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J~~ternational Council for.. •. Exploration of the Sea
the C.M.1975/B : 1Administrative Report
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I
Gear and Behaviour Committee
by P. J. G. Carrothers
1974
Belgium
(G. Vanden Broucke)
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The investigations on the double beam trawls were continued. Theseinvestigations have shown that an optimum net opening must berealized in order to increase the catch capacity: this may beobtained by an adaptation of the taper ratio. Further experimentswere carried out to this effect. Aseries of preliminary comparativefishing experiments were also carried out and the warp tension wasmeasured.
As regards the semi-pelagic nets for pair-trawling an extensivestudy on the net, the rigging, hauling and shooting and the fishinggrounds was carried out on board 20 middle water trawlers. Thismethod may be considered as successful.
The study of a one boat semi-pelagic net was also continued. Mainlythe rigging and the height of the net were investigated by means ofechograms recorded by echosounders. It was observed that·it is ofgreat importance to determine the correct flotation, ballasting andthe different leg systems.
A study of a pelagic net for pair trawling was started to investigatethe behaviour of the net in relation to flotation,· weights, speedof the vessels and warp length.
~ With respect to the electrical fishery the study on the practicalpossibilities of this fishery at national and international levelwas further extended. A first series of comparative experimentswith a traditional and an electrified bottom trawl was undertaken.
~The method of alternative hauls was applied.
The research concerned the adjustment of the pulse generator(frequencies, peak voltages), the variations between the electrodesand the different environmental factors. A compact pulse generatorwill be designed. The experiments will be carried out on roundfishand Norwegian lobster.
As regards the fishery with artificial light a preliminary programmeis being drawn up.
Via log-sheets of fishermen an analysis was made of sole and plaicecatches by day and by night on thc same fishing ground.
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A preliminary series of aeoustieal measurementson fishing gear wascarried out.
The effeet of the vessel on the sclectivity was studied for~ twovessels of different size but fishing with the same type of net.
Comparative fishing experiments will be undertaken with two vessels,one fishing with a bottom trawl and the other fishing with a beamtrawl.
A theoretieal study on the polyvalency of side trawlers was carriedout.
The wear of netting will be determined as a funetion of its locationin the net, the fishing method and the fishing ground.
Research was also earried out on wear, on degradation of yarns bymarine baeteria and on identifieation of synthetic fibres.
A theoreetieal study on an automatie feeding system for the shrimprinsing and sorting machine on board cornrnereial vessels was started.
Future Work
Plans for future work include:
Experiments with double beam trawls on middle water beam-trawl vessels.
Study of the behaviour of semi-pelagie and pelagic nets (length ofbridles, taper ratio, ete.).
Development of a compact pulse generator for the electrical fishery.
Further research on the design of multi-purpose vessels.
Further acoustieal measurements on fishing gear.
Continuation of testing of ne~ting yarns and netting (breaking load, ~
mesh sizes, ete.). ,.,
Canada
(P. J. G. Carrothers)
Fishing gear engineering research has concentrated on the demersalotter trawl study, with little progress in the netting hydrodynamics project. After failure of a trawl data processing contract, good progress is now being made in-house and a majorreport on trawl behaviour and data analysis teehniques is plannedfor 1975.
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The computerized, echo-counting system (not integrator) has beenapplied to groundfish stock assessment problems, calibratingagainst trawl catches. Count/catch correlation was good by daybut not significant from dusk to dawn. Development of techniquesfor direct calibration of the system has taken priority overstudies of fish reaction to trawling, pending further developmentof the towed, servo-altitude-control, instrument vehicle.
Three different methods forestimating variance in acoustic information on fish densities were studied. Cluster sampling appears tobe the best model currently available, autocorrelated regressiontechniques are being explored further, but the method based onsuccessive differenceshas been dropped.
Acoustic survey design experiments have been initiated and willbe continued in 1975 to establish optimal survey patterns, andsystem appraisal will continue.
The groundfish counter system is being modified to store digitizedvoltages of incoming echos for refined estimates of fish sizeand density. Also, an integration routine is being developed forabundance estimates of small, densely-schooled, pelagic fish,particularly capelin and herring.
As a feasibility study, the distribution of euphasiids in threeareas were mapped and vertical movement over a 24-hour period wasrecorded, using a 120-200 kHz transducer in a towed vehicle.Accurate abundance'estimates will be difficult but apparently not'impossible. The system will bri computerized for future work.
The distribution of phytoplankton continues to be studied by means'of a Variosens fluorometer on a "batfish" manoeuverable towed .vehicle, with magnetic tape recording ~f data.
An lB-m. long-liner has been convertcd to stern seining. Thedouble-ended drum seine, with bunt centre and no purse line, ishandlcd on two net reels by four men to compete successfully withpair ring nets requiring two boats and eight men. Operation hasbeen at the surface for herring and mackereI, but modificationsare planned for operation in mid-water and on the sca bed.
A 50-rn. stern ramp,trawler has been converted to the "tripleparallel" gear handling system. The main deck is divided intothree lanes, each with a net reel at its forward end. Normally,the trawl is shot and hauled over the ramp in the centre lane.However, .a mid-water ora demersal trawl can readily be shot invery little time from either of the side lanes,without clearingthe centre lane if the net in use becomes torn or if the typeof trawling should be changed. Both pelagic and demersal doorsare immediately accessible from their positions inboard at therail in the two outer lanes. The gallows are hydraulic gantrieswhich can lower the blocks into the ramp for towing in ice. Astern seine suitable for this vessel is to be designcd.
