Plettenberg Bay Research Articles

Coastal shipping and the early development of the Southern Cape

The economic development of the region east of the Hottentots-Holland Mountains (at that time the districts of Graaff-Reinet and Swellendam) could not be explored at first, because of the lack of local markets and the distance to Cape Town. To solve the problem the Dutch East India Company established harbour facilities at Mossel Bay in 1786 and two years later at Plettenberg Bay. This, however, did little if anything for the economic development of the southern Cape, mainly because residents were indifferent and not prepared to shoulder the costs involved in coastal shipping. After 1795 a few individuals, in partnership with the British authorities, took the initiative in promoting coastal shipping between Cape Town and the east coast, thereby linking the inhabitants and resources of that region to the Cape market. This reduced transport costs considerably, while also increasing the margins of profit.

Co-creation and internal place branding: a case study of Plettenberg Bay, South Africa

Co-creation is a common term used in place branding to describe the involvement of stakeholders in the creation of a place’s brand. The motivation behind co-creation is that it will add depth and legitimacy to the brand. Through a process of co-creation, it is also hoped that stakeholders will become active ambassadors of the brand and its values. Co-creation, however, is far from simple in practice—places are complicated, budgets are often small and competing interests are many. This paper examines the processes of co-creation that were initiated by Plett Tourism, a tourism office in a South African seaside town called Plettenberg Bay. By considering this case study, and case studies from other places, it is hoped that a broader conception of co-creation can be understood, one that goes beyond the early stages of involving stakeholders in the creation of a place brand and instead creating a platform for continuous engagement with stakeholders. Part of this engagement is sometimes called internal place branding, and so the ways in which internal place branding intersects with co-creation will discussed in this paper too.

Exploring South African Pacific oyster mariculture potential through combined Earth observation and bioenergetics modelling

The combined use of satellite-derived environmental data and a dynamic energy budget (DEB) model to determine Pacific oyster growth potential was adapted for the South African marine environment. Study areas consisted of the West Coast (high-chlorophyll, low temperature) and the South Coast (variable chlorophyll, higher temperature) ecoregions. Chlorophyll-a and sea surface temperature products from the Moderate Resolution Imaging Spectroradiometer (MODIS) were used to simulate yearly growth for 18 years. Average growth performance at the end of the culture period was mapped and compared for prominent sectors. Industry-relevant growth indicators, “days to reach commercial weight” and “optimal culture period length” were also established.High growth potential was found in eastern nearshore sectors of the South Coast, particularly Plettenberg Bay, where oysters reached a median total weight (TW) of 271 g within 9 months. Other sectors in the region yielded Large commercial size within 150 days. However, South Coast growth hotspots were found to be highly variable, with transient unfavourable growth conditions leading to low flesh mass relative to TW. Growth potential was favourable in northern sectors of the West Coast, where oysters reached a median TW of up to 148 g in 9 months, Large commercial size within 200 days, and contained high flesh mass relative to TW.Current oyster production sites were not found to be optimal for growth. Higher-growth sites coincide with areas in economic decline or with high levels of poverty. However, due to constraints of applying DEB models over large spatial scales, these results are considered preliminary and await in situ verification, as well as a spatial multi-criteria analysis, before investment and development.

Sedimentology of a coastal shelf sector characterised by multiple bedload boundaries: Plettenberg Bay, inner Agulhas Bank, South Africa

