A First Look At Whale Sharks In Hawaiian Waters

With baited breath, the underwater photographer bobbed at the surface of the ocean, eyes scanning the turquoise blue around them. The excursion leader had coaxed them into the water, assuring them their target was on its way.

As the largest fish in the sea, you wouldn’t think it would be that hard to spot a whale shark (Rhincodon typus). Reaching lengths of 18 – 20 meters (59 – 66 feet) long, the star-studded filter feeders are surprisingly well camoflauged, making them hard to see until the endangered species is practically on top of you. Having a circumglobal distribution in tropical and warm temperate seas where it can be found in both pelagic and coastal habitats, they are highly mobile and have been tracked through satellite telemetry to travel between 10 – 30 kilometers (6.2 – 18.6 miles) per day, and are capable of long-distance movements of over 1,000 km (621 mi).

But today, in Hawai’i, a chance encounter allows for the perfect shot – for both photographer and citizen science efforts.

Whale shark locations of known ‘constellations’ include the Gulf of California and Quintana Roo (Mexico), Ningaloo Reef (Western Australia), Inhambe Province (Mozambique), and multiple sites in the Philippines, amongst others. Most of these sites are dominated by juvenile male whale sharks, highlighting the persistent knowledge gaps scientists have about these majestic giants, including the unknown areas where adults, neonates and juvenile females spend the majority of their time.

“The main Hawaiian Islands are not known to have large aggregations of whale sharks; however, they have been anecdotally reported here with some regularity. To date, little is known about this charismatic species in Hawaiian waters,” say the authors of a new study. “This study is the first effort to examine whale shark demographics and movements in a previously unstudied region of the world.”

What makes this research special is that not only did scientists team up to study these animals, but citizen science was used to investigate the abundance, seasonality (if any) and occurrence of whale sharks in the waters around the main Hawaiian Islands. “Hawai’i Uncharted Research Collective (HURC), a Hawai’i-based non-profit research organization, started an online social media and community outreach campaign on 9 October 2017. Through various education outlets and public presentations, members of the community were asked to submit photos and videos of both current and past whale shark sightings in Hawaiian waters,” the authors explained. “Along with the photos or videos, it was requested that submissions include sighting information including date of sighting, approximate location, time of day when sighted, estimated size of the animals and the sex. Sightings could be submitted through the HURC website with a form that prompted the user for the above information or by email.” Getting people to participate seemed to be easy, as the community members were given the opportunity to name the individual whale shark if they provided clear and identifiable images or footage of the left side, and the individual was identified as unique to the growing catalogue.

The turn-out was incredible: a total of 309 individual whale sharks were identified from sightings between 1991–2020 by their unique spot patterns, most of which (74%) were reported between 2018 and 2020. Both juvenile and mature males and females were seen represented in the dataset. The data also suggests that these individuals sighted in Hawaiian waters are most likely transient in nature, passing by as they make their way to their final destination. This supports the empirical data, which shows 88% of sharks were only sighted once. “To further understand their movement patterns and habitat use, monitoring will continue through citizen science and photo-ID to understand their long-term abundance and seasonal trends in Hawai’i, and how these movements relate to global patterns,” the authors conclude. “International cross-matching with similar whale shark research programmes on both sides of the Pacific Ocean (i.e. Baja California, Galapagos and Peru to the east, and Philippines, Indonesia, Taiwan and Japan to the west) will help to understand if whale sharks sighted in Hawai’i are indeed moving across ocean basins.”

Assessed as Largely Depleted by the IUCN Green Status of Species, the authors believe that highlighting Hawai’i as an important habitat for the whale shark – mainly as a migratory corridor or navigational waypoint – is a crucial step in understanding their ecology in the Pacific in order to develop effective management plans.

#Whale #Sharks #Hawaiian #Waters

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