Earth’s freshwater ecosystems are among the many most in danger from human-induced threats together with overfishing, dam constructing, air pollution and local weather change.But biologists know comparatively little in regards to the animals that stay within the murky depths of our rivers and lakes, maybe least of all about a few of their largest inhabitants.In a brand new e-book, fish conservation biologist Zen Hogan groups up with journalist Stefan Lovgren to unravel a curious query: What is the world’s largest freshwater fish?An exploration of the world’s freshwater ecosystems from Australia to the Amazon, “Chasing Giants” additionally seems into the vary of threats large fish face the world over and what scientists, policymakers and the general public can do to assist their conservation.
In 2005, fishers in northern Thailand captured a Mekong large catfish of gargantuan proportions. Tipping the scales at 293 kilograms (646 kilos), the critically endangered Pangasianodon gigas raised a query in conservation biologist Zeb Hogan’s thoughts: Is this the most important freshwater fish ever caught?
Posing the query in a public announcement following the discover, Hogan anticipated to be inundated with cellphone calls and emails from fish biologists, researchers and fishers detailing shut encounters with leviathans residing within the murky depths of our planet’s lakes and rivers. But that by no means occurred. He acquired no communications.
Probing the query additional, Hogan quickly realized that no one had ever regarded on the problem on a worldwide scale. Simply, no one knew the identification of the world’s largest freshwater fish. Hogan, at the moment a conservation biologist on the University of Reno, Nevada, within the U.S., and co-lead of the USAID-funded Wonders of the Mekong venture, was hooked. His curiosity piqued, he launched into a decades-long worldwide exploration of the lakes and rivers the world over to uncover the mysteries of their large inhabitants.
Chasing Giants: In Search of the World’s Largest Freshwater Fish is the story of his discoveries throughout that search. He and co-author Stefan Lovgren, a journalist, join freshwater science with journey, recounting extinctions, rediscoveries of species lengthy regarded as misplaced, and, in fact, shut encounters of the aquatic form with among the most spectacular fish on Earth.
In the e-book, Hogan and Lovgren are desperate to not solely instill marvel about large fish themselves, but additionally to encourage motion to guard them. During his search, Hogan recognized greater than two dozen freshwater species that may be termed “megafish” that might develop to lengths of a minimum of 2 meters (6 ft) or attain weights of 90 kg (200 lbs). Although they’re all colossal, the species vary extensively in biology, form, conduct and habits, from ponderous and historic sturgeon to skittish and energetic large trout.
The 646-pound Mekong large catfish (Pangasianodon gigas) caught in northern Thailand in 2005 that spurred Hogan’s seek for the world’s largest freshwater fish. Photo by Suthep Kritsanavarin
Never one to relaxation aboard a ship or on the shore, Hogan typically will get within the water along with his research topics. Each of the megafish has a novel persona, he says, which is simply actually obvious whenever you’re of their setting, interacting with them on their very own phrases. In the e-book, he recounts coming nose to nose with huge arapaima (Arapaima gigas) and shoals of piranha (household Serrasalmidae) within the Amazon, alligator gar (Atractosteus spatula) in Texas, pigeon-eating wels catfish (Silurus glanis) in France, stingrays (Urogymnus polylepis) in Cambodia, and the gnarled-toothed sawfish (Pristis pristis) in Australia.
The e-book closes with a scene in a biologically wealthy stretch of the Mekong River in Cambodia and a record-breaking large fish discover. It supplies clear proof of what could be achieved when communities, scientists and coverage consultants come collectively. It’s additionally a motive for hope in a river system that’s nonetheless resilient and supporting life regardless of an onslaught of human-induced threats. “People are recognizing and appreciating the significance of those fish and taking motion to guard them,” Hogan says. “But we nonetheless have an extended option to go.”
Zeb Hogan just lately spoke with Mongabay’s Carolyn Cowan forward of the e-book’s April 25 launch. The interview has been flippantly edited for size and readability.
