Characteristics of a manta ray Manta alfredi population off Maui, Hawaii, and implications for management

Published on 16. May 2011

Mark H. Deakos, Jason D. Baker, Lars Bejder


Late maturity, few offspring and a residential nature are typical characteristics of Manta
alfredi that make this species vulnerable to localized anthropogenic threats. Improving its life history
information is crucial for successful management. A total of 229 surveys was conducted from 2005 to
2009 at a manta ray aggregation site off Maui, Hawaii, to qualitatively and quantitatively describe the
abundance, movements and temporal habits of this population. Photo-identifications revealed 290
unique individuals, but a discovery curve showed no asymptotic trend, indicating that the number of
individuals using the area was much larger. Resightings and manta ray follows revealed that this population
and a population off the Big Island may be independent, island-associated stocks. High
resighting rates within and across years provided strong evidence of site fidelity. Findings were consistent
with a population of manta rays moving into and out of the Maui aggregation area, with a
varying portion of the total population temporarily resident at any given time. Males, accounting for
53% of all individuals, resided for shorter periods than females around the study area. Manta rays
were usually absent at first light with numbers increasing throughout the day. More frequent mating
trains were observed during the winter months. Shark predation was evident in 33% of individuals,
and 10% had an amputated or non-functional cephalic fin. This small, demographically independent
population appears vulnerable to the impacts from non-target fisheries, primarily from entanglement
in fishing line, and could suffer from exploitation by commercial, unregulated ‘swim-with manta ray’
programs. Management on an island-area basis is recommended.


Vol. 429: 245–260, 2011, doi: 10.3354/meps09085

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