Precision of exploitation-rate estimates in the Tasmanian rock-lobster fishery based on change-in-ratio techniques

1997 ◽  
Vol 48 (8) ◽  
pp. 1069 ◽  
Author(s):  
S. D. Frusher ◽  
R. B. Kennedy ◽  
I. D. Gibson
Keyword(s):  
Confidence Intervals ◽  
Stock Assessment ◽  
Management Strategies ◽  
Reference Points ◽  
Rock Lobster ◽  
Bootstrap Analysis ◽  
Size Number ◽  
Exploitation Rate ◽  
Lobster Fishery

Determination of exploitation rate is considered important for both stock assessment and establishment of fishery reference points. From 1992 to 1996, a project was undertaken to evaluate the change-in-ratio technique for estimating exploitation rates for male lobsters off southern Tasmania. Confidence limits of exploitation rate estimates were determined by bootstrap analysis. This showed wide confidence intervals around the estimates for the fishing years from 1992–93 to 1994–95. Bootstrap analysis was used to determine the appropriate sample size (number of pot-lifts) for improved precision in exploitation rate estimates for the 1995–96 fishing year. Results from field estimates confirm the expected decrease in confidence intervals. The level of exploitation had an inverse relationship to the precision of exploitation rate estimates. Relationships can be determined between the level of exploitation in the fishery and the degree of precision achievable for a set number of pot-lifts. Thus, sampling programmes can be designed to minimize cost and provide the degree of precision required for management strategies.

scholarly journals Assessing global marine fishery status with a revised dynamic catch-based method and stock-assessment reference points

2012 ◽  
Vol 69 (8) ◽  
pp. 1491-1500 ◽  
Author(s):  
Sean C. Anderson ◽  
Trevor A. Branch ◽  
Daniel Ricard ◽  
Heike K. Lotze
Keyword(s):  
Stock Assessment ◽  
Original Method ◽  
Reference Points ◽  
Marine Science ◽  
Marine Fishery ◽  
Stock Biomass ◽  
Exploitation Rate ◽  
Realistic Assessment ◽  
Fishery Status

Abstract Anderson, S. C., Branch, T. A., Ricard, D., and Lotze, H. K. 2012. Assessing global marine fishery status with a revised dynamic catch-based method and stock-assessment reference points. – ICES Journal of Marine Science, 69: . The assessment of fishery status is essential for management, yet fishery-independent estimates of abundance are lacking for most fisheries. Methods exist to infer fishery status from catches, but the most commonly used method is biased towards classifying fisheries as overexploited or collapsed through time and does not account for still-developing fisheries. We introduce a revised method that overcomes these deficiencies by smoothing catch series iteratively, declaring fisheries developing within three years of peak catch, and calibrating thresholds to biological reference points. Compared with status obtained from stock-assessment reference points for 210 stocks, our approach provides a more realistic assessment than the original method, but cannot be perfect because catches are influenced by factors other than biomass. Applied to FAO catches, our method suggests in 2006 32% of global fisheries were developing, 27% fully exploited, 25% overexploited, and 16% collapsed or closed. Although less dire than previous assessments, this still indicates substantial numbers of overexploited stocks. Probably because median exploitation rate decreased since 1992, our catch-based results do not reflect recent stabilization of assessed-stock biomass. Whether this outlook also applies to unassessed stocks can only be revealed with increased or more representative collection of biomass- and exploitation-rate trends.

scholarly journals Evaluation of the robustness of maximum sustainable yield based management strategies to variations in carrying capacity or migration pattern of Atlantic bluefin tuna (Thunnus thynnus)

2007 ◽  
Vol 64 (5) ◽  
pp. 837-847 ◽  
Author(s):  
Laurence T Kell ◽  
Jean-Marc Fromentin
Keyword(s):  
Carrying Capacity ◽  
Management Strategy ◽  
Stock Assessment ◽  
Management Strategies ◽  
Maximum Sustainable Yield ◽  
Reference Points ◽  
Sustainable Yield ◽  
Size Limit ◽  
Atlantic Bluefin Tuna ◽  
Spawning Stock

