Urban manta rays: potential manta ray nursery habitat along a highly developed Florida coastline

Jh Pate,Ad Marshall

doi:10.3354/esr01054

Abstract

The giant oceanic manta rayMobula birostriswas listed in the US Endangered Species Act as a threatened species in 2018, yet insufficient data exist on manta populations throughout US waters to designate critical habitat. Taxonomic and genetic evidence suggests that manta rays in the Western Atlantic are a separate species (M.cf.birostris) and little is understood about the ecology and life history of this putative species. The juvenile life stage of bothM. birostrisandM.cf.birostrisis particularly understudied. Here, we are the first to describe the characteristics of a manta ray population along a highly developed coastline in southeastern Florida using boat-based surveys and photo identification of individuals. Fifty-nine manta individuals were identified between 2016 and 2019. All males were sexually immature based on clasper development, and 96% of females were classified as immature based on size and absence of mating scars or visible pregnancies. Twenty-five (42%) individuals were observed more than once during the study period and 8 individuals were sighted over multiple years. The occurrence of juveniles, high site fidelity and extended use of the study area by juvenile manta rays suggest that southeastern Florida may serve as a nursery habitat. High occurrence of fishing line entanglement (27% of individuals) and vessel strike injury were documented, and rapid wound healing was observed. Future research and conservation efforts will focus on identifying the physical and biological features of the potential nursery habitat and on mitigation of anthropogenic impacts.

Highlights

Manta rays (Mobula birostris and M. alfredii) are classified as Vulnerable on the IUCN Red List, mainly due to targeted fishing and bycatch (Marshall et al 2018)
Documenting nursery habitats is a priority in manta ray research and conservation (Stewart et al 2018a), yet only 2 nurseries (Mobula birostris in Texas, USA: Stewart et al 2018b; M. alfredi in Indonesia: Germanov et al 2019a) have been identified that meet the criteria of an elasmobranch nursery habitat (Heupel et al 2007)
Lucie Inlet and Boynton Beach Inlet in southeast Florida has been identified as a potential nursery habitat for manta rays

Summary

Introduction

Manta rays (Mobula birostris and M. alfredii) are classified as Vulnerable on the IUCN Red List, mainly due to targeted fishing and bycatch (Marshall et al 2018). Manta and mobula rays have been targeted globally for their gill plates, which are transported and sold in Asia as health tonics (Dulvy et al 2014, Croll et al 2016). The conservative life-history traits of manta rays (i.e. late age of maturity, long gestation period, low fecundity) make them susceptible to exploitation (Dulvy et al 2014) and rising anthropogenic threats. M. alfredi associates with neritic habitats and is the better studied of the 2 manta

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