Browsing by Author "Wanless, Ross M"

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    African penguin (Spheniscus demersus) distribution during the non-breeding season : preparation for, and recovery from, a moulting fast
    (2016) Roberts, Jennifer; Ryan, Peter G; Pichegru, Lorien; Wanless, Ross M; Hagen, Christina
    Little is currently known about the spatial ecology of the endangered African penguin during the non-breeding season. As foraging success during this period is critical to adult survival, this project explores their dispersal patterns, as well as the degree of overlap with commercial purse-seine fisheries which target the same prey. African penguins from two colonies (Bird Island, Algoa Bay, south coast and Dassen Island, west coast) were tracked over 3 non-breeding seasons using Platform Terminal Transmitters and Global Positioning System devices to explore their pre- and post-moult dispersal patterns. Dispersal trips varied greatly between individuals, but there were still significant differences in the dispersal patterns found between islands and between life history-stages at Dassen Island. Bird Island penguins tended to make frequent, short trips, returning to their breeding colony in between, whereas Dassen Island penguins followed one of two strategies: either making few (up to 3) very long trips (up to 4000km), or adopting a central-place foraging pattern based at a point along the coast, distant from their breeding colony. At Dassen Island a clear spatial divide is evident with most pre-moulters dispersing south whereas most post-moult birds dispersed north, off the west coast. Bird Island penguins all moulted at their breeding colony and seldom visited either the adjacent coastline or other islands. During pre-moult, Dassen Island birds often spent nights close to shore along the coast or at other colonies and about a quarter of them moulted at another colony, most often at Stony Point, on the mainland east of Cape Point. Five dispersal patterns (defined in terms of the direction and distance of the furthest point reached) were identified for birds from Dassen Island and there is some indication that different dispersal patterns have distinct survival implications. Over 60% of PTT loss (a proxy for penguin mortality) occurred in a small area in the northern part of St Helena Bay, offshore from Lambert's Bay and Strandfontein and could be due to high levels of seal predation, which has been previously documented in the area. Commercial small pelagic fishing data were analysed over three years (2012-2014). Average fishing effort decreased each month from September to December (when hardly any fishing occurred in any of the three years) and there was much greater fishing effort along the west coast than on the south coast. Commercial fishing effort was compared to penguin track data to assess the degree of potential overlap between these two pelagic predators. Firstly, the spatial overlap between core penguin non-breeding dispersal areas and core fishing areas was assessed on a broad temporal scale (three years). Bird Island penguins were found to be more spatially removed from fishing activity with no overlap in core fishing and dispersal areas on the south coast. Compared to the size of their dispersal area, Dassen Island penguins which stayed along the lower west coast showed the highest overlap with core fishing areas. The two most common dispersal patterns exhibited by Dassen Island penguins both involve journeying to areas outside the range of purse-seine fishing, indicating the possibility of avoidance behaviour once the pressures of breeding are lifted. Direct (daily) overlap between commercial fishing effort and penguin tracks was studied although the low frequency of the penguin position data restricted the analysis to a 20 km scale. The results were similar to those described above, with most direct overlap occurring between Dassen Island and Gansbaai.
