Foraging Strategies of Laysan Albatross Inferred from Stable Isotopes: Implications for Association with Fisheries

Abstract

Fatal entanglement in fishing gear is the leading cause of population decline for albatross globally, a consequence of attraction to bait and fishery discards of commercial fishing operations. We investigated foraging strategies of Laysan albatross (Phoebastria immutabilis), as inferred from nitrogen and carbon isotope values of primary feathers, to determine breeding-related, seasonal, and historic factors that may affect the likelihood of association with Alaskan or Hawaiian longline fisheries. Feather samples were collected from live birds monitored for breeding status and breeding success on Midway Atoll in the northwestern Hawaiian Islands, birds salvaged as fisheries-bycatch, and birds added to museum collections before 1924. During the chick-rearing season (sampled April-May), means and variances of stable isotope values of birds with the highest, most consistent reproductive success were distinct from less productive conspecifics and completely different from birds caught in Hawaiian or Alaskan longline fisheries, suggesting birds with higher multi-annual reproductive success were less likely to associate with these fisheries. Contemporary birds with the highest reproductive success had mean values most similar to historic birds. Values of colony-bound, courting prebreeders were similar to active breeders but distinct from prebreeders caught in Alaskan longline fisheries. During the breeding season, δ15N values were highly variable for both contemporary and historic birds. Although some historic birds exhibited extremely low δ15N values unmatched by contemporary birds (< 11.2‰), others had values as high as the highest fishery-associated contemporary birds. During the non-breeding season (sampled July-September), isotopic variability coalesced into a more narrow set of values for both contemporary and historic birds. Our results suggest that foraging strategies of Laysan albatross are a complex function of season, breeding status, and multi-annual breeding success, factors that likely affect the probability of association with fisheries.

Seasonality of decadal-scale trophic declines and nutrient regime shifts in the Laysan albatross and Newell’s shearwater

“…Furthermore, both species historically exhibited seasonal variation in nutrient regime use, and this disparity has increased over time in Newell's shearwaters due to foraging shifts during the nonbreeding season. These phenomena, because they are isolated to the breeding season for Laysan albatross and weighted either heavily or exclusively toward the nonbreeding season in Newell's shearwater, went undetected in previous studies of the 2 species' isotope ecology (Edwards et al 2015, Gagne et al 2018, Morra et al 2019. While seasonal foraging shifts are a widespread phenomenon in sea-birds (Le Corre et al 2003, Cherel 2008, Young 2009, Gutowsky et al 2015, our data show that foraging seasonality itself might have shifted dramatically in the past 50− 100 yr, coincident with substantial anthropogenic alterations to marine food webs.…”

“…Breeding Laysan albatrosses rely on fisheries bait, target catch, and offal for food, with some individuals even specializing on these foods; typical fishery-associated prey items include Pacific saury Cololabus saira, swordfish Xiphius gladius, and neon flying squid (Bisson 2008, Conners et al 2018. A previous study suggested that modern individuals with higher reproductive success are less likely to associate with fisheries and more likely to have whole feather δ 15 N values that are similar to those of birds from before 1930 (Edwards et al 2015). Thus, comparing the results of this study to amino acid δ 15 N data from modern Laysan albatrosses with known reproductive success that may not scavenge from fisheries could further develop our understanding of the relationship between industrial fishing and Laysan albatross populations.…”

Fisheries Exploitation by Albatross Quantified With Lipid Analysis

“…Bycatch induced mortality rates for both species are well-monitored from ship-based surveys. Not surprisingly, the highest rates of albatross bycatch in the Hawaiian longline fisheries occur when attendance at breeding colonies is the highest (January-May), presumably due to maximum spatial overlap between birds and these particular fisheries in these months (see Edwards et al, 2015). While bycatch mortality is regularly monitored, detailed information on the diet composition of breeding albatrosses is notably lacking, particularly from periods in the annual cycle outside of chickrearing (McInnes et al, 2016).…”

“…For example, we know little about how fisheries exploitation varies across colonies or sex and age-classes or how fisheries exploitation of a breeding colony relates to variability in oceanographic conditions. Additional limitations in vessel-based research are necessary to consider: for one, bycaught birds may be a distinct subset of the populations, introducing a sampling bias, (Edwards et al, 2015). Also, encounters with fishing vessels cannot be used as a proxy for direct interactions with fisheries (Bodey et al, 2014;Sugishita et al, 2015;Collet et al, 2017).…”

Evaluating Native American Bird Use and Bird Assemblage Variability along the Oregon Coast

“…The presence of pelagic seabirds in archaeological assemblages has been interpreted as evidence for offshore hunting (e.g., Greenspan and Wigen 1991;Ulrich 2009). North Pacific procellariids are attracted to modern fishing vessels (Edwards et al 2015) and may have tracked offshore fishers and marine mammal hunters in the past, perhaps through chumming (DePuydt 1994). Breeding birds were available on offshore islands, such as Goat Island on the southern Oregon coast (Gard 1990).…”