Cover of Chasing Giants: In Search of the World’s Largest Freshwater Fish, written by Zeb Hogan and Stefan Lovgren.
Mongabay: What made you wish to write Chasing Giants?
Zeb Hogan: Megafish are understudied and underappreciated — there are lots of people that don’t even know they exist — and so they’re extremely endangered. So I felt it was necessary to put in writing this e-book to inform their story in order that extra folks learn about them and the habitats by which they stay and to spice up folks’s appreciation for them.
The total purpose of this seek for the world’s largest freshwater fish was to search out, research and defend these gargantuan species. It all started in 2005 when fishers in northern Thailand captured what was reported on the time to be the world’s largest ever recorded freshwater fish. It was a Mekong large catfish.
Following that discovery, I requested myself what I assumed was a easy query: “Is this actually the world’s largest freshwater fish?” I didn’t notice on the time that that query was then going to occupy the subsequent twenty years of my life!
I’ve labored with National Geographic for a very long time, and mixing storytelling with science to achieve folks and encourage them to guard the planet is a philosophy that underpins my work with them and likewise the e-book: telling the story of those superb creatures that folks don’t know very a lot about; telling the story of the rivers and lakes the place they stay; and the story of the individuals who depend upon them for his or her livelihoods.
Megafish are additionally underwater and out of sight. The freshwater locations they inhabit are a world that folks usually don’t have the chance to expertise themselves. So this e-book is a option to take folks there, to locations which can be really shut and necessary to us all — freshwater rivers and lakes — however that folks don’t sometimes immerse themselves in.
When I consider different National Geographic explorers like Bob Ballard, who found the Titanic, and Sylvia Earle, who was one of many pioneers of marine exploration, I feel as scientists, we wish to share our work, share our discoveries with others as a result of in case you don’t know that it exists, then you definately’re not going to worth it … so it’s necessary to search out these massive fish species to encourage folks to make higher selections.
While engaged on this venture, I’ve had the possibility to journey to 30 totally different areas all over the world. So I used to be uniquely positioned to inform this necessary story that brings all my experiences in these locations collectively.
Arapaima (Arampaima gigas) are native to the Amazon River and one of many species Hogan studied throughout his worldwide exploration for large fish. Image courtesy of Zeb Hogan
Mongabay: With so many watercourses, on fully separate continents, to select from, how did you resolve the place to start your search?
Zeb Hogan: Since massive fish usually want numerous habitat, the obvious place to look was the world’s largest rivers and lakes, and that method usually labored. The Amazon, the Mississippi, the Nile, the Danube and the Yangtze all come to thoughts. And all these rivers do have fish which can be over 6 ft lengthy and weighting greater than 200 kilos, which was the factors for this venture.
But as soon as you progress past the concept massive fish want massive rivers and lakes, you start to search out exceptions. The massive rivers of Africa don’t even have many massive fish species; and the Amazon, which is the world’s most biodiverse river system when it comes to freshwater fish biodiversity, additionally has fewer massive fish than you’d count on.
Talking with native scientists was essential to search out these exceptions, to find smaller rivers and lakes that really had massive fish. And in that means, the search turned extra focused.
Mongabay: Your e-book actually put the large fish that stay within the Mekong River system in Southeast Asia in context, given the a number of environmental pressures the river system is going through lately, not least because of the spate of hydropower dam development over the previous few many years. What is it in regards to the Mekong River that makes it such a hotspot for large fish?
Zeb Hogan: The Mekong is definitely house to extra massive fish than any river on Earth, and I don’t have a definitive reply for why that’s. We know that the Mekong is likely one of the best rivers on Earth, nevertheless it’s not essentially the most biodiverse when it comes to fish. It’s house to about 1,000 species of freshwater fish, in comparison with the Amazon, which has 3,000 to 4,000. The Mekong can also be among the many high 20 largest rivers on the earth. It’s house to eight species of megafish that may develop to greater than 200 kilos and have developed to stay within the Mekong, which appears to swimsuit these massive fish very properly. There are large catfish and large carp, and then you definately even have freshwater stingrays, so it’s a various and attention-grabbing group of huge fish residing within the Mekong. They appear to have the ability to discover loads of meals within the productive river system and sufficient different habitat, from shallow wetlands and flooded forests to deep swimming pools too.
