North Atlantic right whale population decline confirmed

NOAA Fisheries researchers and colleagues at the New England Aquarium have developed a new model to improve estimates of abundance and population trends of endangered North Atlantic right whales, which have declined in numbers and productivity in recent years. The findings are published in the journal Ecology and Evolution.

A North Atlantic right whale mother and calf, sighted June 8, 2014, during an aerial survey by the Northeast 
Fisheries Science Center [Credit: NOAA Fisheries/Christin Khan, NEFSC]

Between 1990 and 2010, the abundance of North Atlantic right whales increased just under three percent per year, from about 270 animals in 1990 to 482 in 2010. After relatively steady increases over that time, abundance has declined each year since 2010 to 458 animals in 2015. The analysis shows that the probability that the population has declined since 2010 is estimated at 99.99 percent. Of particular concern is decline of adult females in the population, estimated at 200 in 2010 but 186 in 2015, the known deaths of 14 North Atlantic right whales this year, and the widening gap between numbers of males and females.

"Although our work directly reveals a relatively small decrease, the subtext is that this species is presently in dire straits," said lead author Richard Pace.

Pace is a large whale researcher at NOAA's Northeast Fisheries Science Center. Other authors include NEFSC whale researcher Peter Corkeron, and Scott Kraus of the New England Aquarium.

The new statistical method reported today provides a clearer and timelier picture of North Atlantic right whale numbers. While both existing methods and the new statistical method for estimating North Atlantic right whale numbers show a decline in the population since 2010, the new estimates are less affected by changes in whale distribution, less reliant on sighting frequency, and better account for animals that are still alive but are not frequently seen.

Right whale (Eubalaena glacialis) skim feeding, with baleen clearly visible 
[Credit: NOAA Fisheries/Elizabeth Josephson, NEFSC]

In the past few years, these whales have not aggregated as consistently at the times and places where they have in the past. This reduces the likelihood that they will be sighted since survey efforts are most efficient when conducted while whales are coming together in larger groups to feed, calve, and care for young. This change in behavior has made the census-based estimate of their populations less reliable than in the past, and led to development of the new statistical model for estimating abundance.

The New England Aquarium has conducted research on right whales for more than three decades and also maintains the North Atlantic Right Whale Catalog. All methods for estimating abundance rely extensively on this record. The catalog combines information on individually identified North Atlantic right whales collected through annual surveys undertaken by a variety of researchers. The result is a comprehensive photographic census of the population for at least the past 25 years.

For this study, data from more than 61,000 sightings were reviewed. Analysis included sighting histories from 658 whales, including 280 females, 328 males and 50 animals of unknown sex. Of the 658 whales seen during the study period of 1990 to 2015, 247 were first seen before 1990.

NOAA Fisheries works directly with fishermen and shipping companies to reduce harm that can be caused if whales entangle in gear or collide with ships, two well-documented causes of whale deaths and serious injuries, and with researchers throughout the region to understand the biology and condition of animals in the population. The agency is also assisting Canadian officials and scientists with their efforts to reduce risks to these whales in Canadian waters.

Source: NOAA Northeast Fisheries Science Center [September 19, 2017]

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Old fish few and far between under fishing pressure

Like old-growth trees in a forest, old fish in the ocean play important roles in the diversity and stability of marine ecosystems. Critically, the longer a fish is allowed to live, the more likely it is to successfully reproduce over the course of its lifetime, which is particularly important in variable environmental conditions.

A large, old yelloweye rockfish [Credit: Victoria O'Connell]

A new study by University of Washington scientists has found that, for dozens of fish populations around the globe, old fish are greatly depleted -- mainly because of fishing pressure. The paper, published in Current Biology, is the first to report that old fish are missing in many populations around the world.

"From our perspective, having a broad age structure provides more chances at getting that right combination of when and where to reproduce," said lead author Lewis Barnett, a UW postdoctoral researcher at the School of Aquatic and Fishery Sciences and the Joint Institute for the Study of the Atmosphere and Ocean.

