ROCK LOBSTERS

HABITAT

ANATOMY

LIFE CYCLE

DISTRIBUTION

Food

Moulting

Life Cycle

Eggs

Larval Stages

Juvenile Stage

Growth

Migrations

Size

Feeding, Reproductive Cycle and Life Cycle

Berried female with newly deposited eggs under her tail

Photos: A Blacklock

Food and feeding

Lobsters feed on a wide range of small shellfish, crabs, starfish and kina, depending on local availability.  They generally hold the prey with their front legs and crush it in their mandibles (or mouthparts).

 

Moulting and mating

Female lobsters can only mate when the carapace is soft (i.e. within a few weeks of moulting). Red rock lobsters moult as early as late February in southern waters, but not until late June in warmer northern waters, and shortly after moulting (2 hours to 63 days) do they mate .        Lobsters are selective about who they mate with; large males prefer to mate with large females and females also prefer the largest male available.

 

Once a mate has been selected the lobsters begin courtship which may last just a few minutes or several days.  When they are ready to mate they rear up, belly to belly and embrace before toppling over with the female uppermost.  The male then deposits a sperm package (or spermatophore) onto the belly of the female.

 

The sperm package begins to disintegrate immediately, so the female rapidly starts to extrude her eggs.  Normally she will cling to a rock face head up and form a brood chamber with her tail, spreading the tail fans to cover the genital pores and the sperm mass.  Eggs are extruded from the genital pores and fertilised as they pass through the sperm package before attaching to the long hairs on the pleopods, under the tail. Small females may extrude as few as 20,000 eggs while large females may produce up to half a million.  The fertilised eggs are carried for between 3 and 5 months, before hatching.

 

Large males become aggressive during the mating season, which usually results in one male per den.  Females are also less likely to shelter together during mating when they are competing for the large males.

 

Life Cycle of Red Rock Lobster

Life Cycle Summary

  1. Lobsters have a long and complex life history

  2. The adults mate and the females carry eggs (berried) for 3-5 months

  3. Larvae hatch and swim in the open ocean for 18-24 months, during which they undergo numerous moults and changes (11 phyllosoma stages)

  4. The puerulus stage settles and moults into the juvenile stage

  5. Juveniles mature and become adults after 4-5 years

Eggs and hatching

Females carry the eggs under the tail for 3-5 months.  During this time the female keeps the eggs aerated by slowly beating the pleopods and groomed using small pincers on her rear walking legs.  The embryos in the eggs develop through a number of stages, developing prominent eyes and legs (below), before becoming ready for hatching.

Hatching occurs at daybreak during the spring. The female stands on tips of her legs with her tail held upright into the water current. She vigorously beats her pleopods for a few seconds, which releases a swarm of the first larval stage (naupliosoma).  The eggs hatch into spider-like larvae which drift in the water for 12 -15 months, growing to around 50 mm in length before returning to inshore areas to settle on the seafloor.

Well-developed eggs just prior to hatching

Photo: L. Tong

Larval stages

Naupliosoma larvae swim up to the light and within minutes moult into the transparent second stage Phyllosoma larva (below left).  This small spider like creature has a body about 2 mm in length.

 

The phyllosoma stages are carried seaward by ocean currents and spend the next 18-24 months growing through eleven phyllosoma stages and seventeen instars, up to 1000 km from

the shore.  The long larval life and poor swimming of the phyllosomas mean that they get carried about by currents and caught up in eddies.

 

When they reach about 35-50 mm, the leaf-shaped phyllosomas (above right) metamorphose into the puerulus stage.

 

Pueruli look like small (25 mm) transparent juvenile lobsters (below).  They are good swimmers and can swim up to 150 km to the shore.  During this stage they do not feed and survive on fat stores laid down during the phyllosoma stages.

 

Phyllosoma Larva in 2 different stages

Photo: G. Moss

Photo: A. Blacklock

Photo: A. Blacklock

Settlement, juvenile stage

Pueruli that successfully reach the shore, settle into small holes and crevices on shallow reefs and within 2-3 weeks moult into the juvenile stage and start to feed. Juveniles mature and become adults after 4-5 years.

