Blue marlin mean length: simulated response to increasing fishing mortality

Mean length of caught fish often declines noticeably with increased fishing mortality and this trend is regarded as an indicator of excessive fishing mortality. The most recent stock assessment results for Atlantic blue marlins and Atlantic white marlins indicate that these stocks are heavily overfished. However, available data do not suggest a strong trend of decreasing lengths of marlins in the catch. The lack of such a trend has been used to argue that the assessment results are in error. This study uses population simulation to characterize the expected response of the size distribution of blue marlin to the vector of fishing mortality and FMSY estimated for the base case in the most recent stock assessment, and contrasts the results with a similar analysis for Atlantic swordfish. The results indicate that blue marlin should not be expected to exhibit strong trends in mean length with respect to fishing mortality within the range of fishing mortality estimated in the most recent stock assessment, and that the trends in the observed size composition are consistent with the findings of the stock assessment. The findings indicate that declining mean length is not a necessary outcome of excessive fishing mortality in all species.

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PRELIMINARY STOCK ASSESSMENT RESULTS FOR SHAD IN AZOV-BLACK SEA BASIN IN TERMS OF DATA LUCKING (2007–2020)

Ecology Economy Informatics System analysis and mathematical modeling of ecological and economic systems ◽

10.23885/2500-395x-2021-1-6-34-39 ◽

2021 ◽

Vol 1 (6) ◽

pp. 34-39

Author(s):

I.D. Kozobrod ◽

◽

M.M. Piatinski

Keyword(s):

Black Sea ◽

Stock Assessment ◽

Safe Zone ◽

Fishing Mortality ◽

Stock Status ◽

Azov Sea ◽

Stock Biomass ◽

Stock Recovery ◽

Assessment Results

Black-azov sea shad Alosa immaculate (Bennett, 1835) stock assessment performed by trending model CMSY in terms of data lucking for period 2007–2020 in R. Model results showed current stock status in biological safe zone (B2020 = 2291 t, BMSY = 1855 t, B2020/BMSY = 1,23) with signs of minor overexploitation by fishing mortality (F2020 = 0,35, FMSY = 0,28, F2020/FMSY = 1,25). Obtained stock biomass estimates shows minor Black-Azov sea shad stock recovery evidence in period 2007–2020. Evidence of light population fishery overexploitation after 2018 are found, perhaps, was caused by IUU-fishery. Paper results underline to eliminate and regulate shad illegal, unreported, unregistered fishery in Azov-Black sea basin

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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 ◽

10.1093/icesjms/fsq029 ◽

2010 ◽

Vol 67 (6) ◽

pp. 1185-1197 ◽

Cited By ~ 16

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.

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The influence of metrics for spawning output on stock assessment results and evaluation of reference points: An illustration with yellowfin tuna in the eastern Pacific Ocean

Fisheries Research ◽

10.1016/j.fishres.2018.09.022 ◽

2019 ◽

Vol 217 ◽

pp. 35-45 ◽

Cited By ~ 2

Author(s):

Carolina V. Minte-Vera ◽

Mark N. Maunder ◽

Kurt M. Schaefer ◽

Alexandre M. Aires-da-Silva

Keyword(s):

Pacific Ocean ◽

Stock Assessment ◽

Yellowfin Tuna ◽

Reference Points ◽

Eastern Pacific ◽

Eastern Pacific Ocean ◽

Assessment Results

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An integrated tagging model to estimate mortality rates of Albemarle Sound – Roanoke River striped bass

Canadian Journal of Fisheries and Aquatic Sciences ◽

10.1139/cjfas-2016-0141 ◽

2017 ◽

Vol 74 (7) ◽

pp. 1061-1076 ◽

Cited By ~ 6

Author(s):

Julianne E. Harris ◽

Joseph E. Hightower

Keyword(s):

