Some aspects of the dynamics of populations important to the management of the commercial marine fisheries

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The occurrence of two new plankton diatom populations in the English Lake District: Aulacoseira islandica

Samples of planktonic algae from major lakes in the English Lake District have been investigated over many years as part of a long-term monitoring programme set up by the Freshwater Biological Association and continued by the Institute For Ecology. Some lakes have been sampled regularly for long periods, others less frequently or only occasionally. Windermere north and south basins, and the neighbouring lakes Blelham Tarn and Esthwaite Water, have been under observation, mostly on a weekly basis, since the programme began in 1945. During this time diatoms have played a significant role in the population dynamics of these lakes.

The distribution of native and introduced species of crayfish in Austria

This account concentrates on the six species of crayfish found in Austria, and the current state of knowledge on their distribution and laws affecting conservation. In general the occurrence and distribution of crayfish in Austria is poorly known, although information obtained by researchers and the general public, after careful checking, is increasing. Three native crayfish species occur in Austria: Austropotamobius torrentium which is relatively widespread, A. pallipes with a restricted distribution, and Astacus astacus which is widespread. Three species of non-native (alien) crayfish have been recorded from a total of 158 localities in Austria. They are Astacus leptodactylus from eastern Europe, and two Nearctic species: Pacifastacus leniusculus and Orconectes limosus. The introduction of alien species causes considerable problems as they act as vectors of crayfish plague and are able to outcompete native species by higher reproductive capacities.

Monitoring fish populations in Lower Lough Erne, Northern Ireland: applicability of current methods and implications for future monitoring under the EC Water Framework Directive

The proposed EC Water Framework Directive (WFD) will require member states to monitor both biotic and abiotic components of lake environments. With adoption of the WFD some measurement of fish populations will also be required. This paper describes work carried out since 1971, and particularly since 1991, on the status of fish populations in Lower Lough Erne, Northern Ireland, with an emphasis on defining change over time due to human impacts on the lake. This offers a reasonable starting point from which to develop a monitoring programme suitable for the needs of the WFD in this lake. The implications for as yet unmonitored fish populations in lakes are also determined.

Predation and selection in copepod populations of Alpine waters [Translation from: Bollettino di Zoologia 21 541-545, 1954]

Zooplankton was studied in four alpine lakes in Switzerland, France and Italy. The presence the presence of the invertebrate predator Heterocope in three lakes was stated. It is then discussed why in three of these four lakes, the copepod Arctodiaptomus denticornis is present in the absence of Arctodiaptomus bacillifer, and vice versa respectively in the second and first parts of the lacustrine summer.

Herpetofaunal Inventories of the National Parks of South Florida and the Caribbean: Volume II. Virgin Islands National Park

Amphibian declines and extinctions have been documented around the world, often in protected natural areas. Concern for this alarming trend has focused attention on the need to document all species of amphibians that occur within U.S. National Parks and to search for any signs that amphibians may be declining. This study, an inventory of amphibian species in Virgin Islands National Park, was conducted from 2001 to 2003. The goals of the project were to create a georeferenced inventory of amphibian species, use new analytical techniques to estimate proportion of sites occupied by each species, look for any signs of amphibian decline (missing species, disease, die-offs, etc.), and to establish a protocol that could be used for future monitoring efforts. Several sampling methods were used to accomplish these goals. Visual encounter surveys and anuran vocalization surveys were conducted in all habitats throughout the park to estimate the proportion of sites or proportion of area occupied (PAO) by amphibian species in each habitat. Line transect methods were used to estimate density of some amphibian species and double observer analysis was used to refine counts based on detection probabilities. Opportunistic collections were used to augment the visual encounter methods for rare species. Data were collected during four sampling periods and every major trail system throughout the park was surveyed. All of the amphibian species believed to occur on St. John were detected during these surveys. One species not previously reported, the Cuban treefrog (Osteopilus septentrionalis), was also added to the species list. That species and two others (Eleutherodactylus coqui and Eleutherodactylus lentus) bring the total number of introduced amphibians on St. John to three. We detected most of the reptile species thought to occur on St. John, but our methods were less suitable for reptiles compared to amphibians. No amphibian species appear to be in decline at this time. We found no evidence of disease or of malformations. Our surveys provide a snapshot picture of the status of the amphibian species, so continued monitoring would be necessary to determine long-term trends, but several potential threats to amphibians were identified. Invasive species, especially the Cuban treefrog, have the potential to decrease populations of native amphibians. Introduced mammalian predators are also a potential threat, especially to the reptiles of St. John, and mammalian grazers might have indirect effects on amphibians and reptiles through habitat modification. Finally, loss of habitat to development outside the park boundary could harm some important populations of amphibians and reptiles on the island.

