- Email: [email protected]
Underwater photographs in the study of oceanic squid
Underwater photographs in the study of oceanic squid A . DE C. BAKER
Al~xact--A technique for photographing squid at great depths has been developed, which allows the species and size to be determined. Those photographed so far appear to be the same species as is commonly seen at the surface. I~ some recent short cruises of the R.R.S. Discovery II, attention has been given, among other things, to the populations of oceanic squid mainly in the region between the English Channel, The Azores and Gibraltar ; and the observations and material collected have provided some new information on their distribution. These studies have now received a considerable stimulus through the use of the deep sea camera designed by Dr. A. S. LAUCHTOr~and described by him in a separate article in the present issue of Deep Sea Research (p. 120). In a cruise in September, 1956, the camera w a s successfully adapted for photographing living squid in mid-water. MACKIntOSH (1956) has given a brief preliminary account of this work, but it may be useful now to give further information on the previous observations and to explain, with some technical details, the special value of the camera in these investigations. Very little is known at present about the habits, distribution, numbers, or even the species of oceanic squid, but it is apparent that these animals must play an important role in the economy of the ocean both as prey and predators. The world population of squid must be extremely large, for they form the major part of the diet of sperm and other toothed whales, and in certain areas are also eaten by great numbers of seals and birds. From the observations of the Discovery H it is clear that they are plentiful everywhere in at least a large part of the North East Atlantic, for in these recent cruises they have nearly always been seen when lights are shone on the surface at night ; sometimes as many as twenty or thirty are in sight at one time. As predators squid feed mainly on fish and possibly other squid. Ommastrephes pteropus, the form commonly seen at the surface in this warm-temperate part of the North Atlantic, feeds to a great extent on garfish (Scombresox spp. which are extraordinarily abundant in the area covered), and also on the smaller Myctophidae. The larger squid are very fast moving animals and are consequently rarely taken in nets of any kind. A wide variety of other methods of sampling the population has been tried. Large cage traps, spring loaded traps of various kinds, vertical long lines, towed lures, handnets and an ordinary rod and line have all been used at different times. For taking the surface feeding O. pteropus the last two methods mentioned have been by t~tr the most successful, as many as fifteen having been taken by handnetting in one night. Specimens up to an overall length of four feet or more can readily be taken by rod and line. Collections from the surface however, while providing material for systematic and anatomical work, provide very little information on their vertical distribution, a matter which is of particular interest. Sperm whales around the Azores are known to feed mostly on species of Histioteuthis and Cucioteuthis 126
Underwater photographs in the study of oceanic squid
127
(CLAltKE, 1956), yet these squid have never been seen at the surface during the cruises o f the Discovery 1L Further information about the vertical distribution of squid w a s obtained in 1954 in the Bay of Biscay when the arm of a squid was caught in a reversing water bottle at 1205 m. There is little doubt that this was from a species which has not been seen at the surface. This evidence shows that it is desirable to find some means of examining the populations in the deeper water layers. Limited information about the deep-living squid has been obtained from the vertical long lines fitted with baited paternosters. These consist of horizontal rods three feet long with a two foot length of cod line, a short wire trace, and a triple hook, attached at one end. They are clamped onto the 4 mm wire used for working vertical plankton nets and are strengthened by a strut which is also clamped to the wire, and which supports the rod half way along its length. While the wire is being paid out any number of paternosters can be attached to it at the desired intervals. They have been fished from the surface to 2500 m during both day and night. Although a squid has been caught by this method on only one occasion (an O. pteropus from 500 m), the baits, which are tied on to the hooks, have frequently been attacked ; this is indicated by the bait being completely removed, by marks o f squid beaks on the bait or by suckers left on the hooks. Surface observations and the use of paternosters during recent cruises have given the impression that squid perform a diurnal vertical migration, rising towards the surface at night and descending during the day, but the data for the upper 500 m during daylight are not yet sufficient to confirm this. The paternoster method has certain limitations. There must always be doubt whether, on every occasion that the bait has been taken, it has in fact been taken by a squid. This doubt does not arise when the bait bears marks of squid beaks, or suckers are found on the hooks ; even then, however, identification of the species is almost impossible. The limitations of the method also result in little or no information being obtained concerning the sizes and numbers of squid. When the automatic underwater camera was developed it was suggested that, with suitable modification, it could be used to show the presence, size, and probably the species of squid at a particular depth. With this object in view an attachment was designed which triggers off the flash unit of the camera when a vertical downward pull is applied to the end of a pivoted horizontal bar similar to one of the