- Email: [email protected]
Specifications of zoo[lankton standard net to be used in the International Indian Ocean Expedition, and a design of a new closing net (In Japanese; English abstract)
Oceanographic Abstracts
551
(Refer to SCOR circular letters of November 22, 1961, and May 24, 1962, and a letter from Dr. W. S. Wooster, Director of Office of Oceanography, UNESCO, in Paris, of May 8, 1962). MOTODA S. 1962. Specifications of zooplankton standard net to be used in the International Indian Ocean Expedition, and a design of a new closing net. (In Japanese; English abstract). Inform. Bull., Planktol. Japan, No. 8: 30-40. At a meeting of zooplankton workers from several countries, and the representatives of SCOR and UNESCO, held in India in August 1962, it was proposed that all ships participating in the International Indian Ocean Expedition should sample zooplankton in standard haul using a standard net as the minimum sampling necessary for an initial survey of the zooplankton distribution. Clearly many ships will make, in addition to the standard samples, will supplement the standard haul with more extensive and detailed sampling. The type of the Indian Ocean Standard Net was discussed for some time and finally the standard net agreed upon will have the following specifications: Section (ref. to Fig. 3a) A B C D E
Diametre 113 cm 113 cm 113 cm 113-10 cm (tapering) 10 cm
Length
Material
70 cm 30 cm 100 cm 300 cm
Coarse netting Sail cloth Filtering cloth, 0.33 mm mesh Filtering cloth. 0.33 mm mesh
10 cm
Sail cloth
According to the above specifications a model of the standard net has been constructed in Japan (Figs. 4-6), which will be tested on cruise in September 1962. When this model production was completed a report of Mr. R. I. CURRI6 (1962) arrived, in which detailed descriptions on the structure of the standard net are given (Figs. 2, 3). The two nets do not differ in fundamental particulars, and it is thought that either net can be used as a standard, q-he Japan-style standard net is rigged with two rings, mouth ring and trunk ring, to prevent the cylindrical portion of the filtering cloth from collapse during the haul (Figs. 4, 6). However, this increases the weight of the gear and makes handling troublesome. It seems that the trunk ring is not necessarily needed (Figs. 5, 6c, 6d). CURRIE (1962) mentioned that the recommended bucket for the net is of the type used in the Discovery NTOV net, but a similar type of bucket can be used; the standard net haul is a vertical haul from 200 m to the surface; the speed of hauling should be one metre per second; normal hydrographic wire (4 m m diametre) is quite adequate for hauling the net. Since vertical net hauls are rarely absolutely vertical, the use of a flow-metre is strongly recommended. Ideally a flow-metre should be suspended centrally from a ring mounted inside the sail cloth band (B), it may be preferable in some cases to mount it in the centre of the net ring. While in this position the water passing the flow-metre can escape either through the wide mesh section (A) or through the nylon (C) and (D) sections, but it seems fairly certain on the basis of known properties of this design that the ratio of water escaping from A, C and D will remain reasonably constant and the flow-metre will therefore give a sufficiently accurate relative measurement between different hauls. One way to suspend a flow-metre in a proper place is to suspend it from the mouth ring to the centre of the canvas band by means of three iron bars each of which can be bent at about the middle portion into two pieces (Fig. 6h). When the net is collapsed during the lowering, the iron bars will be bent allowing collapse of the net. A test will be made on the cruise in September by attaching a flow-metre to the net in this way, and by comparing the revolutions of a flow-metre which is mounted at the centre of the mouth ring. According to the recommendation of SCOR the net haul should be made at night as close to 8.00 p.m. (zone time) as possible. Replicate hauls are most desirable, because there is usually a considerable variation of the catch. Although Currie (1962) suggested that a sinker, about 25 kg, should be suspended below the net bucket, the heavier the sinker, the faster it will sink. A sinker, about 100 kg, can be suspended below the net when 4 mm hydrographic wire is used. Resistance (R) of the Indian Ocean Standard Net is calculated by the following formula:
