Meeting report
A working group met in Sète on the 25th January 1997 to review the characteristics and the use of the Medits gear.
Participants: L. Fiorentini (IRPEM), P.Y. Dremière (Ifremer) and J. Bertrand (Ifremer).
The work of this group was based on the analysis of the answers to a questionnaire sent early in January to the co-ordinators of the Medits sampling vessels. The goal of this survey (cf. the form of the questionnaire in annex I) was to identify the types and the extents of the modifications possibly done by the different teams during the Medits 96 survey, facing the official rules. From this analysis, this group had also to formulate recommendations to aim at the Medits Steering committee, concerning the characteristics and uses of the sampling gear for the ‘97 Medits survey. It has been considered that the objective of the group was mainly to clarify the rules in use and to try to improve as much as possible the present situation. So, the group has distinguished the modifications which could be considered essential from those which should be accessory.
The group worked with the replies of the questionnaire available for seven (the last one been added just after the formal meeting) from the nine sampling vessels used during the Medits ‘96 survey. From a first global analysis of these replies, the group separated the questions from which no particular problem was noted (Table 1). Then, it considered one by one the points for which specific comments have been presented.
1. Mesh size and twine diameter
No comment or modification
2. Other modification on the design of the gear
No comment or modification
3 & 4. Use and problems linked with the tickler chain (" racasseur ")
Some teams did not use at all a tickler, others used it from time to time according to the depth and the bottom type. It is highlighted that the main problems are linked with muddy, rocky or irregular bottom and the risk of high quantities of benthonic material.
Recommendation
Total elimination of the tickler chain, for all the depths.
5. Length of sweep for depth between 10 and 200 m
No comment or modification
6. Length of sweep down to 200 m
No comment or modification
7. Length of bridles
No comment or modification
8. Length of the set chain
No comment or modification
9. Buoyancy
The answers show that the number of floats had been modified in one area, but not in the others. Moreover, the existing " Manuel des protocoles " gives no indication on the distribution of the floats along the upper rope.
Recommendation
In order to better clarify the buoyancy characteristics, the types and numbers of the floats should be fixed as below:
Number of floats: 40, distributed according to the following description
Diameter of each float: about 20 cm
Maximum working depth: 1300 m
Individual buoyancy: 2.7 kgf ± 5%
Resulting total buoyancy: 108 kgf ± 5%
The 40 floats are distributed along the headline as below: from the tip of each wing, one single float is attached every 1.5 m, five times; then the floats are attached by pair every 1.5 m all along the remaining headline, with a small spacing adjustment in the bosom.
10. Weighting chain
The group has noted with interest the test made by one team to substitute the chain by lead on the footrope. But it appears that all the other teams did not modify the weighting of their trawl in such a way and wrote no comment on this question.
Recommendation
The group recommends to maintain the present protocol rules.
11. Type and rigging of the doors
The group has noted with interest that one team has reduced the length of the upper backstrope (" patte haute ") by one chain link, with good result.
Recommendation
The group recommends to maintain the length of the middle backstrope as close as possible to the one indicated in the " Manuel des protocoles ", but to accept an allowance of more or less 10% for the upper and the lower backstropes (" patte haute et patte basse ") length.
12. Relationship between the warp length and the depth
The group has noted that some adaptations have been made according to local conditions in some cases.
Recommendation
Taking into account that, in a few particular situations, some adaptations should be necessary, the group recommends to respect as close as possible the pre-established relationship between water depth and warp length.
13 & 14. Safety device to recover the trawl by the codend
It appears that a safety rope had been used by most of the teams, sometimes with and sometimes without fixation. Underwater observations will be made in 1997 (EURESMED cruise) to study the possible impact of this rope on the trawl behaviour.
Recommendation
The group recommends to maintain fixations or to try to put them as much as possible when a safety rope is used.
15. Rules of gear shooting to allow the best trawl setting on the bottom
No comment, except in one case were the speed was increased to avoid to dig the doors in the mud.
Recommendation
Taking into account that, in a few particular situations, some adaptations should be necessary, the group recommends to respect as close as possible the pre-established rules, but to lightly adapt them when strictly necessary.
