Sharks in Hadera – research milestones, discoveries, and a glimpse into the future:07.01.2020
In the Mediterranean Sea, the majority of shark populations have been drastically reduced to the point where over 90% of shark species have become extinct. In the marine ecosystem, dusky sharks (Carcharhinus obscurus) and sandbar sharks (Carcharhinus plumbeus) are considered to be the system’s apex marine predators. The ecological meaning of this is that there are no natural predators that rely on these sharks as prey. Both species are classified by the International Union for Conservation of Nature (IUCN) as vulnerable. In the Mediterranean Sea the dusky sharks are classified as data-deficient and the sandbar sharks as endangered.
During the winter months (November to May), an interesting anthropogenic event occurs: forty to eighty sharks gather next to the power plant in Hadera, where the hot water from the turbines pours into the Hadera River. This spectacular clustering draws a large interested audience including divers, snorkelers, kayakers, researchers, and many more.
The Morris Kahn Marine Research Station, of the Charney School of Marine Sciences at the University of Haifa, headed by Professor Dan Tchernov, conducts long-term ecological research in many spheres connected to the Mediterranean Sea. Dr. Aviad Scheinin is the project manager of the “Top Predator Project” of which sharks make up a significant part. The project, which is in its fifth year, studies many aspects of these sharks, including: genetic studies examining the origins of sharks and their distribution (Adi Barash), ways to calculate biomass of these (and other) apex predators using advanced and innovative methods (Eyal Bigal), measuring shark blood (Tal Strostintzki Malonk ), and shark behavior (Ziv Zemah Shamir). As part of the study, we capture sharks to take measurements, take blood and DNA samples, and implant acoustic/satellite transmitters. It is important to note that no sharks were injured by these captures, with the exception of the minor stress likely associated with the capture itself. All activities are carried out with the permission of the Israel Nature and Parks Authority (INPA). The capture procedures are based on established scientific protocols and were approved by the relevant professionals at the INPA.
Using acoustic transmitters showed us a fascinating phenomenon called site-fidelity, the tendency of many individuals to return to the specific site they were at in the past. Indeed, we were surprised to find a not insignificant number of sharks returning to Hadera year after year. Another interesting finding from the transmitters is the tendency of some sharks to roam around back and forth from the gathering point. These sharks are not a herd and do not behave like one. They come to a certain area and usually congregate there for two reasons – food and reproduction. Analysis of the acoustic results showed us that, over the course of the winter season, the sharks leave the gathering area every few days (and sometimes move all the way to Ashdod) and then return to the gathering area.
We also investigated the growing tourism surrounding these sharks. For this research we worked with two environmental economists – Professor Nir Becker and Dr. Shiri Zemah Shamir, who calculated the economic potential of the location, while striving for minimal damage to the sharks, and tested the effects of the people on the sharks. These results have been published in the scientific literature. In order to further an additional current study, we added an environmental psychologist, Professor Nurit Carmi, to the economists and biologists in order to examine the impact of diving with sharks and other related activities on changing attitudes about marine conservation.
New additional studies at the research station include: (1) looking at the behavior and interplay between the two species (dusty and sandbar) and within each species by itself, using acoustic recordings and video cameras attached to foundations in the sea; (2) identifying the populations of bacteria living on the sharks (microbiome), as well as in the surrounding water and sand (Johnny Bergman under the supervision of Dr. Dalit Meron); and (3) research to identify the presence of apex predators by identifying the presence of their DNA in the water (eDNA) with the goal of developing long-term monitoring techniques (Rebecca and Linney under the supervision of Dr. Danny Morick).
There are a lot of reasons to be optimistic today – there is productive cooperation between many organizations, including the research station, INPA, EcoOcean, Sharks in Israel, and others, that helps raise public awareness to protect sharks in particular, and preserve the marine environment in general. We have also garnered support from the diving authority, the Israeli Diving Federation, divers, diving clubs, the city of Hadera, and visitors from the sea and the beach, and you can see a real change in the attitude of people to the sea, the sharks, and the environment.
We are less optimistic regarding expectations for the future. Although the whole area is anthropogenic (built by people), we were still blessed with an impressive aggregation of sharks during the winter months. However, extensive municipal building plans to develop the coastal stretch from Hadera to Givat Olga, along with plans to close two of the four currently operating pumps that cool the generators of the electric company (which would in turn cut the amount of hot water in half) may reduce the presence of sharks in the area or cause them to disappear altogether. It is important to keep the importance of sharks in the marine ecosystem in mind, they are a key species responsible for the health and integrity of the system, by eliminating weak and sick fish, and thereby helping maintain the marine biodiversity. In recent years we are actually both eating and drinking the sea, and therefore protecting the “protectors” is more essential than protecting one specific species or another in the sea.
Translated by Daphna Shapiro Goldberg