R = ½ C x . p. v L S where Cx is resistance coefficient, which is 1'33 taking the value in usual case; p is density of water divided by acceleration of gravity (1000 kg/m 3 divided by 9.8 m/sec% v is speed of haul (1 m/sec); S is the mouth area (1 m2). Therefore, R = 68 kg Then the force (F) required to haul the net is as follows: F=R+W where W is total weight of gear and sinker in the water; 3.5 kg (three bridles), 6 kg (mouth ring), 2 kg (flow-metre case), 1"5 kg (small net type bucket), about 3 kg (shackles, etc.) and 100 kg (sinker),
552
Oceanographic Abstracts
a total of 116 kg of which weight in the water is 101 kg 0apan style Indian Ocean standard net, without trunk ring). Therefore, F = 169 kg The breaking strength of 4 ram, 3 mm and 2 mm ordinary hydrographic wires is about 1760 kg, 990 kg and 440 kg respectively. Therefore, the safety factor is calculated 10 for 4 mm wire. I he power necessary for hauling 169 kg is calculated 2.2 H.P. and so a winch with power 5 H.P. or more will be needed. In addition to the standard net haul, Japanese ships are strongly urged to make divided vertical hauls with a closing net from great depths, preferably dividing the water column into 0-200 m, 200500 m, 500-1000 m, 1000-2000 m and 20(~3000 m. Oblique hauls are desirable, but the operation will be difficult in ships which are hardly able to keep constant low speed. Any type of closing net can be used, but the cloth should be made of fine mesh nylon or silk, because the sampling is planned to collect plankton as small as possible. One of the purposes of the standard net haul is the measurement of biomass of medium-sized zooplankton in the upper 200 m. Sampling of small-sized organisms is not attempted. A design of the vertical closing net is shown in Figs. 7, 8. The net is made of bolting silk having 0.I m m × 0"1 mm mesh apertures, qhe closing device is similar to that of the Juday net (JUDAY,1916). Although Bogorov's vertical standard net (BOGOROV, 1959) has an enlarged trunk ring, which enables the water flow to enter the net without disturbance, the net has the same diametre of trunk ring as that of the mouth ring to reduce the size of the gear. The water flow actually entering the net can be measured by a flow-metre mounted at the centre of the mouth ring or preferably at the centre of the trunk ring. Between the release mechanism of a similar design to that of the Discovery (KEMPand HARDY, 1929) and the trunk ring suspender there should be a swivel (Figs. 8b, 8d), since the strong rotation of the wire cable caused twisting when the long wire is paid out, forces the rotation of the release, often resulting in the breaking of the connection between the release and the closed net if suspended by a single suspender. The rings of the net made of iron pipes might be collapsed by very high pressure when the gear is lowered to great depths. Small holes pierced in the pipes will allow the water to expand inside the pipes. According to the above-mentioned formula, the resistance of 80 cm closing net is 34 kg when it is hauled at 1 m/sec, qhe weight of gear is 3 kg (release), 4 kg (brides and trunk ring suspender), 4"5 kg (mouth ring), 2 kg (flow-metre case), 4'5 kg trunk ring), about 4'5 kg (bucket, shackles, etc.); a total of 22.5 (19.6 kg in the water) kg. a sinker of 50 kg (43.5 kg in the water) is suspended, the force required to haul the net becomes 97.1 kg. 7he 4 mm wire cable weighs about 177 kg (154.2 kg in the water) when it is paid out by 3000 m, so that the force required to haul the net from 3000 m depth is 251"3 kg. This force is still within the allowance of tensile strength of 4 mm wire cable with safety factor 7. Power required for hauling is calculated 3-3 H.P. and so a winch with power 5 H.P. or more is needed. The Indian Ocean Standard Net is being made by the Marine Biological Association of the United Kingdom, the Aquarium, Citadel Hill, Plymouth, Devon, England. The cost of the net alone will be about £45 (about U.S. $130.00; about Y 45,000). The Plymouth Laboratory can also supply the rigging including the galvanized iron net ring and a simple galvanized bucket, which