Signal crayfish (Pacifastacus leniusculus) is important invasive species in European freshwaters. Its influence on other freshwater organisms is well known from the literature, as well as direct and indirect impact on fish assemblages. This work was focused on the experimental evaluation of non-indigenous signal crayfish as a predator of salmonids compared to indigenous noble crayfish (Astacus astacus). Moreover, the possible importance of young-of-the-year signal crayfish as a prey for salmonids was assessed. There were carried out experiments using eggs and hatchings of grayling (Thymallus thymallus) as a prey for adult and subadult specimens of both, signal and noble crayfish. Next experiment used young-of-the-year signal crayfish as a prey for young-of-the-year of brown trout (Salmo trutta). Results showed that the danger of signal crayfish for grayling eggs is slightly higher. However, detected differences were surprisingly lower and in the majority of parameters even insignificant. In the case of grayling hatchings, was not detected any significant difference at all. The abilities of both tested species to prey on eggs and hatchings are therefore very similar, comparable. Even so, the effect of signal crayfish can be importantly higher in natural conditions because of its more dense populations, higher growth rate and fast maturation. In accordance to our findings, it is evident that brown trout has no so high effect of crayfish juveniles compared with crayfish effect on salmonids early developmental stages. Crayfish are therefore more likely able to limit salmonids than conversely.

La plasticité comportementale et les interactions entre organismes sont connues pour avoir une influence sur l’utilisation de l’espace, notamment la sélection de l’habitat de chasse. Dans l’Atlantique Nord-Est, les phoques gris et veaux marins vivent en sympatrie. Ces deux espèces sont réparties dans différentes colonies où les interactions entre organismes (liées à la taille de la colonie et à la présence simultanée ou non des deux espèces) ainsi que la disponibilité de l’habitat (et donc des proies) varient localement. L’objectif de cette thèse était d’étudier l’utilisation spatiale et la sélection d’habitat de chasse à l’échelle locale de ces deux espèces dans des situations contrastées de dynamique de colonies. Pour cela, plusieurs individus de différentes colonies situées en Irlande, en Écosse et en France ont été équipés de balises GPS/GSM. Les données récoltées ont permis de caractériser leurs trajets en mer ainsi que d’identifier les zones de chasse permettant par la suite la sélection d’habitat. Contrairement aux veaux marins, qui ont réalisé des déplacements restreints aux alentours des colonies, la plupart des phoques gris se sont déplacés entre différentes colonies. Ainsi, l’étude de la sélection d’habitat à l’échelle individuelle pour les individus se déplaçant entre différentes colonies a mis en évidence l’influence de la plasticité comportementale et suggéré celle de la personnalité de l’animal. A l’échelle de la colonie, chez les deux espèces, les résultats ont mis en évidence l’influence de la disponibilité de l’habitat (et indirectement de la disponibilité des proies) ainsi que des interactions intra-spécifiques (liée à l’effet de densité dépendance) sur l’utilisation spatiale et la sélection de l’habitat de chasse. Cependant, la sélection de l’habitat de chasse était principalement liée à la distance au reposoir et la bathymétrie. Ces deux paramètres sont liés aux caractères de chasseur à place centrale et benthique des phoques. Cette étude a également mis en évidence, pour les sites où les deux espèces étaient présentes, une certaine ségrégation spatiale et des différences de sélection d’habitat entre les deux espèces. / The behavioural plasticity and the interactions between organisms are known to influence foraging habitat selection and spatial usage. In the Northeast Atlantic, greyand harbour seals live in sympatry. These two species are spread into different colonies where interactions between organisms (linked to the colony size et and the presence of one or both species) and habitat availability (linked to the prey distribution) vary locally. The objective of this PhD was to study the spatial usage and foraging habitat selection of these two species at the local scale, in contrasted situations of population dynamics. Several individuals were tagged with GPS/GSM tags in different colonies located in Ireland, Scotland and France. Telemetry data was used to characterize the seals’ trips at sea and to identify their foraging areas in order to model foraging habitat selection. While harbour seals only performed trips restricted around their haulout sites, grey seals moved between colonies. Studying habitat selection at the individual scale, for individuals moving between colonies, highlighted the influence of behavioural plasticity and suggested the influence of individual personality. At the colony scale, for both species, results highlighted the influence of habitat availability (indirectly linked to prey availability) and intra-specific interactions (linked to density dependence effects) on spatial usage and foraging habitat selection. However, the foraging habitat selection was mainly explained by the distance from the last haulout and the bathymetry. These two parameters are linked to the central place forager and benthic feeder characteristics of the seals. Furthermore, this study also highlighted, for study sites where both species occur, a spatial segregation and differences in foraging habitat selection between grey and harbourseals.

