Sustainability assessment for fishing effects (SAFE) on highly diverse and data-limited fish bycatch in a tropical prawn trawl fishery

2009 ◽  
Vol 60 (6) ◽  
pp. 563 ◽  
Author(s):  
Shijie Zhou ◽  
Shane P. Griffiths ◽  
Margaret Miller
Keyword(s):  
Mortality Rate ◽  
Fishery Management ◽  
Sustainability Assessment ◽  
Cost Effective ◽  
Mortality Rates ◽  
Assessment Method ◽  
Reference Points ◽  
Fishing Mortality ◽  
Point Estimates ◽  
Large Numbers

A new sustainability assessment for fishing effects (SAFE) method was used to assess the biological sustainability of 456 teleost bycatch species in Australia’s Northern Prawn Fishery. This method can quantify the effects of fishing on sustainability for large numbers of species with limited data. The fishing mortality rate of each species based on its spatial distribution (estimated from detection/non-detection data) and the catch rate based on fishery-dependent or fishery-independent data were estimated. The sustainability of each species was assessed by two biological reference points approximated from life-history parameters. The point estimates indicated that only two species (but 21 when uncertainty was included) had estimated fishing mortality rates greater than a fishing mortality rate corresponding to the maximum sustainable yield. These two species also had their upper 95% confidence intervals (but not their point estimates) greater than their minimum unsustainable fishing mortality rates. The fact that large numbers of species are sustainable can be attributed mainly to their wide distributions in unfished areas, low catch rates within fished areas and short life spans (high biological productivity). The present study demonstrates how SAFE may be a cost-effective quantitative assessment method to support ecosystem-based fishery management.

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.

scholarly journals Optimal fishing mortality assignment for southern hake Merluccius australis in Chile

2020 ◽  
Vol 48 (4) ◽  
pp. 613-625
Author(s):  
Felipe Lopez ◽  
Jorge Jimenez ◽  
Cristian Canales
Keyword(s):  
Mortality Rate ◽  
Economic Benefit ◽  
Mortality Rates ◽  
Fish Population ◽  
Fishing Effort ◽  
Economic Benefits ◽  
Historical Background ◽  
Total Catch ◽  
Fishing Mortality ◽  
Objective Functions

Since 1979, southern hake (Merluccius australis) has been exploited in Chile from the Bio Bio to the Magallanes regions, between the parallels 41°28.6'S and 57°S. There is evidence of a constant fishing effort and a sustained reduction of the fish population, consistent with a progressive decrease in total annual catches. Management strategies based on the maximum sustainable yield (MSY) and quota assignment/ distribution criteria have not been able to sustain acceptable biomass levels. A non-linear optimization model with two objective functions was proposed to determine an optimal total catch quota for more sustainable exploitation of this fishery. The first function maximizes the total catch over time in response to an optimal assignment of fishing mortality rates per fleet; the second function maximizes the total economic benefit associated with the total catch. The dynamics of the fish population were represented with the equations of a predictive age-structured model. Decision variables were fishing mortality rates and annual catch quotas per fleet, subject to constraints that guarantee a minimum level of biomass escape over a long-term period. The input parameters were obtained from the last stock evaluation report carried out by the Instituto de Fomento Pesquero (IFOP) of Chile. The historical background data of the fishery and the regulatory framework were relevant aspects of the methodology. Five scenarios were evaluated with the two objective functions, including a base scenario, which considered the referential mortality rate as input data as the average mortality rate per fleet from 2007 to 2012. Total economic benefits fluctuate between 102 and USD 442 million for total catches in the range of 108 to 421 thousand tons, which were obtained from maximizing the economic and biological objective functions. Economic benefit/catch ratios were reduced for scenarios with higher constraints on catch limits, and they were more efficient from a biological point of view. Situations with lighter constraints showed in general higher economic benefits and better performance ratios than those with stronger restrictions. The use of optimization models may provide a useful tool to evaluate the effect of regulations for adequate conservation and economical utilization of a limited resource.

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

2014 ◽  
Vol 72 (1) ◽  
pp. 137-150 ◽  
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.

