What the Heck Does "Pelagic" Mean?

The world’s oceans are immense, covering over 70% of the Earth’s surface and hosting some of the planet’s most unique and complex ecosystems. The pelagic zone stands out as one of our favorites, which is why it became the namesake for Pelagic Blue Cruising Services. That’s why today we’re talking about what the pelagic zone is, what makes it so cool, and we’re introducing you to some of the fantastic critters that call it home.

Pelagic (adjective):

1. Of or relating to the open seas or ocean

2. Living or growing at or near the surface of the ocean, far from land, as certain organisms

Pelagic Blue:

That stunning color!

What is the Pelagic Zone?

The pelagic zone essentially refers to the open ocean. That includes everything we call “offshore” in non-science terms. Critters that reside in this offshore, open ocean area are often referred to as “pelagic”. So pelagic is both a specific part of the ocean environment and a descriptor of the species that reside there.

Unlike coastal or benthic environments (near the ocean floor), the pelagic zone encompasses the entire water column and can extend to depths of more than 10,000 meters (32,800 feet). This zone hosts much of the world's marine life and is divided into several layers, each with distinct characteristics based on light availability, pressure, and temperature. There are a total of five zones or layers within the pelagic zone that stretch all the way down to the deepest, darkest reaches of the ocean.

Vertical Ocean Zones

Epipelagic Zone: 0-200 meters

Mesopelagic Zone: 200-1,000 meters

Bathypelagic Zone: 1,000-4,000 meters

Abyssopelagic Zone: 4,000-6,000 meters

Hadalpelagic Zone: 6,000 meters and beyond

As you move deeper through the ocean layers, environment conditions become increasingly hostile. Temperatures near freezing, immense pressure, and complete darkness characterize many of the deeper zones. Life here is sparse but highly specialized. In the mesopelagic and bathypelagic, we find organisms that have adapted to the absence of light through bioluminescence, extreme pressure tolerance, and unique feeding strategies, such as scavenging or filtering nutrients from the water.

Most of us work and play primarily in the epipelagic zone. This is the surface layer (0-200 meters) where sunlight penetrates. It's the most biologically productive zone, and where you’ll find species such as fish, dolphins, and an abundance of marine plankton which are the foundation of the marine food web.

The pelagic zone also plays a major role in regulating global climate and ocean currents. Ocean circulation in the pelagic zone, known as the thermohaline circulation, helps redistribute heat and nutrients around the globe, impacting weather patterns and marine ecosystems. Additionally, the pelagic zone supports massive populations of phytoplankton, which absorb carbon dioxide and help mitigate the effects of climate change.

Pelagic Fish: Masters of the Open Ocean

Pelagic fishes inhabit the open ocean. They have evolved to survive in the vast, ever-changing conditions of the pelagic zone, where they must undertake long distance migrations, constantly be searching for food, and avoid predators in a habitat where there is truly nowhere to hide.

Pelagic fish can be further categorized as coastal and oceanic fish, based on the depth of the water they inhabit. Coastal pelagic fish inhabit the sunlit epipelagic waters up to about 200 meters deep, typically above the continental shelf. These would be species like anchovies, sardines, menhaden, and other forage fish that predatory fish feed on. Oceanic pelagic fish typically inhabit waters that extend beyond the reaches continental shelf. Examples include larger fish like swordfish, tuna, mackerel, and even some sharks.

There is no distinct boundary from coastal to ocean waters which means some oceanic fish become partial residents of coastal waters, typically during different stages of their lifecycle. However, true oceanic species will spend their entire lives in the open ocean. It was a tall order for us to narrow it down to our favorite pelagic fishes, but here’s our top three:

Mahi-Mahi (Coryphaena hippurus)

Also known as dolphin fish or dorado, mahi-mahi are colorful, fast-swimming fish that are found in tropical and subtropical offshore waters. Mahi-mahi have a high metabolism and are known for their speed and agility in the water. They often leap out of the water and make sharp turns while chasing prey. They don’t really hang out in large schools or groups, especially as they grow older and may partake in cannibalism. If you’re crossing an ocean and the water is warm enough to swim, it’s highly likely that with the right fishing setup you’ll be able to land yourself a tasty mahi. They love to eat flying fish, so lures and lure behaviors that mimic the skimming locomotion can be a productive way to fish for them.

Flying Fish (Genus: Exocoetus)

Flying fish are a remarkable group of species known for their ability to leap out of the water and glide through the air. They have specially adapted, large, wing-like pectoral fins that allow them to take short flights, often to escape predators. These fish can glide for distances of up to 100 meters (330 feet) by flapping their tails to gain momentum before launching into the air. Typically found in warm ocean waters, flying fish are agile swimmers, using their fins and tails to navigate both underwater and airborne.

Tuna! (Genus: Thunnus)

And then of course we have everyone’s favorite sushi catch, tuna! Tuna are apex predators on the high seas. They have super streamlined bodies that allow them to reach speeds of up to 75 km/h (46 mph). It’s a good thing too, because they must migrate thousands of miles across the world’s oceans in search of food. Tuna are actually warm-blooded, a rare trait for fish, which allows them to maintain a higher body temperature than the surrounding water and gives them a metabolic advantage for high-speed swimming. Tuna typically associate in schools, which means once you’ve found one you’ve probably discovered a big pile of them.

Check out these closeup shots of what we like to call "tuna wings". Tuna are incredibly specialized for the life they live. Their football-shaped bodies are remarkably hydrodynamic. Even their fins drop down into hidden slots on their bodies so they can be perfectly smooth and totally streamlined as they cruise through the water.

