Female Lobsters Research Articles

Gender- and oxygen-related irrigation behaviour of the decapod Nephrops norvegicus

The Norway lobster Nephrops norvegicus (L.) inhabits burrows in muddy clay sediments (e.g. on the Swedish west coast), where an autumnal oxygen deficiency in the bottom water can occur. Our experiments investigated whether the irrigation of the burrows would reflect a behavioural adaptation to hypoxia, and whether any gender differences of such behaviour exist. Irrigation is performed by the pleopods which may compensate for a decreasing oxygen tension. Pleopod activity (total number of strokes per sampling time), associated with oxygen concentration and gender, was studied in N. norvegicus kept in artificial burrows resembling their natural habitat. Male and female lobsters were separately exposed to either normoxia (70% oxygen saturation) or hypoxia (30% oxygen saturation). A sexual difference in behaviour was found, where females irrigated the burrow less than males during normoxia. Females showed a significant increase of pleopod activity in hypoxia compared with normoxic conditions, which was not displayed by the males probably due to the degree of individual variation found. However, when only males were studied during progressive hypoxia (from 60 to 5% oxygen saturation), following any changes of irrigational behaviour, a significant increase of accumulated pleopod activity occurred. A major increase of pleopod activity appeared between 60 and 50% oxygen saturation, below which the activity remained high until a critical point (<10% saturation, 11 °C, 33 psu) where irrigation dropped to a level close to that of normoxic values. Activity sessions during hypoxia were longer and had a higher stroke rate than during normoxia.

Comparative Analysis of Escape Behavior in Male, and Gravid and Non-Gravid, Female Lobsters.

Few studies exist in which the parameters of a single behavior have been quantitatively compared for male and female lobsters. Here, we have examined the effects of sex and gravidity on the parameters of the escape behavior of the American lobster, Homarus americanus, elicited by a visual threat. Both non-gravid females and male lobsters readily tailflipped in response to the stimulus, but gravid females failed, with one exception, to initiate a swim, even when stimulus strength was increased. Although the total distance swum by males and non-gravid females was not statistically different, males covered more ground in the initial power swim and during the subsequent swims than did non-gravid females. Males swam for a longer time, performing more tailflips, than females. Relative to their length and weight, males swam a greater distance at each stroke during the initial power swim and the subsequent swims, although, females might have compensated by swimming at a higher frequency. There were no significant differences in swimming velocity or acceleration, nor in the calculated force or work performed by the two sex classes (male and non-gravid females). Therefore, apart from egg-bearing, which severely inhibits the escape response, it remains to be seen whether the subtle physiological and anatomical sexual dimorphism that produces longer and more swim strokes in males but higher frequency tailflips in females results in the same chances of survival for the sexes.

Involvement of the hyperglycemic neurohormone family in the control of reproduction in decapod crustaceans

Summary In the last few years, (bio)chemical and molecular biological studies have shown that several members of the hyperglycemic hormone family are present in different molecular forms. In vivo and in vitro bioassays revealed that some of these isoforms also play a role in the control of reproduction in decapod crustaceans. This communication gives a review of the cytological aspects of the eyestalk X-organ sinus gland complex, responsible for the synthesis, storage and release of these neuropeptides, and the molecular and functional aspects of those members involved in the control of reproduction. Finally, the role of the hyperglycemic hormone family in the regulation of reproduction in the female lobster is described as an example of the (possible) interactions of the members of the hyperglycemic hormone family with other (neuro)endocrine factors in the reproductive process of crustaceans.

Ultrastructural Study of the Neurosecretory Granules and Crustacean Hyperglycemic Hormone (CHH) Immunolocalization in the Sinus Gland of Homarus gammarus

ABSTRACT Seven different types of neurosecretory granules have been observed in the axon terminals of the sinus gland of the adult female lobster Homarus gammarus. They were discriminated through morphometrical and morphological criteria such as size, shape, frequency of occurrence, electron density, and axon-matrix density. Each size distribution followed a single Gaussian-type distribution. Each axon terminal contained I type of granule. The mean granule diameter ranged from 50 nm (type 1) to 161 nm (type 7). Type 6 and type I axon terminals were, respectively, the most and least frequent. An immunopositive reaction against an anti-Homarus americanus CHH was detected in the 2 largest types of granules: type 6 (mean diameter, 128 nm) and type 7 (mean diameter, 161 nm).