Hogan underwater with a colossal redtail catfish (Phractocephalus hemioliopterus), a species that inhabits the river methods of South America, together with the Amazon River. Image courtesy of Zeb Hogan.
Mongabay: In your seek for large fish over time, it’s essential to have had some up-close encounters and have some insights about these animals within the wild. What experiences from the sphere stand out for you and why?
Zeb Hogan: Being underwater with the fish of their pure setting has led to my most memorable experiences. Once fish have been captured for monitoring or measuring, they’re now not displaying their pure conduct, however the occasions I’ve had the possibility to work together with them of their pure habitat on their very own phrases has been exhilarating. Freshwater fish are generally tough for folks to really feel a reference to, however being within the water with the wild fish, you may really feel a powerful connection and really feel their majesty and curiosity.
From swimming with many various species, I’ve seen that every one has its personal persona. Giant stingray could be very curious — they’ll elevate their snout and sense the world round them virtually like they’re sniffing round. Sturgeon have a form of historic, plodding method about them, they appear very comfy after I’ve been within the water with them. On the opposite hand, large trout (that are the most important fish of their setting) are very skittish and appear to react fearfully to human presence, maybe as a result of they are often aggressive and even cannibalistic to 1 one other.
The Wonders of the Mekong venture works with fishermen in Cambodia who inform the crew once they catch an endangered fish in order that researchers can tag and launch the fish to study extra about its motion patterns. We sometimes stick with the fish for some time to test it isn’t injured or drained from being caught within the internet. We take the fish into the center of the river and numerous the time I’ll get within the water and dive down with the fish to get it slightly deeper. The water within the Mekong may be very muddy and so it will get darkish in a short time as you descend, the world goes black and your ears pop from the stress. You’re coming into the fish’s world that’s fully unfamiliar to us people, despite the fact that you’re lower than 10 ft [3 m] from the floor.
For me personally, all it takes to fall in love with every species is studying extra about them; to be within the river the place they stay and to speak to the native folks — the fishermen and the scientists — who learn about them.
An alligator gar (Atractosteus spatula), an historic species of freshwater fish native to North America. Image by vhines200 through Creative Commons (CC BY-ND 2.0)
Mongabay: There have been megafish extinctions in the course of the interval you have been trying to find the world’s largest freshwater megafish. In 2020, scientists declared the Chinese paddlefish (Psephurus gladius) extinct. Can you inform us your reflections on that loss and about your expertise trying to find it within the Yangtze River?
Zeb Hogan: In 2007, I went to China to fulfill with Dr. Qiwei Wei, a paddlefish knowledgeable who was doing Chinese paddlefish surveys on the Yangtze River system. We didn’t discover it, and what we didn’t notice on the time was that it might’ve already been extinct means again then.
The Chinese paddlefish was very distinctive and distinctive and one in every of solely two species of paddlefish on the earth (the opposite being in North America). It was a big and unusual-looking predator that might develop to over 7 meters (23 ft) lengthy. The lack of one in every of solely two species of paddlefish on the earth in the course of the lifetime of this venture was sobering, and one in every of our targets of our search and this e-book is to cease the extinction of different species.
As the primary of those massive megafish species to go extinct, the Chinese paddlefish was a very unhappy instance as a result of there have been none in captivity and no breeding program for them, so their loss from the wild meant the species was completely misplaced. It served as a wake-up name. People actually took discover and requested, “How might we let one of many largest fish on Earth simply disappear on our watch?”
Mongabay: How a lot bother are large freshwater fish in?
