The Planning Group for the Coordination of Acoustic Surveys off Northwest Africa was held in Dakar, Senegal, from 22 to 23 October 2004. The meeting was the third of its kind, following two meetings in Dakar, Senegal, from 26 to 28 October 2002 and from 28 to 29October 2003. The general objective of the Planning Group is to plan the coordination of acoustic surveys in the region including intercalibration of research vessels and to act as a forum for discussion on issues important to acoustic surveys such as standardization of methods, acoustic research and training.
The meeting was organized by FAO in cooperation with the Oceanographic Research Centre Dakar-Thiaroye (CRODT) as one of the activities under project International cooperation with the Nansen Programme: Fisheries Management and Marine Environment (GCP/INT/730/NOR).
A total of eight scientists from Gambia, Mauritania, Morocco, Norway and Senegal participated in the meeting. The list of participants is provided in Appendix A. Mr Abdoulaye Sarre (CRODT, Senegal) was the Chairperson of the meeting. The revised Agenda for the meeting is attached as Appendix B.
The terms of reference of the Planning Group were to:
Mr Birane Samb, representative of CRODT, opened the meeting. He welcomed everyone and commented on the successful acoustic training course on target strength measurement held earlier in November.
After this opening Mr Sarre led the participants through the programme. The Agenda was approved with minor amendments. (Appendix B).
Many echograms were collected during the 2003 survey with R/V DR FRIDTJOF NANSEN. The echograms were collected from areas were trawl hauls yielded more than 75 percent of the target species, sardinella, sardine, anchovy and horse mackerel. The aim of this work was to aid operators in scrutinizing acoustic data during acoustic surveys. The first draft of the report is now available. It was recommended that the report be completed in order to have a reference collection of a large number of typical echograms from target species within the subregion.
Mauritanian representatives proposed to present some typical echograms from 38 kHz and 120 kHz transducer collected onboard R/V AL AWAM.
An acoustic survey will be conducted onboard R/V DR. FRIDTJOF NANSEN and local vessels in the region from 25 October 2004. The participants agreed that it is important to analyse the data from the parallel survey during the next year and finalize a common report.
The Gambian participant expressed the wish that the Senegalese R/V ITAF DEME be authorized to trawl in Gambia and do biomass estimation in his country during the upcoming survey. The fishing permit for R/V ITAF DEME in Gambia was not available for the 2004 October parallel survey. It was acknowledged by the Gambian representative that they needed to send a request to Senegal to participate in the Senegalese surveys. This had not yet been done.
The intercalibration between R/V DR. FRIDTJOF NANSEN and R/V AL AMIR MOULAY ABDALLAH in December 2003 was conducted. A report was produced from the experiment and would be made available to the participants of the survey working group. The results were analysed by using a regression curve of SA values recorded with the two vessels. The difference between the vessels was between 150 and 250 percent, which is a disturbingly high figure. Moroccan scientists explained the difference with fish avoidance due to the high noise level generated from their vessel. A Japanese expert would visit the vessel and look at the problem. A new intercalibration would be conducted during this year's parallel survey.
The target strength course was conducted successfully in Senegal from 12 to 21 October 2004. The course was conducted by Messrs E. Ona and I. Svellingen with the participation of two Moroccan, three Mauritanian, one Gambian and two Senegalese scientists. A report will be made available from the course describing the methodology, the different steps to follow to conduct TS measurements and some results. The participants were very satisfied with the course and only regretted that the course was too short to cover all subjects.
A recommendation from the Survey Planning Group was made to perform a regional TS measurement survey in the region with a local vessel where the participants from the TS course could put their new knowledge into practice. If possible this survey should be coordinated by FAO. It was emphasized that the TS results from such a survey is equally important for all the countries in the region, and that all countries should agree on the same TS constants for the different species to be used during their acoustic surveys. Until further studies were conducted, the function developed by Foote (1993) for Norwegian spring spawning herring, TS=20 log L-72 db, would be used as recommended in the Guidelines for acoustic surveys in the Northwest African region.
