Female lobsters generally lay their eggs between spring and autumn. The eggs remain attached to the swimming legs (pleopods) on the underside of the tail until they hatch between March and September the following year. When the eggs are first laid they are very small and dark green. As they get closer to hatching the eggs grow in size, changing colour to black and then to red in the days leading up to hatching.
Throughout the UK, there is a fisheries byelaw in place which prevents fishermen from landing any egg carrying female lobster (berried hen). However, the relevant authorities have granted special permission to a number of fishermen which allows them to land a limited number of berried hens to the hatchery where they are kept in our brood-stock facility until the eggs hatch. Once all the eggs have hatched, the mother lobsters are then returned.
Larval collection and rearing
Hatching normally takes place overnight, with a single female spawning up to 12,000 eggs over a three-five day period. The larvae are automatically collected into a collection vessel which is transferred each day into the Larval rearing system. Before being transferred the larvae are sterilized with a mild disinfectant to prevent introduction of harmful pathogens into the larval system.
The vessels used to rear the lobster larvae are cones containing 80 litres of seawater which is constantly recirculated through a filtration system and fed back into the culture vessels. The larvae are normally stocked in the cones to a density of 20 to 25 larvae per litre for best survival rates. The larvae remain in the cones for the planktonic phases of their life cycle (metamorphic stages I, II and III) which normally lasts between two and three weeks, dependent on water temperature. Whilst in this phase of their lives they are fed a mixture of frozen and prepared dry diets. Food densities are monitored closely throughout the day because surplus food in rearing vessels may cause problems with water quality, yet a shortage of food can induce cannibalistic tendencies amongst the young lobsters!
In the wild, when the larvae metamorphose into ‘stage IV’ of their life cycle, they transform from a planktonic to a benthic lifestyle (they settle out of suspension and live on the seabed). At this stage in the lobster hatchery, they are removed from the larval cones and placed in individual on-growing containers. The lobsters are kept separate to avoid cannibalism and harm caused by aggression with one another. The lobsters are kept in long raceway tanks, or a system known as an Aquahive tm. This is a multi-level upwelling grow-on system which allows 3,500 juveniles to be fed at once (per tube) and has a much smaller footprint than the raceways. The Aquahives have significantly increased our holding capacity for juveniles.
The juvenile lobsters we keep in the raceways are fed a diet of dried pellets every day. This is quite a time consuming process because each lobster is given one pellet each. Thankfully we now only keep relatively few animals in raceways and this is to house controls for research and so that our visitors can get a good view of the different stages of our juvenile lobsters. Juveniles are kept in the hatchery for up to three months before they are released into the sea surrounding Cornwall and the Isles of Scilly.