Browsing by Author "Ryan, Peter"

Now showing 1 - 20 of 23
  • Thumbnail Image
    Item
    Open Access
    Assessing sea turtle, seabird and shark bycatch in artisanal, semi-industrial and industrial of fisheries in the Cabo Verde Archipelago
    (2020) Montrond, Gilson; Ryan, Peter; Jabado, Rima; Wanless, Ross
    Firstly, I am very grateful to Birdlife International for the MSc scholarship. I am also very grateful to Professor Peter Ryan of the FitzPatrick Institute of African Ornithology, University of Cape Town, for agreeing to supervise this project and for his guidance, insights and comments on the write-up. I am grateful to Sarah Saldanha, for all the support during this MSc. Many thanks also to Dr Ross Wanless, Dr Rima Jabado and Ruben Rocha for all support, guidance and advice. I want to thank a lot Andy Angel for their accommodation and all support in South Africa. I am grateful to all the UCT staff and BirdLife Senegal Staff for all the support during this study. Many thanks to my family for all the encouragement and support. I want to thank to all the Cabo Verde fishers for their willingness to share their knowledge and experience. Finally, many thanks to the Conservation Biology class of 2019, for all their support.
  • Thumbnail Image
    Item
    Open Access
    Assessing the effect of feather wear on carbon and nitrogen stable isotope ratios, and the use of stable isotopes to determine predator diets in the Namibian Islands marine protected area
    (2019) Johnson, Laurie; Ryan, Peter; Connan, Maëlle
    The stable isotope (SI) approach is widely used in ecological research to tackle problems such as delineating food web structure or tracing the migratory origins of various organisms. This thesis first tested the widely accepted assumption that SI ratios are fixed in an inert tissue, and then used the SI approach to infer the food web structure, from a marine top predator point of view, of a profoundly impacted marine ecosystem off southern Namibia. In bird research, it is assumed that SI ratios are fixed in feathers once they have completed their growth during moult. This assumption is crucial in determining where birds moult, and has been used to infer changes in the environment over time, as well as changes in the trophic levels of individuals. Recent comparisons of feathers collected from several penguin species during their annual moult have shown systematic differences between newly moulted and old feather SI ratios. I thus tested whether a change in SI ratios occurs as feathers age by comparing the carbon and nitrogen SI ratios of black and white feathers collected from captive, individually known African (Spheniscus demersus) and northern rockhopper (Eudyptes moseleyi) penguins at three occasions over a year. I found a clear trend for the rockhopper penguin feathers with new and old black feathers differing in their δ13C and δ15N values; this trend was not as clear for the African penguins. I then tested factors related to feather wear as a possible mechanism for differences in SI ratios between new and old feathers; these factors were feather reflectance and microstructure. In both penguin species, old black feathers reflected more light, and had a larger proportion of their barbs without barbules near their tips compared to new feathers. Feather wear may result in melanin leakage, which may explain the observed trends in the SI ratios between new and old pigmented penguin feathers. Differences in SI values were observed between species and may be a result of facility at which the penguins were housed, where one facility was exposed to more sunlight than the other, rather than the differences being a result of species. Although the differences observed were subtle, the state of feather wear (i.e. timing of feather collection within the moult cycle) should be considered in order to make accurate ecological inferences based on their SI ratios. Further research is needed to fully understand the phenomenon and to test whether the same process affects pigmented feathers of flying birds. I then used SI ratios to update our knowledge of resource partitioning among a marine top predator community in southern Africa, and to infer the marine food web structure in a Marine Protected Area off the southern Namibian coast. The Namibian Islands Marine Protected Area supports the most important breeding population of bank cormorants (Phalacrocorax neglectus; Endangered), and historically was important for two other Endangered seabirds: African penguins and Cape gannets (Morus capensis). Non-threatened marine top predators studied in the system were: greater crested terns (Thalasseus bergii) and Cape fur seals (Arctocephalus pusillus). In the last 50 years, shelf waters off southern Namibia have been overfished, resulting in an altered marine ecosystem; shoaling fish have been replaced by less nutrient-rich species such as hake (Merluccius spp.), jellyfish, and salps. Previous studies of the region’s food webs were based on traditional dietary analyses such as stomach content and scat analysis which provide short-term diet information. Here, I measured carbon and nitrogen SI ratios in several tissues of the marine top predators, and those of their potential prey species, to infer the marine food web for this region, and to complement short-term data obtained from traditional dietary analyses. Among the predator guild, Cape gannets had the lowest δ13C and δ15N values, indicating that they fed the farthest offshore and at the lowest trophic level both during the breeding season (from whole blood) and moulting period (from feathers). As expected, bank cormorant δ13C values indicated that they fed more benthically than the other predators, and Cape fur seals fed at the highest trophic level. African penguin tissue SI ratios were intermediate between those of Cape gannets and Cape fur seals. Greater crested terns exhibited the highest δ13C values, suggesting that they fed closest to shore. Bayesian mixing models used with species-specific discrimination factors (when available) revealed some resource partitioning among the marine top predators in this region but many made use of similar resources; sardine (Sardinops sagax), squid (Loligo reynaudii), and rock lobster (Jasus lalandii). This work highlights the most likely prey items used by marine top predators outside of the breeding period, and provides new insights into the food web of this region. Prior to the start of industrial fishing, marine top predators in this region mainly ate sardine and anchovy. Despite the collapse of these species’ populations in the 1970s, marine top predators currently still make use of these prey resources, which concurs with the results found from stomach content and scat analyses. In this thesis, I have shown experimentally that SI ratios vary slightly as feathers age in penguins. I have also used the SI technique in an ecological context to add to the knowledge on the diet of marine top predators of an overfished ecosystem. Overall I have shown how the SI approach can add to our understanding of trophic ecology, and also how the method is dependent on accurate SI inputs in order to make accurate dietary inferences.
  • Thumbnail Image
    Item
    Open Access
    Collisions & biases: estimating the impact of low-voltage distribution lines on the Ludwig's Bustard (Neotis ludwigii)
    (2012) Schutgens, Maurice; Ryan, Peter
    Bird collision mortality associated with power lines is a global conservation challenge. The Ludwig's Bustard (Neotis ludwigii) population is probably declining throughout its range as a result of collisions with power lines. Collision estimates derived from periodic carcass counts along power lines are likely to be underestimates because of two main bias factors: scavenger and search bias. In this study 44 Egyptian geese (Alopochen aegyptiacus) and Spurwing geese (Plectropterus gambensis) were used as surrogates to explore the levels of the bias by conducting a scavenger trial (90-day period) and three search trials (conducted after 24 hours, 48 and 90 days). Scavengers had detected 88% and removed 11 % of carcasses after the first week, and only 14% of carcasses were removed by the end of the 90-day trial period. On average, observers located 70% of carcasses across the three trials with no clear pattern in detection rate over time. Scavenger bias and search bias for this site in the Karoo were calculated at 0.14 and 0.30 respectively. Five low-voltage distribution power line transects (approximately 99 km) were surveyed in the Namakwa District, South Africa, to calculate a crude collision rate for Ludwig's Bustard. A total of 22 Ludwig's Bustard carcasses were located and used to estimate an unadjusted collision rate of 0.27 km-1. / (95% Cl 0.03-0.29 km-1. /). This collision rate extrapolated across the 63,000 km of distribution lines crossing the bustard's range represents an annual mortality of 13,000 individuals. The bias adjusted collision rate estimate increased to 0.45 km-1 ./ (95% CI 0.04-0.48 km-1 f 1 ), which suggests 22,000 individuals are killed annually. The combined mortality of low-voltage and high voltage lines could be in the order of 32 000 individuals annually. Implementation of existing mitigation devices and research into additional measures are necessary to prevent further decreases of this endangered species.
