Western Rock Lobster Panulirus Cygnus Research Articles

Have Different Inducements Used with the Western Rock Lobster Mail Survey of Recreational Licensees Had an Effect on Total Catch Estimates?

AbstractMail surveys have been used over the last 17 years to estimate the recreational catch of western rock lobster Panulirus cygnus in an Australian fishery. Because nonresponse bias has been recognized as having a likely effect on these survey results, different inducements have been used over the years to increase returns. If these inducements have succeeded in reducing the effects of nonresponse bias, a catch model built from the resulting catch estimates would need to include inducement as a factor. At the end of the 2002–2003 season, 5,000 recreational license holders were sent identical surveys, along with one of the six different inducements that had been tried in previous seasons. The results showed that none of the inducements was likely to have affected total catch estimates in previous seasons. The age of the licensee and the license type held were identified as possible strata for future mail surveys to help reduce nonresponse bias.

Predicting survival of western rock lobsters Panulirus cygnus using discriminant analysis of haemolymph parameters taken immediately following simulated handling treatments

Instances of morbidity amongst rock lobsters (Panulirus cygnus) arriving at factories in Western Australia (WA) have been attributed to stress during post‐harvest handling. This study used discriminant analysis to determine whether physiological correlates of stress following a period of simulated post‐harvest handling had any validity as predictors of future rejection or morbidity of western rock lobsters. Groups of 230 western rock lobsters were stored for 6 h in five environments (submerged/flowing sea water, submerged/recirculating sea water, humid air, flowing seawater spray, and recirculated seawater spray). The experiment was conducted in late spring (ambient sea water 22°C), and repeated again in early autumn (ambient sea water 26°C). After 6 h treatment, each lobster was graded for acceptability for live export, numbered, and its haemolymph was sampled. The samples were analysed for a number of physiological and health status parameters. The lobsters were then stored for a week in tanks in the live lobster factory to record mortality. The mortality of lobsters in the factory was associated with earlier deviations in haemolymph parameters as they emerged from the storage treatments. Discriminant analysis (DA) of the haemolymph assays enabled the fate of 80–90% of the lobsters to be correctly categorised within each experiment. However, functions derived from one experiment were less accurate at predicting mortality when applied to the other experiments. One of the reasons for this was the higher mortality and the more severe patho‐physiological changes observed in lobsters stored in humid air or sprays at the higher temperature. The analysis identified lactate accumulation during emersion and associated physiological and haemocyte‐related effects as a major correlate of mortality. Reducing these deviations, for example by submerged transport, is expected to ensure high levels of survival. None of the indicators tested predicted mortality with total accuracy. The simplest and most accurate means of comparing emersed treatments was to count the mortality afterwards.

Effect of reproductive state and sex on movement and food consumption of western rock lobster (Panulirus cygnus) in a tank environment

The catchability of western rock lobsters (Panulirus cygnus) during the spawning season (October and November) may be affected by their reproductive state. In this study, movement and food consumption of males and females of different reproductive states held in laboratory tanks were measured as proxies for catchability. Density of lobsters was found to influence both movement and food consumption. Solitary animals and, to a lesser extent, two lobsters per tank, were more sedentary and consumed significantly less food than animals at a density of three or four specimens per tank. Tests using three animals per tank confirmed that mature, unmated, and ovigerous females carrying early stage eggs moved more frequently away from their shelters than males or females carrying late stage eggs (P < 0.0001, d.f. = 3). Further, unmated females and females with early stage eggs recorded significantly higher food consumption (P < 0.0061, d.f. = 3) compared with males or females carrying late stage eggs. The greater time spent away from shelter and also food consumption make unmated females and females with early stage eggs likely to be more catchable than males or females with late stage eggs. As catchability is commonly used to obtain population estimates from survey data, these results have implications for surveys which use catch rates of breeding animals as indicators of egg production.

Temporal variation of recruits as a basis of ephemeral genetic heterogeneity in the western rock lobster Panulirus cygnus

Allozymes were examined in quantitative lunar monthly collections of larval recruits of the western rock lobster Panulirus cygnus George over three recruitment seasons at two sites nearly 350 km apart in Western Australia. At Alkimos, the southern site, recruitment occurs in a relatively narrow peak early in the spring, whereas at the northern Houtman Abrolhos Islands, recruitment extends into the summer months. In the 1995/1996 recruitment season, the frequency of the GPI*100 allele increased from early to late in the season, but the frequencies were indistinguishable at the two sites in each monthly collection. The combination of this temporal variation in allelic frequencies with the contrasting patterns of recruitment at the Abrolhos Islands and Alkimos resulted in genetically different cohorts at the two sites. This pattern was ephemeral, as it was not repeated in the subsequent two years. Thus, ephemeral genetic patchiness in P. cygnus can be generated by the locally-specific genetic mix of recruits obtained from a common larval pool. This mechanism is the probable explanation of previously observed temporal and possible spatial genetic variation in adult P. cygnus, and highlights the importance of studying recruitment in order to understand the genetic structure of marine species.