The study deals with a large sand body (spit-bar) attached to the eastern tip of the Robberg Peninsula, Plettenberg Bay, South Africa. To date, the bar has prograded about 8 km beyond the tip of the peninsula. The bar top is predominantly composed of medium sand, the upper slope of fine sand, and the lower slope of fine muddy sand. Stratigraphically, the sedimentology thus documents an upward coarsening, calcareous quartz-arenitic depositional sequence. The spit-bar as a whole forms the eastern end of a sediment compartment that is clearly distinguishable from neighbouring compartments on the basis of its geomorphology, the textural characteristics of the sediment, and the distribution of sediment thicknesses. Aeolian overpass across the peninsula appears to have formed a fan-like sand deposit in its rear, which is perched upon the upper shoreface of the bay as suggested by the bathymetry to the north of the peninsula. It forms an integral part of the sediment body defining the spit-bar. The estimated volume of sand stored in the spit-bar amounts to 5.815 km3, of which 0.22 km3 is contributed by the aeolian overpass sand. The sediment sources of the spit-bar are located up to 100 km to the west, where a number of small rivers supply limited amounts of sediment to the sea and numerous coastal aeolianite ridges in the Wilderness embayment have been subject to erosion after becoming drowned in the course of the postglacial sea-level rise since about 12 ky BP. By contrast, the sediment volume in the adjacent compartment B to the north (Plettenberg Bay), which has been supplied by local rivers, amounts to only 0.127 km3. In a geological context, large sand bodies such as the Robberg spit-bar are excellent exploration models for hydrocarbons (oil and gas).

Pleistocene and Holocene procurement of the clam Donax serra (Bivalvia: Donacidae) along the southern Cape coast of south Africa

Humans began to exploit aquatic resources routinely since the late Middle Pleistocene (c. 162 ka), as evidenced by PP13B Cave in the southern Cape of South Africa. Hard bottom or rocky shore species were among the first to be collected, and although they dominate Pleistocene and Holocene archaeomalacological assemblages locally, the soft-bottom Donax serra clam began to be collected systematically near PP13B by 110 ka. Since then, D. serra appears intermittently in early and Holocene middens. Earlier studies on PP13B D. serra assemblages dated to 110–91 ka concluded that initial collection of D. serra ~ 110 ka was unselective in terms of shell size and was undertaken along the entire tidal gradient. In later visits ~ 91 ka, foragers narrowed their collection to the mid-intertidal where most larger clams live, thus increasing the efficiency of D. serra procurement. In this paper, further metrical data from other Pleistocene and late Holocene assemblages is presented in order to test these conclusions. Pleistocene data from mainly the Klasies River main site also reflect small sizes as in contemporary levels from PP13B; however, it is not possible to generalise that the increase in foraging efficiency observed in PP13B also applies to post 90 ka contexts overall due to a lack of Pleistocene samples dating to this latter period. However, it is clear that foraging efficiency was comparatively higher in the Plettenberg Bay and Mossel Bay areas since the early Holocene. Variability among Holocene D. serra assemblages appear to be explained also in terms of foraging ranges. Settlement patterns, group size and/or its composition may be factors behind the generally intermittent presence of D. serra in the southern Cape middens.

Benthic Foraminifera of the Agulhas Bank coastal shelf in the vicinity of Plettenberg Bay, South Africa: a reconnaissance survey

The study area is located on the inner Agulhas Bank around Plettenberg Bay, southern Cape Province, South Africa (Fig. 1). The Agulhas Bank is a transitional environment between the cold-temperate Benguela Current regime of the south-eastern South Atlantic and the warm-temperate Agulhas Current regime of the south-western Indian Ocean. Three distinct faunal assemblages (A, B and C) were identified in the study area. These are aligned in three consecutive, coast-parallel belts, assemblage A forming the inshore belt, assemblage C the offshore belt and assemblage B the in-between belt. Assemblage A is composed of Textularia-group individuals and Pararotalia sp., Cibicides lobatulus and Planorbulina mediterranensis. It occupies the nearshore belt up to 50 m water depth in sediments composed of very fine, fine and medium sands, with some coarse and very coarse sands. Assemblage B is composed of Bolivina cf. pseudopunctata, Cassidulina laevigata, Ammonia beccarii, Bolivina tortuosa and Bulimina elongata. It occupies water depths from 50–70 m, but may locally extend down to 90 m and, within the bay itself, upward to 20 m in fine and very fine sands containing some medium sand and mud. Assemblage C is dominated by Cassidulina laevigata, Bolivina cf. pseudopunctata, Bulimina elongata and Ammonia beccarii. In contrast to assemblage B which is dominated by B. cf. pseudopunctata, assemblage C is dominated by C. laevigata. Assemblage C is mainly confined to water depths of 70–100 m in sediments dominated by very fine sand (0.063–0.125 mm) containing some coarser sediment and mud. The distribution of the forams with respect to water depth, sediment composition and other environmental parameters suggests that it is mainly controlled by a combination of environmental parameters. No tangible relationship was found between the open shelf foraminifer communities and those of estuaries and lagoons along the South African coast.

