This paper not to be cited without prior reference to the authors

International Council for the.Exploration of the Sea

CM1985/L:7Biological Oceanography Committee

•

A NEW MULTIDEPTH HIGH SPEED PLANKTON SAMPLER

by

J. Dunn, R.B. Mitchell, B.J. Ritchie

DAFS Marine LaboratoryVictoria Road

AberdeenScotland

ABSTRACT

This paper describes a plankton sampier capable of taking discrete sampies at selecteddepths, at high speed.

The sampier is monitored and controlled by means of an acoustic telemetry systemwhich provides on ship, real time, recorded information on depth, temperature, batteryvoltage and net function.

, ,RESUME

Ce m~moire d6crit un engin d'e"chantillonnage au plankton, capable de prelever ~grande vitesse des echantillons discrets aune serie de profondeurs determinees.

L'engin est surveille et commande au moyen d'un systeme acoustique de teh~mesure quifournit a bord, des informations enregistrees au temps reel, sur la profondeur, latemperature, la tension de la battei-ieet le fonctionnement de l'engin de p~che.

INTRODUCTION

Since 1969 the Dutch version of the Gulf m sampier (Zilstra 1970) has been used by theDAFS Marine Laboratory in Aberdeen for larval fish and zooplankton surveys.However i t cannat provide discrete depth sampies because there is na way of apeningor closing it. .

The Multidepth Gulf sampier is .a robust, easily handled, high speed, acousticallycontrolled system which can collect uncontaminated sampies from selected depths.

1

As the Aberdeen laboratory has had many years of experience in the use of the DutchGulf m the decision was taken to use a modified body to act as a chassis to carry a setof nets and the necessary acoustic electronics for the proposed high speed multidepthsampier. The modification enables a set of four nets to be fitted, each with a mouthaperture of 150mm - elose to the diameter of the Standard Gulf m nose cone aperture.The initial design incorporated a fixed offset nose cone delivering water to a rotatingset of nets - after the fashion of chambered handgun. Tbis approach was discarded infavour of the present design where only the plate and tube in the nose cone revolve(Figures 1 and 1c).

The Body

,The body of the sampier is in component form. It consists of a nose cone, a topsection, a bottom section and three taU fins. All of these components aremanufactured from bigh density fibre glass. Tbe exterior surfaces have a smooth gelcoat finish.

All areas subject to high impact and stress forces are substantially thicker tban themain body. Tbe, towing and depressor eyes are manufactured from stainless steel asare the fin attachment brackets. All bolts and fastenings are also in stainless steel.(Figures 1, 1a, 1b and 1c).

Tbe Nose Cone

In order to maintain a flow rate, into the four small nets, comparable with that into aStandard Gulf m a clip-on reducing nose cone is fitted (Figures 1 and Z). Tbe bush

, (Figures 1 and 3) wbich is fitted to the leading edge of tbe main nose cone provides theseating for the DELRIN swivel coupling on tbe end of tbe CRYSTAFLEX hose joined totbe driven plate. It also provides tbe seating for tbe clip-on nose, cone. Tbisarrangement provides fall back potential; as in the event of multidepth samplingsystem failure operators can continue to use the sampier as a standard Gulf m.

The Internal Frame

The frame which carries tbe nets and the OCEANO motor is based on tbe internalframe which holds and tensions tbe net in a Dutch Gulf m. Tbe construction is of Zcm, •aluminium tube, space frame with reinforcing hoops bolted to a 1cm thick, circularaluminium end plate. Tbis bas the stainless ste'el OCEANO motor bolted to it on thesame side as the net fastening collars. Tbe stainless steel drive shaft adaptor passes'through a TUFSET bearing in the centre of this plate (Figures 1, 4, 5, 6, 7). On thecircumference of tbe end plate face there are fourpegs wbich locate into a stainlesssteel ring (Figures 1 arid 8) bolted about 16cms inside the front of the fibre glass body.This ring provides tbe internal frame stop and ensures tbat the centre of tbe OCEANOmotor drive shaft adaptor'is in allgnment' witli the centre of the nose cone. It alsoprevents' distortion of tbe fibre glass body shell at the point where the driven plate andtube revolve.

'The internal frame is securely held in the fibre glass shell by two stainless steel togglebolts which locate into slotted bars welded to the internal frame. These bars fit intoreinforced slots in the body shell.

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•

The stainless steel wing nuts on the toggle bolts are hand tightened to ensure a securefit and shock cord hooks fitted to the end of the internal frame are clipped over theends of the wing nuts to prevent accidental release of the trame during deployment orrecovery.

The front face of the circular end plate is covered with a bondable P.T.F.E. material. FLUOBOND - as in the face of the driven plate fastened to the delivery tube. Thismaterial provides a low friction water tight seal between the two end plates.

Motor

The OCEANO MD120 motor drive unit in the sampier is the type used in mechanicalrelease apparatus. Under load it draws approximately 20 milliamps and althoughnorma1ly powered from a 12 volt DC supply it is run on a 30 volt supply in the sampier.

Electronic Package

Sampier depth, temperature and battery voltage are acoustically telemetered to atransducer mounted on a towed shark by a modified I.O.S. monitor on the sampier.Data is displayed on an E.P.C. 3200 S recorder. The electric motor which operates thenets is controlled by 10kHz command pulses transmitted from the surface. Successfuloperation of the motor is indicated by an offset on the battery voltage trace.

The I.O.S. monitor is modified to produce an 8 millisecond reference pulse. This pulseis detected by an interface unit designed at DAFS Marine Laboratory Aberdeen. Thepulse triggers the E.P.C. recorder and the resulting display is therefore synchronisedto the recorder and remains stationary even during shooting and hauling (Figure 9).

Nets

The four 25011 nets have mouth diameters of 150mm and are 150cms in length. Theyterminate in 5.08cms diameter polypropylene threaded ma1ejfemale codends which arefitted with 25011 bags. Tbe nets are fastened to the collars On the c:ircular end plate bystainless steel jubilee clips and tensioned at the rear by shock cord loops.

The system described has undergone successful sea trials on F.R.V. SCOTIA and is tobe used in future herring larval surveys. Further development and refinement of thesystem is underway. Tbe aim being to provide computer control and display ofmonitored parameters on a colour VDU.

REFERENCE

Zilstra, J.J. 1970 Herring larvae in the centra1 North Sea. Ber. Dt. Wisse Komm.Meresforsch., 21, 92-115.

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