Trophic markers of marine predators in the Southern Ocean

Brief description

Stable isotope data, fatty acid and diet data was collected from a number of predator species in the southern ocean. Data was collected from blood, blubber, feathers and whisker samples

Lineage

Maintenance and Update Frequency: irregular

Statement: Common methodologies: Blubber analysis of southern elephant seals The biopsy site was located by measuring 5–7 cm laterally from a site on the posterior dorsal surface of the seal (Best et al. 2003). A 2 cm x 2 cm square area was shaved and disinfected with an alcohol swab. A 1 cm anterior–posterior line was cut through the skin, and the biopsy corer (6 mm in diameter) was inserted into this incision. Biopsies contained ‘whole’ cores of blubber from the skin to the muscle layer. No suturing of the incision was required. Each core was placed into a vial containing a solvent mixture of 2 : 1 v/v chloroform and methanol, and 0.05% by weight of the anti-oxidizing agent, butylated hydroxytoluene. Samples were maintained at 220 °C until lipid analysis. Lipids were extracted following Best et al. (2003). Briefly, we used a modified version of the Bligh & Dyer (1959) one-phase methanol–chloroform–water extraction (ratio modified to 2 : 1 : 0.8 by volume). Chloroform and saline water were added to separate the phases following overnight extraction (final solvent ratio of 1 : 1 : 0.9 by volume). Solvents were removed using rotary evaporation (40 °C), and the total lipid (TL) extracted (greater than 98%) was dissolved in chloroform and an aliquot treated with methanol–hydrochloric acid–chloroform (10 : 1 : 1 v/v/v; 80 °C; 2 h). TL samples were vortexed two to four times during that time to maximize conversion to FA methyl esters (FAME). The FAME were extracted three times into hexane–chloroform (4 : 1 v/v, 3 ml ´ 1.8 ml; 11 ml water) and subjected to gas chromatographic analyses using a Hewlett Packard 5890A GC (Avondale, PA, USA). Peaks were quantified with Waters Millennium software (Milford, MA, USA). Individual components were identified by comparing retention-time data with authentic and laboratory standards. Integrated chromatograms were normalized by expressing the FA components as percentages of the total FA. FA components that occurred at less than 0.5% were not included in the statistical analyses, as the precision of their determination is low (Walton & Pomeroy 2003). Total saturated FA (SFA), monounsaturated FA (MUFA), short-chain MUFA (SC-MUFA), long-chain MUFA (LCMUFA) and polyunsaturated FA (PUFA) were also calculated (Best et al. 2003). Diet analysis by stomach lavaging in southern elephant seals Once anaesthetised, the seals were weighed (± 1 kg), measured (± 10 mm) and lavaged (Slip 1995). The regurgitant was filtered through a 1-mm sieve to retrieve the stomach contents. The lavage procedure was repeated three times to remove the bulk of the stomach contents. The filtered stomach contents were then placed into a storage jar and filled with 70% ethanol until the contents were sorted and the prey items identified. In preparation for sample sorting and identification, the stomach contents were flushed with fresh water and placed in a sorting tray. From the stomach samples, the presence of fish otoliths, eyes and bones, squid mouthparts (consisting of an upper and lower beak), penn and eyes, crustaceans and other invertebrates, parasitic worms, sediment and plastic particles were identified. Lower squid beaks were identified to the lower taxa possible, using voucher specimen collections (from Malcolm Clarke held at the Australian Antarctic Division) and descriptions in Clarke (1986), and the lower rostral lengths (LRL) measured to ± 0.01 mm. Fish otoliths were also identified to genus or species level where possible using a voucher collection (from Dick Williams held at the Australian Antarctic Division) and the descriptions in Williams and McEldowney (1990). Stable isotope analysis in whiskers of southern elephant seals Vibrissae samples were taken while seals were sedated. A large vibrissa was cut at the base (part closest to the face) with a small pair of wire cutters and placed in a labeled air-tight glass vial. Prior to sample analysis, each vibrissa was soaked in a bath of 2 parts chloroform and 1 part methanol for 2 min then rinsed in the same mixture. This was repeated 3 times. Any remaining residue on vibrissae was scrubbed off with a small scrubbing brush and the soaking process repeated. After washing, the vibrissae were placed in an oven at 60°C for 72 h. Once washed and dried, the vibrissae were sectioned into approximately 2 mm sections (ranging in mass from 0.5–2.2 mg). Sample analysis: Each section was analysed using an Isoprime continuous-flow isotope-ratio mass spectrometer (Micromass). Results are presented in the usual δ notation relative to Pee Dee Belemnite (PDB) and atmospheric N2 (air) for 13C and 15N, respectively. Replicate measurements of internal laboratory standards (acetanilide) indicated measurement errors <0.15‰ and <0.20‰ for δ13C and δ15N, respectively.

Notes

Credit
Australian Research Council (ARC)

Credit
Australian Antarctic Division

Credit
SeaWorld

Purpose
To describe foraging behaviour of primarily southern ocean seals and other species.