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Mapping the path of the biggest fish: The whale shark from the Mexican Pacific side

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Abstract

The 4th International Whale Shark Conference, 16–18 May 2016, Doha, Qatar
OPEN ACCESS The 4th International Whale Shark Conference, 16–18 May 2016, Doha, Qatar
Cite this article as: Ramírez-Macías D, Vázquez-Haikin A, Luja V, Murillo R, Mata R. Mapping the
path of the biggest sh: The whale shark from the Mexican Pacic side. QScience Proceedings
(The 4th International Whale Shark Conference) 2016:iwsc4.46 http://dx.doi.org/10.5339/
qproc.2016.iwsc4.46
http://dx.doi.org/10.5339/
qproc.2016.iwsc4.46
2016 Ramírez-Macías,
Vázquez-Haikin, Luja, Murillo, Mata,
licensee HBKU Press. This is an open
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Attribution license CC BY 4.0, which
permits unrestricted use, distribution
and reproduction in any medium,
provided the original work is properly
cited.
1Tiburón Ballena México de Conciencia
México, México
2Asociación de Pesca Deportiva y
Ecoturismo de Bahía de los Ángeles,
México
3Universidad Autónoma de Nayarit, México.
4Experiencias eco turísticas Mata, México.
*Email: tiburonballena@gmail.com
Mapping the path of the biggest
sh: The whale shark from the
Mexican Pacic side
Dení Ramírez-Macías1,*, Abraham Vázquez-Haikin2, Victor Luja3,
Ricardo Murillo3, Roberto Mata4
Background
Monitoring of animal populations is critical for proper management. To have a better understanding
of the population dynamics and migratory pattern of the whale shark, data is required from locations
close to key aggregation sites where hypothesized connections can be validated. Photo-ID is an
eective marker for capture-mark-recapture studies. Underwater photographs of sharks, combined
with photo-comparison soware, are used to identify re-sighted sharks, which, in turn, contribute
to estimations of population size, age structure, sex ratio, site delity, trends in abundance, and
movement patterns.
Approach
Since 2003 we have established and maintained a photographic identication research program in
the Gulf of California, at Los Angeles Bay (LAB), La Paz Bay (LPB), Espiritu Santo Island (ESI) and Los
Cabos (LC), and since 2010 at the Archipelago of Revillagigedo (AR, at the Mexican Pacic). Recently,
we included Nayarit (Na, in the Mexican Pacic) to the study area, San Luis Gonzaga (SLG) and Coyote
Bay (CB, Gulf of California) in order to address if connectivity exists in this region.
Results
The whale sharks appear to segregate by size. In coastal waters of LAB (n=501), LPB (n=380),
SLG (n=51), Na (n=36), and CB (n=16) aggregations are exclusively juvenile sharks (<8 m). In the
oceanic waters of ESI (n=20) and LC (32), pregnant adult females (>9 m) aggregate. At AR (n=11)
both pregnant females and juveniles exist but are separated by time. From 2003 to 2014 we have
identied 898 sharks over the course of the study; of these 841 were juveniles and 57 were adults,
mainly pregnant females. Photo-identication showed the movements of 133 juvenile sharks between
LAB, LPB, SLG, Na and CB and movement of 2 pregnant females between LC and AR. We found high
levels of delity in the juveniles. For example in LPB up to 61% of the juveniles have been re-sighted
between years. In contrast only one pregnant female has been re-sighted at the same locality
aer 7 years.
Conclusions
This study demonstrated the importance of a collaborative eort to have a better understanding of
the population on a regional level. The connectivity data showed the necessity to generate a regional
conservation strategy; of the eight localities where we study these gentle giants, currently three are
protected, the other four require protection.
Keywords: Mexican Pacic, photo-identication, movements, conservation, collaboration
Article
Full-text available
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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