Abundance of Indo-Pacific bottlenose dolphins (Tursiops aduncus) along the south coast of South Africa.

Coastally distributed dolphin species are vulnerable to a variety of anthropogenic pressures, yet a lack of abundance data often prevents data-driven conservation management strategies from being implemented. We investigated the abundance of Indo-Pacific bottlenose dolphins (Tursiops aduncus) along the south coast of South Africa, from the Goukamma Marine Protected Area (MPA) to the Tsitsikamma MPA, between 2014 and 2016. During this period, 662.3h of boat-based photo-identification survey effort was carried out during 189 surveys. The sighting histories of 817 identified individuals were used to estimate abundance using capture-recapture modelling. Using open population (POPAN) models, we estimated that 2,155 individuals (95% CI: 1,873–2,479) occurred in the study area, although many individuals appeared to be transients. We recorded smaller group sizes and an apparent decline in abundance in a subset of the study area (Plettenberg Bay) compared to estimates obtained in 2002–2003 at this location. We recorded declines of more than 70% in both abundance and group size for a subset of the study area (Plettenberg Bay), in relation to estimates obtained in 2002–2003 at this location. We discuss plausible hypotheses for causes of the declines, including anthropogenic pressure, ecosystem change, and methodological inconsistencies. Our study highlights the importance of assessing trends in abundance at other locations to inform data-driven conservation management strategies of T. aduncus in South Africa.

All washed up: spatial and temporal variation in the wash-up and fate of chondrichthyan egg cases along a section of the Garden Route, South Africa

Washed-up chondrichthyan egg cases were collected along three different sandy beaches around Plettenberg Bay, South Africa, between April 2016 and March 2017. GPS location was recorded upon collection, and, after being soaked in fresh water for 12 hours, egg cases were identified to species level. Additionally, boreholes, damage, biofouling and state of the hatchling slit were recorded. The hatching success of each egg case was inferred from these factors. Over the year, 6 996 egg cases of nine species were collected. Egg cases of the tiger catshark Halaelurus natalensis had the highest hatching rate at 70%. Egg cases of the leopard catshark Poroderma pantherinum had the highest predation rate at 57%. Season had no significant effect either on overall egg-case counts or on per-species counts. Location, however, significantly affected the overall egg-case counts, as well as per-species counts, with the exceptions of H. natalensis and the St Joseph Callorhinchus capensis. The results of this study provide insight into chondrichthyan species occurrence and spatial variation along a section of the Garden Route in the Western Cape Province and can act as a baseline for future research.

