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Preliminary observations on whale sharks in Nosy Be, Madagascar

Authors:
Stella Diamant
Stella Diamant
Stella Diamant
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Simon James Pierce at Marine Megafauna Foundation
Simon James Pierce
Deni Ramirez-Macias
Deni Ramirez-Macias
Deni Ramirez-Macias
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Michael Heithaus at Florida International University
Michael Heithaus
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Abstract

Background The northern Mozambique Channel is a global hotspot for whale shark sightings, based on observer records from the tuna purse-seine fleet and published literature. Nosy Be Island (NW Madagascar) hosts a flourishing marine tourism industry based on viewing whale sharks and other species. Following reports of declining sightings in other regional hotspots, such as Tofo in Mozambique, it is important to establish if these declines represent a simple shift in aggregation site, or a broader reduction. Approach Data on population structure were also collected during a preliminary field season from August to December 2015. Results Approximately 200 sightings were recorded by a single operator during 2015. Preliminary analysis indicates that the majority of whale sharks sighted were males of lengths between 3 and 10 meters. Most whale shark sightings were from October to December. Conclusions Regular whale shark sightings occur off the Nosy Be area from August to December. Limited sex and size data suggests a juvenile male-biased aggregation where whale sharks were most commonly observed traveling and feeding on copepods. New data will help to establish whether oceanographic variability has resulted in a shift in abundance to Madagascar, or whether a broad-scale decline has taken place. No species-level legislation protects whale sharks in Madagascar, and the whale shark tourism industry is presently unregulated with regard to interactions. Further work on the population ecology, movements and social importance of whale sharks in the country is justified and will inform the development of effective conservation and tourism management initiatives.
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OPEN ACCESS The 4th International Whale Shark Conference, 16–18 May 2016, Doha, Qatar
Cite this article as: Diamant S, Pierce SJ, Ramírez-Macías D, Heithaus MR, d’Echon AG,
d’Echon TG, Kiszka JJ. Preliminary observations on whale sharks in Nosy Be, Madagascar.
QScience Proceedings (The 4th International Whale Shark Conference) 2016:iwsc4.15
http://dx.doi.org/10.5339/qproc.2016.iwsc4.15
http://dx.doi.org/10.5339/
qproc.2016.iwsc4.15
2016 Diamant, Pierce, Ramírez-
Macías, Heithaus, Guillemain
d’Echon, Guillemain d’Echon, Kiszka,
licensee HBKU Press. This is an open
access article distributed under
the terms of the Creative Commons
Attribution license CC BY 4.0, which
permits unrestricted use, distribution
and reproduction in any medium,
provided the original work is properly
cited.
1Marine Megafauna Foundation, USA
2Whale Shark Mexico, Mexico
3Florida International University, USA
4Baleines Rand’eau, Madagascar
*Email: stella.diamant@gmail.com
Preliminary observations on whale
sharks in Nosy Be, Madagascar
Stella Diamant1,*, Simon J. Pierce1, Dení Ramírez-Macías2,
Michael R. Heithaus3, Arthur Guillemain d’Echon4,
Tanguy Guillemain d’Echon4, Jeremy J. Kiszka3
Background
The northern Mozambique Channel is a global hotspot for whale shark sightings, based on observer
records from the tuna purse-seine fleet and published literature. Nosy Be Island (NW Madagascar)
hosts a flourishing marine tourism industry based on viewing whale sharks and other species.
Following reports of declining sightings in other regional hotspots,such as Tofo in Mozambique,
it is important to establish if these declines represent a simple shi in aggregation site, or a
broader reduction.
Approach
Data on population structure were also collected during a preliminary eld season from August to
December 2015.
Results
Approximately 200 sightings were recorded by a single operator during 2015. Preliminary analysis
indicates that the majority of whale sharks sighted were males of lengths between 3 and 10 meters.
Most whale shark sightings were from October to December.
Conclusions
Regular whale shark sightings occur o the Nosy Be area from August to December. Limited sex and
size data suggests a juvenile male-biased aggregation where whale sharks were most commonly
observed traveling and feeding on copepods. New data will help to establish whether oceanographic
variability has resulted in a shi in abundance to Madagascar, or whether a broad-scale decline has
taken place. No species-level legislation protects whale sharks in Madagascar, and the whale shark
tourism industry is presently unregulated with regard to interactions. Further work on the population
ecology, movements and social importance of whale sharks in the country is justied and will inform
the development of eective conservation and tourism management initiatives.
Keywords: photo-identication, population ecology, Madagascar, Indian Ocean
Does bathymetry drive coastal Whale Shark (Rhincodon typus) aggregations?
Article
Full-text available
  • Jun 2018
Background The whale shark ( Rhincodon typus ) is known to aggregate in a number of coastal locations globally, however what causes these aggregations to form where they do is largely unknown. This study examines whether bathymetry is an important driver of coastal aggregation locations for R. typus through bathymetry’s effect on primary productivity and prey availability. This is a global study taking into account all coastal areas within R. typus’ range. Methods R. typus aggregation locations were identified through an extensive literature review. Global bathymetric data were compared at R. typus aggregation locations and a large random selection of non-aggregation areas. Generalised linear models were used to assess which bathymetric characteristic had the biggest influence on aggregation presence. Results Aggregation sites were significantly shallower than non-aggregation sites and in closer proximity to deep water (the mesopelagic zone) by two orders of magnitude. Slope at aggregation sites was significantly steeper than non-aggregation sites. These three bathymetric variables were shown to have the biggest association with aggregation sites, with up to 88% of deviation explained by the GLMs. Discussion The three key bathymetric characteristics similar at the aggregation sites are known to induce upwelling events, increase primary productivity and consequently attract numerous other filter feeding species. The location of aggregation sites in these key areas can be attributed to this increased prey availability, thought to be the main reason R. typus aggregations occur, extensively outlined in the literature. The proximity of aggregations to shallow areas such as reefs could also be an important factor why whale sharks thermoregulate after deep dives to feed. These findings increase our understanding of whale shark behaviour and may help guide the identification and conservation of further aggregation sites.
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