New methods further discern extreme fluctuations in forage fish populations

Anchovy, sardine, and hake scale deposition rate from AD 1000 − 1500 derived from a recent, age-calibrated sediment core from Santa Barbara Basin, California. Representative fish scales and the respective fishes are shown on the right. Image credit: I.L. Hendy, University of Michigan; S. McClatchie, NOAA Fisheries; NMFS image library

ANN ARBOR—California sardine stocks famously crashed in John Steinbeck’s “Cannery Row.” New research, building on previous since the late 1960s, shows in greater detail that such forage fish stocks have undergone boom-bust cycles for centuries, with at least three species off the U.S. West Coast repeatedly experiencing steep population increases followed by declines long before commercial fishing began.

Natural population fluctuations in Pacific sardine, northern anchovy and Pacific hake off California have been so common that the species were in collapsed condition 29 to 40 percent of the time over the 500-year period from A.D. 1000 to 1500, according to the study published online Feb. 9 in Geophysical Research Letters.

Using a long time series of fish scales deposited in low-oxygen, offshore sedimentary environments off Southern California, researchers from the National Oceanic and Atmospheric Administration and the University of Michigan described such collapses as “an intrinsic property of some forage fish populations that should be expected, just as droughts are expected in an arid climate.”

The findings have implications for the ecosystem, as well as fishermen and fisheries managers, who have witnessed several booms, followed by crashes every one to two decades on average and lasting a decade or more, the scientists wrote. Collapses in forage fish—small fish that are preyed on by larger predators for food—can reverberate through the marine food web, causing prey limitation among predators such as sea lions and sea birds.

“Forage fish populations are resilient over the long term, which is how they come back from such steep collapses over and over again,” said Sam McClatchie, supervisory oceanographer at NOAA Fisheries’ Southwest Fisheries Science Center in La Jolla, Calif., and first author of the paper.

“That doesn’t change the fact that these species may remain at very low levels for periods long enough to have very real consequences for the people and wildlife who count on them,” he said.

Downturns in sardine and anchovy linked to changing ocean conditions have contributed to the localized stranding of thousands of California sea lion pups in recent years.

Former University of Michigan graduate student Karla Knudsen, left, and former U-M undergraduate Athena Eyster sample deep-sea sediment collected in 2009 with a coring device beneath the Santa Barbara Channel in California. The sediments were used in a fish-scale analysis. Image credit: Ingrid Hendy

Scientists traced the historic abundance of sardine, anchovy and hake by examining deposits of their scales collected on the floor of the Santa Barbara Channel from A.D. 1000 to 1500. While previous studies had shown that forage fish exhibited collapses prior to commercial fishing, the new research used methods developed by climatologists to examine the frequency and duration of the fluctuation in finer detail.

“The Mediterranean climate of California, with wet winters and dry summers, produces a sediment layer we can pull apart like pages in a book,” said U-M paleoceanographer and study co-author Ingrid Hendy. “Although these sediments have been studied before, we are using new technology to examine them in unprecedented detail.”

Hendy and members of her lab collected the California sediments in 2009 using a coring device that allowed them to sample large portions of the sea floor beneath the Santa Barbara Channel. Hendy is an associate professor in the U-M Department of Earth and Environmental Sciences.

In the lab, fish scales from the core were identified under a binocular dissecting microscope by comparing them to reference specimens from the U-M Museum of Zoology collection. Anchovies in the collection were bought at the San Pedro Fish Market, near Long Beach, Calif., in 1922. The sardines came from Barkley Sound, on the west coast of Vancouver Island, and were collected in 1933.

From left to right: Former University of Michigan undergraduate Athena Eyster, former U-M graduate student Karla Knudsen, Ingrid Hendy and former U-M graduate student Meghan Wagner examine a sediment core collected in the Santa Barbara Channel, California, in 2009. Image credit: Arndt Schimmelmann

The fish-scale analysis was performed by former U-M undergraduate Alexandra Skrivanek, who is now a graduate student at the University of Florida. Hendy’s lab has also helped to advance techniques used to date the layers within marine sediment cores. Those advances involve improved radiocarbon dating of organic materials in the sediments and better ways to count the annual layers, Hendy said.

The scientists described a collapse as a drop below 10 percent of the average peak in fish populations, as estimated from the paleorecord. Anchovy took an average of eight years to recover from a collapse, while sardine and hake took an average of 22 years.

The record also showed that sardine and anchovy fluctuated synchronously over the 500-year study period. Combined collapses may compound the impact on predators and the fishery, the scientists said. The finding runs counter to suggestions that the two species’ cycles alternate.

Sardine and anchovy have at times been the most heavily harvested fish off Southern California in terms of volume. Hake, also known as Pacific whiting, spawn off California but are harvested in large volumes off the Pacific Northwest and Canada.

The new study concludes these forage fish are well-suited to variable fishing rates that target the species in times of abundance, “while recognizing that mean persistence of fishable populations is one to two decades, and that switching to other target species will become a necessity.”

Collapses last, on average, “too long for the industry to simply wait out the return of the forage fish.”

The study authors concluded that “well-designed reserve thresholds” and adjustable harvest rates help protect the forage species, the fishery and nonhuman predators for the long term. However, they added that “reserve thresholds only protect the seed stock for recovery, and cannot prevent collapses from occurring.”

