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Shark: hunter or hunted?

By Claudia Namiki

English edit by Lidia Paes Leme and Katyanne Shoemaker

*post originally published in Portuguese on May 17, 2018

Illustration adapted from Joana Ho


If you enjoy a good fish stew, you have likely eaten dogfish meat. Or perhaps you have seen the beautiful cuts of dogfish on display at fish markets and fishmongers. But do you know what dogfish is?


Dogfish is nothing more than the name given to the meat of the sharks and rays that we eat ( in the U.S. “dogfish” refers more specifically to a family of small shark species). In other words, when we buy dogfish, it means we are going to eat sharks! Surprisingly, most people do not know this, according to a study conducted in Curitiba, Brazil, where more than half of the people said that they eat dogfish, but have never eaten ray or shark (check out the study by Bornatowski and collaborators in 2015, listed below).


Photograph focusing on a large shark cut in half for sale at a fish market. To the left there are flounders and other fish and at behind the fish are two men that work at the market

Shark meat being sold at a fish market in Morocco

(Source: Flickr, under license CC BY-NC-ND 2.0)


The problem is that there are 145 species of sharks and rays in Brazil, of which 33% are endangered. But since every species of ray or shark is sold under the name of dogfish, already cut into filets (probably so as not to scare the customers), there is no way to know exactly what is being sold. Therefore, by consuming dogfish, we may be contributing to the extinction of a species. Considering that Brazil ranks 11th in production, and first on the list of shark meat importers in the world (according to the FAO - Food and Agriculture Organization of the United Nations - report), Brazilians’ chances of contributing to this terrible end becomes quite high. The consumption of shark fins in some countries in Asia, where they are considered a delicacy and are sold for high prices, has contributed to the increase in shark fishing. The removal of valuable shark fins is called finning. Normally, after finning, the animals are cruelly thrown overboard while still alive, as the low sale price of shark meat is not worth the cost of storage. However, the practice of finning is prohibited by law in Brazil. So the fishermen store the “finned body” to be sold at a very low price, further encouraging the consumption of dogfish.


Photograph of a dorsal fin of a shark that has been cut off from the body of the animal. A man’s hand holds the fin with a bloody glove and holds a large knife. In the background, there is an out of focus blue sea.

Finning - Freshly removed dorsal fin from a hammerhead shark.

Picture:© Jeff Rotman/jeffrotman.com .


If neither the extinction of a species nor the cruelty of finning moves some people, there are other reasons to avoid eating shark meat. One of them is to preserve our own health: as top predators, sharks accumulate large amounts of heavy metals, such as mercury and lead, in a process called biomagnification (we have already talked about this subject here on the blog). When a person eats shark, they become the next consumer in the food chain and accumulate the heavy metals present in its meat (check out the references at the end of the text). Heavy metals are extremely toxic to the body, especially in large quantities, causing various health problems.


The other reason is an ecological service: sharks control the growth of populations of various species, either by direct predation or by keeping them away from a certain area for "fear" of being eaten. Great white sharks may feed on other sharks, sea lions, turtles, and other charismatic megafauna. However, many shark species feed primarily on invertebrates, such as shrimp and crabs. Unfortunately, even plastic can be part of the shark's diet. There is also a filter-feeding species that feeds on plankton, the whale shark. Recently, American researchers discovered that a species of hammerhead shark (Sphyrna tiburo), feeds mainly on sea grasses when young. It is not yet known whether the young shark ingests the grass by accident when hunting other animals, or whether it is actually able to digest and feed on these vegetables. This discovery may reveal the existence of interactions in the marine food chain previously ignored by researchers (check out the the world's first salad-eating shark).


Despite their reputation as bad guys, thanks to the Jaws franchise and other trash movies (in my humble opinion), humans are not a part of these animals' diet. Attacks on humans usually occur by mistake. Places with a high frequency of shark attacks are usually associated with places where sharks feed. On the urban beaches of Recife, Brazil, the high rate of shark attacks is due to a number of factors, among them the construction of the Suape Port, which destroyed the mangrove swamp where female sharks used to give birth. Without this location, the sharks began to frequent the waters of the Jaboatão river estuary, which flows into the beaches, increasing the frequency of encounters with bathers and consequently increasing the number of attacks.


Researcher Dana Bethea, who devotes her life to studying sharks and rays, suggests some measures to avoid shark attacks: avoid swimming at sunrise and sunset, as sharks are most active during twilight; avoid swimming in water with poor visibility, that way the shark can see you better and won't bite you; avoid areas where sharks feed; don't swim alone; and remove jewelry before entering the water, as its glare can lead the shark to believe you are a leaping silver fish. And if you are still afraid, Dana suggests that you do not enter the water, as sharks cannot survive on dry land (lol).


The fact is that while shark attacks on humans are very sad accidents, they could be prevented for the most part, and it is these large animals that are being attacked by us, with such a high frequency that we may drive them to extinction.

 

To learn more:

http://www.sciencemag.org/news/2018/01/meet-world-s-first-salad-eating-shark


https://swfsc.noaa.gov/textblock.aspx?Division=FRD&ParentMenuId=87&id=959


https://mundoestranho.abril.com.br/mundo-animal/por-que-ocorrem-tantos-ataques-de-tubarao-em-recife/


https://chooseyourcurrent.org/2017/08/whats-in-a-tiger-sharks-stomach/


http://sero.nmfs.noaa.gov/shark/dana_bethea/index.html


http://www.icmbio.gov.br/cepsul/images/stories/legislacao/Instrucao_normativa/2012/in_inter_mpa_mma_14_2012_normasprocedimentoscapturatubaroes_raias.pdf)


Barreto, R.R., Bornatowski, H., Motta, F.S., Santander-Neto, J., Vianna, G.M.S., Lessa, R.. 2017. Rethinking use and trade of pelagic sharks from Brazil. Marine Policy, 85: 114–122.


Hugo Bornatowski, Raul Rennó Braga, Carolina Kalinowski, Jean Ricardo Simões Vitule. 2015. “Buying a Pig in a Poke”: The Problem of Elasmobranch Meat Consumption in Southern Brazil. Ethnobiology Letters, 6 (1): 196-202.


Luís M.F. Alves, Margarida Nunes, Philippe Marchand, Bruno Le Bizec, Susana Mendes, João P.S. Correia, Marco F.L. Lemos, Sara C. Novais. 2016. Blue sharks (Prionace glauca) as bioindicators of pollution and health in the Atlantic Ocean: Contamination levels and biochemical stress responses. Science of the Total Environment, 563–564: 282–292.


Sebastián A. Lopez, Nicole L. Abarca, Roberto Meléndez C. 2013. Heavy metal concentrations of two highly migratory sharks (Prionace glauca and Isurus oxyrinchus) in the southeastern Pacific waters: comments on public health and conservation. Tropical Conservation Science, 6 (1): 126-137.


Ofelia Escobar-Sánchez, Felipe Galván-Magaña, René Rosíles-Martínez. 2011. Biomagnification of Mercury and Selenium in Blue Shark Prionace glauca from the Pacific Ocean off Mexico. Biol Trace Elem Res 144:550–559. DOI 10.1007/s12011-011-9040-y.


#MarineScience #Dogfish #Flake #Finning #Shark #Extinction #ClaudiaNamikiChat #JoanaHo


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