In this study, we examine the performances of current stock assessment methods with respect to their ability to (i) provide estimates of maximum sustainable yield (MSY), FMSY, and BMSY and (ii) assess stock status and exploitation level relative to MSY targets. The robustness of the current International Commission for the Conservation of Atlantic Tunas (ICCAT) management strategy is then evaluated with respect to uncertainty about the true population dynamics and contrasted with a simpler management strategy based solely on a size limit. Reference points are more robust to dynamic uncertainty than the estimates of absolute values and trends in F and spawning stock biomass. However, their performances depend on the underlying dynamics (they perform better when fluctuations come from changes in the carrying capacity than migration) and on when they are implemented relative to the intrinsic cycle of the population. Reference points based on F were less biased and more precise than those based on biomass and (or) yield. Although F0.1 appeared to be the best proxy for FMSY, it cannot indicate past and current levels of exploitation relative to FMSY when there is uncertainty about the dynamics. Finally, the F0.1 management strategy of ICCAT performed only slightly better than a simpler strategy based on size limit and led to lower catch levels.

scholarly journals Consequences of growth variation in northern Baltic herring for assessment and management

2004 ◽  
Vol 61 (3) ◽  
pp. 338-350 ◽  
Author(s):  
Mika Rahikainen ◽  
Robert L. Stephenson
Keyword(s):  
Baltic Sea ◽  
Stock Assessment ◽  
Management Strategies ◽  
Reference Points ◽  
Common Reference ◽  
Baltic Herring ◽  
Marked Variability ◽  
Growth Variation ◽  
Definition Of ◽  
The Impact

Abstract Growth rates of herring in the northern Baltic Sea differ among areas, and have changed substantially over time in some areas in response to environmental change. Weight-at-age of adult herring in some areas of the Finnish herring fishery fluctuated by as much as 60% over the past three decades. Elsewhere, there have been similar but more subtle changes. Growth variation has implications for stock assessment and management: differences suggest a need for considering a smaller spatial structure, at least at the scale of the ICES subdivision, in the case of northern Baltic herring. Changes in growth have an impact on the calculation and use of common biological reference points, and erode the capability of yield projections beyond the short term. Investigation of the impact of growth variation on common reference points of northern Baltic herring revealed that F0.1 was a robust reference despite the marked variability in growth, whereas Fx%SPR (e.g. F35%SPR) was less robust, depending on the definition of maximum spawning-per-recruit. Herring in different areas of the northern Baltic Sea probably require different reference points and possibly different management strategies, as a consequence of differences and variability in growth characteristics.

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.

scholarly journals Assessing the adequacy of current fisheries management under changing climate: a southern synopsis

2011 ◽  
Vol 68 (6) ◽  
pp. 1305-1317 ◽  
Author(s):  
Éva E. Plagányi ◽  
Scarla J. Weeks ◽  
Tim D. Skewes ◽  
Mark T. Gibbs ◽  
Elvira S. Poloczanska ◽  
...  
Keyword(s):  
Climate Change ◽  
Fisheries Management ◽  
Environmental Changes ◽  
Stock Assessment ◽  
Management Strategies ◽  
Single Species ◽  
Rock Lobster ◽  
Management Tools ◽  
Changing Climate ◽  
Impacts Of Climate Change

Abstract Plagányi, É. E., Weeks, J. S., Skewes, T. D., Gibbs, M. T., Poloczanska, E. S., Norman-López, A., Blamey, L. K., Soares, M., and Robinson, W. M. L. 2011. Assessing the adequacy of current fisheries management under changing climate: a southern synopsis. – ICES Journal of Marine Science, 68: 1305–1317. Climate change is likely to have a significant impact on both target and non-target marine stocks worldwide, with the concomitant need for management strategies capable of sustaining fishing in future. We use several southern hemisphere fisheries to highlight the likely impacts of climate change at a range of levels, from individual to population responses, as well as ecosystem ramifications. Examples span polar (Antarctic krill fishery), temperate (west coast pelagic fishery, abalone and rock lobster), and tropical (Torres Strait rock lobster) commercially important fisheries. Responses of these fisheries to either past observed environmental changes or projected future changes are used to deduce some anticipated implications of climate change for fisheries management, including economic impacts and governance considerations. We evaluate the effectiveness of current single-species assessment models, management strategy evaluation approaches and multispecies assessment models as future management tools to cope with likely climate-related changes. Non-spatial stock assessment models will have limited ability to separate fishery effects from the impacts of climate change. Anthropogenic climate change is occurring at a time-scale relevant to current fisheries management strategic planning and testing. Adaptive management frameworks (with their feedback loops) are ideal for detecting and adapting to changes in target stocks.

scholarly journals Growth, Mortality and Yield-per-recruit of Nile Tilapia (Oreochromis niloticusM/em>) in Garmat Ali River, Iraq