Recruitment overfishing reference point for the American lobster, Homarus americanus

A 21-year series of annual estimates of egg production and recruitment in a Newfoundland lobster population indicates similar asymptotic relationships for recruitment to the fishery and to the adult population, both derived from legal stock estimates. Lines with slopes equal to the 90th-percentile and median survival ratios drawn through the origin of the egg production–adult recruitment scatterplot were examined as potential recruitment overfishing reference points for the Arnold’s Cove lobster stock. If the inverse of the estimated lifetime egg production per recruit (E/R) for a given exploitation rate exceeds the slope of the selected reference point, the risk of recruitment overfishing is high. For the Arnold’s Cove stock, the E/R level at a nominal 90% exploitation rate is estimated at 4.2% of the unfished population, compared with 2.5% for the overfishing reference point corresponding to the median survival ratio. Female lobsters at Arnold’s Cove mature at sizes below the minimum legal size, providing a buffer against high exploitation rates. Small, scattered refugia of large lobsters could also help to explain how heavily exploited populations of this species persist at such a low level of egg production.

Pharmacokinetics of 2-naphthol following intrapericardial administration, and formation of 2-naphthyl- beta --glucoside and 2-naphthyl sulphate D in the American lobster, Homarus americanus

1. Following a 0 25-mg kg intrapericardial dose of the phenolic compound, 2- naphthol, to the American lobster, Homarus americanus, a two-compartment model best described the disposition of parent \\ [C]-2-naphthol in the haemolymph. Male and female lobsters had similar alpha -phase half lives of 26 19 min (mean SD, n 4) and 29 15 min respectively. The beta -phase half lives were significantly longer in males,63 9 30 9 h, thanin females, 30 6 6 8 h (p 0 05). The total body clearance for females was 26 4 6 5 ml h kg and was higher than that of males, 11 1 5 9 ml h kg (p 0 05). 2. 2-Naphthol was converted to 2-naphthyl- beta -D-glucoside (major metabolite) and 2- naphthyl sulphate (minor metabolite) such that at 24 h 39-60 6% of the radioactivity in haemolymph was 2-naphthyl- beta -D-glucoside, 38 6-58 9% 2-naphthol and 0 5-4% 2- naphthyl sulphate. 3. The2-naphthol-derivedradioactivity was 99%boundtohaemolymphproteinsat 1 min and 90% bound at 1 day after the dose, indicating that both 2-naphthol and 2- naphthyl- beta -D-glucoside were highly protein bound. 4. 2-Naphthyl- beta -D-glucoside was slowly eliminated from haemolymph in both males and females, with elimination half lives of 34-78 h. 2-Naphthyl- beta -D-glucoside was the major metabolite in urine samples collected at 5 days after the dose. Hepatopancreas and antennal gland contained glucosidase activities, and the long half life of 2-naphthyl- beta -Dglucoside could be explained by conjugation-deconjugation cycling. 5. 2-Naphthyl sulphate was eliminated from haemolymph with a half-life 10 h and was excreted in urine.

Reproductive cycle and size-dependent spawning of female spiny lobsters (Panulirus japonicus) off Oshima Island, Tokyo, Japan

Reproductive biology of the spiny lobster Panulirus japonicus was histologically examined by monthly sampling between March 1993 and September 1994 at Oshima Island, near Tokyo. P. japonicus had a well defined reproductive cycle. Yolk accumulation became manifest in February and ovaries grew rapidly in March. Females spawned from late April to mid August and were ovigerous to mid September. Of large females with a carapace length (CL) of ≥47 mm, 93% were estimated to spawn twice during the spawning season. Size at which 50% of females reached sexual maturity was estimated to be 41.8 mm CL, as calculated from a logistic model. Some individuals considered to be primiparous showed delayed vitellogenesis and were estimated to spawn only once during the season.

ULTRASTRUCTURAL STUDY OF THE NEUROSECRETORY GRANULES AND CRUSTACEAN HYPERGLYCEMIC HORMONE (CHH) IMMUNOLOCALIZATION IN THE SINUS GLAND OF HOMARUS GAMMARUS

ABSTRACT Seven different types of neurosecretory granules have been observed in the axon terminals of the sinus gland of the adult female lobster Homarus gammarus. They were discriminated through morphometrical and morphological criteria such as size, shape, frequency of occurrence, electron density, and axon-matrix density. Each size distribution followed a single Gaussian-type distribution. Each axon terminal contained I type of granule. The mean granule diameter ranged from 50 nm (type 1) to 161 nm (type 7). Type 6 and type I axon terminals were, respectively, the most and least frequent. An immunopositive reaction against an anti-Homarus americanus CHH was detected in the 2 largest types of granules: type 6 (mean diameter, 128 nm) and type 7 (mean diameter, 161 nm).

