Changes in the fish community and water quality during seven years of stocking piscivorous fish in a shallow lake

SUMMARY 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.     

OPEN WARD MANAGEMENT OF ACUTE ALCOHOLISM—Experience with a Pilot Program

Sixty acutely alcoholic patients were treated in unsegregated rooms of two to twelve beds in a general hospital to determine the feasibility of open ward care. Personnel caring for them were first educated in the nature of alcoholism, the aberrations it produces and treatment with tranquilizing drugs. Fears and objections were overcome.Violent or unpredictable patients were excluded from the test, but those with alcoholic hallucinations or delirium suspectible to control were admitted. Preliminary physical examination was done to find out whether there was coincidental disease. In three patients, one with subarachnoid hemorrhage, one with severe anemia and one with pneumonia and shock, this examination followed by prompt treatment was probably life-saving. Tranquilizers, fluids and vitamins were given routinely, by mouth as soon as possible.Alcoholic patients were found to be no more unmanageable than others.If it were generally accepted that acutely alcoholic patients, diagnosed as such, could be admitted to open ward care in general hospitals, candor in diagnosis would be encouraged thereby, coincident disease probably would be promptly recognized if present, and long-term treatment for the alcoholic addiction could be begun early.     

Relationships between fish feeding guild and trophic structure in English lowland shallow lakes subject to anthropogenic influence: implications for lake restoration

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.     

Visual tracking from a rigid‐hulled inflatable boat to determine foraging movements of breeding terns

ABSTRACT Defining the at‐sea foraging movements of seabirds is fundamental to understanding their ecology and can also be important in assessing the potential impact of marine developments such as offshore wind farms (OWFs). Surveys of predefined areas using aerial or boat‐based transect surveys may not allow adequate assessment of the relative importance of different areas to birds. Individual‐based satellite or radio‐telemetry can be effective in identifying foraging ranges and preferred areas, but may not be suitable for some species. We developed a method to determine the foraging movements of breeding terns (Sterna spp.) by visually tracking individuals using a rigid‐hulled inflatable boat (RHIB). Sandwich Terns (S. sandvicensis), Common Terns (S. hirundo), and Arctic Terns (S. paradisaea) were tracked from colonies in Norfolk and Anglesey, United Kingdom, from 2006 to 2008. The proportion of complete (from and to colony) trips varied from 29–60% among species, years, and colonies. Individual Sandwich Terns were tracked for periods up to 126 min over distances up to 72 km and as far as 54 km from the breeding colony, further than Arctic (up to 57 km and 29 km from the colony) and Common (to 29 km and <9 km from the colony) terns. Mean values were much smaller. Multivariate modeling of Sandwich Tern foraging trips indicated that flight speeds >50 km/hr coupled with greater distances from shore (>25 km) significantly reduced the likelihood of tracking a bird for an entire foraging trip. Use of different boats that differ in speed and performance may alleviate such issues. Visual tracking allowed us to collect data on foraging behavior, flight height, and prey capture rates, and also permitted comparisons between species. Our results indicate that visual tracking may be an effective means of determining the foraging movements and at‐sea behavior of a variety of short‐ranging, day‐active seabirds.     

Trophic interactions in a shallow lake following a reduction in nutrient loading: a long-term study

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 l^-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.     

The relationship between cladoceran body size and the growth of underyearling roach (Rutilus rutilus) (L.) in two shallow lowland lakes: a mechanism for density-dependent reductions in growth

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.