Shark Fisheries
Shark Fishing © Marcia Moreno Baez, Marine Photobank.

The most pressing issue facing sharks, skates and ray populations around the world - including in UK waters and the wider Northeast Atlantic - is the scale and sustainability of commercial fisheries.

Commercial fishing is a globally important economic activity; 93 million tonnes of marine fish and fish products landed in 2011, worth US$111,791 million. As well as supporting livelihoods - and a much wider peripheral economy - commercial fishing can also be an important part of the cultural heritage of a region, forming the backbone of many coastal communities. Shark fisheries are themselves significant, with around 766,000 tonnes of shark landed in 2011, worth an estimated value of US$598 million.

The UK has a rich shark fishing heritage dating back centuries; for example in 1569 a London newspaper reported the sale of a 17ft Thresher Shark (Alopias vulpinus) at Billingsgate fishmarket (1), while in 1658 French merchants were visiting St. Ives, Cornwall specifically to purchase freshly caught White Skate (Rostroraja alba) from local fishermen (2). 

Today, sharks are taken in target fisheries and as bycatch in mixed fisheries. Despite significant improvement in the management of fisheries in shallower, continental shelf waters, populations of many shark species remain heavily depleted due to decades of unregulated fishing. Much further offshore, outside of national Exclusive Economic Zones (EEZ), high sea and deep-sea fisheries are often less effectively managed. Here, many oceanic, pelagic sharks such as Blue (Prionace glauca), mako (Isurus spp.), Oceanic Whitetip (Carcharhinus longimanus) and Silky Sharks (C. falciformis) are caught in huge volumes. These species often dominate the catch component in many tuna and billfish fisheries, and are subject to few, if any, catch limits or regulations.

Sharks are caught for their fins, meat, liver oil, cartilage and skin. In recent decades, reflecting growing economic affluence in China, shark fins emerged as the most valuable product, being the central ingredient in the prestigious shark fin soup. Shark species such as the Porbeagle (Lamna nasus) and Shortfin Mako (Isurus oxyrinchus) are renowned for the quality of their meat, which is often sold as steaks and likened to tuna or swordfish in quality and price.

Sharks demonstrate what is known to biologists as a K-selected life-history strategy - meaning they exhibit a series of highly conservative biological traits more akin to that of a mammal than a fish. Sharks are relatively slow growing, late to mature and produce few young.

A growing body of research indicates that when sharks are overfished in an area, prey populations can explode in size with a significant, often irreversible ‘snow‐ball’ effect for the wider marine ecosystem. As top predators, sharks play a pivotal role in maintaining a healthy, balanced marine ecosystem - in turn supporting productive fisheries for other species such as teleost (bony) fish and shellfish. Many sharks are considered as ‘keystone species’, with their removal or depletion through overfishing disrupting the functioning of a marine ecosystem. As smaller, more abundant prey species are released from predation by large sharks their populations increase rapidly, with a cascading effect on species further down the food-chain. This process is known as ‘trophic cascading’.


References:

1. Miyake MP, et al. 2010. Recent developments in tuna industry: stocks, fisheries, management, processing, trade and markets. Rome, Italy: FAO.

2. Gilman EL. 2011. Bycatch governance and best practice mitigation technology in global tuna fisheries. Mar Policy 35: 590-609.