Size structure and reproductive variation of the spiny lobster Panulirus homarus over a relatively small geographic range along the Dhofar coast in the Sultanate of Oman

This paper reports variations in size structure, size at sexual maturity, and reproductive potential in the Panulirus homarus population sampled from commercial catches at three sites: Shuwamiyah, Sudh and Mugsyl along the Dhofar coast in the Sultanate of Oman. The size structure of the lobster population showed significant variation (P &lt; 0.001) among the three sites. Size at sexual maturity, based on the presence of spermatophores or an ovigerous condition, indicated variation within the population. Females mature at a smaller size at Shuwamiyah than they do at Sudh and Mugsyl. The relationship between the number of eggs (E) and carapace length (L, in mm) of female lobsters is expressed by E = –249322 + 8942L (r2 = 0.95; n = 11) over the size range 65–95 mm carapace length. Length frequency, size at sexual maturity, and fecundity were used to estimate the index of reproductive potential (IRP) of each 5-mm size class. The size class with the highest IRP varied among the three sites. The variation in size structure and size at sexual maturity was explained by fishery exploitation and by different oceanographic and ecological conditions caused by seasonal upwelling in the study region.

Maximizing lobster, Homarus gammarus (L.), egg and larval viability

The viability of batches of larvae reared to produce lobsters, Homarus gammarus (L.), for stock-supplementation experiments varied widely and rendered the timing and numbers of juveniles available for release unpredictable. Egg lipid reserves, time of hatching, exposure to low salinity during incubation and the influence of feeding regimes on water quality during larval culture were among the factors judged most likely to have affected viability. There was considerable variation in the lipid content of eggs from different females captured in 1989 and 1990. The proportion of lipid in eggs from females caught in 1990 was higher (10-20%) than that in eggs from females caught in 1989 (6-11%). The fatty acid content of eggs declined 72-80% during development although the overall proportions of fatty acids remained similar. Analysis of eggs and larvae from a single brood showed that rapidly developing eggs and the larvae that hatched from them contained greater triacylglyceride lipid reserves (by 49% and 15% respectively) than those which developed more slowly and hatched later. Exposure to reduced salinity (below 29 psu) prolonged development (by 30%), increased losses (to > 50%) and reduced the ratio of n-3:n-6 fatty acids (from 35-48 to 18-29) of eggs being incubated by captive, wild-caught, female lobsters. Larvae hatching from eggs held in reduced salinity (23 psu) survived less well (3% compared with 15%) than those incubated in sea water of 29 psu. The rate and degree to which fouling organisms became attached to larvae was related to feeding regime but not to development rate. A diet of mysids supplemented with mussel produced most fouling, generally poorer growth and a higher incidence of moulting abnormalities than a diet of mysids supplemented with Artemia nauplii. Among larvae fed Artemia, those developing early were significantly larger at instar 4 than late developers (56.4 mg cf. 49.8 mg, P < 0.05), but such differences in weight were not maintained by juveniles during the following 31 days of culture. The ecological and aquacultural implications of the results are discussed.

PCB and metal concentrations in American lobsters from the Acushnet River Estuary and Long Island Sound

The American lobster, Homarus americanus, is commonly found in coastal waters adjacent to heavily industrialized areas where pollutant input generally occurs. Environmental contamination is known to affect many aspects of lobster biology. Heavy metals, pesticides, pulp mill effluent, petroleum hydrocarbons and other pollutants can adversely affect lobster physiology and behavior. Sublethal concentrations of contaminants can stress lobsters, making them more susceptible to disease or other conditions that would normally be tolerated. Lobster embryos and larvae, particularly the first-stage, are sensitive to a variety of organic and metal pollutants. Sediments in New Bedford Harbor, Massachusetts, are heavily contaminated with polychlorinated biphenyls (PCBs); edible tissues of lobsters collected there have been found to contain PCB concentrations exceeding the FDA action level of 2 [mu]g/g wet wt. PCBs are strongly lipophilic and accumulate in fatty tissues including egg masses. Metals and PCBs are contaminants of concern in Long Island Sound. This study examines whether field exposure of ovigerous female lobsters to PCBs results in subsequent contamination of embryos, first-stage larvae, postlarvae, and juvenile offspring of [open quotes]berried[close quotes] lobsters from New Bedford Harbor and selected locations in Long Island Sound. Metal contamination in the embryos and offspring of Long Island Sound lobsters wasmore » also measured. 15 refs., 3 tabs.« less

