migrating

Ocean Oxygen Levels And The Future Of Fish | Earth Wise

June 23, 2023 By EarthWise Leave a Comment

Climate change is creating a cascade of effects in the world’s oceans. Not only are ocean temperatures on the rise, but oceans are becoming more acidic, and oxygen deprived. The warming temperatures and acidification have grabbed headlines and prompted academic research. Declining oxygen levels have not garnered as much attention. But they spell bad news for fish.

Oxygen levels in the world’s oceans have dropped over 2% between 1960 and 2010 and are expected to decline up to 7% over the next century. There are places in the northeast Pacific that have lost more than 15% of their oxygen. There are a growing number of “oxygen minimum zones” where big fish cannot survive but jellyfish can.

Oceans are losing oxygen for several reasons. First, warmer water can hold less dissolved gas than colder water. (This is why warm soda is flatter than cold soda.) Deeper in the ocean, oxygen levels are governed by currents that mix oxygen-rich surface water from above. Melting ice in the warming polar regions add fresh, less-dense water that resists downward mixing in key regions. Finally, increasing amounts of ocean bacteria in warming waters gobble up oxygen creating dead zones in the ocean.

In many places, fish species that cannot cope with lower oxygen levels are migrating from their usual homes, resulting in a decline in species diversity. Our future oceans – warmer and oxygen-deprived – will not only hold fewer kinds of fish, but also smaller fish and even more greenhouse-gas producing bacteria.

Climate change is bad news for fish and for the more than 3 billion people in the world who depend on seafood as a significant source of protein.

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As Ocean Oxygen Levels Dip, Fish Face an Uncertain Future

Photo, posted January 10, 2022, courtesy of Willy Goldsmith via Flickr.

Earth Wise is a production of WAMC Northeast Public Radio

Marine Life Moving The Wrong Way | Earth Wise

October 26, 2020 By EarthWise Leave a Comment

As the oceans have warmed in recent decades, various marine species ranging from whales to corals have begun to shift poleward in search of cooler waters. But a new study, reported in the journal Nature Climate Change, found that many sedentary marine species – including snails, worms, and mussels – are actually being transported in the wrong direction.

What is happening is that bottom-dwelling species – also known as benthic species – in the northwest Atlantic Ocean are spawning earlier in the year because of the warmer water temperatures. But earlier in the year is when ocean currents travel southward. As a result, the larvae of these animals are being carried into warmer waters rather than cooler ones, threatening their survival and shrinking their ranges. These larvae grow into adults in these warmer regions and are basically trapped there. This creates a feedback loop where the situation for the species gets worse and worse. Species like common sand dollars and the economically important blue mussel have had a 30 to 50% contraction of their ranges.

The result is that a number of bottom-dwelling species that previously were quite abundant have entirely disappeared from the outer shelf.

The researchers at Rutgers University likened this “wrong-way migration” of bottom-dwelling marine life to so-called elevator-to-extinction events that have been taking place in mountainous regions. This is where species such as birds and butterflies move to higher and higher elevations to escape rising temperatures until there is nowhere else for them to go.

The essential fact that this research reveals is that species don’t necessarily move to places where the climate is congenial for them. They may unfortunately end up migrating to even worse conditions.

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As Oceans Warm, Some Species Are Moving in the Wrong Direction

Photo, posted June 10, 2016, courtesy of James_Seattle via Flickr.

Earth Wise is a production of WAMC Northeast Public Radio.

Dangerous Cities For Migrating Birds

May 14, 2019 By EarthWise Leave a Comment

Billions of birds migrate north in the spring and south in the fall. The majority of them fly at night. But as they pass over large cities, the birds can become disoriented by bright artificial light – so-called light pollution, causing them to crash into buildings or windows.

Researchers estimate that 600 million birds die from building collisions in the United States every year. Now, a new paper from researchers at Cornell University reveals which metropolitan areas are most dangerous for birds and why.

The researchers ranked cities where, as a result of geography and exposure to light pollution, birds are at the greatest risk of becoming attracted to and disoriented by lights and crashing into buildings. They combined light pollution levels with bird density data in order to make their calculations. Their paper was recently published in the journal Frontiers in Ecology and the Environment.

Chicago, Houston, and Dallas finished as the three most dangerous cities for migrating birds. While migration routes vary depending on the season, these three cities still topped all others during both the spring and fall migrations due to their size and geographic positioning in the heart of North America’s most trafficked aerial corridors.

Audubon’s Lights Out program is one of several national efforts encouraging cities to reduce light pollution, particularly on heavy migration nights, in order to reduce bird mortality.

But homeowners need to do their part as well since an estimated quarter-million birds die from collisions with residential houses every year. The suggestion to cities and homeowners alike is the same: If you don’t need the lights, turn them off.

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Chicago tops list of most dangerous cities for migrating birds

Photo, posted May 18, 2017, courtesy of Pedro Szekely via Flickr.

Earth Wise is a production of WAMC Northeast Public Radio.