Expert topic: Blue crab
by Rebecca Sherratt, Production Editor, International Aquafeed
Blue crabs are named so due to their sapphire claws. Their shells, or carapace, are a mottled brown colour, whilst females have
red highlights on the ends of their pincers. Their Latin name,callinectes sapidus, also literally translates into savoury, beautiful swimmer, so it is unsurprising that they are so very popular in coastal towns for their tender, sweet meat.
These Western Atlantic crustaceans weigh in at between one to two pounds, being up to four inches tall and nine inches wide. Blue crabs have short lifespans, only living between one and three years and are unfortunately beginning to struggle due to the extensive farming and harvesting of their species. Over the past ten years harvesting limitations have been put into place in many bays, in order to ensure the continuation of the species and to prevent overharvesting.
Blue crabs are often found in coastal lagoons and estuaries,all over the world. From up north near Nova Scotia, throughthe Gulf of Mexico, and down south near Uruguay. They also commonly travel and expand elsewhere. In the 1940s reports of blue crab sightings were seen in Egyptian waters, and in the past few decades they have additionally been reported in Italy,
As omnivores, blue crabs eat almost anything they can get theirclaws on. From mussels, snails, fish and plants, the occasionalblue crab will also grow cannibalistic and eat smaller blue crabs if desperate. They are considered crucial to their local ecosystems, as their recent decline in numbers has resulted in their chosen food increasing drastically in numbers, especially periwinkles and marshgrass-eating snails. The lack of blue crabs also causes problems for those marine animals that would usuallyfeed upon them, especially menhaden, oysters and other filterfeeders who frequently indulge in blue crab larvae.
The Chesapeake Bay in Virginia, USA, is the world"s largestblue crab fishery, established in 1607. Originally famous for itsoyster harvests, Chesapeake Bay soon became the hotspot for blue crabs, providing over 60 percent of the nation"s blue crabs.The bay now fights issues that are threatening the abundance ofthese brilliant crustaceans, such as pollution, habitat loss and underwater grass restoration. In 2014, as part of the Chesapeake Bay Watershed Agreement, the bay committed to the goal of maintaining over 125 million adult female blue crabs, alongside working with recreational crabbers towards a sustainable method of harvesting these crustaceans.
The blue crab is one of the most sought-out shellfish in the mid-Atlantic region, caught commercially for food, but alsorecreationally by many fishers residingupon the coast, or simply travelling to the coast for some relaxing crabbing. Areas with ample cover, particularly areas ripe with submerged aquatic vegetation, are the places where blue crabs tend to nestle.
Blue crabs can be caught relatively easily, usually they are harvested only with simple gear such as a pot, trotline, handline, dip net, scrape or dredge. The equipment used to catch crabs has little to no effect on habitat, however, the mass number of crustaceans being harvested has led to multiple associations establishing regulations to maintain and increase their numbers.
Since the 1990s, fishermen have gone to an extended effort toensure that less crabs are harvested from the oceans. Since then, a drastic improvement has been seen in the numbers of crustaceans, however, there still remains a steady decline in numbers.
The Chesapeake Bay Stock Assessment Committee (CBSAC) reported numbers exceeding 49 million blue crabs being harvested from their bay in 2016 alone. Recreational harvests were estimated to be 3.5 million pounds, while commercial harvests from those waters were estimated to be 53.1 million pounds. These numbers were 40 percent higher than the harvest of 2015, which came to 35.2 million pounds, but was still considered to be a below average harvest.
By the start of the 2018 crabbing season, approximately 147 million female adult blue crabs, at over one year old, were estimated to be present in Chesapeake Bay, a worryingly lowfigure compared to the Bay"s aim to have 215 million female spawning-age crabs. It is not the first time that the bay has fallenshort of numbers; in 2017 the Bay, aiming for 254 million crabs present, had even less numbers than in this current year.
The total abundance of male and female blue crabs in the Bay has reportedly decreased 18 percent, from 553 million crabs
in 2018 to 455 million crabs in 2017. The reports suggest that juvenile crabs rarely survived into adulthood or were harvested before reaching maturity.
Based upon the Bay"s 2017 Blue Crab Advisory Report, these declining numbers are not yet at a worrisome level and blue crabs" numbers can still somewhat easily be increased. The bluecrabs in Chesapeake Bay are not considered to be over-fished orover-harvested, and the 2018 Blue Crab Advisory Project also supports this statement.
Despite blue crabs being very flexible in terms of locations and habitats, they are especially sensitive to changes in relation to breeding and the mating season. Chesapeake Bay have experienced extreme declines in blue crab spawn rates, when certain conditions have not successfully been met, which have by extension led to negative carry-on effects for the ecosystem.
The clams, oysters and mussels usually eaten by blue crabs have been noted to be overpopulated due to the lack of crabs eating them, whilst the blue crab natural predators, such as striped bass, red drums and herons have been struggling due to the lack of food present.
