Jarvis: A Giant Surprise

By Kevin Lino

A whale shark was spotted at Jarvis Island for the first time by researchers from the Coral Reef Ecosystem Division.

The island of Jarvis is consistently exciting for coral reef researchers, as this remote equatorial haven is full of colorful life and diversity within its pristine waters. Whether it’s your first or tenth trip to this isolated island, you are certain to be humbled and mesmerized by nature’s creativity and splendor. The 2012 US Line Islands research expedition followed through on that standard and possibly even raised the bar a notch or two. One specific reason was the first recorded whale shark (by Coral Reef Ecosystem staff), Rhincodon typus, in the tropical waters off Jarvis Island. It was not odd to see or expect such a huge shark; the largest fish in the world actually, taking advantage of the waters surrounding Jarvis. Jarvis is a highly productive environment, owing to the current-driven vertical uplift of dense, cool, nutrient-rich water towards the ocean surface, replacing the warmer, nutrient-depleted surface water (see previous blog post “The Oceanographic Conditions at Jarvis Island”). But with limited opportunity to explore these waters just a few days every couple of years, this was our first sighting.

The whale shark is a slow-moving distinctively-marked fish that is the only member of the genus Rhincodon and family, Rhincodontidae, belonging to the subclass Elasmobranchii (which also includes sharks, skates and rays) and class Chondrichthyes, or cartilaginous fish. The species originated about 60 million years ago and is found in tropical and warm oceans where it lives in the open sea with a lifespan of about 70 years. Whale sharks migrate both to feed and possibly to breed. 

Oceanographer Chip Young, hovering.

This peaceful giant was observed by several scientific teams, lazing near the surface throughout the first day of field operations. Without much concern for us, the inquisitive behemoth lounged around and investigated the researchers that temporarily occupied its serene realm. After circling amongst the divers and taking in the new temporary occupants, the whale shark drifted off into the abyss only to reappear later in the day to reenact the same behavior. Despite being longer than each of the small vessels we use for research, this magnificent specimen was ~20 feet long and therefore fairly young, as whale sharks have been known to reach lengths of up to 12.65 meters (41.50 ft) and weigh up to 21.5 tonnes (47,000 lb). Although large, whale sharks do not pose any significant danger to humans as they're docile fish and are actually quite gentle, sometimes interacting with divers.

Because of their size, whale sharks have very large mouths but primarily feed on small plants and animals, including macro-algae, plankton, krill, larvae, and other nektonic life such as small squid or vertebrates. Whale sharks also feed on small fish as well as clouds of eggs and sperm during mass spawning of fish shoals. Feeding occurs either by ram filtration, in which the animal opens its mouth and swims forward, pushing water and food into its mouth, or by active suction feeding, in which the animal opens and closes its mouth, sucking in volumes of water that are then expelled through the gills.

Not to take away from the many other observations and encounters with various wildlife over several days of scientific operations, but the time spent with this docile nomad was an unforgettable experience for the researchers participating in this expedition, reinforcing Jarvis Island as one of the most remote and amazing coral reef ecosystems we have the privilege to experience.