Blue sharks are one of the most common shark species in the world. With their slender, sleek bodies and distinct blue coloration, these stunning fish are a fascinating sight. Blue sharks are also one of the most studied shark species, as they are a popular subject for scientific research due to their behavior and ecological importance. However, despite their popularity, blue sharks face numerous threats from human activities, including overfishing and plastic pollution.
Science In The Spotlight
Blue sharks are highly sought after by fishermen worldwide due to the demand for their meat and fins. However, apart from fishing, these sharks face significant threats from marine pollution. Researchers conducted a study between June 2017 and August 2018 to observe how blue sharks in the South Atlantic Ocean interacted with large debris such as plastic and fishing gear. During the study, they made some unexpected observations.
Blue Sharks and Their Plastic Plight
Scientific Study: Macro-debris ingestion and entanglement by blue sharks
(Prionace glauca Linnaeus, 1758) in the temperate South Atlantic Ocean by Rodrigo Barreto, Hugo Bornatowski, Fernando N. Fiedler, Monica Pontalti, Ketyllen J. da Costa, Caiame Nascimento, and Jorge E. Kotas
What Are These Blue Sharks Eating?
The blue shark is a highly targeted species for fishing worldwide, and its popularity has been increasing because of the demand for shark meat and fins in both local and international markets. Besides fishing, blue sharks also face threats from marine pollution, such as getting caught in abandoned fishing gear, eating trash by accident, and having toxins build up in their bodies.
Female blue shark (Prionace glauca) caught by a Southern Brazil longline fishing vessel on August 2018. Onboard observer processing the individual; and PPE boot found in the animal’s stomach.
Between June 2017 and August 2018, researchers observed how blue sharks in the South Atlantic Ocean interact with large pieces of debris, like plastic and fishing gear. The researchers didn’t set out specifically to study this, but they took advantage of chances to observe these interactions when they occurred.
Female blue shark (Prionace glauca) caught by a Southern Brazil longline fishing vessel on July 2017. Onboard observer measuring the individual, and the 65-liter plastic black trash found in the stomach of the blue shark. The 65-liter plastic black trash taking from the P. glauca stomach with deformities resulting from attempted digestion.
Pictures credit: Caiame J. Nascimento
In June 2017, a young female blue shark was caught by fishermen who were trying to catch swordfish. When they cut open her stomach on the boat, they found a 65-liter plastic bag, which is similar in size to a big backpack. In addition, two other blue sharks got caught in the same type of fishing line earlier that year and died because they got tangled in the straps that held the bait. In August 2018, the same fishermen caught another female blue shark and found a synthetic boot in her stomach.
Why Are Sharks Starving?
Plastic severely impacts sharks, causing problems like eating it by mistake, getting tangled, and even suffocating. When sharks eat plastic, it fills their stomachs and prevents them from getting the food they need, leading to starvation. They also suffer from injuries and infections when they encounter plastic waste. Researchers have found that juvenile and adult blue sharks are especially affected by mesoplastics, which are commonly used as packaging material, with juvenile sharks being more likely to eat plastic than adults. Another study discussed young blue sharks getting caught in plastic straps around their gills from a tuna longline fishery. This caused injuries to their back muscles and fins. The straps also made it hard for them to breathe properly.
Blue shark’s entanglements with bait box straps registered at the same fishing trip realized by a Brazilian longline vessel between May and June 2017.
A lot of the trash that ends up in the oceans comes from people on land or ships traveling at sea. To reduce the amount of trash in the ocean, we need better ways to control how people dispose of their waste. Sharks can be injured and die if they eat plastic or other debris that people leave in the ocean, so it is essential that we reduce the amount of human-made trash in the sea to help keep sharks and other marine animals safe and healthy.
Blue shark Prionace glauca entangled with strapping bands. (A) General view of the fifth specimen. (B) Dorsal view of the second specimen showing the severe erosion caused by a plastic band. (C) Lateral view of the head of the Mediterranean specimen showing damage on the gill region and the pectoral fin by a plastic debris collar.
References
1. Barreto, R., Bornatowski, H., Fiedler, F. N., Pontalti, M., Da Costa, K. J., Nascimento, C., & Kotas, J. E. (2019). Macro-debris ingestion and entanglement by blue sharks (Prionace glauca Linnaeus, 1758) in the temperate South Atlantic Ocean. Marine Pollution Bulletin, 145, 214–218. https://doi.org/10.1016/j.marpolbul.2019.05.025
2. Colmenero, A. I., Barría, C., Broglio, E., & García-Barcelona, S. (2017). Plastic debris straps on threatened blue shark Prionace glauca. Marine Pollution Bulletin, 115(1–2), 436–438. https://doi.org/10.1016/j.marpolbul.2017.01.011
3. Bernardini, I., Garibaldi, F., Canesi, L., Fossi, M. C., & Baini, M. (2018). First data on plastic ingestion by blue sharks (Prionace glauca) from the Ligurian Sea (North-Western Mediterranean Sea). Marine Pollution Bulletin, 135, 303–310. https://doi.org/10.1016/j.marpolbul.2018.07.022
4. Marine plastic pollution. IUCN. (2021, November). https://www.iucn.org/resources/issues-brief/marine-plastic-pollution#:~:text=Marine%20wildlife%20such%20as%20seabirds,to%20swim%2C%20and%20internal%20injuries.