Lobsters must moult in order to grow, that means they must shed their carapace. The carapace of the cephalothorax splits in two, and the lobster pulls its body through first, then its claws, its legs and its tail. Once through, the lobster is as soft as gelatine. The lobster absorbs a large quantity of water to increase volume. At first, the new carapace is very flexible and not very solid. It will harden with time. Approximately a month is needed for the carapace to harden completely. After having moulted, lobsters are 15% to 20% larger than before and their weight increases approximately by 40% to 50%.

At the beginning of their benthic life, lobsters grow quickly and very often change carapace. They can moult 4 to 5 times in the first year. As adults, lobsters moult approximately once per year. When they reach a certain size, they grow slower and sometimes several years will pass before they change carapace. Before attaining their commercial size, lobsters will have moulted approximately 20 times. Generally, lobsters moult in the summer when water temperatures are warmer. Growth and moulting are greatly influenced by temperature. Lobsters moult more often and grow more rapidly when in warm water. Therefore, two lobsters of the same size can be of different ages depending on where they lived. In the Magdalen Islands, it is estimated that lobsters reach their commercial size at around 8 years of age. However, lobsters can reach their commercial size at the age of 5 in certain areas where the water is warmer. In areas where the water temperature remains cold year-round, it can take up to 10 years.

Courtesy of NOAA

Currently, there are no techniques to determine a lobster's precise age. Every time they grow, lobsters change carapace. Therefore, there is no trace of growth on their body that can indicate their age (such as the growth rings found on the scales of fish, for example). We therefore don't know how long lobsters can live. Age is estimated according to size and growth rate based on temperature. We know however that they can live many years (at least 50) and reach very large sizes. In 1977, a lobster weighing 20 kg and measuring approximately 1 meter (overall length) was caught in Nova Scotia. Off the coast of Massachusetts in the U.S., a similar lobster was also reported (20 kg, overall length: 91 cm). Moreover, certain records document the capture of a lobster with an overall length between 1.5 and 1.8 meters.