Report of the Planning Group on North Sea Cod and Plaice Egg Surveys in the North Sea (PGEGGS)
reportposted on 2007-01-01, 00:00 authored by ICESICES
The Planning Group on North Sea Cod and Plaice Egg Surveys (PGEGGS) was set up to address the fact that there had never been a complete ichthyoplankton survey of the North Sea. In particular, the need to monitor commercial fish spawning areas was identified by the Expert Panel which followed the Bergen Ministerial Meeting. Although spawning grounds can be monitored to some extent by adult trawl surveys, ichthyoplankton surveys have a number of potential advantages. Since individual fish spawn thousands of eggs it is often more reliable to sample the eggs rather than the adult fish and surveying spawning grounds of species producing planktonic eggs is also not restricted by bottom-type so a more complete spatial coverage can be achieved. In addition, if the area can be repeatedly surveyed over the spawning period, an estimate of total annual egg production can be made. When combined with fecundity data, such estimates are useful as additional stock assessments and can act as a validation of stock assessments made using standard methods based on commercial fisheries data.Because of the current poor state of the cod and plaice stocks, it was decided to focus on those species. Given the scale of the proposed ichthyoplankton survey it was hardly surprising that it took several years to organise but finally in 2004 the field-work was undertaken. This work has now resulted not only in the most complete maps of cod and haddock spawning areas in the North Sea ever produced but also distribution maps of several other species of interest, in an egg-production estimate for plaice in the southern North Sea and new insights into the relationship between hydrography and fish egg and larval distributions.Clearly a single survey, even of the scale undertaken is of limited value since we need to build up a picture of changes over time. This is especially relevant as we are most probably entering a period of rapid environmental change that may exacerbate the conservation challenges of dealing with low stock sizes for valuable species such as cod and plaice.Following a meeting of PGEGGS in Copenhagen (22–24 November 2005) and the adoption of the latest ToR, the group was asked to work by correspondence to begin planning for a repeat survey in 2009. Because PGEGGS relies upon national support to undertake field work, the countries who participated in the 2004 survey, plus France, were contacted.
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