Velvet crab

The velvet crab, known scientifically as Necora puber, is a unique marine crustacean. It lives in the North-East Atlantic and the Mediterranean Sea. This species is also known by several common names. Some call it the velvet swimming crab or the velvet crab. Others call it the devil crab because of its aggressive nature and bright red eyes.

In the Scottish fishing industry, they are often called "velvets." Other names include the lady crab, the velvet fiddler crab, and the Kerry witch. These crabs are considered very common in their natural habitats.

Physically, the velvet crab has a very distinct appearance. Its carapace, which is the hard upper shell, is dark and flattened. The color of this shell ranges from black to brown. The carapace is usually about 6.5 cm long and up to 10 cm wide. It can weigh as much as 250 grams. A key feature is the pubescence, which means the shell is covered in short yellowish hairs. These hairs create a texture that feels like velvet.

The surface also has small bumps called tubercles. These bumps are more concentrated toward the front of the shell. The front edge of the carapace is mostly straight but bends slightly inward. It features seven to ten tooth-like indentations. The claw-bearing legs, or chelipeds, also have short hairs. The "wrist" of the leg has a single spine on its outer side.

Scientists have worked for a long time to classify this crab correctly. Carl Linnaeus first described the species in 1767. He originally named it Cancer puber. At that time, all crabs were placed in the genus Cancer. However, Linnaeus's original description was very brief and somewhat unsatisfactory. Some researchers believe his description actually matched a different species, Polybius corrugatus. Since 1767, the velvet crab has undergone four different reclassifications. In 1798, Fabricius moved it to the genus Portunus. In 1958, Holthuis and Gottlieb transferred it to Macropipus. In 1981, Manning and Holthuis moved it to Liocarcinus. Finally, in 1987, Holthuis placed it in the genus Necora. This is the only species in that genus. The name Necora comes from a local word used in Galicia.

Modern science uses phylogenetics to study how these crabs are related to others. Phylogenetics is the study of evolutionary relationships among biological entities. Recent studies have looked at the group known as Portunoidea. In 2022, a study in Frontiers in Zoology used morphological characteristics to analyze the species. This study placed Necora puber in a monophyletic Carcinidae clade. This means they belong to a group that includes a single common ancestor. The study found that Necora was a sister group to a combination of Macropipus rugosus and Thia. Other studies have used different methods to find connections. A 2009 study used nuclear DNA to look at relationships. That study placed Thia as a sister to a group containing Necora and several other genera. This shows that scientists are still learning how these species connect through evolution.

Velvet crabs are very important to various fishing industries. In France, they are considered a culinary delicacy. However, the French fisheries in south Brittany faced a major crisis in the late 20th century. Between 1984 and 1988, the catch dropped by 96 percent. This mass mortality was linked to infections by dinoflagellates. These are single-celled organisms that can cause disease. A 1996 investigation suggested these infections belonged to the genus Hematodinium. In the United Kingdom, the industry is strictly regulated. The Undersized Velvet Crabs Order 1989 sets a minimum landing size of 6.5 cm for the carapace. It is also common practice for fishermen to return egg-bearing females to the sea to protect the population.

In Ireland, the fishing of velvet crabs is a more recent development. Targeted fishing began in the 1980s. This happened because the Spanish velvet crab fisheries collapsed, causing a shortage in southern European stocks. In Ireland, crabs are often caught as bycatch. Bycatch refers to organisms caught unintentionally while fishing for a different species, like lobster. Between 2006 and 2014, the volume of the Irish catch fell by nearly 100 tonnes. It dropped from 230 tonnes to a much lower amount. This decline has caused concern for the local fishing industry. In 2003, the annual value of the Irish catch was £5,812.

Scotland has become a major player in the velvet crab market. While they were once seen as pests, the 1980s supply crisis changed that view. Today, Scotland is the largest fisher of velvet crabs in Europe. Most crabs are caught alongside edible crabs and lobsters. The most productive areas are near the Scottish islands and the west coast. The industry started around the Hebrides and Orkney islands. In 2011, the Scottish fishery was worth £5.8 million. During that year, they caught more than two thousand tonnes.

In England, the fishery reached its peak in 2006. In 2011, English fishermen landed about 200 tonnes of crabs. This catch was worth approximately £290,000. Even with these large numbers, some areas like the Firth of Clyde may be facing overfishing.

Understanding the velvet crab helps us see how many different systems are connected. The health of the crab population affects the economy of many coastal towns. Changes in the ocean, like the dinoflagellate infections in France, can change entire industries. The way we classify these animals changes as our technology for looking at DNA improves. We see how a single species can move from being a pest to a valuable resource. The history of the velvet crab is a story of biology, economics, and human interaction with the sea.