Seismic stratigraphy of the inner to mid Agulhas bank, South Africa

The inner to mid continental shelf of the Agulhas Bank, which forms part of the Palaeo-Agulhas Plain, is scattered with Pleistocene deposits. Their wide lateral extension is the expression of a flat underlying substrate, availability of accommodation space, and depositional processes in response to glacio-eustatic sea-level change. We present seismic sub-bottom profiles up to 30 m deep, sediment cores up to 5 m in length and Pleistocene deposits that date back to Marine Isotope Stage (MIS) 7 from the inner to mid shelf between the Breede River in the West and Plettenberg Bay in the East. Radiocarbon and optically stimulated luminescence dates are integrated with microfossil analysis into a seismic stratigraphic model comprised of twenty Quaternary facies units within two depositional sequences bounded by shelf-wide unconformities. Sequence Boundary 1 (SB1) corresponds to the erosional unconformity with bedrock and SB2 to the MIS 2 glacial lowstand. Incised palaeo-river channels are associated with both sequence boundaries and cored deposits also mapped seismically from estuarine, lacustrine and fluvial systems are grouped to represent the lower floodplain. The most pervasive stratigraphic pattern in these shelf deposits is made up of the depositional sequence remnant of the Falling Stage Systems Tract (FSST) forced regression from MIS 5e–2. The other dominant stratigraphic group is the Transgressive Systems Tract (TST) associated with the Post-glacial Marine Transgression. The TST makes up an almost equal proportion of deposits in both sequences in the sedimentological record as the FSST, despite the shorter temporal span of the TST. A Wave Ravinement Surface marks the rise in sea level from the Last Glacial Maximum in a landward direction.

Identification of potential signature whistles from free-ranging common dolphins (Delphinus delphis) in South Africa

Conveying identity is important for social animals to maintain individually based relationships. Communication of identity information relies on both signal encoding and perception. Several delphinid species use individually distinctive signature whistles to transmit identity information, best described for the common bottlenose dolphin (Tursiops truncatus). In this study, we investigate signature whistle use in wild common dolphins (Delphinus delphis). Acoustic recordings were analysed from 11 encounters from three locations in South Africa (Hout Bay, False Bay, and Plettenberg Bay) during 2009, 2016 and 2017. The frequency contours of whistles were visually categorised, with 29 signature whistle types (SWTs) identified through contour categorisation and a bout analysis approach developed specifically to identify signature whistles in bottlenose dolphins (SIGID). Categorisation verification was conducted using an unsupervised neural network (ARTwarp) at both a 91% and 96% vigilance parameter. For this, individual SWTs were analysed type by type and then in a 'global' analysis whereby all 497 whistle contours were categorised simultaneously. Overall the analysis demonstrated high stereotypy in the structure and temporal production of whistles, consistent with signature whistle use. We suggest that individual identity information may be encoded in these whistle contours. However, the large group sizes and high degree of vocal activity characteristic of this dolphin species generate a cluttered acoustic environment with high potential for masking from conspecific vocalisations. Therefore, further investigation into the mechanisms of identity perception in such acoustically cluttered environments is required to demonstrate the function of these stereotyped whistle types in common dolphins.

Distribution and habitat use of Indo-Pacific bottlenose dolphins Tursiops aduncus along the south coast of South Africa

The distribution and habitat use of the Indo-Pacific bottlenose dolphin Tursiops aduncus along the south coast of South Africa was investigated using bi-monthly boat-based surveys, from 2013 to 2016, over a distance of 145 km between the Goukamma and Tsitsikamma marine protected areas (MPAs). Survey effort totalled 6 239 km and 750.6 hours. Encounters occurred throughout the area (n = 200) and more frequently during winter. Pod sizes ranged from 1 to 350 animals (mean = 45), with calves mostly associated with larger groups. During 70% of the encounters, at least a single calf was present (up to 80 calves; mean = 5) and calves were more prevalent during summer. Encounters occurred mostly in shallower (mean = 11.3 m) and warmer (mean = 17.4 °C) waters. Groups aggregated in larger sizes in colder waters. Most encounters were in Plettenberg Bay and the Goukamma MPA, both of which are characterised by sandy bottoms and sheltered areas. Encounter rates were lowest in rocky and exposed areas, but dolphin groups in such locations were larger and usually travelling. There was a relatively low association of T. aduncus groups with MPAs, except for a sandy area in the Goukamma MPA in particular, suggesting some mismatch between favourable T. aduncus habitat and habitat protection.

