The thesis investigated the proximate factors affecting selection among different prey types by coastal otters. From a broad description of coastal otter diet, and its relationship to prey availability, the work progressed to a detailed study of the predatory behaviour of individuals and age classes, and thence to the formulation and testing of specific hypotheses regarding prey choice. Spraint analysis showed that the diet of otters in Loch Spelve consisted principally of small, demersal inshore fishes and shore crabs. It was demonstrated that while the frequency of occurrence of most fish species in spraints seemed to reflect availability, the occurrence of shore crabs did not. Direct observations of foraging otters showed that there were large differences in prey selection and foraging behaviour between age classes of otter. In particular shore crabs were consumed almost exclusively by juvenile otters and rarely appeared in the diets of adults. Foraging efficiency was shown to improve gradually with age and experience, and as it did so the proportion of shore crab in the diet decreased. It was surmised that shore crabs were not a preferred prey, but were relatively easy for juvenile otters to locate and capture. It was hypothesised that the apparent preferences of otters for certain prey types, such as for fish over shore crabs, were based on the relative energetic profitabilities of those prey types. A detailed examination of the costs and benefits, in terms of time and energy respectively, to otters of feeding on the main prey species supported this hypothesis. Shore crabs were markedly unprofitable, requiring considerable time expenditure for relatively little energy return. An apparent preference for rocklings and eelpout over butterfish was also consistent with the relative profitabilities of these species.

No description available.

Thesis advisor: Sarah Goo / This is a made up abstract. Here is more content. / Thesis (BA) — Boston College, 2020. / Submitted to: Boston College. College of Arts and Sciences. / Discipline: Departmental Honors. / Discipline: Philosophy.

The ecology of otters (Lutia lutia L.) was studied at a number of locations to investigate specific aspects of carnivore behaviours and trophic niche breadth. Otter inhabiting the Gower Peninsular, in South Wales, ate freshwater fish (58.7%), marine fish (24.6%), non-fish (16.2%) and unidentified prey (0.6%). Bullhead was the core prey on Gower, although eel, stickleback, flatfish, brown trout and amphibians were also important dietary components. There was significant temporal and spatial variation in the composition of otter diet on Gower. A year long study of otters on the Pembrokeshire coast found that diet was composed of marine fish (56%), freshwater fish (29%) and non-fish prey (15%). O tter diet was very diverse on Gower and the Pembrokeshire coast, with slow swimming demersal fish the most frequent prey items. A systematic meta-analytical review of otter dietary studies demonstrated that otters have a very brbad trophic niche across Europe (H' - 0.77) and suggested that otters are facultative foragers. There was no evidence of latitudinal or Mediterranean trends in trophic diversity. Variation in trophic diversity and dietary composition appeared to be driven at the habitat level. A rigorous assessment of the techniques used to monitor otter populations and investigate otter diet was also undertaken. The standard 600 m transect used to determine otter distribution was inadequate at detecting otters on small lowland rivers, due to a high rate of type II error. Increasing transect size, making repeat visits and surveying additional sites improved the detection power of otter surveys. Five different spraint analysis methods produced dietary data with a low level of comparability. Potential limitations of volumetric analysis in highly diverse diets were identified. Molecular tools and new technologies need to be applied in carnivore dietary studies to advance theories of foraging, competition and lifehistory strategies.