Eggs-per-recruit model for management of the California market squid (Loligo opalescens) fishery

2005 ◽  
Vol 62 (7) ◽  
pp. 1640-1650 ◽  
Author(s):  
Michael R Maxwell ◽  
Larry D Jacobson ◽  
Ramon J Conser
Keyword(s):  
Mortality Rate ◽  
Egg Laying ◽  
Reference Points ◽  
Model Parameters ◽  
Natural Mortality ◽  
Fishing Mortality ◽  
Loligo Opalescens ◽  
Maturation Rate ◽  
Sampling Procedures ◽  
Yield Per Recruit

We develop a per-recruit model for the management of the California market squid (Loligo opalescens) fishery. Based on recent confirmation of determinate fecundity in this species, we describe how catch fecundity (i.e., eggs remaining in the reproductive tracts of harvested females) can be used to simultaneously infer fishing mortality rate along with management reference points such as yield-per-recruit, spawned eggs-per-recruit, and proportional egg escapement. Rates of mortality and egg laying have important effects on these reference points. Somewhat surprisingly, increasing the rate of natural mortality decreased spawned eggs-per-recruit while increasing proportional egg escapement. Increasing the rate of egg laying increased both spawned eggs-per-recruit and egg escapement. Other parameters, such as the maturation rate and gear vulnerability of immature females, affected the reference points. In actual practice, the influence of these parameters for immature squid may go undetected if immature squid are excluded from analysis of the catch. Application of this model to routine management is feasible but requires refinement of sampling procedures, biological assumptions, and model parameters. This model is useful because it is grounded on empirical data collected relatively inexpensively from catch samples (catch fecundity) while allowing for the simultaneous calculation of instantaneous fishing mortality rate and egg escapement.

scholarly journals Discard mortality rates in the Bering Sea snow crab, Chionoecetes opilio, fishery

2015 ◽  
Vol 72 (5) ◽  
pp. 1525-1529 ◽  
Author(s):  
J. Daniel Urban
Keyword(s):  
Mortality Rate ◽  
Bering Sea ◽  
Fishery Management ◽  
Stock Assessment ◽  
Mortality Rates ◽  
Snow Crab ◽  
Commercial Fishing ◽  
Chionoecetes Opilio ◽  
Discard Mortality ◽  
The Bering Sea

Abstract Fish and invertebrates that are unintentionally captured during commercial fishing operations and then released back into the ocean suffer mortality at unknown rates, introducing uncertainty into the fishery management process. Attempts have been made to quantify discard mortality rates using reflex action mortality predictors or RAMP which use the presence or absence of a suite of reflexes to predict discard mortality. This method was applied to snow crab, Chionoecetes opilio, during the 2010–2012 fisheries in the Bering Sea. Discard mortality in the fishery is currently assumed to be 50% in stock assessment models, but that rate is not based on empirical data and is widely recognized to be in need of refinement. Over 19 000 crab were evaluated using the RAMP method. The estimated discard mortality rate was 4.5% (s.d. = 0.812), significantly below the rate used in stock assessment models. Predicted discard mortality rates from the 2010 to 2012 study were strongly correlated with the air temperature at the St Paul Island airport in the Pribilof Islands. Using this relationship, the discard mortality rate from 1991 to 2011 was estimated at 4.8% (s.d. = 1.08).

A data-limited method for assessing cumulative fishing risk on bycatch

2019 ◽  
Vol 76 (4) ◽  
pp. 837-847 ◽  
Author(s):  
Shijie Zhou ◽  
Ross M Daley ◽  
Michael Fuller ◽  
Cathy M Bulman ◽  
Alistair J Hobday
Keyword(s):  
Sustainability Assessment ◽  
Cumulative Risk ◽  
Additive Model ◽  
Mixture Distribution ◽  
Fishing Effort ◽  
Reference Points ◽  
Distribution Model ◽  
Fishing Mortality ◽  
Bayesian Mixture ◽  
Gear Efficiency

Abstract To assess fishing effects on data-poor species, impact can be derived from spatial overlap between species distribution and fishing effort and gear catchability. Here, we enhance the existing sustainability assessment for fishing effect method by estimating gear efficiency and heterogeneous density from sporadic catch data. We apply the method to two chondrichthyan bycatch species, Bight Skate and Draughtboard Shark in Australia, to assess cumulative fishing mortality (Fcum) from multiple fisheries. Gear efficiency is estimated from a Bayesian mixture distribution model and fish density is predicted by a generalized additive model. These results, combined with actual fishing effort, allow estimation of fishing mortality in each sector and subsequently, the Fcum. Risk is quantified by comparing Fcum with reference points based on life history parameters. When only the point estimates were considered, our result indicates that for the period 2009 and 2010 Bight Skate caught in 14 fisheries was at high cumulative risk (Fcum ≥ Flim) while Draughtboard Shark caught by 19 fisheries was at low cumulative risk (Fcum ≤ Fmsy). Because of the high cost of conducting cumulative risk assessments, we recommend examining the distribution of fishing effort across fisheries before carrying out the assessments.