Use of lipofuscin for resolving cohorts of western rock lobster (Panulirus cygnus)

We evaluated lipofuscin age pigment as an approach to age determination of western rock lobster (Panulirus cygnus). Lipofuscin was measured using fluorescence image analysis of olfactory lobe sections from 184 juvenile lobsters from coastal nursery reefs at Seven Mile Beach, Western Australia. Modal analysis of a lipofuscin concentration-frequency histogram for this sample suggested the presence of additional age-classes, not apparent in conventional size-frequency distributions but expected to be present from earlier tag-recapture studies. Modal progression suggested a remarkably constant average lipofuscin accumulation rate of 0.31% by volume per year in the wild lobsters, which was supported by blind-trial measurements of lipofuscin in known-age laboratory-reared specimens. Lipofuscin-based age estimates, indicating that most juvenile lobsters are 3-5 years old immediately prior to recruitment to the fishery at 76 mm carapace length, agree with the long-established relationship between puerulus settlement and lobster catch 3-4 years later. Results indicate that the lipofuscin ageing technique will permit independent assessment of current population parameter estimates and be useful for determining sexual and regional differences in these for the western rock lobster.

Delay-difference model to estimate the catch of different categories of the western rock lobster (Panulirus cygnus) for the two stages of the annual fishing season

The annual exploitation rate of the limited-entry rock lobster fishery of Western Australia is controlled by constraining the total allowable effort. An important aspect of the harvest strategy introduced in 1993 was the use of annual levels of allowed fishing effort that could be varied in accordance with predicted levels of recruitment to the fishery in order to increase the abundance of spawning females and to reduce the variability in the level of annual catch. A model was needed that could examine the impact of alternative management strategies on the catches both within and between fishing seasons. The model that has been developed uses a delay-difference structure in which the fishing season is divided into two periods. Growth between the periods, and over the closed fishing season, is determined from tagging data. Recruitment is estimated from the observed levels of puerulus settlement. The model has been fitted to the observed effort within the southern sector of the fishery. This model allows the evaluation of alternative levels of fishing effort within the management zone, providing managers and industry with a tool to explore alternative harvest strategies.

Nucleic acid levels, cellular activity and growth during the puerulus stage of the Western Rock Lobster ( Panulirus cygnus (George); Decapoda: Palinuridae)

The potential impact of non-feeding in pueruli of the Western Rock Lobster Panulirus cygnus (George; Decapoda, Palinuridae) on cellular activity and growth was investigated through fluorometric quantification of nucleic acid levels. Late phyllosomata, post-settlement pueruli and juveniles were collected along the Western Australian coast between August and December 1992, by means of plankton nets and puerulus collectors. Early phyllosomata were obtained through laboratory rearing. Nucleic acid levels, as well as dry weights (DW), increased gradually during early phyllosomal stages; the RNA DNA ratio remained fairly constant between 0.3 and 0.5 units. During puerulus development, DNA levels (a measure for cellular growth) demonstrated a slight but insignificant increase; DW remained fairly constant. However, after ecdysis to the first juvenile stage, DNA levels were significantly higher (~ 0.93 mg DNA · individual −1), compared with early post-settlement pueruli (~0.35 mg DNA · ind. −1), and increased further during juvenile development (~ 1.08 mg DNA · ind. −1 in the second moult juvenile). DW of the second juvenile stage (142.5 mg) was approximately double that of the puerulus. RNA levels demonstrated a slight but insignificant decrease during puerulus development, and an increasing trend during juvenile development. RNA DNA ratios (an indicator for cellular activity) are high in the final phyllosoma (1.17 ± 0.13 units), and decrease significantly during the puerulus stage (to 0.49 ± 0.05 units in the early post-settlement puerulus) and first moult juveniles (0.26 ± 0.13 units), and only demonstrates a slight but insignificant recovery after the second moult juveniles (0.45 ±0.07 units). Water temperature appears to have an important impact on RNA levels, which approach zero immediately after ecdysis to the first juvenile stage when post-settlement pueruli were maintained at 23 °C; those maintained at 18 °C did not demonstrate a significant decrease. These observations are consistent with absence of feeding during the puerulus stage and further suggest that water temperature may have a substantial effect on puerulus development.

