Habitat utilization of Cape clawless otters Aonyx capensis

[摘要] ENGLISH ABSTRACT:This study tested several hypotheses regarding various aspects ofhabitat use by Cape clawless otters Aonyx capensis, in varioushabitats. The hypotheses, namely that A. capensis do not selectany prey types, prey sizes or habitat type were tested. Habitattype was investigated at a scale that enabled separating theeffects of types of riparian vegetation, geomorphology andanthropogenic influences. Aspects of the resource dispersionhypothesis (RDH) and optimal foraging theory were tested. This wasdone in both the marine and freshwater environments.The annual and seasonal diets of A. capensis in the Olifantsand Eerste Rivers, Western Cape Province, are described. Crabswere found to be the main prey and fish the second most importantprey of A. capensis in both the rivers during all seasons. Thepercentage occurrence of prey of A. capensis in both rivers,showed an increase in the amount of crab in summer and acorresponding decrease in the number of fish eaten. The seasonalfluctuation in crabs and fish found in the spraints (faeces),corresponded with the expected frequencies as determined fromtrapping.Seven A. capensis were caught in the two rivers and radiotrackedbetween 1993 and 1995. Total home range length varied from4.9 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 corearea used from 1.1 to 138.9 ha. As predicted using the RDH totalhome range length was correlated to mean reed bed nearestneighbour distance. The otters were typically active from dawn for2.6 h and moved a mean of 0.9 km. They were also typically activefrom sunset for a mean of 2.3 h moving a mean of 1.3 km. Theywere found to select for areas with boulders and/or reed beds.Aonyx capensis were found to be mainly solitary in all thehabitats. The pattern of female home ranges was suggestive ofterritoriality. The males, however, had overlapping home ranges,both with other males and females.From spraint analysis and direct observations, the seasonaldiet and foraging behaviour of A. capensis feeding in the surfzone in False Bay, Western Cape Province, were determined. Themost common prey species during all seasons was Cape rock crabPlagusia chabrus. Diversity of prey was lowest in winter,increasing through the seasons from spring to autumn. Foragingbehaviour data support the optimal breathing hypothesis, whichpredicts that both surface and dive times should increase fordives of greater depths. However, diving efficiency did notdecrease with increasing depth, nor did percentage time at thesurface increase with increasing depth. These results arecontrary to the optimal breathing hypothesis.How A. capensis use their habitat in the presence ofpotential competitors spotted-necked otters Lutra maculicollisand water mongooses Atilax paludinosus was also determined byinvestigating their trophic overlap during enforced cohabitationin a relatively small range during drought conditions.The analysis of trophic overlap showed that even duringenforced cohabitation in a relatively small range during droughtconditions, there was separation of diets of A. capensis, L.maculicollis and A. paludinosus.These results and their implications for conservationmanagement are discussed.

[发布机构] Stellenbosch University