OpenUCT :: Browsing by Author "Cunningham, Carryn L"

Browsing by Author "Cunningham, Carryn L"

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Open Access
Adjusted anchovy assessment with implications for OMP-08
(2008) Cunningham, Carryn L; Butterworth, Doug S
This corrected assessment fits the survey data better. Unlike for the previous assessment which used incorrect catch data, there now appears to be no compelling reason to change the juvenile natural mortality from the 0.9 yr-1 used for the 2004 assessment and in testing OMP-04, particularly since estimates of the ratios of biases for the acoustic survey abundances
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The assessment of Iberian sardine: A Bayesian State-Space model incorporating migration and Spatially-Disaggregated data
(2006) Cunningham, Carryn L; Roel, B A
One of the assessment models for Iberian sardine (Sardina pilchardus) to be considered as part of work package 7 of the EU-project Sardine Dynamics and Stock Structure in the North-East Atlantic (SARDYN), is that of a Bayesian state-space model. This model, based on the one developed for the North East Atlantic mackerel population (Cunningham 2002), explicitly models the migration of the sardine between different areas during the year and incorporates, where possible, new data resulting from other SARDYN work packages. This model is used to evaluate an initial set of alternative hypotheses of stock-structure and migration.
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Assessment of the South African anchovy resource
(2007) Cunningham, Carryn L; Butterworth, Doug S
The assessment of the South African anchovy resource has been updated from the last assessment (Cunningham and Butterworth 2004) to take account of new data and data adaptations as follows: i) an update in the time series of November spawner biomass and May recruitment estimates from acoustic surveys, such that the new time series reflects uncapped estimates of biomass based on new target strength calculations throughout, ii) a new method of using a monthly cut-off length to split recruits from 1-year-olds in the commercial catch (previously recruits and 1-year-olds were assumed to be caught in different months), and iii) new data for 2004 to 2006 which were not included in the last assessment conducted in 2004. In addition, this assessment has been modified from previous assessments to include: iv) a plus group of age 4 (previously anchovy were assumed to spawn at age 4 and then die), v) accounting for the introduction of the additional season by assuming the juvenile catch was taken in a pulse on 15th June prior to 1999 and on 15th July from 1999 onwards, and iv) the adult catch now assumed to be taken in a pulse on 1st April (previously assumed to be taken halfway between November and March). This document details the updated assessment model and gives the assessment results for the base case and robustness tests.
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Base case assessment of the South African sardine resource
(2007) Cunningham, Carryn L; Butterworth, Doug S
The assessment of the South African sardine resource is in the process of being updated. This document outlines the base case assessment which has been updated from the last assessment (Cunningham and Butterworth 2004) to take account of new data.
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A Bayesian state-space model for mixed-stock migrations, with application to Northeast Atlantic mackerel Scomber scombrus
(National Inquiry Services Centre (NISC), 2007) Cunningham, Carryn L; Reid, D G; McAllister, M K; Kirkwood, G P; Darby, C D
Management of fisheries that exploit mixed-stock populations relies on assumptions made concerning stock structure and mixing in different areas. To address the problems of accounting for uncertainty when formulating scientific advice for the management of highly migratory fish stocks, management decisions need to be based upon assessment models that represent plausible alternative hypotheses for stock structure and migration patterns of the exploited populations. We present a multi-stock, multi-fleet, multi-area, seasonally structured Bayesian state-space model in which different stocks spawn in spatially different areas and the mixing of these stocks is explicitly accounted for in the absence of sufficient tagging data with which to estimate migration rates. The model is applied to the Northeast Atlantic mackerel Scomber scombrus population, accounting for the annual spawning-feeding-overwintering migration patterns of the three spawning components, together with uncertainty in the extent to which the southern component migrates north to feed and overwinter, and consequently the extent to which it mixes with the other components and is subject to exploitation. The model allows the effect of exploitation on the individual components to be assessed, and the results suggest that the fishing mortality of southern spawning adults was insensitive to the extent to which they migrated north.
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Development and testing of OMP-08
(2007) Cunningham, Carryn L; Butterworth, Doug S
The current Operational Management Procedure (OMP-04) for the South African sardine and anchovy resources is due to be updated and replaced by OMP-08 by the end of 2007. A number of iterations of proposed “Straw” OMP-08 options have been presented thus far. This document details the latest proposed OMP-08 option, termed here “Straw3” OMP-08 and numerous results are given for this case, for alternative constraints within the OMP rules and for alternative underlying assessment (operating model) assumptions.
Open Access
The estimation of uncapped acoustic survey biomass from capped data
(2007) Cunningham, Carryn L; Butterworth, Doug S; Coetzee, J
Management of the South African sardine and anchovy resources is critically dependent on estimates of recruitment and spawner biomass obtained from hydroacoustic surveys. These surveys commenced in 1984, but in 1997 new equipment (an EK500 echo sounder) replaced the older EK400 echo sounder. The introduction of the EK500 echo sounder revealed a saturation problem with the EK400 echo sounder, particularly for sardine (Coetzee 2003). Survey estimates since June 1997 were initially ‘capped’ at - 29dB for assessment purposes, to maintain a comparable time-series from 1984.
