REPORT OF THE WORKSHOP ON TRAWL SURVEY ... - FAO.org

• The use of robust parameters of general application in population dynamics such as the “Life
Expectancy”, as an integral of the survival.
• Application of a non-equilibrium surplus production model assessment using
MEDITS data (by Tserpes G., Haralabous J. and Maravelias C.)
Abstract: Biomass and MSY estimates for the hake stocks in the Greek seas were obtained from a non-equilibrium
surplus model approach utilizing CPUE time series derived from the MEDITS surveys and fishery production data.
The model was developed in the freely available R-language and the results demonstrated the existence of fisheries
over-exploitation.
• Permanent control of the state of trawl fisheries started in 1997 (By Djurovic M.)
Abstract: Estimated population dynamics parameters of important species: Pandora, Pagellus erythrinus, Red
Mullet, Mullus barbatus, Hake, Merluccius merluccius, Pink shrimp, Parapaeneus longirostris. Estimated total
biomass of economical important demersal resources on the shelf area (hake, red mullet, red pandora, squid,
octopus, pink shrimp) was about 2 700 tons.. Estimated MSY of demersal resources was 600 tons per year.
Estimated average catch per unit effort (CPUE) of demersal resources last four years was about 19.47 kg/h. In
October 2004 and February 2007 in frame of FAO Adriamed Project has been performed AdriMed trawl survey
(MEDITS protocol) in Montenegrin territorial and adjacent waters. In 1997 CPUE has fallen to 20 kg/h and for the
last few years this value did not change. This indicates that some kind of the state of equilibrium was reached
between fishing effort and resources.
Conclusions from the Session 2
14. The main conclusions from the discussion following the presentations are summarized
below:
• It has been noted that analyses of time series data trends derived from surveys, other
than of MEDITS, are also performed.
• Since the first MEDITS surveys covered only those species listed in the primary and
secondary list of the sampling manual, it has been pointed out that the consistency of
data should be checked when analyzing spatio-temporal variations for those species
not included in any of the above-mentioned MEDITS lists.
• Assessment studies should be supported besides the MEDITS data with all the data
available such as the fishing effort or commercial catch data.
• The use of trawl surveys data in tuning the application of analytical models for stock
assessment was stressed.
• It was noted that in the Mediterranean region the data for defining nursery areas of
hake already exist and this should be taken into account for recommending closed
areas when needed.
• The experience achieved in the ICES region by the trawl surveys should encourage
Mediterranean scientists to engage in common activities on assessment studies.
SESSION 3. APPLICATION TEST FOR SURPLUS PRODUCTION MODELS
15. The aim of this session was to test an application of surplus production models with the
data brought by the participants. The application was made during the meeting with a tool at
the participants’ disposal. The methods and the information to be brought by the participants
are described in a document made available on the GFCM website before the workshop. Mr
Alvaro Abella was the moderator for this application test.
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