No description available.

No description available.

No description available.

No description available.

No description available.

The aim of this study was to investigate the effects of changes in various environmental parameters on the underwater foraging behaviour of the American mink, Mustela vison. The study was conducted in an indoor pool. The effects of changes in the following parameters were investigated: (i) Water Depth. This was altered from 0.3 m to 1.65 m. (ii) Current Flow. Presence of either a deep or a surface current was compared to no current flowing. (iii) Prey Density. Four prey densities were used, 25%, 50%, 75% and 100%. (iv) Habitat Complexity. Hides were arranged in a regular, random or clumped pattern. The effects of habitat complexity were investigated in conjunction with prey density. Results are presented for gross changes in foraging behaviour, i.e. dive rate (number of dives per min), successful dive rate, hide visit dive rate, proportion of dives visiting a hide, proportion of successful dives and proportion of successful hide visits, and for finer changes within each dive, i.e. dive duration, time on bottom, number of hides visited per dive, mean time in hide, proportion of time on bottom spent hide searching, distance travelled underwater, proportion of direct to indirect dives, mean number of turns per dive, directionality of dives and revisiting of hides. The results showed that as depth increased, animals made fewer dives, but the dives were of longer duration. The extra time on bottom appeared to be used for locating hideswhich could no longer be located aerially before diving. Deep current was found to be not strong enough to seriously affect foraging behaviour. However, the surface disruption caused by the surface current, led to an increased dive rate, possibly in an attempt to locate hides that could no longer be located aerially, although other parameters such as proportion of dives visiting hides, dive duration etc., were generally unaffected by current flow. The conclusion was that mink were well able to continue foraging with current speeds of up to 0.86 m s(^-1). It was found that as prey density increased, animals, generally, made fewer dives of shorter duration, more of which were successful, although there was considerable individual variation. For habitat complexity, animals, generally, behaved similarly if hides were arranged randomly or in clumps, but when hides were regularly distributed, fewer hide visit dives were performed. However, mean time on bottom tended to be longer, resulting in little difference in foraging efficiency between the three conditions. A brief review of individual strategies revealed that there were considerable individual differences in foraging strategy. These were not related to sex, thus, some individuals consistently used a strategy of many short duration dives, generally visiting only one hide per dive. Others opted for fewer, longer duration, dives, generally involving more than one hide visit. Further, mean dive duration was not related to body weight. An investigation into the maximum underwater swimming speed achieved by mink showed that animals could reach speeds of over 1 m s(^-1). However, comparison with swimming speeds of fish species preyed on by mink, revealed that the fish swam faster. A review of the habits of the fish eaten, however, revealed that most were sedentary, bottom dwellers. The implications from this are that commercially important fish, e.g. salmon and trout, may well be taken mainly as diseased or spent individuals. The overall conclusion reached was that mink are highly versatile mustelids, and have 'specialised' in the ability to utilize both terrestrial and aquatic habitats.

No description available.

Both theoretical and practical importance can be attached to attempts to model human threshold and supra-threshold visual performance under water. Previously, emphasis has been given to the integration of visual data from experiments conducted in air with data of the physical specification of the underwater light field. However, too few underwater studies have been undertaken for the validity of this approach to be assessed. The present research therefore was concerned with the acquisition of such data. Four experiments were carried out: (a) to compare the predicted and obtained detection thresholds of achromatic targets, (b) to measure the relative recognition thresholds of coloured targets, (c) to compare the predicted and obtained supra-threshold appearance of coloured targets at various viewing distances and under different experimental instructions, (d) to compare the predicted and obtained detection thresholds for achromatic targets under realistic search conditions. Within each experiment, observers were tested on visual tasks in the field and in laboratory simulations. Physical specifications of targets and backgrounds were determined by photometry and spectroradiometry. The data confirmed that: (a) erroneous predictions of the detection threshold could occur when the contributions of absorption and scattering to the attenuation of light were not differentiated, (b) the successful replication of previous findings for the relative recognition thresholds of colours depended on the brightness of the targets, (c) the perceived change in target colour with increasing viewing distance was less than that measured physically, implying the presence of a colour constancy mechanism other than chromatic adaptation and simultaneous colour contrast; the degree of colour constancy also varied with the type of target and experimental instructions, (d) the successful prediction of the effects of target-observer motion and target location uncertainty required more than simple numerical corrections to the basic detection threshold model. It was concluded that further progress in underwater visibility modelling is possible provided that the tendency to oversimplify human visual performance is suppressed.

Typescript. / Thesis (Ph. D.)--University of Hawaii, 1968. / Bibliography: leaves [31]-32. / v, 32 l maps, graphs

Thesis (Ph. D.)--University of Texas at Austin, 2007. / Vita. Includes bibliographical references.