A novel photodegradation approach for the efficient removal of natural organic matter (NOM) from water

The presence of natural organic matter (NOM) in water can negatively affect water quality if NOM is present in excessive amounts during certain stages of water treatment. It is known that NOM constituents serve as precursors for DBPs (disinfection by-products) during the disinfection step of the water treatment process. Removal of natural organic matter (NOM) before disinfection is therefore essential to control DBP formation; however, owing to the heterogeneity and complexity of NOM, most water treatment processes are unable to attain complete removal of NOM from water sources. There is therefore a great need to develop methods that can effectively degrade NOM into smaller and relatively harmless compounds that are easily removed during water treatment processes. In this study, multi-walled carbon nanotubes/nitrogen, palladium co-doped titanium dioxide (MWCNT/N, Pd co-doped TiO2) (0.5–5% MWCNTs) were fabricated for the enhancement of NOM degradation under visible-light illumination. Different MWCNT/N, Pd co-doped TiO2 (also referred to as CT) nanocomposites were synthesised via a modified sol-gel method and characterised using ultraviolet visible (UV-Vis), X-ray diffraction spectroscopy (XRD), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), Fourier transform infrared (FTIR) Spectroscopy and energy-dispersive X-ray spectroscopy (EDS) analysis. The UV-Vis results showed that introducing the MWCNTs on the nanocomposites was accompanied by a red shift, with CT (0.5% MWCNTs) occurring at a longer wavelength than the others. The efficiency and effectiveness of the synthesised nanocomposites was quantified through measuring the NOM degradation rate in raw water samples collected from two South African water treatment plants. These two drinking water treatment plants were selected as the raw water treated in these plants contains different NOM fractions: the raw water treated at Midvaal (MV) Water Company contains transphilic NOM fractions, while that treated at Plettenberg Bay (P) Water Treatment Plant contains high amounts of hydrophobic NOM. The changes in the amount of NOM in a sample were monitored by measuring the UV absorbance at 254 nm (UVA254) as there is a strong correlation between absorbance at this wavelength and the aromatic content. The highest photocatalytic activity was observed with CT (0.5% MWCNTs) which attained 69.4% UVA254 reduction for MV and 97.7% UVA254 reduction for P raw waters. Compared to conventional methods applied by the two water treatment plants of interest, NOM removal efficiency (in terms of UVA254 reduction) by CT (0.5% MWCNTs) increased by up to 9.4% and 11.5% for MV and P water treatment plants, respectively. The enhanced photocatalytic activity of this CT nanocomposite (0.5% MWCNTs) is attributable to the large surface area of the synthesised nanocomposites which allows huge amounts of NOM to be adsorbed onto the surface of the TiO2, thereby increasing their photodegradation. It is also due to the synergistic effect of N and Pd which enhanced the photoactivity of the TiO2 in the MWCNT/N, Pd co-doped TiO2 composite. Overall, it is clear that the use of the conventional processes is not effective in removing NOM from water. Findings obtained show that CT (0.5% MWCNTs) nanocomposite is a promising future NOM removal method that could complement the available water treatment processes in enhancing the removal of the aromatic component of NOM in water.

Draft Genome Sequence of Gordonia lacunae BS2T.

ABSTRACTWe report here the draft genome sequence of the soil bacterium Gordonia lacunae BS2T (= DSM 45085T = JCM 14873T = NRRL B-24551T), isolated from an estuary in Plettenberg Bay, South Africa. Analysis of the draft genome revealed that more than 40% of the secondary metabolite biosynthetic genes encode new compounds.