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Automatie long-lining is being used sueeessfully on three 20-mvessels and on one l4-m. vessel. However, sueeess depends onextensive training of the erew in operating and maintaining theequipment and on the proper eondition of the bait. Frozen baitof the right size is held in the hold and transferred to twoeoolers whieh are used alternately to supply the baiting maehine.
A powered rotor on the headline of a "diamond"-type, high-lift,bottom trawl was able to lift the trawl as mueh as 55 m. offbottom in a very short time and to maintain a stable altitude,demonstrating its value for "aimed" trawling. All problems wereteehnieal and the prineiple has been proven, but no furtherdevelopment is planned for 1975.
A prototype hydraulie dredge, initially for sampling benthosin relatively deep water, shows promise for eventual eommereialapplieation.
The ,government of the Provinee of Quebee is beeoming inereasingly ttaetive in matters of interest to the Committee. Aeoustie methodsare being used to study eapelin,behaviour, seleetive and experi-mental shrimp trawls are being designed and built, new high-liftbottom trawls are being tried, eomparative fishing studies onbottom trawls are being eondueted in eonjunetion with a Frenehvessel, and a trawl dynamometer is under development.
Denmark
(0. Bagge)
Mesh selection experiments on cod with Nymplex 50 - 3/20 have been carriedout in the Baltic and the Sound.
Catch of cod and flatfish in bottom trawl haB been investigated in relationto salinity and oxygen content near the bottom in the Sound.
In the Kattegat the catchability of Norway lobster has been related tooxygen content and temperature near the bottom in the eastern Kattegat.
The inveBtigations will be continued in 1915.
Finland
(Veikko Sjöblom)
No gear und behaviour work earried out.
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France
(Maroel Portier)
Chaluts, ohalutage
Les essais BUr le fond de ohaluts a 4 faces de grande dimension, derivesdes chaluts pelagiques et munis de bourrelets ont ete pourBUivis. Les filetsqui possedent generalement des mailIes de 4oo'mm (maille etiree) a l'entreeont ete utilises: soit avec un greement semblable a oelui du pelagique, comprenantdes panneaux travaillant entre deux eaux et le oontröle permanent du netsonde,soit'avec un greement a fourches et des panneaux de fond.
On a tente de determiner l'influence de In posee du bourrelet, generalementconstituo de til d'aoier garni de caoutchOllc, BUr les captures. Les obs~rvations
Bont encore.inBUffisantes mais on sait que des poisBons ronds sont Busceptibles,generalemont la nuit Oll a oartaines saisons, d'effeotuer des migrations vertica1es.Dans oes conditions, une grande adherence du bOllrre1et au fond niest pas necessaire.
Par contra, i1 a ete possible de capturer au coura d'une campagne etfectueeon Mer de Barants, des especes (morue, eglefin~ fortement collees BUr le fond aveole greement comportant des panneaux entre deux eaux. Dans ce cas, la posee du bourrelet,contrölee par le netsonde ~tait importante. Des essais ont egalement ete faitsen playant des lests a 50 m en avant du chal~t pour obtenir un effet de rabattementdes bras.
Ces travaux BUr le chalutage contröle seront POUrsulvls an 1975 et on y ajouterales essais de chaluts dont les rnaquettes ont ete etudiees en bassin.
11 s'agira d'uncha1ut a 4 faces de petite dimension speoialement adaptea la prospection BUr las fonds dura Oll accidentea que l'on emploiera aveo des panneauxdegagea du fond et d'un chalut de fond egalement a 4 facea derive de l'AtlantioWestern Trawl et que l'on utilisera aveo des panneaux de fond.
Lea parties anterieures da oes chaluts seront rea1isees en mailIes de 200 et400 mm etirees.
Les chaluts pelagiques a un Oll deux bateaux pOBsedent generalement dos mailIesde 800 mm etirees et des essais ont ete effectues avoo des mailies de 1 200 mm.La changement des maillages dans les parties adjacentes des cha1uts est generalementprogressif et l'on trouve apres le 200 mm des mailles dc 160, 120, 80 ct 5Ö mm.Toutefois, 'l'efficacite da nombreux chaluts de fond employespar la p~che artisana1eet qui etaient en mailIes da 120 mm a ete augmentee par l'adjonction d'une entetureen 200 mm.
Le textile le plus utilise pour la oonstruction des chaluts ost 10 polyamide,mais occasionnellement le polyethylene est employe pour realiser oertaines piecosdu dessous du filet. Leo poches sont toujours faiteo en polyamide.
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Chaluts seleotifs, seleotivite
Une experience a ete faite:.pour determiner'le coefficient de seleotivitedes poohes de chaluts a 1angoustines et une etude entreprise par les laboratoiresde Lorient et de Boulogne - pour pettre au point un chalut saleotif a langoustine.Deux maquettes de'ohalut plat type americain ont eta realisees et les' essaisdevraient en Gtre effeotues cette annee.
Pour tenter d'estimer l'influence de 1a force motrice sur la seleotivitedes euls de ohalut, on a compare au moyen de la methode de la double pochela selection du merlu par deux chaluts de fond de taille differente remorquesrespeotivement par un navire de 300 CV dont la vitesse de traine etait en moyenne3,5 noeuds et un navire utilisant 720 CV et chalutant a.3,7 noeuds.
Dans les oonditions de l'experienee les facteurs da Beleetion n'ont pasdiffere de fa90n significative pour les deux puissances et se sont situes entre3,6 et 3,9.
