The North Pacific dolphin that looks like a seal and lacks a dorsal fin

Nature · Published 3 October 2026 · Updated 22 October 2026 Swipe more like this →

In short: In the deep, cold waters of the North Pacific, a sleek, finless creature often mistaken for a sea lion glides through the waves. These acrobatic dolphins can reach speeds of 22 miles per hour, leaping gracefully across the surface in groups that sometimes swell to 3,000 individuals.

The northern right whale dolphin (Lissodelphis borealis) is a biological outlier in the North Pacific. It is the only dolphin species in the region that lacks a dorsal fin, a feature that contributes to its streamlined, dark appearance. Because of this, observers at sea sometimes misidentify them as herds of fur seals or sea lions. They are relatively small, measuring roughly 6.5 to 10 feet in length and weighing between 130 and 250 pounds. Their physical design supports high-speed travel, allowing them to maintain average speeds of 16 miles per hour with bursts reaching 22 miles per hour.

These mammals are highly social, typically traveling in groups of 100 to 200, though they occasionally congregate in massive pods of up to 3,000. Their behavior is complex; they are known to perform low, graceful leaps and sometimes slap their tails against the water surface. While they generally avoid vessels, they have been observed surfing the waves created by ships. They are deep-water hunters, capable of diving for up to six minutes to feed on prey such as hake, lanternfish, squid, and octopi. Their range spans the North Pacific, from the waters of Japan and Russia to the western coast of North America.

The species faces significant environmental and human-made challenges. Historically, they suffered high mortality rates due to entanglement in driftnets during the 1970s and 1980s, a threat that has since been mitigated by international bans on certain squid fisheries. Today, they remain vulnerable to underwater noise pollution, which interferes with their ability to echolocate and communicate. Conservation efforts by NOAA Fisheries include monitoring population health and implementing take reduction plans. With a lifespan of 42 years or longer, these dolphins continue to be a subject of ongoing research as scientists work to better understand their biology and the ecological pressures they face in their oceanic habitat.

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