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    From both sides: dire demographic consequences of carnivorous mice and longlining for the critical endangered Tristan albatrosses on Gough Island
    (2009) Wanless, Ross M; Ryan, Peter G; Altwegg, Res; Angel, Andrea; Cooper, John; Cuthbert, Richard; Hilton, Geoff M
    The IUCN recently uplisted the Tristan albatross (Diomedea dabbenena) to Critically Endangered. Here we present new data indicating negative population trends on Gough Island arising from low adult survival (∼91%, ascribed to accidental mortality on fishing gear) and low breeding success (averaging 32%, due to mouse predation). Fledgling production from 1979 to 2007 and numbers of incubating adults from 1956 to 2007 have both decreased by ∼1% p.a. Consecutive annual counts of incubating adults and a population model permit the first reliable estimates of the Tristan albatross population, presently 5400 breeding adults and 11,300 birds in all age- and stage-classes. Population models explore scenarios of likely demographic trends using combinations of hypothetical best-case estimates vs. observed estimates for two key parameters: adult survival and breeding success. These scenarios highlight the relative benefits to the species of eradicating mice or mitigating bycatch. The model scenario using observed estimates predicts annual growth rate at −2.85%. Adult survival rates have probably decreased in recent years, concomitant with increased longline fishing effort, which might explain the discrepancy between counts and modelled trends. Negative trends cannot be reversed by improving breeding success alone, and adult survival must exceed an improbable 97% to balance the current chick production. A worst-case scenario including a fixed number of adult deaths annually predicted a catastrophic 4.2% p.a. decrease and extinction in ∼30 years. Population growth was most sensitive to adult survival, but even using an adult survival estimate without fishery mortality, current breeding success is insufficient to maintain the population. These findings do not support the ‘compensatory mitigation of bycatch’ model (offsetting bycatch impacts by eradicating invasive species), and the impacts of both fishery mortality and mouse predation must be addressed to improve the conservation status of the Critically Endangered Tristan albatross.
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    Impacts of the introduced house mouse on the seabirds of Gough Island
    (2007) Wanless, Ross M; Cooper, John
    Introduced house mice Mus musculus on Gough Island were suspected of widespread predation of Atlantic Petrel Pterodroma incerta and Tristan Albatross Diomedia dabbenena chicks in 2000/01. Video cameras recorded six fatal attacks by mice on live, healthy Atlantic Petrel chicks in 2004. Crude estimates of annual breeding success were 47%, 7% and 7% in 2003, 2004 and 2006, respectively. Mouse attacks were responsible for most chick failures. Mice were largely responsible for high numbers of Tristan Albatross chick failures in 2004-2006. Total failures were significantly related to total attempts but breeding success and total attempts were not correlated. There was little spatio-temporal consistency in total failures or breeding success. No environmental or biological variables examined explained the pattern. Proximity to a failed nest was a significant predictor of failure, suggesting a localised effect possibly due to a few predatory mice. Fledgling production has decreased by 1% annually since 1979-1982. Annual adult Tristan Albatross survival and breeding success averages are extremely low (91% and 32%, respectively) and modelled population growth using these parameters was - 2.85% p.a. Either parameter will drive decreases so reversing negative trends requires improving both.
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    The reintroduction of the Aldabra rail Dryolimnas cuvieri aldabranus to Picard Island, Aldabra Atoll
    (2002) Wanless, Ross M; Hockey, Phil A R
    The rallid genus Dryolimnas is endemic to western Indian Ocean islands. Formerly widespread, it is now restricted to Aldabra Atoll (the Aldabra Rail D. cuvieri aldabranus) and Madagascar (the White-throated Rail D. c. cuvieri). Before this project began, the Aldabra Rail was restricted to Polymnie, Malabar and lIe aux Cedres, having been extirpated from Grande Terre and Picard by Domestic Cats Felis catus (still found on Grande Terre) and humans. In 1999, following IUCN guidelines, I captured 20 Aldabra Rails and brought them to now Cat-free Picard. Two Rails died in captivity, an indirect result of incorrect sexing based on a published field sexing method; a subsequent genetic sexing technique confirmed the unreliability of sexing Aldabra Rails in the field. All 18 remaining birds were released on Picard and survived beyond the first breeding season. Eight pairs had bonded and successfully reared a minimum of 13 chicks within five months of release. Eleven monitored pairs reared 20 chicks in 2000/2001, with one-year-old birds breeding successfully. Average chick production was significantly higher on Picard than on Malabar in both breeding seasons. The Picard population at the end of the 2000/2001 breeding season was at least 51, an increase of 283% in 18 months. There are excellent prospects for continued, exponential population growth until the population reaches carrying capacity (ca 1000 pairs), predicted to be between 2007 and 2009. Limited genetic data suggest some population structure between extant populations, and the Picard population is genetically healthy relative to that of Malabar. There has been no substantial change 111 the Aldabra Rail population since the 1960s. However, I have revised an earlier population estimate downwards to ca 3500 pairs. I also estimate the floating population on Malabar was around 1700 Rails in early 2000. A population model of the Malabar Rails predicts a likely minimum annual adult survival rate of 85 %, with a fluctuating floater population. It also shows the population to be very robust to the removal of territorial birds for other proposed reintroductions, but highly vulnerable to the establishment of a predator. The soft release protocol (including a period of acclimatisation before release and supplementary feeding, as required, after release) is believed to have played a crucial role in the success of the reintroduction by allowing individuals to acclimatise and providing an energetic cushion between release and self-sufficiency. A soft release is recommended as the conservative and precautionary method of choice for avian reintroductions and translocations.
