large fish to penetrate deeply into cover. Management of eutrophic waters to encourage tench should take this habitat preference into account.

Scroby Sands offshore wind farm was built close to a haul-out and breeding site for harbour seal, a species of conservation concern. An aerial survey programme conducted during a five-year period spanning wind farm construction, revealed a significant post-construction decline in haul-out counts. Multivariate model selection suggested that the decline was not related to the environmental factors considered, nor did it mirror wider population trends. Although cause and effect could not be unequivocally established, the theoretical basis of hearing in pinnipeds and previous studies suggested that extreme noise (to 257 dB re 1 μ Papp @ 1 m) generated by pile-driving of turbine bases led to displacement of seals. A lack of full recovery of harbour seal during the study was also linked to their sensitivity to vessel activity and/or rapid colonisation of competing grey seal. Any impact of offshore wind farm development upon pinnipeds would be much reduced without pile-driving.

Despite widespread interest in the impacts of wind farms upon birds, few researchers have examined the potential for indirect or trophic (predator-prey) effects. Using surface trawls, we monitored prey abundance before and after construction of a 30 turbine offshore wind farm sited close to an internationally important colony of Little terns. Observations confirmed that young-of-the-year clupeids dominated chick diet, which trawl samples suggested were mainly herring. Multivariate modelling indicated a significant reduction in herring abundance from 2004 onwards that could not be explained by environmental factors. Intensely noisy monopile installation during the winter spawning period was suggested to be responsible. Reduced prey abundance corresponded with a significant decline in Little tern foraging success. Unprecedented egg abandonment and lack of chick hatching tentatively suggested a colony-scale response in some years. We urge a precautionary approach to the timing and duration of pile-driving activity supported with long-term targeted monitoring of sensitive receptors.

Large planktonic Cladocera are typically the most important components of the diet of underyearling roach. Selection for large species and individuals by fish can result in a shift in the species composition of the cladoceran community as well as a reduction in the mean size of the individuals of large species and in the assemblage as a whole. Laboratory experiments demonstrated that underyearlings feeding on Daphnia hyalina smaller than 1 mm in length has a significantly lower intake of prey volume per unit time than when feeding on prey greater than 1.5 mm. A decrease in the nutritional quality of zooplankton prey, brought about by increasing predation pressure is suggested as the mechanism for density-dependent reductions in the growth of underyearling roach in eutrophic water bodies.

The two volumes of this handbook provide a comprehensive account of the emerging and vibrant science of the ecological restoration of both habitats and species. Ecological restoration aims to achieve complete structural and functional, self-maintaining biological integrity following disturbance. In practice, any theoretical model is modified by a number of economic, social and ecological constraints. Consequently, material that might be considered as rehabilitation, enhancement, re-construction or re-creation is also included. Principles of Restoration defines the underlying principles of restoration ecology, in relation to manipulations and management of the biological, geophysical and chemical framework. The accompanying volume, Restoration in Practice, provides details of state-of-the-art restoration practice in a range of biomes within terrestrial and aquatic ecosystems. The Handbook of Ecological Restoration will be an invaluable resource to anyone concerned with the restoration, rehabilitation, enhancement or creation of habitats in aquatic or terrestrial systems, throughout the world.

The Norfolk Broads are a series of shallow, man-made lakes dug in medieval times for peat extraction, in Eastern England. Their eutrophic state has been well-documented and, since the early 1980s, their restoration has been attempted using a variety of techniques. The restoration began with the removal of point sources of phosphorus from sewage treatment works, which then revealed the role of sediment release when lake phosphorus levels failed to decline following inflow phosphorus levels. Small-scale removal of sediment layers in isolated broads demonstrated the feasibility, both technical and economic, of this technique, but experience then showed that sediment removal alone could not provide long-term restoration. Biomanipulation following sediment removal now offers the most reliable route to restoration, but the mechanisms by which a stable submerged plant community can be maintained after biomanipulation are still not clear.