  • No Thumbnail Available
    Item
    Open Access
    Conservation in a changing world: assessing the conservation status of an agriculturally adapted species, the blue crane
    (2024) Craig, Christie Anne; Ryan, Peter
    With rapid human development and global change, conservation scientists need to stay abreast of changes to threatened species' demographics. The Blue Crane Anthropoides paradiseus has adapted to land-use change in some parts of its range. By the 1980s, numbers of cranes in their natural core range in the eastern grasslands and Karoo of South Africa had declined dramatically due to agricultural development and poisoning, leading to the species being listed as Vulnerable. These impacts were partly offset by the species colonising a novel ecosystem, the Western Cape wheatlands. Currently approximately half of all Blue Cranes are found in these wheatlands. However, there are concerns that the Western Cape population may be decreasing, given the many threats in intensive agricultural landscapes. This thesis assesses the conservation status of the Blue Crane, with particular focus on the Western Cape wheatlands. In Chapter 1 I frame the topic, review the literature, and describe the study areas. In Chapter 2, I use aerial survey data to estimate the Blue Crane population at 51000 (range 34000–68000) cranes, which is double the last conservative estimate in 2002. To assess population trends for Blue Crane over the last 30 years, I analyse two citizen science datasets: Southern African Bird Atlas Projects (SABAP) and Coordinated Avifaunal Road-counts (CAR). These datasets indicate that Blue Crane numbers have increased over the long term but CAR data show that the population trend changed from positive to negative in 2010. Since 2011, summer crane counts have declined by 19% (95% CI –31% to –5.2%), driven primarily by numbers in the Overberg (southern Cape wheatlands) declining by 22% from 2011–2019 (–37% to –1.9%). In Chapter 3 I focus on one of the key threats to Blue Cranes, collision with powerlines. For two years I conducted quarterly surveys for dead birds along powerlines in the Karoo, and annual surveys in two areas in the Western Cape wheatlands (Overberg and Swartland), where agricultural activity prevented quarterly surveys. The Blue Crane was the most frequently recorded species in all three regions, with collision rates of 0.18 (95% CI 0.13–0.24) cranes/km/year in the Karoo, 0.08 (0.02–0.17) in the Swartland and 0.05 (0.02– 0.08) in the Overberg. Estimates of scavenger, observer and crippling bias indicate that we may underestimate collision rate by factors of 6, 7 and 8 times respectively. I developed the first predictive model based on rigorous survey data to identify key collision risk factors for Blue Cranes. Using a binomial Generalized Linear Mixed Model, I found proximity to seasonal water to be the strongest predictor of Blue Crane collision on powerlines; collision probability reduced to nearly zero for powerlines > 2.5 km from a seasonal water body. This finding could guide placement of new powerlines, and to guide marking of existing powerlines close to water bodies. 7 In Chapter 4, I explore Blue Crane movements and survival from GPS-GSM and Iridium satellite trackers fitted between 2016 and 2021, on 31 adults, 3 juveniles and 25 Blue Crane fledglings. Using autocorrelated kernel density home range analysis, I demonstrate that Western Cape Blue Crane home ranges were on average 1655 km2 (SD 2757). Mean daily distance travelled did not differ between regions, Swartland: 9.5 km (SD 11.7), Overberg: 7.5 km (SD 9.8), but non-breeding cranes moved significantly farther per day, 9.5 km (SD 13.3) than breeding cranes, 5.8 km (SD 5.4). As a result, non-breeding cranes intersect powerlines twice as often as breeding cranes. This may contribute to the lower immature survival rate than adult Blue Cranes. Using a Known Fate Mark Recapture Model, I estimate survival for non-breeding birds to be 0.85 (95% CI 0.61–0.95, n = 13), and 0.95 (0.71–0.99, n = 12) for breeding birds. In Chapter 5, I summarise my findings and use these insights to assess the Blue Crane on the IUCN Red List and the Green Status of Species. In the Red List assessment, I draw from a population viability analysis and the CAR data in Chapter 2 and project that the Blue Crane population (currently 21860 mature individuals) will decline by 53% (95% CI –19% to –72%) over three generations, narrowly meeting the criteria for Endangered. However, with the lower end of uncertainty indicating that a Near Threatened listing is appropriate, I recommend that Blue Crane be listed as Vulnerable. I conclude that the Western Cape wheatlands may pose an ecological trap for the species, and that declines are likely being driven by poor breeding productivity and recruitment (Appendix 1). Drawing from the literature, and interviews with farmers (Appendix 2), I contextualise Blue Crane conservation in this landscape and make recommendations for the conservation of this flagship species. This study highlights some of the risks in land-sharing conservation approaches, and the challenges of conservation in man-made ecosystems. In this context, it is important for conservation science to be interdisciplinary and crosscutting in its approach.
