Fisheries Models Overlook a Spreading Nuisance: Jellyfish
A decade ago, swarms of large jellyfish unexpectedly filled the cold waters of the Bering Sea. They clogged nets, attached themselves to fishing lines, and stung the fishermen who hauled in the unintended catch. The area became notorious as "The Slime Bank."
"Area fishermen didn't want to go there because they caught almost entirely jellyfish," said Richard Brodeur, a fisheries biologist with U.S. National Oceanic and Atmospheric Administration (NOAA) who observed the jellyfish bloom that peaked in 2000.
Although jellyfish populations have since declined off Alaska's coasts, swarms of hundreds or thousands of the gelatinous creatures are frequently occurring elsewhere, such as in the Gulf of Mexico and in the Black and Mediterranean. Marine scientists attribute the blooms to a variety of possible factors, including climate change, worsening ocean pollution, and the spread of invasive species.
A surge in research is seeking to understand how these swarms may affect seafood industries, coastal power plants, and tourist-lined beaches. Yet jellyfish still do not receive the attention they deserve, some researchers say.
Most fisheries analysts exclude the creatures from models of marine ecosystems, one of the latest trends in sustainable fisheries management. This exclusion may make it more difficult to predict the effects of jellyfish blooms on fisheries.
"The reality is that the jellies are not even in [most] existing ecosystem models," said Monty Graham, a senior marine scientist at the Alabama-based Dauphin Island Sea Lab. "They completely ignore jellies."
Ecosystem models typically incorporate a broad range of variables in an effort to generate more detailed population predictions. These include data on the diets, reproduction rates, and death rates of all interacting species. The United Nations Food and Agriculture Organization suggests that fisheries authorities and the fishing industry implement "ecosystem-based approaches" as part of wider climate change adaptation plans, according to the recent State of World Fisheries and Aquaculture report.
A global study published in January, led by Graham and Daniel Pauly, a marine scientist at the University of British Columbia, found that only about a quarter of the most popular marine ecosystem models explicitly include gelatinous zooplankton such as jellyfish. And when jellyfish are included, the models often "collapse all things considered gelatinous into a single functional "jellyfish' group," the study said. By doing so, the models often do not adequately factor the role of jellyfish and related species in the interconnected web of undersea life.
Jellyfish and fish species interact in various ways: some jellyfish eat fish, and some larger fish dine on jellyfish. Species such as herring, sardines, and anchovies have also been known to compete with jellyfish for the same zooplankton meals.
"When managing from an ecosystem level, there is talk about prey and predators of fishes," said Graham, who teaches on the faculty of University of South Alabama. "But it's not just about prey and predator.... Jellyfish can be competitors, too."
Jack Costello, a biology professor at Rhode Island-based Providence College, says the creatures have historically received less attention because most marine research focuses on species preferred by the seafood industry. With the exception of fisheries in East and Southeast Asia, jellyfish have not been captured and consumed commercially.
"Studying the ocean by humans is very much influenced by perception of value," said Costello, who has researched swarms of comb jellies in Narragansett Bay.
The lack of historical data is just one of many factors hampering greater knowledge of jellyfish populations. Studying the secretive creatures can be a challenge in itself - and their sting is merely the beginning.
Juvenile jellyfish, which begin in a polyp stage attach themselves to the seafloor, where they are often hidden under sea grasses - making at least one portion of their life nearly impossible to observe. Once jellyfish mature, captured adults often become tangled messes in research nets. "We really don't have a good way to collect and preserve them in the field," Costello said.
The research challenges have resulted in a large knowledge gap about jellyfish and fish interactions. Mike Ford, a NOAA oceanographer, has attempted to measure the growing population of comb jellies off the New England coast over the past two decades. His research has used an alternative approach: peering inside the stomachs of thousands of dogfish, a jellyfish predator. Even after he collects the data, however, its importance is not entirely clear.
"If you look at all the prey a dogfish eats, how significant is the consumption of jellyfish in a dogfish's life? I don't think it has the caloric value of its other prey," Ford said. "We need more studies of dogfish eating jellyfish. It doesn't exist in the literature now."
Research data is improving steadily with advancements in aerial counting, video monitoring, and scuba observations. And despite the ongoing challenges, more regions are including jellyfish in ecosystem models as the data becomes available, according to Tim Essington, a marine scientist at the University of Washington.
"These models always have lots of simplifications and abstractions," Essington said. "You're never going to know every interaction in any system, especially marine."
Brodeur, the biologist at NOAA's Pacific Northwest laboratories, has become the envy of jellyfish researchers. His studies have relied on jellyfish records that Alaskan scientists first gathered in the early 1980s, several years before most fisheries paid much attention to the species. As a result, the Bering Sea has become one of the few ecosystems to include jellyfish in its fisheries models.
"People asked why are we wasting our time studying jellyfish," Brodeur said. "But everything is all related, we're now starting to realize."
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