Assessing multiple threats to seabird populations using flesh-footed shearwaters Ardenna carneipes on Lord Howe Island, Australia as case study

Globally, seabird populations have been in decline due to multiple threats throughout their range. Separating simultaneous pressures is challenging and can require significant amounts of data over long periods of time. We use spatial contrasts to investigate the relative importance of several drivers for the purported decline in a species listed as in decline as an example species, the Flesh-footed shearwater (Ardenna carneipes). On Lord Howe Island in the Tasman Sea, Australia, this seabird suffers from habitat loss due to housing development, intensive mortality in fisheries, plastic ingestion, and roadkill due to vehicular traffic on its breeding island. We repeated a quantitative survey of the population to ascertain whether the decline previously reported had continued and to evaluate the purported mortality sources (Reid et al. in PLoS ONE 8(4):e58230, 2013, Lavers et al. in Global Ecol Conserv 17:e00579, 2019). We measured burrow density, area of occurrence, occupancy and breeding success, integrating them with previous surveys using a Bayesian statistical model to generate longer term estimates of demographic rates. We used spatial patterns to test whether mortality on roads or proximity to human habitation was influencing population demographics. In contrast to predictions, we found the population had stabilised or increased. Characteristics such as burrow occupancy and breeding success showed little pattern, with weak evidence for impacts from road mortality and housing development. Such a data-rich approach is substantially more informative and can better support seabird conservation and management efforts does require more field-time and additional equipment than most contemporary surveys, the data is substantially more informative and can better clarify the results of efforts in seabird conservation and management.

A contribution to reducing bycatch in a high priority area for seabird conservation in Portugal

Summary Bycatch is one of the main threats to marine biodiversity, affecting ocean ecosystems at a worldwide scale. The main focus of bycatch studies has been on the impact of larger vessels, with few studies assessing the impact of artisanal fisheries. Moreover, bycatch studies are often limited to a small number of marine regions, and significant gaps still exist in our knowledge of the spatial and temporal patterns of seabird bycatch. Here we present a multi-approach method to accurately quantify seabird bycatch driven by small- and medium-sized fishing fleets operating in a high priority area for seabird conservation on the Portuguese mainland. Results of three mitigation measures to reduce seabird bycatch on fishing gear where seabird bycatch is most likely to occur were also tested: high contrast panels in bottom gillnets, black hooks in demersal longlines and a bird scaring device in purse seines. The efficacy, acceptance, and economic viability were tested for each mitigation measure. Sixty-seven individuals of seven seabird species were bycaught during 295 monitored fishing trips between 2015 and 2018. Bycatch occurred mainly in demersal longlines (0.07 birds fishing event-1), followed by purse seines (0.02 birds fishing event-1) and bottom gillnets (0.01 birds fishing event-1). Nevertheless, the bird scaring device caused birds to interact less with the vessel (the presence of gulls was reduced by 11%), thus decreasing the likelihood of bycatch. This device has proved to be low-cost (representing less than 5% income of a single day’s landings) and easy to implement, being also well accepted by purse seine fishermen. It was not possible to evaluate the efficacy of high contrast panels and black hooks, as no bycatch events were recorded during trials.