2020 ◽  
Vol 8 (6) ◽  
Author(s):  
Ayat N. Salman ◽  
Abdul-Razak M Mohamed
Keyword(s):  
Assessment Tool ◽  
Growth Parameters ◽  
Stock Assessment ◽  
Total Mortality ◽  
Reference Points ◽  
Fishing Mortality ◽  
Exploitation Rate ◽  
Biological Target ◽  
Mean Size ◽  
Yield Per Recruit

The study was conducted to estimate the growth, mortality, recruitment and yield-per-recruit of Oreochromis niloticus from Garmat Ali River, Basrah, Iraq from October 2019 to September 2020. The population parameters were analyzed using the FAO-ICLARM stock assessment tool (FiSAT). A total of 2696 O. niloticus ranged from 7.0 to 25.0 cm and the sizes 13.0-18.0 cm constituted 64.2% of the total catch. The length-weight relationship was W= 0.012L3.109 suggesting that the species shows positive allometric growth. The growth parameters for the species were estimated as L∞= 30.45 cm, K= 0.45, to= -0.313 and Ǿ= 2.622. The coefficients of total mortality (Z), natural mortality (M) and fishing mortality (F) were 3.26, 1.03 and 2.24, respectively. The exploitation rate for the species computed to be 0.69. Fish were recruited to the fishery at a mean size of L50= 14.92 cm. The peak of recruitment was 23.51% in June. The analysis of yield-per-recruit (Y/R’) indicates that stock is not being overfished since the present exploitation rate was below the biological target reference points (E0.1 and Emax). So, more yields could be achieved by reducing the mesh sizes of the nets for fishing the species

scholarly journals Growth, mortality and stock assessment of greenback mullet, Planiliza subviridis from northwest Arabian Gulf, Iraq

2021 ◽  
Vol 6 (2) ◽  
pp. 142-148
Author(s):  
Abdul-Razak M. Mohamed ◽  
Ali H. Al-Hassani
Keyword(s):  
Mortality Rate ◽  
Stock Assessment ◽  
Population Analysis ◽  
Arabian Gulf ◽  
Total Mortality ◽  
Reference Points ◽  
Fishing Mortality ◽  
Fish Samples ◽  
Exploitation Rate ◽  
First Maturity

The growth, mortality and stock parameters of greenback mullet, Planiliza subviridis from Iraqi marine waters, northwest Arabian Gulf was assessed using FiSAT II software for length-frequency data collected from February 2020 to January 2021. P. subviridis is one of the species caught in large quantities as commercial by artisanal fishers. Fish samples were collected by the Shaheen steel-hulled dhow and from the artisanal fishermen. The total length and body weight relationship of fish was estimated as W= 0.034L2.670, indicating negative allometric growth. Of 3350 specimens, growth and mortality parameters were evaluated. The asymptotic length (L∞), growth rate (K) and growth performance index (Ø') were 33.8 cm, 0.30 and 2.535, respectively. The total mortality rate (Z), natural mortality rate (M), and fishing mortality rate (F) were 1.11, 0.74 and 0.38, respectively. The present exploitation rate (Epresent) of P. subviridis computed as 0.34. Length at first capture (L50) was 17.47 cm. Recruitment of P. subviridis was observed throughout the year, with a peak during July. The yield per recruit analysis indicates that the current exploitation rate was below the biological target reference points (E0.1 and Emax), which refers to the stock of P. subviridis is underexploited. Virtual population analysis results showed that mid-lengths (16-22 cm) experienced the highest fishing mortality. The length at first capture (L50) was higher than the length at first maturity (Lm) of the species. So, for management purposes, more yields could be obtained by increasing the fishing activities on this species for a substantial harvest.

scholarly journals Applying bayesian population assessment models to artisanal, multispecies fisheries in the Northern Mokran Sea, Iran

2018 ◽  
Vol 28 ◽  
pp. 61-89
Author(s):  
Abdul Rashid Jamnia ◽  
Ahmad Ali Keikha ◽  
Mahmoud Ahmadpour ◽  
Abdoul Ahad Cissé ◽  
Mohammad Rokouei
Keyword(s):  
Fisheries Management ◽  
Stock Assessment ◽  
Bayesian Models ◽  
Management Strategies ◽  
Demersal Fish ◽  
Reference Points ◽  
Small Scale ◽  
Parameter Estimates ◽  
Multiple Sources ◽  
Small Scale Fisheries

