Assessments of abundance for British seal populations

Abstract

The harbour (Phoca vitulina) and grey seal (Halichoerus grypus) populations around Britain have experienced dramatic and contrasting changes over the last thirty years. In many areas grey seal numbers have recently started to level off after a long period of near exponential growth, while most of the harbour seals populations have suffered substantial reductions.

The main part of this thesis investigates these changes, primarily using aerial survey data from the long-term monitoring programmes carried out by the Sea Mammal Research Unit. It concentrates on the analysis and interpretation of the data rather than the methodology of collection.

An analysis of recent moult counts of harbour seals is presented. This shows that the population in East Anglia has not recovered from the effects of the 2002 epidemic of phocine distemper, and that there have been declines in all the populations in eastern Scotland. Electronic flipper tags are used to show that the proportion of the Orkney population that is hauled out during the moult has remained high, indicating that the reductions in the counts represent real declines in abundance.

A simplified method, based on Approximate Bayesian Computing, is used to fit agestructured population models to pup production estimates for the British grey seal population. Archived data from telemetry studies are combined with aerial survey data to show that the recent deceleration in the population’s growth is due to reductions in pup survival.

The setting of conservation goals for, and allowable takes from, such populations is also examined. In particular, the assumptions underlying the use of Potential Biological Removal and other common approaches are described. The thesis concludes with a brief discussion that considers how these results fit together and might contribute robust scientific information to support the conservation and management of these populations.

Date of Award	20 Jun 2012
Original language	English
Awarding Institution	University of St Andrews
Supervisor	Phil Hammond (Supervisor)