Community analysis from a range of Norfolk Broads (a series of shallow lakes in Eastern England) reinforces the general perception that species such as roach (Rutilus rutilus) and bream (Abramis brama) dominate in turbid, nutrient-enriched lakes, whereas species such as perch (Perca fluviatilis)), tench (Tinca tinca) and pike (Esox lucius) dominate when submerged macrophytes are abundant. The presence of the latter leads to high piscivore: planktivore ratios. Amongst non-piscivorous species, the relative competitive ability of the different species in the presence of macrophytes is thought to be instrumental in causing these shifts. The fish communities in a number of case-studies undergoing restoration conform to expectations with rapid shifts in community structure once submerged macrophytes become established. There is little evidence that piscivory by pike, the dominant piscivore in the lakes, is important in causing species shifts in the presence of vegetation or in determining overall fish abundance or biomass. Most importantly, even a high biomass contribution of piscivores (to 90%) seems unable to buffer the recruitment of undesirable zooplanktivorous fish should macrophytes fail. Pike thus appear to contribute little to the overall stability of the macrophyte-dominated state. This may be linked, in part, to population regulation by cannibalism and the potential for adults of many cyprinid species to grow beyond predation, thus always providing a source of recruits. The manifestation of high numbers of zooplanktivores is, in turn, a function of high nutrient levels. Reduction of nutrient concentrations to a level at which piscivory may exert an effect amongst a suite of other mechanisms, all contributing to stability, thus remains a central theme of lake restoration.

Zooplankton, using macrophytes as refuges from predation by zooplanktivorous fish, are believed to be important in maintaining the macrophyte-dominated state in shallow lakes. Their grazing upon phytoplankton is also believed to be instrumental in preserving water transparency in the establishment phase of macrophytes which follows an attempt to restore a shallow lake from the effects of eutrophication. This paper interprets the results of fish, zooplankton and macrophyte interactions from an intensive 3-year study in the Norfolk Broads of eastern England. In the presence of even a low density of 0+ fish (0.2 m−2), Daphnia spp. which typically dominate the cladoceran community in spring, and through grazing are responsible for producing clear water, are typically reduced to very low levels. This decline may become protracted, but not eliminated, by the presence of macrophytes, implying a refuge effect. The efficacy of any refuge effect appears to increase with an increasing proportion of the water column occupied by macrophytes (PVI). As macrophytes develop, the grazing role is taken over by Ceriodaphnia spp. and Simocephalus spp., and may be at a sufficient rate to maintain clear water at least within macrophyte stands and possibly in intervening open water areas through diel migration of the zooplankton. A macrophyte PVI of 30–40% may provide an adequate refuge for these species through the mechanism of predation-free space, although this depends on fish density and community structure. At high densities (1 m−2) of a suite of fish species, including efficient foragers in open water (roach, Rutilus rutilus) and within macrophytes (perch, Perca fluviatilis), any refuge effect is nullified. In stable macrophyte-dominated lakes, the shift in fish community structure towards a higher proportion of piscivorous compared to zooplanktivorous fish may have a role in promoting the refuge effect through changing the distribution of zooplanktivorous fish. Predation upon zooplankton may also be reduced through the provision of alternative prey in the form of macrophyte-associated macroinvertebrates for an alternative fish stock dominated by perch, rudd ( Scardinius erythrophthalmus) and tench (Tinca tinca).

In the past, aquatic birds were largely overlooked by limnologists, receiving scant attention in hydrobiological journals and no more than passing mention in limnology texts. There has recently been rapid growth in interest in their roles in lake ecosystems, with the integration of bird studies into intensive limnological programs, comparative investigations over large groups of lakes, an increase in the number of experimental studies, and increasing contact with water bird biologists (Kerekes and Pollard, 1994; Farago and Kerekes, 1997). Much of this interest stems from recent scientific focus on the factors that lead to shallow eutrophic lakes being dominated alternatively by phytoplankton or by macrophytes (Schef-fer et al., 1993) and management investment in the restoration of eutrophic lakes to a clear macrophyte-dominated state (e.g., National Research Council [USA], 1992; Broads Authority [UK], 1994; National Environmental Research Institute [Denmark], 1994). It is now clear that aquatic bird populations may, at times, be very sensitive to ecological changes in lakes and that they can also play significant roles in producing such changes.

