CCAMLR

Penguin censuses on the Antarctic Peninsula are often subject to logistical challenges that preclude nest censuses being conducted at the peak of egg laying as established by the CCAMLR Ecosystem Monitoring Program (CEMP) (Scientific Committee for the Conservation of Antarctic Marine Living Resources 2004). Additionally, the historical literature, necessary for establishing baseline conditions, also includes many census counts with non-standard timing. The challenge is, therefore, to correct ‘off-peak’ census counts to make them comparable with current standard methods. Census correction involves knowing 1) how the census is timed relative to the peak of egg laying and 2) how nest numbers change through the breeding cycle. In this paper we present an analysis relating to both of these two challenges. Clutch initiation dates for four penguin breeding sites are examined (Cape Shirreff, Livingston Island (62°28′ S, 60°46′ W), Admiralty Bay, King George Island (62°10′ S, 58°30′ W), Humble Island (64°46′ S, 64°06′ W), and Petermann Island (65°10′ S, 64°10′ W)) in relationship to potential drivers of clutch initiation (e.g. temperature, precipitation, sea ice, sea surface temperature, etc.). We find that mean October temperatures constitute the most consistent significant factor related to the timing of clutch initiation in all three of the penguin species examined (Adélie, gentoo, and chinstrap). We present a statistical model for determining the peak of clutch initiation for any given year and site and, along with a simple estimation of species-specific nest attrition rates, we use this model to step through the procedure for correcting off-peak census counts.

This paper reports the results of a ground survey of fur seal colonies from in the South Shetland Islands in 2007/08. Multiple counts of pups at each colony were conducted to establish confidence limits on pup production. Total pup production was 7,602 (±103) pups down 24.4% from the last census in 2001/02 (10,057 ±142 pups born). Dead pups accounted for 1.64% of the total. A comparison with previous censuses over a 20yr period (1987, 1992, 1994, and 1996) indicates the rate of increase in fur seal populations has diminished substantially. The averaged annual rate of increase from 1987-1994 was between 13.5-13.9%. From 1994-1996 it was 8.5% and from 1996-2002 the average annual rate was +0.9%. Since 2001/02, pup production for the entire archipelago declined at an average annual rate change of -4.3%. Sources of error in pup production estimates include unobserved neonate mortality prior to census, natality rates of the adult female population and leopard seal predation on pups. Neonate mortality up to 30 days after the median date of pupping was estimated for the years 1997-2007 at 4.5% (±0.60). Adult female natality for the same period was 0.79 (±0.02) and in 2007/08 was below average at 0.73. Leopard seal predation was estimated from the rate of mother-pup failed pairs after pups begin entering the water (~30d after the median date of pupping [MDP]). Leopard seal predation for the first 75d post MDP for 2003-2007 was estimated at 0.376 (±0.043) and for the 2007/08 was above average at 0.522. Thus, higher neonate mortality, reduced natality, and an increase in leopard seal predation all contributed to lower pup production estimates in 2007/08.

Potential Adélie penguin breeding habitat (defined as ice-free land with area >4000 m2 and within 500 m of the ocean) in the Australian Antarctic Territory (AAT) was mapped using a GIS, and the literature reviewed for evidence of the mapped habitat being searched for occupation by breeding Adélie penguins. The total area of potential breeding habitat was estimated to be close to 700 km2. Definitive or reasonably strong evidence of search effort was found for 63% of all potential habitat sites and 40% of the total potential habitat area. There were marked regional differences in search effort, and the majority of search effort occurred in the 1980s. Incomplete search effort is a possible source of negative bias for AAT-wide estimates of Adélie penguin breeding abundance derived from published search effort and count data.

This paper very briefly summarises some aspects Adelie penguin count data from east Antarctica to demonstrate the extent and nature of variability in data from this large region, and to provide some background to some aspects of the R program SEABIRD outlined in McKinlay and Southwell (submitted working paper).