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Further analyses regarding the exceptional circumstances provisions for OMP-08
(2008) Cunningham, Carryn L; Butterworth, Doug S
OMP-08 was implemented for the South African sardine and anchovy resources in December 2007, with provisional rules governing the declaration of exceptional circumstances. It was agreed that the rules and thresholds for exceptional circumstances provisions would be finalised before June 2008 and some initial tests and alternatives to these exceptional circumstances provisions were given in Cunningham and Butterworth (2008b). This document presents some further analyses relating to the rules and thresholds for exceptional circumstances provisions for OMP-08. During such analyses it has become evident that the anchovy risk threshold could be reconsidered in the light of new results; this is also addressed in this document.
Open Access
Further considerations for OMP-08
(2008) Cunningham, Carryn L; Butterworth, Doug S
OMP-08 has been updated following the recommendations of the Pelagic Working Group. The implications of such changes to the OMP are shown in this document, together with the implications for some further alternatives to the sardine and anchovy exceptional circumstances rules and the additional season anchovy TAC rule.
Open Access
Further robustness tests for the South African anchovy and sardine resources, including maturity-at-age
(2005) Cunningham, Carryn L; Butterworth, Doug S
Cunningham and Butterworth (2004d) presented some results of robustness tests to the base case assessments of South African sardine and anchovy resources. A comparison between some summary statistics resulting when the resources were projected using OMP-04 was also made. However, a few of those results were still preliminary, given the poor convergence diagnostics for some of the MCMC chains simulated for the Bayesian analyses.
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Further update: Proposals for issues to be addressed in the revision of the pelagic OMP
(2006) Cunningham, Carryn L; Butterworth, Doug S
The present models all assume a single southern Benguela sardine population. Is there sufficient evidence to consider as plausible an alternative that there could be two populations, with one distributed more towards the east and of a size that is not trivially small compared to the “conventional” population fished off the west coast? For a two-population scenario, would the May recruit survey be regarded as indexing recruitment for the “west” population only; further, need the model attempt to incorporate spatial distribution shifts over time for the two populations
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Initial sardine and anchovy TACs and sardine TAB for 2007, using Re-Revised OMP-04
(2006) Cunningham, Carryn L; Butterworth, Doug S
As the observed sardine biomass was less than 800 thousand tonnes, the recently accepted modification to the directed sardine TAC came into effect (Cunningham and Butterworth 2006). This resulted in the directed sardine TAC dropping more than the maximum of 15% from the previous year’s TAC that would otherwise have applied unless the biomass estimate had been below the Exceptional Circumstances level of 250 thousand tonnes.
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Initial sardine and anchovy TACs and sardine TAB for 2008, using OMP-08
(2007) Cunningham, Carryn L; Butterworth, Doug S
Following the recent 2007 spawner biomass survey, the initial 2008 TACs for South African sardine and anchovy and initial sardine TAB are to be recommended. The following data have been used: 1) November 2007 survey sardine 1+ biomass: 260 685 tonnes. 2) November 2007 survey anchovy spawner biomass: 2 507 501 tonnes. 3) Directed sardine TAC for 2006: 162 436 tonnes. 4) Directed anchovy normal season TAC for 2006: 386 942 tonnes1 . Using the above data, the initial 2008 TACs and TAB recommendations are calculated by OMP-08 to be: Directed sardine TAC: 90 776 tonnes Initial normal season anchovy TAC: 247 500 tonnes Initial normal season sardine TAB: 28 565.9 tonnes The equations used to calculate these TAC/Bs are given in the appendix.
Open Access
Is the sardine population now outside the range tested for OMP-04, and if so, what are the implications for the basis for recommending a 2007 directed sardine TAC
(2006) Cunningham, Carryn L; Butterworth, Doug S
The below average recruitment to the sardine population in 2004 and 2005 has sparked concern as to whether this has taken the population outside the range projected when OMP-04 was tested. OMP-04 (Cunningham and Butterworth 2005) was developed on the basis of assessments taking data up to November 2003 into account, a period ending when the sardine biomass was at a peak (Cunningham and Butterworth 2004).
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Issues surrounding the development of a revised OMP for the SA pelagic fishery for sardine and anchovy
(2006) Cunningham, Carryn L; Butterworth, Doug S
The current Operational Management Procedure (OMP) for South African sardine and anchovy, OMP-04, is based on assessments using data up to November 2003 (Cunningham and Butterworth 2004a,b). This OMP will need to be updated in the near future to take account, in particular, of: i) Updated series of observed spawner biomass and recruitment, following correction for the saturation effect (capping), new target strength expressions and signal attenuation in dense sardine schools (Coetzee et al. 2006). The previous assessments did include an updated series, but this was not based on an entirely satisfactory calibration analysis. The assessment also needs to be updated to take further survey results since 2003 into account. In particular, recent surveys suggest that the peak in sardine abundance is now past, and this will impact a re-assessment of the stock-recruitment relationship to which resource projections are particularly sensitive.