In forestry, a tree farm with only 20-year-old trees may be healthy and productive, but the loss of old-growth trees should not go unnoticed. The giant trees have unique traits that support a number of animal and plant species and make for a diverse, robust ecosystem. In a similar sense, the same is true for old fish.

"More age complexity among species can contribute to the overall stability of a community," Barnett said. "If you trim away that diversity, you're probably reducing the marine food web's ability to buffer against change."

The designation of an "old fish" varies from species to species, depending on life history. Some types of rockfish might live to 200 years, while few herring live past age 10.

After female fish release eggs, many factors must align for a healthy brood to hatch and grow to adult size. Because the marine environment is so variable, species might go a whole decade between successful broods. Older fish in a population have more years to produce eggs, increasing the chance for success over time.

The face of an old halibut fish [Credit: Andrea Pokrzywinski]

"In the marine world, the success rate of producing new baby fish is extremely variable," said co-author Trevor Branch, a UW associate professor of aquatic and fishery sciences. "I think of old fish as an insurance policy -- they get you through those periods of bad reproduction by consistently producing eggs."

In addition to having more opportunities to reproduce, older fish also behave differently than younger fish. As they age, some fish change what they eat and where they live in the ocean. They also take on different roles in the marine food web, sometimes becoming a more dominant predator as they get older, and bigger.

When you take old fish out of the mix, the diversity and stability of an ecosystem can suffer, the authors explain.

"Big fish are in a lot of ways different from smaller fish," said co-author Tim Essington, a UW professor of aquatic and fishery sciences. "Having that diversity acts as a hedge against risk and helps stabilize the system a bit."

The researchers looked at model output gathered from commercial and recreational fisheries and scientific observations that describe the status of fish populations over the years. In their analysis of 63 populations living in five ocean regions worldwide, they found that the proportion of fish in the oldest age classes has declined significantly in 79 to 97 percent of populations, compared with historical fishing trends or unfished figures, respectively. The magnitude of decline was greater than 90 percent in 32 to 41 percent of the groups.

This is mainly due to fishing pressure, the researchers say. In general, the longer a fish lives, the more encounters it has with fishing gear, and the greater the likelihood it will be caught. However, some environmental factors like disease and pollution might also contribute to the loss of old fish.

These findings could inform fisheries management, which often sets limitations based on the total weight of fish caught over a season without considering factors such as the size or age of a fish. The authors suggest fishing methods to protect young and old fish by prohibiting the harvest of fish below and above a specific size range. Other solutions include closing certain areas to fishing permanently, or rotating areas where fishing can take place each year to let fish grow older and bigger -- similar to agricultural crop rotations that allow the soil to recover between planting cycles.

Author: Michelle Ma | Source: University of Washington [September 14, 2017]

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How openings in Antarctic sea ice affect worldwide climate

In 1974, images acquired from NOAA satellites revealed a puzzling phenomenon: a 250,000 square kilometer opening in the winter sea ice in the Weddell Sea, south of South America. The opening, known as a polynya, persisted over three winters. Such expansive ice-free areas in the ocean surrounding Antarctica have not been seen since, though a small polynya was seen last year.

A polynya, or an opening in the sea ice, was present in the Southern Ocean in the 1970s. This image shows the sea ice 
concentration averaged over three September months 1974-1976 during the Weddell Polynya, made with data from 
the NIMBUS-V satellite from the National Snow Ice Data Center [Credit: University of Pennsylvania]

In a new analysis of climate models, researchers from the University of Pennslyvania, Spain's Institute of Marine Sciences and Johns Hopkins University reveal the significant global effects that these seemingly anomalous polynyas can have. Their findings indicate that heat escaping from the ocean through these openings impacts sea and atmospheric temperatures and wind patterns around the globe and even rainfall around the tropics. Though this process is part of a natural pattern of climate variability, it has implications for how the global climate will respond to future anthropogenic warming.

