Linking at-sea mortality of a pelagic shearwater to breeding colonies of origin using biogeochemical markers

Abstract

An emerging issue in seabird conservation is the ability to link at-sea mortality with observed demographic changes at breeding colonies. Applications of modelling and biochemical markers can be used to assign mortalities of unknown provenance to a colony of origin ensuring conservation actions are targeted at those colonies identified as the most affected. We analysed feathers (n = 120) from flesh-footed shearwater Puffinus carneipes collected from 5 breeding colonies throughout their range. Using stable isotopes (δ 15 N and δ 13 C) and trace element concentrations (Mn, Ni, Cu, Mo, Ag, Ba, Pb), we assigned birds recovered from fishing vessels off Australia, New Zealand, and the North Pacific to colony of origin, and investigated the rate of correct assignment at 3 spatial scales. Using quadratic discriminant analysis, samples of known origin were correctly assigned to basin, region, and breeding colonies at similar rates (92.3, 81.3, and 88.1%, respectively). Stable isotopes succeeded in assigning individuals among basins (72.8%), performing less well at the region and colony level (52.5 and 36.4%, respectively). In contrast, correct assignment was consistent at all 3 scales using only trace elements (93.2, 95.7, and 96.6%, respectively). Applying our final model based on trace elements to 116 flesh-footed shearwaters taken as bycatch in eastern Australia (n = 30), Western Australia (n = 32), New Zealand (n = 16), eastern North Pacific (n = 27) and western North Pacific (n = 11), we assigned individuals to colonies in New Zealand (35.3%), Western/South Australia (36.2%), Western Australia (27.6%), and Lord Howe Island (0.9%). Bycatch in fisheries may help explain ongoing declines in fleshfooted shearwater populations across the species' range, highlighting the utility of assignment tools to account for unobservable mortality of wildlife at-sea.

Climate change alters the trophic niche of a declining apex marine predator

“…Details of samples collected, and methods used for stable isotope analysis are presented by Lavers et al . (). Briefly, adult Flesh‐footed Shearwaters were caught at breeding sites in Western and South Australia (Fig.…”

“…This resulted in a total of 119 birds originating in Western and South Australia (Table ). There were insufficient samples from other breeding sites (Lord Howe Island or New Zealand) to examine changes in δ 13 C and δ 15 N over time (Lavers et al ., ).…”

“…Lavers et al . () predicted the provenance of these bycatch individuals of unknown provenance using spatially varying trace elements (e.g., Gómez‐Díaz & González‐Solís, ). This resulted in a total of 119 birds originating in Western and South Australia (Table ).…”

“…δ 13 C values are also negatively influenced by higher CO 2(aq) (Louanchi & Hoppema, ), but the magnitude of change in the southern Indian Ocean is small; Hilton et al . () and Jaeger & Cherel () estimated the maximum change in δ 13 C to be 0.16 ‰, which is within, or close to, analytical error in stable‐isotope analysis (see Lavers et al ., ), so we did not adjust δ 13 C values further.…”

Flesh-footed Shearwaters (<em>Puffinus carneipes</em>) in the northeastern Pacific Ocean: summary and synthesis of records from Canada and Alaska

“…Using biogeochemical markers, Lavers et al (2013) predicted that most Flesh-footed Shearwaters collected off British Columbia and Washington originated from Western and South Australia and smaller numbers from New Zealand. Population estimates from Western and South Australia in the 1970s and 1980s (more than 350 000 pairs) are erroneous, and recent more rigorous surveys suggest a much smaller population (less than 36 000 pairs); therefore, the actual population trend is difficult to ascertain given the vast overestimates in the 1970s and 1980s (Lavers 2015).…”