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Making management procedures operational—innovations implemented in South Africa
(Oxford University Press, 2007) Plagányi, Éva E; Rademeyer, Rebecca A; Butterworth, Doug S; Cunningham, Carryn L; Johnston, Susan J
Operational management procedures (OMPs) have become an indispensable fisheries management tool in South Africa in light of their ability to consider the consequences of the main sources of assessment uncertainty. An overview is provided of the MP approaches applied to the major South African fisheries for hake, sardine and anchovy, and west coast rock lobster. As these are among the first OMPs to be implemented worldwide, some for periods longer than 10 y, they provide useful examples of some of the successes and problems encountered with the approach. Particular emphasis is given to some recent innovations and adaptations. These include moves to (i) joint two-species OMPs for the hake and sardine/anchovy resources; (ii) a reference set of weighted operating models for primary testing and tuning in preference to a single model; (iii) consideration of a “research-conditional” approach for hake to allow greater catches in the short term, conditional on research being implemented to resolve a key uncertainty; and (iv) incorporation of some ecosystem considerations by developing appropriate robustness tests (which link with moves towards an ecosystem approach to fisheries). Key lessons gained from experience over the past decade of OMP implementation in South Africa are summarized.
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Modelling the proportion of sardine and anchovy in the diet of Cape gannets: some initial investigations
(2006) Cunningham, Carryn L; Butterworth, Doug S
The breeding success, and consequently population size, of Cape Gannets has been hypothesised to be strongly dependent on the size of the sardine and anchovy resources in South Africa. The quantification of such relationships is a pre-requisite for attempts to tailor management approaches for these fish resources so as to take adequate account of the needs of predators for which these species provide forage. As a first step towards this end, this document presents the results from some analyses of the relationships between the contributions in percentage (by mass) of sardine and of anchovy in the diet of Cape Gannets to the abundances of these resources.
Open Access
MSYR—should the information which has become available since selections were made for RMP development in 1987 have changed perceptions on the likely range and relative plausibilities of values for this parameter for baleen whales
(2007) Butterworth, Doug S; Punt, A E; Cunningham, Carryn L
It is argued that continued attempts to estimate MSYR from accumulating data, to refine the plausible range of values for this parameter and relative plausibilities within this range, cannot be other than a crucial component of the process of development (and, in due course, refinement) of the Revised Management Procedure (RMP) and of the interpretation of the results of the associated Implementation Simulation Trials (ISTs) for particular RMP applications. In 1987, when the range of MSYR values for RMP trials was first specified, four of the six independent sources of information available suggested definite "low" MSYR values (~1%). None of these four sources appears to have survived to the present. Estimates of MSYR for twenty populations have become available since 1987 - eleven based on population model fits and the balance on the relationship MSYR > r(0)/2. Two arguments advanced previously against the use of this last relationship are considered: the one is dismissed because it lacks support in empirical data, while the other appears negated by an analysis by Best (1993). In the fourteen cases where estimates of MSYR (in terms of uniform selectivity harvesting on the 1+ population) are determined with reasonable precision, most lie in the 2%-6% range, and only one of these has a lower 90 or 95% confidence/probability bound below 1%. Cases of low point estimates of MSYR show wide confidence intervals not incompatible with this 2-6% range. Thus, evidence forthcoming since 1987 (much of it subsequent to 1993 when the Scientific Committee last discussed this issue substantively) would seem to support a change in the Committee's perception at that time of the likely range of values for MSYR for baleen whale stocks, as well as informing judgments on the relative plausibilities of values within this range.
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OMP-04 under robustness test to the base case assessments of the South African anchovy and sardine resources
(2004) Cunningham, Carryn L; Butterworth, Doug S
The results at the posterior mode for some robustness tests to the base case sardine and anchovy assessments were presented in Cunningham and Butterworth (2004x). These results are repeated here together with a few further tests, including a robustness test designed to mimic a perceived slower growth in sardine since 2000. New results presented in this document include those obtained from projecting the resource into the future using OMP-04 and the fishery management system outlined in Cunningham and Butterworth (2004c). The thresholds and rules for exceptional circumstances provisions as recommended in Cunningham and Butterworth (2004z) are used for all projections with OMP-04 in this document. Such projections are initially done using the results from the posterior modes in order that tests that show a substantial difference could be singled out. Bayesian analyses of these selected tests were then run and the resource projected using the Bayesian results.
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OMP-08 development, with preliminary results
(2007) Cunningham, Carryn L; Butterworth, Doug S
The current Operational Management Procedure (OMP-04) for the South African sardine and anchovy resources is due to be updated and replaced by OMP-08 by the end of 2007. This document details the framework used to test the new management procedure and provides some VERY preliminary results.