(Courtesy Photo)

Researchers at Cal State Long Beach have discovered high concentrations of contaminants in young great white sharks along the coast of Southern California.

But the toxic chemicals DDT and polychlorinated biphenyl - which researchers say is passed on from their mothers - seem to cause little harm to the young sharks.

"We were unable to find any sort of indication to suggest that the contaminants were having any negative effects on the sharks," said Professor Christopher G. Lowe, a co-author of the report and director of CSULB's Shark Lab.

The study was conducted as part of a 10-year project in partnership with marine biologists from the Monterey Bay Aquarium and the Southern California Marine Institute. The goal was to understand the migrations of juvenile great white sharks in waters off Southern California and Baja California.

Findings from the study will be featured in the online science journal PLOS ONE.

Researchers looked at the remains of young sharks incidentally caught in commercial fishing nets. They concluded that mother sharks acquire toxic chemicals from the food chain and likely pass them on to their young.

Adult sharks feed on California sea lions and seals, which are known to have high levels of PCBs and DDT. Researchers found that young great whites had the highest levels of DDT and second highest levels of PCBs ever reported for a shark.


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"This was particularly alarming given their young age, some likely weeks to months old, and the fact that other shark species with comparable levels were often decades old," said lead author Christopher Mull, in a statement. "Even though we know Southern California is a DDT hot spot, we suspected that these levels couldn't have been obtained solely by young sharks feeding, and that mothers were a likely source. "

Millions of pounds of DDT were dumped into ocean waters from the Montrose Chemical Corporation's manufacturing plant in Torrance, from the late 1940s to the early 1970s, according to the Department of Justice. Wildlife is still impacted by the contaminant discharge, despite a federal effort to restore and protect the habitat.

Mull, now a Ph.D. candidate at Simon Fraser University in Burnaby, British Columbia, first became involved in the study while completing his master's degree at the Shark Lab.

Researchers ran a computer simulation on a virtual newborn shark pup with no contaminants. They fed the virtual pup a meal of the most contaminated fish it could eat daily.

Lowe said the simulated levels were not nearly as high as what was found in necropsy results from incidentally caught sharks. The findings led researchers to believe that young sharks could not acquire the high levels of contaminants through their own diet.

"When we got the numbers back, my jaw hit the ground," Lowe said. "We didn't understand how these levels could be this high. That's when we started to put the pieces together. "

Many species pass on contaminants to their offspring, but the transfers among white sharks were not previously studied, researchers said.

Lowe said white sharks are pregnant for about 12 months. Developing embryos eat unfertilized egg yolks rich in fats and oils, but because the shark mothers eat contaminated fish and marine mammals, they pass the contaminants to their offspring via the eggs, Lowe said.

At the same time, researchers found no evidence of physiological damage from the contaminants. In fact, the white shark population appears to be on the upswing from record lows, as they have been protected.

Lowe said it appears that a shark with high levels of contaminants is not weaker than one with low levels, and necropsies revealed no signs of internal cancers or lesions that usually indicate contaminant exposure.

"It's very possible that they've got some tricks to dealing with these contaminants that other vertebrates and species of fish don't have," he said.