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    Rory lines : silver lining for seabirds in South Africa's demersal trawl fisheries
    (2012) Rice, Edward; Ryan, Peter G; Wanless, Ross M; Maree, Bronwyn
    Seabird bycatch in commercial fisheries is one of the major factors causing decreases in many seabird populations. In trawl fisheries, high mortalities have been recorded as a result of seabirds being struck by trawl warps (the cables used to tow the trawl net). Tori (bird-scaring) lines have been used to decrease seabird mortality in some trawl fisheries by up to 90%. However, tori lines are not effective at reducing the number of birds that drift towards the trawl warps while feeding on factory discards alongside the vessel. The Albatross Task Force (ATF) helped to develop and test a new device, the Rory Line (RL), to be used in conjunction with tori lines, and designed to reduce warp strikes by placing a physical barrier between the scupper (where factory discards are released) and the danger zone (where the trawl warps enter the water) at the stern of the vessel. This study tests the efficacy of the RL at reducing the number of birds drifting into the danger zone and the number of birds being struck by the trawl warps.
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    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.
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    Understanding and mitigating seabird bycatch in the South African pelagic longline fishery
    (2017) Rollinson, Dominic Paul; Ryan, Peter G; Wanless, Ross M
    Seabirds are considered one of the most threatened groups of birds in the world. They face additional mortality both on their breeding islands from introduced predators and at sea by fishing fleets, as fisheries bycatch, as well as other human impacts. Seabird bycatch has negatively affected many seabird populations worldwide, with trawl, gillnet and longline fisheries considered the most destructive to seabird populations. Seabird bycatch from trawl and gillnet fisheries has been significantly reduced in recent years, but large numbers of seabirds are still killed annually by longline fisheries. Of the two types of longline fisheries (demersal and pelagic), pelagic longlining is considered the most harmful to seabirds as lines remain closer to the surface for longer periods than demersal longlining, and it is harder to weight lines to ensure rapid sinking beyond the depth they are accessible to birds. Seabirds are killed when they swallow baited hooks and consequently drown. Despite the large number of studies investigating seabird bycatch from pelagic longline fisheries, there remain gaps in our understanding of seabird bycatch from pelagic longline fisheries. This thesis addresses some of these knowledge gaps and makes recommendations as to how seabird bycatch from pelagic longliners can be reduced at both a local and global scale. Chapters 2 and 3 investigate the factors affecting seabird bycatch from pelagic longliners off South Africa, provide a summary of seabird bycatch from the fishery for the period 2006–2013 and quantify the structure of seabird assemblages associated with pelagic longline vessels off South Africa. This was achieved by analysing seabird bycatch data collected by fisheries observers as well as data from sea trials onboard pelagic longliners. Seabird bycatch by pelagic longliners off South Africa over the 8-year study period has been significantly reduced from the 8-year period (1998–2005), mainly driven by a significant reduction in seabird bycatch rates from foreign-flagged vessels, which are responsible for c. 80% of fishing effort off South Africa. Seabird bycatch rates from South African vessels still remain high, four times higher than the interim national target of < 0.05 birds per 1000 hooks. The species composition of seabird bycatch off South Africa is best explained by an understanding of the structure of the seabird assemblage associated with longline vessels. For most species, bycatch and attendance ratios were similar, but for some species such as shy-type and black-browed albatrosses there were large mismatches, likely caused by differences in foraging behaviour and foraging dominance hierarchies. In Chapters 4 and 5 the foraging ecology of the most commonly recorded bycatch species off South Africa, the white-chinned petrel (Procellaria aequinoctialis), is investigated. An understanding of the foraging ecology of commonly recorded bycatch species enhances our understanding of