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 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 A two-stage biomass model to assess the English Channel cuttlefish (Sepia officinalis L.) stock

2014 ◽  
Vol 71 (9) ◽  
pp. 2457-2468 ◽  
Author(s):  
Michaël Gras ◽  
Beatriz A. Roel ◽  
Franck Coppin ◽  
Eric Foucher ◽  
Jean-Paul Robin
Keyword(s):  
Reference Points ◽  
Sea Surface ◽  
Sepia Officinalis ◽  
Sustainable Utilization ◽  
English Channel ◽  
Two Stage ◽  
Stock Biomass ◽  
Exploitation Rate ◽  
Spawning Stock ◽  
Age Structured

Abstract The English Channel cuttlefish (Sepia officinalis) is the most abundant cephalopod resource in the Northeast Atlantic and one of the three most valuable resources for English Channel fishers. Depletion methods and age-structured models have been used to assess the stock, though they have shown limitations related to the model assumptions and data demand. A two-stage biomass model is, therefore, proposed here using, as input data, four abundance indices derived from survey and commercial trawl data collected by Ifremer and Cefas. The model suggests great interannual variability in abundance during the 17 years of the period considered and a decreasing trend in recent years. Model results suggest that recruitment strength is independent of spawning–stock biomass, but appears to be influenced by environmental conditions such as sea surface temperature at the start of the life cycle. Trends in exploitation rate do not reveal evidence of overexploitation. Reference points are proposed and suggestions for management of the sustainable utilization of cuttlefish in the English Channel are advanced.

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.

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 Population dynamics of an invasive species Carassius auratus in the Shatt Al-Arab River, Iraq

2020 ◽  
Vol 5 (3) ◽  
pp. 384-389
Author(s):  
Abdullah N. Abood ◽  
Abdul-Razak M. Mohamed
Keyword(s):  
Population Dynamics ◽  
Carassius Auratus ◽  
Assessment Tool ◽  
Growth Parameters ◽  
Stock Assessment ◽  
Relative Yield ◽  
Reference Points ◽  
Fish Length ◽  
Exploitation Rate ◽  
Precautionary Measures

The population dynamics of the crucian carp, Carassius auratus in the Shatt Al-Arab River, Iraq was studied from November 2015 to October 2016 with monthly samples collected by different fishing gears. The FAO-ICLARM Stock Assessment Tool (FiSAT II) software was used for the mathematical analysis. Length-weight relationship was calculated as W= 0.0149L3.065 for fish length 4.6 to 26.8 cm. Growth parameters L∞, K and Ø were computed as 29.1 cm, 0.51 and 2.635. The total (Z), natural (M) and fishing (F) mortalities were 2.69, 1.09 and 1.60, respectively. Exploitation rate (E) was 0.59. Length at first capture (Lc) was found to be 10.04 cm. C. auratus displayed one main pulse of annual recruitment. The relative yield per recruit analysis revealed that the exploitation rate (E) of C. auratus was higher than the biological target reference points E0.1 and equivalent to Emax. It could be concluded that the C. auratus stock in the Shatt Al-Arab River is operating nearby the exploited situation and needs some precautionary measures to avoid the overexploitation by activating the national law of fishing, exploiting and protecting aquatic resources, in particular preventing illegal fishing methods and follow up the execution of the closed season to prevent the decline of our fish resources.

scholarly journals Choosing the observational likelihood in state-space stock assessment models

2017 ◽  
Vol 74 (5) ◽  
pp. 779-789 ◽  
Author(s):  
Christoffer Moesgaard Albertsen ◽  
Anders Nielsen ◽  
Uffe Høgsbro Thygesen
Keyword(s):  
State Space ◽  
Stock Assessment ◽  
A Priori ◽  
Reference Points ◽  
Assessment Model ◽  
Model Fit ◽  
Total Allowable Catch ◽  
Stock Biomass ◽  
Spawning Stock ◽  
Using Data

Data used in stock assessment models result from combinations of biological, ecological, fishery, and sampling processes. Since different types of errors propagate through these processes, it can be difficult to identify a particular family of distributions for modelling errors on observations a priori. By implementing several observational likelihoods, modelling both numbers- and proportions-at-age, in an age-based state-space stock assessment model, we compare the model fit for each choice of likelihood along with the implications for spawning stock biomass and mean fishing mortality. We propose using AIC intervals based on fitting the full observational model for comparing different observational likelihoods. Using data from four stocks, we show that the model fit is improved by modelling the correlation of observations within years. However, the best choice of observational likelihood differs for different stocks, and the choice is important for the short-term conclusions drawn from the assessment model; in particular, the choice can influence total allowable catch advise based on reference points.

