Trends in sightings and environmental influences on a coastal aggregation of manta rays and whale sharks

Rohner, Christoph A.; Pierce, Simon J.; Marshall, Andrea D.; Weeks, Scarla J.; Bennett, Michael B.; Richardson, Anthony J.

doi:10.3354/meps10290

“…These aggregations leave the species vulnerable to targeted fisheries. The rising demand for mobulid products in Asia has led to increasing targeted fisheries for Manta and Mobula species in several parts of the world , and local M. alfredi populations have declined in some fished areas (Marshall et al 2011b;Rohner et al 2013). The species is vulnerable to localise fishing pressure because of its conservative life history strategy (i.e.…”

mentioning

confidence: 99%

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

Couturier

¹

,

Dudgeon

²

,

Pollock

³

et al. 2014

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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.

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“…160 conditions.!Current!direction!and!strength!can!influence!the!cleaning!behaviour!of!mantas! 161 (Rohner!et!al.,!2013)!and!were!included!in!the!models.!The!sightability!of!animals!at!these! 162 sites!can!be!influenced!by!underwater!visibility!…”

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confidence: 99%

Steep declines in sightings of manta rays and devilrays (Mobulidae) in southern Mozambique

Rohner

¹

,

Flam

²

,

Pierce

³

et al. 2017

Preprint

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Mobulid rays are one of the most vulnerable chondrichthyan groups due to their low population growth rates and high susceptibility to fisheries. While estimates of human-induced mortality are lacking, sighting trend data can provide an index of their status. We recorded underwater sightings data of Mobula alfredi, M. birostris and M. kuhlii over a 14-year period in southern Mozambique. Generalised linear models were used to standardise sightings and adjust for influences other than time. Standardised sightings of the three species, individually, declined by >90%. Declines in sightings were driven primarily by a rapid decrease between 2003–2007, although the declines continued to 2016. While environmental variables did influence sightings, they did not explain this steep decline over time. Increasing mortality from fisheries is likely to have played a significant role in the declining sightings of these vulnerable species.

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“…(Agenbag!et!al.,!2003;!Jaine! 157 et!al.,!2012;!Rohner!et!al.,!2013).!Observers!recorded!weather!conditions!in!four!categories! 158 (sunny,!partial!overcast!(0-50%!cloud!cover),!overcast!(51-100%!cloud!cover),!or!raining)!to!…”

mentioning

confidence: 99%

Steep declines in sightings of manta rays and devilrays (Mobulidae) in southern Mozambique

Rohner

¹

,

Flam

²

,

Pierce

³

et al. 2017

Preprint

View full text Add to dashboard Cite

Mobulid rays are one of the most vulnerable chondrichthyan groups due to their low population growth rates and high susceptibility to fisheries. While estimates of human-induced mortality are lacking, sighting trend data can provide an index of their status. We recorded underwater sightings data of Mobula alfredi, M. birostris and M. kuhlii over a 14-year period in southern Mozambique. Generalised linear models were used to standardise sightings and adjust for influences other than time. Standardised sightings of the three species, individually, declined by >90%. Declines in sightings were driven primarily by a rapid decrease between 2003–2007, although the declines continued to 2016. While environmental variables did influence sightings, they did not explain this steep decline over time. Increasing mortality from fisheries is likely to have played a significant role in the declining sightings of these vulnerable species.

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Trends in sightings and environmental influences on a coastal aggregation of manta rays and whale sharks

Cited by 121 publications

References 62 publications

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

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

Steep declines in sightings of manta rays and devilrays (Mobulidae) in southern Mozambique

Steep declines in sightings of manta rays and devilrays (Mobulidae) in southern Mozambique

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