After living happily in the Yarkon River for generations, the Potamon potamios, a semi-terrestrial crab, is threatened by a much bigger and aggressive species of Australian crayfish.
Ecologists fear the newcomer – identified as the Australian red claw crayfish (cherax quadricarinatus) – could attack local species, disrupt their breeding and compete with them for food sources and living areas, upsetting the ecosystem in the Tel Aviv area’s Yarkon Park.
After receiving a number of reports from hikers of a large crab near the river, the River Authority and Nature and Parks Authority last week conducted a search of the area.
“We used special traps for river crabs and, to our dismay, we found 10 crayfish,” said Dr. Dana Milstein, aquatic ecologist for theNature and Parks Authority. “All of them were found up-river, in the less polluted part of it.”
She added there were probably more crayfish than those that had been found in the search.
The crayfish, originating from rivers in north Australia, can grow to a length of 35 cm. It was first spotted in the Kinneret area four years ago and identified by Dr. Bella Gallil, a scientist at the National Institute of Oceanography.
“We’ve seen it sporadically since then in several places, but the Yarkon is the first water source in which it has managed to settle down,” Milstein said.
While scientists don’t know much about the Yarkon’s new tenant, they say its impact is most likely to be negative and could undermine the efforts to preserve and rehabilitate the river.
“We do know it competes with local crab species,” says Milstein. “It’s said to be omnivorous so we’re afraid it could endanger the iridescent toothcarp, a species of killifish that used to live here and became extinct, which we were planning to return to the river soon.
“The crayfish could also have an indirect impact because its activities, like uprooting plants, could alter the natural habitat and affect other species. We’re consulting with experts to get more information.”
The red claw crayfish, which is bred for eating in many countries, is legally imported to Israel and is popular among fish tank owners. However, it often turns into a nuisance for domestic owners as it endangers other animals. Ecologists speculate that the Yarkon crayfish were dumped there by someone who grew tired of his pets.
“What was he thinking?” asked Yarkon River Authority director David Pergament on Wednesday. “That he could get rid of his problem by causing harm to a place people visit and walk in?”
Milstein says it may take several years to remove the crayfish from the Yarkon River. In the meantime, the authority is trying to find a solution to the new threat, possibly including asking the Agriculture Ministry to revoke import permits for the crayfish.
“It’s enough for a crayfish to even so much as bother a female tilapia, which carries its eggs in its mouth during breeding season, and the tilapia will have to spit them out,” Menachem Goren, a zoology researcher at Tel Aviv University, told Haaretz in May 2011, after the species was discovered in the Kinneret.
At the time the crayfish was first imported to Israeli for breeding 19 years ago, experts suggested raising it in artificial pools in the desert only. They warned that otherwise they might escape into the wild. But the Agriculture Ministry eventually allowed fish breeders to bring the crayfish further north.
Today Israel raises millions of crayfish every year, both for the local market and for export to Europe.