Long-term population trends of Sooty Shearwater (Puffinus griseus) revealed by hunt success

Abstract

The annual hunt of Muttonbirds (chicks of the Sooty Shearwater, Puffinus griseus), undertaken by the Rakiura Māori people of southern New Zealand, is economically and socially integral to their cultural identity. Muttonbirders concerned at ensuring that the hunt remains viable for coming generations have provided catch records to help ascertain historic trends in hunt success. Analysis of eight catch diaries for a 67-year period demonstrates considerable consistency across diaries in the variability of hunt success, as measured by annualized mean daily hunt tallies. A conservative estimate of the overall annual decline in hunt success is -1.89% (95% CI: -1.14% to -2.65%). Birders' observations of a changing relationship between chick quality and hunt success was evidenced across diaries. Reduced hunt success from the 1990s indicates that possible adult "knockdowns" and/or sustained substantial reductions in breeding proportions have occurred. Chick size has remained constant, suggesting little change in the provisioning environment. Catch per unit effort data, provided by a single diary, confirms a link between variability in annual hunt success and chick abundance. The Pacific Decadal Oscillation (PDO) and the Southern Annular Mode (SAM) are correlated with hunt success and chick size, respectively. Interannual PDO+ (or PDO-) values are correlated with higher (or lower) tallies, whereas SAM+ (or SAM) values are associated with larger (or smaller) chick size. Uncertainty in the relationship between the breeding Sooty Shearwater population, chick catch, and environmental perturbation in their feeding grounds could be reduced with the inclusion of hunt time in all diary records. Ongoing prolonged decline in a top-trophic-level predator such as the Sooty Shearwater raises serious concern that long-term oceanic changes have been occurring and that long-term sustainability of muttonbirding is in doubt.

Pattern recognition in long‐term Sooty Shearwater data: applying machine learning to create a harvest index

“…The non-detrended index that we created showed a 2% decline in the harvest index from 1957 to 2010. This is in line with a decline also found by Clucas (2011). Sooty Shearwaters have been in decline in other colonies around New Zealand as well (Jones 2000, Scott et al 2008.…”

“…Because of the importance of the harvest, there have been some attempts to investigate the diaries or information gathered from Rakiura Māori as a way of monitoring population trends over time (Lyver 2000, Moller et al 2009b, Clucas 2011, Clucas et al 2012). Clucas et al (2012) used general linear models to create an index that took into account several important parameters affecting daily tallies of the harvest.…”

Stable isotope values delineate the non-breeding distributions of sooty shearwaters Puffinus griseus in the North Pacific Ocean

“…Migratory connectivity, the relationship between population distributions during the breeding and non-breeding periods, affects the linkages between spatial variation in environmental conditions and reproductive performance and survival (e.g. see Webster et al 2002) and is increasingly important in a world where the rate of oceanographic and climatic change is unprecedented (Veit et al 1996, 1997, Ainley & Hyrenbach 2010, Clucas 2011.…”

Reconstructing shifts in vital rates driven by long‐term environmental change: a new demographic method based on readily available data

“…; Parr et al. ; Clucas ). Also, this kind of data can be rapidly collected for several populations that represent different stages of environmental change, and integrated into a chronosequence (Matthews and Whittaker ; Mori et al.…”