The Editor says: Have you ever spotted cetaceans in Taiwan? Deep-diving cetaceans have been sighted in the waters off Hualien and Taitung, but documented records are extremely scarce. If you ever hope to see them with your own eyes, good weather is essential — but what you really need is luck! So how exactly are these deep-sea species studied and surveyed? Follow along with BlueTrend to find out! <Full article reprinted from the Kuroshio Ocean Education Foundation; Written by Hu Jie-Xi2024.02.15>
Deep-diving cetaceans never fail to spark our curiosity, and they carry an air of mystery, as if perpetually veiled in a layer of fine gauze. Among the cetacean friends familiar to Kuroshio, there is a group of deep-sea eccentrics — including sperm whales (Physeter macrocephalus), beaked whales (Ziphiidae), pygmy sperm whales (Kogia breviceps), and dwarf sperm whales (Kogia sima). As unpredictable as cats, every sighting of one of these creatures feels as thrilling as winning the lottery.
Encountering Deep-Sea Mystery Visitors off Hualien
"It's a beaked whale — everyone seize the moment, they may dive again in just a few seconds!" the naturalist guide called out.
With adrenaline surging and camera shutters clicking, a few seconds passed — and then the beaked whales slowly arched their backs and vanished into depths the naked eye could never reach.
A rare sighting of Cuvier's beaked whale in the waters off Hualien — the current world record holder for deepest dive. photo credit: Jiang Wen-Long
Deep-diving cetaceans are like a band of mystery visitors. Take Cuvier's beaked whale (Ziphius cavirostris) as an example: the longest recorded dive for this species exceeds three hours. Compare that to a typical whale-watching cruise, which lasts only 1.5 to 2 hours — meaning that from the moment a boat leaves port to the moment it returns, these whales may never have surfaced at all. Because these mystery visitors spend so much time active or foraging in the deep sea, sighting data is extremely limited — not just in Taiwan, but internationally as well. As a result, scientists have great difficulty analyzing information on their distribution, life history, and population size. A look at the IUCN Red List reveals that the status of most beaked whale species remains listed as Data Deficient.
How Is the International Community Studying Deep-Diving Cetaceans?
The deep sea below 2,000 m is cold, lightless, and subject to pressure hundreds to thousands of times greater than at the surface. So how does one go about studying deep-diving cetaceans? In terms of population size and distribution research, because sighting records for deep-sea species are so scarce, several studies have employed species distribution models — using factors such as surface chlorophyll concentration, water depth, and the location of potential prey areas — to predict where suitable habitat might exist. There is also ongoing work in the Northeast Atlantic that combines transect surveys from multiple ocean regions to estimate population size.
Satellite-linked tag records for Cuvier's beaked whales off the coast of North Carolina, 2014–2017. Colored tracks show cetacean movement paths; yellow circles indicate tagging locations (image source).
To understand the dive depths, home ranges, preferred habitats, and physiology of deep-sea species, satellite-linked tags are another research method. Because tag deployment is an invasive procedure, its use on wild cetaceans in Taiwan is still being evaluated for risk and feasibility, even though some terrestrial wildlife tagging programs are already underway¹. Given just how elusive deep-sea species are, researchers have also begun collecting trace amounts of environmental DNA (eDNA) left behind in the water column as evidence of their presence — a method analogous to inferring which animals have passed through an area by examining tracks and droppings. Stranded individuals, meanwhile, can yield genetic and age-structure data, as well as clues about what the animals ate during their lifetimes.
Hualien Is a Blessed Stretch of Sea
By this point, readers may be wondering: deep-sea species research sounds like one big challenge — so why did Phase II of the Ocean Oasis Project take on such a demanding subject? Based on more than 20 years of research in Hualien waters and the whale-watching sighting records we have compiled, there are in fact quite a few documented occurrences of these species off Hualien. This may well be connected to the underwater topography of the nearshore zone, where the seafloor plunges to depths of over a thousand metres just a short distance from shore. At the same time, experienced fishermen report that squid and other cephalopods are more readily caught in deeper waters — and cephalopods happen to be a critical food source for these deep-sea species.
The waters off Hualien at dusk, with the Coastal Mountain Range in the background. photo credit: Kuroshio Ocean Education Foundation.
The waters off Hualien are, in fact, a highly promising survey ground for deep-sea species — one capable of filling critical data gaps for Taiwan and even for the international scientific community. This year, we will launch 20 offshore cetacean surveys, focusing primarily on recording deep-sea species such as Risso's dolphins (Grampus griseus), sperm whales, beaked whale family species, and members of the genus Kogia, documenting their spatiotemporal distribution alongside environmental variables. Because these animals tend to congregate farther offshore, our survey transects will extend further out to sea — bridging the data gap beyond the reach of conventional whale-watching routes and bringing the true faces of these deep-sea creatures to light, one by one.
This article is reprinted with permission from the Kuroshio Ocean Education Foundation. Original title: World Whale Day: The Survey of Deep-Sea Mystery Visitors Has Officially Begun!
Editor in Charge: Jenny Tsai
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