Zeb Hogan: There are between 30 and 40 species of freshwater fish that develop to over 6 ft or weigh greater than 200 kilos. Seventy % on them are prone to extinction, and lots of are critically endangered. Overfishing, habitat fragmentation and water air pollution are the three key dangers that they face.
Overfishing is a giant risk since these species are gradual to mature, so once they’re harvested at excessive charges, they don’t have an opportunity to get large enough to start reproducing. Habitat fragmentation and degradation can also be a giant problem as a result of so many of those massive fish are migratory. Migrations are essential to set off replica and for younger to disperse downstream as a part of their life cycle. In some components of the world, water high quality and points with air pollution are issues. Some species are very delicate to water air pollution: there’s been massive die-offs of large freshwater stingrays, for example, within the Mae Klong and Chao Phraya rivers in Thailand resulting from poor water high quality.
Overfishing alone hardly ever causes extinctions. Habitat fragmentation and modification of river circulation tends to be what finally causes extinctions as a result of these elements change the habitat in such a means that the fish can now not full their life cycle. For occasion, whenever you dam a river, it may possibly alter the circumstances in order that they’re now not conducive to fish spawning, so you find yourself with outdated fish within the system, however the inhabitants isn’t being replenished with younger fish, and over time, clearly, that can trigger the extinction of the species. That’s what occurred to the Chinese paddlefish: dams just like the Three Gorges Dam blocked the species from accessing essential spawning habitat and altered the water circumstances. When you’ve such wholesale adjustments in river methods, then species begin to disappear.
An huge Wallago catfish (Wallago leeri), a species that inhabits rivers in Southeast Asia. Image courtesy of Zeb Hogan
Mongabay: What species of large freshwater fish are most in peril of extinction?
Zeb Hogan: Several species of megafish are getting ready to extinction proper now, and it’s tough to know what to do to avoid wasting them. Obviously, now we have to maintain rivers free-flowing and now we have to maintain the water clear and freed from pollution. The large salmon carp [Aaptosyax grypus], a predatory species that may attain a size of 6 ft and is endemic to the Mekong River, springs to thoughts. It was thought extinct till late in 2022 when it was rediscovered. There’s no breeding program for it and there are none in captivity. So if it disappears from the river, it’s gone.
It’s tough to know what to do to avoid wasting the species since we don’t know what number of people are left and so they’re so tough to search out. As a end result, now we have little or no details about them, which makes it difficult to impress governments and the general public towards the form of conservation motion that’s wanted to make sure the species’ survival.
The particular person large salmon carp that was present in 2022 was mature, and, as is the case with so many river methods which have been dammed, juveniles of the species are hardly ever encountered. So it’s clear some adults are hanging on, however their life cycle has maybe been so disrupted by dams that it’s affecting their capability to breed.
One ray of hope is that though the Mekong is present process numerous adjustments, numerous dams are moving into and circumstances are altering fairly quickly, there’s nonetheless sufficient of the decrease Mekong River that’s free-flowing that the large salmon carp might grasp on for a short time longer till we will research it extra and perceive how greatest to reserve it.
Mongabay: Why ought to we make an effort to safeguard large fish species?
Zeb Hogan: Megafish could be seen as umbrella species, and so they’re indicators of ecosystem well being — by defending them, then we’ll even be retaining the rivers and lakes by which they stay wholesome. In order to guard massive fish, you must safeguard the freshwater ecosystem as a complete. That implies there may even be wholesome populations of smaller fish that assist different wildlife and fisheries upon which many thousands and thousands of individuals rely. So by defending the massive fish, we additionally protect aquatic biodiversity.
In the Mekong, for example, Mekong large catfish use the identical migration corridors as a whole lot of different species of fish. By retaining the Mekong large catfish habitat wholesome and retaining the river free-flowing in these areas which can be necessary for the species’ life cycle, then all these different fish species are additionally sustained, a few of that are commercially necessary which can be essential to folks’s diet and livelihoods within the area.
