Fisheries Exploitation by Albatross Quantified With Lipid Analysis

Abstract

Mortality from incidental bycatch in longline fishery operations is a global threat to seabird populations, and especially so for the albatross family (Diomedeidae) in which 15 out of 22 species are threatened with extinction. Despite the risks, fisheries remain attractive to many species of seabird by providing access to high-energy foods in the form of discarded fish and offal, target fish, and baited hooks. Current policy regarding fisheries management is increasingly aimed at discard reform, exemplified by a discard ban initiated in the European Union Common Fisheries Policy in 2014. While there is global agreement on the importance of minimizing the waste inherent in bycatch and discards, there is also growing concern that there is a need to understand the extent to which marine animals rely on fisheries-associated resources, especially at the colony and individual levels. We used a novel adaptation of quantitative fatty acid signature analysis (QFASA) to quantify fisheries-associated prey in the diet of two threatened North Pacific albatross species. Diet was estimated with QFASA using multiple lipid classes from stomach oil collected from incubating and chick-brooding Laysan and black-footed albatrosses across three breeding seasons. Prey-specific error was estimated by comparing QFASA estimated diets from known "simulated" diets, which informed the level of precaution appropriate when interpreting model results. Fisheries-associated diet occurred in both albatross species across both the incubation and chick-brood stages; however, neither species relied on fisheries food as the dominant food source (consisting of <10% of the total pooled proportional diet in each species). While total diet proportion was low, the incidence of fisheries-associated resources in albatross diets was highest in the 2009-2010 breeding season when there was a strong central Pacific El Niño. Additionally, the diets of a few individuals consisted almost entirely of fisheries-associated food, indicating that some birds might specialize on this foraging tactic. QFASA proved a tractable method for estimating the importance of fisheries-associated resources in albatross diet, and, as a tool, has the potential to enable long-term monitoring of diet and fisheries reliance of breeding colonies in the northwestern Hawaiian Islands.

Energy-Rich Mesopelagic Fishes Revealed as a Critical Prey Resource for a Deep-Diving Predator Using Quantitative Fatty Acid Signature Analysis

“…Elephant seals use suction feeding to consume prey whole, so we homogenized each whole prey item separately, then combined mass-specific aliquots from each individual into a species-homogenate (n = 3-15 individuals/homogenate). Three to five 1.5 g subsamples (replicates) were taken from each preyhomogenate, except when there was a single representative individual (Conners et al, 2018). Using a prey-homogenate gives an average prey FA profile but eliminates data on within-species variation between individuals in FA composition; however, within-species variability is likely small compared to betweenspecies variation (Budge et al, 2002).…”

“…NMDS ordination allowed us to see the relations of prey species in FA space, and, importantly, showed distinct separation between fish and squid FA profiles. Squids can be problematic in QFASA models (Conners et al, 2018), because most of their lipids are found in the large digestive gland, rather than other tissues like the mantle (Phillips et al, 2002). This results in a FA profile that may strongly resemble that of recently consumed prey present in the digestive gland.…”

“…Quantitative fatty acid signature analysis (QFASA) has become a widespread method of diet determination for diverse marine predators, such as sea birds, seals, sea lions, fish, and polar bears (Thiemann et al, 2008;Tucker et al, 2009;Meynier et al, 2010;Budge et al, 2012;Conners et al, 2018). The basic concept of FA analysis is that, molecularly speaking, "you are what you eat, " albeit with some predictable metabolic processing.…”

“…Using calibration coefficients and a subset of dietary FAs common to both predator and prey, the QFASA model finds which combination of prey minimizes the distance between prey and predator FA signatures (Iverson et al, 2004;Budge et al, 2006). Typically, studies utilizing QFASA have used small to moderate prey libraries (<30 prey species); however, QFASA can effectively differentiate among larger numbers (∼30-50) of potential prey species (Piché et al, 2010;Conners et al, 2018). This capability is important for determining the diets of mesopelagic predators, because the deep scattering layer is a highly interconnected food web where many prey species exploit similar resources.…”

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

“…glass and flying squid), as well as fish (e.g. lanternfish -Myctophidae -and flying fish), crustaceans, and fish eggs (Harrison et al 1983, Bisson 2008, Conners et al 2018. Despite the ecological differences between them, both the endangered Newell's shearwater and the abundant Laysan albatross have experienced trophic declines within the past century (Morra et al 2019).…”