Cormorants are piscivorous birds with a daily food intake (DFI) of approximately 500 g. They are a protected species under the Wildlife and Countryside Act 1981. In the UK, the number of over-wintering, inland cormorants increased steadily between 1970 and 1987, at a rate of between 5 and 10 % per annum. An increase of 74 % occurred between winter 1987/88 and 1990/91, and the population is still believed to be rising. The population growth was observed in all regions of the UK, on all habitat types. As cormorants exploited new habitats, ornithologists welcomed their increased presence. This contrasts with the views of angling bodies, who assert that the presence of cormorants, feeding daily on their fisheries, has a damaging impact on fish stocks with inevitable financial losses. Due to a lack of effective non-lethal control methods, the angling bodies wish to see the cormorants removed from the protected species list so their inland numbers can be controlled. Ornithologists insist that there is no scientific evidence proving cormorants are damaging to inland fisheries and so are opposed to any culling. A review of previous cormorant studies was undertaken to evaluate information on their ecology, feeding behaviour and predation impact. The general conclusion was no study had been able to prove cormorant predation damages fish populations, because few studies had moved beyond determining the mass of fish removed by the birds over the particular study period. No assessment had been made of the impact of that fish removal on the fish population dynamics and the angling performance of the fishery. This highlighted the requirement for research into the impact of cormorant predation on inland fisheries. This study was formulated to estimate cormorant predation impact on fisheries in a more realistic and robust manner than had previously been undertaken. The principal objective of the study was to integrate fish population and cormorant feeding dynamics data on specific fisheries (study sites) in such a way as to quantify, where possible, the full impacts of the cormorant predation. This required the following criteria at each study site: - evaluation of the historical status of fish and cormorant populations; - determination of the population and community dynamics of the fish stocks; - analysis of the angling effort and angling performance; - identification of the species, and estimation of the numbers and sizes of fish consumed and wounded by cormorants, and comparison with the numbers and sizes of the fish populations present; - determination of the occupancy on, and use by, cormorants at the selected sites. The work programme ran between September 1995 and July 1998, covering three winters of cormorant predation. At each study site, the cormorant feeding dynamics were assessed by detailed feeding observations and cormorant counts. This enabled data to be collected on the species, size and amount of fish being ingested during each foraging bout, and the diurnal and seasonal patterns of cormorant occupancy. As feeding observations were unable to completed at each site everyday, a modelling system was designed, using a Monte Carlo Simulation (MCS), to estimate the number and mass of fish being removed from the site over the whole winter period. The fisheries data were collected by electric fishing, seine netting, hydro-acoustics and angler catch analysis. The actual methods used at each site were dependent upon the physical conditions present. The data were analysed for fish population dynamics, including length frequency of species, year class strength, natural mortality rate and growth indices; and for angling performance, including catch per unit effort and the relative importance of species. Combining site-specific data for the fish species composition, and the length frequency distribution from fisheries surveys and the cormorants' diet, allowed preliminary predation impact assessment. Reconstruction of life tables from the fisheries data allowed integration of the cormorant feeding data from the Monte Carlo Simulation to assess impact in terms of the numbers of fish consumed on subsequent population densities. This enabled the status of the fish population at each study site to be shown, with and without cormorant predation over the three-year period, resulting in a detailed predation impact assessment. The fisheries studied were located in two regions of the UK, the Midlands and the North West of England. This enabled the research to be completed in two distinct geographical areas, with known and established over-wintering cormorant roosts. The Midland study sites were Holme Pierrepont Rowing Course, Colwick Park Trout Lake and the River Trent. The North West study sites were the lower River Ribble and Grimsargh number 3 Reservoir. These sites encompassed cyprinid and salmonid fish populations, and covered riverine and lacustrine fisheries.