The Western Rock lobster Panulirus cygnus (George, 1962) (Decapoda: Palinuridae): the effect of temperature and developmental stage on energy requirements of pueruli

Pueruli of the Western Rock Lobster Panulirus cygnus (George, 1962) are thought to be nonfeeding. Consequently, the metabolic rate is expected to be low during this stage in order to conserve energy reserves. Furthermore, since water temperature potentially has a substantial impact on energetic needs, the puerulus possibly exhibits mechanisms to reduce the effect of temperature on energy consumption. To test these propositions the metabolic rate was measured in post-settlement pueruli and in juveniles at two water temperatures. A respirometer of variable volume (10–50 ml) was designed for this purpose, incorporating a dark-type oxygen sensor. Results were compared with data available from the literature. Oxygen consumption in pre-molt pueruli and in intermolt juveniles (1.48 to 5.65 μmol O 2· individual −1·h −1 on average) was substantially higher than in post-settlement pueruli (1.06–1.41μmol O 2·ind. −1h −1). These significant changes could only partly be explained through changes in biomass. Furthermore, no significant effect of an increased water temperature (from 18 to 23 ° C) could be detected on the metabolic rate in post-settlement pueruli, and the effect is moderate in pre-molt pueruli ( Q 10 = 1.95). The water temperature has, however, a substantially greater impact on first and second molt juveniles ( Q 10 = 2.46 to 4.80). The energetic demand was calculated from oxygen consumption and indicate that energetic needs of post-settlement pueruli is low compared with both pre-molt pueruli and juveniles. A low energetic demand and a reduced effect of temperature on energy consumption is of considerable benefit to a non-feeding larva, and may provide the puerulus with a means of extending the duration of the non-feeding stage and increasing the chance for survival beyond metamorphosis to the first feeding stage. Results indicate that the energetic demand during metamorphosis may be considerable. It is postulated that energetic requirements of the planktonic (actively swimming) puerulus larvae are considerably higher and are likely to be more temperature dependent.

Biochemical evidence for absence of feeding in puerulus larvae of the Western rock lobster Panulirus cygnus (Decapoda: Palinuridae)

Changes in energy-reserves during the transition from phyllosoma through peurulus to juvenile in the Western rock lobster Panulirus cygnus (George, 1962) were studied by means of carbon: nitrogen analysis. Specimens were collected by means of plankton nets and puerulus collectors along the Western Australian coastline between July 1992 and January 1993. Reserves are accumulated during the last phyllosoma stage and are consumed during the puerulus stage. These observations support the hypothesis that the puerulus is a non-feeding stage. Based on basal metabolic rate and observed changes in reserves, the natant puerulus stage is calculated to last a maximum of ∼21.6d. When the estimated cost of swimming is taken into account, the duration is reduced to perhaps a week. The latter time-span corre-sponds with field observations that both abundance of planktonic pueruli in oceanic waters and inshore settlement of pueruli peak in the week around new moon. At 18°C, the puerulus metamorphoses to the first juvenile stage within 12.8 d after settlement; at 23°C this is reduced to ∼8.3 d. After settlement, puerulus larvae have an energetic advantage at elevated temperatures; the increased cost of metabolism is compensated by an accelerated development. The natant puerulus, however, appears to be slightly disadvantaged energetically at elevated temperatures; both C:N ratio and ash-free dry weight of pueruli just after settlement show a decreasing trend as the water temperature increases. The effect of water temperature and the distance from the edge of the continental shelf to the shore on consumption of energy reserves might provide a mechanism to partially explain temporal and spatial patterns in puerulus settlement.

Arsenic lipids in the digestive gland of the western rock lobster Panulirus cygnus: an investigation by HPLC ICP-MS

The digestive gland of the western rock lobster, Panulirus cygnus, was shown to contain phosphatidylarsenocholine and a phosphatidyldimethylarsinylriboside by HPLC ICP-MS examination of lipid materials rendered water-soluble by hydrolysis. Water-soluble arsenic material in the digestive gland was chiefly arsenobetaine but the deacylated analogue of the phosphatidyldimethylarsinylriboside and an unidentified compounds were also present.