will cost an additional £10 (about $28.00; about Y10,000). An aluminium net ring and a Discovery type net bucket are available from the National Institute of Oceanography, Wormley, Godalming, Surrey, England, probably costing together about £25 (about $70-00; about Y25,000) (CuRRIE, 1962). In Japan the Indian Ocean Standard Net, under similar construction to Figs. 5, 6 is being manufactured by Rigosha & Co., Ltd., 2 Kajicho 1 Chome, Kanda, Chiyodaku, Tokyo, and Tsurumi-Seiki Kosakusho & Co., Ltd., 1506, Tsurumi, Tsurumi-ku, Yokohama. MOTODA S. 1962. Proposed biological apparatus and methods to be used on Japanese ships in the International Indian Ocean Expedition. (In Japanese; English abstract). Inform. Bull., Planktol. Japan, No. 8: 40-53. The plan presented here is the one originally proposed by Dr. Y. Saijo (primary production), Dr. R. Marumo and the writer (plankton) and Dr. M. Sakai (marine bacteria), based on the discussion at the assembly of the Japan National Committee on Oceanic Research and working scientists in the International Indian Ocean Expedition Programme on June 2-3, 1961, and was submitted to the meeting of JNCOR on March 20, 1962. (MOTODA, MARUMOand SAIJO, 1962). This was slightly changed and approved at the meeting of JNCOR on July 2, 1962. (1) Eye observation at sea All ships should record the following: diseoloured water, plankton patches (sampling with a simple high-speed sampler is recommended), dead fish floating on the sea surface; swimming squids, sharks, sea turtles, sea snakes, seals, Sirenia, dolphins, porpoises, killer-whales; drifting Portuguese man-of-war, Velella planktonic snails (Janthina) pieces of wood, kelps, land plants, cuttlefish skeletons, Spirula shells, pumice; fish schools; insects in the air; birds in the air or on the sea surface (ref. to ALEXANDER, 1954 revised). In addition, bird flocks should be recorded daily between predetermined times, e.g. 6.00-6.30 a.m. This is very useful for the study of geographical distribution of sea birds, as the number and species of birds near ships vary with the time of day. Morever, some birds come close to the ship when stopped, but fly away from it when underway, so that entries should indicate whether they were made when stopped or underway.
551
(Refer to SCOR circular letters of November 22, 1961, and May 24, 1962, and a letter from Dr. W. S. Wooster, Director of Office of Oceanography, UNESCO, in Paris, of May 8, 1962). MOTODA S. 1962. Specifications of zooplankton standard net to be used in the International Indian Ocean Expedition, and a design of a new closing net. (In Japanese; English abstract). Inform. Bull., Planktol. Japan, No. 8: 30-40. At a meeting of zooplankton workers from several countries, and the representatives of SCOR and UNESCO, held in India in August 1962, it was proposed that all ships participating in the International Indian Ocean Expedition should sample zooplankton in standard haul using a standard net as the minimum sampling necessary for an initial survey of the zooplankton distribution. Clearly many ships will make, in addition to the standard samples, will supplement the standard haul with more extensive and detailed sampling. The type of the Indian Ocean Standard Net was discussed for some time and finally the standard net agreed upon will have the following specifications: Section (ref. to Fig. 3a) A B C D E
Diametre 113 cm 113 cm 113 cm 113-10 cm (tapering) 10 cm
Length
Material
70 cm 30 cm 100 cm 300 cm
Coarse netting Sail cloth Filtering cloth, 0.33 mm mesh Filtering cloth. 0.33 mm mesh
10 cm
Sail cloth
According to the above specifications a model of the standard net has been constructed in Japan (Figs. 4-6), which will be tested on cruise in September 1962. When this model production was completed a report of Mr. R. I. CURRI6 (1962) arrived, in which detailed descriptions on the structure of the standard net are given (Figs. 2, 3). The two nets do not differ in fundamental particulars, and it is thought that either net can be used as a standard, q-he Japan-style standard net is rigged with two rings, mouth ring and trunk ring, to prevent the cylindrical portion of the filtering cloth from collapse during the haul (Figs. 4, 6). However, this increases the weight of the gear and makes handling troublesome. It seems