Cloning and expression of mRNA encoding prepro-gonad-inhibiting hormone (GIH) in the lobster Homarus americanus

The gonad-inhibiting hormone (GIH) is produced in the eyestalk X-organ sinus gland complex of male and female lobsters, and plays a prominent role in the regulation of reproduction, e.g. inhibition of vitellogenesis in female animals. To study this neurohormone at the mRNA level, we cloned and sequenced a cDNA which encodes GIH in the lobster Homarus americanus. The structure of preproGIH consists of a signal peptide and the GIH peptide itself. A comparative analysis revealed that lobster GIH, together with crab molt-inhibiting hormone, belongs to a separate group of the crustacean hyperglycemic hormone (CHH) peptide family which seems to be unique for crustaceans. Expression studies showed that GIH mRNA is expressed in the eyestalk, indicating that the neuroendocrine center in this optic structure is the only source of GIH. As this center modulates the other (neuro)endocrine organs in crustaceans, it is postulated that GIH regulates production and release of hormones involved in reproduction/molting processes.

The behavior of lobsters in response to reduced salinity

Two experiments were conducted to measure the behavioral responses of lobsters, Homarus americanus (Milne-Edwards), to reductions in salinity. In the first experiment animals were placed in a 3 ft diameter tank that was divided in half by plastic mesh. Spontaneously active lobsters were able to move between the two halves of the tank by passing through either of two conduits. The conduits were equipped with optical sensors to monitor the passage of animals, and a perfusion system to control the salinity of the area in, and around, the conduit. When the salinity in the vicinity of both conduits was the same (28–32 ppt), lobsters exhibited no preference for either conduit. However, when the salinity in one of the conduits was lowered, lobsters preferred to pass through the high salinity (20–25 ppt) conduit rather than the one with low salinity (10–15 ppt). In addition, females appeared to be more selective in their preference and exhibited higher overall activity than males when exposed to reduced salinity. In the second experiment, individual lobsters were placed in a shelter at one end of a long seawater table and exposed to seawater of gradually decreasing salinity. The salinity required to cause a movement out of a shelter, i.e. an avoidance response, was recorded. On average, lobsters first ventured small distances (< one body length) out of their shelter when the salinity reached a level of 18.4 ppt ± 1.42 (SEM), and definitively moved away from their shelter (> one body length) when levels approached 12.62 ppt ± 1.59. Although it was not statistically significant, females again seemed to be either more sensitive to salinity or found it more aversive, because they tended to initiate movements at salinities greater than those required to influence males. These behavioral data indicate that: 1. (1) adult lobsters are capable of detecting changes in salinity which are comparable to the levels found during natural fluctuations in coastal bays and estuaries; 2. (2) when exposed to low salinity of sufficient magnitude, they attempt to avoid it, and; 3. (3) females appear to be more sensitive to drops in salinity and/or they find it more aversive. Previous studies have demonstrated that estuarine lobster populations are dominated by males and that there are seasonal migrations of lobsters into, and out of, estuaries. We conclude that the behavioral responses of male and female lobsters to low salinity may determine, in part, the distribution and movements of lobsters in estuarine habitats.

Characterization and Expression of Lobster Preprohormones Involved in Metabolism, Moulting and Reproduction

A combined molecular biological, (bio)chemical and immunocytochemical study was carried out on the role of neuropeptides in the control of the biannual reproductive cycle in the female lobster.

A Comparison of the Tuning Properties of Chemoreceptor Cells in the First and Fourth Walking Legs of Female American Lobsters