Pelagic Marine Mammals: Welcome Visitors at Sea

Fish aren’t the only critters you’ll encounter while sailing offshore. We treasure every visit from marine mammals when we’re at sea. In fact, we’ve seen more species of whales and dolphins since we started cruising than we ever did as marine biologists. How wild is that? A big part of that is because most science happens nearshore. It’s more accessible, cheaper, and you can go back to the same places day after day looking for critters.

Offshore days on research vessels are wildly expensive for scientists. Typically there are a multitude of different research projects going on simultaneously to capitalize on that huge effort, and you rarely get to deviate from a set itinerary or transect run, otherwise everyone’s science gets out of whack. But on a cruising boat? You have the option to sail with dolphins for days, or heave to and enjoy some bow time with your middle-of-the-ocean visitors.

Dolphins (Family: Delphinidae)

Dolphins are intelligent, social creatures that live in the epipelagic zone and often form pods. They are known for their playful behavior and sophisticated hunting techniques. Dolphins have complex social structures and use echolocation to find prey and navigate in the open ocean. Their streamlined bodies and large brains make them effective hunters. The most commonly encountered species varies depending on what ocean and what part of said ocean you are sailing.

Offshore Bottlenose Dolphins (Tursiops truncatus) are a larger, more robust close relative of the stereotypical Flipper Bottlenose Dolphin. They hunt in deep ocean waters and often enjoy associating with sailing vessels. We had about two weeks of a nonstop dolphin escort on a passage. What a treat!

Risso’s Dolphins (Grampus griseus) are fairly easy to identify by their unique scarred appearance, stemming from interactions with other dolphins and parasites. They are typically solitary animals, feeding on squid and deep-sea fishes.

Blue Whales (Balaenoptera musculus)

Blue whales are the largest animals to ever live on Earth, reaching lengths of up to 30 meters (98 feet). These gentle giants can be found in pelagic waters, migrating between feeding and breeding grounds. Blue whales are filter feeders, using their baleen plates to strain massive amounts of krill from the water. Despite their size, they are efficient swimmers and can travel long distances across the oceans.

A true cosmopolitan species, they are found in all the world’s oceans but encounters are rarer than you’d expect given their wide distribution. Most interactions humans have with blue whales take place in certain nearshore areas known for breeding, such as the Sea of Cortez, or where ocean conditions encourage nearshore migration routes, as in Monterey Bay, CA.

It’s a rare treat to spot a blue whale at sea, but if you are passionate about offshore sailing, there’s a good chance you’ll encounter one eventually. Their broad, flat tail fins (called flukes) are the giveaway for identifying blues.

Sperm Whales (Physeter macrocephalus)

Sperm whales are deep-diving marine mammals that hunt squid in the bathypelagic zone. They are known for their large heads and exceptional diving abilities, able to plunge to depths of over 3,000 meters (9,800 feet) and dive for up to 90 minutes. Sperm whales have a specialized organ in their head, called the spermaceti organ, which helps them with buoyancy and echolocation during deep dives. Encounters tend to be more common in the Atlantic than the Pacific, particularly near the Azores where they are known to congregate. But, being another cosmopolitan species, you could encounter them almost anywhere during your cruising adventures. We haven’t met one of these behemoths yet but they’re on our hot list!

Killer whales (Orcinus orca)

There are three widely recognized ecotypes of killer whales: Transient, Resident, and Offshore. Offshore killer whales have the largest range of the three, and often occur more than 9 miles offshore. They are not, however, exclusively “offshore”, as they are sometimes seen in coastal nearshore waters. That's why we don't consider them to be true pelagic species, although they are out in the pelagic zones and you could certainly encounter them in any of the world's oceans.

Resources for Pelagic Cruising

Offshore sailing offers a unique opportunity to experience the pelagic zone firsthand. If it’s your first time out there, you may be shocked by the sheer scale and isolation of the open ocean. For many, sailing across the Atlantic or Pacific Oceans provides an incredible sense of awe and respect for the vastness and volume of the ocean. It’s pretty incredible to witness the types of marine life that thrive out there. Dolphins riding the bow wave and tuna darting below the surface can be somewhat regular sights in an area that often appears as desolate and empty as a desert.

Before you take off on your grand cruising adventures, be sure to stash a few pelagic species identification and marine biology resources in your ship’s library. You want references that are both informative and practical for quick reference. Here are three (plus a bonus fourth!) books we highly recommended having onboard:

National Audubon Society Guide to Marine Mammals of the World is by far the best marine mammal book we’ve seen to date with exceptional identification resources. You might want to compliment this with waterproof folding identification guide for quick reference.

National Audubon Society Field Guide to Fishes: North America is part of a 25 book series. And while you don’t necessarily need all 25 books on rocks, minerals, plants, and animals, we encourage you to pick a few of your favorites. These books are compact, durable, and are always wonderful to flip through.

The Offshore Anglers’ ABC’s by Michelle Supplee is a fun, easy read if the science stuff is too heavy for you. It covers all the major pelagic fishes, and you can refer to your fish guide for specific species identifications when you need an extra reference.

Essentials of Oceanography by Alan P. Trujillo and Harold V. Thurman. Full disclosure, this is a textbook. But it is exceptionally well done and totally entertaining if you want to be dazzled by what science has to say about how ocean stuff works. And another full disclosure, Julie works with author Al Trujillo on Nat Geo ships, so if you find a typo let her know!

Hungry For More Learning?

Then you need to come sail with us! In case you haven't noticed, we are ocean nerds. Even though we left our professional biology careers for a life at sea, our appreciation for marine life runs deep. We heave to for whales, run out on deck to greet dolphins, and always have a line in the water trolling for mahi and tuna offshore. Apply for an expedition, and let's go find some wildlife together.

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