The study examined competition between the two main hunters of the Mediterranean, the Bottlenose Dolphin and commercial fishing nets dragged near the bottom of the sea, known as trawlers.
While trawlers typically hunt codfish, sole, and red mullet fish, the stomachs of deceased dolphins studied for the investigation contained mostly non-commercialized fish, causing initial hypotheses that commercial fishing did not have a severe impact on the Mediterranean's dolphin population.
However, living dolphins led to a much different conclusion, according to Dr. Aviad Scheinin. Over 3,000 kilometers of Israel's central coast and 232 marine surveys were studied to examine the behavior of dolphins as a result of trawling.
According to Dr. Scheinin, the chances of seeing schools of dolphins around a trawler are 10 times higher than usual. Though dolphins cannot reach the fish caught by the nets, they are able to feed on other schools of fish which swim around the trawlers.
This is where the danger lies, according to Dr. Scheinin. "Eight dolphins die each year off the coast of Israel on average, and of those, four die after having been mistakenly caught in trawling nets," Dr. Scheinin told Science Centric. "Seeing as many studies have proven the high intelligence of the dolphin, it is clear that these sea mammals are aware of this danger. But [they] are left with little choice due to their need to search for food around the trawlers due to the scarcity of other food sources," he said.
This theory is reinforced by the activity of suckling female dolphins. They require more caloric intake than other dolphins, and are found even more regularly around the trawlers, despite the risk to their inexperienced offspring.
Lastly, the study has determined that dolphins off Israel's coast spend more time hunting than their counterparts around the world, who spend more time playing and socializing. There are approximately 350 dolphins living in the Mediterranean off Israel's coast.
The study cites data by the Ministry of Agriculture's Department of Fisheries, showing that commercial trawling is depleting the amount of the three most sought fish faster than they are reproducing, meaning their population has dropped between 1949 and 2006.