"This small, isolated opening in the sea ice in the Southern Ocean can have significant, large-scale climate implications," said Irina Marinov, a study author and assistant professor in Penn's Department of Earth and Enviromental Science in the School of Arts & Sciences. "Climate models suggest that, in years and decades with a large polynya, the entire atmosphere warms globally, and we see changes in the winds in the Southern Hemisphere and a southward shift in the equatorial rain belt. This is attributable to the polynya."

The study appears in the Journal of Climate. Marinov coauthored the work with Anna Cabre, a former postdoc in Marinov's lab and now an oceanographer with the Institue of Marine Sciences in Barcelona, and Anand Gnanadesikan, a professor in the Department of Earth and Planetary Science at Johns Hopkins.

Typically, the Southern Ocean is covered in ice during the Southern Hemisphere's

winter. Polynyas occur when warm subsurface waters of North Atlantic and equatorial origin mix locally with cold surface waters, a process known as open-ocean convection.

Until recently, climate scientists and oceanographers believed that atmospheric and ocean conditions around the tropics were the primary drivers in affecting conditions outside the tropics. But in the last few years, Marinov and collaborators and others have shown that the opposite is also true: the Southern Ocean has an important role in affecting tropical and Northern Hemisphere climates.

Marinov's team uncovered a natural climate pattern originating from openings in the sea ice of the Weddell Sea. This 
diagram shows the Weddell Sea surface temperature (in black) and Southern Ocean sea ice cover percentage (red) for 
500 years in the researchers' climate model simulation. At bottom: the temperature in the Weddell Sea is shown over 
sea depth for the same 500 years of the simulation. In non-convective years the heat is stored in the Southern Ocean 
subsurface, the surface is cold and there is extensive sea-ice. In convective years the subsurface heat is released 
from the deep ocean, heating the surface ocean and melting the sea ice, resulting in polynyas 
[Credit: University of Pennsylvania]

In the current work, Marinov and colleagues used powerful models that simulate past and future climate to determine how the effects of polynya ripple out around the globe.

Their model indicated that polynyas and accompanying open-ocean convection occur roughly every 75 years. When they occur, the researchers observed, they act as a release valve for the ocean's heat. Not only does the immediate area warm, but there are also increases in overall sea-surface and atmospheric temperatures of the entire Southern Hemisphere and, to a lesser extent, the Northern Hemisphere, as well.

Changes in north-south temperature gradients lead to changes in wind patterns as well.

"We are seeing a decrease in what we call the Southern Hemisphere westerlies and changes in trade winds," Marinov said. "And these winds affect storms, precipitation and clouds."

Among these changes in precipitation is a shift in the Intertropical Convergence Zone, an equatorial belt where trade winds converge, resulting in intense precipitation. When a polynya occurs, this rain belt moves south a few degrees and stays there for 20 to 30 years before shifting back.

"This affects water resources in, for example, Indonesia, South America and sub-Saharan Africa," said Marinov. "We have a natural variation in climate that may be, among other effects, impacting agricultural production in heavily populated regions of the world."

Given these broad-scale implications of a Southern Ocean phenomenon, Marinov underscores the need to increase monitoring in the region. She is part of an effort called SOCCOM, for Southern Ocean Carbon and Climate Observations and Modeling, placing robotic floats in the Southern Ocean to collect data on ocean temperature, salinity, carbon, nutrients and oxygen.

"We're also urging people to keep a close eye on the satellites to look for other polynyas, this year and going forward," Marinov said.

Earlier research by Marinov's group and collaborators suggested that, under climate change, polynyas may become less frequent. As sea ice melts it freshens the top layer of the sea surface, making it lighter and less likely to mix with the heavier bottom waters. Marinov notes that the fact that no significant polynyas opened up from the mid-1970s until last year may have contributed to the so-called "climate hiatus" in the late 1990s and early 2000s, when global average surface temperatures appeared to stall in their otherwise persistent upward climb.

