- If the spawning stock falls below B(pa), the procedure for establishing TAC should be based on a fishing mortality that is linearly reduced from F(pa) at B(pa) to F = 0 at SSB equal to zero. At SSB-levels below B(pa) in any of the operational years (current year and a year ahead) there should be no limitations on the year-to-year variations in TAC.
ICES Advice on TAC for NEA haddock for 2008
Based on the assessment provided by AFWG-2007, the catch for 2008 should in accordance with the rule be less than 178 000 tonnes.
However, HCRs are not recommended by ICES for the management of NEA haddock in 2008. ICES stated in their 2007 report on the TAC level for 2008 the following:
"... the management plan was only in agreement with the precautionary approach in the absence of implementation error. Unreported landings have increased in recent years (2002-2006). When implementation errors of this order of magnitude are used in the simulations, the agreed management plan is no longer in agreement with the precautionary approach."
"No stock assessment has been accepted since the revision of the catch data in 2006. This revision resulted in a substantially different perception of the stock dynamics."
Thus, due to the absence of a reliable assessment of stock status and high level of implementation error the advice from ICES on TAC for NEA Haddock for 2008 was not made on the basis of the agreed HCR but based on the other considerations:
"The recent increase in SSB (through the years 2001-2004) has been associated with catches less than 130 000 tonnes (including misreported catches). In the absence of a reliable assessment and since these catches appear to have led to an increase in the stock, ICES recommends keeping catches below this level."
The main reason why the haddock assessment was not accepted was that the trends in the stock abundance from the surveys and from the VPA are substantially different. This is illustrated in Fig. 1.
Haddock, 3+, VPA vs. Survey
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Fig. 1. Biomass of age 3 and older haddock (1000 tonnes), calculated from the VPA as well as from the survey indices. When calculating biomass from survey indices, the same weight at age as in VPA is used. VPA and Norwegian surveys are shown on the left axis, the Russian survey is shown on the right axis.
4. Harvest control rule for Northeast Arctic Saithe
Norway has asked ICES to evaluate a proposal for a management strategy for Northeast Arctic saithe:
"to evaluate whether the harvest control rule for setting the annual fishing quota (TAC) is consistent with the precautionary approach. The proposed harvest control rule contains the following elements:
- Estimate the average TAC level for the coming 3 years based on F(pa), TAC for the next year will be set to this level as a starting value for the 3-year period.
- The year after, the TAC calculation for the next 3 years is repeated based on the updated information about the stock development, however, the TAC should not be changed by more than +/- 15% compared with the previous year's TAC.
- If the spawning stock biomass (SSB) in the beginning of year for which the quota is set (first year of prediction), is below B(pa), the procedure for establishing TAC should be based on a fishing mortality that is linearly reduced from F(pa) at SSB = B(pa) to 0 at SSB equal to zero. At SSB-levels below B(pa) in any of the operational years (current year and 3 years of prediction) there should be no limitations on the year-to-year variations in TAC."
ICES concluded that the HCR is consistent with the precautionary approach for all simulated data and settings, including a rebuilding situation under the condition that the assessment uncertainty and error are not greater than those calculated from historic data. This also holds true when an implementation error (difference between TAC and catch) equal to the historic level of 3% is included.
The highest long-term yield was obtained for an exploitation level of 0.32, i.e. a little below the target F used in the HCR (F(pa)), and ICES recommends using a lower value in the HCR. The HCR is expected to rebuild a depleted stock to a level above B(lim) within three years.
Technical details of the evaluation of the harvest control rule are provided in the Appendix.
The advice on levels of catch and effort for 2008 is consistent with the harvest control rule for Northeast Arctic saithe provided in ICES advice.
5. Optimal long-term harvest in the Barents Sea Ecosystem
The work of IMR and PINRO on the joint Program for estimation of optimal longterm harvest in the Barents Sea Ecosystem adopted at the 33rd session of the Commission continues.