  • No Thumbnail Available
    Item
    Open Access
    Determining key catchments for litter trap installation in urban rivers using a GIS-based approach
    (2023) Gonlag, Shaidan; Ryan, Peter
    Litter generated in urban centres has fast become a major problem across the world and poses risks to economic, human and environmental health. It is estimated that around 2.0 billion tonnes of solid waste are produced per year. Rivers and stormwater drainage systems are the primary mechanism through which urban litter is transported into the ocean. In South Africa, widespread littering coupled with poor waste management in many communities results in large amounts of litter entering river systems. South Africa has an extremely diverse socio- economic landscape that results in many challenges, both socio-economically and environmentally. Strategies around waste management must be well-informed, locally applicable and data driven if they are to make a significant impact on reducing urban litter loads. Currently, there are few data on the input and magnitude of urban litter entering into river systems. Measurements of daily litter accumulation rates along urban streets in low, medium and high-income suburbs in Cape Town were modelled using a GIS approach to estimate the amount of plastic litter produced across the different hydrological catchments. There was an inverse relationship between income level and daily street litter generation rate in residential areas. The low-income site generated an order of magnitude more litter daily than the high–income site, with the mid-income site having an intermediate value. The model predicted that on average 26.0 (15.3–36.6) tonnes∙day–1 of litter is produced in Cape Town with 56% of this litter being loaded into three major river networks; Salt/Black, Eerste and Diep Rivers. Distribution of current litter traps in the city was poorly correlated (R2 = 0.28) to the catchments receiving the largest plastic litter weight daily. The findings from this study will help better inform the City of Cape Town management with regards to focusing their urban litter mitigation efforts. The approach used could be readily applied in other urban areas to determine weights of urban litter loads and identify key areas for litter trap interventions. Key words: GIS, Plastic, Catchment delineation, Street litter, Litter traps
  • No Thumbnail Available
    Item
    Open Access
    Disentangling entanglement in Cape fur seals for better management of plastic pollution impacts
    (2023) Winroth, Forsberg Sara Trine; Ryan, Peter
    Marine litter is a widespread issue threatening marine biodiversity and coastal economies. Entanglements and ingestion are among the most common impacts of marine litter on wildlife. While most marine litter is assumed to come from land-based sources, marine items such as fishing gear tend to be responsible for most entanglement incidents. Entanglement is a frequent threat to pinniped species leading to suffering and potential death of affected individuals. I use a long-term dataset to investigate temporal trends in entanglement rates as well as to describe the most common material, type and probable source of entanglements of Cape fur seals (Arctocephalus pusillus pusillus) in the Victoria and Alfred (V&A) Waterfront and broader Cape Town harbour area. Between 1986-2018, 5843 entanglements (annual mean and standard deviation: 177±166) were recorded through systematic surveys, of which 5530 contained descriptive data relating to entanglement type. From 1994-2018 the number of seals checked, as well as the number of entangled seals were recorded. The mean entanglement rate, calculated as the total number of entanglements observed divided by the total number of seals checked, was 8% (range per year: 3–17%, n= 4488 entangled seals). This is the highest entanglement rate reported for a pinniped, albeit in a highly modified environment. Entanglement rates increased from 2007-2009, with a peak in 2009, and decreased to below 1990s levels in 2016. Significantly more seals were entangled in winter (rainy season) than in summer. Most entanglement items were made of plastic, with fishing line, rope and packing straps most commonly observed. The proportion of packing straps and rope decreased slightly in recent years, whereas the proportion of fishing line was relatively constant. Items associated with fishing and/or shipping activities accounted for 67% of entanglement cases, with fishing gear alone responsible for 33%. Offshore activities as well as the harbour itself were probable sources of most entanglement items, although a large storm drain that enters the harbour from central Cape Town probably also contributes to the problem. Key management interventions include education programmes targeting harbour employees and fishermen about the adverse impacts of marine litter, and implementing guidelines on appropriate waste disposal in the harbour. Putting up signage where seals commonly haul out highlighting the entanglement problem may also improve waste disposal habits. The V&A Waterfront is one of South Africa's leading tourist destinations and provides an opportunity to reach a large audience about the negative impacts of littering.
  • Thumbnail Image
    Item
    Open Access
    The ecology, genetics and conservation of a translocated population of Cnemidophorus Vanzoi (Teiidae) on Praslin Island, St. Lucia
    (2000) Dickinson, Hannah Christiana; Ryan, Peter; Fa, John; Durrel,
    This study investigates the colonisation of Praslin Island by C. vanzoi, three years after the translocation event. An examination of habitat use, lizard abundance, distribution and population genetics was conducted and population comparisons investigated changes in morphometrics or lizard condition since translocation. These investigations were cunducted during the wet season and the dry season. This information will help determine the value of translocation as a tool for the conservation of this species.
  • Thumbnail Image
    Item
    Open Access
    Exploring South Africa’s southern frontier: A 20-year vision for polar research through the South African National Antarctic Programme
    (CrossMark, 2017-06) Ansorge, Isabelle J; Skelton, Paul; Bekker, Annie; de Bruyn, P J Nico; Butterworth, Doug S; Cilliers, Pierre; Cooper, John; Cowan, Don A; Dorrington, Rosemary; Fawcett, Sarah; Fietz, Susanne; Findlay, Ken P; Froneman, P William; Grantham, Geoff H; Greve, Michelle; Hedding, David; Hofmeyr, G J Greg; Kosch, Michael; le Roux, Peter; Lucas, Mike; MacHutcho, Keith; Meiklejohn, Ian; Nel, Werner; Pistorius, Pierre; Ryan, Peter; Stander, Johan; Swart, Sebastiaan; Treasure, Anne; Vichi, Marcello; Jansen van Vuuren, Bettine
    Antarctica, the sub-Antarctic islands and surrounding Southern Ocean are regarded as one of the planet’s last remaining wildernesses, ‘insulated from threat by [their] remoteness and protection under the Antarctic Treaty System’1 . Antarctica encompasses some of the coldest, windiest and driest habitats on earth. Within the Southern Ocean, sub-Antarctic islands are found between the Sub-Antarctic Front to the north and the Polar Front to the south. Lying in a transition zone between warmer subtropical and cooler Antarctic waters, these islands are important sentinels from which to study climate change.2 A growing body of evidence3,4 now suggests that climatically driven changes in the latitudinal boundaries of these two fronts define the islands’ short- and long-term atmospheric and oceanic circulation patterns. Consequently, sub-Antarctic islands and their associated terrestrial and marine ecosystems offer ideal natural laboratories for studying ecosystem response to change.5 For example, a recent study6 indicates that the shift in the geographical position of the oceanic fronts has disrupted inshore marine ecosystems, with a possible impact on top predators. Importantly, biotic responses are variable as indicated by different population trends of these top predators.7,8 When studied collectively, these variations in species’ demographic patterns point to complex spatial and temporal changes within the broader sub-Antarctic ecosystem, and invite further examination of the interplay between extrinsic and intrinsic drivers.
  • Thumbnail Image
    Item
    Open Access
    Extinctions: Past and Present Week 5 - Threats to sea birds
    (2017-03-17) Chinsamy-Turan, Anusuya; Ryan, Peter
    In this video, Professor Anusuya Chinsamy-Turan interviews Professor Peter Ryan, an ornithologist who describes the threats to birds from human activity as being different in terrestrial and marine environments. He explains why and how conservation efforts have to take an ecosystem approach, and emphasises the need for legislative frameworks and individual behavioural change.