16 to 20. Gear damages or losses
The damage frequency seems to have been very low regarding the total number of hauls of the whole survey. The problems have been encountered mainly on rocky, muddy and coral bottom and heavy amount of algae or rubbish. Total or partial losses were indicated only in three cases linked with wreck, coral or muddy bottom. In fact, most of those were linked with bottom characteristics and not with the gear itself. In the same situations, any type of gear might encountered the same problems.
Recommendation
The group consider that no new particular recommendation can be done about general gear conception and use to reduce the gear damage.
21 & 22. Observations on the efficiency of the Medits gear as a sampling gear
Some teams have highlighted the relatively low bottom contact of the Medits trawl reducing its efficiency to catch bottom fish, mainly for the depths down to 50 metres. One team has suggested to increase the vertical opening of the trawl. The question of intercalibration between different trawls and fishing vessels has also been pointed out. One team emphasized that the doors dug in muddy bottom. The group suggests to refer to its recommendation at the question 11 for that point.
The group reminds that the bottom contact and the vertical opening of the trawl imply opposite technical characteristics and can not easily be reached simultaneously. Furthermore, the group reminds that the Medits gear has been designed to work regularly on a great variety of depth and grounds. For that reason, it can not offer, in each of the specific situation, results directly comparable with those obtained by a commercial boat and gear strictly adapted to a particular local context. The group also reminds that modifications in weight and buoyancy have been made in 1995 in order to increase the bottom contact of the Medits trawl. Furthermore, an additional weighting could increase the risk of digging on some light grounds.
Concerning the intercalibration among different sampling vessels in Mediterranean, the group refers to the recommendations adopted by the plenary session in Paris (28-30 November 1996).
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|
Question |
ES |
FR |
IT1 |
IT2 |
IT3 |
IT4 |
IT5 |
GR1 |
GR2 |
|
1 |
N |
N |
N |
N |
N |
N |
N |
||
|
2 |
N |
N |
N |
N |
N |
N |
N |
||
|
3 |
|||||||||
|
4 |
|||||||||
|
5 |
N |
N |
N |
N |
N |
N |
N |
||
|
6 |
N |
N |
N |
N |
N |
N |
N |
||
|
7 |
N |
N |
N |
N |
N |
N |
N |
||
|
8 |
N |
N |
N |
N |
N |
N |
N |
||
|
9 |
N |
N |
N |
N |
N |
N |
|||
|
10 |
N |
N |
N |
N |
N |
||||
|
11 |
N |
N |
N |
N |
N |
N |
|||
|
12 |
N |
N |
N |
N |
N |
||||
|
13 & 14 |
N |
N |
N |
N |
N |
||||
|
15 |
N |
N |
N |
N |
N |
N |
|||
|
16 |
N |
||||||||
|
17 |
N |
N |
N |
N |
N |
N |
|||
|
18 |
N |
N |
N |
N |
|||||
|
19 |
N |
N |
N |
N |
N |
N |
N |
||
|
20 |
N |
N |
N |
N |
N |
N |
|||
|
21 |
N |
N |
N |
||||||
|
22 |
N |
N |
N |
N |
N |
N |
|||
|
N: |
No modification or no comment |
||||||||
|
Comment (cf. text) |
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|
Table 1. Results of the survey on the use of the sampling gear |
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Annexe I
CHALUT ET GREEMENT
ENQUETE SUR LES MODIFICATIONS APPORTEES AU PROTOCOLE
Navire
: Campagne de référence: Medits 96Coordonnateur : Zone :
Pour répondre aux questions, prière de vous reporter au Manuel des protocoles Medits de juin 1996 (pour les campagnes 1995 et 1996); les numéros de pages, de paragraphes et de figures fournis ci-après s’y réfèrent. Les cadres de réponse peuvent être agrandis en tant que de besoin.
Question 1
- P.11, fig.2 et P.4, §1.1: Les maillages et/ou les grosseurs de fil de certaines pièces du chalut ont-ils été modifiés?
Si oui, dans quelle(s) pièce(s)? (donner les dimensions en nombre de mailles, longueur, largeur, hauteur, maillage et grosseur du protocole et modifiés)
Question 2
D’autres modifications ont-elles été apportées au plan?
