For centuries, people living along the coast of Jamaica have made their livings catching fish. The island is often cited as an example of how overfishing has dramatically reduced the sizes of coral reef fishes. Researchers and policy makers have long held that overfishing has led to a decline in coral reef fish sizes. But such might not be the case, according to recent findings by ecological biologist Murray Itzkowitz.
Itzkowitz, together with Matthew Draud, a former graduate assistant and now dean of the College of Arts and Sciences at Siena Heights University, analyzed data from systematic surveys conducted in 1977 and collected data in 2013-14 of the sizes and relative richness of striped parrotfish, stop-light parrotfish, ocean surgeon and the blue tang, four common algae-grazing fishes in the shallow back reef habitats of Jamaica and Grand Cayman. Itzkowitz’s work originated when he was on the faculty of the University of the West Indies and studying coral reef fish. During that time, he had the opportunity to travel to Grand Cayman, and it was in this period he performed the initial study. The work was resurrected four years ago when he invited Draud to join him.
“We went to Grand Cayman and Jamaica believing the fishes had to be smaller because of overfishing,” says Itzkowitz, professor of biological sciences. “Everyone believes it’s due to overfishing and that fish have been smaller for decades. You have to appreciate how many people have published saying Jamaica was overfished and declining. I assumed that fishes would be huge in Grand Cayman and tiny in Jamaica.”
The researchers collected and measured fish along the reefs. The species examined are important to reef ecosystems as algae grows faster than coral. The fast-growing algae will overgrow the coral and kill it. These herbivorous fish eat the algae growing on the reefs, trimming the algae and protecting the coral.
“We selected these four species for three important reasons,” Itzkowitz says. “First, all four species are subjected to heavy fishing pressure in Jamaica. They are all commonly targeted in the spear-fishing, netting and fish-trapping fisheries. Second, all four were commonly observed during our surveys in all sites on both islands and in both sampling periods. Finally, the two families differ significantly in body, and we were interested in investigating whether those differences are related to changes in population demographics across time.”
Taken as a whole, the researchers’ results fail to provide strong support for the notion that populations in Jamaica have been more strongly affected by fishing pressure than those in Grand Cayman. Statistical comparisons of the size distributions of all four species in 1977 revealed no significant differences between Jamaican and Grand Cayman populations. Similar results were found in comparisons in 2013-14, with the sole exception of the striped parrotfish, which was found to differ in size distribution but not with regard to median body size.
Itzkowitz concludes that his results do not support the hypothesis that these four species of fish in Jamaica uniformly declined in size from 1977 to 2013-14. His findings show that conservation efforts that reduce fishing intensity in Jamaica may not enhance fish sizes.