Herpetofaunal Inventories of the National Parks of South Florida and the Caribbean: Volume III. Big Cypress National Preserve

Amphibian declines and extinctions have been documented around the world, often in protected natural areas. Concern for this trend has prompted the U.S. Geological Survey and the National Park Service to document all species of amphibians that occur within U.S. National Parks and to search for any signs that amphibians may be declining. This study, an inventory of amphibian species in Big Cypress National Preserve, was conducted from 2002 to 2003. The goals of the project were to create a georeferenced inventory of amphibian species, use new analytical techniques to estimate proportion of sites occupied by each species, look for any signs of amphibian decline (missing species, disease, die-offs, and so forth.), and to establish a protocol that could be used for future monitoring efforts. Several sampling methods were used to accomplish these goals. Visual encounter surveys and anuran vocalization surveys were conducted in all habitats throughout the park to estimate the proportion of sites or proportion of area occupied (PAO) by each amphibian species in each habitat. Opportunistic collections, as well as limited drift fence data, were used to augment the visual encounter methods for highly aquatic or cryptic species. A total of 545 visits to 104 sites were conducted for standard sampling alone, and 2,358 individual amphibians and 374 reptiles were encountered. Data analysis was conducted in program PRESENCE to provide PAO estimates for each of the anuran species. All of the amphibian species historically found in Big Cypress National Preserve were detected during this project. At least one individual of each of the four salamander species was captured during sampling. Each of the anuran species in the preserve was adequately sampled using standard herpetological sampling methods, and PAO estimates were produced for each species of anuran by habitat. This information serves as an indicator of habitat associations of the species and relative abundance of sites occupied, but it will also be useful as a comparative baseline for future monitoring efforts. In addition to sampling for amphibians, all encounters with reptiles were documented. The sampling methods used for detecting amphibians are also appropriate for many reptile species. These reptile locations are included in this report, but the number of reptile observations was not sufficient to estimate PAO for reptile species. We encountered 35 of the 46 species of reptiles believed to be present in Big Cypress National Preserve during this study, and evidence exists of the presence of four other reptile species in the Preserve. This study found no evidence of amphibian decline in Big Cypress National Preserve. Although no evidence of decline was observed, several threats to amphibians were identified. Introduced species, especially the Cuban treefrog (Osteopilus septentrionalis), are predators and competitors with several native frog species. The recreational use of off-road vehicles has the potential to affect some amphibian populations, and a study on those potential impacts is currently underway. Also, interference by humans with the natural hydrologic cycle of south Florida has the potential to alter the amphibian community. Continued monitoring of the amphibian species in Big Cypress National Preserve is recommended. The methods used in this study were adequate to produce reliable estimates of the proportion of sites occupied by most anuran species, and are a cost-effective means of determining the status of their populations.

The fish populations of the River Avon, Hampshire, downstream of Salisbury, in 1987

The objective of this study is to describe the present statu s of the coarse fish populations of the River Avon, Hampshire. The study arose from a widespread concern among anglers and riparian owners that fish numbers had decreased since the early 1970's, and from a scarcity of accurate information on population densities on which to assess this complaint. It was realised at the outset that, without such information from earlier years, the survey would not reveal the extent of any decline in the fisheries. The result s of the survey are compared with available data from other rivers , chiefly the nearby R. Frome and R. Stour. They may be used to assess any futur e changes in population densities and growth rates, and to indicate promising areas for future research. The data were collected from a quantitative survey of twelve river sections along the fifty kilometres of river between Salisbury and Sopley, and a qualitative survey of three weir pools within the same area from 14 September to 9 October, 1987.

Variation in bacterial populations in time and space

Obtaining a reliable estimate of the bacterial population is one of the main problems facing the bacterial ecologist. The author discusses the various methods available and concludes that the observed variability in bacterial populations depends on the sampling interval used.

The impact of Cow Green Reservoir on invertebrate populations in the River Tees

Cow Green is a new reservoir situated in Pennine moorland. It has an area of 312 ha, a capacity of 40 . 9 x 10 SUP-6 m SUP-3 and a maximum depth of 22 . 8 m. The function of the reservoir is to regulate flow in the River Tees to provide industrial Teesside with sufficient water during the dry spells. Invertebrate studies were carried out in the Tees to monitor changes resulting from the construction of the reservoir both in the flooded basin and below the dam. The overall effect of the reservoir on the Tees has been to increase the numbers and biomass of certain taxa, but generally not at the expense of previous fauna. Some of the positive effects, ie. increase in number and biomass, and maintenance of faunal diversity, may in part be attributable to the presence of the rapids and waterfall. Turbulence resulting from this rapid flow over heterogeneous bottom is sufficient to prevent clogging of interstitial spaces by silt and to maintain the variety of ecological niches necessary for a diverse fauna.

Effects of Cow Green Reservoir upon downstream fish populations

Post impoundment observations on the fish populations of the River Tees, downstream from the Cow Green Reservoir were made between 1971 and 1980. Both bullhead (Cottus gobio L.) and brown trout (Salmo trutta L.) population densities increased in the river after impoundment but changes in growth rate were small. Investigations into the stomach contents of the two species reflects the results of other work on increases of benthos in the river. Following regulation there was an increase in the quantity of Ephemerella ignita found in trout stomachs while in the bullhead, regulation caused an increase in the importance of Mollusca and a decrease in importance of Ephemeroptera and Plecoptera.