Reference points for the length-based indicator Lmax5% for use in the assessment of data-limited stocks

2019 ◽  
Vol 76 (7) ◽  
pp. 2125-2139 ◽  
Author(s):  
Tanja Miethe ◽  
Yves Reecht ◽  
Helen Dobby
Keyword(s):  
Life Histories ◽  
Stock Assessment ◽  
Reference Points ◽  
Length Frequency ◽  
Frequency Distributions ◽  
Simulation Tools ◽  
Spawning Potential Ratio ◽  
The Mean ◽  
Commercial Sources ◽  
Length Frequency Data

Abstract In the absence of abundance indices from scientific surveys or commercial sources, reliable length frequency data from sampled commercial catches can be used to provide an indirect assessment of fishing mortality. Length-based indicators are simple metrics which describe length frequency distributions. The length-based indicator Lmax5%, the mean length of the largest 5% of individuals in the catch, combined with appropriately selected reference points, can be used to evaluate the presence of very large individuals in the catch and hence determine exploitation level. Using analytical per-recruit models, we derive reference points consistent with a spawning potential ratio of 40%. The reference points depend on the life history parameters for natural mortality, maturity, and growth (M, Lmat, L∞, k, CVL∞). Using available simulation tools, we investigate the sensitivity of the reference points to errors in these parameters and explore the usefulness of particular reference points for management purposes for stocks with different life histories. The proposed reference points are robust to uncertainty in length at first capture, Lc, and take into account the maturation schedule of a species. For those stocks with high M/k ratios (>1), Lmax5%, combined with the appropriate reference point, can be used to provide a data-limited stock assessment.

scholarly journals Quirky patterns in time-series of estimates of recruitment could be artefacts

2014 ◽  
Vol 72 (1) ◽  
pp. 111-116 ◽  
Author(s):  
M. Dickey-Collas ◽  
N. T. Hintzen ◽  
R. D. M. Nash ◽  
P-J. Schön ◽  
M. R. Payne
Keyword(s):  
Time Series ◽  
Stock Assessment ◽  
Meta Analysis ◽  
Reference Points ◽  
Fish Stocks ◽  
Stock Recruitment ◽  
Modelling Assumptions ◽  
Meta Analyses ◽  
Recruitment Model ◽  
Recruitment Time

Abstract The accessibility of databases of global or regional stock assessment outputs is leading to an increase in meta-analysis of the dynamics of fish stocks. In most of these analyses, each of the time-series is generally assumed to be directly comparable. However, the approach to stock assessment employed, and the associated modelling assumptions, can have an important influence on the characteristics of each time-series. We explore this idea by investigating recruitment time-series with three different recruitment parameterizations: a stock–recruitment model, a random-walk time-series model, and non-parametric “free” estimation of recruitment. We show that the recruitment time-series is sensitive to model assumptions and this can impact reference points in management, the perception of variability in recruitment and thus undermine meta-analyses. The assumption of the direct comparability of recruitment time-series in databases is therefore not consistent across or within species and stocks. Caution is therefore required as perhaps the characteristics of the time-series of stock dynamics may be determined by the model used to generate them, rather than underlying ecological phenomena. This is especially true when information about cohort abundance is noisy or lacking.

scholarly journals Can stock–recruitment points determine which spawning potential ratio is the best proxy for maximum sustainable yield reference points?

2013 ◽  
Vol 70 (6) ◽  
pp. 1075-1080 ◽  
Author(s):  
Christopher M. Legault ◽  
Elizabeth N. Brooks
Keyword(s):  
Life History ◽  
Mortality Rate ◽  
Maximum Sustainable Yield ◽  
Reference Points ◽  
Sustainable Yield ◽  
Marine Science ◽  
Fishing Mortality ◽  
Scatter Plots ◽  
Stock Recruitment ◽  
Spawning Potential Ratio

Abstract Legault, C. M., and Brooks, E. N. 2013. Can stock–recruitment points determine which spawning potential ratio is the best proxy for maximum sustainable yield reference points? – ICES Journal of Marine Science, 70: 1075–1080. The approach of examining scatter plots of stock–recruitment (S–R) estimates to determine appropriate spawning potential ratio (SPR)-based proxies for FMSY was investigated through simulation. As originally proposed, the approach assumed that points above a replacement line indicate year classes that produced a surplus of spawners, while points below that line failed to achieve replacement. In practice, this has been implemented by determining Fmed, the fishing mortality rate that produces a replacement line with 50% of the points above and 50% below the line. A new variation on this approach suggests FMSY proxies can be determined by examining the distribution of S–R points that are above or below replacement lines associated with specific SPRs. Through both analytical calculations and stochastic results, we demonstrate that this approach is fundamentally flawed and that in some cases the inference is diametrically opposed to the method's intended purpose. We reject this approach as a tool for determining FMSY proxies. We recommend that the current proxy of F40% be maintained as appropriate for a typical groundfish life history.

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