paternosters referred to above. This is done by means of a micro-switch enclosed in an oil-filled waterproof casing. The amount of pull required to close the switch can be varied by altering the tension in a spring. The apparatus is attached to a short length of scaffold tube clamped below the normal photographic and flash units, and the whole instrument is fastened to the end of the 4 mm wire by a swivel. It will be seen from Fig. 1 that the positions of the photographic and flash units are the reverse of those used for bottom photography. During the first trials of the camera with the paternoster attachment, it was found that except in very calm weather, the movement of the ship caused a pull on the paternoster and as a result many blank photographs were taken. For this reason the adjusting spring had to be set to almost maximum tension. Another modification was the addition of a pressure switch which can be adjusted to trigger off the flash and wind on the film at a predetermined depth. Such a switch was necessary since the camera has no shutter and the first frame on the film is fogged owing to exposure on deck and in the upper water layers. It is hoped in the
128
A. DE C. BAKER
future to incorporate a depth gauge in the field of the camera to provide permanent accurate depth records with each exposure. In September, 1956 R.R.S. Discovery H was on station in position approximately 40°N, 20°W for two periods of a week each with an interval of a week when work was done in the vicinity of the Azores. During these three weeks the camera was lowered on fourteen occasions of which six yielded one or more photographs of squid. When the first successful photographs were taken the baited hook was set 12 feet from the photographic unit. Later, to improve the contrast on the negative this distance was shortened to 5½ feet. I ~P'losh unit Also, since the squid photographed were only one to two feet in length, the wide angle lens (f.3-5 cm) was changed for one of longer focal length (f.5.0cm)so that the squid filled more of the negative. The short trace wire was dispensed with and the hook was fastened directly onto the paternoster, thus ensuring that the bait and squid appeared in the centre of the field. Photogr'ophic unit This arrangement produced very much better results. Figs. 2 and 3 show five photographs of II \\\ \ squid taken with the underwater camera at depths between 600 m and 1000 m with the modified system. A measure of the size of the squid is given by the marks on the paternoster which are at intervals of three inches. Fig. 2 (a) shows the long body and triangular fin characteristic of the Ommastrephidae; also the angular membrane on the third arm can be seen clearly just below the paternoster. In Fig. 2 (b) the difference II \ \\ \ between the suckers of the long tentacles \ and the arms is apparent; the tentacle has two rows of large suckers with a row o f smaller suckers on either side while the ~L_J~-Pr,essure switch arms have just a double row of medium sized suckers. In Fig. 2 (c) the fins appear 1 foot to be of a different form from that seen Fig. 1. The underwater camera fitted with the paternoster attachment. in Fig. 2 (a) and it is possible that this is another species. It seems more likely that the fins are being actively used for swimming and are in a position where the dorsal surface has been turned to face anteriorly. The squid has its ventral surface facing the camera and the siphon can be seen as the lower white mark above the arms.
~
\\ \ , \\\~ \ \
N '\\\ W \\\\\\ II
\
I
I
Fig.
2.
Underwater photographs of oceanic squid. (a) Station 3482, taken at 600 m. (b) and (c) Station 3485, taken at 1OOOm.
Fig. 3. Underwater
photographs
of oceanic squid. (a) Station 3484, taken at 700 m. (b) Station 3483, taken at 600 m.
Underwater photographs in the study of oceanic squid
129
The whiteness is due to reflection from the lining of the siphon as the squid forces a jet of water out through it. (This can be seen clearly in Fig. 3 (b)). As the squid appears to have one arm caught on the hook, the position of the fins, the open siphon and the outspread attitude of the arms suggest that it is resisting an upward pull from the movement of the ship which would have caused the photograph to be taken. In Fig. 3 (a) the mantle cavity is very distended by water taken into it just before it is forced out through the siphon as a jet - a process frequently seen when squid are caught at the surface with a rod and line. The two tentacles are seen gripping the bait and the tip of the horny beak shows as a dark mark in the centre of the white buccal mass between the arms. In Fig. 3 (b) the whole head has been turned sideways and upwards to grasp the bait. The head of the bait is lying along the paternoster and the tail is held by one of the squid's arms. When the camera was brought to the surface the tail half of the bait had been removed. All these photographs, with the possible exception of Fig. 2 (c), are probably of Ommastrephes pteropus. This species, which is found over such a wide area in the North East Atlantic, was observed and caught at the surface at the same time as the camera was recording it at 1000 m. Clearly it occurs in considerable numbers over a wide range of depth, and it would appear that, throughout this vertical range, O. pteropus is the dominant species of squid. It is, of course, possible that other species are less attracted to the garfish used as bait. It may be possible in the future to modify the present underwater camera so that not only black and white, but also colour film or even a cine-camera, can be used. In any case it is likely to be developed and improved, and may have applications which cannot be foreseen at present.
National Institute of Oceanography Wormley, hr. Godalming, Surrey REFERENCES R. 0956) Sperm whales of the Azores. Discovery Rep. XXVIII, pp. 237-298. MACKr~rroSHN. A. 0956) 2,000 feet down. The New Scientist (1), 60.