  • Thumbnail Image
    Item
    Open Access
    Fine-scale drivers of African Penguin prey dynamics in Algoa Bay, South Africa, and their impacts on penguin foraging ecology
    (2016) Mcinnes, Alistair McIntyre; Ryan, Peter; Pichegru, Lorien; Lacerda, Miguel
    African Penguins (Spheniscus demersus) have undergone a dramatic decrease in their population since the turn of this century prompting the up-grading of their conservation status to 'endangered'. There is growing evidence that variation in the availability of their principle prey, pelagic shoaling fish, are driving this trend. This prey variability is driven by oceanographic factors as well as commercial purse-seine fishing operations. To isolate the direct impacts of fishing on the foraging performance of African Penguins, the primary oceanographic drivers of fish distribution and abundance were investigated by conducting fine-scale pelagic fish surveys around two of the largest breeding colonies of African Penguins in Algoa Bay, St Croix and Bird islands, between 2011 and 2014. Quantification of fish parameters were facilitated by a novel method using a recreational fishfinder and calibrating this instrument to a conventional scientific device. The specific types of fish assemblages selected for by African Penguins were then evaluated by looking at the correspondence in associations of fish and penguins recorded at sea using both counts and locations of foraging birds tracked simultaneously during a subset of fish surveys. Activity budgets of penguins calculated from these simultaneous deployments were modelled against the abundance of their prey to elucidate hypothesised functional relationships. Finally, the direct influence of purse-seine fishing on both targeted fish assemblages and penguin activity budgets were assessed by modelling interactions between known physical drivers of targeted fish assemblages and different levels of cumulative catches. Physical drivers of the three-dimensional distribution and abundance of fish varied between colonies with primary production playing the most important role around Bird Island but having little influence on fish around St Croix Island where factors associated with surface and sea-profile temperatures had a stronger influence. Results of both penguin count and track data highlight the importance of the vertical distribution of prey to the distribution of foraging African Penguins with the abundance of these assemblages having a significant influence on this species' activity budgets. Evidence for local depletion of pelagic fish was demonstrated for the waters around St Croix Island and the effects of purse-seine fishing on African Penguin foraging effort were significant when controlling for natural drivers of prey distribution. Results of this research should be applied to current conservation measures, most notably alleviating direct competition by purse-seine fishing operations during periods of reduced primary productivity and when the abundance of targeted fish aggregations are significantly diminished three months prior to and during the onset of the African Penguin breeding season.
  • No Thumbnail Available
    Item
    Open Access
    Flight feather moult patterns and stable isotope analysis in the Woodland Kingfisher
    (2024) Ramudzuli, Abigail; Ryan, Peter
    The Woodland Kingfisher Halcyon senegalensis is an intra-African migrant that is widely distributed south of the Sahara. Migrating populations have to undergo an annual cycle that includes two migrations between the breeding and non-breeding grounds, the renewal of feathers and reproduction. All the mentioned processes are energetically expensive and they need special physiological adaptations. I investigated the timing of moult by actively catching Woodland Kingfishers in the field and scoring them for moult. This showed that migrating Woodland Kingfishers that breed in South Africa do not moult their flight feathers while they are on their breeding grounds. Resident populations in Ghana and Uganda sampled between June and August, during their breeding season, were also not in moult, but some individuals were growing feathers that they had lost through mechanical damage. Moult data from the SAFRING database also showed no evidence of active moult for all adult birds in the southern Africa region, suggesting that they moult on the non-breeding grounds. This knowledge of moult allows us to use natural markers that are fixed in feathers to potentially infer where migrant birds spend their non-breeding period. To infer non-breeding grounds of the Woodland Kingfisher, I measured stable isotope ratios of carbon (δ 13C), nitrogen (δ 15N) and hydrogen (δ 2H) in primary (P1), secondary (S1) and tail (R1) feathers from birds caught in Ghana, South Africa and Uganda between 2015 and 2018 during the respective breeding seasons. Feather δ 13C of Woodland Kingfishers caught in Ghana suggest that these birds grow their feathers in areas dominated by C3 plants, whereas feathers from Woodland Kingfishers caught in Uganda and South Africa indicated that they moulted in areas dominated by C4 plants. This enables us to assign birds to different feeding areas. The δ 2H values were highest in South African feathers but not significantly different from the Ghanaian feathers, while the Ugandan δ 2H feather values were the lowest. The similar δ 13C and δ 2H values of feathers of birds from Uganda and South Africa suggests that the non-breeding grounds of the migrant South African population lies within the same isoscape band as that of Ugandan birds. δ 15N values, which indicate trophic levels, were similar for all the birds, suggesting that Woodland Kingfishers in Ghana, South Africa and Uganda forage on similar prey. The observations of colourringed Woodland Kingfishers in Uganda outside the breeding seasons confirm the Ugandan population to be sedentary and this enabled us to infer that the birds that were caught in this area were sedentary. While yet-unpublished telemetry data indicates Woodland Kingfishers that breed in South African spend their non-breeding period in areas around Chad, Sudan and Central African Republic. This region is within the same δ 13C isoscape as Uganda. The use of stable isotopes, especially when combined with other techniques, shows a lot potential as means of inferring the nonbreeding grounds of migrating Woodland Kingfishers. The approach of exploring moult patterns and analysing SI signals should be expanded for use on other intra-African migratory bird species because the migratory behaviour of most intra-African migrants still remains unknown.
  • Thumbnail Image
    Item
    Open Access
    Influence of ecosystem variability on the demography and reproductive performance of two Eudyptes penguins, Macaroni and Eastern Rockhopper Penguins, at sub-Antarctic Marion Island, 1994–2019
    (2022) Dakwa, Farisayi E; Makhado, Azwianewi; Ryan, Peter
    Penguins are among the most important avian predators in the Southern Ocean, consuming large amounts of prey. Macaroni Penguins Eudyptes chrysolophus and Eastern Rockhopper Penguins E. filholi are listed as Vulnerable due to large-scale population declines across their distributions. The aim of my thesis is to update trends in the breeding populations of Macaroni and Eastern Rockhopper Penguins at Marion Island from 1994–2019. The breeding population of Macaroni Penguins has decreased more or less consistently at an average rate of 1.9% per year since 1994, whereas Eastern Rockhopper Penguins showed a rapid initial decline of 13% per year from 1994–2001, then stabilised to fluctuate between 55 000 and 80 000 pairs. I assess the long-term trends in pre-breeding condition (arrival dates and mass on arrival for breeding) and breeding performance (breeding success and fledgling mass) of both Macaroni and Eastern Rockhopper Penguins. I also compare within and between these variables to explain trends in the breeding population of both penguins for the last two decades. There was inter-annual variation in pre-breeding variables (arrival dates and mass on arrival) and breeding variables (breeding success and fledging mass) in both penguins which could indicate variability in prey availability and climatic conditions across the breeding seasons from 1994–2019. Over the study period, Macaroni Penguins arrived to breed 3–5 weeks earlier than Eastern Rockhopper Penguins on Marion Island. There was no consistent trend in mass on arrival among male or female Macaroni Penguins but Eastern Rockhopper Penguin mass on arrival decreased from 1994 to 2007 and then had an increasing trend post 2007 for both sexes. Breeding success of Macaroni Penguins fluctuated annually with no obvious trend, whereas the breeding success of Eastern Rockhopper Penguins increased at all three study locations. This increase in body condition and breeding success could explain the stabilising population of Eastern Rockhopper Penguins at Marion Island. Breeding variables (breeding success, fledgling mass) of both penguins were related to pre-breeding variables (arrival dates and mass at arrival). The breeding performance of both penguins is not only affected by localised prey availability and climatic conditions during breeding, but the effect might potentially be at a broader scale, before the onset of breeding. I used diet samples collected from these two species during