First photographic evidence of oceanic manta rays (Mobula birostris) at two locations in the Fiji islands

Abstract

Until the revision of the genus Manta in 2009, when a second manta species (Manta alfredi) was resurrected based on morphological and meristic data, all available records in Fijian literature were recorded as Manta birostris. Subsequently, documented sightings were recorded as M. alfredi. Another reclassification of the genus Manta was undertaken in 2018 when both manta ray species (Manta alfredi, Manta birostris) were moved to Mobula based on phylogenetic analysis. Here, we present the first unequivocal evidence of oceanic manta ray (Mobula birostris) occurrence in Fijian waters. In November 2018, two individuals were sighted foraging in Laucala Bay, a large lagoon adjacent to Suva, the capital city of Fiji. Subsequently, three more individuals were sighted in December 2018, two individuals in July 2020, at least six individuals were observed in November 2021, and eight individuals in May/June 2022, all foraging in the same geographical area. Unique ventral identification patterns could be obtained for nine individuals, and all nine individuals have been re-sighted since first identification, with one individual being documented in 2018, 2020, 2021 and 2022. Two additional individuals were recorded in the Yasawa Island Group in the west of Fiji while passing through and foraging in a channel between Drawaqa and Naviti Island in April and September 2020. We provide photographic identification of ten M. birostris individuals from two sites and discuss our findings in the context of local environmental parameters and other recorded sightings in the South Pacific region. In light of the global extinction risk of M. birostris and the recent reclassification from Vulnerable to Endangered on the Red List of Threatened Species, the expansion of their known distribution range to Fijian waters and the recurrence of individuals over consecutive years in the same location adds valuable information for the development of effective and data-driven conservation strategies.

Comparative population genomics of manta rays has global implications for management

“…As a result of these differences in habitat use, M. alfredi and M. birostris have long been considered to display marked differences in their migratory abilities and levels of gene flow. Yet, only a handful of long-distance movements have ever been recorded in M. birostris (Andrzejaczek et al, 2021; Knochel, Cochran, et al, 2022) alongside observations of site-fidelity (Cabral et al, 2023; Garzon et al, 2023; Gordon & Vierus, 2022), raising questions about the extent to which population structure and genetic variation may differ across species. To date, assessments of genetic differentiation in M. alfredi have focussed on local and regional patterns (Lassauce et al, 2022; Venables et al, 2021; Whitney et al, 2023) and we have little understanding of how genetic variation is distributed across the species’ range.…”