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- Struggling freshwater fish populations within the Mekong River catchment acquired a lift earlier this month when a staff of scientists and fisheries specialists launched 1,500 captive-reared juvenile fish into Tonle Sap Lake in Cambodia.
- Specialists say the discharge is step one in rejuvenating the Mekong’s depleted fish populations and fisheries, which have been struggling in recent times resulting from overfishing, drought, habitat destruction, and the impacts of upstream dams on the Mekong River’s pure stream.
- The fish, together with critically endangered Mekong large catfish and large barb, and endangered striped river catfish, have been launched right into a collection of fish sanctuaries and neighborhood conservation areas that defend essential fish nursery habitat in Tonle Sap Lake, the world’s most efficient inland fishery.
- Lengthy-term survival of the Mekong’s threatened fish species will even rely upon safety of migration corridors and upstream spawning grounds, and on upkeep of free-flowing and linked watercourses, say specialists.
At a younger age, Mekong large catfish look the identical as striped river catfish, their regular-size, extensively consumed family members. However as they mature, the large catfish rapidly eclipse their smaller kin, reaching a weight of 200 kilograms (440 kilos) in simply six years.
It was this astonishing progress price that alerted a fish farmer in Prey Veng province in Cambodia to the truth that she had mistakenly stocked her pond with one of many critically endangered goliaths. Over 13 years, it grew so huge that she may not accommodate it and was obliged to donate it to the native fisheries authority for launch again into the wild.
Earlier this month, a global staff of scientists and fisheries specialists liberated the behemoth right into a community of protected areas in Tonle Sap Lake in central Cambodia, alongside 1,500 different captive-reared juvenile fish, in an effort to spice up native fish numbers.
Along with two Mekong large catfish (Pangasianodon gigas), among the many world’s largest freshwater fish, the staff launched a whole lot of nutritionally vital and endangered striped river catfish (Pangasianodon hypophthalmus) and critically endangered large barbs (Catlocarpio siamensis), a sort of freshwater carp and Cambodia’s nationwide fish.
A lot of the fish had been collected as larvae from the mainstream Mekong River close to Phnom Penh and reared at a fisheries analysis facility operated by the Cambodian Fisheries Administration in partnership with the USAID-supported Wonders of the Mekong challenge.
Struggling fish populations
The discharge was step one towards restoring depleted freshwater fish populations all through the Mekong River, in accordance with Zeb Hogan, a fish biologist on the College of Nevada, Reno, and lead researcher for Wonders of the Mekong.
“[Events] like this encourage folks to consider the Tonle Sap Lake and the Mekong River extra broadly … in ways in which catalyze extra motion,” Hogan informed Mongabay in an e-mail. He added that the discharge has helped increase consciousness of no-fishing rules within the lake’s fish sanctuaries that goal to safeguard susceptible species and defend beneficial fisheries.
In recent times, the mixed threats of overfishing, drought, habitat destruction and the impacts of upstream dams on the Mekong River’s pure stream have wreaked havoc on fish populations and aquatic habitats all through the river system.
Tonle Sap Lake, a UNESCO Biosphere Reserve, lies inside the Decrease Mekong Basin. Through the moist season, between June and August, the lake can swell to 5 instances its dimension because the Mekong River’s annual flood pulse surges up the Tonle Sap River, flooding the lake’s surrounding forests and wetlands. These habitats are essential nurseries for greater than 300 species of fish, whose larvae are carried downstream into the lake by the flood pulse.
In consequence, the lake is dwelling to the world’s most efficient inland fishery, clocking annual fish catches of as much as 400,000 metric tons. Nonetheless, abnormally dry situations in recent times resulting from droughts and a weakened flood pulse from the Mekong, partly resulting from upstream engineering, have severely depleted catch sizes.
Freshwater fish reserves work
To rejuvenate the fish populations and fishery in Tonle Sap Lake, eight government-mandated no-take zones have been established in 2013. Along with a collection of neighborhood conservation areas, the fish reserves kind one of many world’s most intensive freshwater protected space networks.