Senegal reconfirmed that they were interested in performing acoustic surveys in Gambia with Gambian personnel onboard. However, the Gambia should contribute to the vessel fuel cost of R/V ITAF DEME to cover their national waters, EEZ. Cooperation has not yet been put in place since Gambian authorities have not sent an official request to take part in these surveys. The Representative for the Gambia would follow up the matter in Gambia.
This issue was discussed last year, and it was revealed that the institutes in the region do not have a strategy for safeguarding survey data, and that data in the past had been accidentally deleted. Last year the Survey Planning Group recommended that the Steering Committee discuss a common strategy for the countries in the region to safeguard the survey data collected in the region. This issue was not discussed in detail during this year's Steering Committee meeting and the Survey Planning Group decided to renew this recommendation to the Steering Committee.
Mr Krakstad gave an orientation about survey data storage at the Institute of Marine Resources (IMR) and on the development of the new version of the Nan-Sis survey database that are being developed at IMR for surveys in the region. This database will be offered to the countries in the region free of charge.
R/V ITAF DEME
Two acoustic surveys were conducted in Senegal this year. The first was conducted to estimate the pelagic fish stocks during the cold season. The second survey was conducted to improve the performance of pelagic trawling onboard R/V ITAF DEME.
(a) Acoustic survey in March 2004
This survey was conducted from 23 March to 6 April. The south of Dakar was covered from 27 March to 2 April and the north from 2 to 4 April. A survey report is available.
General objectives
The acoustic survey forms part of the fish stock of the EEZ of Senegal, and its aim being to evaluate and map the distribution of coastal pelagic fish on the Senegalese continental shelf. The main aims are to:
The major finding during this survey was the presence of Sardina pilchardus found on the Petite Côte and the high biomass. The total biomass of all pelagic species was estimated to be 1568000tonnes, 30 percent being sardine. The main part of the sardinellas found were S.maderensis. The biomass of this species was estimated to be 383000 tonnes. For S. aurita the estimated biomass was only 36000 tonnes. T. trecae was present on the whole shelf and was predominant on the Petite Côte. The biomass was estimated to be 264000 tonnes.
(b) Trawl performance survey in June 2004
A survey to increase the performance of the pelagic trawl onboard R/V ITAF DEME was conducted in June 2004 with support of JICA and Japanese experts on trawling. A survey report is pending and should be available soon.
A new pelagic trawling technique was exercised during the survey. More training is needed before it is possible to see if this technique has improved trawling performance. However, this technique can only be used in areas deeper than 50 m. The first results are therefore not promising.
Acoustic TS training course survey
The survey was conducted as planned. A separate report attached to this document describes the training course and the survey (Appendix F).
R/V AL-AWAM
Two surveys were conducted between the two Planning Group meetings this year and last year. Survey reports are available.
The two surveys took place during an abnormal cold period characterized by intrusion of cold waters in Senegal. This is confirmed by the data from sea surface temperature maps and the presence in the region of species expected to be found only in temperate waters.
(a) Acoustic survey, 14–30 December 2003
The results showed the presence of sardine south of 18°00N. A high biomass of more than 4 million tonnes was estimated in December 2003.
(b) Acoustic survey, 13–28 April 2003
An intensive decrease of the temperatures was observed in the region as well as mixing of surface waters. The surface temperature was much lower than usual during the season, and upwelling was also low. Biomass was dominated by sardine (Sardina pilchardus) on the continental shelf both in the north and south of Mauritania, and was estimated to be more than 2 million tonnes.
R/V AL AMIR MOULAY ABDALLAH
An intercalibration was conducted with R/V DR. FRIDTJOF NANSEN in December 2003. A report is available from this survey.
The biomass of sardine during the parallel survey was estimated to be 180 000 tonnes. This biomass was much smaller than the biomass estimated by the Norwegian vessel, probably due to avoidance caused by noise from the Moroccan vessel. One must note that Morocco is searching for a solution to the noise problem and that no further acoustic surveys will be conducted before this problem has been solved.
