Report of the Working Group on Mackerel and Horse Mackerel Egg Surveys (WGMEGS)
The ICES Working Group on Mackerel and Horse Mackerel Egg Surveys (WGMEGS), chaired by Cindy van Damme (IMARES, The Netherlands) and Finlay Burns (MSS, UK), met in Galway from 18–21 April 2012, to plan the Mackerel and Horse Mackerel Egg Survey in 2012. For the first time Iceland participated in the meeting. As in 2010 both the Faroe Islands and Iceland will contribute to the triennial survey with their own vessel in addition to the participation of Portugal, Spain, Scotland, Ireland, The Netherlands, Norway and Germany. The main aim of the survey is to relate the number of freshly spawned eggs found in the water to the number of females having produced these eggs. Knowing the fecundity of the females and sex ratio provides an estimate for the spawning-stock biomass.
As in 2010, the 2013 survey has been based on six sampling periods, again commencing with the Portuguese DEPM survey for horse mackerel (Section 3 of the report). There continues to be no participation from Cefas at a time when the temporal and spatial broadening of mackerel and horse mackerel distribution during spawning has led to a considerable expansion of the potential survey area. This, combined with other ship-time restrictions, created difficulties with the 2010 survey with respect to defining egg distribution boundaries for both species. The working group anticipates that these problems might become even more prominent in future. The group stresses, that in future triennial surveys only the participation of more states exploiting mackerel and horse mackerel will enable sufficient coverage of the spawning area over the complete reproductive periods of both species.
Prior to the WGMEGS meeting a Workshop on Survey Design and Mackerel and Horse Mackerel Spawning Strategy (WKMSPA) was convened. At WKMSPA evidence was presented that supported the conclusion that both mackerel and horse mackerel are most likely to be indeterminate spawners. In indeterminate spawners it is not possible to determine a reliable estimate of potential fecundity. An estimate using DEPM being more suitable for a reliable SSB estimate of indeterminate spawners. It was decided that during the 2013 survey WGMEGS will carry out an AEPM as in previous years to continue the time-series of mackerel and horse mackerel egg production estimates and mackerel SSB estimates. However WGMEGS will also try to carry out intensive DEPM sampling in the peak spawning periods (mackerel period 3, horse mackerel period 5) to attempt a DEPM SSB estimate and thereby facilitating a comparison using both methods.
Sampling protocols for mackerel and horse mackerel fecundity analysis were established during the meeting (Sect. 4), for adoption of both AEPM and DEPM sampling schemes. Fecundity analysis will be conducted by Norway (IMR), the Netherlands (IMARES), Scotland (MSS), Ireland (MI) and Spain (IEO and AZTI). Sampling procedures will be finalized during the fecundity workshop in Vigo, October, 2012.
In order to produce reliable preliminary egg production estimates, any participant unable to process samples to the required deadline will have to achieve an agreement about the selection of egg sample subsets in liaison with the survey data coordinator, WGMEGS chairs and an independent referee.
In preparation of the 2013 survey a workshop dealing with egg identification and staging will be held in Ĳmuiden in November, 2012. Procedures for fecundity and atresia estimation will be standardized and training conducted on the fecundity workshop to be held in Vigo in October 2012. Once again WGMEGS points out that these workshops are essential for quality assurance of the mackerel and horse mackerel egg surveys.
The survey manual (Annex 5) was updated where necessary. It will be further improved during the workshops in autumn.
The manual on fecundity and atresia estimation was also updated (Annex 6). It is planned to be further improved during the workshop in Vigo.
Between 30 May and 2 July 2011 the Netherlands and Norway conducted the Mackerel Egg Survey in the North Sea (Section 7). The main spawning area was detected in the southwest of the surveyed area, but peak of egg production was in the first sampling period. No mackerel ovaries could be collected for potential fecundity estimation because the survey only took place during peak spawning and prespawning females were rare. North Sea mackerel fecundity will be monitored in between the survey years. The North Sea mackerel SSB was calculated as 165,000 tons.
The group discussed SCICOM’s recommendation to consolidate icthyoplankton survey EGs, in particular WGMEGS, WGEGGS, WCACEGG, SGSIPS and related workshops into 1 large working group. After careful evaluation of the pros and cons associated with such a merger the group decided to remain as an autonomous working group. This decision was based primarily around the necessity of provision and continued delivery of quality assured survey results that underpin the WGWIDE assessments for these species.
Published under the auspices of the following ICES Steering Group or Committee
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