Dragues
En 1974 une etude a ete entreprise pour etudier le oomportement des draguesa coquilles Saint-Jacques (Peeten maximus) et en particu1ier 1a Beleotivitades dragues aveo ou sans voiet • 11 a eta remarque que les dragues a voletremorquees a vitesse elevee (3 a 4 noeuds) permettaient une penetration maximumdes dents et ne lais~aient pratiquement auoune chance aux jeunea ooquilles 'de s'echapper. On a pu observer egalement qu'une certaine seleotivite se produisaitau niveau de la partie superieure du sac. '
Une etude a long terme de l'effet de oes dragues sur le benthos figureau programme d'un laboratoire de Nantes, speoialise dans la qoquil1e Saint-Jacques.
Etudes sur maquettes
Los travaux sur maquettes se Bont poursu~v~a dans le bassin de BoulogneoU on a , en particulier, tente de determiner la repartition des foroeB agissantBur difforents types de panneaux divergents.
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L'ouverture du bassin d'essaia de chalut de Lorient, initialement prevuepour l'automne 1974, a du etre retardee. Elle devrait avoir lieu vers la fin de 1975.
Senne a thon
L'etude de la senne a thon entreprise a Lorient en 1973 n'a pas pu etrepourauivie. le materiel de mesure ayant fait defaut.
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Bateaux de p3che, amenagements
11 taut noter dans le Nord de la France 10 developpemant d'une serieda ohalutiers en fer destines a 1& peohe artisanale et con~s pour pecherpar l'arriere. La majorite de ces navires a une longueur de 20 m et leur puisDancevarie de 500 a 700 av J ils sont souvent munis daune tuyere fixe destineea. augmenter leur force de traotion et possedent des tambours enrouleurs de chalut.
Sur la cote Atlantique, la construotion reste, a quelques exceptions pres,plus traditionnelle - bateaux en bois peohant par le cote - mais on observeegalement le developpement des tuyeres.
En 1974, a veritablement dobute l'installation des tambours cnrouleurs surcertains navires rampe arriere de gros tonnage. Ce sont generalement des enginspuissants et de grande dimension qui sont utilises pour virer les chaluts pelagiqueset les chaluts de fond, et servent egalement a. hisser la poohe sur le pont.
Peohe eleotriguo
L'etude en laboratoire du oomportement des poissons marins soumis a un champelectrique qui a fait 1'objet d'un oontrat avcc le C~~O, devait permettrede definir le stimulus 1e plus efficace pour la peche eleotrique en mer.A la suite des experiencea effcctuees, il es~ apparu deux points qu'il fallaitelucider : .
- la directionnalite des taxies aux basses frequences (20 Hz environ)qui s'averent par aill~rs interessantes quant a l'ecart entre les seuils de taxieet de tetanie. '
- la difference apparente de comportement des poissons suivant qu'ils ont ou nondeja subi les effeta du courant electrique.
En 1975, ces deux points vont etre etudie~ dans des baos de plus grandesdimensions que ceux dont nous disposions pour les premieres experienoes.
Acoustique
Pour 1975, un programme de oartographie aooustique des bancs de poissons. pelagiques cotiers (sardines, 'anchois, sprats) a eta elabore.
Ce programme comporte 7 campagnes dans 1e Golfe de Gascogne, au coursdesquelles des chalutages pelagiques Bont prevus pour l'identification des especesdetectees. A la suite de chaque campagne, seront etablies des cartes indiquantles zones de concentration des bancs et leur importance principalement par rapporta la situation thermique.
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Federal Repulic of Germany
(H. Bohl)
Fishing Gear and Apparatus
In 1974, research on high-opening bottom trawls was continued.The work was rnainly concentrated on the relationship between thelength of the wings, the types of otter boards and dynamic headline lifting devices on the one hand and the vertical net openingon the other.
As to midwater trawls, the influence of different weights, lengthsof legs and types of otter boards,' ki tes and floats on the shapeof the net mouth was observed by means of a multi-netsonde. The socalled "Tauwerk-Netz", whose fore part consists of parallel ropes,proved very successful in catching spawning saithe off the Shetland 4tIslands. The complicated handling of the gear requires furthertrials.
Concerning deep water trawling for commercial application, in 1974two cruises were conducted to the continental slope west of the'British Isles. Hauls were systematically carried out in depthsfrom 400 - 1200 m and occasionally down to 1800 m. The gears usedwere modern high-opcning bottom trawls specially designed for deepsea trawling (solid plastic bobbins, inflatable floats etc). Onrough grounds (corals) a standard (140-foot) trawl was used whichwas less exposed to damage but also less efficient. On the samegrounds the catches of grenadiers, scabbards, smoothheads, rabbitfish and sharks were much better in spring than in winter.
Due to the facts that full-scale experiments with trawls are veryexpensive and that small models often do not yield results trans-'ferable to trawls of commercial size, models of the scale 1:4 weretested as already done several years ago. The experiments wereconducted in the shallow and rather clear coastal waters of thewestern Baltic and a number of recently developed trawls werc investigated under controlled conditions. The gears were observedby means of a multi-netsonde and by skin-divers equipped withunderwater cameras.
The increasing size of midwater trawls demands very large otterboards. Thus, on German distant-water trawlers Süberkrüb boardsup to 12 m2 are in use. In 1974, full-scale trials with differenttypes of otter board were started in order to compare theirperformance and efficiency. For 1975 additional wind tunnel testsare planned to determine the lift and drag coefficients of the boards.
