Evaluation of a management decision rule for a New Zealand rock lobster substock

1997 ◽  
Vol 48 (8) ◽  
pp. 1093 ◽  
Author(s):  
Paul J. Starr ◽  
Paul A. Breen ◽  
Ray H. Hilborn ◽  
Terese H. Kendrick
Keyword(s):  
New Zealand ◽  
Decision Rule ◽  
Maximum Sustainable Yield ◽  
Assessment Model ◽  
Management Decision ◽  
Catch Per Unit Effort ◽  
Rock Lobster ◽  
Management Actions ◽  
Age Structured ◽  
The Impact

The performance of a proposed management ‘decision rule’–an algorithm that specifies management actions when specified criteria are met–was evaluated by exploring the impact of different choices for three decision-rule parameters on the ability of the rule to achieve management objectives. To do this, forward simulations from an age-structured assessment model for the substock of red rock lobster (Jasus edwardsii) off southern New Zealand were used. The size of this substock is currently estimated to be about one-third of BMSY (the level of vulnerable biomass that would produce maximum sustainable yield), and the management goal is to rebuild it to BMSY. A target rebuilding trajectory to BMSY was generated by allowing the model population to rebuild under the current catch regime with constant recruitment. The decision rule is based on comparison of observed catch per unit effort (CPUE) to predicted CPUE. Process and observation errors, each with a coefficient of variation of 20%, were introduced, and five values were used for each of the three parameters of the rule. The decision rule was effective in removing all instances of failure to rebuild and all excessively slow rebuilding trajectories. The decision rule was also applied to an arbitrarily depressed starting substock size, and the conclusions were the same.

Modeling no-take marine reserves in regulated fisheries: assessing the role of larval dispersal

2008 ◽  
Vol 65 (11) ◽  
pp. 2509-2523 ◽  
Author(s):  
Carey R. McGilliard ◽  
Ray Hilborn
Keyword(s):  
Larval Dispersal ◽  
Marine Reserves ◽  
Dispersal Distance ◽  
Maximum Sustainable Yield ◽  
Catch Per Unit Effort ◽  
Long Distance ◽  
Total Allowable Catch ◽  
Dispersal Distances ◽  
The Impact

We explored the effects of larval dispersal distance on the impact of no-take marine reserves (NTMRs) implemented in fisheries with catch regulations. NTMRs exist in many fisheries with harvest regulated by annual catch limits. In these fisheries, catch is taken from outside NTMRs, potentially resulting in reduced abundance outside NTMRs and an overall reduction in catch. We used a spatial model with two life stages (larvae and adults) to evaluate the effects of larval dispersal distance for fisheries managed by a total allowable catch (TAC) and an NTMR. We examined effects of the timing of density-dependent mortality in relation to larval movement. Abundance reached similar values for populations with long and short larval dispersal distances. Catch declined substantially for stocks with short larval dispersal distances. When larval dispersal distances were long, catch declined to values below maximum sustainable yield (MSY), but stabilized. Catch per unit effort (CPUE) declined to 9% of CPUE at MSY for stocks with short distance larval dispersal after the implementation of an NTMR; with long distance larval dispersal, CPUE declined to approximately 50% or less of the CPUE at MSY. The CPUE did not reflect trends in abundance after the implementation of an NTMR.

Performance of a fisheries catch-at-age model (Stock Synthesis) in data-limited situations

2011 ◽  
Vol 62 (8) ◽  
pp. 927 ◽  
Author(s):  
Chantell R. Wetzel ◽  
André E. Punt
Keyword(s):  
Stock Assessment ◽  
Estimation Method ◽  
Assessment Method ◽  
Assessment Model ◽  
Limited Data ◽  
Composition Data ◽  
Spawning Stock ◽  
Age Model ◽  
Age Structured ◽  
The Impact

Limited data are a common challenge posed to fisheries stock assessment. A simulation framework was applied to examine the impact of limited data and data type on the performance of a widely used catch-at-age stock-assessment method (Stock Synthesis). The estimation method provided negatively biased estimates of current spawning-stock biomass (SSB) relative to the unfished level (final depletion) when only recent survey indices were available. Estimation of quantities of management interest (unfished SSB, virgin recruitment, target fishing mortality and final depletion) improved substantially even when only minimal-length-composition data from the survey were available. However, the estimates of some quantities (final depletion and unfished SSB) remained biased (either positively or negatively) even in the scenarios with the most data (length compositions, age compositions and survey indices). The probability of overestimating yield at the target SSB relative to the true such yield was ~50%, a risk-neutral result, for all the scenarios that included length-composition data. Our results highlight the importance of length-composition data for the performance of an age-structured assessment model, and are encouraging for the assessment of data-limited stocks.