At the meeting in Svanhovd in September 2007, the work in the following subprojects was summarized: cod growth, recruitment, including fecundity and skipped spawning, and cannibalism. These subprojects have so far been the main ones. At the meeting in Svanhovd the approaches for implementation of regressions on cod growth rate and skipped spawning in the population models were agreed. Capelin abundance and temperature are identified as the main ecosystem factors that influence cod stock dynamics. During the first stage of the project these were the primary ecosystem factors taken into account for estimation cod long-term yield. The inclusion in estimations of other ecosystem factors such as plankton, herring and marine mammals in estimations of long-term yield of cod will be realized in the next stage of the project.
During the first stage of the project, three models: EcoCod, STOCOBAR and Bifrost were developed as tools for estimation of long-term yield and optimization of the cod management strategies in the ecosystem aspect. The descriptions of these models are presented on the web-site of the project (www.assessment.imr.no/Request/index.html). All of these models have both advantages and shortcomings. All models satisfactorily describe the necessary biological processes (growth, maturation, recruitment, cannibalism), however, they treat uncertainties to a different extent. In this respect Bifrost is the most advanced. It is planned to hold a joint meeting in February 2008 that will be devoted to testing the developed models and to estimating of reliability in calculations of maximum long-term yield for cod.
Two working meetings between the specialists from PINRO and IMR within the framework of the joint Programme of research were held in 2007 (one in Murmansk and one in Svanhovd).
The annual report on joint work will be presented by the co-ordinators of the project in PINRO and IMR at the meeting of scientists in March 2008.
APPENDIX:
3.3.3 Special requests
3.3.3.1 Norwegian request for advice on Northeast Arctic saithe (Suhareas I and II)
Norway has asked ICES lo evaluate a proposal for a management strategy lor Northeast Arctic saithe:
to evaluate whether the harvest control rule for setting the annual fishing quota (TAC) is consistent with the precautionary approach. The proposed harvest control rule contains the following elements:
- Estimate the average TAC level for the coming 3 years based on Fpa, TAC for the next year will be set to this level as a starting value for the 3-year period.
- The year after, the TAC calculation, for the next 3 years is repealed based on the updated information about the slock development, however, the TAC should not be changed by more than +/- 15% compared with the previous year's TAC.
- If the spawning stock biomass (SSB) in the beginning of year for which the quota is set (first year of prediction), is below Bpa, the procedure for establishing TAC should be based on a fishing mortality that is linearly reduced from Fpa at SSB=Bpa to 0 at SSB equal to zero. At SSB-levels below Bpa in any of the operational years (current year and 3 years of prediction) there should be no limitations on the year-to-year variations in TAC.
ICES comments
The evaluation of the harvest control rule is provided below. The advice on levels of catch and effort for 2008 consistent with the harvest control rule for Northeast Arctic saithe is provided in Section 3.4.4.
ICES concluded that the HCR is consistent with the precautionary approach for all simulated data and settings, including a rebuilding situation under the condition that the assessment uncertainty and error are not greater than those calculated from historic data. This also holds true when an implementation error (difference between TAC and catch) equal lo the historic level of 3% is included.
The highest long-term yield was obtained for an exploitation level of 0.32, i.e. a little below the target F used in the HCR (F(pa)), and ICES recommends using a lower value in the HCR.
The ICES is expected to rebuild a depleted stock to a level above B(lim) within three years.
Technical Annex to the ICES response
The evaluation of HCRs for Northeast Arctic saithe has been carried out using simulation models. Important issues for the evaluation of harvest control rules are the choice of population model, inclusion of uncertainty in population model, the choice of initial values for simulations, the formulation of harvest control rules for use in the evaluation (constant F rules, how to reduce F when SSB < B(pa), limit on year-to-year variation in catch, etc.), and performance measures for harvest control rules (yield, stock size, F, probability of SSB < B(lim), annual variation in catches, etc.). The evaluation of the HCR takes the implementation error into account.
The model used for Nortlieast Arctic saithe was:
- A Beverton-Holt spawning stock-recruitment model with a log-normal error distribution.
- Assessment error and bias are estimated as age-dependent, normally distributed.
- Density-dependent weight-at-age in catch (average for 1981-2005 used for age groups where density-dependence was not found).