Aerial Surveying of Grey Seal Breeding Colonies on the Blasket Islands, Co
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ARTICLE IN PRESS Journal for Nature Conservation ] (]]]]) ]]]—]]] 1 3 www.elsevier.de/jnc 5 7 9 Aerial surveying of grey seal breeding colonies on 11 the Blasket Islands, Co. Kerry, the Inishkea Group, 13 Co. Mayo and the Donegal Coast, Ireland 15 a,à b a 17 Michelle A. Cronin , Callan D. Duck , Oliver O´ Cadhla 19 aCoastal and Marine Resources Centre, University College Cork, Haulbowline Naval Base, Cobh Co., Cork, Ireland 21 bSea Mammal Research Unit, Gatty Marine Laboratory, University of St Andrews, St. Andrews, Fife KY168LB, UK 23 Received 15 September 2005; accepted 15 November 2006 25 27 KEYWORDS Summary Census; The status of Ireland’s grey seal population and its relationship with that of Britain 29 Digital imagery; and Western Europe, are poorly understood. The existing population estimate for Photography; grey seals in Ireland is outdated and urgency exists to establish a reliable national 31 Population estimate; population estimate for this species, listed as an Annex II species under the EU Pup production Habitats Directive. Prior to the initiation of a survey on a national scale, the success 33 or otherwise of aerial techniques in surveying grey seal breeding habitat on the Irish coastline first needs to be established. Previously, surveys were boat-based and were 35 susceptible to adverse weather conditions frequently encountered during the autumn breeding season. The feasibility of using aerial techniques to survey grey 37 seal breeding colonies in Ireland was tested during the breeding season of 2003. & 2006 Published by Elsevier GmbH. 39 57 41 inadequate indicator of today’s population size. 59 43 Introduction Between 1994 and 2003, a number of surveys were conducted at breeding and haul-out colonies of 61 45 Ireland’s most recent minimum population esti- mate for grey seals (Halichoerus grypus) dates back recognised national importance. The most recent of these surveys was of the Inishkea Island group, in 63 47 to boat-based ground counts conducted by the Forestry and Wildlife Service in the late 1970s and County Mayo (O´ Cadhla & Strong, 2003). Results from these local or regional population surveys 65 49 early 1980s (see Summers, 1983). The figure derived fromUNCORRECTED ground counting during this period indicate that PROOF the national grey seal population size is considerably greater today than was estimated in 67 51 (2000–2500 seals of all ages) is, without doubt, an 1983 (O´ Cadhla & Mackey, 2002). Due to limitations à of the data upon which historic estimates are based 69 53 Corresponding author. Tel.: +353 21 47033114. E-mail address: [email protected] (M.A. Cronin). and the absence of a national census in the last 20 71 55 1617-1381/$ - see front matter & 2006 Published by Elsevier GmbH. doi:10.1016/j.jnc.2006.11.001 Please cite this article as: Cronin, M. A., et al. Aerial surveying of grey seal breeding colonies on the Blasket Islands, Co. Kerry, the Inishkea Group, Co. Mayo and the Donegal Coast, Ireland. Journal for Nature Conservation, (2006), doi:10.1016/j.jnc.2006.11.001 8:07f=WðJul162004Þ JNC : 25053 Prod:Type:FTP ED:S:Shilpa XML:ver:5:0:1 pp:1À11ðcol:fig::NILÞ PAGN:anu SCAN: ARTICLE IN PRESS 2 M.A. Cronin et al. 1 years, it is not possible to determine trends in the counts carried out at these sites in 2002; and one 57 grey seal population size at present. aerial survey of the Donegal coastline, a section of 3 The only component of grey seal populations to the Irish coastline from which little data are 59 provide reliable population estimates when presently available (Fig. 1). We could then examine 5 counted, are pups during the first few weeks of the success of the aerial survey method to be 61 life, when they spend most of their time ashore at incorporated into the development of an appro- 7 the breeding colonies. Boat-based surveys present priate national census technique. 63 operational difficulties, particularly during the 9 annual breeding season (September–December) 65 when site-visits may be prone to cancellation due 11 to rough sea conditions. While boat-based surveys 67 are adequate for assessing local populations, they Methodology 13 would be exceedingly difficult to implement effec- 69 tively on a national basis in a reasonable time- Surveys were conducted from a high-winged 15 71 scale. Due to similar difficulties in the UK the single-engine Cessna 172 aircraft. Oblique photo- standard method used for determining population graphs were taken out of an opened window on the 17 73 size since the 1960s has been the use of aerial left side of the aircraft using a Canon EOS 1DS photography from fixed-wing aircraft. The surveys digital camera with a Sigma 70–210 mm lens. 19 75 use a large format aerial camera mounted in a Efforts were made to