Dozens of porbeagle sharks gather every winter in the warm waters of the Hadera and Ashkelon power plants – Dr. Adi Barash reveals a species that is not considered Mediterranean at all, explains their role as apex predators, the threats from fishing and sea warming, and the dilemma between shark tourism and safety and nature conservation
Adi Weinberger, Zavit – Science and Environmental News Agency
The sand shark It is a relatively common shark in the world, and can be found in temperate waters in all oceans. Worldwide, it is classified as endangered. However, in the Mediterranean Sea, it is classified as a species with insufficient information, because until recently it was not known to be found in the Mediterranean Sea. Nevertheless, it is a shark that is hard to miss once you see it: it reaches 4 meters in length and excels at swimming long distances.
We spoke with Dr. Adi Barash, a postdoctoral researcher at the Steinhardt Museum of Natural History, the scientific director of Shark Association in Israel And a colleague interface program In the 15th grade, she told us how little is known about such a large fish, about the sharks in her room, and how rising sea temperatures could affect them.
Why did you decide to research sharks?
"When I finished my first degree, I was looking for a research topic that lacked information. I was driving with a friend on the coastal road, and we said to ourselves, 'What about the sharks in Hadera?' It's a topic that no one had dealt with before, and they knew nothing about it except for a few people who went there and fishermen who tried to catch sharks."
Barash discovered that during the winter season, dozens of sharks of the finfish and sandbar species gather in the warm water stream emitted from the coastal power plants – mainly Orot Rabin in Hadera and Rotenberg in Ashkelon. In recent years, the Hadera Stream estuary has become a center of attraction for those who want to witness the marine predator with their own eyes.
What surprised you to discover about the sand shark?
"At the beginning of the research, I thought the identification in Hadera was incorrect. Reports came in about sightings of sand sharks near the Hadera power plant, but according to the scientific literature, there are no sand sharks in the Mediterranean Sea, where it is considered a very rare shark, with 20 sightings ever. Today, 13 years later, we understand that sand sharks in the Mediterranean Sea are almost exclusively found in our country. There are a few sightings from Turkey and Libya, but in terms of an established population, it is only here."
"When we looked for the reason for this, it turned out that at least some of the sharks probably migrated from the Red Sea to the Mediterranean Sea through the Suez Canal. In other words, they joined a population of Atlantic origin that was already in the Mediterranean Sea. Another possibility is that a few individuals that entered the Mediterranean Sea from the Atlantic Ocean met the few individuals that passed through the Red Sea, and some kind of local population was created, which is a mixture. What we know is from genetic research, which only shows a small part of the picture. It is difficult to complete this picture without learning more about their distribution by tracking them using transmitters to find out where they are."
She said that since 2015, researchers from the University of Haifa's Maurice Kahn Marine Research Station have been tagging sharks at the power plant with acoustic tags. The tags transmit an acoustic signal that can be read by acoustic receivers placed in the area. "That means that once sharks leave the area, we know nothing about them." In addition, "satellite tags have been attached to some sandbar sharks, but so far it hasn't worked."
What is the role of sand sharks in the ecosystem?
"These are predators. Like predators on land, predators in the sea also eat the weak, sick, less fit animals from their prey population, and by doing so, they strengthen it. They keep the fish populations healthy."
"In addition, when they eat and swim to other places, they transfer food from the deep sea to the shallow water, and between different areas, thus causing the transport of nutrients. In other words, they eat in one place, and defecate in another, and thus substances that are not found in a particular place reach there in low doses. This allows nutrients to reach areas in the sea that are poorer in nutrients; this is important for the balance of the ecosystem."
What are the most significant threats to the sand shark today?
"Because the sandbar shark is a large fish, and also swims relatively close to shore, it is caught quite a bit by fishermen "– mainly as bycatch (i.e., unintentionally), and in some parts of the world as a target fish. It is greatly affected by coastal fishing, as well as pelagic fishing (fishing in the open sea). We are seeing declines of about 70–80 percent in population size around the world. Like many other sharks, this species also has a very low reproductive rate. It only reaches sexual maturity at around 15 or 20 years of age, and the females' pregnancy cycles last about two or three years, with relatively few offspring. The sharks' reproductive rate is not keeping up with the rate of harm to them."
How does the climate crisis affect the sand shark?
