MANUAL for the BALTIC INTERNATIONAL TRAWL SURVEYS Agreed During the Meeting Ofthe Baltic International Fisheries Survey Working Group Helsinki, Finland 6-10 May 1996
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4· International Council for the Addendum to ICES CM 1996/J: 1 Exploration ofthe Sea - »/0 MANUAL FOR THE BALTIC INTERNATIONAL TRAWL SURVEYS Agreed during the Meeting ofthe Baltic International Fisheries Survey Working Group Helsinki, Finland 6-10 May 1996 • This report is not to be quoted without prior consultation with the General Secretary. The document is areport of an expert group under the auspices ofthe International Council for the Exploration of the Sea and does not necessarily represent the views ofthe Council. International Council for the Exploration ofthe Sea Conseil International pour l'Exploration de Ja Mer Palregade 2-4 DK-1261 Copenhagen K Denmark Table of Contents Seetion Page 1 INTRODUCTION I 2 THE FISHING METHOD 1 2.1 Fishing Positions I 2.2 Standard Fishing Method 1 3 SAMPLING OF TRAWL CATCHES 1 3.1 Length Composition 1 3.2 Sampling for Age, Sex and Maturity 2 4 ENVIRONMENTAL DATA 2 5 EXCHANGE TAPE SPECIFICATIONS FOR BITS DATA 3 5.1 Floppy Disk Requirements 3 5.1.2 Format ofdata 3 5.1.3 File structure 3 5.2 Record Type 1 4 5.3 Record Type lA 5 5.4 Record Type 2 6 5.5 Record Type 4 7 Appendix I BITS Clear Tow Data 8 Appendix 11 Maturity Key 10 Appendix III Alpha code for countries and ships 11 Appendix IV Preliminary alphanumeric code for gears 12 Appendix V Recorded species codes. Examples ofrecorded species codes 13 Appendix VI Species names and NODC codes for standard and c10sed by-catch lists 15 Appendix VII NODC codes for fish species in taxonomic order 16 Appendix VIII Species validity codes 27 Appendix IX Sub-divisions, rectangles and "4-rectangle" codes 28 1 INTRODUCTION At the ICES Annual Science Conference in September 1995, the Baltic Fish Committee decided, that a manual to be used at trawl surveys in the Baltic urea should be elaborated (C. Res. 1995/2:41). l1Jis manual should in context be as the manual used at the International Bottom Trawl Surveys (JBTS). The objective of the BITS programme is to standardise fishing gear and methods throughout all the surveys where data are used as indices for assessment purposes. However, it is anticipated that the change from national gears to the standard gear in some instances cannot be achieved immediately. The present manual applies to all bottom trawl surveys that are conducted within the framework ofthe BITS. The standard sampling procedures are uniform for all surveys. At present no critically rewiewing ofthe gears used is available. FTFB Working Group has been asked to evaluate possible new standard(s) gear for this area (C.Res. 1995/2: 16 f.). It is expeeted that this study will result in further amendments to the present manual in the near future. 2 THE FISHING METIIOD 2.1 Fishing Positions Vessels are free to choose fishing positions in the rectangles they have been allocated. For practical reasons they are • encouraged to use positions from 30 list of c1ear tow data. This database is based on international information on c1ear trawling positions and whieh can be obtained from the Danish Institute for Fisheries Research, and which will be regularly updated. Participants are requested to report clear tow positions to the Danish Institute for Fisheries Research, using the standard format given in Appendix I. Stations in adjacent rectangles, worked by the same vessel, should be separated by at least 10 miles. Fishing should not be directed towards fish shoals located by sonar or echo sounder. 2.2 Standard Fishing Method Standard fishing speed is 3-4 knots measured as trawl speed over the ground. The reeommended speed is set as a target and actual (ground)speed and distance towed should be monitored and reported. It is also recommended that the speed of the trawl through the water should be monitored and reported. Each haullasts 30 minutes. Start time is defined as the moment when the vertical net-opening and doorspread are stable at a • trawl speed of3 - 4 knots. Stop time is defined as the start ofpull back. Vertical net opening and doorspread should be monitored at 30 second intervals and mean values should be reported. It is recommended that also wing spread is measured. These measurement may be reeorded ifa "Seanmar" or another system are available. Maxiqlum fishing depth in the Baltic is 150 m. Trawling may only be carried out during day time. The daylight period is defined as the time between 15 minutes before sunrise until 15 minutes past sunset. 