The Heat Is Online

Warming Drives Turnover of Portuguese Fish Population

Warmer water changing Portugal fish species, April 2, 2002

LISBON - Rising water temperatures have dramatically changed the species of fish in Portugal's Tejo River estuary, the biggest in Western Europe, a researcher said yesterday.

Maria Jose Costa, director of oceanography at the University of Lisbon, said global warming had caused such cold-water species as flounder and red mullet almost to disappear in the last two decades.

At the same time, the numbers of warm-water fish such as Senegal sea bream, common to North African waters, and dogfish have vastly increased.

"This can only be explained by the temperature allowing it to happen by going up," said Costa, one of the authors of a recent study on the estuary.

The findings about environmental changes in the estuary, where the Tejo's fresh water mixes with the Atlantic Ocean, is scheduled to be discussed at a seminar this week. The Lisbon meeting will include researchers from England and Scotland.

Many scientists believe that polluting gases, such as carbon dioxide, trap the sun's heat and make the Earth warmer. The Tejo's surface temperature has risen more than one degree Celsius from 1980 to 1996, the study said.

The study notes that flounder eggs often die when winter temperatures top 12 degrees Celsius. Surface temperatures for March 1995-96 were 15.33 degrees, and for November 1995-96 were 16.67.

The estuary embraces 320 square km (123.6 sq miles) where the Tejo's fresh water water mixes with the Atlantic Ocean. The 1,000 km (621.4 mile) long river flows west into Portugal from Spain, where it is called the Tagus.

Costa said Portugal was on a frontier between warm-and cold-water species, making it a natural laboratory for study.