breeding to determine interannual variation in prey composition to assess whether long-term changes in diet might explain trends in their breeding populations. The population size of the two penguins at Marion Island is more evenly matched compared to any other location where the two Eudyptes penguins breed sympatrically. They are expected to exhibit a level of segregation in their biology to allow their co-existence, from selection of breeding grounds, foraging strategies, diet and response to changing oceanographic conditions. I also tested for differences in preferred prey species. Both penguins mainly fed on euphausiids Thysanoessa vicina and Euphausia vallentini. Myctophid fishes (mainly Krefftichthys anderssoni and Protomyctophum tenisoni) were more important in the diet of Macaroni than Eastern Rockhopper Penguins. There was no long-term change in their diets that could explain their decreasing population trends at Marion Island. However, the more diverse diet of Macaroni Penguins could potentially allow them to compensate for years of low euphausiid availability compared to Eastern Rockhopper Penguins. The considerable overlap in diet between the two penguins suggests potential competition of resources between the two penguins, during breeding. Variation in breeding performance of both Macaroni and Eastern Rockhopper Penguins was related to breeding diet composition. Macaroni Penguins had higher breeding success when they fed more on myctophids, whereas Eastern Rockhopper Penguins fledged lighter chicks when they preyed on myctophids. Macaroni Penguins are more efficient at foraging on myctophids compared to Eastern Rockhopper Penguins and hence, foraging on myctophids could have opposing effects on duration of foraging, provision rate and parental care between the two penguin species. Variation in the diet composition when breeding was related to the latitudinal position of the oceanic fronts. Macaroni and Eastern Rockhopper Penguins fed on more fish Protomyctophum tenisoni when the Sub-Antarctic Front (SAF) and Antarctic Polar Front (APF) were further away from Marion Island and fed on more crustaceans Thysanoessa vicina when the fronts were closer to the island. The variable latitudinal position of the fronts is known to influence species composition and oceanographic conditions around the Island. Variation in breeding performance was not readily explained by large-scale oceanographic conditions or local scale oceanographic conditions except for sea surface height (SSH). Macaroni Penguins tended to fledge heavier chicks in years of low SSH, associated with more upwelling and mesoscale eddies, whereas Eastern Rockhopper Penguins tended to fledge heavier chicks in years of higher SSH associated with less upwelling and fewer mesoscale eddies. This indicates the difference in habitat preference and response to oceanographic conditions between the two penguin species: Macaroni Penguins forage in cooler waters compared to Eastern Rockhopper Penguins. In summary, this study reports trends in the population size, breeding performance and diet of two sympatric penguin species and how they respond to their environment. Both penguins' populations have been decreasing since 1994 but for the Eastern Rockhopper Penguin most of the decline happened before 2001 and their population has since stabilised. The two-closely related penguins manage to segregate some aspects of their ecology to facilitate co-existence on the same island while foraging in broadly the same area and feeding on the same prey. Macaroni Penguins arrive on the Island 3–5 weeks earlier than Eastern Rockhopper Penguins, which reduces competition for resources during breeding. Macaroni Penguins have a more diverse diet and feed on more fish compared to Eastern Rockhopper Penguins. The breeding performance of Macaroni Penguins responded positively to fish in their diet while Eastern Rockhopper Penguin chick condition was negatively affected by fish in their diet. The breeding biology and diet of the two penguins responded to changes in oceanographic settings around Marion Island, showing the possible effect of climate change on these two species.
  • Thumbnail Image
    Item
    Open Access
    Quantifying land-based sources of plastic pollution in South Africa
    (2020) Weideman, Eleanor A; Ryan, Peter
    It is widely claimed that at least 80% of the plastic litter entering marine environments comes from land-based sources, yet there is little empirical evidence to support this. Most studies to date predict the flux of litter from land to sea using global models based on a handful of field studies conducted mostly in developed, Northern Hemisphere countries; others use proxies such as per capita waste generation and proportion of mismanaged waste to predict litter loads entering the sea. It thus remains unclear how accurate these predictions are, particularly for African countries where few field studies have been conducted. Due to its rapidly growing human population, Africa is expected to become a much more significant source of litter into the sea. It is therefore important to identify major land-based sources of litter from the continent so as to implement effective mitigation strategies aimed at stopping this leakage of waste plastics into the marine environment. In this thesis I investigate two possible land-based sources of plastic pollution in South Africa. In Chapter 2 I show that stormwater run-off from Cape Town, a large coastal city, is a significant land-based source of litter into Table Bay. By placing nets over three stormwater outlets, each draining a different land-use type in the city, I estimate that some 70-630 tonnes of plastic litter are released as part of urban runoff from Cape Town each year which is a similar order of magnitude as estimates based on run-off litter collected in the 1990s and stranded beach litter. Overall, 40- 78% of litter items by count and 52-64% by mass was plastic, of which most was single-use packaging. Compared to a similar survey of the same three stormwater outlets conducted in 1996, litter densities by count decreased by 50% in two of the three catchments but increased threefold in the commercial/residential area. It is clear that urban run-off is a significant source of litter into Table Bay, but the total amount is considerably less than model predictions that identified South Africa as the 11th worst source of marine plastics from land-based sources globally. While several of South Africa's large cities are on the coast, the largest industrial centre and most densely populated part of the country is inland in the Gauteng Province. Much of this province lies within the catchment of the Orange-Vaal River system, which flows west across the country to eventually drain into the Atlantic Ocean. In Chapter 3 I present the results of two extensive field surveys to assess the amounts of plastic debris transported by the Orange-Vaal River system into the sea. By sampling for micro- and macro-plastics at 33 bridges spanning the lengths of both the Orange and Vaal rivers I show that densities of larger plastic items were highest at sites in the densely populated and highly urbanised upper reaches of the Vaal River, while microfibres were particularly abundant in the arid, sparsely populated lower reaches of the Orange River at the end of the wet season. It therefore appears that the Orange-Vaal River system may be a source of microfibres to the Atlantic Ocean, but most larger plastic items are retained near point sources in the upper reaches of the Vaal River. The Orange-Vaal River system thus does not appear to be a major source of plastics into the Atlantic Ocean and there is considerably less than the 0.095 tonnes·yr-1 predicted to be washed out of the Orange River by global models. I also investigated whether dams retain microplastics and microfibres within their reservoirs by collecting bulk water and neuston net samples from above and below the walls of the five major dams in the Orange-Vaal River system. I present these results in Chapter 4 and show that microplastic and microfibre concentrations were highest in dams on the densely populated Vaal River during dry conditions, whereas the opposite pattern occurred at dams farther downstream or on the sparsely populated Orange River during wet conditions. Overall, microplastic and microfibre densities were similar at sites collected above versus below dam walls and there was no significant correlation between microplastic and microfibre densities at a site and the distance from the site to the dam wall. Dams therefore do not appear to trap floating microplastics and microfibres, although the data were noisy (average CV = 184%) and so provide only a rough estimate of differences in plastic densities among sites. Lastly, in Chapter 5 I summarise the main results from the previous chapters and present recommendations for future research. Combining the findings from Chapters 2 and 3 I make a first, very crude estimate of the amount of plastic entering the sea from land-based sources in South Africa and compare this to the 0.09-0.25 million tonnes predicted by Jambeck et al. (2015) based on national estimates of waste production and management. I conclude that actual plastic emissions are some 1-2 orders of magnitude less than the global model estimate, which concurs with estimates based on beach litter data.
