Spatial Model for the Population Dynamics and Exploitation of the Western Australian Rock Lobster, Panulirus cygnus

1993 ◽  
Vol 50 (8) ◽  
pp. 1650-1662 ◽  
Author(s):  
Carl J. Walters ◽  
Norm Hall ◽  
Rhys Brown ◽  
Chris Chubb
Keyword(s):  
Carapace Length ◽  
Temporal Dynamics ◽  
Population Analysis ◽  
Fishing Effort ◽  
Management Policy ◽  
Rock Lobster ◽  
Breeding Grounds ◽  
Panulirus Cygnus ◽  
Biological Assessments ◽  
Western Australian

There is concern about whether long-standing regulatory measures (size and effort limits) are adequate to protect spawning stocks of the Western Australian rock lobster, Panulirus cygnus, and assure the highest average yields. Virtual population analysis and tagging studies indicate that exploitation rates are extremely high (possibly exceeding 70%/yr) on younger, mainly immature lobsters. To predict the efficacy of alternative regulatory schemes, it has been necessary to explicitly model the spatial and temporal dynamics of lobster abundance and fishing effort. Puerulus settlement (at age 9–11 mo) is mainly into shallow-water (< 40 m) areas, and at 3–5 yr of age in most areas, there is a migration into deeper water where the animals mature after a further 1–2 yr. The size at migration (70–90 mm carapace length) ensures that at least some animals will have a chance to reach the breeding grounds offshore, where fishing effort has historically been lower than inshore, before they reach the minimum legal size (76 mm carapace length). By explicitly modelling the effort distribution as well as lobster movement and stock distribution, we hope to anticipate some consequences of changes in management policy that could not be predicted from biological assessments alone.

scholarly journals The orientation and migratory dynamics of the western rock lobster, Panulirus cygnus, in Western Australia

2014 ◽  
Vol 71 (5) ◽  
pp. 1052-1063 ◽  
Author(s):  
Simon de Lestang
Keyword(s):  
Large Scale ◽  
Economic Benefits ◽  
Rock Lobster ◽  
Commercial Catch ◽  
Breeding Grounds ◽  
Mean Size ◽  
Catch Rates ◽  
Panulirus Cygnus ◽  
The Impact ◽  
Oceanic Currents

Abstract Large-scale migrations are known to occur in numerous species, and in the case of the Western Rock Lobster, Panulirus cygnus, result in juveniles moving from nursery areas into deeper offshore breeding grounds. In 2008 the Western Rock Lobster fishery reduced harvest rates to increase legal and spawning biomass throughout the fishery, which also allowed greater numbers of lobsters to migrate. Increased lobster migration could potentially reduce biomass in some areas, thus adversely impacting commercial catch rates. Over 20 000 tag–recaptured lobsters were analysed to determine the dynamics underlying migration in this species and to assess the impact reduced harvest rates may have had on catches. This study showed that P. cygnus migration was associated with body size and water depth, and that magnetism and oceanic currents appear to be the most likely guideposts used for orientation. Size at migration varied in a constant fashion along the coast, being larger towards the southern end of the fishery and smallest at the offshore Abrolhos Islands. During the migration period, up to 50% of lobsters at their mean size of migration moved from coastal areas out towards deeper waters (>40 m), whereas <15% of those in deeper water at the same size moved significant distances northward. This behaviour appears to be contranatant, counteracting the downstream redistribution of larvae after their 9–11 month larval life. Reduced harvest rates and catches being focussed onto higher valued sedentary lobsters have allowed more lobsters to migrate. However, the numbers moving between management areas are relatively small, with the biological and economic benefits of fishing at a reduced exploitation rate outweighing losses to catches.

Fish predators of the western rock lobster (Panulirus cygnus George) in a nearshore nursery habitat

1988 ◽  
Vol 39 (3) ◽  
pp. 307 ◽  
Author(s):  
RK Howard
Keyword(s):  
Fish Species ◽  
Fish Community ◽  
Carapace Length ◽  
Nursery Habitat ◽  
Rock Lobster ◽  
Lack Of Information ◽  
Gill Net ◽  
Fish Predators ◽  
Panulirus Cygnus ◽  
A Current

Nearshore limestone reefs of Western Australia represent an important nursery habitat for juveniles of the western rock lobster (Panulirus cygnus). As part of a trophic study of the fish community associated with these reefs, fishes were examined for evidence of predation on western rock lobsters. Six fish species were found to have ingested P. cygnus. Of these, Psammaperca waigiensis (sand bass), Pelsartia humeralis (sea trumpeter), Pseudolabris parilis (brown-spotted wrasse) and Plectorhyncus flavornaculatus (gold-spotted sweetlips) were among the ten most abundant fish in gill-net collections from the study site. P. cygnus formed a significant portion of the diet of P. waigiensis, but was < 5% of the dietary volume of other species. Predation occurred at all times of the day and was concentrated on small, newly-settled P. cygnus (8-15 mm carapace length). The vulnerability of lobsters to predation appears to be strongly related to size, and the cryptic habits that are unique to newly-settled stages can be explained in terms of the risks of predation. Assessment of the proportion of mortality of P. cygnus due to predation is hampered by a current lack of information on the natural densities of both fishes and small rock lobsters. However, conservative estimates indicate that an annual removal by fish of thousands of lobsters per hectare is likely, suggesting that predation is a major factor affecting the survival of P. cygnus on nursery reefs.