Striped Bass ◽

Stock Assessment ◽

Mortality Rates ◽

Natural Mortality ◽

Fishing Mortality ◽

Albemarle Sound ◽

High Reward ◽

Accuracy And Precision ◽

Summer Mortality ◽

Roanoke River

We developed an integrated tagging model to estimate mortality rates and run sizes of Albemarle Sound – Roanoke River striped bass (Morone saxatilis), including (i) a multistate component for telemetered fish with a high reward external tag; (ii) tag return components for fish with a low reward external or PIT tag; and (iii) catch-at-age data. Total annual instantaneous mortality was 1.08 for resident (458–899 mm total length, TL) and 0.45 for anadromous (≥900 mm TL) individuals. Annual instantaneous natural mortality was higher for resident (0.70) than for anadromous (0.21) fish due to high summer mortality in Albemarle Sound. Natural mortality for residents was substantially higher than currently assumed for stock assessment. Monthly fishing mortality from multiple sectors (including catch-and-release) corresponded to seasonal periods of legal harvest. Run size estimates were 499 000–715 000. Results and simulation suggest increasing sample size for the multistate component increases accuracy and precision of annual estimates and low reward tags are valuable for estimating monthly fishing mortality rates among sectors. Our results suggest that integrated tagging models can produce seasonal and annual mortality estimates needed for stock assessment and management.

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POPULATION BIOLOGY OF MUD CRAB Scylla serrata - Forsskal, 1775 IN MANGROVE ECOSYSTEM OF SUBANG DISTRICT, WEST JAVA

Jurnal Ilmu dan Teknologi Kelautan Tropis ◽

10.28930/jitkt.v9i1.17928 ◽

2017 ◽

Vol 9 (1) ◽

pp. 173

Author(s):

Ayu Annisa Kumalah ◽

Yusli Wardiatno ◽

Isdradjad Setyobudiandi ◽

Achmad Fahrudin

Keyword(s):

Population Dynamics ◽

Size Distribution ◽

Population Biology ◽

Stock Assessment ◽

Mangrove Ecosystem ◽

Mature Female ◽

Scylla Serrata ◽

Mud Crab ◽

Growth Coefficient ◽

Exploitation Rate

The study of population biology of mud crab Scylla serrata is necessary to analyse the population dynamics, such as growth of crabs, size distribution, mortality and exploitation rates of S. serrata. Population biology data collection was carried out from March to June 2016 at estuary and silvofishery areas of three stations (Mayangan, Tanjung Tiga and Blanakan villages). Data were analyzed using analytical methods of FISAT-II (FAO-ICLARM Stock Assessment Toool II)instruments. The results showed the growth of S. serrata male in Subang distric was positive allometric and the female was negative allometric. Growth coefficient (K) ranged from 0.21 to 0.43 in the estuary and from 0.28 to 0.89 in silvofishery area. Exploitation rate in the silvofishery area has been above the maximum exploitation rate. The size distribution of S. serrata in Subang district has the highest frequency at class interval of 106-110 mm (male) and of 101-105 mm. The highest abundance of mature female crabs is in May.Keywords : population biology, Scylla serrata, Subang District

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Population dynamics and stock assessment of Hilsa shad, Tenualosa ilisha (Hamilton, 1822) along the coast of Bangladesh

Bangladesh Journal of Zoology ◽

10.3329/bjz.v48i2.52365 ◽

2021 ◽

Vol 48 (2) ◽

pp. 231-241

Author(s):

Md Khairul Islam ◽

Md Humayun ◽

Manmatha Nath Sarker ◽

Md Sharifuddin ◽

M Niamul Naser

Keyword(s):