Small-scale fisheries substantially contribute to the reduction of poverty, local economies and food safety in many countries. However, limited and low-quality catches and effort data for small-scale fisheries complicate the stock assessment and management. Bayesian modelling has been advocated when assessing fisheries with limited data. Specifically, Bayesian models can incorporate information of the multiple sources, improve precision in the stock assessments and provide specific levels of uncertainty for estimating the relevant parameters. In this study, therefore, the state-space Bayesian generalised surplus production models will be used in order to estimate the stock status of fourteen Demersal fish species targeted by small-scale fisheries in Sistan and Baluchestan, Iran. The model was estimated using Markov chain Monte Carlo (MCMC) and Gibbs Sampling. Model parameter estimates were evaluated by the formal convergence and stationarity diagnostic tests, indicating convergence and accuracy. They were also aligned with existing parameter estimates for fourteen species of the other locations. This suggests model reliability and demonstrates the utility of Bayesian models. According to estimated fisheries’ management reference points, all assessed fish stocks appear to be overfished. Overfishing considered, the current fisheries management strategies for the small-scale fisheries may need some adjustments to warrant the long-term viability of the fisheries.

scholarly journals Stock assessment methods for sustainable fisheries

2014 ◽  
Vol 72 (1) ◽  
pp. 1-6 ◽  
Author(s):  
Steven X. Cadrin ◽  
Mark Dickey-Collas
Keyword(s):  
Fishery Management ◽  
Stock Assessment ◽  
Management Strategies ◽  
Assessment Methods ◽  
Reference Points ◽  
Fish Stock ◽  
Mortality Trends ◽  
Sustainable Fisheries ◽  
Management Procedures ◽  
Pseudo Data

Abstract This special volume of the ICES Journal compiles contributions from the World Conference on Stock Assessment Methods for Sustainable Fisheries (July 2013, Boston, USA). The conference was the product of a strategic initiative on stock assessment methods that engaged many national and regional fishery management organizations to assure that scientists can apply the most appropriate methods when developing management advice. An inclusive workshop was designed to evaluate the performance of a variety of model categories by applying multiple models to selected case study data as well as simulated pseudo-data that had realistic measurement error. All model applications had difficulties in recovering the simulated stock and fishing mortality trends, particularly at the end of the assessment time series, when they are most important for informing fishery management. This general result suggests that the next steps in evaluating the performance of stock assessment methods should include stock status relative to sustainable reference points, catch advice, multi-model consideration, and alternative management procedures. Recognition of the limitations of conventional stock assessment methods should promote further development of data-limited approaches, methods with time-varying parameters, or spatial complexity, and a more revolutionary shift towards the application of multispecies and ecosystem models. The contributions in this volume address methodological themes that are expected to improve the scientific basis of fishery management. Furthermore, the limitations of stock assessment methods and associated uncertainty should be more extensively considered in fishery management strategies and tactical decisions. Recommendations developed during the conference called for the establishment of a global initiative to synthesize regional advances, form guidance on best practices, promote strategic investments, and highlight research needs for fish stock assessments.

Population dynamics and sustainability of the spiny lobster (Panulirus meripurpuratus Giraldes & Smyth, 2016) fishery on the Amazon continental shelf

2021 ◽  
Vol 72 (1) ◽  
pp. 99
Author(s):  
Ualerson I. Peixoto ◽  
Esther M. C. Mesquita ◽  
Israel A. I. Cintra ◽  
Alex G. M. Klautau ◽  
Nelson A. Gouveia ◽  
...  
Keyword(s):  
Growth Parameters ◽  
Stock Assessment ◽  
Spiny Lobster ◽  
Management Strategies ◽  
Length Distribution ◽  
Cephalothorax Length ◽  
Northern Brazil ◽  
Lobster Fishery ◽  
Exploitation Status ◽  
Distribution Frequency

The assessment of fishery resources is key to the development of management strategies for exploited stocks. Analysis of specific parameters provides information regarding the state of the stock and indicators of exploitation levels. The aim of the present study was to analyse the growth and mortality parameters, as well as investigate the exploitation status, of Panulirus meripurpuratus caught on the Amazon coast, northern Brazil. Growth parameters and stock assessment were estimated using R with bootstrapping and FISAT II, based on cephalothorax length–distribution frequency. Specimens were collected by the commercial lobster fishery off the coast of the states of Pará and Amapá between 2001 and 2002. The results indicate that the P. meripurpuratus stock assessed is composed of individuals with low growth rates and high estimates of maximum asymptotic length, with relative longevity of 21.37 years. The exploitation rate was operating at near the maximum limit of sustainability in 2001 and 2002. This is the first estimate of the exploitation status of P. meripurpuratus on the Amazon coast. We strongly recommend new monitoring efforts and further studies to support the conservation and management of the spiny lobster stock.

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