seabird bycatch and helps to improve the design of current and future mitigation measures. The year-round movements of white-chinned petrels from Marion Island were investigated with Global Location Sensors (GLS loggers) and GPS loggers. Adult white-chinned petrels undertake only limited east-west movements of, with all birds remaining between southern Africa and Antarctica. These results strengthen the theory that there is limited spatial overlap year-round between white-chinned petrel populations from South Georgia, the southern Indian Ocean islands and New Zealand sub-Antarctic islands, suggesting that these populations can be managed as separate stocks. The diving behaviour of white-chinned and grey petrels (P. cinerea), another common bycatch species in Southern Ocean longline fleets, were examined with the use of temperature-depth recorders (TDRs), deployed on birds from Marion Island and Gough Island. My study was the first to analyse TDR dive data from any Procellaria petrel, and recorded them reaching maximum dive depths of 16 and 22 m, respectively. Current best practise suggests that baited hooks be protected to a depth of 5 m by bird-scaring lines, but my results suggest this depth should be increased to at least 10 m. Although line weighting is a proven mitigation measure to reduce seabird bycatch from pelagic longliners, fishers have concerns that it will compromise fish catches, crew safety and operational efficiency. In Chapter 6 I analyse line weighting data from trials onboard three pelagic longline vessels, to address the concerns of fishermen. My results show that sliding leads can be incorporated into pelagic longline fisheries without compromising fish catch, crew safety or operational efficiency. I thus recommend that sliding leads be used on pelagic longline vessels fishing off South Africa. By incorporating studies investigating the factors affecting seabird bycatch, seabird foraging ecology and the efficacy of seabird bycatch mitigation measures, my thesis has broadened our understating of seabird bycatch from pelagic longliners and makes meaningful recommendations to further reduce bycatch, both locally and globally. Although seabird bycatch rates have declined off South Africa, through the use of a number different mitigation measures, they still remain higher than the South African national target and thus more work is needed to achieve this target. To reduce seabird bycatch from pelagic longliners to acceptable levels, studies from the world's various longline fleets needs to be considered and improved upon, with seabird conservationists and fishermen working together to achieve this goal.
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    Using stable isotopes as a tool to understand the trophic relationships and movement of seabirds off Southern Africa
    (2012) Barquete, Viviane; Ryan, Peter G; Wanless, Ross M
    Stable isotopes (SI) have been widely applied in ecology to investigate the trophic relationships of animals. Stable isotope analyses were used to augment our understanding of the foraging ecology and movements of three globally threatened seabirds: African Penguins (Spheniscus demersus), Cape Gannets (Morus capensis) and White-chinned Petrels (Procellaria aequinoctiallis). The diets of captive penguins were varied to estimate the 15N turnover rates and discrimination factors of toenails and blood fractions. Plasma δ15N showed a faster turnover rate (7.6 ± 0.7 days) than erythrocytes (14.3 ± 1.6 days). Discrimination factors varied among tissues. No shift in nail δ15N signature was detected after 5 months, suggesting that toenails are insensitive to short to medium-term diet shifts. Among wild penguins and gannets sampled across the Benguela region, tow different responses to the effects of fisheries were observed,due to different feeding strategies, Age, sex year and colony location accounted for isotopic variation. Age-based differences may be linked to limited foraging skills of juvenile birds and their wider dispersion. Female gannets apparently feed on more live natural prey whereas males take more fishery discards, although the sex-based difference was confounded by colony effect. Marked inter-colony variation probably results from regional differences in oceanic conditions between, prey availability and among gannets, variation in dependence on fishery discards. Inter-annual variation in SI signatures might be linked to variation in primary production (African Penguins), or variation in prey availability (Cape Gannets)...