Pregnant Females Congregate Around Power Station Outflow in Israel
I have been diving with sharks around the world for more than 20 years - but I never thought I would find an aggregation of four-metre-plus mature female sharks just 40 minutes from my home in Israel in the relative marine deserts of the Mediterranean Sea.
But researchers from Haifa University have been investigating something unusual going on near the outflow of a major power plant in the Hadera Stream National Park on the Mediterranean coast and I volunteered to help the project.
My first dive blew my mind! In three metres of slightly murky waters on a bland, sandy, seabed we came across eight to ten individual dusky sharks. Some were more than four metres in length and for more than an hour they circled and swam back and forth. Forget the Indian Ocean or even the Pacific, this was one of my best ever shark experiences.
No one really knows why these sharks congregate in the same spot year after year, from end October through to April. But some circumstances have surely helped. In 2005 Israel passed a law protecting all sharks in its waters and from 2008 the authorities starting strictly enforcing the ban on any shark fishing.
The duskies are gathering next to an electric power plant. The hot jets of fresh water from the plant flow into of the Hadera Stream which joins the salty water of the Mediterranean and keep the water temperature around the outflow at 24ºC compared with the average of 18ºC for the Med in winter. The warm water attracts small schools of jacks, sea breams and mullet upon which the duskies predate.
Dusky sharks (Carcharhinus obscurus) live in tropical and warm-temperate seas worldwide mostly at the point where the continental shelves plunge off into the depths of the open ocean. Populations migrate seasonally towards the poles in the summer and towards the equator in the winter, travelling hundreds to thousands of kilometres.
One of the largest requiem sharks, the dusky shark reaches 4.2m (14ft) in length and 347kg (765lb) in weight. It has a slender, streamlined body and can be identified by its short round snout, long sickle-shaped pectoral fins, a ridge between the first and second dorsal fins, and faintly marked fins.
Adult dusky sharks have a broad and varied diet, consisting mostly of bony fishes, sharks and rays, and cephalopods, but also occasionally crustaceans, sea stars, bryozoans, sea turtles, marine mammals, carrion, and garbage. This species is viviparous with a three-year reproductive cycle; females bear litters of 3–14 young after a gestation period of 22–24 months, after which there is a year of rest before they become pregnant again.
Dusky sharks are one of the slowest-growing and latest-maturing sharks, not reaching adulthood until around 20 years of age.
The numbers of the sharks at Hadera vary from one year to year. During 2015-16, more than 100 were spotted in the area. This year by using VTOL (Vertical Take-off and Landing) drones on a regular basis to monitor their presence, about 40 individuals have been spotted.
An interesting fact is that most of the sharks are females and only later in the season do a few sandbars male sharks appear. The sandbar sharks (Carcharhinus plumbeus) are significantly smaller than the dusky females and reach two metres length.
From my experience of diving with dusky sharks elsewhere in the world, the girth of the females in Hadera is much bigger. That might suggest that the female are pregnant. This thesis is part of the research project.
Conditions can be quite varied at this time of year so if planning a dive trip to see the duskies of Hadera expect to be checking the weather forecasts. The shark season starts at the end of November when the water temperature drops to 24ºC and ends at March-April when it goes above 24ºC.
The dive site is not far from the parking lot of the national park where you can gear up followed by a 300m walk to the entry point.
It takes few minutes of fining to get to where the sharks gather. It is a shallow dive as most encounters with the sharks are at depth of 2m to 4m. The max depth is 6m so 7lt or 10lt tanks are more than enough.
The bottom varies from sandy to boulders and most of the dive you are on your knees and waiting for the sharks approach you.
It doesn't take long after settling on your knees to see a distant shadow approaching from the murky shadows of the stream of warm water. Getting closer you realise this is a 4m, 350 kg giant coming to check you out.
Some sharks come alone, others come in pairs or in small schools of three. Their swimming pattern is usually from the current heading to the sandy bottom and back to the current but they can show up from every direction. The whole idea is to stay calm and let the sharks approach you without fear. They have never shown any aggressive behaviour even if they approach us really close. Sometimes they come just few centimetres from us.
We have encountered in most of our dives more than 20 sharks, mostly female and occasionally smaller sandbar male sharks.
Viz can be varied. On good days you get 4m to 6m and average viz at the site is around 3m. It drops to almost zero if you approach the stream of hot water coming from the power plant. The area is a favourite for anglers and the rocky part of the site is full of hooks and loose fishing lines that can pose a risk. It is advised to carry a cutting tool in your BCD. A 5mm wetsuit is perfect for the dive.
• To find out more about diving with the dusky sharks contact Yuval at Ocean Traveler. He can also arrange diving trips to the ancient port of Caesarea and the coral reefs diving in Eilat. Website or Facebook