Funding for the study was provided by NOAA and the National Science Foundation.

Read the original post: http://www.ns.umich.edu/

Scientists: Major Oxygen Loss to Oceans Linked to Warming Climate

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SEAFOODNEWS.COM [Washington Post] by By Chris Mooney – February 16, 2017

A large research synthesis, published in one of the world’s most influential scientific journals, has detected a decline in the amount of dissolved oxygen in oceans around the world — a long-predicted result of climate change that could have severe consequences for marine organisms if it continues.

The paper, published Wednesday in the journal Nature by oceanographer Sunke Schmidtko and two colleagues from the GEOMAR Helmholtz Centre for Ocean Research in Kiel, Germany, found a decline of more than 2 percent in ocean oxygen content worldwide between 1960 and 2010. The loss, however, showed up in some ocean basins more than others. The largest overall volume of oxygen was lost in the largest ocean — the Pacific — but as a percentage, the decline was sharpest in the Arctic Ocean, a region facing Earth’s most stark climate change.

The loss of ocean oxygen “has been assumed from models, and there have been lots of regional analysis that have shown local decline, but it has never been shown on the global scale, and never for the deep ocean,” said Schmidtko, who conducted the research with Lothar Stramma and Martin Visbeck, also of GEOMAR.

Ocean oxygen is vital to marine organisms, but also very delicate — unlike in the atmosphere, where gases mix together thoroughly, in the ocean that is far harder to accomplish, Schmidtko explained. Moreover, he added, just 1 percent of all the Earth’s available oxygen mixes into the ocean; the vast majority remains in the air.

Climate change models predict the oceans will lose oxygen because of several factors. Most obvious is simply that warmer water holds less dissolved gases, including oxygen. “It’s the same reason we keep our sparkling drinks pretty cold,” Schmidtko said.

But another factor is the growing stratification of ocean waters. Oxygen enters the ocean at its surface, from the atmosphere and from the photosynthetic activity of marine microorganisms. But as that upper layer warms up, the oxygen-rich waters are less likely to mix down into cooler layers of the ocean because the warm waters are less dense and do not sink as readily.

“When the upper ocean warms, less water gets down deep, and so therefore, the oxygen supply to the deep ocean is shut down or significantly reduced,” Schmidtko said.

The new study represents a synthesis of literally “millions” of separate ocean measurements over time, according to GEOMAR. The authors then used interpolation techniques for areas of the ocean where they lacked measurements.

The resulting study attributes less than 15 percent of the total oxygen loss to sheer warmer temperatures, which create less solubility. The rest was attributed to other factors, such as a lack of mixing.

Matthew Long, an oceanographer from the National Center for Atmospheric Research who has published on ocean oxygen loss, said he considers the new results “robust” and a “major advance in synthesizing observations to examine oxygen trends on a global scale.”

Long was not involved in the current work, but his research had previously demonstrated that ocean oxygen loss was expected to occur and that it should soon be possible to demonstrate that in the real world through measurements, despite the complexities involved in studying the global ocean and deducing trends about it.

That’s just what the new study has done.

“Natural variations have obscured our ability to definitively detect this signal in observations,” Long said in an email. “In this study, however, Schmidtko et al. synthesize all available observations to show a global-scale decline in oxygen that conforms to the patterns we expect from human-driven climate warming. They do not make a definitive attribution statement, but the data are consistent with and strongly suggestive of human-driven warming as a root cause of the oxygen decline.

“It is alarming to see this signal begin to emerge clearly in the observational data,” he added.

“Schmidtko and colleagues’ findings should ring yet more alarm bells about the consequences of global warming,” added Denis Gilbert, a researcher with the Maurice Lamontagne Institute at Fisheries and Oceans Canada in Quebec, in an accompanying commentary on the study also published in Nature.

Because oxygen in the global ocean is not evenly distributed, the 2 percent overall decline means there is a much larger decline in some areas of the ocean than others.

Moreover, the ocean already contains so-called oxygen minimum zones, generally found in the middle depths. The great fear is that their expansion upward, into habitats where fish and other organism thrive, will reduce the available habitat for marine organisms.

In shallower waters, meanwhile, the development of ocean “hypoxic” areas, or so-called “dead zones,” may also be influenced in part by declining oxygen content overall.

On top of all of that, declining ocean oxygen can also worsen global warming in a feedback loop. In or near low oxygen areas of the oceans, microorganisms tend to produce nitrous oxide, a greenhouse gas, Gilbert writes. Thus the new study “implies that production rates and efflux to the atmosphere of nitrous oxide … will probably have increased.”

The new study underscores once again that some of the most profound consequences of climate change are occurring in the oceans, rather than on land. In recent years, incursions of warm ocean water have caused large die-offs of coral reefs, and in some cases, kelp forests as well. Meanwhile, warmer oceans have also begun to destabilize glaciers in Greenland and Antarctica, and as they melt, these glaciers freshen the ocean waters and potentially change the nature of their circulation.

When it comes to ocean deoxygenation, as climate change continues, this trend should also increase — studies suggest a loss of up to 7 percent of the ocean’s oxygen by 2100. At the end of the current paper, the researchers are blunt about the consequences of a continuing loss of oceanic oxygen.

“Far-reaching implications for marine ecosystems and fisheries can be expected,” they write.

Copyright © 2016 Seafoodnews.com