Intra- and interspecific variability in the distribution patterns and diet of the two most common catsharks caught in demersal trawls off the West and South coasts of South Africa: Evidence for habitat and resource partitioning?van der Heever, Grant Mark January 2017 (has links)
Magister Scientiae (Biodiversity and Conservation Biology) - MSc (Biodiv and Cons Biol) / The objective of this thesis was to elucidate intra- and interspecific variability in the distribution patterns and diet of the two most common demersal catsharks taken as by-catch by the commercial trawling industry targeting the two Cape hake species off the West and South coasts of South Africa. Samples and data were collected during routine demersal hake biomass surveys conducted by DAFF, with distribution data collected from 1994 to 2015 and stomach content and stable isotope data collected from 2014 to 2015. On examination of the distribution data, Holohalaelurus regani was found to be more abundant on the West Coast and Scyliorhinus capensis was found to be more abundant on the South Coast. Both catsharks were observed to display size-based segregations, with catshark size increasing with depth in both species. Differences in the distribution patterns of male and female H. regani were also noted, with female catsharks inhabiting inshore areas and male catsharks inhabiting offshore areas. The two catsharks appeared to display high levels of dietary overlap, with individuals feeding on the most abundant crustaceans and cephalopods caught as by-catch in the trawl on each coast.
Sebastian, Lemόne Margeaux
Magister Scientiae (Biodiversity and Conservation Biology) - MSc (Biodiv and Cons Biol) / Tonic immobility (TI) can be defined as an unlearned behavioural response described by a physical state of immobility. This behaviour can last from a few seconds up to several hours. Tonic immobility in sharks has not been investigated extensively, despite being observed and used widely. Due to this limited research, there is still uncertainty about the significance of this response, especially in smaller shark species. Anecdotal evidence suggests that females may enter a tonic state during courtship, but this has never been scientifically investigated. Alternatively, tonic immobility may function as an anti-predator response. The aim of this study was thus to examine the behaviour and physiology associated with tonic immobility in two closely related species of catshark, Haploblepharus edwardsii and Haploblepharus pictus, and to test for differences between males and females (if the evolutionary significance of TI was related to courtship), and between the two species (if TI evolved in response to species-specific drivers).
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