  • Thumbnail Image
    Item
    Open Access
    Rupturing the terrain vague
    (2011) Ho-Tong M; Ryan, Peter
    This thesis started with the above statement made by Jean Nouvel in conversation with Jean Baudrillard on the metamorphosis of architecture. This project set out as both a manifestation of the above philosophy, using it as an approach towards making architecture, and as an exploration to test whether architecture can really achieve this - to create a human appreciation of what is, of what is not plainly seen and of existing in space and in a built world which exists with respect to a geological layer applied to all cities across the earth. In this thesis, architecture is explored as a tool for revelation; specifically of existing situations and scenarios in the built world which are overlooked or unappreciated.
  • No Thumbnail Available
    Item
    Open Access
    Seabirds as monitors of marine plastic pollution
    (2025) Perold, Vonica; Ryan, Peter
    Small buoyant plastic items are one of the most pervasive and abundant marine pollutants. They pose significant environmental impacts, including threatening the health of marine life through plastic ingestion, necessitating efforts to reduce plastic leakage into the sea. To evaluate the effectiveness of mitigation strategies, it is essential to understand trends in marine plastic densities, types, and sources, which requires a reliable baseline for repeated assessments. While sea-surface net trawls are commonly used to monitor trends in small floating plastics at sea, they face several challenges. Seabirds, particularly petrels and albatrosses (order Procellariiformes), offer a practical alternative to net sampling as they often ingest and retain buoyant plastics encountered while foraging at sea, making them valuable indicators of this type of plastic pollution. However, few studies have thoroughly tested their utility. Larger species, such as albatrosses and giant petrels, typically ingest macroplastics items like bags, bottle lids, and fishery-related debris, which can often be traced back to specific sources. In contrast, smaller petrels, including storm petrels, prions, and shearwaters, tend to ingest smaller items like industrial pellets and fragments of larger plastic objects, whose sources are more challenging to identify. Due to their high propensity for ingesting plastics and their tendency to consume larger volumes, these smaller petrels may be particularly well- suited for monitoring ingested plastic loads over time. In Chapter 2, I assess trends in litter items collected at the nests of albatrosses and giant petrels breeding on Marion Island in the southwestern Indian Ocean, from 1996 to 2018. Temporal variation in litter composition and amounts were compared to data on Patagonian toothfish Dissostichus eleginoides fishing intensity in the area. Fishery-related litter abundance peaked during industry's height, declining in the following two decades. Other litter items increased over the last decade, when the most frequently recorded identifiable litter items were drink bottle lids from Indonesia. Long-distance drift of buoyant plastic items from Southeast Asia, mainly Indonesia, is a major source of litter to the western Indian Ocean. In Chapter 3, I assess the use of an indirect method to sample plastics ingested by seabirds by examining regurgitated Brown Skua Catharacta antarctica (Stercorariidae) pellets containing prey remains of petrels at Inaccessible Island in the central South Atlantic Ocean. I compare the size of plastics in skua pellets to those collected directly from seabird carcasses, to assess the validity of this method. I also compare the composition of plastics ingested within each seabird taxon to small buoyant plastics sampled with a neuston net, to understand how the ingested plastic compares with that found in the environment. I found that as a community, petrels reflected the composition of small buoyant plastics at sea, providing support for their use as biomonitors of marine plastic pollution. In Chapter 4, I assess how plastic loads in four petrels have changed from 1987 to 2018 in roughly decadal time periods and years. More than 3 700 regurgitated Brown Skua pellets, each containing the remains of a single petrel, indicated fluctuations in plastic loads between periods and years, but no overall clear trend was evident in any species. The number and proportions of industrial pellets among ingested plastics decreased over the study period, indicating that industry initiatives to reduce pellet leakage have been at least partly successful. In Chapter 5, I assess whether the size, mass, and polymer types of ingested plastic items have changed over the study period (1987 – 2018) to help interpret the results from Chapter 4. I found little change in the size and mass of ingested plastics since the 1980s. The ratio of polypropylene to polyethylene has increased consistently among hard fragments of user items over time. Overall, the limited change in plastic characteristics is consistent with the absence of clear trends in plastic loads over time (Chapter 4). In Chapter 6, which also serves as my synthesis, I investigate whether plastics sampled on beaches along the southern Cape coastline of South Africa from 1984 to 2023 exhibit the same trends in composition as small buoyant plastics ingested by petrels from 1987 to 2018. The findings show minimal changes in beached hard fragment sizes, with a recent increase in industrial pellet mass due to two major spills at sea off South Africa in 2017 and 2020. Polymer ratios in hard fragments mirrored those ingested by seabirds in the South Atlantic, indicating common influencing variables. More data are needed to understand the increase in the ratios of polypropylene to polyethylene over time, and how this may influence retention rates of plastics on the sea surface. In summary, this thesis demonstrates that sampling plastics ingested by seabirds provides a comprehensive assessment of marine litter composition and sources. Seabirds offer valuable insights into temporal trends in plastic loads and characteristics which align with variations observed in beached plastics. The lack of clear patterns in plastic loads over time suggests that initiatives to reduce the influx of plastics, and remove existing litter, may be preventing a rapid increase in the density of floating plastics at sea, despite the ongoing increase in global plastic production. However, the possible egestion of plastics by seabirds while out at sea, may also account for the lack of clear trends. More empirical data are needed to assess this, and how turnover rates of floating plastics will change under different plastic emission scenarios, to help interpret patterns in the loads and sizes of plastics in the marine environment. These insights are crucial for assessing the efficacy of mitigation strategies to reduce plastic waste leakage into the marine environment.
