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.

scholarly journals Management options for the Blackwater herring, a local spring-spawning stock in the Thames Estuary

2004 ◽  
Vol 61 (3) ◽  
pp. 297-307 ◽  
Author(s):  
Beatriz A. Roel ◽  
Carl M. O'Brien ◽  
Marinelle Basson
Keyword(s):  
Fishing Effort ◽  
Current Approach ◽  
Slight Reduction ◽  
Trawl Survey ◽  
Management Options ◽  
Fishing Season ◽  
Thames Estuary ◽  
Spawning Stock ◽  
Management Advice ◽  
The Impact

Abstract Herring caught in the Thames Estuary sustain a small local commercial fishery (peak catch of 606 t during the 1972–1973 fishing season). Loss of local consumers' interest in the herring product has resulted in a gradual decline in catches and fishing effort for the stock. The stock is assessed using an age-structured model that relies on the information provided by a scientific trawl survey, and management advice is provided before the fishing season starts in October. Given its current low economic value, managers have requested evaluation of options for multi-annual Total Allowable Catches (TACs) in an attempt to reduce the frequency (and costs) of assessment and associated management advice. A tentative relationship between sea surface temperature and recruitment is used to predict the impact of increasing sea temperatures on future recruitment in the context of global warming. Hypotheses of auto-correlation and of an environmental effect on recruitment, together with trends in weight-at-age and the overestimation of spawning-stock biomass, form the basis for sensitivity tests of the management options considered. Implementation of a 3-year fixed TAC with 40% constraint in TAC variability and a slight reduction in target F would seem appropriate for the stock, given that it is within safe biological limits and compares well in terms of yield and risk with the current approach of annual TAC revision.

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.

scholarly journals Indirect Impacts of COVID-19 on a Tropical Lobster Fishery’s Harvest Strategy and Supply Chain

2021 ◽  
Vol 8 ◽  
Author(s):  
Éva Plagányi ◽  
Roy Aijun Deng ◽  
Mark Tonks ◽  
Nicole Murphy ◽  
Sean Pascoe ◽  
...  
Keyword(s):  
Supply Chain ◽  
Fishing Effort ◽  
Weak Links ◽  
Catch Per Unit Effort ◽  
Critical Data ◽  
Global Pandemic ◽  
Harvest Control Rule ◽  
Harvest Strategy ◽  
Indirect Impacts ◽  
The Impact

The Torres Strait tropical rock lobster Panulirus ornatus (TRL) fishery is of immense social, cultural and economic importance to the region’s Indigenous fishers from both Australia and Papua New Guinea (PNG). During 2020, the COVID-19 pandemic indirectly impacted this fishery as well as a number of other fisheries reliant on international export markets. The TRL fishery is managed using an empirical (data-based) Harvest Control Rule (eHCR) to rapidly provide a recommended biological catch (RBC), based on catch, fishery-independent survey indices and catch-per-unit-effort (CPUE). Here, we summarize the impacts of COVID-19 on each of these critical data inputs and discuss whether the eHCR was considered adequately resilient to this unprecedented disruption to the system. Next, we use a quantitative supply chain index to analyze the impact of disruptions to the supply chain, and inform on potential adaptation strategies. The catch and CPUE data were impacted to varying degrees by external constraints influencing fishing effort, but the fishery-independent survey wasn’t affected and hence there remains an unbroken survey time-series for the fishery extending back to 1989. The eHCR was shown to be reasonably robust because it incorporates longer-term trends over a 5-year period, and accords substantially more weighting (80%) to the fishery-independent survey rather than CPUE data which can be affected by trade and other disruptions. Despite the eHCR not having been tested for scenarios such as a global pandemic, this robustness is a positive given the types of disruptions we will likely face in future climate. The weak links identified in the supply chain were the same as those previously highlighted as sensitive to climate change disruptions. Our supply chain analysis quantifies the impact on system resilience of alternative paths connecting producers to consumers and reinforces that supply chains may be particularly vulnerable to external disruptions if they are not sufficiently diverse.