3 SAMPLING OF TRAWL CATCHES AND SAMPLING AREAS 3.1 Length composition Length distributions are recorded for all fish species caught. Length is defined as totallength (measured from tip ofsnout to tip ofcaudal fin). Length is measured to 0.5 cm below for herring and sprat, and to I cm below for all other species. In ease the eateh ofa eertain species is too large to measure all individuals, a sub-sampIe may be taken which should eontain at least 100 specimens of the main speeies (eod, herring, sprat and flounder). For other speeies at least 50 specimens should be measured. If a eertain species (notably eod) is eaught in two clearly distinet size groups, eaeh of these size groups should be sampled separately by measuring at least 100 fish from eaeh ofthem. In ease oflarge eatehes ofeod (n > 1000), the minimum sampIe size given above should be doubled. Certain related speeies that are hard to distinguish from one another may be grouped by genus or larger taxonomie unit. 3.2 Sampling for Age, Sex and Maturity Otolith sampIes are eolleeted within eaeh Sub-Division. For all speeies the same areas are used. For the 4 target speeies the following minimum sampling levels should be maintained for each sampling area: herring 15 otoliths per 1/2 em group sprat 15 otoliths per 1/2 em group eod 10 otoliths per I em group flounder 10 otoliths per I em group • For the smallest size groups, that presumably eontain only one age group, the number of otoliths per length class may be redueed. It is reeommended that eaeh eountry eolleet otoliths by eaeh haul, so the otolith sampling is destributed all over the Sub Divisions. Sex and maturity data may be reported for eaeh species for which age data are eolleeted. Maturity stages should be classified aecording to the simplified maturity seale given in Appendix II. Ifposssible the SMALK information should be eompiled on a haul by haul basis. 4 ENVIRONMENTAL DATA At eaeh trawl haul, the following hydrographical data are eolleeted: - surfaee temperature - bottom temperature - surfaee salinity - bottom salinity - bottom oxygen. When using a CTD-probe for measuring temperature and salinity, the CTD should be ealibrated against sampIes eolleeted at eaeh station. For further specifieations eontaet the ICES Hydrographer. 2 .--------------- ---- --- 5 EXCHANGE SPECIFICATIONS FOR BITS DATA Note: in force from 1 July 1996 5.1 Floppy Disk Requirements - ASCII coding - all standard disk fonnats are acceptable - preferably 3.5 inch disks 5.1.2 Formatofdata Four distinct types ofcomputer records have been defined for standard storage ofthe BITS data: TYPE I: Record with detailed haul infonnation TYPE IA: Record with additional haul infonnation TYPE 2 : Length frequency data TYPE 4 : Sex-maturity-age-Iength keys (SMALK's) The detailed fonnats ofthese five record types are given on following pages. Details ofenvironmental data should be submitted to the Hydrographie Service ofICES according to established procedures. The national hydrographie station number must be reported in Record TYPE I to enable the link to be made between haul data and environmental data. 5.1.3 File structure The records must be ordered in such a way that each record ofTYPE I is followed by a variable number ofrecords ofTYPE 2, ordered by species. The number and kinds ofspecies recorded must agree with the species recording code as specified in record TYPE l. For examples ofthe various codes see Appendix V. Records ofTYPE 4 should follow at the end ofthe file after the last species record ofTYPE 2 forthe last haul. Records ofTYPE IA should be submitted in aseparate file. • 3 5.2 Record Type 1 SPECIFICATIONS FOR RECORD TYPE 1 (Haut information) POSITION NAME TYPE* MlO" RANGE COMMENTS I · 2 Record type 2A M Fixed value 1111. 3 Quarter IN M 1104 4 - 6 Country 3A M See Appendix III ICES alpha code for Countries. 7 - 10 Ship 4AN M See Appendix III 11 - 20 Gear 10A M See Appendix IV Preliminary code. I) 21 - 26 Station no 6AN 0 National coding system. 27 - 29 Haul no 3N M 110999 Sequential numbering by cruise. 30 · 31 Year 2N M 65 to 99 or 00 to 20 32 - 33 Month 2N M I to 12 34 - 35 Day 2N M I to 28/29/30/31 36 - 39 Time shot 4N MI to 2400, 9999 InUTC. 40 - 42 Haul duration 3N M 5 to 90 In minutes. 43 DaylNight IA M D, N, space Not known=space filled. 44 · 45 LaI. degrees 2N M 53 to 66 Shooting position: Degr. Latitude. 46 - 47 LaI. minutes 2N M 01059 Shooting position: Min. Latitude. 48 - 49 Lon. degrees 2N M 11 to 31 Shooting position: Degr. Longitude. 50 - 51 Lon. minutes 2N M Oto 59 Shooting position: Min. Longitude. 52 East/West IA M E • 53 - 55 Depth 3N M 0,10 to 150 Depth from surface in metres: not known=O. 56 Haul validity IA M I,P,V,N Invalid;!. Partly valid;P. Valid;V. No oxygen=N. 2) 57 - 64 Ilydrographic 8AN M Station number as reported station number 10 the ICES hydrographer.