Growth Parameters ◽

Stock Assessment ◽

Population Analysis ◽

Total Mortality ◽

Maximum Sustainable Yield ◽

Fishing Mortality ◽

Recruitment Pattern ◽

Weight Relationship ◽

Tenualosa Ilisha ◽

Highly Correlated

Stock Assessment of Tenualosa ilisha (Hamilton, 1822) were estimated using FiSAT-II software with length-frequency data collected from different landing centers. The Southeast Coast of Bay Of Bengal, Cox's Bazar. The Von Bertalanffy growth parameters Land K for the species were asymptotic length (L∞) was 51.41 cm, growth rate (K) was 0.75 year-1 and t0 = -0.2 year respectively. The estimated value of total mortality (Z) based on length converted catch curve using these growth parameters was 2.35 year-1.Natural mortality (M) based on growth parameters and mean environmental temperature (T = 27° C) was 1.00 year-1 and fishing mortality (F) was 1.35 year-1. Optimum length of hilsa at first capture (Lc=L50) was 28.36 cm TL. Growth performance indices (ϕ') was 3.30. The estimated value of the exploitation rate (E) using the length-converted catch curve was 0.57. The recruitment pattern of this species was continuous and two peaks per year. The present investigation clearly showed the over fishing (E > 0.50) condition for T. ilisha in Bangladesh. The estimated length-weight relationship for the combined sex was found to be W = 0.0109 L3. Virtual population analysis (VPA) showed that the maximum fishing mortality occurring in the length between 30 to 35 cm with a maximum value in the length of 32 cm that repeatedly indicate high fishing mortality in the T. ilisha. The generalized length-weight relationship was fitted with the pooled data of all monthly samples were BW = 0.029 TL2.718 (R2= 0.833) respectively. The results revealed that all length-weight relationships were highly correlated (r > 0.993). Maximum sustainable yield (MSY) was estimated as 435,554 t. Bangladesh J. Zool. 48(2): 231-241, 2020

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Detecting mortality variation to enhance forage fish population assessments

ICES Journal of Marine Science ◽

10.1093/icesjms/fsy160 ◽

2018 ◽

Vol 76 (1) ◽

pp. 124-135 ◽

Cited By ~ 1

Author(s):

Nis S Jacobsen ◽

James T Thorson ◽

Timothy E Essington

Keyword(s):

Test Performance ◽

Size Structure ◽

Stock Assessment ◽

Reference Points ◽

Forage Fish ◽

Natural Mortality ◽

Time Varying ◽

Fishing Mortality ◽

Catch Data ◽

Over Time

Abstract Contemporary stock assessment models used by fisheries management often assume that natural mortality rates are constant over time for exploited fish stocks. This assumption results in biased estimates of fishing mortality and reference points when mortality changes over time. However, it is difficult to distinguish changes in natural mortality from changes in fishing mortality, selectivity, and recruitment. Because changes in size structure can be indicate changes in mortality, one potential solution is to use population size-structure and fisheries catch data to simultaneously estimate time-varying natural and fishing mortality. Here we test that hypothesis, using a simulation experiment to test performance for four alternative estimation models that estimate natural and fishing mortality from size structure and catch data. We show that it is possible to estimate time-varying natural mortality in a size-based model, even when fishing mortality, recruitment, and selectivity are changing over time. Finally, we apply the model to North Sea sprat, and show that estimates of recruitment and natural mortality are similar to estimates from an alternative multispecies population model fitted to additional data sources. We recommend exploring potential trends in natural mortality in forage fish assessments using tools such as the one presented here.

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Time-varying natural mortality in fisheries stock assessment models: identifying a default approach

ICES Journal of Marine Science ◽

10.1093/icesjms/fsu055 ◽

2014 ◽

Vol 72 (1) ◽

pp. 137-150 ◽

Cited By ~ 43

Author(s):

Kelli F. Johnson ◽

Cole C. Monnahan ◽

Carey R. McGilliard ◽

Katyana A. Vert-pre ◽

Sean C. Anderson ◽

...

Keyword(s):

Stock Assessment ◽

Assessment Method ◽

Reference Points ◽

Natural Mortality ◽

Time Varying ◽

Fishing Mortality ◽

Total Allowable Catch ◽

Robust Approach ◽

Structured Population Models ◽

Trade Offs

Abstract A typical assumption used in most fishery stock assessments is that natural mortality (M) is constant across time and age. However, M is rarely constant in reality as a result of the combined impacts of exploitation history, predation, environmental factors, and physiological trade-offs. Misspecification or poor estimation of M can lead to bias in quantities estimated using stock assessment methods, potentially resulting in biased estimates of fishery reference points and catch limits, with the magnitude of bias being influenced by life history and trends in fishing mortality. Monte Carlo simulations were used to evaluate the ability of statistical age-structured population models to estimate spawning-stock biomass, fishing mortality, and total allowable catch when the true M was age-invariant, but time-varying. Configurations of the stock assessment method, implemented in Stock Synthesis, included a single age- and time-invariant M parameter, specified at one of the three levels (high, medium, and low) or an estimated M. The min–max (i.e. most robust) approach to specifying M when it is thought to vary across time was to estimate M. The least robust approach for most scenarios examined was to fix M at a high value, suggesting that the consequences of misspecifying M are asymmetric.