that the trunk ring is not necessarily needed (Figs. 5, 6c, 6d). CURRIE (1962) mentioned that the recommended bucket for the net is of the type used in the Discovery NTOV net, but a similar type of bucket can be used; the standard net haul is a vertical haul from 200 m to the surface; the speed of hauling should be one metre per second; normal hydrographic wire (4 m m diametre) is quite adequate for hauling the net. Since vertical net hauls are rarely absolutely vertical, the use of a flow-metre is strongly recommended. Ideally a flow-metre should be suspended centrally from a ring mounted inside the sail cloth band (B), it may be preferable in some cases to mount it in the centre of the net ring. While in this position the water passing the flow-metre can escape either through the wide mesh section (A) or through the nylon (C) and (D) sections, but it seems fairly certain on the basis of known properties of this design that the ratio of water escaping from A, C and D will remain reasonably constant and the flow-metre will therefore give a sufficiently accurate relative measurement between different hauls. One way to suspend a flow-metre in a proper place is to suspend it from the mouth ring to the centre of the canvas band by means of three iron bars each of which can be bent at about the middle portion into two pieces (Fig. 6h). When the net is collapsed during the lowering, the iron bars will be bent allowing collapse of the net. A test will be made on the cruise in September by attaching a flow-metre to the net in this way, and by comparing the revolutions of a flow-metre which is mounted at the centre of the mouth ring. According to the recommendation of SCOR the net haul should be made at night as close to 8.00 p.m. (zone time) as possible. Replicate hauls are most desirable, because there is usually a considerable variation of the catch. Although Currie (1962) suggested that a sinker, about 25 kg, should be suspended below the net bucket, the heavier the sinker, the faster it will sink. A sinker, about 100 kg, can be suspended below the net when 4 mm hydrographic wire is used. Resistance (R) of the Indian Ocean Standard Net is calculated by the following formula:
R = ½ C x . p. v L S where Cx is resistance coefficient, which is 1'33 taking the value in usual case; p is density of water divided by acceleration of gravity (1000 kg/m 3 divided by 9.8 m/sec% v is speed of haul (1 m/sec); S is the mouth area (1 m2). Therefore, R = 68 kg Then the force (F) required to haul the net is as follows: F=R+W where W is total weight of gear and sinker in the water; 3.5 kg (three bridles), 6 kg (mouth ring), 2 kg (flow-metre case), 1"5 kg (small net type bucket), about 3 kg (shackles, etc.) and 100 kg (sinker),
552
Oceanographic Abstracts
a total of 116 kg of which weight in the water is 101 kg 0apan style Indian Ocean standard net, without trunk ring). Therefore, F = 169 kg The breaking strength of 4 ram, 3 mm and 2 mm ordinary hydrographic wires is about 1760 kg, 990 kg and 440 kg respectively. Therefore, the safety factor is calculated 10 for 4 mm wire. I he power necessary for hauling 169 kg is calculated 2.2 H.P. and so a winch with power 5 H.P. or more will be needed. In addition to the standard net haul, Japanese ships are strongly urged to make divided vertical hauls with a closing net from great depths, preferably dividing the water column into 0-200 m, 200500 m, 500-1000 m, 1000-2000 m and 20(~3000 m. Oblique hauls are desirable, but the operation will be difficult in ships which are hardly able to keep constant low speed. Any type of closing net can be used, but the cloth should be made of fine mesh nylon or silk, because the sampling is planned to collect plankton as small as possible. One of the purposes of the standard net haul is the measurement of biomass of medium-sized zooplankton in the upper 200 m. Sampling of small-sized organisms is not attempted. A design of the vertical closing net is shown in Figs. 7, 8. The net is made of bolting silk having 0.I m m × 0"1 mm mesh apertures, qhe closing device is similar to that of the Juday net (JUDAY,1916). Although Bogorov's vertical standard net (BOGOROV, 1959) has an enlarged trunk ring, which enables the water flow to enter the net without disturbance, the net has the same diametre