Si oui, veuillez les détailler.
Question 3
P.11, fig.2 et P.5, §1.3: Avez-vous ou non utilisé régulièrement le racasseur (chaîne de 30 mètres de diamètre 8 mm, environ 42 kg) prévu au protocole pour les sondes de 10 à 100 mètres?
Si non, pourquoi?
Question 4
Lorsque vous l’avez utilisé, le racasseur vous a-t-il occasionné des problèmes de manoeuvre ou autres?
Question 5
- P.12, fig.3 et P.4, §1.2: Avez-vous utilisé une longueur de bras différente de 100 m, pour les sondes de 10 à 200 mètres?
Si oui, quelle longueur, dans quelles conditions, pourquoi?
Question 6
- P.12, fig.3 et P.4, §1.2: Avez-vous utilisé une longueur de bras différente de 150 m, pour les sondes de 200 à 800 mètres?
Si oui, quelle longueur, dans quelles conditions, pourquoi?
Question 7
- P.12, fig.3 et P.4, §1.2: Avez-vous utilisé une longueur d’entremises différente de celle prévue (30 m en haut et 29 m en bas)?
Si oui, quelle longueur, dans quelles conditions, pourquoi?
Question 8
- P;12, fig.3D et P.4, §1.2: Avez-vous utilisé une longueur de chaîne de réglage très différente de 1 mètre?
Si oui, quelle longueur, dans quelles conditions, pourquoi?
Question 9
- P.12, fig3 et P.4, §1.2: Avez-vous modifié la valeur de la flottabilité totale (120 kgf) prévue pour le chalut?
Si oui, quelle flottabilité totale avez-vous installé, comment et pourquoi?
Question 10
- P.12, fig.3, P.13, fig.4E et P.4, §1.2: Avez-vous modifié le poids total du lestage en chaîne prévu à la partie inférieure du chalut (3x40 kg plus 15 kg au centre du carré) et/ou le mode d’amarrage des chaînes?
Si oui, quel autre poids avez-vous utilisé, réparti comment?
Question 11
- P.14, fig.5 et P.5, §1.4: Avez-vous utilisé un autre modèle, une autre surface, un autre poids, ou un autre réglage des panneaux que ceux prévus?
Si oui, quelles modifications avez-vous apportées? Pourquoi?
Question 12
- P.15, fig.6 et P.5, §1.5: Avez-vous utilisé une autre relation filage/sonde que celle prévue sur le graphique?
Si oui, quelle autre relation? Pourquoi?
Question 13
- P.16, fig.7 et P.5, §1.6: Avez-vous utilisé régulièrement un dispositif de sécurité permettant la récupération du chalut par le fond de la poche?
Question 14
Si oui, était-il fixé conformément aux indications de la fig.7, P.16?
Si non, comment était-il fixé? Pourquoi?
Question 15
- P.7, §2.2.5: En présence de Scanmar, mais surtout pour les navires non équipés de ce système: avez-vous respecté les normes de manoeuvre indiquées dans cette partie du manuel des protocoles en vue de permettre une bonne posée du chalut sur le fond?
Si non, comment avez-vous manoeuvré? Pourquoi?
Question 16
- D’une manière générale, avez-vous eu à déplorer -régulièrement, épisodiquement ou rarement (préciser SVP)-:
* des avaries graves dans le chalut
si oui, dans quelle partie du chalut, sur quels fonds?
Question 17
* des avaries graves dans le gréement
si oui, dans quelle partie du gréement, sur quels fonds?
Question 18
* une perte de tout ou partie du chalut (précisez SVP)
si oui, dans quelles conditions?
Question 19
* une perte de tout ou partie du gréement (précisez SVP)
si oui, dans quelles conditions?
Question 20
* une perte d’un ou des deux panneaux (précisez SVP)
si oui, dans quelles conditions?
Question 21
- D’une manière générale, avez-vous, à partir des données et résultats existants, des observations concrètes à formuler quant à l’efficacité relative et absolue du chalut Medits en tant qu’engin d’échantillonnage?
Question 22
Auriez-vous des propositions concrètes et constructives à faire dans le domaine des caractéristiques de cet échantillonneur?
Merci pour votre collaboration.