Population dynamics of the reef manta ray Manta alfredi in eastern Australia

Abstract

The reef manta ray Manta alfredi aggregates at several sites along the east coast of Australia. Photographic identification and mark-recapture methods were used to report on the site affinity, size and structure of this population of M. alfredi. A total of 716 individuals were identified in 1982-2012, including 636 at Lady Elliot Island (LEI), southern Great Barrier Reef. Over 60 % of individuals identified were resighted at least once during the study period. Multiple resightings within and among years imply a high degree of site affinity by individuals to aggregation sites. One individual was sighted 11 times at LEI over a 30-yr period. The sex ratio of this population was significantly biased towards females (1.2:1 female-tomale ratio), and females were more commonly resighted than males. Robust design population models were used to estimate the population size of the winter aggregation at LEI over a 4-yr period. The models estimated up to 456 (95 % CI 399-535) M. alfredi individuals in the population within one winter season and a high annual apparent survival. This study demonstrated that waters around LEI form a key aggregation site for a large portion of the M. alfredi population in east Australian waters.

The geographic distribution of reef and oceanic manta rays (Mobula alfredi and Mobula birostris) in Australian coastal waters

“…It is well-established that M. alfredi exhibits strong migratory behaviour and movements of up to 500 km are not uncommon (Couturier et al, 2011;Germanov & Marshall, 2014;Jaine et al, 2014), with few confirmed dispersals in Australia up to 1150 km . Individual rays have demonstrated affinity for particular sites and regions (Braun et al, 2015;Couturier et al, 2014;Kessel et al, 2017;Marshall et al, 2011), although most photo-ID and tagging studies have focused on populations separated by large distances and/or by regions of deep water (Deakos et al, 2011).…”

Sex-Specific Patterns in Abundance, Temporary Emigration and Survival of Indo-Pacific Bottlenose Dolphins (Tursiops aduncus) in Coastal and Estuarine Waters

“…Photo-ID has been widely used across taxonomic groups, such as terrestrial and marine mammals (Kelly, 2001;Langtimm et al, 2004), reptiles (Schofield et al, 2008;Gardiner et al, 2014) and fish (Couturier et al, 2014;Kanive et al, 2015). Photo-ID is considered a largely non-invasive method by which animals are initially "captured" in photographs, and subsequently matched through photographic "recaptures" to create an individual's capture history.…”

Long-term body pigmentation changes on a manta ray (Mobulidae)

“…Individual manta rays have been identified from patterns of ventral markings in recent studies to assess the population size of M. alfredi in Hawaii (Deakos, Baker & Bejder, 2011), Mozambique (Marshall, Dudgeon & Bennett, 2011c), the Maldives (Kitchen-Wheeler, Ari & Edwards, 2012), and Australia (Couturier et al, 2014), or the seasonal occurrence of M. birostris in Brazil (Luiz et al, 2009). To identify individual manta rays, Luiz et al (2009) and Deakos et al (2011) used the entire ventral pattern of each individual sighted, whereas Marshall et al (2011c) defined the standardized region as a rectangle-shaped area extending posterior from the anterior margins of the anterior gill slits, including the pelvic fins.…”

“…The software MANTA MATCHER, used for individual identification, also relies on the spot patterns in the rectangular area on the ventral side, including the spot markings at the end of the gill slits (Town, Marshall & Sethasathien, 2013, Fig. 1A), and the same rectangular area was also used by Couturier et al 2014.…”