of trunk ring as that of the mouth ring to reduce the size of the gear. The water flow actually entering the net can be measured by a flow-metre mounted at the centre of the mouth ring or preferably at the centre of the trunk ring. Between the release mechanism of a similar design to that of the Discovery (KEMPand HARDY, 1929) and the trunk ring suspender there should be a swivel (Figs. 8b, 8d), since the strong rotation of the wire cable caused twisting when the long wire is paid out, forces the rotation of the release, often resulting in the breaking of the connection between the release and the closed net if suspended by a single suspender. The rings of the net made of iron pipes might be collapsed by very high pressure when the gear is lowered to great depths. Small holes pierced in the pipes will allow the water to expand inside the pipes. According to the above-mentioned formula, the resistance of 80 cm closing net is 34 kg when it is hauled at 1 m/sec, qhe weight of gear is 3 kg (release), 4 kg (brides and trunk ring suspender), 4"5 kg (mouth ring), 2 kg (flow-metre case), 4'5 kg trunk ring), about 4'5 kg (bucket, shackles, etc.); a total of 22.5 (19.6 kg in the water) kg. a sinker of 50 kg (43.5 kg in the water) is suspended, the force required to haul the net becomes 97.1 kg. 7he 4 mm wire cable weighs about 177 kg (154.2 kg in the water) when it is paid out by 3000 m, so that the force required to haul the net from 3000 m depth is 251"3 kg. This force is still within the allowance of tensile strength of 4 mm wire cable with safety factor 7. Power required for hauling is calculated 3-3 H.P. and so a winch with power 5 H.P. or more is needed. The Indian Ocean Standard Net is being made by the Marine Biological Association of the United Kingdom, the Aquarium, Citadel Hill, Plymouth, Devon, England. The cost of the net alone will be about £45 (about U.S. $130.00; about Y 45,000). The Plymouth Laboratory can also supply the rigging including the galvanized iron net ring and a simple galvanized bucket, which will cost an additional £10 (about $28.00; about Y10,000). An aluminium net ring and a Discovery type net bucket are available from the National Institute of Oceanography, Wormley, Godalming, Surrey, England, probably costing together about £25 (about $70-00; about Y25,000) (CuRRIE, 1962). In Japan the Indian Ocean Standard Net, under similar construction to Figs. 5, 6 is being manufactured by Rigosha & Co., Ltd., 2 Kajicho 1 Chome, Kanda, Chiyodaku, Tokyo, and Tsurumi-Seiki Kosakusho & Co., Ltd., 1506, Tsurumi, Tsurumi-ku, Yokohama. MOTODA S. 1962. Proposed biological apparatus and methods to be used on Japanese ships in the International Indian Ocean Expedition. (In Japanese; English abstract). Inform. Bull., Planktol. Japan, No. 8: 40-53. The plan presented here is the one originally proposed by Dr. Y. Saijo (primary production), Dr. R. Marumo and the writer (plankton) and Dr. M. Sakai (marine bacteria), based on the discussion at the assembly of the Japan National Committee on Oceanic Research and working scientists in the International Indian Ocean Expedition Programme on June 2-3, 1961, and was submitted to the meeting of JNCOR on March 20, 1962. (MOTODA, MARUMOand SAIJO, 1962). This was slightly changed and approved at the meeting of JNCOR on July 2, 1962. (1) Eye observation at sea All ships should record the following: diseoloured water, plankton patches (sampling with a simple high-speed sampler is recommended), dead fish floating on the sea surface; swimming squids, sharks, sea turtles, sea snakes, seals, Sirenia, dolphins, porpoises, killer-whales; drifting Portuguese man-of-war, Velella planktonic snails (Janthina) pieces of wood, kelps, land plants, cuttlefish skeletons, Spirula shells, pumice; fish schools; insects in the air; birds in the air or on the sea surface (ref. to ALEXANDER, 1954 revised). In addition, bird flocks should be recorded daily between predetermined times, e.g. 6.00-6.30 a.m. This is very useful for the study of geographical distribution of sea birds, as the number and species of birds near ships vary with the time of day. Morever, some birds come close to the ship when stopped, but fly away from it when underway, so that entries should indicate whether they were made when stopped or underway.