Rising Water Temperatures Have Ill Effect on Fish, Two Studies Show

Two studies, one in Lake Tanganyika in Africa and the other in the River Wye in Wales, indicate that rising water temperatures are causing fish populations to decline. Researchers from Brown University and the University of Arizona, said core samples from Lake Tanganyika — the second-deepest lake in the world — show that surface water temperatures in the lake are the highest they’ve been in 1,500 years. Now roughly 80 degrees F, the higher surface temperatures intensify temperature stratification in the lake and inhibit upwelling of cool waters and nutrients. The study, published in Nature Geoscience, showed that over the centuries warmer lake temperatures led to less production of algae and other marine organisms, which impact fish populations. The researchers said rising surface temperatures and overfishing are leading to a drop in catches of sardines and other fish on which millions of people in the region depend. In the Wales study, researchers from the Cardiff School of Biosciences said populations of trout and salmon in the River Wye declined by 67 percent and 50 percent respectively from 1985 and 2004, as stream temperatures rose by up to 1.2 F in summer and 1.8 F in winter. Hot dry summers in 1990, 2000, and 2003 caused higher fish mortality in trout and salmon, which have evolved to live in cooler waters.