The distances between Lhe otter boards tluring towing and of thetensions in the warps and legs were mcasured and the dataprocessed by ship-borne computer.
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As in previous years, and in compliance with C.Res.1972/5:7,the relationship between fish distribution and water temperaturewas studied by means of a combined thermo-netsonde in theSpitzbergen/Barents Sea area and in the Gulf of St. Lawrence.
Little progress was made in the field of electrical fishing.The work was restricted to preliminary trials with an electrifiedbeam trawl which is intended to replace the heavy gears now inuse for catching flatfish.
Net Materials
Polyamide is still the most important material for the manufactureof t~awls in the FRG: 100% of the midwater trawls and about 90% ofthe bottom trawls are made of this material. The remaining 10% ofthe bottom trawls are made of plaited polyethylene yarns.
Although the prices for net materials are rising rapidly, the extrastrong cod-end netting yarns (R 14-18 ktex) are now used morefrequently than ever before in bottom trawling.
The cooperation with national and international bodies concernedwith net materials and standardisation of testing methods was con-tinued. .
A new method for measuring the flexural stiffness of fairly thicknetting yarns has been developed, and the influence of a repeatedwetting on the mesh o~ening was studied.
Selectivity Experiments
The long-term research program on the influence of the load/elongation properties of polyamide netting yarns on the selectivityof bottom trawl cod-ends was brought to completion in April/May1974 in the Gulf of St. Lawrence. As in 1973, cod selectionfactors could be established for two double-braided cod-ends whichwere made of a) the original Soviet CAPRON (50,1% elongation) andb) the PA standard netting yarn (23,8% elongation). The selectionfactors obtained were 3,16 for CAPRON and 3,25 for PA standard inICNAF Div. 4T, and 3,38 for CAPRON and 3,23 for PA standard inICNAF Div. 4R. These results and those of the previous experimentsshow clearly that there is no scientific basis for a mesh differentialwithin the group of PA netting yarns.
Experiments carried out in'September 1974 with FRV "Solea" inthe central Baltic yielded cod selection factors of 2;82 and2,96 for single-braided, bottom-trawl, PA cod-ends of 92 mmand 103 mm mesh open1ng. These factors are much lower thanthose found aboard Polish and German research vessels duringthe period 1972/73 (3,00 - 3,43). Further effort is needed toestablish reliable selection data for the mesh regulations inthe Baltic.
The research program for 1975 and the following years includesstudies of the selectivity of midwater l:rawls.
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Fish Behaviour, Noise Measurements
Concerning the reactions of fish during trawling, observationsby various echo sounding equipment were continued to preparea comprehensive catalogue'of the behaviour patterns of thecommercially important species.
Since the behaviour of fish is often influenced by acousticstimuli, noise measurements were conducted while towing a recentlydesigned 250-foot trawl. The intensity of the noise was shown todepend on the contact of the bobbins with the sea-bed. Since .bottom type and weather conditions affect the noise considerably,the influence of these factors will be studied in more detail inthe future.
Iceland
(G. Thorsteinsson)
In 1974 selective prawn trawl experiments were resumed and two typesof experimental trawl were tested. In the first type there was nooverhang and the whole trawl opening was closed by aseparator of60 mm mesh. Three midlines were used along the separator panel butthere were no trash chutes. In the second type, a separator panelof 60 mm mesh was mounted into the front part of the belly of aconventional trawl thus closing it completely. In order to get ridof the trash a few holes were made in the lower panel just in frontof the separator. Here the separator was oblique (15-23°) and cuton the bar on all sides. Both selective trawl types happened tocatch similar quantities of prawns as did conventional trawls, butthe comparative hauls were too few for reliable conclusions. Thenumber of undersized fish of commercial value taken differed somewhat, depending on fishing ground, species and probably several otherfactors. Roughly speaking, as compared to conventional gear, thefirst trdwl excluded 75-95% of the important species available(cod, haddock, herring) whereas the second type did not do quiteso weIl. In this case the limited number of hauls must also betaken into account. Commercial fishermen have already testedthe belly-selective type of trawl. They found the experimentalgear worked satisfactorily on hard bottom, whereas on soft groundthe trash did not pass through the belly holes but was collectedby the separator. This is to some extent caused by the otterboards, which were smaller than those used by the research vessel,not stretching the separator panel enough horizontally.
Experimental midwater trawling for redfish and blue whiting was unsuccessful because dense enough schools could not be found. On theother hand, commercial trawlers got good catches of cod off the NWcoast during August and September. Thus this fishing method, sosuccessfully carried out in the fifties, has now been rediscovered.
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In the 1975 program the selective prawn trawl experiments will begiven preference to other investigations. Selection experimentson demersal species (cod, redfish) in midwater trawls will becarried out if pelagic occurrence of these species permits. .
Ireland
(F. A. Gibson)
No report received.
Netherlands
(J. G. de wit)
The newly developed high-opening bottom trawl has been introducedin the trawler fleet. Many beam trawlers had to be adjusted to thisfishing method. This conversion transferred them to multi-purposetrawlers. A major problem was presented by the different warprequirements for beam trawling and .for demersal or pelagic trawling.In the first case they are thicker and shorter. A method has beendeveloped to use thinner warps for beam trawling.