Female blue crabs mate only once in their lives. Their egg mass develops under their chests, which are also called aprons. These aprons can contain up to 2 million eggs, but only one per million will survive into adulthood. The female will carry the eggs for two weeks, before releasing them into waters what carry them out into the ocean. The larvae, also called zolt, will molt over twenty-five times before returning to the estuaries and salt marshes asmaturing crabs, ready to start reproducing with their partner.
Crabs that pair up to mate are called doublers, and the woman is called sponge crab when carrying the eggs. Sponge crabs are under especially strict protection, and if they are caught they must be released immediately. These females usually appear in rivers and oceans in early April and are common until August or September.
Despite less blue crabs, in numbers, being harvested, the farmingof these crabs for commercial value has increased significantlyfrom 2014 onwards. A 15 percent increase in commercial harvesting was present in Maryland, a 24 percent increase for Virginia and 60 percent increase for the Potomac river, all alternative sources for blue crabs aside from Chesapeake Bay.
Recreational harvest of female blue crabs is no longer permitted in or around the Maryland tributaries, so the eight percent of commercial harvest of blue crabs around this area consists solely of male blue crabs.
Blue crabs remain such a popular animal to be farmed, due totheir flexibility of habitat and environment. These crustaceanscan be farmed in irrigation ditches, pond systems, fry farming systems, cage systems and integrated recycling systems, to name a few. They are therefore an easy form of livestock for farmersto include in their fish farms, taking minimal effort and requiringonly a small amount of space.
Crab farmers focus on the state of the carapace, when farming these animals. In order to grow, blue crabs must shed their
hard carapace, at which point they are called "peeler" crabs. Experienced crabbers can quickly spot signs that a crab is due tomolt, and these specific crabs are harvested and held for a briefamount of time in shedding tanks until they molt. These newly molted crabs are then removed from the water and sold. Catchingcrabs at this specific stage is crucial to a successful harvest.
The most common method of farming blue crabs is using a crab pot, which involves a cubical wire trap, and two-to-four entrance funnels. The pot has two chambers, the lower chamber comprising of the primary entrance funnels and some bait, oftena fish head or some chicken. The upper chamber is separated by apartition with two holes. The crabs enter the chamber for the bait, and the entrance closes.
When trying to escape the crustaceans naturally swim upwards and enter the second chamber what also closes securely. These crab pots were introduced into Chesapeake Bay in 1936, and soon became a common crabbing tool from the 1950s onwards. If youwant to fish with more than two crab pots simultaneously, then acrabbing license is required.
Drop nets, dip nets and collapsible traps are also used to catch blue crabs, often baited with herring. These methods require a long-handled dip net and multiple yards of string. Recreational crabbers are more likely to utilise these methods. It is considered the prime time to harvest blue crabs between October and December, when they are a most common occurrence in rivers and creeks.
To continue supplying more crabs for both harvesting and sustainability, the Blue Crab Advanced Research Consortium is a development programme that focusses on hatchery technologies. The research team are looking at the production of juvenile crabs, in order to improve the quantity of world stock and enhancing the development of aquaculture techniques for the year-round production of soft-shell, young blue crabs.
Blue crab is the perfect meal for someone who is looking forplenty of protein. With a significantly lesser amount of fat, whencompared to beef, chicken and pork, blue crab is also low in calories. Blue crab meat has the best protein-to-calorie ratio, when compared to all other types of crab we eat.
Omega-3: Also known as fish oil, these polyunsaturated fattyacids help us maintain normal metabolisms, alongside lowering the risk of heart disease. Omega-3"s can often be prescribed to you by a doctor as a supplement, but blue crab is a great way to get some from the source.
Selenium: Key for a healthy immune system, reproductive health and cognitive function, selenium is a trace mineral found in a variety of foods. The best sources of selenium include brazil nuts and seafood.
Riboflavin: Formerly known as vitamin G, riboflavin assists
in fighting off anaemia by promoting iron metabolism. It alsoprovides great antioxidant protection and serves well as a source of energy.
Blue crab can be purchased either fresh or pasteurised, where it is heated and sealed to kill any pathogenic organisms.Crustaceans in general are usually most flavourful between Juneand August, when they are harvested, and the largest specimens are usually found in September and October. Crabs are often measured in bushels or jimmies, which equate to roughly 60-70 crabs. A half-bushel of male blue crabs can cost approximately £100. Male crabs are more expensive, but much more easily accessible than female blue crabs.
This admired crustacean is continuing to prove its popularity amongst consumers, and the market for blue crab only continues to grow. Provided regulations and companies like Chesapeake Bay and the Blue Crab Research Consortium continue to work hard to ensure their numbers improve and they are cared for accordingly, the blue crab will continue to be a staple meal and key aquacultural form of livestock.