Figure 2. Records of bending-reflex motor activity in larval and pupal Manduca sexta. Larval extracellular records are responses ofmotor neurons in the IeJi (L) and right (R) motor nerves innervating the intersegmental muscles (ISM). The responses areproduced by electrical stimulation ofthe IeJi stretch receptor sensory neuron (SRSN) alone (indicated by long bar); the right sensory nerve (DNa) carrying axons,fiom mechanosensillae (indicated by short b ar ); or the stretch receptor and DNa together. When the SRSN was stimulated alone, the stimulus induced motor activity coincident with the stimulus and a long burst of motor activity that occurred after a period of inactivity (mean duration of inactivity = 3.7 s, n = 5). Stimulation oJthe DNa only produced a typical, prolonged burst of activity on the stimulated side (mean duration of activity = 5.5 s, n = 5) and weak, or no, activity on the opposite side. The response evoked by stimulation ofthe DNa and the SRSN was virtually the same as that evoked by DNa stimulation only, and the response evoked by SRSN stimulation alone was absent. Pupal responses to stimulation ofthe IeJi DNa and the right SRSN are shown in recordings of IeJi (L) and right (R) motor nerves and in an intracellular recording ofa motoneuron innervating an intersegmenial muscle on the right (RMN). Stimulation ofthe pupal SRSN only produced &frequency motor activity coincident with the stimulus. Stimulation ofthe DNa only produced a typical, triphasic patterned response in which two high.frequency bursts of activity were separated by a period of inhibition. The response to simultaneous SRSN and DNa stimulation showed a weaker,hrst burst of activity, a period of hyperpolarization during which action potentials occurred, and a high,frequency second burst of activity (n = 4).

Arsenic in Norway lobster (Nephrophs norvegicus L.) from Kvarnerić Bay—Northeastern Adriatic

Arsenic is of concern as environmental pollutant because it is a ubiquitous element known to give rise to adverse human health effects ranging from minor disorders to cancer and acute death. Arsenic occurrence in the environment depends on such human activities as coal burning, use of pesticides, glass industry, electric application, veterinary medicine, etc. It has long been known that marine fishery products may contain high levels of arsenic. Fortunately, mainly in the organic, non-toxic form, with the average proportion of organic form in total arsenic between 71-79% and 50-97%. According to Lawrence et al., arsenic in marine fish was identified as arsenobetaine and, in shrimp only, arsenocholine. This paper examines the levels of total arsenic in the sample of the muscle and hepatopancreas of female and male Norway lobster, Nephrophs norvegicus L. from the area of Kvarneric Bay, Northeastern Adriatic (Croatia). The average values of arsenic in muscle from female and male lobster were 13.26 mg (kg and 14.20. mg/kg), respectively. In hepatopancreas the values were 17.12 mg/kg and 13.34 mg/kg for female and male, respectively. 11 refs., 1 fig., 1 tab.

Glucose and sulfate conjugations of phenol, β-naphthol and 3-hydroxybenzo[a]pyrene by the American lobster ( Homarus americanus)

Little is known of the potential for conjugation of phenolic compounds by lobsters. Studies were designed to determine the ability of American lobster tissues to conjugate the phenolic compounds phenol, β-naphthol and 3-hydroxybenzo[a]pyrene (3-OH BaP). Aryl sulfotransferase (ST) activity was present in the cytosolic fraction of the antennal gland (AG), but not hepatopancreas (HP), whereas UDP-glucosyltransferase (UDPGT) activity was found in musomal fractions of both AG and HP. We observed differences between male and female lobsters in their ability to conjugate phenols. For example, in males the apparent K m for PAPS of AG β-naphthol ST was 9.0 ± 4.2 μM (mean ± SD, n = 5) and V max was 77 ± 7 pmol/min/mg protein, whereas in females K m was 62 ± 3 μM ( n = 3) and V max was 254 ± 92 pmol/min/mg protein ( P < 0.05). The β-naphthol UDPGT exhibited different pH optima in HP (10.5) and AG (7.5) musomes, suggesting that more than one form of β-naphthol UDPGT exists in the American lobster. With few exceptions, K m values for the phenolic substrates were in the μM range for both UDPGT and ST, whereas K m values for the cosubstrates were lower for PAPS than for UDP-glucose.

Sexual maturity, reproductive season and fecundity of the spiny lobster Panulirus penicillatus from the Gulf of Eilat (Aqaba), Red Sea

Panulirus penicillatus Olivier (1791) (Decapoda: Palinuridae) is widely distributed in the Indian and Pacific Oceans and is the most common spiny lobster in the Red Sea. Female lobsters (n =234), were collected on four occasions in 1986 from the coral reef of Dahab, 110 km south of Eilat, Israel. Field data and the gonadal index indicated that the reproductive season was from February to October, during which the females spawned 2-4 times. In nature, females became sexually mature at a carapace length (CL) of 50 mm. This result was confirmed by morphometric analysis of the regression between pleopodal exopodite length and carapace length. The number of eggs per spawn (E) was related to CL by the equation E=2.715 ×(CL)2.581. The incubation period of eggs was 35.5�1.0 days (�s.d.) at temperatures of 24-27�C in the aquarium. The results are compared with data on P. penicillatus from other parts of its geographic range, and the effect of geographic isolation on reproduction is discussed.

