Size-structured population modelling and risk assessment of the Victorian southern rock lobster, Jasus edwardsii, fishery

2001 ◽  
Vol 52 (8) ◽  
pp. 1495 ◽  
Author(s):  
David Hobday ◽  
André E. Punt
Keyword(s):  
Egg Production ◽  
Stock Assessment ◽  
Reference Points ◽  
Assessment Model ◽  
Data Series ◽  
Population Modelling ◽  
Rock Lobster ◽  
Southeastern Australia ◽  
Jasus Edwardsii ◽  
Catch Rates

Current annual landings of southern rock lobster, Jasus edwardsii, from southeastern Australia are around 5000 tonnes valued at A$140 million. The Victorian component of this catch during the 1998-99 fishing season was 550 t, valued at A$18 million. During the past 20 years catch rates have declined from 0.8 kg per pot lift to 0.6 and 0.3 kg per pot lift in the western and eastern management zones respectively. The fishery has been managed with input controls during this period, but at the time of writing, the direction of future management is not clear. A size-structured model was developed to assess risk associated with both effort (input) and catch (output) controlled harvest strategies in each zone. The stock-assessment model was fitted to historical catch data (in weight and by number) from 1951, catch rates, and the length-frequency by sex. The uncertainty associated with the estimates of exploitable biomass and egg production was assessed according to Bayesian methods. The output of the assessment formed the basis for projections intended to determine the risk associated with different future levels of effort and catch. Reference points based on estimated biomass and egg production relative to the start of the data series in 1951 were considered.

Population modelling of Tasmanian rock lobster, Jasus edwardsii, resources

1997 ◽  
Vol 48 (8) ◽  
pp. 967 ◽  
Author(s):  
André E. Punt ◽  
Robert B. Kennedy
Keyword(s):  
Growth Rate ◽  
Egg Production ◽  
Stock Assessment ◽  
Assessment Model ◽  
High Yield ◽  
Population Modelling ◽  
Rock Lobster ◽  
Jasus Edwardsii ◽  
Northern Regions ◽  
Catch Rates

From 1980 to 1995, annual catch rates of southern rock lobster (Jasus edwardsii) in Tasmanian waters declined from 1·6 to 0·9 kg per pot lift. From March 1998, the Tasmanian government intends to base management of this fishery on output controls using individual transferable catch quotas. This has necessitated the development of a stock assessment model that can be used to evaluate the relative merits of a variety of alternative catch limits in terms of the trade-off between protecting the rock lobster resource and achieving a high yield. Each of eight regions around Tasmania is assessed separately because of spatial heterogeneity between regions in lobster growth, size at maturity and catch rates. The stock assessment model is size-structured and is fitted to catch, effort and length–frequency data as well as to estimates of exploitation rate from experimental data. A Bayesian estimation framework is employed to estimate the quantities needed for risk analysis. Egg production differs markedly among the eight regions: from as low as 6% of the unexploited equilibrium level in the northern regions, where the growth rate is fast, to more than 80% in the south-west, where the growth rate is slowest.

Relationship between settlement of southern rock lobster pueruli, Jasus edwardsii, and recruitment to the fishery in Tasmania, Australia

2001 ◽  
Vol 52 (8) ◽  
pp. 1271 ◽  
Author(s):  
C. Gardner ◽  
S. D. Frusher ◽  
R. B. Kennedy ◽  
A. Cawthorn
Keyword(s):  
Interannual Variation ◽  
Stock Assessment ◽  
Catch Rate ◽  
Assessment Model ◽  
Rock Lobster ◽  
Commercial Catch ◽  
Jasus Edwardsii ◽  
Catch Rates ◽  
Additional Support ◽  
Northeast Coast

Puerulus catches on artificial collectors were measured monthly at four sites around Tasmania from 1991 to April 2000, with the aim of predicting future changes in recruitment to the fishery. Support for the potential of catch-rate prediction in Tasmania was provided at the two sites that have overlap of several years between indices of puerulus settlement and indices of the abundance of recruits to the fishery. At Bicheno, on the northeast coast, correlations between annual puerulus index and commercial catch rates were highly significant, with a lag of 5 years (P< 0.01). Similar interannual trends in puerulus index and estimates from a stock-assessment model of the biomass of recruits to the fishery provided additional support for a link with puerulus index. A 5-fold interannual variation in puerulus index detected at Bicheno, with a peak in 1995, was preceded by 3 years of relatively low puerulus catch. The peak in puerulus index appears to lead to an increase in the abundance of sublegal males in research sampling 3 years later. Correlation between annual measures of puerulus index and catch rate also appeared significant at King Island (P= 0.06) although data at this site had less contrast.