Island in the Stream: Oceanography and Fisheries of the Charleston Bump

2001 ◽  
Keyword(s):  
North Atlantic ◽  
Fishery Management ◽  
Population Analysis ◽  
Mortality Rates ◽  
Fishing Mortality ◽  
Stock Biomass ◽  
The Status ◽  
Eastern North Atlantic ◽  
Charleston Bump ◽  
Definition Of

<em> Abstract.</em>—The status of the wreckfish <em> Polyprion americanus </em>stock caught on the Blake Plateau in the southeastern United States Atlantic was analyzed by calibrated virtual population analysis (VPA) to estimate trends in fishing mortality and population (or stock) biomass. Calibration of the FADAPT VPA program was to fishery-dependent catch-per-unit effort (CPUE) for a range in assumed values for natural mortality (M). Age-length keys were developed from two aging studies of wreckfish (1988– 1992 and 1995–1998). Keys were developed annually (pooled across seasons to create three “annual” age-length keys to represent 1988–1990, 1991–1993, and 1994–1998) and seasonally (pooled across years to create three seasonal age-length keys to represent April–June, July–September, and October to end of fishing year on 15 January). Analyses based on both annual and seasonal catch matrices showed similar patterns and values, with the seasonal catch matrix producing slightly lower estimates of fishing mortality rates (F) and higher estimates of biological reference points based on F. Fishing mortality rates peaked in 1989, as did the maximum annual U.S. landings (4.2 million pounds). Subsequently, both landings and fishing mortality rates have generally declined. Although stock biomass has generally declined over the study period, recruitment at age 7 has risen since about 1994. Meanwhile, annual estimates of static spawning potential ratio (SPR), which are inversely related to F, have risen since 1994. Fishing mortality rates from recent low landings are at or near the South Atlantic Fishery Management Council’s threshold definition of overfishing (static SPR of 30%), while the process of rebuilding with improving recruitment appears to be underway. Concern persists because the assessment is based on the underlying assumption that wreckfish from the Blake Plateau form a single stock separate from the eastern North Atlantic and genetic evidence suggests the stock encompasses the entire North Atlantic.

scholarly journals Measurement Error Affects Risk Estimates for Recruitment to the Hudson River Stock of Striped Bass

2002 ◽  
Vol 2 ◽  
pp. 238-253 ◽  
Author(s):  
Dennis J. Dunning ◽  
Quentin E. Ross ◽  
Stephan B. Munch ◽  
Lev R. Ginzburg
Keyword(s):  
Measurement Error ◽  
Mortality Rate ◽  
Striped Bass ◽  
Power Plants ◽  
Fishery Management ◽  
Hudson River ◽  
Management Plan ◽  
Fishing Mortality ◽  
Beach Seine ◽  
Indian Point

We examined the consequences of ignoring the distinction between measurement error and natural variability in an assessment of risk to the Hudson River stock of striped bass posed by entrainment at the Bowline Point, Indian Point, and Roseton power plants. Risk was defined as the probability that recruitment of age-1+ striped bass would decline by 80% or more, relative to the equilibrium value, at least once during the time periods examined (1, 5, 10, and 15 years). Measurement error, estimated using two abundance indices from independent beach seine surveys conducted on the Hudson River, accounted for 50% of the variability in one index and 56% of the variability in the other. If a measurement error of 50% was ignored and all of the variability in abundance was attributed to natural causes, the risk that recruitment of age-1+ striped bass would decline by 80% or more after 15 years was 0.308 at the current level of entrainment mortality (11%). However, the risk decreased almost tenfold (0.032) if a measurement error of 50% was considered. The change in risk attributable to decreasing the entrainment mortality rate from 11 to 0% was very small (0.009) and similar in magnitude to the change in risk associated with an action proposed in Amendment #5 to the Interstate Fishery Management Plan for Atlantic striped bass (0.006)— an increase in the instantaneous fishing mortality rate from 0.33 to 0.4. The proposed increase in fishing mortality was not considered an adverse environmental impact, which suggests that potentially costly efforts to reduce entrainment mortality on the Hudson River stock of striped bass are not warranted.