R/V DR. FRIDTJOF NANSEN
From 30 October to 19 December 2003, R/V DR. FRIDTJOF NANSEN conducted a survey of the whole Northwest African region from the border between Guinea Bissau and Senegal to north of Agadir in Morocco. Survey reports are available from the survey and were handed out to participants of the workshop. The survey was conducted within the framework of the cooperation with FAO and the Nansen Programme, project GCP/INT/730/NOR and the countries in the region. The biomass estimated during the survey was as follows:
| Sardina pilchardus | : 5 652 000 tonnes |
| Sardinella aurita | : 1 260 000 tonnes |
| Sardinella maderensis | : 1 769 000 tonnes |
| Engraulis encrasicolis | : 29 000 tonnes |
| Trachurus trachurus | : 320 000 tonnes |
| Trachurus trecae | : 1 239 000 tonnes |
The summary sheet with main results from each vessel can be found in Appendix C. More detailed information is available from the respective cruise reports.
All the countries in the region adopted the standard report format agreed on during last year's Survey Planning Group meeting. No changes to the report format were suggested.
A report on age reading was presented to the meeting. All participants appreciated progress done and are convinced of its importance in resources estimation in the region. Participants expressed their hope to have an age-length key for the different species in the region.
Trawling is performed regularly during acoustic surveys to identify acoustic targets and to obtain length frequency samples and biological data on target species. It is therefore of high importance to obtain representative trawl samples. In the past all countries in the region reported problems related to trawl performance during surveys, thus particular attention should be given to this problem.
Since last year, Mauritania has replaced the pelagic trawl and good results have been registered. However, Senegal and Morocco are still encountering difficulties in trawling. A parallel survey between Russian vessel R/V ATLANTIDA and the Moroccan vessel R/V AL AMIR MOULAY ABDALLAH had been conducted to analyse trawling equipment on board and propose improvements. The results however, were not positive and the pelagic trawl will probably be replaced.
In Senegal, Japanese scientists from the Japanese International Cooperation Agency (JICA) presented a new pelagic trawling technique during a survey in June 2004, but the results were not encouraging and discussions are ongoing at CRODT on how to solve the problem. One solution was to ask JICA to donate a new pelagic trawl to the vessel, as problems are encountered during bottom trawling.
A preliminary report prepared during the 2003 survey onboard R/V DR. FRIDTJOF NANSEN was presented during the workshop. This report presented typical echograms from the main species in the region. The data was collected from monospecific schools where the target species, identified from trawl catches, dominated by at least 75percent of weight of the catch. Echograms from the main small pelagic target species have been collected, but this work should be completed.
In addition to the report prepared during the survey on R/V DR. FRIDTJOF NANSEN, Mauritanian participants presented some monospecific echograms of sardine, sardinella and anchovy.
The parallel survey and intercalibration had been discussed in detail to adopt a common strategy for the operations in all countries. The guidelines for acoustic surveys in the Northwest African region was followed, and it was decided to:
Data from the parallel survey would be analysed by comparing biomass estimates and average acoustic recordings from the different vessels participating in the survey. Data from the intercalibration will be analysed by ping-to-ping SA comparison. The parallel survey will also provide an opportunity to compare trawl catches from parallel trawls, and evaluate the scrutinizing procedures and biomass calculations conducted onboard the different vessels.
The Survey Planning Group suggested having a meeting at the end of January 2005 to evaluate the results from the parallel survey and intercalibration exercises in October–December 2004. This meeting should produce a report from the regional parallel surveys and intercalibration experiments in 2004. It was suggested to hold the meeting in Morocco.
The guidelines for acoustic surveys in the Northwest African region had been adopted. The text of the guidelines was discussed and evaluated by the Planning Group. The necessary corrections were made, both to the French and English versions, and these would be submitted to FAO immediately after the regional survey.
The planning group has suggested to have a meeting during the last week of January 2005 (in Morocco) to analyze the data from the parallel survey and produce a common report.