Parameterizing age-structured models from a fisheries management perspective

2008 ◽  
Vol 65 (8) ◽  
pp. 1586-1600 ◽  
Author(s):  
Steven J.D. Martell ◽  
William E. Pine ◽  
Carl J. Walters
Keyword(s):  
Analytical Solution ◽  
Maximum Sustainable Yield ◽  
Assessment Model ◽  
Informative Priors ◽  
Biological Variables ◽  
Management Perspective ◽  
Stock Recruitment ◽  
Age Structured ◽  
Management Advice ◽  
Two Parameters

Age-structured models are widely used in fisheries stock assessments and contain two very important parameters that determine the rate and amount of harvest that can be safely taken: the compensation rate in juvenile survival (κ) and the unfished biomass (Bo). These two parameters are often confounded. It is common for relative abundance indices to lack contrast, and the use of informative priors, or fixing at least one of these parameters, is necessary to develop management advice. Providing management advice proceeds by transforming estimates of biological variables such as Bo and κ into management variables such as the maximum sustainable yield (C*) and the fishing mortality rate that would achieve this yield (F*). There is no analytical solution for the transformation of Bo, κ to C*, or F* for age-structured models with commonly used stock–recruitment functions and therefore must be done numerically. The opposite transition, however, does have an analytical solution for both the Beverton–Holt and Ricker recruitment models with partial selectivities for all age classes. Use of these analytical solutions allows for age-structured assessment models to be directly parameterized in terms of the management variables C* and F*. The effects of informative priors on C* and F* on the results of the assessment model are completely transparent to management.

A length-based Bayesian stock assessment model for the New Zealand abalone Haliotis iris

2003 ◽  
Vol 54 (5) ◽  
pp. 619 ◽  
Author(s):  
Paul A. Breen ◽  
Susan W. Kim ◽  
Neil L. Andrew
Keyword(s):  
New Zealand ◽  
Stock Assessment ◽  
Assessment Model ◽  
Data Sets ◽  
Catch Per Unit Effort ◽  
Commercial Catch ◽  
Data Set ◽  
Future Directions ◽  
Common Component ◽  
Joint Posterior Distribution

We describe a length-based Bayesian model for stock assessment of the New Zealand abalone Haliotis iris (paua). We fitted the model to five data sets: catch-per-unit-effort (CPUE) and a fishery-independent survey index, proportions-at-length from both commercial catch sampling and population surveys, and tag–recapture data. We estimated a common component of error and used iterative re-weighting of the data sets to balance the residuals, removing the arbitrary data set weightings used in previous assessments. Estimates at the mode of the joint posterior distribution were used to explore sensitivity of the results to model assumptions and input data; the assessment itself was based on marginal posterior distributions estimated from Markov chain–Monte Carlo simulation. Assessments are presented for two stocks in the south of New Zealand. One may be recovering after recent catch reductions; the other is over-exploited and likely to decline further. Assessment for the first stock was robust; assessment for the second stock was sensitive to the CPUE data and may be too optimistic. We discuss future directions and potential problems with this approach.

scholarly journals Trade-offs between invertebrate fisheries catches and ecosystem impacts in coastal New Zealand

2015 ◽  
Vol 72 (5) ◽  
pp. 1380-1388 ◽  
Author(s):  
Tyler D. Eddy ◽  
Marta Coll ◽  
Elizabeth A. Fulton ◽  
Heike K. Lotze
Keyword(s):  
New Zealand ◽  
Maximum Sustainable Yield ◽  
Trophic Levels ◽  
Management Approach ◽  
Ecosystem Structure ◽  
Catch Per Unit Effort ◽  
Ecosystem Impacts ◽  
Ecosystem Effects ◽  
Trade Offs ◽  
Exploitation Rate

Abstract Invertebrate catches are increasing globally following the depletion of many finfish stocks, yet stock assessments and management plans for invertebrates are limited, as is an understanding of the ecosystem effects of these fisheries. Using an ecosystem modelling approach, we explored the trade-offs between invertebrate catches and their impacts on the associated ecosystem on the south coast of Wellington, New Zealand. We simulated exploitation of lobster (Jasus edwardsii), abalone (Haliotis australis, H. iris), and sea urchin (Evechinus chloroticus) over a range of depletion levels—from no depletion to local extinction—to estimate changes in target catches and associated effects on other species groups, trophic levels, and benthic and pelagic components. Exploitation of lobster showed the strongest ecosystem effects, followed by abalone and urchin. In all three fisheries, the current exploitation rate exceeds that which produces maximum sustainable yield, with considerable ecosystem effects. Interestingly, a reduced exploitation rate is predicted to increase target catches (and catch-per-unit-effort), thereby strongly reducing ecosystem effects, a win–win situation. Our results suggest that invertebrate exploitation clearly influences ecosystem structure and function, yet the direction and magnitude of responses depend on the target group and exploitation rate. An ecosystem-based fisheries management approach that includes the role of invertebrates would improve the conservation and management of invertebrate resources and marine ecosystems on broader scales.