Evaluation of quota management policies for developing fisheries

1998 ◽  
Vol 55 (12) ◽  
pp. 2691-2705 ◽  
Author(s):  
Carl Walters
Keyword(s):  
Mortality Rate ◽  
Relative Abundance ◽  
Cumulative Effect ◽  
Mortality Rates ◽  
Reference Trajectory ◽  
Fishing Mortality ◽  
Small Probability ◽  
Abundance Indices ◽  
Management Policies ◽  
Quota Management

Losses can be measured as deviations from a desired reference trajectory of quotas that would be taken if there were no uncertainty and are highly dependent on assessments prior to and during development. Simulations of assessment and quota setting under various quota setting rules indicate that variability in relative abundance indices can cause substantial losses, especially considering cumulative effect of early quota errors on later departures of biomass from that needed to produce the desired quotas, even if optimum fishing mortality rate is known in advance. Conservative assessments (low biomass estimates for which there is only a small probability that biomass is actually lower) are favored during development when loss is measured as the relative departure from the best quota for each year. But if loss is measured as absolute departure from the best quota, it is generally better to base the quota on the biomass estimate for which there is nearly a 50% chance that the stock is smaller. Deliberate overfishing (probing) is not favored under either loss measure. Losses can be reduced with minimum biomass surveys and closed areas that directly cushion fishing mortality rates from being more than 50% too low or high.

Incorporating Uncertainty into Fishery Models

2002 ◽  
Keyword(s):  
Mortality Rate ◽  
Blue Crab ◽  
Stock Assessment ◽  
Probability Distributions ◽  
Mortality Rates ◽  
Fishing Mortality ◽  
Statistical Hypothesis Testing ◽  
Control Laws ◽  
Decision Confidence ◽  
The Status

<em>Abstract.—</em>Stock assessment methodology has increasingly employed statistical procedures as a means to incorporate uncertainty into assessment advice. Deterministic values of fishing mortality rates (<em>F<sub>t </sub></em>) estimated from assessment models have been replaced by empirical distributions that can be compared with an appropriate biological reference point (<em>F</em><sub>BRP</sub>) to generate statements of probability (e.g., Pr[<em>F<sub>t </sub></em>≥ <em>F</em><sub>BRP</sub>]) regarding the status of the resource. It must be recognized, however, that terminal year fishing mortality rates and the biological reference points to which they are compared are both estimated with error, which will impact the quality of decisions regarding the status of the stock. We propose a two-tier stochastic decision-based framework for a recently conducted stock assessment of the Delaware Bay blue crab stock that specifies not only the probability for the condition Pr(<em>F<sub>t </sub></em>≥ <em>F</em><sub>BRP</sub>), but also the statistical level of confidence (i.e., 90%) in that decision. The approach uses a mixed Monte Carlobootstrap procedure to estimate probability distributions for both the terminal year fishing mortality rate (<em>F<sub>t </sub></em>) and the replacement fishing mortality rate, approximated by <em>F</em><sub>MED</sub> as an overfishing definition. Probability density functions (PDFs) for <em>F<sub>t </sub></em>and <em>F</em><sub>MED</sub>, generated using the mixed Monte Carlo-bootstrap procedure, show that recent fishing mortality rates (80% CI from 0.6 to 1.2) are generally below the <em>F</em><sub>MED</sub> overfishing definition (80% CI from 0.9 to 1.6), with significant overlap in the PDFs. Using the PDFs, the stochastic decision-based approach then generates a probability profile by integrating the area under the <em>F<sub>t </sub></em>PDF for different decision confidence levels (e.g. 90%, 80%, 70%, etc.), which can be thought of as one-tailed <em>α</em>-probability from standard statistical hypothesis testing. For example, at the 80% decision confidence level (value of <em>F </em>corresponding to the upper 20% of the <em>F</em><sub>MED</sub> PDF), Pr(<em>F<sub>t </sub>> F</em>MED) is about 0.03. Thus, with high confidence (80%), we can state that the blue crab stock is not currently being overfished. This approach can be extended to decisions regarding control laws that specify both maximum fishing rate and minimum biomass thresholds.

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