DOI: 10.5285/fb9bd975-e6fe-406c-84be-01e57d612b5e
title: Annual samples and measurements of diet composition of gentoo penguins at Signy Island, from 1998 to 2010.

description: This dataset captures information on the diet composition and mass of gentoo penguin stomach contents at Signy Island, from 1998 to 2010. The monitoring period occurred over four weeks each year and involved sampling adults returning to feed their chicks during the creche period. Sampling took place approximately every five days. Numbers of birds sampled on each occasion varied over the entire period of the dataset from a maximum of eight to a minimum of six, equating to an annual maximum of forty birds and annual minimum of thirty, depending on the year. All adult penguins were sampled on their return to the colony using the stomach lavage methodology specified in CCAMLR CEMP Standard Methods A8A. The stomach samples were then weighed and categorised into krill, cephalopods, fish and non-food and identified to species level where possible. Krill carapaces and otoliths were removed and measured. Ecosystems component of BAS Polar Science for Planet Earth Programme, funded by NERC.
description: Diet samples were taken each year from approximately 30-40 gentoo penguins, over a four-week period during creche. Birds were captured when returning to feed their chicks and samples were obtained using the stomach lavage method (Wilson 1984; Williams 1991; CCAMLR CEMP Standard Method A8A). The contents were subsequently drained through two sieves (3.34 and 250 micrometres) and wet meal mass was recorded. Samples were then categorised into crustacean, fish, and cephalopod components, and weighed by category. Prey items were also further categorised by species, when possible. Fish otoliths and krill carapaces were separated and measured. Otolith characteristics were used to identify the fish species consumed. Individual krill specimens all suffered varying degrees of damage prior to identification due to the process of consumption and partial digestion. The sex and age group of individual krill was determined by measuring the removed carapace length (RCL) using times 6 magnification under a binocular microscope and identifying specific diagnostics. Measurements were to the nearest eyepiece unit. Maturity stages were determined using the measured removed carapace length (RCL) per the code index from Morris et al. 1988, and are included as a csv file with the data. For a full explanation of the methodology used see Hill HJ. 1990; Polar Biol, 10(4):317-20; Reid K. 1998; Polar Biol, 19(2):145-147, CCAMLR CEMP Standard Method A8A. For reference to the code index in Morris et al. 1988, see Morris, D.J., J.L. Watkins, C. Ricketts, F. Buchholz and J. Priddle. 1988. An assessment of the merits of length and weight measurements of Antarctic krill Euphausia superba. British Antarctic Survey Bulletin, 79: 27-50. For otolith measurements, the microscope was first set to an appropriate magnification - allowing otoliths to fit onto one measurement scale. The magnification was then checked using the stage micrometer and adjusted when necessary. Otolith lengths were then measured using the measuring scale in the microscope eye piece. Depending on the species of fish the length measurement was taken in slightly different places.