scholarly journals Stock assessment and projections incorporating discard estimates in some years: an application to the hake stock in ICES Divisions VIIIc and IXa

2010 ◽  
Vol 67 (6) ◽  
pp. 1185-1197 ◽  
Author(s):  
C. Fernández ◽  
S. Cerviño ◽  
N. Pérez ◽  
E. Jardim
Keyword(s):  
Time Series ◽  
Stock Assessment ◽  
Reference Points ◽  
Assessment Model ◽  
Marine Science ◽  
Fishing Mortality ◽  
Change Over Time ◽  
Age Structured ◽  
Available Information ◽  
Over Time

Abstract Fernández, C., Cerviño, S., Pérez, N., and Jardim, E. 2010. Stock assessment and projections incorporating discard estimates in some years: an application to the hake stock in ICES Divisions VIIIc and IXa. – ICES Journal of Marine Science, 67: 1185–1197. A Bayesian age-structured stock assessment model is developed to take into account available information on discards and to handle gaps in the time-series of discard estimates. The model incorporates mortality attributable to discarding, and appropriate assumptions about how this mortality may change over time are made. The result is a stock assessment that accounts for information on discards while, at the same time, producing a complete time-series of discard estimates. The method is applied to the hake stock in ICES Divisions VIIIc and IXa, for which the available data indicate that some 60% of the individuals caught are discarded. The stock is fished by Spain and Portugal, and for each country, there are discard estimates for recent years only. Moreover, the years for which Portuguese estimates are available are only a subset of those with Spanish estimates. Two runs of the model are performed; one assuming zero discards and another incorporating discards. When discards are incorporated, estimated recruitment and fishing mortality for young (discarded) ages increase, resulting in lower values of the biological reference points Fmax and F0.1 and, generally, more optimistic future stock trajectories under F-reduction scenarios.

scholarly journals Ecological Reference Points for Atlantic Menhaden Established Using an Ecosystem Model of Intermediate Complexity

2020 ◽  
Vol 7 ◽  
Author(s):  
David Chagaris ◽  
Katie Drew ◽  
Amy Schueller ◽  
Matt Cieri ◽  
Joana Brito ◽  
...  
Keyword(s):  
Striped Bass ◽  
Fishery Management ◽  
Stock Assessment ◽  
Reference Points ◽  
Atlantic Menhaden ◽  
Assessment Model ◽  
Total Allowable Catch ◽  
Important Species ◽  
Ecosystem Impacts ◽  
Intermediate Complexity

Atlantic menhaden (Brevoortia tyrannus) are an important forage fish for many predators, and they also support the largest commercial fishery by weight on the U.S. East Coast. Menhaden management has been working toward ecological reference points (ERPs) that account for menhaden’s role in the ecosystem. The goal of this work was to develop menhaden ERPs using ecosystem models. An existing Ecopath with Ecosim model of the Northwest Atlantic Continental Shelf (NWACS) was reduced in complexity from 61 to 17 species/functional groups. The new NWACS model of intermediate complexity for ecosystems (NWACS-MICE) serves to link the dynamics of menhaden with key managed predators. Striped bass (Morone saxatilis) were determined to be most sensitive to menhaden harvest and therefore served as an indicator of ecosystem impacts. ERPs were based on the tradeoff relationship between the equilibrium biomass of striped bass and menhaden fishing mortality (F). The ERPs were defined as the menhaden F rates that maintain striped bass at their biomass target and threshold when striped bass are fished at their Ftarget, and all other modeled species were fished at status quo levels. These correspond to an ERP Ftarget of 0.19 and an ERP Fthreshold of 0.57, which are lower than the single species reference points by 30–40%, but higher than current (2017) menhaden F. The ERPs were then fed back into the age-structured stock assessment model projections to provide information on total allowable catch. The ERPs developed in this study were adopted by the Atlantic menhaden Management Board, marking a shift toward ecosystem-based fishery management for this economically and ecologically important species.