Fish have a major structuring impact on the Zooplankton communities in lakes (Hrbacek et al., 1961; Brooks and Dodson, 1965) that may cascade to the lower trophic levels and chemical environment (Carpenter et al., 1985; Carpenter and Kitchell, 1993). Ample evidence is available from enclosure experiments (e.g., Christoffersen et al., 1993), whole-lake experiments (e.g., Shapiro et al., 1975; Benndorf, 1987; Gulati et al., 1990; Carpenter and Kitchell, 1993), and empirical analyses (Jeppesen et al., 1990, 1997). More recently, it has become evident that 0+ fish may play a key role in Zooplankton population dynamics (Cryer et al., 1986; Mills et al., 1987), and some studies suggest that fish larvae are responsible for the midsummer decline in Zooplankton (Luecke et al., 1990; Jeppesen et al., 1997), a phenomenon that is often attributed to increased density of inedible phytoplankton such as cyanobacteria (e.g., De Bernardi and Guisanni, 1990). Whole-lake (Sondergaard et al., 1997) and enclosure (He and Wright, 1992) experiments support the structuring role of 0+ fish. How the importance of top-down control of Zooplankton by fish varies along a trophic gradient is debated extensively. McQueen et al. (1986) suggested that the cascading effect of zooplank-tivorous fish is stronger in oligotrophic lakes than in eutrophic lakes, but a growing body of literature argues that the cascading effect of fish is greater in eutrophic and hypertrophic lakes with respect to the food web in the classic sense

The effects of piscivores upon zooplanktivore behaviour and distribution and the impact of zooplanktivores on the abundance and distribution of zooplankton are well documented. However, the potential indirect effect of piscivores reducing the predation pressure upon grazing zooplankton through behavioural changes of zooplanktivores has received little attention, even though this may be an important mechanism in enhancing the stability of submerged macrophytes in shallow lakes. Preliminary observations from an unreplicated large-scale field enclosure experiment and a replicated pond experiment suggest that this mechanism is plausible with the set of piscivores (pike Esox luciusand perch Perca fluviatilis)and the zooplanktivores (0+ roach Rutilus rutilusand perch) common in temperate Europe. The presence of piscivores typically changed the habitat use and the activity level of zooplanktivores and the presence of zooplanktivores typically changed the habitat selection of cladoceran zooplankton. In the case of piscivore/zooplanktivore interactions, the risk of predation was enough to generate clear responses even where the losses to predation were low. However, only in the enclosure experiment was an indirect impact of the presence of piscivores, enabling Daphnia spp. to utilise open water in the presence of a high density of zooplanktivorous fish observed. Whether the magnitude and direction of the effect of piscivores is sufficient to benefit zooplankton may depend on the functional group (capable of foraging within structured habitats) of the predator (both piscivore and zooplanktivore), absolute and relative densities of predator and prey and predator dietary choice.

Grazing by herbivorous birds is often cited as an important factor in suppressing macrophyte development in shallow lakes undergoing restoration, thus delaying the attainment of the stable clear water state. Development and succession of macrophyte communities and size, diet and grazing pressure of coot (Hypophthalmichthys molitrixpopulations upon macrophytes, were monitored over the seasonal cycle at ten shallow lakes of varying nutrient status, in the Norfolk Broads in eastern England. In spring, territorial breeding birds were at relatively low density and included only a small proportion of macrophytes in their diet, resulting in low grazing pressure on macrophytes. In summer, there was a significant relationship between macrophyte cover and bird density, illustrating the importance of macrophytes in the dispersion phase for birds following breeding. Macrophytes comprised the bulk of bird diet where they were available and the consumption of macrophytes was up to 76 fold higher than in spring. However, losses to grazing in both periods were negligible when compared to potential growth rates documented in the literature. Grazing experiments at two biomanipulated lakes confirmed that birds were not responsible for limiting macrophytes during the spring colonisation phase or in the summer growth period. During the period of autumnal senescence and over the winter months where some macrophyte species remain available, e.g. as developed individuals or dormant buds, grazing by birds may conceivably have an impact on the development and structure of macrophyte populations in subsequent growing seasons.

