NEW YORK, N.Y. (Nov. 3, 2023) -- The heightened value of croaker swim bladders, or maws, is contributing to the endangerment of multiple marine species, including the Critically Endangered vaquita porpoise that exists only in Mexico’s Gulf of California, the authors of a new article in the journal Aquatic Conservation: Marine and Freshwater Ecosystem have found. Other species affected include a variety of globally threatened dolphins, sharks, rays, marine turtles, and the croaker fish themselves.

“The intensification of gillnet and longline fisheries, driven by trade demand for croaker maws, is exacerbating a conservation crisis facing marine wildlife due to fishery bycatch,” said Brian D. Smith, lead author of the journal article and Director of the Wildlife Conservation Society (WCS) Marine Wildlife Bycatch Initiative.

WCS is following up on results of the study outlined in the journal article with a new global initiative aimed at reducing the bycatch of marine wildlife. The initiative works with fishers and policymakers to identify and implement multi-species solutions to save the world’s most endangered marine wildlife while sustaining rights-based small-scale fisheries. It will enhance existing conservation investments and pursue solutions to protect marine wildlife as flagships for a healthy ocean and healthy people.

Swim bladders are internal gas-filled organs that help bony fish control their buoyancy and remain at the same depth without having to swim. They also act as stabilizers and resonating chambers to produce and receive sound.  

In his seminal book Origin of Species, Darwin hypothesized that the lungs of higher vertebrates evolved from the swim bladders of fish. However, recent genetic evidence suggests that it was the other way around, that the lungs of air-breathing primitive fish evolved into swim bladders.

How croaker maws went from being used for disposable condoms during Darwin’s era to a key component of the contemporary illicit global fisheries trade is a cautionary tale for marine species, Smith said. He noted that among the 899 wildlife species known to live in coastal waters, almost half are threatened with extinction, including the vaquita porpoise, which is the world’s most endangered marine mammal.

In 2020, two seizures of fish bladders from totoabas, a threatened species of croaker confined to Mexico’s upper Gulf of California, were estimated to be worth about USD $160,000 per kilogram, compared with the price of gold, USD $60,000 per kilogram. That has driven illegal gillnet fisheries targeting the endangered fish, while bycatch deaths threaten the vaquita porpoise.

The extraordinary prices paid for totoaba maws, which are bought for luxury food and as a financial investment, follow the dramatic decline of another large croaker, the Chinese bahaba, which is also threatened with extinction due to overexploitation. In 2012, a single maw from a particularly large bahaba sold in China for almost USD $500,000.

Based on research conducted by WCS, the journal article found that as catches of the bahaba and totoaba have declined, the demand for croaker swim bladders is spreading to other species around the world that also have valuable maws. This has disastrous implications for marine wildlife that are caught incidentally in fishing gears targeting croakers. It also threatens at least six croaker species, two of which are considered Critically Endangered. 

Smith said there is an urgent need for gear restrictions in areas where threatened croakers and other marine wildlife face the greatest extinction risk, and more rigorous enforcement of existing fisheries regulations and monitoring of croaker catches and marine wildlife bycatch. “As is so often the case, we also need greater public awareness, to bring these changes about,” Smith said. “And there is a need for alternative income-generating activities for affected fishers.”

Coauthor Elisabeth Fahrni Mansur, Senior Manager of the WCS Bangladesh Marine Conservation Program, noted that a motion for controlling and monitoring trade in croaker swim bladders to protect target croakers, and to reduce incidental catches of threatened marine megafauna, was approved at the 2021 IUCN World Conservation Congress.

“The motion called on member nations to support the establishment of trade regulations on fish maws through national laws and the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES),” Mansur said. “To prevent the extinction of marine wildlife and protect high-value croakers, this needs to happen as soon as possible.”