Recruitment variation in abalone: Its importance to fisheries management

1995 ◽  
Vol 46 (3) ◽  
pp. 555 ◽  
Author(s):  
PE McShane
Keyword(s):  
Egg Production ◽  
Field Experiments ◽  
Stock Assessment ◽  
Reference Points ◽  
High Fecundity ◽  
Spatial And Temporal Scales ◽  
Recruitment Failure ◽  
Spawning Stock ◽  
Stock Recruitment ◽  
Many Sources

Recruitment failure has been implicated in the decline of several abalone fisheries. Traditionally, fisheries scientists invoke theoretical stock-recruitment relationships to predict trends in abundance of an exploited stock under various harvest regimes. The empirical evidence in support of a positive relationship between spawning stock and recruits is not strong. A further problem in interpretation of such relationships is that both 'stock' and 'recruitment' have various definitions in fisheries and ecological literature. The definition of a stock for abalone is not clear. As emphasized in this review, which considers each stage in the life history of abalone, the abundance of spawners is one of many sources of variation in recruitment. The evidence for invertebrates, particularly those with high fecundity, is that recruitment varies independently of the abundance of spawners. This is also the case for abalone, where recruits have been measured as the density of immediate post-settlement individuals, juveniles, or as adults entering the exploitable stock. A problem with stock-recruitment hypotheses is that they have intuitive appeal. It is considered 'dangerous' to manage fisheries under the assumption that a reduction in the number of spawners by fishing will not affect recruitment. Such danger to abalone stocks has been more recently assessed by egg-per-recruit analyses, whereby various harvest strategies are examined relative to reference points for egg production. These studies are reviewed and assessed relative to the often conflicting aims of managers and scientists. This review of studies of recruitment variation in abalone emphasizes the need for a more rigorous, autecological approach to stock assessment in which field experiments are conducted over realistic spatial and temporal scales, permitting robust testing of hypotheses.

Contrasting fecundity, size at maturity and reproductive potential of southern rock lobster Jasus edwardsii in two South Australian fishing regions

2008 ◽  
Vol 88 (3) ◽  
pp. 583-589 ◽  
Author(s):  
A.J. Linnane ◽  
S.S. Penny ◽  
T.M. Ward
Keyword(s):  
Egg Production ◽  
Spatial Scales ◽  
Reproductive Potential ◽  
South Australia ◽  
Egg Mass ◽  
Rock Lobster ◽  
Commercial Catch ◽  
Southern Zone ◽  
Significant Difference ◽  
Jasus Edwardsii

The annual commercial catch from the Southern Zone of the South Australian rock lobster (Jasus edwardsii) fishery is ~1900 tonnes, representing ~50% of total landings from south-east Australia. A single minimum legal size (MLS) of 98.5 mm carapace length (CL) exists across the entire zone. Fecundity (F), size at onset of maturity (SOM) and relative reproductive potential (RRP) of female rock lobsters were investigated in two major fishing regions, i.e. the North Southern Zone (NSZ) and South Southern Zone (SSZ) with a view to providing a basis for future fine-scale spatial management of the resource. F ranged from 45,292 to 466,800 eggs per female and increased proportionally with CL according to the relationship: F = 0.0584 × CL3.1642. F was significantly higher in the NSZ compared to the SSZ but was attributed to differences in lobster size between regions. There was no significant difference in the number of eggs · g−1 of egg mass between areas. SOM, estimated as the size at which 50% of females reached sexual maturity (L50) was higher in the NSZ (104.1 mm CL) compared to SSZ (92.3 mm CL). Approximately 20% of lobsters above the MLS in the commercial catch in the NSZ were under the L50 estimate. RRP, as a measure of egg production, was calculated for each size-class from the product of F, SOM and population length–frequency. The modal RRP size-classes in the NSZ were 117.5–122.5 mm CL, while in the SSZ it was 97.5–102.5 mm CL. Only 6% of RRP was contributed by female rock lobsters below the MLS in the NSZ, compared to 34% in the SSZ. Regional differences in SOM and RRP in the Southern Zone of South Australia suggest that different MLSs may be beneficial, particularly if the fishery is to be effectively managed at finer spatial scales.

scholarly journals Fewer eggs from larger size limits: counterintuitive outcomes in a spatially heterogeneous fishery

2014 ◽  
Vol 72 (suppl_1) ◽  
pp. i252-i259 ◽  
Author(s):  
Caleb Gardner ◽  
Klaas Hartmann ◽  
André E. Punt ◽  
Eriko Hoshino
Keyword(s):  
Marine Protected Areas ◽  
Egg Production ◽  
Slow Growth ◽  
Minimum Length ◽  
Bioeconomic Model ◽  
Rock Lobster ◽  
Total Allowable Catch ◽  
Jasus Edwardsii ◽  
Negative Impacts ◽  
Size Limits