The provision of a refuge from fish predation for large-bodied Cladocera among stands of submerged macrophytes is thought to be an important stabilising mechanism against nutrient-induced phytoplankton increases in clear water shallow lakes. The occurrence of any refuge effect in relation to the seasonal impact of both macrophyte development and recruitment of zooplanktivorous fish was monitored over the summer months (May to September) in three lakes (Cromes Broad, Hoveton Little Broad/Pound End, and Upton Broad) of variable trophic status, fish community structure and nature and extent of macrophyte cover, in the Norfolk Broads in Eastern England. At all sites, Daphnia spp. exhibited a early summer peak of abundance but had declined rapidly by July probably as a result of predation from underyearling fish. In extensive macrophyte stands (Cromes Broad) Daphnia spp. persisted after its elimination in open water, indicating some refuge effect. At sites with macrophyte cover and/or low fish predation pressure, Daphnia spp. was replaced by Ceriodaphniaspp., both with and without Simocephalussp., thus maintaining large populations of grazing Cladocera, apparently capable of exerting a high grazing pressure on phytoplankton. This occurred, even under high predation pressure from a relatively high density of zooplanktivorous 0+ fish (Cromes Broad), consistent with the refuge hypothesis. In addition, at this site, significant positive associations of cladoceran abundance with increasing macrophyte cover were apparent throughout the summer. From information on the distribution of fish it is suggested that dense macrophytes offer the most suitable refuge through provision of predator-free space.

After the diversion of a nutrient-rich inflow, the eutrophic lake, Alderfen Broad, initially showed reduced total phosphorus concentrations and phytoplankton populations, clear water and the establishment of submerged macrophytes. Internal P loading then increased, perhaps stimulated by the senescence of submerged macrophytes and exacerbated by the lack of flushing. Cyanophytes appeared in the summer of two years. As a consequence of poor recruitment of roach (Rutilus rutilus (L.)), the chief zooplanktivore, and a summerkill of the fish population, populations of large-bodied Cladocera (Daphnia hyalina/longispina and ultimately D. magna) developed. In the long-term, these may have limited the further development of phytoplankton populations and clear water and submerged macrophytes returned. During this latter period, internal P release has remained high (> 380 µg 1−1), thereby indicating the scope for biomanipulation even in eutrophic conditions. However, isolation of the lake has led to a decrease in water level (which through increased temperatures and lowered dissolved oxygen levels was probably responsible for the fish deaths) and further concentration of internal P load. Sediment is now being removed to reestablish greater water depth.

Recruitment success of roach varied dramatically between 1978 and 1985 in Alderfen Broad, a small lake in eastern England. All size classes of roach feed to a significant extent upon zooplankton, but the underyearling fish have the greatest effects upon the abundance, species composition and mean size of zooplankton. During years of good recruitment (1979, 1981, 1983 and 1985) when the 0 + age group was abundant, they showed poor growth as a result of the depression of their prey populations. Older fish also tended to grow poorly in these years and may have been less fecund the following year. In years of poor recruitment (1980, 1982 and 1984), with the release of the depressive effect upon the zooplankton exerted by underyearling fish, the older size classes tended to grow well with higher fecundity the following season, giving rise to good recruitment of underyearling fish, even when the number of spawners was low. The evidence indicates that there is a 2-year cycle of roach recruitment in Alderfen and this will be described.