Keurbooms Estuary floods and sedimentation

The Keurbooms Estuary at Plettenberg Bay lies on a wave-dominated, microtidal coast. It has a dune-topped sandy barrier, or barrier dune, almost 4 km long, with a narrow back-barrier lagoon connected to its source rivers, the Keurbooms and Bitou. The estuary exits to the sea through this barrier dune, and it is the geomorphology and mouth position in relation to floods, which is the subject of this paper. Measurements of rainfall, water level, waves and high- and low-tide water lines were used to analyse the mouth variability over the years 2006–2012. Two major floods occurred during this time, with the first in November 2007 eroding away more than 500 000 m3 of sediment. The new mouth was established at the Lookout Rocks limit – the first time since 1915. The second flood occurred in July 2012 and opened up a new mouth about 1 km to the north-east; high waves also affected the position of the breach. The mouth has a tendency to migrate southwards against the longshore drift, but at any stage this movement can be augmented or reversed. The effectiveness of floods in breaching a new mouth through the barrier dune depends on the flood size and the nature of the exit channel in the back-barrier lagoon. Other factors such as ocean waves, sea level, vegetative state of the dune and duration of the flood are also important and can determine where the breach occurs, and if the new mouth will dominate the old mouth.

Abundance and degree of residency of humpback dolphins Sousa plumbea in Mossel Bay, South Africa

Indian Ocean humpback dolphins Sousa plumbea inhabit nearshore waters from South Africa to eastern India. Humpback dolphins are vulnerable to conservation threats due to their naturally small population sizes and use of nearshore habitats, where human activities are highest. We investigated the abundance and residency of this species inhabiting Mossel Bay, South Africa, using photographic mark-recapture. Data were collected during 81 surveys in Mossel Bay between 2011 and 2013. Open population modelling using the POPAN parameterisation produced a ‘super-population’ estimate of 125 individuals (95% CI: 61–260) and within-year estimates of between 33 and 86 individuals (2011: 71 [95% CI: 30–168]; 2012: 33 [15–73], 32 [15–70]; 2013: 46 [20–108]). Although less appropriate, closed capture models were also run for comparison with previous studies in the region and generated similar, but slightly smaller, population estimates within each year. We compared our catalogue with opportunistic data collected from East London, Plettenberg Bay, De Hoop and Gansbaai. The only catalogue matches attained were between Plettenberg Bay (n = 44 identified) and Mossel Bay (n = 67 identified), separated by 140 km. Population exchange was moderate, with nine individuals resighted in multiple years between these two areas. This study supports previous findings of long-range movements for this species and provides a baseline from which to assess future impacts on the population.

On some sea cucumbers (Echinodermata: Holothuroidea) from off the south and west coasts of South Africa collected by the South African Environmental and Observation Network (SAEON).

Twenty four specimens of holothuroids recently received from the South African Environmental and Observation Network (SAEON), collected from off the south and west coasts of South Africa, are herein recorded and/or described. The specimens comprise eight nominal and one indeterminate species and represent both shallow-water and deep-sea forms, distributed from Plettenberg Bay to just north of Lambert's Bay in the Western Cape Province. There are no new species but two new records for the South African region and extensions of horizontal and bathymetric distributions of the other species. Additions to the South African fauna are Zygothuria lactea (Théel, 1886) and Synallactes cf. challengeri (Théel, 1886). The paper also contains the first definite record of Thyone venusta Selenka, 1868, originally described from the Red Sea. Distribution ranges of the following species have been altered Synallactes viridilimus Cherbonnier, 1952; S. mollis Cherbonnier, 1952 and Psuedostichopus langeae Thandar, 2009.

Vagrant elephant seal predation on Cape fur seal pups, Plettenberg Bay, South Africa

Vagrant southern elephant seals (Mirounga leonina) are occasionally sighted along the coast of South Africa and are known to feed primarily on fish and squid. Phocid seals are not known to predate on mammals making the events described here exceptional. This note describes the successful and failed attempts of a vagrant male southern elephant seal (M. leonina) to consume Cape fur seal (Arctocephalus pusillus pusillus) pups in Plettenberg Bay, South Africa. Observations were made by crew and passengers aboard a commercial whale-watching vessel during November 2012. This is the first account of elephant seals eating anything other than fish, squid and penguins and suggests considerable plasticity in prey choice dictated by environmental conditions.