Predator-prey interactions in seagrass beds. III. Impacts of the western rock lobster Panulirus cygnus George on epifaunal gastropod populations

Caging experiments and calculations of daily consumption rates indicate that the western rock lobster Panulirus cygnus has a significant negative impact on the population dynamics of the seasonally abundant trochid gastropod Cantharidus lepidus. At the Cliff Head study site, P. cygnus caused most of the autumn and winter decline of the C. lepidus population, and was also presumably responsible for much of the mortality of the larger ( > 2.0 mm) size classes of C. lepidus during the rest of the year. At other seagrass sites where juvenile rock lobsters occur in high densities, they probably also influence the population dynamics of large epifaunal gastropods. As the predatory impact of juvenile rock lobsters causes rapid declines in gastropod populations, and rock lobsters grow most rapidly when an excess of animal prey is available, P. cygnus presumably compete intraspecifically for food resources. The growth rates of rock lobsters are probably also influenced by a complex hierarchy of interspecific interactions amongst the macrofauna and megafauna. Rock lobsters were inferred to have an amensal or competitive relationship with the crab Portunus pelagicus, and to be adversely affected by competition amongst the epifauna.

Estimating the Density and Mortality of Juvenile Western Rock Lobsters (Panulirus cygnus) in Nursery Reefs

Studies of juvenile rock lobsters (Panulirus cygnus) in the nursery reefs of Western Australia indicated that density-dependent processes on the reefs were the major determinant of year-class strengths of recruitment to the fishery. Reassessment of early data, plus additional information, indicates that these estimates may have been inaccurate. Alternative methods of estimating juvenile densities were examined; application of length–frequency analysis to calculate the age-classes; visual estimates, and single-night trapping. Length–frequency analysis indicated that either immigration onto the test reefs had occurred, or the data were inaccurate. Visual estimates and single-night trapping were more rapid and used less manpower and resources than mark–recapture methods, but the estimates were of unknown accuracy. No truly satisfactory method of making reliable estimates of either the density of natural mortality rate of juveniles in the nursery reefs is yet available. Nevertheless, the data on the levels of larval settlement and subsequent catches, suggest that density dependent processes probably have a significant effect on the levels of recruitment to the fishery, although the upper level to this recruitment has not been reached over the past 20 yrs.

Distribution of newly settled western rock lobsters Panulirus Cygnus

Distribution of newly settled western rock lobsters Panulirus Cygnus

ANTENNAL RECEPTORS IN PUERULUS AND POSTPUERULUS STAGES OF THE ROCK LOBSTER PANULIRUS CYGNUS (DECAPODA: PALINURIDAE) AND THEIR POTENTIAL ROLE IN PUERULUS NAVIGATION

ABSTRACT This study describes the sensory structures on the antennae and antennules of the puerulus and postpuerulus stage juveniles of the western rock lobster Panulirus cygnus. Both stages have short and long spines, which probably function in protection and in contact-detection. Both also possess setae structurally similar to those shown to be near-field vibration receptors in other crustaceans. Both have aesthetasc setae on the antennules and petaloid setae on the antennae, with both types of setae appearing to be chemosensory. The puerulus stage has an almost continuous linear series of pinnate setae that overlie each other and also the segmental boundaries along the antenna in such a way that the series is well positioned to act as a detector for vibration of the whole antenna. This arrangement is unique to the puerulus stage, which is also noted for its 40-60-km directional swim from the offshore waters to the coast. We suggest that the complex receptor system formed by the antennae and the pinnate setal system plays a role in navigation by allowing the animal to orient to vibrational clues associated with the coast.

Prediction of Commercial Catches of the Western Rock Lobster Panulirus cygnus

Predictions of the size of the Western Australian commercial catch of the western rock lobster Panulirus cygnus have been successfully made 4 yr ahead. The predictive system, which has operated for 9 yr has been recognized by industry and government as an important tool in the management of Australia's most valuable single-species fishery. The accurate prediction depends on demonstrated relationships between the number of rock lobsters at the puerulus stage of their development (the last stage of its pelagic existence) and the level of recruitment to the fishery, and the total catch of the fishery, 4 yr after settlement. Since 1980, predictions of the catches have been based on settlement data from a single site, Seven Mile Beach, which is near the centre of the distribution of the species. The catches of the fishery from 1961–62 to 1983–84 ranged from 6.8 × 106 kg in 1973–74 to 12.4 × 106 kg in 1982–83. Based on a regression of total catches from 1969 to 1979 on puerulus settlement, and allowing for a trend of increasing catch with time, the total catch is predicted to fall to about 7.72 × 106 kg in 1986–87 because of the low level of puerulus settlement in 1982–83. However, increased settlement in 1983–84 and the highest settlement ever recorded in 1984–85 indicate that catches should increase for the 1987–88 fishing season. Similar relationships between life history stages can be discerned for other crustacean species, provided accurate, long-term data are available.