"Around the world, we see that warming waters are causing a change in the migration routes of sharks, especially pelagic sharks (in the open sea), which swim a lot. In Israel, the power plants create a place to stay during the season when the sea is cold, and thus the sharks can find water in tropical sea conditions all year round."
"We see that with global warming, The Mediterranean Sea is warming faster "From the pace of the World Climate Organization's forecast, it is becoming more and more suitable for the temperature range preferred by the sand shark. From acoustic tagging, we found that the sharks in Hadera prefer temperatures around 22–26 degrees Celsius. When the sea cools down in winter, and the temperature drops below 20 degrees, they begin to gather near the power plants. When the sea warms above 20 degrees, they begin to leave and return to the open sea. The increase in water temperature will accordingly change the locations where the sharks prefer to stay during the different seasons."
So could climate change even be good for them?
"According to the observations we made, the eastern Mediterranean Sea will become more adapted to sand sharks as the sea warms. It's hard to say whether this is good or bad. From the individual point of view, the shark itself, it will probably be 'happy.' From the point of view of the ecosystem, we don't know how to assess the significance of this. We may see more sand sharks in the coming years, and in a wider distribution range; that is, not only in Israel but we will start seeing them in Libya, Egypt, Tunisia, Turkey and Greece."
How do you keep the sand shark?
"In various countries around the world there are restrictions on fishing, a mandatory release in the event of a catch, and a reporting obligation. In Israel, sharks and rays are comprehensively protected."
Alongside the conservation efforts led by organizations and authorities, Barash claims that there is something that each and every one of us can do, and that is to learn about sharks: "Learn about their role in the sea, about their presence in our nature, about their importance, and come and watch them from the shore near the power plants. We have an abysmal fear of sharks. When you see the animal in the wild, the feeling is different than sitting at home, imagining it and being afraid."
The shark attack in Hadera last April, which cost a life, is a very rare event – and it happened nonetheless. What could have caused it?
"I don't know what caused the attack itself, but the situation in Hadera was unreasonable with very intense interaction between humans and wildlife. We saw feedings, chasing, lots of people in the water along with about 50 sharks. If it was a pack of 50 dogs, no one would think of going into it. Every year in April, the water in the streams warms up, and when there are major heatwaves, a lot of dead fish end up in the sea. The sharks feed, hang out in very shallow water near the shore, and are probably preparing to go back to the open sea. At the same time, the warming weather attracts many hikers and even more so during the Passover holiday, which creates a situation of people, sharks, and a power plant with all that implies, a very explosive combination. The warm water area in Hadera is unnatural and has long had a large number of sharks near the shore. This is a great opportunity to come and learn about them, but we don't need to be in the water with them."
What new scientific discoveries are there about the sandbar shark?
"We recently discovered that the sharks at the power plants perform a diurnal movement. This is a behavior known from swimming sharks (pelagic sharks, which swim long distances in the open sea) from all over the world. They descend to depth at a certain time of day. An article that surveyed several species of sharks showed that they take turns, with each species having different times of day at a specific site, so there was almost no overlap between them."
"We discovered that these shifts also work at the Hadera power plant, between the sand shark and the fin shark. At night, both species ascend to a shallower depth range, while during the day they stay deeper. In our case, this is very strange because the depth near the Hadera power plant reaches a maximum of 7 meters. The sand shark goes from a depth of 2 meters at night to a depth of 4 meters during the day, and the fin shark goes from a depth of 4 meters at night to 6.5 meters during the day. This is a daily movement of 2 meters made by sharks that are 4 meters long. This is probably part of their natural movement that they maintain even when they are in a small area, in a limited depth range."
Barash says there is still much to discover. Only female sand sharks are observed at the power plant. "We thought it might be related to pregnancy, but in the case of finless sharks we see males." Another intriguing question is where the sharks are in the summer, when they are not in the warm waters near the power plants: "Where do the sharks go when the lake is not frozen?"
As part of the association's activities, divers, fishermen, other seafarers, and citizens who were in the right place at the right time photographed cartilaginous fish in the wild, i.e. Sharks and betas (which have been nicknamed sea cats), and send the documentation that is later used for research. If you or you are lucky enough to see a shark in the Mediterranean Sea, or while visiting Eilat, then you can report the sighting in the Facebook group Sharks in Israel.
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