Analysis of the impact of stoats, Mustela erminea, on northern brown kiwi, Apteryx mantelli, in New Zealand

1999 ◽  
Vol 26 (2) ◽  
pp. 227 ◽  
Author(s):  
B. Basse ◽  
J. A. McLennan ◽  
G. C. Wake
Keyword(s):  
New Zealand ◽  
Population Analysis ◽  
Recruitment Rate ◽  
Predator Control ◽  
Mustela Erminea ◽  
Small Areas ◽  
Structured Population ◽  
A Value ◽  
Age Structured ◽  
The Impact

An age-structured population analysis is used to determine recruitment levels and a condition for survival which can assist management decisions and hence improve the viability of populations of northern brown kiwi, Apteryx mantelli, in forests on the New Zealand mainland. Currently, in the absence of predator control, recruitment rates are less than 5% due to high levels of stoat, Mustela erminea, predation on juvenile kiwi. Predation levels on adult kiwi are very low. The analysis predicts that a recruitment rate of 19% is required to maintain population stability. To achieve this target, stoat populations have to be reduced by about 80% in some years, and maintained at a critical residual density estimated to be a value less than two animals per square kilometre for up to nine months until immature kiwi reach a safe size of about 1200 g (50% of their adult weight). Recent predator-control initiatives indicate that stoat numbers can be reduced and maintained at low levels in relatively small areas of mainland forest (up to 1000 ha). New techniques are needed to protect kiwi over larger areas.

scholarly journals Assessment of offshore shrimp stocks of Bangladesh based on commercial shrimp trawl logbook data

2018 ◽  
Vol 65 (1) ◽  
Author(s):  
Suman Barua ◽  
Arni Magnusson ◽  
Nasiruddin MD Humayun
Keyword(s):  
Confidence Intervals ◽  
Maximum Sustainable Yield ◽  
Reference Points ◽  
Assessment Model ◽  
Catch Per Unit Effort ◽  
Harvest Rate ◽  
Stock Size ◽  
Considerable Uncertainty ◽  
Logbook Data

This study presents the results of analytical assessment of offshore shrimp stock in Bangladesh marine waters. A time series of annual catch per unit effort (CPUE) was derived from commercial logbook data during the period from 1986 to 2016 and used as a turning series for a Schaefer biomass model. The current stock size and annual harvest rate were estimated to be around 20300 t and 20% respectively, with the stock size increasing in the last ten years. The estimated maximum sustainable yield (MSY) reference points with 95% confidence intervals are optimal biomass BMSY = 15800 t (11300-22000 t) and optimal harvest rate uMSY = 30% (21-42%). The average annual catch was 4650 t, close to the estimated MSY of 4710 t (4570-4860 t). Overall, the stock is estimated to be in a good state and the data show that CPUE in recent years is slightly above the long-term average. The assessment results are subject to considerable uncertainty, reflected in wide confidence intervals around the estimated stock status. Moreover, the simple assessment model has restrictive assumptions that may not capture the underlying dynamics of the Bangladesh shrimp fishery, a multispecies tropical fishery with changes in the fleet composition and fishing technology. Nevertheless, the model fits well to the CPUE data and the assessment is a valuable basis for giving short-term and long-term management advice.

scholarly journals The advantage of explicitly incorporating predation mortality into age-structured stock assessment models: an application for Atlantic mackerel

2009 ◽  
Vol 66 (3) ◽  
pp. 445-454 ◽  
Author(s):  
H. Moustahfid ◽  
J. S. Link ◽  
W. J. Overholtz ◽  
M. C. Tyrrell
Keyword(s):  
Stock Assessment ◽  
Fish Predation ◽  
Reference Points ◽  
Assessment Model ◽  
Fishing Mortality ◽  
Atlantic Mackerel ◽  
Predation Mortality ◽  
Spawning Stock ◽  
Age Structured ◽  
The Impact

AbstractMoustahfid, H., Link, J. S., Overholtz, W. J., and Tyrrell, M. C. 2009. The advantage of explicitly incorporating predation mortality into age-structured stock assessment models: an application for Atlantic mackerel. – ICES Journal of Marine Science, 66: 445–454. An age-structured assessment programme (ASAP) that explicitly incorporates predation mortality was applied to Atlantic mackerel (Scomber scombrus) in the Northwest Atlantic. Predatory removals were modelled in the same manner as fishing mortality, with a comparable set of time-series, to produce estimates of predation mortality at age and for each year. Results from the analysis showed that incorporating predation into a mackerel stock assessment model notably altered model outputs. When excluding explicitly modelled rates of predation, the model underestimated the magnitude and uncertainty in spawning-stock biomass (SSB) and recruitment. Further, the rates of predation mortality varied across time and were higher for younger fish. Predation mortality was higher than fishing mortality for fish aged 1 year, approximately equal for 2-year-olds, and lower for older fish (3 years and older). Biological reference points for Atlantic mackerel differed considerably when predation mortality was included. For example, SSBMSY was more than twice as high in the model where predation was incorporated than in the fisheries-only model. Although there are several caveats to the predation model outputs, chief of which is that the estimates are conservative because some mackerel predators were excluded, the results demonstrate the feasibility of executing such an approach with an extant tool. The approach presented here ultimately has the advantage of detecting, and upon detection parsing out, the impact of predators relative to fisheries and has the potential to provide useful information to those interested in small pelagic fish and their associated fisheries.

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