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Biological oceanography

“Bienvenidos” to Baja California, Baby White Sharks!

Tamborin, E., Hoyos-Padilla, M., Sánchez-González, A., Hernández-Herrera, A., Elorriaga-Verplancken, F., Galván Magaña, F. (2019). “New Nursery Area for White Sharks (Carcharodon carcharias) in the Eastern Pacific Ocean.” Turk. J. Fish.& Aquat. Sci. 20(4), 325-329.

Big Travelers!

Great white sharks, or simply white sharks, are considered one of the largest predators in the sea. They are globally known for their appearance in tv shows and movies, such as Jaws. The name “white shark” might have come from its all-white belly. However, the dorsal color of the shark can vary from pale to dark grey depending on the lighting and visibility. Their average length is 3.6m (11.8 ft) but can reach lengths of over 6.1m (20 ft) and can weigh up to 2268 kg (5000 lb). White sharks are found in cold temperatures and tropical waters, from 60° N latitude to 60°S latitude. They travel long distances and are known to cross entire oceans. In North American waters there have been reports of white sharks from Alaska to Southern Mexico, and from Newfoundland, Canada down to Florida.

Great White Shark in Mexico by Terry Goss. Wikimedia Common Files.

Unfortunately, despite the wide range of great white sharks, they are becoming increasingly rare. Over the past years, these sharks have been accidentally killed by commercial and sports fisheries over the world. In addition to that, white sharks have low reproductive potential and even after birth, most newborns will not reach adult stages due to their vulnerability to predation. These facts combined elevated white sharks as “vulnerable to extinction” status by the International Union for Conservation of Nature (ICUN).

 

 

The Study

In Mexican waters the white sharks are protected by a fishing ban prohibiting capture, since 2014. Unfortunately, these sharks are still accidentally caught by commercial fisheries in the Baja coast. In response to this, Elena Tamburin and her crew conducted research near Isla Cedros, on the Western Coast of Baja California. These scientists recorded the presence young white sharks in the area, using capture data of local fisheries.

This study focused on the protection of great white sharks in their early stages of life. Scientists believe that the area is a nursery region for young sharks, especially during summertime. Thinking of that, Tamburin’s group trained local fishermen to identify great white sharks and record important biological data, such as length and sex.

Mexican babies!

Most great white sharks studied in the research area were young and about 50% of them were newborns.  Through this research, scientists observed that adult white sharks are using coastal waters around Baja California to give birth to baby sharks.

Scientists believe that the shallow coastal water of Baja California is the perfect environment for baby white sharks. Great white sharks are ovoviviparous, which means that females carry the eggs inside of their uterus until the babies develop and are ready to be born.

Great white shark by Elias Levy. Wikimedia Common Files

The offspring hatch inside the mom`s body and the babies are born soon afterward. Adult females travel long distances to make sure their babies will be born in a warm area, rather than cold and unprotected open waters. The young ones, after being born in warm southern waters, might slowly migrate northward as they grow.

Despite the efforts to understand the great white shark’s reproductive cycle, it is hard for researches to track sharks during reproduction. Size, location, and reproductive behaviors are still big queries in the scientific community. Studying and protecting shark’s nursery areas is an important step towards their population’s recovery.

 

Can sharks affect the oxygen I breathe?

As an apex predator, great white sharks keep the balance of the ocean food chain. In other words, a decline of shark populations could drive an increase in fish they eat. Because some of these fish are herbivores, an increase in these plant eating fish could lead to a decrease aquatic plants population and a theoretical ocean deforestation.

Great white shark by Elias Levy. Wikimedia Common Files

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