Al~xact--A technique for photographing squid at great depths has been developed, which allows the species and size to be determined. Those photographed so far appear to be the same species as is commonly seen at the surface. I~ some recent short cruises of the R.R.S. Discovery II, attention has been given, among other things, to the populations of oceanic squid mainly in the region between the English Channel, The Azores and Gibraltar ; and the observations and material collected have provided some new information on their distribution. These studies have now received a considerable stimulus through the use of the deep sea camera designed by Dr. A. S. LAUCHTOr~and described by him in a separate article in the present issue of Deep Sea Research (p. 120). In a cruise in September, 1956, the camera w a s successfully adapted for photographing living squid in mid-water. MACKIntOSH (1956) has given a brief preliminary account of this work, but it may be useful now to give further information on the previous observations and to explain, with some technical details, the special value of the camera in these investigations. Very little is known at present about the habits, distribution, numbers, or even the species of oceanic squid, but it is apparent that these animals must play an important role in the economy of the ocean both as prey and predators. The world population of squid must be extremely large, for they form the major part of the diet of sperm and other toothed whales, and in certain areas are also eaten by great numbers of seals and birds. From the observations of the Discovery H it is clear that they are plentiful everywhere in at least a large part of the North East Atlantic, for in these recent cruises they have nearly always been seen when lights are shone on the surface at night ; sometimes as many as twenty or thirty are in sight at one time. As predators squid feed mainly on fish and possibly other squid. Ommastrephes pteropus, the form commonly seen at the surface in this warm-temperate part of the North Atlantic, feeds to a great extent on garfish (Scombresox spp. which are extraordinarily abundant in the area covered), and also on the smaller Myctophidae. The larger squid are very fast moving animals and are consequently rarely taken in nets of any kind. A wide variety of other methods of sampling the population has been tried. Large cage traps, spring loaded traps of various kinds, vertical long lines, towed lures, handnets and an ordinary rod and line have all been used at different times. For taking the surface feeding O. pteropus the last two methods mentioned have been by t~tr the most successful, as many as fifteen having been taken by handnetting in one night. Specimens up to an overall length of four feet or more can readily be taken by rod and line. Collections from the surface however, while providing material for systematic and anatomical work, provide very little information on their vertical distribution, a matter which is of particular interest. Sperm whales around the Azores are known to feed mostly on species of Histioteuthis and Cucioteuthis 126
Underwater photographs in the study of oceanic squid
127
(CLAltKE, 1956), yet these squid have never been seen at the surface during the cruises o f the Discovery 1L Further information about the vertical distribution of squid w a s obtained in 1954 in the Bay of Biscay when the arm of a squid was caught in a reversing water bottle at 1205 m. There is little doubt that this was from a species which has not been seen at the surface. This evidence shows that it is desirable to find some means of examining the populations in the deeper water layers. Limited information about the deep-living squid has been obtained from the vertical long lines fitted with baited paternosters. These consist of horizontal rods three feet long with a two foot length of cod line, a short wire trace, and a triple hook, attached at one end. They are clamped onto the 4 mm wire used for working vertical plankton nets and are strengthened by a strut which is also clamped to the wire, and which supports the rod half way along its length. While the wire is being paid out any number of paternosters can be attached to it at the desired intervals. They have been fished from the surface to 2500 m during both day and night. Although a squid has been caught by this method on only one occasion (an O. pteropus from 500 m), the baits, which are tied on to the hooks, have frequently been attacked ; this is indicated by the bait being completely removed, by marks o f squid beaks on the bait or by suckers left on the hooks. Surface observations and the use of paternosters during recent cruises have given the impression that squid perform a diurnal vertical migration, rising towards the surface at night and descending during the day, but the data for the upper 500 m during daylight are not yet sufficient to confirm this. The paternoster method has certain limitations. There must always be doubt whether, on every occasion that the bait has been taken, it has in fact been taken by a squid. This doubt does not arise when the bait bears marks of squid beaks, or suckers are found on the hooks ; even then, however, identification of the species is almost impossible. The limitations of the method also result in little or no information being obtained concerning the sizes and numbers of squid. When the automatic underwater camera was developed it was suggested that, with suitable modification, it could be used to show the presence, size, and probably the species of squid at a particular depth. With this object in view an attachment was designed which triggers off the flash unit of the camera when a vertical downward pull is applied to the end of a pivoted horizontal bar similar to one of the paternosters referred to above. This is done by means of a micro-switch