Conservation of Recruitment of the Western Rock Lobster (Panulirus cygnus) by Improving Survival and Growth of Undersize Rock Lobsters Captured and Returned by Fishermen to the Sea

The western rock lobster (Panulirus cygnus) fishery is one of the largest rock lobster fisheries in the world with an average catch (1974–75 to 1983–84) of 10 million kg. On average, 18 million undersize rock lobsters (sublegal size) are caught, handled, and returned to the sea each season despite the release of many through mandatory escape gaps in traps. Depending on the handling procedure, undersize rock lobsters experience various degrees of exposure, displacement, and damage which adversely affect their survival and growth. Laboratory, field, and tagging experiments showed that handling produced a mortality of 14.6% that costs the industry in excess of $A13 million per season (1984–85 values). An education programme has resulted in improved handling of undersize rock lobsters, and trials have shown that by increasing the size of the escape gap, the number of undersize rock lobsters handled can be reduced by 40–60%. This would result in a significant enhancement of recruitment to the fishery.

Migrations of pre-adult western rock lobsters, Panulirus cygnus, in Western Australia

In September 1978, 5 034 juvenile western rock (spiny) lobsters (Panulirus cygnus George) were tagged on a shallow coastal reef near Cliff Head in Western Australia. Of these, 26% were recaptured and removed from the population during the subsequent commercial fishery between 15 November 1978 and 30 June 1979. A resurvey of the tagging site in September 1979 found that size structure of the population was similar to the tagged population in September 1978 but that the 1979 population was composed of almost completely different individuals and only 2% of the rock lobsters tagged in September 1978 were recaught at this time. A wide range of movement was indicated by the recapture positions of 354 rock lobsters caught off the tagging site. Most travelled almost directly offshore but some also travelled offshore in a northwesterly direction. Both trends were shown in the data from the recaptures of 18 rock lobster released farther offshore from Cliff Head in September 1981, and of 19 released at a close inshore site in earlier years. Maximum offshore rates of movement of up to 622 m d-1 were recorded for distances up to 37 nautical miles (ca. 68 km). Growth rates for the tagged individuals which moved off, and those that were caught on, the tagging site were similar and close to growth rate under optimal conditions for this species. Under the present high levels of exploitation few, if any, of the rock lobsters remain to become permanent residents in the coastal reefs. It is believed that the north-westerly movements of some of the pre-adult rock lobsters, on their way to the breeding grounds on the outer edge of the continental shelf, are due to the upstream movement of these rock lobsters in a current from the north. The north-westerly movements allow the rock lobster population increased utilization of the food supplies of the coastal area.

Diurnal migration and vertical distribution of phyllosoma larvae of the western rock lobster Panulirus cygnus

Studies off the west coast of Australia showed that the phyllosoma larvae of Panulirus cygnus George undergo a diurnal vertical migration, with light as an important factor influencing the depth distribution of all 9 phyllosoma stages. The early stages (I to III) occurred at the surface at night regardless of moonlight intensity, whereas late stages (VI to IX) concentrated at the surface only on nights with less than 5% of full moonlight. Midday peak densities of early-stage larvae occurred in the 30 to 60 m depth range while those of mid (IV to VI) and late stages were in the 50 to 120 m range. Depths of peak densities of larvae increased with distance offshore. The limits of vertical distribution of the phyllosoma remained within ranges of illuminance which were estimated to be in the order of 50 to 250 μE m-2 sec-1 for early stages, 20 to 200 μE m-2 sec-1 for mid stages and 5 to 50 μE m-2 sec-1 for late stages. Minimal rates of net vertical movement were estimated for the larvae. Early stages exhibited mean net rates of ascent and descent of 13.7 and 13.0 m h-1, respectively, while the rates for mid stages were 16.0 and 16.6 m h-1 and for late stages 19.4 and 20.1 m h-1. Diurnal migrations and vertical distribution are shown to have a vital role in the relationships between circulation in the south-eastern Indian Ocean and the transport and dispersal of the phyllosoma larvae. The diurnal migrations of early stages place them at the surface at night, when offshore vectors of wind-driven ocean-surface transport dominate, and below the depth of wind-induced transport during the day, when offshore vectors are small or negative, thus accounting for their offshore displacement. Mid and late stages, because of their deeper daytime distribution and absence from the surface on moonlight nights, are predominantly subject to circulation features underlying the immediate surface layer. This is hypothesized to account for the return of the phyllosoma to areas near the continental shelf edge by subjecting them to a coastward mass transport of water which underlies the immediate surface layer.