Thesis (PhD)--University of Stellenbosch, 2001. / ENGLISH ABSTRACT: This study tested several hypotheses regarding various aspects of habitat use by Cape clawless otters Aonyx capensis, in various habitats. The hypotheses, namely that A. capensis do not select any prey types, prey sizes or habitat type were tested. Habitat type was investigated at a scale that enabled separating the effects of types of riparian vegetation, geomorphology and anthropogenic influences. Aspects of the resource dispersion hypothesis (RDH) and optimal foraging theory were tested. This was done in both the marine and freshwater environments. The annual and seasonal diets of A. capensis in the Olifants and Eerste Rivers, Western Cape Province, are described. Crabs were found to be the main prey and fish the second most important prey of A. capensis in both the rivers during all seasons. The percentage occurrence of prey of A. capensis in both rivers, showed an increase in the amount of crab in summer and a corresponding decrease in the number of fish eaten. The seasonal fluctuation in crabs and fish found in the spraints (faeces), corresponded with the expected frequencies as determined from trapping. Seven A. capensis were caught in the two rivers and radiotracked between 1993 and 1995. Total home range length varied from 4.9 to 54.1 km and core home range length from 0.2 to 9.8 km. Total area of water used ranged from 4.9 to 1062.5 ha and core area used from 1.1 to 138.9 ha. As predicted using the RDH total home range length was correlated to mean reed bed nearest neighbour distance. The otters were typically active from dawn for 2.6 h and moved a mean of 0.9 km. They were also typically active from sunset for a mean of 2.3 h moving a mean of 1.3 km. They were found to select for areas with boulders and/or reed beds. Aonyx capensis were found to be mainly solitary in all the habitats. The pattern of female home ranges was suggestive of territoriality. The males, however, had overlapping home ranges, both with other males and females. From spraint analysis and direct observations, the seasonal diet and foraging behaviour of A. capensis feeding in the surf zone in False Bay, Western Cape Province, were determined. The most common prey species during all seasons was Cape rock crab Plagusia chabrus. Diversity of prey was lowest in winter, increasing through the seasons from spring to autumn. Foraging behaviour data support the optimal breathing hypothesis, which predicts that both surface and dive times should increase for dives of greater depths. However, diving efficiency did not decrease with increasing depth, nor did percentage time at the surface increase with increasing depth. These results are contrary to the optimal breathing hypothesis. How A. capensis use their habitat in the presence of potential competitors spotted-necked otters Lutra maculicollis and water mongooses Atilax paludinosus was also determined by investigating their trophic overlap during enforced cohabitation in a relatively small range during drought conditions. The analysis of trophic overlap showed that even during enforced cohabitation in a relatively small range during drought conditions, there was separation of diets of A. capensis, L. maculicollis and A. paludinosus. These results and their implications for conservation management are discussed. / AFRIKAANSE OPSOMMING: Hierdie studie het 'n aantal hipoteses oor verskeie aspekte van habitat gebruik deur die Groototter Aonyx capensis, in verskillende habitatte, getoets. Die nul hipotese, nl. dat A. capensis nie vir enige prooitipe, prooigrootte of habitat-tipe selekteer nie, is getoets. Habitat tipe is ondersoek teen 'n skaalgrootte wat dit moontlik gemaak het om die effekte van tipes oewer plantegroei, geomorfologie en antropogeniese invloede van mekaar te skei. Aspekte van die hulpbron verspreiding hipotese (HVH) en optimale kossoek gedrag, is in beide die varswater en seewater omgewing getoets. Die jaarlikse en seiseonale diëte van A. capens~s in die Olifants and Eerste Riviere in die Wes-Kaap Provinsie, word beskryf. Daar is gevind dat krappe die hoof prooi en vis die tweede mees belangrike prooi van A. capensis in beide riviere, gedurende al die seisoene, was. Die persentasie A. capensis prooi teenwoordig in beide riviere het 'n toename in krap getalle in die somer en 'n ooreenstemmende afname in die hoeveelheid vis wat geeet word getoon. Die seisoenale verandering van krap en vis wat in die keutels (mis) voorkom, het ooreengestem met die verwagte frekwensies soos bepaal deur fangste in fuike. Sewe A. capensis is in die twee riviere gevang en tussen 1993 en 1995 d.m.v. radiosenders gevolg. Die totale tuisgebied lengte het van 4.9 tot 54.1 km, en die kern tuisgebied lengte van 0.2 tot 9.8 km, gewissel. Die totale area water wat gebruik is het van 4.9 tot 1062.5 ha, en kerngebiede van 1.1 tot 138.9 ha gewissel. Soos voorspel deur gebruik van die HVH, was die totale tuisgebied lengte gekorreleer met die gemiddelde rietbedding naaste-buurman analise afstand. Die otters was tipies aktief vanaf sonsopkoms vir 2.6 ure en het dan 'n gemiddeld van 0.9 km beweeg. Hulle was ook tipies aktief vanaf sonsondergang vir 'n gemiddeld van 2.3 ure en het dan gemiddeld 1.3 km beweeg. Daar is gevind dat hulle selekteer vir areas met rotse en areas met rietbeddings. Dit is ook gevind dat A. capens~s in alle habitatte hoofsaaklik alleenlopend is. Die wyfies se tuisgebied-patroon het op territorialiteit gedui, terwyl die manlike diere se tuisgebiede oorvleuel het met beide dié van wyfies, en met dié van ander mannetjies. Die seisoenale dieet en kossoekgedrag van A. capensis wat in die brander sone van Valsbaai, Wes-Kaap Provinsie, voed, is deur keutel analise en direkte waarneming bepaal. Die mees algemene prooi spesie gedurende al die seisoene was die Kaapse rotskrap Plagusia chabrus. Prooi diversiteit was die laagste in winter en het toegeneem vanaf lente tot herfs. Kossoekgedrag gegewens ondersteun die optimale asemhalings hipotese, wat voorspel dat beide oppervlak- en duik tye toeneem met dieper duike. Duik effektiwiteit het egter nie afgeneem met toenemende diepte nie, en persentasie tyd op die oppervlakte het ook nie toegeneem met toenemende diepte nie. Dit is dus in teenstelling met die optimale asemhalings hipotese. Hoe A. capensis hul habitat in die teenwoordigheid van potesieele kompiteerders nl. Klein otters Lutra maculicollis, en Water muishonde Atilax paludinosus gebruik, is ook bepaal. Dit is gedoen deur hul trofiese oorvleueling gedurende noodgedwonge saamleef, veroorsaak deur droogte kondisies in 'n relatiewe klein tuisgebied, te ondersoek. Die resultate van die trofiese oorvleueling analise het getoon dat selfs gedurende noodgedwonge saamleef gedurende droogte toestande in 'n relatiewe klein gebied, daar 'n verskil was in die diëte van A. capensis, L. maculicollis and A. paludinosus. Hierdie resultate en hul implikasies vir bewaringsbestuur word bespreek.

