Interactions of marine debris with selected seabird species of Eastern Australia and the application of an ecological risk matrix
thesisposted on 18.11.2019, 00:00 by Krista VerlisKrista Verlis
Marine debris is a major persistent pollutant of oceans worldwide, with far reaching effects on the inhabitants and users of the marine environment. Marine plastic pollution is recognised as a key threatening process in Australia because of the harm it can cause wildlife through ingestion and entanglement (Chapter 1). More than 56 % of seabird species globally have been impacted by marine debris, but little is known about marine debris interactions in East Australian seabirds. The southern Great Barrier Reef (GBR) supports a high percentage of breeding and nesting seabirds, however no research existed on the interactions of marine debris with wildlife in this ecologically important area. This project was the first to examine the prevalence of marine debris on southern GBR beaches, and the first to examine marine debris interactions with two seabird species, the wedge‐tailed shearwater (Ardenna pacifica) and the brown booby (Sula leucogaster). A risk matrix for marine debris interactions was applied to help inform decision makers about this pollution threat. The utility of the created risk matrix is that it can be expanded to other organisms or regions within Australia. The prevalence of marine debris within offshore sites in the southern GBR (Capricorn‐Bunker Group of islands) was examined, and compared to levels of marine debris on near‐shore beaches (Sunshine Coast, Queensland, and Coffs Coast, New South Wales) (Chapter 2). Near‐shore sites had double the amount of debris items (0.08 m‐2) than offshore (0.04 m‐2) sites, with significantly higher rates of accumulation near‐shore than offshore (U = 0.000, p = 0.050). Levels of debris increased between the first and second sampling periods at near‐shore beaches only, indicating the possible influence of environmental conditions on the deposition and exhumation of debris items. More sampling is needed to confirm this trend. A Marine Debris Pollution Index was developed to aid in monitoring debris pollution at surveyed sites based on mean amounts and size of collected debris items. Off/white‐clear coloured debris items dominated survey collections (39 % nearshore; 31% offshore). Hard plastic items were the most prevalent debris type at both near‐shore and offshore sites (56 % and 42 %, respectively). Some differences in debris type existed between near and offshore beaches, for instance more fibrous plastic and sheet plastic were recovered at near‐shore sites, and these differences were attributed to source influences. For example, near‐shore sites were more heavily influenced by land‐based sources of pollution (F[2,60] = 546.811, p = 0.021). Plastic ingestion was studied in wedge‐tailed shearwaters (Chapter 3) at offshore GBR sites and near‐shore locations in southern QLD and northern NSW that were also surveyed for beach marine debris (Chapter 2). Overall on average ~13 % of late‐stage wedge‐tailed shearwater chicks had been fed marine debris plastic over two survey seasons with these birds most often ingesting off/white‐clear coloured plastics (~40 %). Interestingly, significant differences existed between debris colour and material type on surveyed beaches compared to that fed to chicks nesting offshore suggesting a selective feeding pattern on these plastics. This trend was not apparent in late‐stage chicks nesting at near‐shore sites. Ingestion appeared to be more frequent in near‐shore birds (~17 %), although this was not a significant pattern (F[1, 11] = 4.792, p = 0.065). While, the number of ingested plastic pieces per bird was significantly higher offshore (U = 40.000, p = 0.032). Marine debris ingestion did not appear to have a negative interaction on the health of surveyed late‐stage chicks as indicated by their body condition (U = 1091.00, p = 0.204). Marine debris from oceanic sources was common in the nests of brown boobies with over one‐third containing this anthropogenic material (Chapter 4). Using a novel photographic technique developed for surveying the nest material of this species, differences in levels of nest marine debris items were determined. The outcomes of this technique detected that the Swain Reefs nests were considerably more contaminated (58 %) than Capricorn‐Bunker nests (11 %). Hard plastic debris dominated Swain Reefs anthropogenic nest material (82 %) and beach debris (77 %) at all surveyed locations. There was a higher prevalence in nests for blue‐purple coloured plastic items in Swains and Fairfax nests (28 % and 29 %, respectively). Specific debris items were chosen by brown boobies for use within nests, limiting the use of nests as a substitute for beach surveys as an indicator of environmental debris levels. The use of marine debris within the nest material of brown boobies did not appear to negatively affect the brown boobies during the sampled periods, with no birds found entangled. A new risk matrix developed by modifying the IMO matrix (IMO, 2014) was applied to determine the level of risk marine debris posed to a region (Chapter 5). The marine debris beach survey data and seabird interaction data gathered from this research was applied to the risk matrix as a proof of concept demonstration. A traffic light colouring was used with the matrix based on marine debris interactions and amounts in in the environment. The results of the applied risk matrix from this study were ‘green’ and ‘yellow’ for seabirds in the southern GBR and nesting locations on the East Australian coastline. The yellow designation given to birds at Heron Island and those nesting in the Swain Reefs is at a tolerable risk level, but calls for actions to be taken to reduce marine debris levels when possible. The green designation given to birds at Northwest Island and Muttonbird Island, represent a more broadly acceptable risk level that requires monitoring and should be reduced further when practical. Further data is needed (i.e. more birds sampled) to provide a more accurate understanding of the risk to seabirds in the surveyed areas however. Recommendations from this research include the need for continued monitoring of marine debris levels (and interactions) on Australian beaches to address this issue; to ascertain the effectiveness of any preventative measures; and to gauge the continued performance of current legislation aimed at mitigating or ameliorating the marine debris problem. Management strategies targeted at the marine debris issue in south‐east Australia could be strengthened through enforcement of current legislation. This is especially important as increased ship traffic is anticipated throughout the region and shipping debris has been shown to be one of the common sources of marine debris in the surveyed areas. This thesis aimed to provide a baseline on the current presence and interactions of marine debris with two seabird species common to this ecologically important area. A number of new and novel tools were developed to undertake this monitoring and can be used by others to help best inform upon this pollution threat. The data collected and presented herein will provide new insights that will aid both the management of seabirds in this region and to improve the management of marine debris.