  • Thumbnail Image
    Item
    Open Access
    Seasonal and long-term change in the abundance, accumulation and distribution of beach litter within Table Bay, Cape Town, South Africa
    (2021) Opie, Brandon; Ryan, Peter; Moloney, Coleen
    There is growing global concern with regard to the pollution of the world's ocean, particularly by marine debris and plastics. The daily accumulation rates of stranded beach litter were measured at two sites within Table Bay, repeating similar studies from 1994/95 and 2012. Milnerton is a popular recreational beach near the city, while Koeberg is a seldom visited beach in a nature reserve 39 km from the city. Daily sampling was conducted for ten days in winter (August), spring (October) and summer (November-December) 2019. Of the 39 602 items (116.6 kg) sampled in 2019, plastics (including expanded polystyrene) dominated at both sites in terms of numbers (Milnerton: 97.8 %; Koeberg: 98.7%) and mass (Milnerton: 45.2%; Koeberg: 58.9%). The accumulation rates were generally an order of magnitude greater at Milnerton than Koeberg. Plastics were dominated by single-use items (eg: expanded polystyrene clam shells, food wrapping and straws) and Milnerton's composition showed that there was a strong urban influence on the debris. Statistical analyses indicated there were large seasonal differences in accumulation rates at both sites. Milnerton's accumulation rate was ~8 times greater in winter (801.8 items·100 m-1 ·day-1 ) than in spring (97.4 items·100 m-1 ·day-1 ) and summer (86.4 items·100 m-1 ·day-1 ) in 2019. The winter peak was attributed to increased rainfall, which flushed the rivers, and to the reduced cleaning efforts in the catchments in the winter. The marine debris at Koeberg consisted of proportionally more buoyant items than Milnerton, items which can be transported vast distances, and debris at both sites was predominantly of local land-based origin. Across most sample years (1994/95, 2012 and 2019) and seasons (winter, and summer) Milnerton had significantly greater accumulation rates (min winter 1994/95: 286.7 items·100 m-1 ·day-1 to max winter 2019: 801.8 items·100 m-1 ·day-1 ; min summer 2019: 86.4 items·100 m-1 ·day-1 to max summer 2012: 1698.0 items·100 m-1 ·day-1 ) than Koeberg (min winter 2019: 55.9 items·100 m-1 ·day-1 to max winter 1994/95: 129.3 items·100 m-1 ·day-1 ; min summer 2019: 45.7 items·100 m-1 ·day-1 to max summer 2012: 151.4 items·100 m-1 ·day-1 ), attributed to many more sources of debris. Across all sample years, both sites had significantly greater winter accumulation rates than summer. A large decrease was seen in summer at both sites from 2012 to 2019, with a 95% (Milnerton) and 70% (Koeberg) reduction in total accumulation rates. The commencement of municipal cleaning efforts in the catchment areas and along the adjacent beach areas in the spring, which continued into summer, was likely a contributing factor to the decreases. Plastics (including expanded polystyrene) dominated the marine debris composition at both sites across all years and seasons and their proportions at both beaches have increased since 1994/95 from approximately 80 % to 95 %. It is evident that plastics are still prevalent in the environment. Improving waste management facilities and implementing effective cleaning measures throughout the year seem to be effective ways to reduce the marine debris problem. There is a need to shift away from single-use plastic items (such as straws, earbuds and food packaging) and to find more sustainable alternatives.
  • Thumbnail Image
    Item
    Open Access
    Survival and reproduction in a biennially-breeding seabird : the Wandering Albatross
    (2008) Vincent, Zachariah David; Ryan, Peter
    I studied a long-term data set for Wandering Albatrosses Diomedea exulans collected at sub-Antarctic Marion Island to investigate adult survival, breeding biology and factors affecting reproductive success of this long-lived pelagic seabird. Until recently, the complex adult life cycle has caused biases in conventional mark-recapture modelling analyses that assume that recapture probability is equal for 'observable' and 'unobservable' states of the biennial adult life cycle. During 'sabbaticals' taken after successful and late-failed breeding attempts, the chances of resighting an adult Wandering Albatrosses are reduced, thus affecting estimated recapture rates. I applied a multi-state mark-recapture method to the colony breeding data from Marion Island (1987-2005). This method allows individual albatrosses to move through a network of breeding states according to previous breeding history using transition probabilities to estimate survival, breeding and breeding success probability. The best fit models in the multi-state analysis were those representing constant survival and independent breeding probabilities, suggesting that Wandering Albatrosses constrain reproductive investment to ensure long-term survival. I used the parameter estimates in a transition matrix to calculate the steady state equilibrium for the Wandering Albatross breeding population. For the first time I was able to estimate that approximately 3000 pairs of Wandering Albatrosses use Marion Island for nesting. I also describe the effects of age, sex and experience on Wandering Albatross reproductive success. Birds that were most successful began breeding at the mean age of first breeding and older and younger birds were less successful in 5/10 year periods after the onset of breeding. Disappearance from the population decreased with an increase of age of first breeding. I tested the selection and experience hypotheses on birds with 'complete' histories defined according to an imposed rule on recovery data. Males appeared to increase breeding success as a result of selective removal of low-quality individuals from the population (the selection hypothesis), whereas females appeared to improve their breeding success as a result of increased experience.
  • No Thumbnail Available
    Item
    Open Access
    The impacts of habitat fragmentation of Tsitsikamma fynbos, South Africa, on avian nectarivore presence, abundance, and pollination
    (2023) Cloete, Daniel; Ryan, Peter
    Habitat loss and fragmentation of natural habitat, and other global change drivers resulting from human expansion and development, are putting ecosystems and biodiversity at risk. The Cape Floristic Region (CFR), confined to South Africa and known for its high biodiversity of especially plants, has been subjected to extensive habitat loss and fragmentation through agriculture and other modifying land uses. Habitat loss and fragmentation have the potential to negatively affect pollination systems. A reduction in flowering abundance can result in lower nectar production and availability. This reduction in reliable food, along with a lack of adequate habitat and nesting resources, can reduce the abundance of pollinators which, in turn, may result in reduced seed-set for the plant species that rely on them. This study considers how selected erica and protea plants and the sunbirds and sugarbird that pollinate them are affected by fynbos habitat fragmentation. The study was conducted in an area of fragmented Tsitsikamma Plateau Fynbos in the eastern region of the CFR. In Chapter 2, I described the study area, reported methods used to choose and delineate the 17 study patches, and derived variables that were used in the analyses in subsequent chapters. I identified an expected fragmentation effect using exploratory analyses that investigated patch-similarity based on patch, fragmentation, and focal plant species variables. Large patches with high protea densities and surrounded by indigenous forest were clustered, while small patches with lower protea densities and surrounded by transformed farmland and alien vegetation were clustered separately. In Chapter 3, I explored how these fragmentation patterns affected bird species richness and nectar-feeding birds in fynbos habitat. Based on repeated bird point-counts at 33 locations in the study patches I showed that the surrounding non-habitat matrix contributed to faster species accumulation that led to higher species richness in small patches. Although habitat fragmentation had little direct impact on general bird species richness, it explained differences in nectarivore abundance among patches. The fynbos endemic Cape Sugarbird (Promerops cafer) and Orange-breasted Sunbird (Anthobaphes violacea), as well as the Malachite