Many of those massive fish species even have cultural significance and so they instill a way of marvel and satisfaction, which might have knock on advantages relating to conservation motion.
A 13-feet-long large freshwater stingray (Urogymnus polylepis) captured unintentionally by fishermen within the deep-water swimming pools in Cambodia’s stretch of the Mekong River in May 2022. Image courtesy of Wonders of the Mekong
Mongabay: Is there any excellent news? Are any of those species doing higher than you’d thought?
Zeb Hogan: There are a couple of messages of hope. One is what’s occurred with different species. Take sharks, for example. Several many years in the past, public notion of sharks was very poor. Sharks have been seen as a menace and scary and never worthy of safety. But right this moment, the three largest species of sharks have worldwide safety, there’s superb analysis being performed on them, and there’s widespread appreciation for a way necessary sharks are as superb animals which can be important parts of our oceans. That shift within the notion of sharks is hopeful to me as a result of I really feel like we’re early on in an identical trajectory with freshwater megafish. We’re starting to study them, there’s extra consideration round them, there’s rising appreciation for them, and I hope that finally what occurred for sharks also can occur for these large freshwater fish.
It’s an uphill battle, although, as a result of freshwater is an inherently native problem. So beginning to view what’s occurring in our freshwaters all over the world as a worldwide problem is necessary. Goals just like the 30 by 30 initiative [a plan to conserve 30% of Earth’s land and sea areas by 2030 through “area-based conservation measures” like protected national parks] may also help in unifying all of us towards a standard purpose.
There are additionally many smaller-scale tales of hope. Fishing golf equipment are defending domestically occurring species via sustainable administration, for example, lake sturgeon in North America are doing properly via this method in some locations. Also, fishermen within the Mekong at the moment are recognizing critically endangered Mekong large catfish as uncommon and underneath risk and releasing them again into the wild in the event that they catch them. All of this exhibits that individuals are recognizing and appreciating the significance of those fish and taking motion to guard them. People are attempting to alter the trajectory, to attempt to gradual the losses to zero after which to enhance the state of affairs for these species, via habitat restoration and fisheries protections. But we nonetheless have an extended option to go.
Giant Mekong catfish captured within the Tonle Sap River in Cambodia. Photo courtesy of Zeb Hogan
Mongabay: What are the primary issues that have to occur for large fish species to thrive and persist into the longer term?
Zeb Hogan: One of the primary issues that should occur for these species to outlive is sustaining as a lot free-flowing stretches of river as attainable all over the world. The idea of defending 30% of habitats by 2030 is an effective purpose. If 30% of rivers stay free-flowing then there shall be habitat refuges obtainable for the fish. We’re seeing in freshwater ecosystems that if we defend areas of aquatic habitat for biodiversity, we see fisheries advantages exterior of these safety zones as a result of these core protected areas are sustaining fish populations that feed into close by areas. So defending 30% of freshwater by 2030 is a superb purpose that has actual potential to gradual or cease the extinction of many of those massive species.
For species getting ready to extinction, attempting to ascertain captive populations and determining how one can breed them in captivity could possibly be one emergency measure which may stop extinction. But we don’t need these large fish species to only survive in captivity. The concept is to maintain rivers and lakes wholesome sufficient to assist wild populations. Besides retaining rivers free-flowing, avoiding overharvesting and ensuring we proceed to collect extra data about these species are important.
Hogan goals to encourage appreciation and motion to guard the world’s largest fish. Here, an enormous catfish is launched into Tonle Sap Lake, Cambodia throughout 2022 as a part of a collaborative conservation effort. Photo courtesy of Wonders of Mekong
Banner Image: Through their e-book, Zeb Hogan (pictured right here on the suitable with fishers and a Mekong large catfish) and co-author Stefan Lovgren are desperate to encourage motion to guard the world’s largest freshwater fish. Image courtesy of Zeb Hogan.
Carolyn Cowan is a employees author for Mongabay. Follow her on Twitter @CarolynCowan11
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