R/V ITAF DEME
27/10/04 to 03/11/04: Parallel survey
with R/V DR. FRIDTJOF NANSEN
15/03/05 to 30/03/05: Cold season
hydroacoustic survey
15/06/05 to 18/06/05: Target Strength
measurements survey
R/VAL-AWAM
01/11/04 to 15/11/04: Parallel survey with
R/V DR. FRIDTJOF NANSEN
15/03/05 to 30/03/05: Cold season
hydroacoustic survey
15/09/05 to 30/09/05: Warm season
hydroacoustic survey
R/V AL AMIR MOULAY ABDALLAH
04/12/04 to 10/12/04: Parallel survey with
R/V DR. FRIDTJOF NANSEN (Cap Juby-Cap Ghir). The plan for acoustic surveys
with R/V AL AMIR MOULAY ABDALLAH depends on the solutions to the noise problems
experienced with the vessel.
R/V DR. FRIDTJOF NANSEN
25/10/04 to 15/10/04: Parallel survey
with the local research vessels in the region. There will be no survey with R/V
DR. FRIDTJOF NANSEN during the cold season in 2005.
The time series of surveys with R/V DR. FRIDTJOF NANSEN has produced important information on distribution and abundance of the pelagic stocks in the region. Changes in stock sizes have been especially well understood after the vessel started conducting two surveys each year in the region, one during spring, and the other during late autumn. Since the vessel will no longer conduct the spring surveys it has been seen as a great benefit to all the countries in the region if they could conduct together a regional survey with their local research vessels. It has therefore been proposed during the Survey Planning Group in 2003 that such a survey should be conducted. Both Senegal and Mauritania conducted a pelagic survey in the spring period, however they were not coordinated. The suggestion of a coordinated Spring Survey was also supported by the Nansen Programme Steering Committee for Northwest Africa. The Planning Group in 2004 has therefore proposed that the national acoustic surveys in Morocco, Mauritania and Senegal in the spring of 2005 will be coordinated so that a total estimate of the abundance of pelagic species can be conducted on an annual basis. This work should be coordinated locally having the support of FAO, and the countries will ask FAO for support for a post survey meeting to compare and summarize the results from each survey.
As part of the proposal it was suggested that a one-day planning meeting be held together with the meeting to analyse acoustic data from the 2004 parallel survey with R/V DR. FRIDTJOF NANSEN. It was also recognized that a post survey meeting is needed to share the results of the survey.
Suggested time schedule for a cold season regional survey would be February–March 2005 starting in Morocco:
Intercalibration between the vessels should be conducted on the borders at the meeting point between the vessels.
The Survey Planning Group is expected to perform another parallel survey in 2005. The need will however be evaluated and discussed during the meeting in January 2005 (in Morocco) when the results from the present parallel survey and intercalibration is clear. The purpose of another parallel survey would be to compare and standardize the procedures for acoustic surveys and compare and control acoustic and trawling equipment.
Only an intercalibration in October 2005 with R/V DR. FRIDTJOF NANSEN is planned as a regional activity in 2005. Each country will perform acoustic calibrations as deemed necessary during every acoustic abundance survey. The calibration will be part of the respective survey report.
The course was successfully conducted, and all participants expressed their satisfaction. A report from the course with TS measurements and related results can be found in Appendix F.
No other regional research activities were planned or carried out last year.
The scientists from the Northwest African region expressed their commitment to conduct their own acoustic surveys. The timeframe of the continued surveys with R/V DR. FRIDTJOF NANSEN and the support through the Nansen Programme is unknown and high priority must therefore be given to the improvement of scientists skills in acoustic abundance estimation.
Of high priority for the moment are (not in prioritized order):
training technical personnel to solve problems related to the acoustic equipment and computer networks onboard local vessels (all countries)
It is realized that it may be impossible to perform regional surveys if the Moroccan vessel does not solve the problem with vessel noise. The Survey Planning Group therefore requested assistance from a qualified expert to solve this problem.