 

Moulting and growth

Lobsters have a hard shell (or ‘exoskeleton’) and in order to grow they must shed this shell (below) and replace it with a bigger one.

 

Before moulting (‘ecdysis’) the lobster begins to grow a new layer of exoskeleton beneath the old shell and begins to remove calcium from the old skeleton.

When the lobster is ready to moult the membrane on the back of the lobster, between the carapace and the tail, splits and then the animal pulls itself out of the old shell.  The lobster then takes up water, to swell up and enlarge the new shell, before re-depositing the calcium and hardening the new shell.

 

 

 

Intact moult from a juvenile lobster

Photo: G. Moss

This process of shedding  the  shell (or ‘moulting’) occurs frequently in small lobsters (4-6 weeks) when they are growing rapidly but usually occurs once a year in adult lobsters.  The amount of growth is dependent on the size of the lobster the temperature of the seawater in which it has been held and the amount and type of food it has eaten.

 

Migrations

In spring and early summer some juveniles migrate against the prevailing current. It is believed these migrations help counter the effect of downstream larval drift.  Adult lobsters undertake seasonal inshore-offshore movements associated with moulting, breeding and feeding.

Size at onset of maturity

The size at onset of maturity for female rock lobsters, J. edwardsii, has been defined as the size or size class at which 50% of the rock lobsters in a sample are mature.  Animals are regarded as mature if they are bearing external eggs attached to the pleopods or if there are well developed setae on the endopodites of the pleopods.

 

Immature females usually moult twice a year until maturity, then annually.  Where size at 50% maturity is large, some females may begin moulting once a year before maturity.

 

The size at which 50% of females are mature varies considerably for J. edwardsii throughout New Zealand, from 72 mm Carapace Length (CL) near Gisborne to 121 mm CL in eastern Foveaux Strait.  This size appears inversely related to water temperature.  No data are available from the Chatham Islands.

 

Size at 50% female maturity in most areas is less than the minimum legal size of 60 mm tail width (TW) (approximately 93 - 98 mm CL).  Most females from these areas breed at least once before reaching the minimum legal size.   However, from Banks Peninsula through western Foveaux Strait (CRA 7 and part of CRA 8), size at 50% maturity is greater than the minimum legal size.  The effects of this are not known, but these areas have sustained high catches over time.

 

At sexual maturity the female lobster’s pleopods increase in size and the inner branch grows a fringe of pale hairs to which the eggs attach after mating.   The males mature at about the same size but there are no obvious external changes.  Large male red rock lobsters have been measured at 23 cm carapace length (54 cm body length) and weighing 5.4 kilograms.  Females have reached 17 cm carapace length (45 cm body length) and weighing 2.3 kilograms.

 

Most mature J. edwardsii females moult and mate sometime between February and May. Females carrying eggs occur in greatest numbers from April to October, though a few are found during any month of the year.  Females bear eggs only once each year and most mature females carry eggs during the egg-bearing season.  Successful reproduction requires mature male and female lobsters of similar size.

 

The number of eggs carried by J. edwardsii depends on size, ranging from about 125,000 for a female of 95 mm carapace length (CL) to about 540,000 for one of 170 mm CL.

 

Most mature female S. verreauxi moult between July and November, bear eggs during late September to January, and hatch the eggs from December to January.  The number of eggs carried by S. verreauxi ranges from about 375,000 for a female of 152 mm CL to 2,000,000 for one of 230 mm CL.

 

Rock lobsters of both species develop through a series of stages from egg to adult.  Fertilised eggs are attached to pleopods (swimmerets) on the underside of the female’s tail.  The eggs develop for 3 to 6 months and hatch as small nauplisoma larvae.   Within a few days these metamorphose into phyllosoma larvae, which develop through 11 stages during the 10 to 20 months they spend in the ocean. The last phyllosoma stage metamorphoses into the puerulus larva, a strong swimmer that returns to the coast and moults into the first juvenile stage if it finds suitable substrate.

© NZ Rock Lobster Industry Council Ltd