obtain near-vertical images vibration-damped motion-compensating cradle. by tightly circling the breeding colonies at an 21 77 Counts of pups are made directly from the photo- altitude of approximately 200 m. graphs on a microfiche reader, which magnifies Five surveys were carried out at the Blasket 23 79 photos by 22 times (Hiby, Thompson, & Ward, Islands, Co. Kerry during September, October and 1988). Furthermore, grey seal populations have November 2003. The survey method was based on 25 81 been surveyed by aerial means throughout most that used by the Sea Mammal Research Unit (SMRU) part of their geographical range in the North at the University of St. Andrews, Scotland, to 27 83 Atlantic and the Baltic Sea; in Canada, the US, census the British grey seal population (Hiby et al., Iceland, Sweden, Finland and Norway (Bowen, 1988). Each colony is surveyed between four and six 29 85 McMillan, & Mohn, 2003; Corkeron, Nilssen, & times through the breeding season at intervals of Haug, 2003; Hammill, Gosselin, & Stenson, 2003; 10–12 days. Known breeding sites used in 1995 and 31 87 Harding & Ha¨rko¨nen, 1999; Hauksson, 2003; Wood 1996 (Kiely & Myers, 1998) and potential breeding & Brault (2003)). Aerial survey had not been tried in sites were surveyed. Potential breeding sites were 33 89 Ireland before, as it was previously thought that a identified based on the availability of suitable significant proportion of the population could be habitat for pupping. 35 91 missed, due to seals breeding in caves or narrow Additional surveys were carried out at the gullies where aerial photography would be very Inishkea Group, Co. Mayo and along the coast of 37 93 difficult. However, developments in digital tech- Donegal in October and November, respectively. nology and familiarity of researchers with a large These were single surveys, primarily to determine 39 95 proportion of the grey seal breeding habitat in the feasibility of surveying these locations by air. Ireland, indicated that aerial survey methods might Known and potential breeding sites were surveyed. 41 97 be used to survey large areas of the coastline and Recent information on existing breeding sites was offshore islands during the grey seal breeding available for the Inishkea Group (O´ Cadhla & 43 99 season. This would include many sites that are Strong, 2003). Efforts were made to collate difficult to access either by land or by boat. information on breeding sites in Co. Donegal using 45 101 The feasibility of using aerial methods to survey historical records, unpublished reports and local grey seal populations along large areas of the Irish knowledge (Fig. 2). 47 103 coastline and offshore islands during the breeding Adobe Photoshop software was used to view the season first needed to be tested before the images. Pups were counted from colour photo- 49 105 technique can be considered for a national census. graphs and classified into three determinable The followingUNCORRECTED surveys were carried out: a series of stages: whitecoats, PROOF moulted and dead. Dead pups 51 107 successive aerial surveys at the Blasket Islands, Co. appeared thin and flaccid compared to live pups Kerry with a view to determining local pup (Fig. 3(ii)). 53 production and an estimate of the size of the 109 associated population; one aerial survey of key 55 breeding colonies among the Inishkea Group, Co. 111 Mayo in order to cross-reference with ground Please cite this article as: Cronin, M. A., et al. Aerial surveying of grey seal breeding colonies on the Blasket Islands, Co. Kerry, the Inishkea Group, Co. Mayo and the Donegal Coast, Ireland. Journal for Nature Conservation, (2006), doi:10.1016/j.jnc.2006.11.001 JNC : 25053 ARTICLE IN PRESS Aerial surveying of grey seals in Ireland 3 1 57 3 59 5 61 7 63 9 65 11 67 13 69 15 71 17 73 19 75 21 77 23 79 25 81 27 83 29 85 31 87 33 89 35 91 37 93 Figure 1. Map of areas surveyed by air during the 2003 grey seal breeding season; breeding sites used during this season 39 identified at the Blasket Islands, Co. Kerry and the Inishkea Group, Co. Mayo (refer to Tables 2 and 3 for site names). 95 41 Pup production estimates and associated Myers, Hammill, & Stenson, 1997). At least four 97 population size surveys are required to estimate pup production 43 and the parameters of the birth date function; 99 The duration of the pupping season exceeds the additional surveys improve the estimates of the 45 minimum length of stay of a pup and therefore only individual parameters of the birth date function 101 a fraction of the total pup production at a colony is (Duck, Hiby, & Thompson (unpublished)). 47 present on any one occasion. Birth rate as a Pup production is linked to total population size 103 function of date can be estimated by fitting a by female fecundity and survival from birth to first 49 series of one or more counts in which pups are reproduction.