The south coast of South Africa represents the extreme western end of the range of the Indo-Pacific humpback (Sousa chinensis, plumbea type) and Indo-Pacific bottlenose dolphins (Tursiops aduncus), which are both confirmed to range as far west as False Bay (Jefferson & Karczmarski, 2001; Hammond et al., 2008). Individual ranging behaviour for both species however is not well resolved. Recent genetic analyses suggest that animals currently considered as plumbea type Sousa chinensis (Reeves et al., 2008) may be a separate species, Sousa plumbea (Mendez et al., 2013). In South African waters less than 1000 adult humpback dolphins (Sousa chinensis, plumbea type hereafter “humpback dolphin”) may comprise the entire population (Karczmarski, 1996), while all estimates suggest the bottlenose dolphin (Tursiops aduncus, hereafter “bottlenose dolphins”) population is relatively large, numbering thousands of animals (Cockcroft et al., 1992; Reisinger & Karczmarski, 2010). Both dolphin species are exposed to variable levels of anthropogenic impacts throughout their range including vessel traffic, chemical pollution and habitat degradation associated with coastal development. This thesis describes the results of a study investigating: 1) the environmental and anthropogenic factors which influence the habitat use of humpback and bottlenose dolphins in two adjacent bays on the southern Cape coast, South Africa – Mossel Bay and Vlees Bay; 2) the abundance of humpback dolphins using Mossel Bay and 3) the interaction of these two dolphin species with white sharks, and the influence this has on dolphin group sizes and habitat use in Mossel Bay. Both land-based and boat-based survey platforms were used in this study with land-based data collected during dedicated watch periods at sites in Mossel Bay (n = 6) and Vlees Bay (n = 4) between February 2011 and March 2013, with a focus on humpback and bottlenose dolphins. A surveyor’s theodolite was used at these sites to collect positional data on animals, while behavioural data were collected through direct observation. Boat-based photographic identification surveys were used to collect data on the presence of individual humpback dolphins in Mossel Bay between April 2011 and November 2013. White shark data from Mossel Bay between February 2011 and March 2013 were provided from boat-based chumming surveys for the collection of photo-ID data from the Master’s thesis of Rabi’a Ryklief, based at Oceans Research. Data were analysed using ANOVA’s, Tukey honest significance tests and generalised additive modelling (Wood, 2006) in programme R, while capture histories of humpback dolphins were analysed with RMark (Laake, 2013) using POPAN open population models (Schwarz & Arnason, 1996) and Huggins heterogeneity closed capture models (Huggins, 1989; Chao et al., 1992). Humpback dolphins socialised over sandy beach habitats in both bays, while feeding/foraging occurred over reef systems in Mossel Bay and off fine grained sandy beach habitats in Vlees Bay. Humpback dolphin resting behaviour was observed at a very low frequency and occurred in all of the primary habitat types in Mossel Bay, while in Vlees Bay resting was only observed over reefs. Bottlenose dolphins in both bays preferentially used wave cut rocky platform habitats for feeding/foraging and resting while socialising occurred in the vicinity of estuaries in Mossel Bay and fine grained sandy beach habitats in Vlees Bay. Higher sighting rates were recorded in the control site, Vlees Bay, than in Mossel Bay for both dolphin species. The largest reverse osmosis desalination plant commenced operations in the sheltered corner of Mossel Bay in October 2011 and discharged approximately five million litres (Ml) of effluent per day (between October 2011 and February 2012) and 18 Ml per day in March and April 2012. In Mossel Bay higher sighting rates of humpback dolphins occurred in the period before desalination began while bottlenose dolphin sighting rates were highest after active desalination decreased to once per month (May, 2012). During the period of peak brine discharge in Mossel Bay, sighting rates were highest for both species in Vlees Bay. Even after desalination operations decreased the sighting rate of humpback dolphins remained low. The operation of the desalination plant at full capacity in Mossel Bay may have led to reduced use of this area by both humpback and bottlenose dolphins. Key habitats in Mossel Bay for both dolphin species are shared with great white sharks (Carcharodon carcharias hereafter “white sharks”) and focus around the three estuaries and their associated near-shore reef systems. The presence of predatory white sharks may limit the time dolphins spend in a specific habitat and influence the number of animals within groups, with larger humpback dolphin groups at sites with high shark utilisation. Both dolphin species had lower individual sighting rates during periods when white shark abundance peaked. Large group sizes of humpback dolphins at Seal Island, and of bottlenose dolphins at Hartenbos and Tergniet, combined with increased rates of travelling and decreased resting and socializing suggest that these areas may pose the largest threat to dolphins due to the variety of shark size classes’ present, especially larger sharks. Closed capture models generated within year population estimates ranging from 48 to 97 individual humpback dolphins (2011: 97, 95% CI: 46 – 205; 2012: 48, 28 – 81; 2013: 68, 35 – 131) while open population modelling produced a ‘super-population’ estimate of 116 animals (95% CI: 54 – 247) using Mossel Bay. During the study 67 humpback dolphins were individually identified with 94.3 % of the individuals in good quality photographs distinctively marked. Fewer humpback dolphins may be present on the south-east and southern Cape coast, including between Algoa Bay and Mossel Bay, than initially thought (Karczmarski, 1996), as definite links exist between Algoa Bay and Plettenberg Bay (Smith-Goodwin, 1997), and Plettenberg Bay and Mossel Bay (this study). The Gouritz River mouth (21º 53' E; Ross, 1984) and De Hoop (20º 30' E; Findlay et al., 1992) were previous suggested as the western limit of this species, but within the last 20 years knowledge on the extent of their range has been greatly improved, and range extension of this species may be occurring to the west with animals present as far west as False Bay (18º 48' E; Jefferson & Karczmarski, 2001). Due to the vulnerability of this species and their wide ranging behaviour, conservation plans need to be implemented on a wide scale to ensure protection of these animals from human impacts throughout their range. A concerted effort is required to further establish the population links between the various locations on the southern Cape coast that these animals frequent. / Dissertation (MSc)--University of Pretoria, 2014. / Zoology and Entomology / MSc / Unrestricted