Sunbird (Nectarinia famosa), were less likely to be recorded at locations surrounded by reduced fynbos habitat, while the habitat-generalist Amethyst (Chalcomitra amethystina), Greater Double-collared (Cinnyris afer), and Southern Double-collared Sunbirds (Cinnyris chalybeus) show the opposite trend. The negative fragmentation impact shown on fynbos specialist bird species presumably resulted from their reliance on fynbos habitat and their exposure to pressures from the surrounding non-habitat matrix. In Chapter 4, I investigated if habitat fragmentation influenced nectar loads in selected erica (Erica discolor and E. densifolia) and protea (Protea neriifolia and P. mundii) flowers through its effect on the abundance of the bird nectarivores that feed on and pollinate these plants. I also considered seasonal protea flowering, nectar availability and Cape Sugarbird abundance in the study area. Although I did not find a marked fragmentation effect on flower nectar load in small patches, total nectar availability per unit area increased with patch size for proteas but decreased for ericas. Orange-breasted Sunbird abundance showed no relationship with erica nectar availability, while numbers of Southern Double-collared Sunbirds and Cape Sugarbirds increased with erica and protea nectar availability, respectively. The number of protea flowers, the amount of nectar available and the number of Cape Sugarbirds per month all showed a strong positive correlation, peaking from around December-June. These findings show the importance of nectar availability in determining nectarivore bird abundance and how fragmentation can affect it between patches. In Chapter 5, I investigated if habitat fragmentation affected seed-set for Erica discolor and Protea neriifolia flowers. I did not find a fragmentation effect on P. neriifolia seed-set, which reflected that Cape Sugarbirds managed to frequent all patches in the study. Erica discolor had higher seed-set in small patches, which might be explained by high sunbird density, thanks mainly to large numbers of Southern Double-collared Sunbirds that visited from the surrounding non-fynbos matrix. As a result, E. discolor seed-set was negatively correlated with Orange-breasted Sunbird abundance because this species was impacted by fragmentation. Protea neriifolia seed-set showed no relationship with Cape Sugarbird abundance. In the summary, Chapter 6, I discuss how habitat fragmentation affected the study system, but note how its impact varies among species. I also consider the limitations of the study and make suggestions for future research. Based on my findings, I suggest that conservation and managing authorities should aim to conserve and expand on remaining fynbos habitat by, for example, clearing the surrounding non-habitat matrix of invasive alien vegetation and/or rehabilitation such as erosion control and reseeding.
  • Thumbnail Image
    Item
    Open Access
    The movement and landscape use of Blue Cranes in the Western Cape
    (2018) Davis, Sydney Pierce; Ryan, Peter; Smith,Tanya
    The Western Cape population of Blue Cranes (Anthropoides paradiseus) is the largest and most stable population for the species. The population is primarily threatened by high mortality due to collisions with power-lines and the development of wind farms. Yet, little is known about how this population uses the agricultural landscape and their movements. Thirteen Blue Cranes were fitted with trackers to collect Global Position System data and tracked for 3 – 18 months in the Overberg region of the Western Cape. With the provided spatial-temporal information, I estimated the home range size, daily flight distances, and distance travelled throughout the day of breeding and non-breeding cranes to determine whether the breeding status/season influences their ranging behaviour. There was no significant difference of the home range size between breeding cranes and non-breeding cranes (p > 0.05). There was also no significant difference of the home range size of breeding cranes between their seasons (p > 0.05). Breeding cranes travelled significantly shorter daily flight distances than non-breeding cranes (p < 0.05). Breeding cranes also travelled significantly shorter daily distances during the breeding season than the non-breeding season (p < 0.01). All cranes, regardless of breeding status or season, travelled further distances in the morning, decreasing distance during the midday and early afternoon with an increase in the late afternoon. Breeding cranes travelled shorter distances throughout the day than non-breeding cranes during the breeding season (p < 0.001). Lastly, breeding cranes travelled significantly shorter distances throughout the day in the breeding season than the non-breeding season (p < 0.001). From this study the results suggest that factors other than breeding status influence the ranging behaviour of these cranes. Factors such as the availability of roost and forage sites, the agricultural landscape of the Overberg and the presence of other Blue Cranes could also affect ranging behaviour. Although this study does not give clear guidelines on the movement of the population, it establishes a baseline for further studies into factors that affect their ranging behaviour and can still be used to aid in conservation strategies for the species. Future studies should focus on recording their time budgets, including overnight GPS fixes and assessing ranging behaviour over multiple years.
  • Thumbnail Image
    Item
    Open Access
    Tracking African penguins (Spheniscus demersus) outside of the breeding season: Regional effects and fishing pressure during the pre-moult period
    (2014-08-15) Harding,Craig Thomas; Wanless, Ross M; Ryan, Peter; Moseley, Christina; Pichegru, Lorien
    African penguins (Spheniscus demersus) have experienced a 60% population decline in the past 30 years due to an eastward shift in the relative abundance of their main food source, anchovy (Engraulis encrasicolus ) and sardine (Sardinops sagax). This shift may be exacerbated by pressure from the small-pelagic fishery targeting these species. A lack of knowledge regarding foraging areas when not breeding has been identified as a deficiency in management planning for African penguins. Satellite transmitters were deployed on 20 adults during the pre-moult foraging period from colonies on the west coast (Dassen Island, n=10) and south coast (Bird Island, Algoa Bay, n=10) of South Africa. Kernel density analyses were produced using nightly locations to create foraging range maps, which were compared to catches made by the small-pelagic fishery during September-December 2012. Birds from the two colonies differed in their foraging strategies. Compared to penguins from Bird Island, those from Dassen Island spent more than six times the number of nights beyond the foraging range used during the breeding season (40 km from their colony). Birds from Dassen Island typically made long, looping trips more than 300 km away from the colony, and travelled further and at higher daily rates to foraging areas than individuals from Bird Island, feeding outside areas where fishing activity was highest. Kernel density analysis showed the foraging range of Dassen Island penguins was between Cape Columbine and the central Agulhas Bank. Individuals from Bird Island continued to central place forage, typically staying within 35 km of the colony. Penguins from Dassen Island that remained on the west coast had to compete with higher levels of fishing pressure than penguins from Bird Island. More than 70% of the fleet-wide, 2012 purse-seine catch occurred within the area where Dassen Island penguins spent 50% of their time. These colony-specific characteristics suggest that management plans for African penguins need to be regionally targeted and incorporate larger foraging ranges during the pre-moult period for birds from western colonies. The larger foraging ranges and effort demonstrated by birds from the west coast suggest that a combination of the low relative fish abundance and higher commercial fishing pressure may force pre-moulting birds to seek food sources farther from the colony, putting them at higher risk of not surviving the annual moult. This project requires more years of data to ensure these foraging patterns are representative, and to more accurately provide management suggestions directed to alleviate stress on African penguins for long-term protection of this endangered seabird.