Research led at Scripps with a distinguished team of government and international experts (including two chief scientific advisors to the United Kingdom) demonstrates that fishing can throw targeted fish populations off kilter.
Fishing can alter the "age pyramid" by lopping off the few large, older fish that make up the top of the pyramid, leaving a broad base of faster-growing small younglings. The team found that this rapidly growing and transitory base is dynamically unstable-a finding having profound implications for the ecosystem and the fishing industries built upon it.This schematic outlines variability on exploited and unexploited.
Imagine a container of water with a 500-pound fish. With food, it grows a little bigger. Without food it gets a bit smaller. Imagine the same container with 500 one-pound fish. They eat, reproduce and the resulting thousands of fish boom, quickly outstripping the resources and the population crashes. These many smaller fish-with the same initial "biomass" as the larger fish-can't average out the environmental fluctuations, and in fact amplify them through higher turnover rates that promote boom and bust cycles.
The study that included academic and government scientists from Alaska, Asia and Great Britain is based on data from the California Cooperative Oceanic Fisheries Investigations (CalCOFI), a program based at Scripps that has monitored fish and oceanographic activities of the California Current for more than 50 years. To arrive at their results, the researchers compared the CalCOFI records of larvae, a key indicator of adult populations, of both fished and non-fished species in the California Current.
The schematic outlines variability on exploited and unexploited.Fishing typically extracts the older, larger members of a targeted species and fishing regulations often impose minimum size limits to protect the smaller, younger fishes.
"That type of regulation, which we see in many sport fisheries, is exactly wrong," said Sugihara. "It's not the young ones that should be thrown back, but the larger, older fish that should be spared. Not only do the older fish provide stability and capacitance to the population, they provide more and better quality offspring."
Thus the danger, according to Sugihara, is that current policies that manage according to current biomass targets (without significant forecast skill) while ignoring fish size pose risks that can further destabilize the population. This instability can in principle propagate systemically to the whole ecosystem, much like a stock market crash or a domino effect, and magnify risk for the fishing industry itself as well as those of ecologically related fisheries.
This is especially true when trying to rebuild fish stocks, Sugihara says.
"This may be the most important implication of this work, as we attempt to rehabilitate fisheries," said Sugihara. "Regulations based solely on biomass harvest targets are incomplete. They must also account for age-size structure in the populations," he said. "Current policies and industry pressures that encourage lifting bans on fishing when biomass is rehabilitated-but where maximum age and size are not-contain risk."
This is currently the case with Atlantic swordfish, for which industry pressures to resume fishing are based on the restoration of historic biomass levels, even though the swordfish are clearly undersized.
"In the extreme case, the danger of such unstable dynamics for certain populations for management is that harvest targets may lag the population, potentially making things worse," said Sugihara. "A high harvest target may be set after an especially abundant period when the population may be poised to decline on it's own. Likewise future abundant periods may represent missed opportunities, despite current low abundances. As senior officials of the Canadian Department of Fisheries and Oceans have said, 'we are often a year behind in our stock projections.'"
Sugihara cautioned that nonlinearity is not unique to fished species. Nonequilibrium overshooting and undershooting occurs in unexploited stocks, but to a lower extent. Therefore, classical single-species population models that require equilibrium are unlikely to be very successful in stock forecasts, except perhaps in the very short term.
"Other methods that do not rely on these assumptions may be more promising," suggests Christian Anderson, paper co-author.
In addition to Sugihara and Anderson, the study included Scripps Oceanography Chih-hao Hsieh (now a professor at National Taiwan University); Stuart Sandin of Scripps; Roger Hewitt of the National Marine Fisheries Service, Southwest Fisheries Science Center; Anne Hollowed of the National Marine Fisheries Service, Alaska Fisheries Science Center; Sir John Beddington of Imperial College London (current Chief Science Advisor to the United Kingdom) and Lord Robert May of Oxford (a former Chief Scientific Advisor to the UK).
The research was supported by NOAA Fisheries and the Environment program, The MacQuown Chair of Natural History, The Deutsche Bank - Jameson Complexity Studies Fund, the Sugihara Family Trust and the Kyoto University grant for Biodiversity Research of the 21st Century.
Mario Aguilera | EurekAlert!
Some brain tumors may respond to immunotherapy, new study suggests
11.12.2018 | Columbia University Irving Medical Center
Climate change and air pollution damaging health and causing millions of premature deaths
30.11.2018 | International Institute for Applied Systems Analysis (IIASA)
The more objects we make "smart," from watches to entire buildings, the greater the need for these devices to store and retrieve massive amounts of data quickly without consuming too much power.
Millions of new memory cells could be part of a computer chip and provide that speed and energy savings, thanks to the discovery of a previously unobserved...
What if, instead of turning up the thermostat, you could warm up with high-tech, flexible patches sewn into your clothes - while significantly reducing your...
A widely used diabetes medication combined with an antihypertensive drug specifically inhibits tumor growth – this was discovered by researchers from the University of Basel’s Biozentrum two years ago. In a follow-up study, recently published in “Cell Reports”, the scientists report that this drug cocktail induces cancer cell death by switching off their energy supply.
The widely used anti-diabetes drug metformin not only reduces blood sugar but also has an anti-cancer effect. However, the metformin dose commonly used in the...
A research team from the University of Zurich has developed a new drone that can retract its propeller arms in flight and make itself small to fit through narrow gaps and holes. This is particularly useful when searching for victims of natural disasters.
Inspecting a damaged building after an earthquake or during a fire is exactly the kind of job that human rescuers would like drones to do for them. A flying...
Over the last decade, there has been much excitement about the discovery, recognised by the Nobel Prize in Physics only two years ago, that there are two types...
12.12.2018 | Event News
10.12.2018 | Event News
06.12.2018 | Event News
14.12.2018 | Power and Electrical Engineering
14.12.2018 | Physics and Astronomy
14.12.2018 | Physics and Astronomy