This study of the fish and fishery of Stocks Reservoir, Lancashire, is the result of contract work undertaken by the researcher for North West Water (NWW). In an attempt to describe the location of the study, relevant information covering the catchment, local geology, reservoir construction and flora and fauna is included.The Authority's remit suggested a study of three facets of the catchment, namely, a study of the native fish populations, a monitoring of the recently opened fishery and an analysis of operational filter plate impingement.In order to minimise disturbance of the sport fishery, native fish population work was necessarily limited to the reservoir's three major afferent streams, the River Hodder, Hasgill Beck and Bottoms Beck.As a preliminary measure of tributary stream status, a simple invertebrate site study was undertaken by the researcher in 1985.Fish population work based on catch per unit effort (CPUE) was pursued in the spring, summer and winter of 1985, 1986 and 1987 at 8 sites, employing D. C. electric fishing equipment, whilst Carle and Strub's (1978) MWL Method was adopted for population estimations. The validity of the electric fishing survey and age determination are discussed in the text.The native species of brown trout, bullhead, stone loach and minnow were encountered, as was the introduced rainbow trout. Species densities and the population structure of the native brown trout were examined in detail for each survey site. The River Hodder was revealed to be the least populous tributary, whilst Hasgill Beck exhibited the greatest fish densities. Spawning migrations of native brown trout were evident, with fry recruitment at its optimum at site 4 on Hasgill Beck and site 8 on Bottoms Beck. The waterfall on Bottoms Beck might well have precluded upstream access to the head waters of this tributary. Observed mean brown trout length for age data were similar to those recorded by authors researching other upland stream locations.The history of Stocks Reservoir as a sport fishery is outlined prior to the present leaseholder's opening of the reservoir as a day ticket fly fishery for the 1985 season. The water was stocked predominantly with rainbow trout, together with some brook trout and brown trout before fishing commenced.The present study covering the seasons 1985 to 1987 was based primarily on data abstracted from catch return forms, which displayed a notably high rate of submission, and stocking consent data provided by NWW. The validity of return form data is discussed.Over the three seasons studied, angler patronage was observed to decline by 16%, whilst the number of fish caught and taken also declined by 34.8% and 20.5% respectively. Angler success was similarly observed to decline in accord with the decrease in patronage and catches. Interestingly, there was an increased reliance on introductions of rainbow trout over the period, including larger fish, and by 1987 a cessation in the stocking of other trout species.From correlations observed between environmental parameters and angler patronage, anglers appeared to prefer fishing in dry, sunny conditions, but decreases in angler success occurred during periods of increased water turbidity. Such declines in success also displayed congruity with decreases in angler patronage.From a comparison undertaken with a cross-section of English and Welsh stillwater trout fisheries, Stocks Reservoir was judged to rate poorly, returning the lowest performance data in the upland stocked category.An examination of the stomach and hind gut contents of 127 rainbow trout, 7 brook trout and 8 brown trout caught by anglers, was undertaken in the 1985 and 1986 seasons, and was compared with the reservoir fauna data of Mills, M. L. (1971).A description of the water treatment plant and its operation is delineated, and a pertinent collection of fish impingement and screening literature is included.Impingement data were collated from lst March 1985 to 31st December 1987 from routine and emergency cleaning of the filter plates. After storage in a freezer, the thawed fish were examined chronologically, identified, measured and weighed. During the examinations a random sample of stomach and hind guts was procured, and scales from brown trout were removed for possible future reference.The total annual impingement was observed to vary considerably, although brown trout habitually exhibited the greatest losses, comprising 71%, 64% and 89% of fish impinged annually. Of the introduced species, rainbow trout and brook trout, brook trout were the more susceptible to impingement, but remarkably few rainbow trout were lost considering the number stocked.Rainbow trout and brook trout of medium (150mm to 300mm) and large (>300mm) length classes were impinged, whereas many smaller (<150mm) brown trout were lost, a phenomenon concurrent with the recruitment of juvenile stream fish to the reservoir population.Brown trout in particular exhibited an annual dissimilarity in rates of impingement, probably suggesting that seasonal migration was not causative of their increased impingement.Impingement of rainbow trout showed limited correlation with environmental parameters. In 1985 and 1986, increased impingement of both brown trout and brook trout was significantly correlated with low reservoir levels, and to some extent might be linked to rising values of water turbidity.The collecting of stomach and hind gut samples from impinged fish was discontinued after 1985 because of problems in collection associated with delays in sampling and probable regurgitation of stomach contents. The problem of eye fluke infestation in impinged fish was noted and enumerated as sampling progressed.A brief discussion of further routes of operational fish loss from the reservoir is included.

