Fish census results skewed by diver presence

The presence of scuba divers conducting fish census counts may actually skew the results, a study has found.

A research project conducted by David Bellwood, a marine biologist at James Cook University in Townsville, found that an average of half of the fish in a given area are scared off by the divers trying to count them. The flight response was more marked in some species, with up to 70 percent of the parrotfish hiding from the divers.

The study, published in the journal PLoS One, involved one diver laying a 50m tape on a section of the Great Barrier Reef, with a second diver following behind and counting the fish. This is the standard method of conducting a fish census.

After waiting five minutes, however, the same area was recounted, with results showing a 52 percent drop in the mean number of fish noted between the first and second counts.

“We recorded a marked decline in fish abundance as a result of ongoing diver presence,” the study concluded, adding that future fish census collectors could consider using methods that mean the fish are counted upon first contact with the diver.

Read more at PLoS One