Experiments on the use of polyvalent otterboards (Morgcre-type)for pelagic trawling have been started and proved to be promising.Preliminary data showed an otterboard spread of 60 m at a warplength of 230 m and of 70 m at a warp length of 320 m. TheMorgcre-type otterboards were found to be about 8 m above theheadrope.
Performances of trawlers and beam trawlers during fishing operations have been measured. Special attention was paid to theperformance of the main engine and trawl winch equipment on boarda 54 m (2000 hp) trawler and a 37.7 m (1115 hp) beam trawler. Theresults of these measurements are expected to become of value formodern trawler designs.
Electrical fishing has furth.:r been investigated in an experimenton board a commercial shrimp trawler in the Scheldt estnaries.One rig was electrified and the other one was of the nOLmal shrimpbeam trawl type. Teething troubles in the pulse-generators andelectrodes systems when used under commercial conditions can becorrected. It is expected that catches of an electrified beam
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trawl will further increase by decreasing the towing speed. Alower speed will resu1t in reduced damage to the undersized bycatch~ However, during the above-mentioned experiments, the speedcould not be reduced below 1.28 m/sec (4.6 kn), because of thestabi1ity of the fishing gear. An adaptation of the gear to towingspeeds 1ess than 1 m/sec (3.6 kn) proved to be necessary.
Althoughthe se1ectivity effects of an electrified beam trawl requirefurther investigations, the experiments tentatively show that thee1ectrified shrimp beam trawl catches fewer undersized soles as aby-catch. Sole 1arger than 24 cm and p1aice larger than 27 cm seemto increase in the by-catch.
Continuation of e1ectrica1 shrimp fishing experiments is p1annedfor other areas with other types of bottom, together with theelectrica1 stimulation of flat fish to increase the se1ectivity.
In the present situation there is an increasing interest amongNether1ands fishermen in more selective fishing gears and slower •lowing speeds. The expectation that the electrified beam trawl cansatisfy these requirements is growing.
A mechanical feeder for the rotating shrimp grader has been deve10pedand was tested on board a commercia1 shrimp trawler for two months.The system proved to be successfu1 by improving the efficiency ofthe grader and by preventing the unwanted by-catch from furtherdeterioration after the catch is on board. This mechanical feederis coming into commercia1 use.
Work has started adapting the rotating shrimp grader for brownshrimps to panda1us for the fishery in the Farne Deeps •
.The experiments to co11ect mus~e1s from the sea bed by suctionh~s been continued. Scvera1 suction heads were comp~rcd. Theinfluence of this method on the benthos, in comparison to dredging,is being studied.
Experiments on c1eaning interna1 sand and silt from musse1s, whilestorcd in a vesse1 in layers of 0.75 to 1.0 m and subjected to avertica1 flow of water through this 1ayer, 'have been continuedwith promising results.
Norway
(S. 01sen)
The previous1y developed Autoline system for mechanized long
lining on larger vesse1s was thoroughly tested with a new baiting
machine which appeared to be a significant improvement,facilitati~g
satisfactory baiting at all practical shooting speeds.
Similar tests were condur,ted with a small scale line hauling/
splitting/storing system,which performed reasonably well as such,
but not well enough in combination with one of the existing baiting
machines.
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Extensive tank experiments to test the cod's preference of
various chemical stimuli were carried out and a progress report
submitted to the last Council Meeting. This work is part of a project
'to develop "artifical" bait.
Deep sea traps similar to ,those developed for black cod fishing
on the Pacific coast of USA were tried in coastal waters. These
proved to catch most of the usual bottom species (cod, haddock, saithe,
tusk, ling, redfish ~tc.), but as yet not in commeroial quantities.
Experim~nts to establish -the relative efficiency of gill nets
made of different materials were:carried out in Lofoten, as reported
to the last Council Meeting. Further tests with sorting net on the
commonly used prawn trawls confirmed the previous findings that this
does not work quite weIl wfth the Norwegian "Sputnik"-trawl, which
is widely used in our prawn fisheries.
Reactions'of blue whiting to an approaching trawl have been
observed and experiments carried out with a high intensity light
source. These studies confirm previous observations that the blue
whiting are greatly affected by acoustic and optic stimuli and
usually react by diving to greater depths.
A study was started for extendina the use of modern acoustic
fish assessment equipment to accurate delection and mapping of bot tom
types. The results are promising,confirming a close relationship
between reflection coefficient and types of sea bed, e.g. mud, sand,
gravel, rocks etc.
Initial trials were successfully carried out in Lofbten with
acoustic tags for plotting individual movements of free swimming cod.
An electronic system for pin point plotting of fish movement
within a closed off bay was tested with good results and utilized for
free field behaviour studies on saithe exposed to various sources of
man-made stimuli.
The long line mechanization program is in 1975 being extended
and continued with the aim of developing systems for use also on
the coastal fleet of smaller vessels.
Similarly, a programme for increased mechanization in the gill
net fisheries is being started in 1975.
Trials with deep sea traps will in 1975 be continued and
extended to various parts of the Norwegian coast~
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Plans for 1975 include further work on selectivety of prawn
trawls, as well as selection experiments with pelagic trawls, and
for blue whiting fishing a pelagic trawl with ropes replacing the
meshes in the front part of the trawl will be tried out.
Further use of acoustic tags is being p1anned in 1975 for
distribution and behaviour studies, and a programme for acoustic
mapping of prawn grounds in the Barents Sea is contemp1ated.
Poland
(W. Cieglewicz)
No report received.
Portugal
(B. Gil)
No gear and behaviour work carried out.
Spain
(R. Robles)
No gear und behaviour work carriecl out.