SUMMARY (1) Two recent studies in small eutrophic lakes have revealed unusual 2-year cycles in recruitment of the fish Rutilus rutilus (L.) but the explanations offered by the investigators were different. In Alderfen Broad, competition between young-of-the-year and breeding individuals acts to reduce growth and fecundity in years following good recruitment. In Slapton Ley, good growth allows the fish to breed at a younger age (at the end of their second year of life), so that a year of good recruitment is followed 2 years later by another, when the previous prolific year-class comes to breed. (2) The aim of this paper is to construct simulation models of the two populations and thus to check whether the two verbal models are tenable. Known features of the populations, including age at first reproduction, inter-age-class competition, fecundity and survival rates, were incorporated into the simulation models, together with reasonable values for parameters that could not be measured. (3) The simulation models for Alderfen Broad confirmed that density-dependent loss of fecundity, operating with a time delay, could produce stable limit cycles with the observed period and amplitude. With slightly different, but still reasonable, parameter values, a perturbation to a stable population yielded a 2-year oscillation that damped out after 10-15 years. This could also be the explanation for the fish dynamics in Alderfen. (4) The simulation models for Slapton Ley revealed that a discrete perturbation was necessary to produce a damped oscillation, with the observed period and lasting for 6-20 years, in such an age-structured population in which breeding individuals are effectively from a single age-class. This perturbation was caused by an epidemic of the cestode parasite Ligula intestinalis. (5) Cycles are absent from both models when annual survival rate is higher than about 50%. Survival rates in Alderfen Broad (19-0%) and Slapton Ley (22-3%) are both

The harvest mouse (Micromys minutus) is understudied compared to other small mammals as a result of its small size and scansorial habits. This study in wetlands dominated by common reed (Phragmites australis) compared nest census, a commonly used technique to confirm presence/absence and monitor populations, with live-trapping using Longworths and a home-made alternative trap (the Jordan trap) set both on the ground and in the stalk zone (∼1 m from ground or water level). Nests were found at only two of the four study sites, which may have suggested an absence of the species. However, harvest mice were caught in traps at all sites. All 108 captures of 39 individuals were made in aerial traps in the stalk zone with none caught in ground traps. Generalised linear mixed model (GLMM) also showed that significantly more captures were made in Longworth traps compared to the Jordan trap, although the efficiency of the latter increased after modification. There were also significant differences in capture rate between sites and season and a preference for higher reed quality as described by PCA in the wetter areas of the reed-beds studied. We conclude that live-trapping is preferable to nest census as a population monitoring technique and that future studies of harvest mice, especially in tall wetland vegetation, should use Longworth traps and/or cheaper home-made alternatives set in the stalk zone.

The restoration of floodplain woodlands demands an understanding of the linkages between process, form and past management history at both a local and catchment scale. Site and reach scale processes that influence the species composition of floodplain woodland species are described with a particular focus on the relationships between hydrological and sediment inputs to floodplains and the regeneration response by tree species. The importance of integrating natural science knowledge gained at the site reach scale with decisions taken at the catchment scale on water allocation priorities is then discussed. Research was carried out on the River Ore in Sweden, The River Ouse in the United Kingdom and the River Isere and River Garonne in France. Research results at the site and reach scale allow broad definition of ideal conditions for the regeneration and growth of floodplain tree species and the flows that provide them: (1) channel movement has to occur for the creation of sedimentation sites required for the regeneration of early successional species and the flows that provide them; (2) flooding events should occur periodically to cause both channel movement and recharge floodplain water tables; (3) water table decline rates following a flood event must be slow enough that seedling roots can maintain contact with the retreating water front; (4) unseasonal flood events can cause high mortality of seedlings and prevent successful regeneration in any season. Some of the requirements for the restoration of floodplain woodlands can be delivered through site and reach scale restoration projects with reasonably predictable ecological outcomes. A more holistic approach to the provision of regeneration sites for floodplain woodlands would also include water allocation decisions targeted at providing flow conditions which could restore geomorphological processes. However, it is difficult to predict ecosystem responses to catchment scale flow allocation measures and, therefore, in the intensively managed river corridors of Western Europe, river restoration initiatives tend to be restricted to the site and reach scale.