In addition to a review of published studies on Adelie penguin abundance at breeding sites in Antarctica, Southwell (2004) proposed a general abundance estimator appropriate for a species of that kind. The present study attempts to implement this estimator in the form of a parametric bootstrap model, utilising as input data published counts of Adelie penguins and estimates of their uncertainty at breeding sites in Antarctica. To achieve this task, a menu-driven suite of routines titled SEABIRD (Seasonal Estimation of Abundance by Bootstrapping Inexact Research Data) has been developed in the R language for statistical computing (R Development Core Team 2008). Software is reliant on data being presented in a specified format congruent with CCAMLR databases designed to store historical survey data relating to penguin abundance. Usual sampling methodology considerations reported in work of this kind are accommodated, such as availability and perception bias, as well as many of the vagaries associated with combining diverse data collected in a variety of ways over many decades. Of particular concern was to ensure that different types of counts (eg. nests, chicks or adults), perhaps made at different time points in a breeding season, might usefully be combined in order to obtain regional-scale estimates of abundance. This was achieved by using independent estimates of availability throughout a breeding season collected at a few, frequently sampled sites, in order to standardise historical estimates to a common reference point of breeding chronology. Equally important was the idea that estimates of uncertainty associated with historical counts be faithfully incorporated and preserved, and methods have been developed to allow these to be combined or interpreted in several different ways. In order to help understand how these and other elements of the procedure contribute toward estimates of uncertainty when combining data, as far as practical different components of the estimation process can be switched on or off to assess their effect. Confidence intervals for final estimates at different scales of spatial aggregation are determined by examining the bootstrap distribution of population estimates at selected percentile intervals. While tailored for Adelie penguins, the method and implementation is sufficiently general to potentially be adapted for other Antarctic species showing seasonal variation in availability to sampling methodology. At the time of writing, SEABIRD is well developed but still very much an evolving work. It is anticipated that use of the software and discussion of the estimation issues involved will identify possibilities for improvement.

Published accounts of population surveys and population estimates for flying seabirds across Area 48 are reviewed. Spatial coverage of count data and population estimates varies greatly between species across their breeding ranges in Area 48. Most population estimates reviewed date from the 1970s and 1980s. Survey methodologies are often poorly described. Potential biases and uncertainties around existing estimates are rarely discussed.

Counts of Adélie penguin populations are most conveniently and most often undertaken at breeding sites during the breeding season. The objective of this paper is to identify and describe the aspects of Adélie penguin population structure, dynamics and demography that are relevant to the interpretation of counts made at breeding sites and the estimation of overall population abundance derived from such counts. To appreciate what counts conducted at different times within a breeding season represent, it is important to understand the population dynamics of the different components of the population throughout the breeding season. The conceptual model described here is specifically based on data obtained from the Adélie penguin population at Béchervaise Island, East Antarctica. While the various life stages described here are also likely to represent other Adélie penguin populations, details in the proportion of each category either at the breeding site or at sea may potentially differ.

The size of two of the inaccessible (non-breeding) components of the Adélie penguin population associated with the Béchervaise Island breeding population is estimated over the past decade using a series of mark-recapture analyses and some simple population modelling techniques.

Broad-scale surveys of penguin breeding abundance generally rely on on-off counts of adults, nests or chicks across several or many breeding sites, and the timing of these counts is often outside the control of researchers. Time series counts of Adelie penguin breeding population attributes (adults, nest and chicks) within the breeding period show considerable variability across space and time (between years). Given this variability, there will be substantial uncertainty in correcting one-off counts with date-specific correction factors to estimate the population attempting to breed at the beginning of the breeding season.

This paper presents spatial modelling based abundance and density estimates of pack-ice seals, crabeater, Weddell and leopard seals, based on aerial survey line transect data collected in January 1999 under the Antarctic Pack-Ice Seal (APIS) programme. Estimates are reported for the Antarctic Peninsula and the western Weddell Sea region (90º to 30º W and 60º to 80º S).