Sweden
(G. Otterlind)
No special uctivity reported and no major changes in gear construction and netting material noted.
United Kingdom
1. England
(A. R. Margetts)
The measurcment of the efficiency of a trawl, using the sec torscanning sona~ ~nd acoustically tagged plaice, was completed fora particular cig of Granton trawl at a level of accuracy of t 10%for the fish positioncd in.the zones 'between otter boards' and'in the path of the nett; results are in press. Studies ofbehavioura1 aspects of trawling, using the same methods, wp.recontinued.
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Further observations were made on the depth of disturbance ofthe sea bed by an otter trawl with tickler chains. The effectsof multiple tickler chains on the working parameters of an ottertrawl were measured.
Again in cooperation with Scotland, observations were made, usingth~ sector-scanning sonar, of the configuration and mode of actionof a fly-dragged Danish seine; the ropes were marked with acoustictags and a running check was kept of the positions of these, thenet and the seiner. The seine was also shot round acousticallytagged plaice and their reactions to thp ropes observed.
The very deep trawling"meter to measure closeness of the trawlto the sea bed was used satisfactorily on the deep trawlingcruises.
Studies on adaptation of cod to pressure changes were continued.
Collection and analysis of commercial trawl haul by haul data wascontinued to determine the effects of environmental factors oncatch rates of cod and plaice. '
The experimental flume tank at the Fishcries Laboratory, Lowestoft,was refurbished during the year. Drag forces of an acoustic tagon a fish were measured.
A prototype telemetry dev lce for mea:mring fish heart beat ratein the open sea was made and tested. The digital system employedfor this was shown to be feasible. Micro-miniaturization presentedmany difficulties but a'technique was developed which should allowthe production of a multichannel instrument.
A survey was made of the morphology of red and white museIe invarious marine fishes. Further sampIes were analysed in an examina-'tion of the possibility of classifying separate stocks of North Seaherring by counting numbers of white museIe fibres.
A new solid state sector scanning sonar has been produced at theFisheries Laboratory, Lowestoft, and brought into service recently.Its performance is slightly improved over that of the original A R Lsystem and it occupies about one-tenth of the volume of the earliermodel.
Adaptation of a'flying spot' recorder which selects signals fromthe sector scanner led to the provIsion of a very high resolutionside scan sonar which has recently been of use in mapping the extentand shape of fish shoals.
2. Scotland
(J. J. Foster)
No report ret;eived.
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u. S. A.
(E. G. Woods)
DIRECT SAMPLING SURVEY GEAR
Tbe modified candidate groundfish survey, high-opening, Yankee Trawl(No. 41) was designed and tested in 1974. Tbc trawl was cmployed for"interim use" during the Spring Groundfish Survey in ICNAF sub-areas4, 5, and 6. Additional field trials were made to calibrate No. 41Trawl against the old standard No. 36. Formulation of eatch eoeffieients by spccies .rcmains to be eomplcted.
Development of the elcctric shrimp trawl system as a defined efficieney survey sampling system was accomplished. A mathcmatieal modelwas established and verified in the laboratory and during fieldstudies. Tbis model, together with the electric shrimp trawl system,can be utilized to accurately estimate shrimp rcsource abundance during rcsource assessment cruises either by day or night. Much moreaccurate population estimates, than those which have been obtained inthc past using standard gcar, are now possible using this tcchnique.
Tbe work on development of instrumentation for monitoring otter trawlperformance has continued with modifications to circuitry and transducer design. Tbe system is intended prilMrily for use with trawlsuscd in rcsource asscssmcnt survcys, rather than in cngincering studiesof trawl performance. TIle system acoustically mcasurcs wing sprcad,hC:ldrope hcight from bottom and footrope hcight from bottom and recordsthe .data on tape in the headrope unit. Results are subsequently plottedby computer.
DIRECT OßSF.RVATION AND PHOTOGRAPIIY
Tbree field trials were accomplished to further evaluate the RemoteUnderwater Fishcries Assessmcnt System (RUFAS)-II. The basic designof the systcm was found to be sound. Upgrading of the electronicspackaging will bc neccssary before the system can be considered fullyoperational.
TIle operational Remote Undenmter Fisheries Assessment System (RUFAS)-I",as modified to include an "anchor/drift mode", expanded field of viewtelevision camerasj and tempecature, salinity, turbidity measurementcapabilities.
Off southern California, photographic tcchniqucs wcrc uscd for analyz.ing pelagic fish (anchovy) sehaol densities and three dimensional spacing.
A positivcly Luoyant 35 mm camera with a strope light tvas droppedinto anchovy [ish schao ls. TIle camera sank at an es tab 1ished ra tetaking pictures through thc school. TI1C systcm automaticallyreturncd to thc surface for recovery und subsequently the data wereannIyzcd and rccorded in a computer eompatible format.
•
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HYDROACOUSTICS
Cooperative investigations into the nature of acoustic backscatteringfrom fishes and other objeets in sea water were eondueted along linesagreed to during ICNAF meetings in January and June 1974. Cooperativeeruises were eondueted aboard the USSR R/V Khronometer in March-April1974, and thc Polish R/V Wieezno in Oetober 1974.
S1gnifieant progress was F.~de on the development of the hydroacousticdata aequisition and processing system. It is dcsigned to provideestimates of integrated signal intensity, fish target strength/sizedistributions and fish density in up to 60 depth intervals simultaneously. Tbe towed vehiele and shipboard control system were extensively tcsted together with a PDP-8 Computer during a Paeifie hakesurvey in 1974.
