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Tank Tuesdays 5

King Scallop (Pecten maximus)

The king scallop (Pecten maximus) is a common species found frequently around the United Kingdom and Ireland (as well as in the Eastern Atlantic and the Mediterranean) and is of great commercial importance to the fishing industry. P.maximus is a bivalve mollusc meaning it is made up of two valves with its organs contained within. On average this species grows between 10-15cm in length on average with an off-white, yellow or light brown colouration on its right valve (with bands or spots of darker pigmentation) and its left valve is light pink to red/brown in colouration. The key difference between the valves is that the left valve is flat, and the right is strongly convex, with the right valve slightly overlapping the left. P.maximus is found at a large range of depths, ranging from 0 to 125m, they prefer to be in open coastal areas or offshore sea beds. The sediment type is important in the settlement of the king scallop and prefer the substrate to be one of the following: clean firm sand, fine gravel or sandy gravel which they will be found in shallow depressions of their own making. Bivalves are suspension feeders, so they use their tentacles to catch food items passing in the water column. The king scallop has a diet comprised of phytoplankton, single celled algae, particulate organic matter and bacteria.

ARC Marine Tank Tuesdays 5 king scallop

Figure 1: P.maximus feeding in ARC Marine’s observational tanks

This bivalve species is a hermaphrodite meaning that each individual contains both the male and female sexual organs. This species reaches maturity at 2 years of age and reaches it maximum maturity at 3-5 years old (individuals live to be between 11-20 years old). They release their eggs into the water column between April-September and have a high fecundity (number of young/eggs produced) where they will commonly produce a million eggs in a single season. Once the eggs have hatched the larvae enter a planktotrophic stage which lasts between 11-30 days. This gives the species an opportunity to widely disperse, which is helped by a secondary dispersal method called byssus drifting. Bivalves have specialised threads known as byssus threads which are commonly used to aid in settlement in which they will attach themselves to a substrate. They also have drifting threads which differ in function from the attachment threads. These threads exceed the length of the attachment threads and increase their surface area which causes the juveniles to descend through the water column at a slower rate, furthering the distance the larvae could disperse (potentially over 10km). They also show bi-modal spawning in which they release a smaller portion of their eggs earlier in the season (around April-May) and then another larger spawn around later in the season (typically around August). This is likely due to the recovery period that the gonads need after producing eggs.

As mentioned previously the king scallop is a very commercially important species to the fishing industry, currently the majority of production of king scallops comes from fishing as opposed to aquaculture sites. According to the Food and Agriculture Organisation (FAO) there was a global average of 50,475 tonnes of P.maximus where acquired from fishing between 2000-2016.

Among this average the UK is one of the top producers of this species, in 1999 35.411 tonnes of scallops where recorded and of this number 19.108 tonnes came from the UK and 12.745 tonnes from France. In comparison global production values from farmed king scallops are incredibly low with only a global average of 91 tonnes between 2000-2016. With the risk of over fishing becoming an ever-increasing problem research is being conducted into farming methods for the king scallop as to make their production more efficient and less damaging to the environment as the predominant collection method is destructive bottom trawling using scallop dredges (see video below).

Figure 2: A video showing how scallop dredging can affect the benthic environment (credit Seafood Watch)

Traditional methods like dredging completely destroy the seabed and delicate habitats in its process. Some dredgers report only retaining 30% of what’s caught in the chain purses due to the rest being damaged making it a hugely inefficient way of catching a prised catch.

ARC Marine pride themselves in pioneering the sustainable sourcing of important shellfish species like the King Scallop. We use divers to hand pick them off the seabed or scallop farming which involves hanging scallops in nets throughout their life cycle. These are the long-term, sustainable solutions to enjoying this tasty product.

The consumer is now starting to shift towards traceability and sustainability of their sea food and hand dived scallops fetch a premium on the market ranging from £1.20-£1.80 depending on size. This opens a huge opportunity for local fisherman to switch to diving methods to gain higher revenue for their catch and help preserve the marine habitat to allow it to keep generating future fish stocks for years to come. We don’t believe in banning fishing, we believe traditional methods such a dredging is ineffective and destructive and with today’s technology in robotics and SCUBA equipment, there are new and creative ways to enjoy shellfish responsibly.

Next time you are in a restaurant and see scallops on the menu, quiz your waiter about where and how they were sourced.

This article was written by Jamie Mathews

Tank Tuesdays is a series of mini articles describing the marine life here at ARC Marine’s aquaria; and their interactions with our artificial habitats.