The staff launched the captive-reared fish into these secure havens, the place they’ll mature earlier than embarking on spawning migrations up and down the broader Tonle Sap and Mekong rivers.
Latest analysis has proven that such freshwater fish reserves are simply as efficient as their marine counterparts in boosting fish biomass and safeguarding fisheries and biodiversity. Particularly, they’re “extremely profitable” at defending huge fish, which is sweet information for populations of huge species, just like the Mekong large catfish and large barb.
In 2020, researchers learning freshwater fish reserves in Thailand discovered that they sustained greater than twice the full variety of fish and greater than 20 instances the full weight of fish in comparison with non-protected stretches of river. Bigger fish have been discovered nearly solely inside the protected areas.
“In northern Thailand, within the dry season when the water is evident, you’ll be able to see a whole lot of massive fish education within the protected areas of the river and only a few fish outdoors the protected zones,” Hogan mentioned, regardless of there being no boundaries within the river separating the 2 areas.
And comparable outcomes are being noticed in Tonle Sap Lake. Hogan mentioned he has witnessed fishing nets forged each inside and out of doors the lake’s fish reserves; invariably, he mentioned, nets contained in the reserves pull in additional fish.
Nonetheless, the fish studied within the 2020 research in Thailand have been wild populations. Whereas wild fish appear to have the ability to study the place the reserve boundaries are and search safety inside them, it stays unclear whether or not the newly launched captive-reared fish will be capable of reply to the reserves in Tonle Sap Lake in an identical method.
One a part of the puzzle
Eager to study extra in regards to the fish themselves, the researchers fitted all 1,500 launched fish with small tags to trace their actions and monitor survival. By asking fishers to return the tags of any fish they catch with a word of the situation, the researchers can assess the extent of fishing mortality and the way far the fish had traveled.
This new information will assist fisheries managers to fine-tune their conservation approaches. “We have to higher perceive the effectiveness of fish reserves as a refuge for threatened fish,” mentioned Ngor Peng Bun, dean of fisheries science on the Royal College of Agriculture in Phnom Penh, who has been learning Mekong fish and fisheries for 25 years.
The current fish launch and subsequent research “will inform future conservation practices, and assist us perceive whether or not such strategies are efficient in supporting the restoration of those species’ wild populations,” he mentioned.
Monitoring fish actions will even allow the researchers to search out out whether or not the captive-reared fish are in a position to answer exterior cues that usually set off migration and spawning. The staff plans to launch extra fish in September 2022, on the peak of the moist season, to evaluate whether or not the timing of the releases has any impact on these behaviors.
However the various advantages of the fish releases, they’re only one small a part of an general resolution to plummeting fish numbers, in accordance with Hogan. Crucially, measures have to be taken to guard the fish throughout all levels of their lives. This additionally means safeguarding migration corridors just like the Tonle Sap River and spawning grounds in upstream elements of the Mekong River, he mentioned.
Sustaining the Mekong River’s pure stream regime can be very important: the river’s stream prompts fish to set off on their upstream spawning migrations and carries younger fish downstream to their nursery habitats in Tonle Sap Lake.
With the Mekong’s annual flood pulse weakening because of droughts and upstream engineering, scientists are involved that fish are much less in a position to efficiently full these essential life levels that give rise to the following technology.
“Nobody desires to lose these iconic fish,” Hogan mentioned. “Saving them would require further motion, corresponding to improvement of species conservation motion plans; enforcement of fisheries rules, together with year-round safety of fish sanctuaries; and upkeep of wholesome, linked rivers that the fish want to finish their life cycles.”
Banner picture: A Mekong large catfish measuring roughly 1.6 meters (5 ft) is launched right into a fish sanctuary in Tonle Sap Lake, Cambodia in March, 2022. Picture courtesy of Wonders of the Mekong challenge
Quotation:
Koning, A. A., Perales, Okay. M., Fluet-Chouinard, E., & McIntyre, P. B. (2020). A community of grassroots reserves protects tropical river fish variety. Nature, 588(7839), 631-635. doi:10.1038/s41586-020-2944-y
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