Abstract The legal minimum length (LML) of female Southern Rock Lobster (Jasus edwardsii) was reduced in the Tasmanian fishery in 1966 for higher sustainable catches. Originally, the LML was to be reduced in slow growth southern areas only; however, the change was implemented across the entire fishery due to lobbying by commercial fishers. The lower LML has been controversial ever since, including during recent years when low recruitment resulted in a lower total allowable catch (TAC). Fishers argued that this could have been prevented with a higher female LML across the jurisdiction. A length- and sex-based bioeconomic model was used to examine probable outcomes of the larger statewide LML. This model showed that management of egg production would be poorly served by raising the statewide LML because of spatial patterns in the stock and fishery. Catch would be displaced from areas where egg production was already high and into the most depleted areas thus reducing production in areas of greatest concern. Spatial variation in biological parameters can have a profound effect on outcomes of management perceived to be conservative, possibly leading to negative impacts. This risk exists wherever catch is displaced, such as with Marine Protected Areas, spatial TACs and gear restrictions.

scholarly journals Environmental influences on commercial oceanic ommastrephid squids: a stock assessment perspective

2017 ◽  
Vol 81 (1) ◽  
pp. 37 ◽  
Author(s):  
Jintao Wang ◽  
Xinjun Chen ◽  
Kisei Tanaka ◽  
Jie Cao ◽  
Yong Chen
Keyword(s):  
Environmental Variability ◽  
Mean Squared Error ◽  
Stock Assessment ◽  
Reference Points ◽  
Assessment Model ◽  
Production Model ◽  
Northwest Pacific ◽  
Dosidicus Gigas ◽  
Southwest Atlantic ◽  
Data Assessment

Ommastrephid squids are short-lived ecological opportunists and their recruitment is largely driven by the surrounding environment. While recent studies suggest that recruitment variability in several squid species can be partially explained by environmental variability derived from synoptic oceanographic data, assessment of ommastrephid stocks using environmental variability is rare. In thisstudy, we modified asurplus production model to incorporate environmental variability into the assessment of threeommastrephid squids (Ommastrephes bartramii in the northwest Pacific, Illex argentinus in the southwest Atlantic and Dosidicus gigas in the southwest Pacific). We assumed that the key environmental variables—suitable sea surface temperature on spawning grounds during the spawning seasons and feeding grounds during the feeding seasons—have effects on the carrying capacity and the instantaneous population growth rate, respectively, in the surplus production model. For each squid stock, the assessment model with environmental variability had the highest fitting accuracy and the lowest mean squared error and coefficient of variation, and the management reference points based on the optimal model were more precautionary. This study advances our understanding of the interactions between the environment and ommastrephid squid population dynamics and can therefore improve the management of these commercially valuable stocks with a short life cycle.

Analytical reference points for age-structured models: application to data-poor fisheries

2009 ◽  
Vol 67 (1) ◽  
pp. 165-175 ◽  
Author(s):  
Elizabeth N. Brooks ◽  
Joseph E. Powers ◽  
Enric Cortés
Keyword(s):  
Stock Assessment ◽  
Meta Analysis ◽  
Reproductive Rate ◽  
Biological Data ◽  
Reference Points ◽  
Assessment Model ◽  
Shark Species ◽  
Stock Status ◽  
Age Structured ◽  
Analytical Reference

AbstractBrooks, E. N., Powers, J. E., and Cortés, E. 2010. Analytical reference points for age-structured models: application to data-poor fisheries. – ICES Journal of Marine Science, 67: 165–175. Analytical solutions for biological reference points are derived in terms of maximum lifetime reproductive rate. This rate can be calculated directly from biological parameters of maturity, fecundity, and natural mortality or a distribution for this rate can be derived from appropriate metadata. Minimal data needs and assumptions for determining stock status are discussed. The derivations lead to a re-parameterization of the common stock–recruit relationships, Beverton–Holt and Ricker, in terms of spawning potential ratio. Often, parameters in stock–recruit relationships are restricted by tight prior distributions or are fixed based on a hypothesized level of stock resilience. Fixing those parameters is equivalent to specifying the biological reference points. An ability to directly calculate reference points from biological data, or a meta-analysis, without need of a full assessment model or fisheries data, makes the method an attractive option for data-poor fisheries. The derivations reveal an explicit link between the biological characteristics of a species and appropriate management. Predicted stock status for a suite of shark species was compared with recent stock assessment results, and the method successfully identified whether each stock was overfished.

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