Localization of messenger RNAs encoding crustacean hyperglycemic hormone and gonad inhibiting hormone in the X-organ sinus gland complex of the lobster Homarus americanus

The localization of messenger RNAs encoding the crustacean hyperglycemic hormone, involved in regulation of carbohydrate metabolism and the gonad inhibiting hormone, which inhibits vitellogenesis, was studied in the eyestalk of the lobster Homarus americanus using complementary RNA probes for in situ hybridization. For the detection of gonad inhibiting hormone messenger RNA, we cloned and sequenced a partial complementary DNA encoding lobster gonad inhibiting hormone and for crustacean hyperglycemic hormone messenger RNA detection an available complementary DNA was used. This approach reveals that there is a frequent but inconsistent cellular co-localization of the two neurohormones. Furthermore, our data show that male lobsters contain an equal number of neuroendocrine gonad inhibiting hormone cells as female lobsters. An additional study, involving the use of in situ hybridization in combination with immunocytochemistry, shows that the synthetic activity of the crustacean hyperglycemic hormone- and gonad inhibiting hormone-producing cells can be followed at the messenger RNA as well as the protein level. This reveals that when strong immunostaining is present, the messenger RNA staining is usually weak or absent and vice versa. In conclusion, the presence of cells, containing only gonad inhibiting hormone messenger RNA or only crustacean hyperglycemic hormone messenger RNA, indicates that lobster crustacean hyperglycemic hormone and gonad inhibiting hormone originate from two different precursors. Co-localization of the two neurohormone messenger RNAs confirms the co-localization at the peptidergic level found by immunocytochemistry and thus these findings were not due to cross-reactions between the two antisera. The presence of gonad inhibiting hormone messenger RNA in the male lobster suggests an important role for this hormone in the reproduction of male Crustacea, perhaps indicating a role similar to the gonadotrophins in vertebrates. Finally, the investigations on the synthetic activity of the neurohormone-producing cells suggest an intracellular feedback mechanism which may inhibit the transcription and/or stability of crustacean hyperglycemic hormone and gonad inhibiting hormone messenger RNA when high levels of these neurohormones are present.

Severe mortality in a breeding population of ornate rock lobster Panulirus ornatus (Fabricius) at Yule Island, Papua New Guinea

Ornate rock lobsters Panulirus ornatus, which emigrate from Torres Strait (north-east Australia) to breed each year, support a seasonal artisanal lobster fishery at Yule Island (eastern Gulf of Papua). The catches are highest in mid-January through mid-February, but then decline rapidly, so by late-March virtually no lobsters remain. It has been hypothesised that most of the decline in catch is due to natural mortality caused by the stress of migrating and breeding. However, there are alternative explanations: fishing mortality may be extremely high, or lobsters may move to deeper habitat, not accessible to divers. These hypotheses were examined through a combination of (i) deploying tangle nets in deep water near the main fishing area, (ii) daily monitoring of the catch and effort of the artisanal fishery, (iii) a tag-recapture study and (iv) daily assessment of physiological condition, using the water content of the hepatopancreas as an index. The tangle net catches showed that female lobsters temporarily moved into deeper water just off the reef to hatch their eggs at the January and February full moons, but then moved back onto the reef. Their emigration did not coincide with the decline in artisanal catch. The annual instantaneous total mortality rates ( Z ann), estimated from catch per unit effort (CPUE) curves, were extremely high: Z ann = 11.6 for females and Z ann = 12.0 for males. About one-third of the tags were returned. Analysis of the tag-return rate and total catch suggested the initial population was 19000–30000 lobsters. The total mortality rate, estimated from the tag-recapture data ( Z ann = 10.2), was consistent with the very high estimate from CPUE data. The annual instantaneous fishing mortality rate indicated that the fishery was responsible for about one-third of the mortality ( Z ann = 4.4), which corresponded well the proportion of tags returned. The remainder of the decline in catch was attributed to natural mortality. The hepatopancreas water content indicated that most lobsters were in poor condition. These results support the original hypothesis that there is extremely high mortality in this breeding population, a phenomenon not reported in any other species of lobster.