Thesis (M. S.)--Oklahoma State University, 2005. / Vita. Includes bibliographical references (p.30-39).

Thesis (M. S.)--Oklahoma State University, 2005. / Vita. Includes bibliographical references (p. 24-32).

Thesis (Ph.D.)--University of Wollongong, 2004. / Typescript. Includes bibliographical references.

Commercial harvest of sh stocks and their appropriate management requires an understanding of their population dynamics and of their ability to sustain exploitation. Here, some ecological and evolutionary consequences of excessive exploitation are examined. In Chapter 2 I evaluate the knowledge base and status of commercially exploited marine populations that undergo formal stock assessment. Despite a bias towards industrialised countries and stocks of commercial importance, I show the pervasiveness of overexploitation and, by using reference points of stock status, identify important regional di erences in the e ectiveness of sheries management. In Chapter 3 I develop a data format suitable for ecological analyses to best disseminate the valuable information contained in scienti c trawl surveys. This data format is suitable for inclusion into the public Ocean Biogeographic Information System (OBIS) and provides detailed observations that are suitable to the reconstruction of important sheries-independent stock indices. In Chapter 4 I examine the spatiotemporal dynamics of ground sh populations. A positive abundance-occupancy relationship was estimated for the majority of ground- sh populations examined suggesting that this well-described terrestrial pattern is also pervasive in the marine environment. Spatial hysteresis was exhibited by numerous populations, indicating that the spatial distribution of individuals failed to recover despite recoveries in abundance. In Chapter 5 I estimate the demographic consequences of changes in growth and maturation characteristics. The ability of a population to sustain harvest, and its ability to recover from previous depletions can be overestimated because of trends towards earlier maturation and slower growth. In Chapter 6 I conclude the thesis by discussing the implications of my research to sheries science and management. I argue that trends in the spatial distribution and the overall productivity of populations must be accounted for when determining sustainable shing levels and when predicting recovery trajectories under various catch abatement scenarios. While successful management measures have been implemented in a number of marine ecosystems, this thesis highlights the importance of improving our capacity to understand the dynamics of exploited populations and to fully use the wealth of available monitoring and assessment data.

Commercial harvest of fish stocks and their appropriate management requires an understanding of their population dynamics and of their ability to sustain exploitation. Here, some ecological and evolutionary consequences of excessive exploitation are examined. In Chapter 2 I evaluate the knowledge base and status of commercially exploited marine populations that undergo formal stock assessment. Despite a bias towards industrialised countries and stocks of commercial importance, I show the pervasiveness of overexploitation and, by using reference points of stock status, identify important regional differences in the effectiveness of fisheries management. In Chapter 3 I develop a data format suitable for ecological analyses to best disseminate the valuable information contained in scientific trawl surveys. This data format is suitable for inclusion into the public Ocean Biogeographic Information System (OBIS) and provides detailed observations that are suitable to the reconstruction of important fisheries-independent stock indices. In Chapter 4 I examine the spatiotemporal dynamics of groundfish populations. A positive abundance-occupancy relationship was estimated for the majority of groundfish populations examined suggesting that this well-described terrestrial pattern is also pervasive in the marine environment. Spatial hysteresis was exhibited by numerous populations, indicating that the spatial distribution of individuals failed to recover despite recoveries in abundance. In Chapter 5 I estimate the demographic consequences of changes in growth and maturation characteristics. The ability of a population to sustain harvest, and its ability to recover from previous depletions can be overestimated because of trends towards earlier maturation and slower growth. In Chapter 6 I conclude the thesis by discussing the implications of my research to fisheries science and management. I argue that trends in the spatial distribution and the overall productivity of populations must be accounted for when determining sustainable fishing levels and when predicting recovery trajectories under various catch abatement scenarios. While successful management measures have been implemented in a number of marine ecosystems, this thesis highlights the importance of improving our capacity to understand the dynamics of exploited populations and to fully use the wealth of available monitoring and assessment data.

Thesis (Ph. D.)--Florida State University, 2005. / Advisor: Richard Iverson, Florida State University, College of Arts and Sciences, Dept. of Oceanography. Title and description from dissertation home page (viewed Jan. 27, 2006). Document formatted into pages; contains xiii, 140 pages. Includes bibliographical references.