Norway Lobster

Appearance

''Nephrops norvegicus'' has the typical body shape of a lobster, albeit narrower than the large genus ''Homarus''. It is pale orange in colour, and grows to a typical length of 18–20 centimetres , or exceptionally 25 cm long, including the tail and claws. A carapace covers the animal's cephalothorax, while the abdomen is long and segmented, ending in a broad tail fan. The first three pairs of legs bear claws, of which the first are greatly elongated and bear ridges of spines. Of the two pairs of antennae, the second is the longer and thinner. There is a long, spinous rostrum, and the compound eyes are kidney-shaped, providing the name of the genus, from the Greek roots and ''ops'' .

Distribution

''Nephrops norvegicus'' is found in the north-eastern Atlantic Ocean and North Sea as far north as Iceland and northern Norway, and south to Portugal. It is not common in the Mediterranean Sea except in the Adriatic Sea, notably the north Adriatic. It is absent from both the Black Sea and the Baltic Sea. Due to its ecological demands for particular sediments, ''N. norvegicus'' has a very patchy distribution, and is divided into over 30 populations. These populations are separated by inhospitable terrain, and adults rarely travel distances greater than a few hundred metres.

Behavior

The typical life span of ''N. norvegicus'' is 5–10 years, reaching 15 years in exceptional cases. Its reproductive cycle varies depending on geographical position: "the periods of hatching and spawning, and the length of the incubation period, vary with latitude and the breeding cycle changes from annual to biennial as one moves from south to north". Incubation of eggs is temperature-dependent, and in colder climates, the duration of the incubation period increases. This means that, by the time hatching occurs, it may be too late for the females to take part in that year's breeding cycle. In warmer climates, the combined effects of recovery from moulting and ovary maturation mean that spawning can become delayed. This, in turn, has the effect of the female missing out a year of egg carrying.

Adult male ''Nephrops norvegicus'' moult once or twice a year and adult females moult up to once a year . In annual breeding cycles, mating takes place in the spring or winter, when the females are in the soft, post-moult state. The ovaries mature throughout the spring and summer months, and egg-laying takes place in late summer or early autumn. After spawning, the berried females return to their burrows and remain there until the end of the incubation period. Hatching takes place in late winter or early spring. Soon after hatching, the females moult and mate again.

During the planktonic larval stage the nephrops larvae exhibit a diel vertical migration behaviour as they are dispersed by the local currents. This complex biophysical interaction determines the fate of the larvae; the overlap between advective pathway destination and spatial distributions of suitable benthic habitats must be favourable in order for the larvae to settle and reach maturity.

Habitat

''Nephrops norvegicus'' adults prefer to inhabit muddy seabed sediments, with more than 40 percent silt and clay. Their burrows are semi-permanent, and vary in structure and size. Typical burrows are 20 to 30 centimetres deep, with a distance of 50 to 80 centimetres between the front and back entrances. Norway lobsters spend most of their time either lying in their burrows or by the entrance, leaving their shelters only to forage or mate.

Food

''Nephrops norvegicus'' is a scavenger and predator that makes short foraging excursions, mainly during periods of subdued light. They feed on active prey, including worms and fish, which they capture with their chelipeds and walking legs, and food is conveyed to the mouth using the anterior walking legs, assisted by the maxillipeds.

There is evidence that ''Nephrops norvegicus'' is a major eater of jellyfish.

Evolution

''Nephrops norvegicus'' was one of the species included by Carl Linnaeus in his 1758 10th edition of ', the starting point for zoological nomenclature. In that work, it was listed as ', with a type locality of ' . In choosing a lectotype, Lipke Holthuis restricted the type locality to the Kattegat at the Kullen Peninsula in southern Sweden . Two synonyms of the species have been published – "''Astacus rugosus''", described by the eccentric zoologist Constantine Samuel Rafinesque in 1814 from material collected in the Mediterranean Sea, and "''Nephropsis cornubiensis''", described by Charles Spence Bate and Joshua Brooking Rowe in 1880.

As new genera were erected, the species was moved, reaching its current position in 1814, when William Elford Leach erected the genus ''Nephrops'' to hold this species alone. Seven fossil species have since been described in the genus.

Populations in the Mediterranean Sea are sometimes separated as "''Nephrops norvegicus'' var. ''meridionalis'' Zariquiey, 1935", although this taxon is not universally considered valid.