enclosed in an oil-filled waterproof casing. The amount of pull required to close the switch can be varied by altering the tension in a spring. The apparatus is attached to a short length of scaffold tube clamped below the normal photographic and flash units, and the whole instrument is fastened to the end of the 4 mm wire by a swivel. It will be seen from Fig. 1 that the positions of the photographic and flash units are the reverse of those used for bottom photography. During the first trials of the camera with the paternoster attachment, it was found that except in very calm weather, the movement of the ship caused a pull on the paternoster and as a result many blank photographs were taken. For this reason the adjusting spring had to be set to almost maximum tension. Another modification was the addition of a pressure switch which can be adjusted to trigger off the flash and wind on the film at a predetermined depth. Such a switch was necessary since the camera has no shutter and the first frame on the film is fogged owing to exposure on deck and in the upper water layers. It is hoped in the
128
A. DE C. BAKER
future to incorporate a depth gauge in the field of the camera to provide permanent accurate depth records with each exposure. In September, 1956 R.R.S. Discovery H was on station in position approximately 40°N, 20°W for two periods of a week each with an interval of a week when work was done in the vicinity of the Azores. During these three weeks the camera was lowered on fourteen occasions of which six yielded one or more photographs of squid. When the first successful photographs were taken the baited hook was set 12 feet from the photographic unit. Later, to improve the contrast on the negative this distance was shortened to 5½ feet. I ~P'losh unit Also, since the squid photographed were only one to two feet in length, the wide angle lens (f.3-5 cm) was changed for one of longer focal length (f.5.0cm)so that the squid filled more of the negative. The short trace wire was dispensed with and the hook was fastened directly onto the paternoster, thus ensuring that the bait and squid appeared in the centre of the field. Photogr'ophic unit This arrangement produced very much better results. Figs. 2 and 3 show five photographs of II \\\ \ squid taken with the underwater camera at depths between 600 m and 1000 m with the modified system. A measure of the size of the squid is given by the marks on the paternoster which are at intervals of three inches. Fig. 2 (a) shows the long body and triangular fin characteristic of the Ommastrephidae; also the angular membrane on the third arm can be seen clearly just below the paternoster. In Fig. 2 (b) the difference II \ \\ \ between the suckers of the long tentacles \ and the arms is apparent; the tentacle has two rows of large suckers with a row o f smaller suckers on either side while the ~L_J~-Pr,essure switch arms have just a double row of medium sized suckers. In Fig. 2 (c) the fins appear 1 foot to be of a different form from that seen Fig. 1. The underwater camera fitted with the paternoster attachment. in Fig. 2 (a) and it is possible that this is another species. It seems more likely that the fins are being actively used for swimming and are in a position where the dorsal surface has been turned to face anteriorly. The squid has its ventral surface facing the camera and the siphon can be seen as the lower white mark above the arms.
~
\\ \ , \\\~ \ \
N '\\\ W \\\\\\ II
\
I
I
Fig.
2.
Underwater photographs of oceanic squid. (a) Station 3482, taken at 600 m. (b) and (c) Station 3485, taken at 1OOOm.
Fig. 3. Underwater
photographs
of oceanic squid. (a) Station 3484, taken at 700 m. (b) Station 3483, taken at 600 m.
Underwater photographs in the study of oceanic squid
129
The whiteness is due to reflection from the lining of the siphon as the squid forces a jet of water out through it. (This can be seen clearly in Fig. 3 (b)). As the squid appears to have one arm caught on the hook, the position of the fins, the open siphon and the outspread attitude of the arms suggest that it is resisting an upward pull from the movement of the ship which would have caused the photograph to be taken. In Fig. 3 (a) the mantle cavity is very distended by water taken into it just before it is forced out through the siphon as a jet - a process frequently seen when squid are caught at the surface with a rod and line. The two tentacles are seen gripping the bait and the tip of the horny beak shows as a dark mark in the centre of the white buccal mass between the arms. In Fig. 3 (b) the whole head has been turned sideways and upwards to grasp the bait. The head of the bait is lying along the paternoster and the tail is held by one of the squid's arms. When the camera was brought to the surface the tail half of the bait had been removed. All these photographs, with the possible exception of Fig. 2 (c), are probably of Ommastrephes pteropus. This species, which is found over such a wide area in the North East Atlantic, was observed and caught at the surface at the same time as the camera was recording it at 1000 m. Clearly it occurs in considerable numbers over a wide range of depth, and it would appear that, throughout this vertical range, O. pteropus is the dominant species of squid. It is, of course, possible that other species are less attracted to the garfish used as bait. It may be possible in the future to modify the present underwater camera so that not only black and white, but also colour film or even a cine-camera, can be used. In any case it is likely to be developed and improved, and may have applications which cannot be foreseen at present.
National Institute of Oceanography Wormley, hr. Godalming, Surrey REFERENCES R. 0956) Sperm whales of the Azores. Discovery Rep. XXVIII, pp. 237-298. MACKr~rroSHN. A. 0956) 2,000 feet down. The New Scientist (1), 60.