| dc.description.abstract | Maintaining healthy marine ecosystems in the face of worsening and accelerating human impacts urgently requires a globally coordinated and multidisciplinary approach. Seabirds are useful indicators of the status and health of marine ecosystems – they are higher-level marine predators that are relatively visible and accessible to researchers. However, their ability to cross political boundaries and high seas in the absence of a global management framework for biodiversity also makes them vulnerable to anthropogenic threats. For example, seabirds interact directly and indirectly with fisheries across the world’s oceans, including through competition for resources, by scavenging on fisheries waste, and through incidental capture in fishing gear. Improving our understanding of seabird-fisheries interactions therefore not only serves the target species, but has the ability to make a vital contribution to global initiatives and multi-disciplinary research aimed at improving the protection and sustainable management of our oceans and climate.
In the Southwest Atlantic, where seabird-fishery overlap is amongst the highest globally, the black-browed albatross Thalassarche melanophris (hereafter BBA) represents the main scavenger at fishing vessels, and is also the dominant seabird species of incidental catch (bycatch). The Falkland Islands hold the world’s largest population (>70% of breeding pairs), which is currently stable / increasing. However, the extent to which fisheries influence this trend remains poorly understood. Given the global significance of this population, as well as its importance to the Patagonian Shelf Large Marine Ecosystem, gaining an improved understanding of the nature and extent of fishery interaction is integral to biological conservation and ecosystem functioning, and supports fisheries management across the Southwest Atlantic.
Following a general introduction that forms Chapter 1, this thesis applied an integrated, multidisciplinary approach to help improve our understanding in relation to (1) BBA bycatch mitigation, (2) BBA diet structure and discard use, and (3) key foraging areas and broad-scale overlap with fishing fleets across the Patagonian Shelf.
Chapter 2 found that, compared to continuous discarding, batch discarding significantly reduced seabird abundance and gear collisions, and zero discarding eliminated gear collisions altogether. The findings validate batch discarding as an effective seabird-bycatch mitigation measure in trawl fisheries where full discard retention is not possible, but highlight the importance of complete waste storage between batches. Further, the positive relationship between bird abundance and collision rates supports the use of abundance as a proxy for collision rates in past and future studies.
Chapter 3 showed that BBA chicks are predominantly fed natural prey. However, discards form an important component in some years, specifically showing a significant increase in years of higher discard availability, higher sea surface temperature anomalies, and lower breeding success. The findings suggest that, although natural prey are the preferred diet, BBA switch to discards when natural foraging conditions are compromised. While fishery discards may act as a buffer, they do not appear to fully offset poor natural foraging conditions for breeding albatrosses in the long term.
Combining stomach content analysis with stable isotope analysis in Chapter 4 provided complementary diet information. Findings confirmed the importance of natural prey for chicks, but highlighted key diet differences between colonies and years. Although less important, results show that discards are still taken regularly, thus exposing a large proportion of breeding adults to a bycatch risk.
Finally, Chapter 5 showed that foraging areas of Falkland Islands breeding BBA correspond with productive shallow waters. During egg incubation and chick brooding, these areas overlapped only moderately with fishing activity, and did so predominantly with trawlers within the Falklands Conservation Zones (FCZs) and the Argentine Exclusive Economic Zone (AEEZ).
The General Discussion that forms Chapter 6 assesses the findings of this thesis in light of the available literature, and discusses the implications for management and future research. Overall, the thesis suggests that BBA-fisheries interactions are relatively low during breeding, and that fisheries have little influence on the ecology and demography of BBA in the Falkland Islands during this period. Efforts to limit fisheries waste and vessel attractiveness would therefore be of overall benefit to this population during breeding. However, important knowledge gaps persist, including in relation to the significance of discards to non-breeders (juvenile and immature birds; adult birds during winter), and the potential indirect impacts that fisheries may have on BBA through food-web alterations. The discussion highlights the importance of interdisciplinary collaborations across national jurisdictions to ensure robust marine science and successful conservation. | en_GB |