Sonar mapping teehniques for measuring pelagie f1sh aggregations havcbeen under development off the southern California eoast. The investigation foeused on the intl.cpretation of "what is seen" eoneurrent withthe dcvelopment of automatie data eollcetion tcehniques.
REMOTE SENSING
Data eolleetcd from thc Earth Resouree Teehnology Satellite (ERTS) 1972Iuvcstigation has been analyzed. Results show that predietions ean bemade with remotely sensed (water-quality indieators) on thc loeation ofmcnhaden fish sehools in the north eentral Gulf of Mcxieo. In 1974,plans were made to refine the ERTS-l Dodel and expand investigations toother s~eeies and loeations •.
Tbe Low Light Level Intensifier System underwent a historieal reviewand areport was prepared. Tbe report deseribes the sueeess of fieldoperations for the prcvious five years.
Data eolleeted from the 1973 Skylab Gamefish Tournament Has analyzedwith favorable results. Experimental results indieated that therc is apredietion eapability, using remote sensing data for the distribution ofwhite rnarlin.
COMHERCIAL FISHING GEAR DEVELOPMENT
Development of a shrimp separator trawl for the Gulf of Mexieo wasinitiated. A " s tate of the art" survey of separator trawls was aeeomplished. A proposcd system design was eompleted with a preliminarilyevaluation. Tbe se;)aration problem in the Gulf of Mexieo is quite different than that fO~lnd in other :treas of the world and new teehniqucs~ust be develop·ed.· Generally, 9u% of a normal shrimp tnml cateh 1S
discards and a broad range of shrimp size and fish size is [ound.Quite often 35-40% of a eateh is eomposed of fish \.,hich are as smallor smaller than thc shrimp. Two prcliminary field trials were eonuucted to cstablish bascline eritcria on thc separation teehniqucsproposed for the (~llf of Mexieo shrimp separator trawl. Resultsindieate that a vertieal separ<ltor panel utilizing a "V" shape tapcr-
_ ing back to the cod end of thc .Ict has good" potential as th~ basicsepärator design for thc' Gulf of 1'1exieo system. A laboratory studyhas presently been initiatcd to optimize the separation of shrimpthrough webbing panels.
- 18 -
A shrimp trawl mesh-sclcction project was concluded undcr thc StatcFedera1 Management Program. Under this project a traw1-mesh regulation for taking Panda1us borealis shrimp from Gulf of ~~ine waters wasestablishcd. The current mesh regulation provides a minimum mesh sizeof 1-3/4" stretched mesh measured between knots in the trawl body and1-1/2" in the cod .end as an interim measurc. A rcvised regulation fora minimum of 1-3/4" body and 1-3/4" cod end was proposcd for proClu1gation as of June 1975.
Field experiments on means to avoid destructive fishing of lost lobsterpots ("ghost pots") were concluded in 1974. This work inc1uded observation of trap-related lobster behavior, development of ca1ibrated escapepanels, and testing of degradable materials and panels designed torelease all entrapped lobsters, crabs, and other animals upon elapse ofdesired time periods. Analysis and manuscript work are in progress.
A contro1led experiment was conducted on the commercial fishing groundsncar Kodiale, Alaska, to determine the ability of king crab to e5capefrom pots. Resu1ts demonstrated that they \-lere capab le of exiting with1itt1e difficu1ty and consequent1y lost or dere1ict pots as presentlyconstructed, should present no conscrvation problem by continuing tofish. In contrast, another experiment in Puget Sound with Dungeness crabpots equipped with tunnel triggers demonstrated that Dungeness crab wereretained in the commercial pots by the trigger devices. These are notused in king crab pot tunnels.
TIle selective pollock trawl development is aimcd at providing gear andtcchniques to rcsolvc theprob1cm of incidcnta1 catchcs of halibut andTanncr crab in thc trawl fishery for Alaska pollock in the Bering Sea.Prescnt estimatcs suggest that 3 to 4 million halibut (mostly juveniles)and 120 million Tanner crabs are dcstroycd annua11y in that fishcry.Dcve10pment efforts have been aimed at gear capab1e of operation linearbottom" and traw1s.capab1e of separating crabs and halibut from the targetspecies in the event that off-bottom fishing 15 impractical.
D.S.S.R.
CA. I. Treschev)
In the field of fishing technique tests were continued on largemeshed p0.1agic trawls and some of their component parts, such as,depres~o~s, hydrodynamic door lifters, wing-shaped doors, andbobbins designed for depths grcatcr than 1000 m. Information onthe hydrodynamic resistance of conica1 nets with large meshes Cupto 600 mm mesh-side lcngth) was obtained for the first time onfull-scale models at sea for more reliable data on the dependenceof netting resistance on mesh size, hanging coefficients, yarnthickncss, tapcr ratio, and traw1ing speeds between 1,5 and3,0 rn/sec. These data can be used when designing trawls.
•
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- 19 -
In 1974 fish behaviour was studied during cruises of R/V "Gemra","Alaid", "Protsion", "Peseus 111", and others. Mackerei, Atlanticsaury, herring, cod and some other species were studied, andobservations were made with the help of photocamera "Triton",hydrostate "Sever-I", and hydroacoustic devices •
New data were obtained on fish behaviour in natural conditionsand in front of the trawl. The probability of different fishesbecoming trapped in the trawl was assessed quantitatively. Theprinciples were formulated for a procedure for determining theabundance of demersal and pelagic fishes with the help of instruments.