Preliminary assessments of stocks of the Western Australian crayfish, Panulirus cygnus George

1966 ◽  
Vol 17 (1) ◽  
pp. 93 ◽  
Author(s):  
BK Bowen ◽  
RG Chittleborough
Keyword(s):  
Western Australia ◽  
Fishing Effort ◽  
Total Catch ◽  
Catch Per Unit Effort ◽  
Stock Size ◽  
Unit Effort ◽  
Exploitation Rate ◽  
Panulirus Cygnus ◽  
Western Australian ◽  
Closed Period

Total catch of Panulirus cygnus in Western Australia rose from 0.6 million lb in 1944-45 to 21.4 million Ib in 1962-63. Fishing effort increased rapidly with the result that the catch per unit effort declined progressively. Effort has been limited by regulation since 1963. From records of catch and effort from specified areas at intervals of one month throughout each season, estimates were made of mortality coefficients (Z1, F, and M1) and catchability coefficient (q). Stock size, recruitment, and exploitation rates were then estimated. As the seasonal catch per unit effort followed the same trend throughout all fishing areas, the detailed results from the selected areas have been applied to the whole fishery. The fishable stock, originally of approximately 140 million lb, had declined to some 35 million lb by 1963. Exploitation rate rose as effort was increased, and then levelled off (generally at above 60%), further increase in fishing effort resulting in a fall in the catchability coefficient rather than a change in the exploitation rate. Because of the high exploitation rate in recent years, the fishable stock available on the grounds at the opening of a season is largely dependent on recruitment (by growth) of juveniles during the preceding closed period. This recruitment has been diminishing from year to year, apparently because of mortality of undersize (pre-recruit) crayfish handled in fishing pots. Provision of escape gaps in all fishing pots is recommended. A sustainable level of catch might be 16,000,000±2,000,0001b per year if recruitment can be stabilized. Some further restriction of fishing effort might be necessary.

Increased density, biomass and egg production in an unfished population of Western Rock Lobster (Panulirus cygnus) at Rottnest Island, Western Australia

2007 ◽  
Vol 58 (3) ◽  
pp. 286 ◽  
Author(s):  
R. C. Babcock ◽  
J. C. Phillips ◽  
M. Lourey ◽  
G. Clapin
Keyword(s):  
Western Australia ◽  
Carrying Capacity ◽  
Egg Production ◽  
Carapace Length ◽  
Spiny Lobster ◽  
Shallow Waters ◽  
Recreational Fishing ◽  
Total Biomass ◽  
Rock Lobster ◽  
Panulirus Cygnus

Surveys of spiny lobster (Panulirus cygnus) populations in shallow waters surrounding Rottnest Island in Western Australia revealed much higher levels of density, biomass and egg production in no-take than in fished areas. Density of lobsters was ~34 times higher in the sanctuary, and density of lobsters above minimum legal size around 50 times higher than in other areas around the island where recreational fishing is allowed. Mean carapace length (CL), total biomass and egg production of lobsters in the sanctuary zone were significantly higher than in adjacent fished areas. Large individuals (≥100 mm CL), especially large males, were found almost exclusively within the sanctuary. The abundance of mature animals in these shallow waters indicates that not all P. cygnus migrate to deep water and that shallow water habitats may currently be well below carrying capacity in terms of biomass and egg production. If implemented in a systematic way, unfished areas such as the Kingston Reefs could also provide a useful fisheries-independent tool for assessing trophic interactions and the structure and density of unfished populations, and for estimating parameters such as growth of larger individuals that may be rare or absent in more widely fished populations.

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

1997 ◽  
Vol 48 (8) ◽  
pp. 949 ◽  
Author(s):  
Norman G. Hall
Keyword(s):  
Management Strategies ◽  
Fishing Effort ◽  
Rock Lobster ◽  
Fishing Season ◽  
Limited Entry ◽  
Harvest Strategy ◽  
Panulirus Cygnus ◽  
Two Stages ◽  
The Impact ◽  
Delay Difference

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.

Relative influence of environmental factors and processing techniques on Panulirus cygnus morbidity and mortality during simulated live shipments

1997 ◽  
Vol 48 (8) ◽  
pp. 839 ◽  
Author(s):  
Patrick T. Spanoghe ◽  
P. K. Bourne
Keyword(s):  
Mortality Rate ◽  
Mortality Rates ◽  
Morbidity And Mortality ◽  
Rock Lobster ◽  
Significant Difference ◽  
Panulirus Cygnus ◽  
Chilling Period ◽  
Processing Techniques ◽  
Western Australian ◽  
Positive Significant Correlation

In this study, conducted in collaboration with the Western Australian rock lobster industry during the 1992–93 fishing season, daily records were made on morbidity and mortality of western rock lobsters, Panulirus cygnus, held in commercial shipping (export) cartons. The aims were to measure the rates of morbidity + mortality and to identify patterns of correlation of morbidity + mortality rates for a range of environmental variables recorded by the processors. In three processing units, the rate of morbidity + mortality in simulated live shipments averaged 5á2% (±0·6), with a highly significant difference (P<0·001) between processing units. Three factors, holding time in export cartons, ambient temperature within the export cartons and chilling period before packing lobsters, had the greatest influence on the rate of morbidity + mortality. Morbidity + mortality rate of animals held for 30–36 h (10·4 ± 2·3%) was twice that of animals held for 20–24 h (5·2 ± 0·6%). A positive significant correlation (r = 0·25, P = 0·001) was identified between morbidity + mortality rate and the internal carton temperature. Aprolongation of the chilling period was reflected by improved survival, possibly resulting from an anaesthesic effect of the chilling treatment.

Prediction of Commercial Catches of the Western Rock Lobster Panulirus cygnus

1986 ◽  
Vol 43 (11) ◽  
pp. 2126-2130 ◽  
Author(s):  
B. F. Phillips
Keyword(s):  
Single Species ◽  
Total Catch ◽  
Rock Lobster ◽  
Commercial Catch ◽  
Life History Stages ◽  
Last Stage ◽  
Panulirus Cygnus ◽  
Western Australian ◽  
Term Data

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.

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