Conservation implications of variation in diet and dietary specialisation in great skuas

• Main Author: Votier, Stephen C.
• Format: Thesis
• Language: English
• Published: ProQuest Dissertations & Theses 2001
• Subjects: QL Zoology; Catharacta skua; Great skua
• Online Access: http://theses.gla.ac.uk/73172/; https://theses.gla.ac.uk/73172/1/10647574.pdf; https://eleanor.lib.gla.ac.uk/record=b2039770

Summary: 1. Great skuas Catharacta skua are the only member of the genus Catharacta in the northern hemisphere. The UK holds around 60% of the World population with 8,000 breeding pairs. 2. Sustained population growth of the great skua in Scotland during the last century appears attributable to an abundant supply of discards (from commercial fisheries) and sandeels Ammodytes marinus. In addition great skuas may scavenge or predate other seabirds and their chicks when other prey is in short supply. 3. Following a decline in sandeels in the 1980s there is some evidence that an increase in predation of seabirds by great skuas may be affecting seabird populations. Future measures to reduce the amounts of fish discarded may result in a further increase in predation by great skuas. This highlights the need to quantify the current impact of great skua predation on seabird populations, and monitor any future change. 4. Accurate assessment of great skua diet is fundamental to this type of research. Many studies have used pellets of indigestible prey to assess diet in skuas and gulls, but have not quantified this technique. Captive great skuas were fed a range of fish and birds to try and understand more fully how pellets reflect diet. Feeding trials showed that skuas fed on a diet of birds produced more pellets than when feeding on fish. Fish species strongly influenced the number of pellets produced as well as the proportion and size of otoliths recovered. The numbers of pellets cast also varied significantly among differing species of bird meals. Field trials revealed that only a small proportion of pellets produced are being sampled. This study highlights the need to carefully validate the use of pellets to assess diet, particularly in a species of conservation concern. 5. The diet of great skuas was estimated based on five different techniques (pellets, prey remains, spontaneous regurgitates, observed feeds and water off-loading) and the results compared. The diet composition based on five sampling techniques in a ...