bears Catching Salmon

Salmon and other predatory fish also devour the euphausiids. So the drop in the population of these large zooplankton near the coastal areas, may be part of the reason the salmon failed to return to the rivers of western Alaska, said Hunt. According to the NOAA report (Brodeur et al. 1998), the salmon populations over the past two summers fell 53 percent below what was expected, putting many fisheries out of business. In addition, more salmon are being found off the coast of Siberia and on Alaska’s southern shores outside the Bering Sea. The salmon that do return to western Alaska vary in age and strength. In earlier years with low turnout, the healthier, larger salmon would normally make up the majority of the returning fish.

The disappearance of the zooplankton probably isn’t the only reason the fish counts are down and the birds are dying, but the disappearance contributes to the problem. Steve Zeeman, a biological oceanographer at the University of Maine and a colleague of William Balch, explained that the disappearance of the zooplankton has to do with size. The diatoms that usually dominate the shelf are quite a bit larger than the coccolithophores. Since larger microscopic animals like euphausiids survive by feeding on larger one-celled plants like diatoms, the absence of the plant will cause a drop in the animal population. "And we then see a decline of wildlife along the food chain," said Zeeman. His conjecture is supported by the NOAA report (Napp et al. 1998), which states that the short-term change in zooplankton coincides with the change in the Bering Sea’s phytoplankton.

source earthobservatory.nasa.gov