Spatial and temporal distribution of early-stage phyllosoma of westren rock lobster, Panulirus cygnus

1980 ◽  
Vol 31 (4) ◽  
pp. 485 ◽  
Author(s):  
DW Rimmer
Keyword(s):  
Early Stage ◽  
Temporal Distribution ◽  
Lunar Cycle ◽  
Stage I ◽  
Western Coast ◽  
Spatial And Temporal Distribution ◽  
Rock Lobster ◽  
Larval Release ◽  
Panulirus Cygnus ◽  
The Impact

Time-series sampling for early-stage phyllosoma of P. cygnus was carried out off the western coast of Australia near the centre of the population of breeding adults. Hatching occurred from November through February in 1973-74 and 1974-75. Spatial distribution of the larvae was similar between the two seasons studied. The density of newly hatched (stage I) phyllosoma was greatest along the off-shore portion of the continental shelf. The majority of larvae moved off shore soon after hatching and the relative abundance of stages 11 and 111 increased with distance off shore. An off-shore extension of the sampling yielded an estimated minimum net rate of off-shore transport of 5.25 km,day for the stage I phyllosoma taken at the station farthest off shore. In 1973-74. larval release increased gradually from a low level in November to a peak in mid January. In 1974-75 larval release commenced at least a month earlier and peaked in late November, tapered off through December, and peaked again in mid January. Water temperature correlated with temporal differences in larval release. Warmer temperatures early in the 1974-75 season apparently induced the onset of breeding early enough to permit a second breeding by some females. There appeared to be no periodicity of hatching related to the lunar cycle. The distribution of early-stage phyllosoma was patchy and the impact of patchiness on quantitative sampling is discussed.

Discrete Versus Continuous Controlled System

1998 ◽  
Vol 06 (02) ◽  
pp. 127-157
Author(s):  
Christophe Béné ◽  
Claude Lobry
Keyword(s):  
Decision Making ◽  
Decision Process ◽  
Continuous Process ◽  
Realistic Model ◽  
Fishing Effort ◽  
Mature Adults ◽  
Shrimp Fishery ◽  
Decision Making Processes ◽  
Two Stages ◽  
The Impact

Because decision making processes involve costly mechanisms, they seldom are implemented continuously but instead take place at discrete time intervals. The question is then: what is the impact of this process discreteness on the systems dynamics? This problem is set here in the context of fisheries. Through a very simple though realistic model representing a shrimp fishery, we show that a discrete decision making process may lead to dynamics that differ completely from those obtained with a continuous process. For this purpose, we consider the interaction between a shrimp stock and the exploiting fleet. We then focus on the decision process that governs the allocation of the fleet fishing effort between the two stages of this stock: the young adults living near the coast and the mature adults located offshore. We first analyze the behaviour of the system when the discreteness in the decision making is not accounted for. In that case, the system turns out to be globally stable. We then identify the behaviour of the system when the decision process is discretised. In that case the solutions of the system yield sustained periodic oscillations. Our conclusion is that discreteness which is known to occur in decision making processes of most anthropic systems should be taken into account, especially in studies aiming precisely at investigating the dynamics of such systems.

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 Immunization Strategies for Funding Multiple Inflation-Linked Retirement Income Benefits

Risks ◽  
2021 ◽  
Vol 9 (4) ◽  
pp. 60
Author(s):  
Cláudia Simões ◽  
Luís Oliveira ◽  
Jorge M. Bravo
Keyword(s):  
Interest Rate ◽  
Yield Curve ◽  
Risk Measure ◽  
Management Strategies ◽  
Interest Rate Risk ◽  
Insurance Companies ◽  
Retirement Income ◽  
Investment Strategies ◽  
Immunization Strategies ◽  
The Impact

Protecting against unexpected yield curve, inflation, and longevity shifts are some of the most critical issues institutional and private investors must solve when managing post-retirement income benefits. This paper empirically investigates the performance of alternative immunization strategies for funding targeted multiple liabilities that are fixed in timing but random in size (inflation-linked), i.e., that change stochastically according to consumer price or wage level indexes. The immunization procedure is based on a targeted minimax strategy considering the M-Absolute as the interest rate risk measure. We investigate to what extent the inflation-hedging properties of ILBs in asset liability management strategies targeted to immunize multiple liabilities of random size are superior to that of nominal bonds. We use two alternative datasets comprising daily closing prices for U.S. Treasuries and U.S. inflation-linked bonds from 2000 to 2018. The immunization performance is tested over 3-year and 5-year investment horizons, uses real and not simulated bond data and takes into consideration the impact of transaction costs in the performance of immunization strategies and in the selection of optimal investment strategies. The results show that the multiple liability immunization strategy using inflation-linked bonds outperforms the equivalent strategy using nominal bonds and is robust even in a nearly zero interest rate scenario. These results have important implications in the design and structuring of ALM liability-driven investment strategies, particularly for retirement income providers such as pension schemes or life insurance companies.

Sign in / Sign up

Export Citation Format

Share Document