"During this hiatus period abnormal amounts of heat were stored in the subsurface ocean waters" Marinov said. "Most research has attributed this hiatus to a prolonged La Nina period, resulting in a storage of heat in the low-latitude Pacific. But I think that a lack of a Weddell Sea polynya also contributed, storing more heat in the Southern Ocean and preventing the additional release of heat to the atmosphere."

The work raises many new questions, such as how a decreasing sea ice extent, including the recent breaking off of a massive chunk of the Antarctic peninsula, will affect the frequency of polynyas and how the presence or absence of polynyas will affect how much atmospheric temperatures warm in response to anthropogenic climate change.

"This investigating into polynyas and Southern Ocean convection turned out to be a very important and interesting story for the global climate that we think a lot of people will be studying in the next decade," Marinov said.

Source: University of Pennsylvania [September 11, 2017]

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Indicators of global climate change are detected in tropical oceans

Researchers from the University of California, Irvine and NASA's Jet Propulsion Laboratory have reported the first observation of sea level "fingerprints," tell-tale differences in sea level rise around the world in response to changes in continental water and ice sheet mass. The team's findings were published in the American Geophysical Union journal Geophysical Research Letters.

"Scientists have a solid understanding of the physics of sea level fingerprints, but we've never had a direct detection 
of the phenomenon until now," says study co-author Isabella Velicogna, a UCI professor of Earth system science
 and Jet Propulsion Laboratory research scientist, shown here on an expedition to Greenland 
[Credit: Maria Stenzel/UCI]

"Scientists have a solid understanding of the physics of sea level fingerprints, but we've never had a direct detection of the phenomenon until now," said co-author Isabella Velicogna, UCI professor of Earth system science and JPL research scientist.

As ice sheets and glaciers undergo climate-related melting, they alter Earth's gravity field, which causes nonuniform sea level change. Certain regions, particularly in the middle latitudes, are harder hit. For instance, Antarctica-generated sea level rise in California and Florida is as much as 52 percent greater than what's average in the rest of the world.

Cumulative sea level fingerprints calculated from observations of Greenland, Antarctica, glaciers 
and ice caps and land water storage mass changes observed with the GRACE satellites for the time
 period January 2003 to April 2014 [Credit: Isabella Velicogna & Chia-Wei Hsu/UCI]

The team calculated sea level fingerprints using time-variable gravity data collected by the twin satellites of NASA's Gravity Recovery & Climate Experiment between April 2002 and October 2014. During that time, according to the study, the global mean sea level grew by about 1.8 millimeters per year, with 43 percent of the increased water mass coming from Greenland, 16 percent from Antarctica, and 30 percent from mountain glaciers. The scientists verified their calculations of sea level fingerprints associated with these mass variations via ocean-bottom pressure readings from stations in the tropics.

Sea level fingerprints in millimeters per year calculated from observations of the mass loss of Greenland, 
Antarctica, glaciers and ice caps and changes in land water storage using time-variable gravity data collected 
by the twin satellites of the U.S./German Gravity Recovery and Climate Experiment mission between April 2002 
and October 2014. The blue contour (1.8 mm/year) is the average sea level rise if the total addition of mass 
of water to the ocean was spread uniformly over the world’s oceans. The SLF are not uniform and bulge
 around the equatorial regions [Credit: Isabella Velicogna & Chia-Wei Hsu/UCI]

"It was very exciting to observe the sea level fingerprints in the tropics, where they were not expected to be detectable," said lead author Chia-Wei Hsu, a graduate student researcher at UCI. "In the tropics, sea level fingerprint values are very close to global average sea level values, making them harder to detect."

Velicogna added: "We know that sea levels climb faster in the middle to low latitudes versus the high latitudes and that Greenland and Antarctica contribute differently to the process. With our improved understanding through GRACE data and other techniques, we're now able to take any point on the global ocean and determine how much the sea level there will rise as a result of glacier ice melt."

Source: University of California - Irvine [September 08, 2017]

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