Whistle vocalizations of Indo-Pacific bottlenose dolphins (Tursiops aduncus) inhabiting the south-west Indian Ocean

Populations of Indo-Pacific bottlenose dolphin (Tursiops aduncus) are distributed along coastal regions of the south-west Indian Ocean (SWIO), from South Africa to Kenya. An account of whistles from wild T. aduncus inhabiting the SWIO is provided here. Recordings were made at Plettenberg Bay (South Africa) and Zanzibar Island (Tanzania) and the frequency trace of whistle contours (n = 1677) was extracted. Multiple parameters were measured from each whistle and compared between regions and encounters. Regional variation was significant in all parameters assessed except for start and middle frequency (frequency at half the duration). Whistles from Zanzibar Island ended on average 4 kHz higher than those from Plettenberg Bay, and had a steeper frequency gradient. However, mean frequencies differed by <1 kHz and population averages for the adopted frequency distribution showed similar patterns, with a peak between 5 and 7 kHz. Whistle parameters were strongly influenced by recording encounter, likely reflecting the presence of different individuals, group compositions and behavioral contexts during recording occasions. Comparisons within the genus showed that T. aduncus from the SWIO have amongst the lowest start and minimum frequency of whistles within Tursiops.

Diet of the Cape fur seal Arctocephalus pusillus pusillus at the Robberg Peninsula, Plettenberg Bay, and implications for local fisheries

Cape fur seals Arctocephalus pusillus pusillus were harvested to extirpation on the Robberg Peninsula, Plettenberg Bay, on the south-east coast of South Africa, between the 17th and early 20th centuries. Seals returned to Robberg in small numbers during the early 1990s and their numbers subsequently increased. We studied the diet of this increasing population using faecal (scat) sampling to determine: the species composition and size of prey in the diet of Cape fur seals at Robberg; to explore temporal variation in the diet; and to investigate the potential for competition between seals and the fisheries around Plettenberg Bay. Of the 445 scats collected, 90% contained hard prey remains and 15 teleost prey species were represented in the 3 127 otoliths that could be identified. The seals’ most important prey species in terms of numerical abundance, frequency of occurrence and mass in the diet, were anchovy Engraulis encrasicolus, sardine Sardinops sagax, horse mackerel Trachurus capensis, sand tongue-fish Cynoglossus capensis and shallow-water hake Merluccius capensis (in decreasing order of importance for numerical abundance). The proportion of anchovy in the diet increased during the study period (2003–2008), whereas the proportion of sardine decreased. The estimated average annual consumption of sardine by seals was higher than the average annual catch made by purse-seine fisheries in this area, suggesting resource competition between seals and purse-seiners, especially in the light of continuing growth of seal numbers in the area. However, direct competition between seals and linefisheries appeared to be minimal. Scat sampling of Cape fur seals holds potential to serve a useful and cost effective indicator of temporal changes in sardine abundance.

Seasonal fluctuations in occurrence of inshore Bryde's whales in Plettenberg Bay, South Africa, with notes on feeding and multispecies associations

Seasonal fluctuations in the occurrence of inshore South African Bryde's whales Balaenoptera edeni were investigated between November 2005 and June 2008. Sighting data were collected in Plettenberg Bay on the south-east coast of South Africa. Bryde's whale occurrence was modelled in relation to the following environmental covariates: sea surface temperature, chlorophyll a concentrations and wind speed. Seasonal increases in encounter rates (sightings per day) were observed during summer and autumn, with a peak in April that corresponded to increased feeding activity and above average aggregation sizes. All three environmental covariates were significant factors in terms of explaining variability in the occurrence of whales. Multispecies associations with common dolphins Delphinus capensis and Cape gannets Morus capensis were most common in summer and autumn, when feeding activity was highest.