Variation in terrestrial mammalian craniodental morphology and skull shape is known to constrain feeding performance, which in turn influences dietary habits and ultimately fitness. Otters have evolved two feeding specializations: underwater raptorial capture of prey (mouth-oriented) and capture of prey by hand (hand-oriented), which likely correspond to craniodental morphology and bite performance. However, feeding biomechanics and performance data for otters, aquatic mustelids that consume prey above water, are sparse. The first goal of the study was to investigate the relationship between feeding morphology and bite performance between two mouth-oriented piscivores (giant river otters and North American river otters) and two hand-oriented invertebrate specialists (sea otters and Asian small-clawed otters) using morphometric approaches. The second goal was to investigate fluctuating asymmetry in the cranium of otters. The third goal was to characterize feeding mechanisms (kinematics and jaw musculature) and role of bite performance in the trophic ecology of sea otters. Mouth-oriented piscivores possessed longer skulls and mandibles, with jaws designed for increased velocity at the expense of bite capability. Hand-oriented possessed more blunt skulls and mandibles designed for increased bite capability. Sea otters displayed a greater degree of fluctuating asymmetry of the skull, which is likely linked to environmental stresses. Bite performance and durophagous feeding behavior in sea otters was characterized in detail in the feeding kinematics. Estimated bite forces of sea otters were large enough to crush all size classes of butter and littleneck clams tested in the lab. However, sea otters are size selective predators and generally choose bivalves of small to medium size. Medium sized butter and littleneck clams required an intermediate breaking force, and are buried at a shallower depth than larger clams. Clams requiring an intermediate breaking force could decrease consumption time, thus overall handling time.

No description available.

No description available.

No description available.

Thesis (M.S.)--Oregon State University, 2007. / Printout. Includes bibliographical references (leaves 100-110). Also available on the World Wide Web.