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Integrating catch-at-age and multiyear tagging data: a combined Brownie and Petersen estimation approach in a fishery context

Canadian Journal of Fisheries and Aquatic Sciences ◽

10.1139/f05-232 ◽

2006 ◽

Vol 63 (3) ◽

pp. 534-548 ◽

Cited By ~ 34

Author(s):

Tom Polacheck ◽

J Paige Eveson ◽

Geoff M Laslett ◽

Kenneth H Pollock ◽

William S Hearn

Keyword(s):

Mortality Rate ◽

Population Size ◽

Stock Assessment ◽

Natural Mortality ◽

Fishing Mortality ◽

Catch Data ◽

Coefficients Of Variation ◽

Southern Bluefin Tuna ◽

Catch Rates ◽

Comprehensive Framework

A comprehensive framework for modelling data from multiyear tagging experiments in a fishery context is presented that incorporates catch data into the traditional Brownie tagrecapture model. Incorporation of catch data not only allows for improved estimation of natural and fishing mortality rates, but also for direct estimation of population size at the time of tagging. These are the primary quantities required to be estimated in stock assessments having an approach for directly estimating them that does not require catch rates provides a potentially powerful alternative for augmenting traditional stock assessment methods. Simulations are used to demonstrate the value of directly incorporating catch data in the model. Results from the range of scenarios considered suggest that in addition to providing a precise estimate of population size (coefficients of variation ranging from ~15% to 30%), including catch data can decrease biases in the mortality rate estimates (natural mortality especially) and improve precision of fishing mortality rate estimates (by as much as 60% at age 1). The model is applied to southern bluefin tuna (Thunnus maccoyii) tagrecapture and catch data collected in the 1990s to provide estimates of natural mortality, fishing mortality, and abundance for five cohorts of fish.

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Uncertainty estimation and model selection in stock assessment models with non-parametric effects on fishing mortality

ICES Journal of Marine Science ◽

10.1093/icesjms/fsx175 ◽

2017 ◽

Vol 75 (2) ◽

pp. 585-595

Author(s):

Leire Citores ◽

Leire Ibaibarriaga ◽

Ernesto Jardim

Keyword(s):

Stock Assessment ◽

Uncertainty Estimation ◽

Point Estimation ◽

Relative Bias ◽

Model Complexity ◽

Fishing Mortality ◽

Multivariate Normal ◽

Smooth Functions ◽

Coverage Probabilities ◽

Wide Range

AbstractUncertainty coming from assessment models leads to risk in decision making and ignoring or misestimating it can result in an erroneous management action. Some parameters, such as selectivity or survey catchabilities, can present a wide range of shapes and the introduction of smooth functions, which up to now have not been widely used in assessment models, allows for more flexibility to capture underlying nonlinear structures. In this work a simulation study emulating a sardine population is carried out to compare three different methods for uncertainty estimation: multivariate normal distribution, bootstrap (without and with relative bias correction) and Markov chain Monte Carlo (MCMC). In order to study their performance depending on the model complexity, five different scenarios are defined depending on the shape of the smooth function of the fishing mortality. From 100 simulated datasets, performance is measured in terms of point estimation, coefficients of variation, bias, skewness, coverage probabilities, and correlation. In all approaches model fitting is carried out using the a4a framework. All three methods result in very similar performance. The main differences are found for observation variance parameters where the bootstrap and the multivariate normal approach result in underestimation of these parameters. In general, MCMC is considered to have better performance, being able to detect skewness, showing small relative bias and reaching expected coverage probabilities. It is also more efficient in terms of time consumption in comparison with bootstrapping.

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