Methods were developed for assessing fishing power of systems, \fishing effort, and fishing productivity.
The selectivity of trawls with capron cod-ends of the followingmesh openings were investigated in the Baltic Sea by 300 trawlerswith 300-horsepower engines:
(a) 80 mm (93,5 tex x 12 yarn) and 90 mm (93,5 tex x 24 yarn)for cod.
(b) 20 mm, 32 mm and 36 mm (93~5 tex x 12 yarn) for Balticherring.
The dependence of the by-catch of undersize fish on their abundancein the fishing area and on the length composition of the populationwas determined.
Commercial, biological and biochemical investigations were continuedon the quantity of wounded fish and the survival rate of'Balticherring which had escaped through trawl meshes. The mortalityrate of wounded herring was not high, supporting the fact that itis possible and advisable to regulate mesh size for conservationof .herring stocks.
In 1974, all trawlers which conducted investigations in the ICESarea used trawls made of capron fibres.
In 1975, investigations will be continueä on the development offishing techniques, on clarification of methods for assessingfishing effort, intensity and selectivity, and on fish behaviourstudies.
International Council for theExploration of the Sea
Gear end Behaviour Committee
Scotland
(Jo J o Foster)
CoMo 1975/B:1Addendum No o 1
..
TI1e main subjects covered in the fish capture and fish detectionprogramme of. interest po. the·committee are indicated without detailedreference to the suppo~t facilities, eoge ,design and development ofinstrumentationo Such facil~ties..~e, described in papers pF~sented to theengineering rorking group of ,the.comm~~tee~
Gear Technology
. Research and development work on a range of 4-panel wide openingdemersal trawls, was continued; ßpecial emphasis was placed on reducingsusceptibility of the geare ·to demage whilst at the same time reducingmaterial thicknesses etc to give low drag characteristicso ,Some suceessfuleommercial trials have been carried out and further trials are plannedo . Ithas been found necessary to use both instrumentation teehniques and direetobservation by divers in order to tune these gears which were scaled versionsof the original 4-panel designs previously reported, designed to suit arange of horse powero
The main studies on pelagie trawling were eontinued and extended toinvestigate the possibility of using pelagie trawls close to and touchingthe sea bed without incurring damageo Special rigging in front of the netwas fqund necessary to allow the high aspect ratio boards to run at afixed distance from the sea bed even when the groundrope is on the sea bedeFast vertical movements of the gearhavebeen achieved such that it can'readily be manoeuvred over pinnacles, etco
Although the project investigating the use of powered rotors on thetrawl boards of pelagic trawls was somewhat curtailed through lack ofavailable sea time, a large rotor was designed for use with existing motorsand geared to run at 700 rpmo The equipment \Jorked weIl with 404 sqomomidwater otter boards operated with a 46 mo headline pelagic trawl; Itproved possible to control depths of the boards by ~ 20 fathoms even usingshort warp lengthso
Danish seine net studies were largely direeted to the produetion of afilm showing the operation of various nets using film material obtained inthe programme reported previouslyo Further studies on the shapes taken upand movement of ropes during the fishinE operation v!ere carried out usingdiving and seetor scanner observation techniqueso
Electrical fishing investigations aimed at increasing the efficiencyof trawls and other towed gears were continuedo Several reports of thiswork have been publishedo With flatfis~ comparative fishing results wereencouraging and the work is being extended initially to study the reaetionof roundfish to static and moving electrieal barriers with a view toenhancing the effectiveness of, for example, traps and passive gearso
The gear technology, data logging and analytieal processing work hasbeen expandedo An extensive data bank system is now in operation and willultimately allow rapid search of vast quantities of data using computerproerammeso The extracted data can then be used in further computerprogrammes to analyse and predict gear performanceo
1 0
Fish Behaviour
TI1e sensitivity and reactivity of commercially important fish to acousticand visual stimuli during fishing operations and the sVlimming ability offish when subjected to fright m1d h~rding stimuli continued to be the mainaspects of the behaviour research programme.
It was established that at sound frequencies below 110 Hz cod areable to determine the direction of sound sources. Other experiments designedto attract or scare free-living fish produced consistent results. Observationof fish behaviour using underwater televisiqn and sector scanning sonar hasshown that low frequency pure 'tones are much more effective than high frequencyton~s in attracting fish to the sound source whereas broad b.and pulsed lowfrequency sounds often produce a pronounced flight reaction.·
Development of acoustic tags for use in this work was c0ntinued incollaboration with the Lowestoft Labor~tory and a new form of barbeddetachment .device for use with ultrason~c transmitting tags w~s developedand proved•. Field work involving tracking .of. !ish indicated that cod showastrang tendency for'home range keeping'. behaviour which may be of majorimportance in population studies.
Initial trials with the use of acoustic stimuli to scare seals fromfixed salmon stations in coastal waters were undertaken and gave promisingresults. Extension of this work is planned.
Studies on swimming performance (burst speed capability and endurance)have led to arevision of previously accepted theories on aspects ofswimming mechanisms of fisho The actual performance equations previouslyused (e.g. swimming speed is directly related to fish Iength) have had tobe modified considerablyo
Fish Detection and Abundance Estimation
Several successful surveys were carried out using the 400 channel echointegrator, particularly for blue whiting stockso A simplified integratorusing digital techniques throughout was planned, and the design was almostcompleted and construction started by the end ofthe year.
o
2.
