Marine phenomena

For well over a hundred years the weather observing logs submitted by British mariners to the Met. Office have been accompanied by recordings of marine life. The extent of these thousands of biological reports over time and space makes them of special importance. Seamen will know that their observations are highly valued by those scientists who receive them, and that reports from merchant ships may sometimes be the first and only indication of an event of ocean-wide significance.

A few reptiles such as turtles and sea snakes may be reported. Insects, commonly noted, always originate from land, often as stowaways; there is only one truly marine insect, a relative of the pond skaters, and even this lives on the surface of the water, not in it.

It may be instructive to list the groups most frequently reported in recent years. The most commonly reported cetaceans are sperm whales, followed by pilot whales, beaked whales generally, humpback whales, bottle-nosed dolphins, killer whales, blue whales and minke whales. In the case of fish, hammerhead sharks are the commonest, followed by manta rays, flying fish, white-tipped sharks, hatchet fish and sunfish; among invertebrates the By-the-Wind Sailor (Velella) and Portuguese Man-o'-War (Physalia) occur most of all, followed by swimming crabs and squid.

Everyone is aware that some watchkeepers keep a better lookout than others. Some have better eyesight, some have a naturally high level of attentiveness and some are less easily bored by watching the sea and sky separated by the straight line of the horizon. Nevertheless, the sharp-eyed spotting of sea-surface life is only the beginning of a useful observation. Those who first sight a marine organism may not necessarily make the best report.

Intellectual curiosity is needed and can be increased by reading. It is suggested that anyone interested in sea life should possess a few books of identification. There are many good books for home waters and several for global groups such as whales and seabirds, while for other waters it is best to search in local bookshops in ports visited for anglers' guides and other publications on marine life. These will be found more useful than the thickest tome for the wrong ocean. Back numbers of The Marine Observer contain many good descriptions and sketches of creatures actually seen by seamen from the deck of a ship, and may prove instructive.

Observers should try and draw what they have seen. An outline drawing, however simple, is one of the best aids to identification. As the drawing is made, careful observation of a whale or fish may reveal how many fins there are and how they are disposed. If the fish is not caught it should be drawn at once, before the memory fades. If the subject is an invertebrate, it should be drawn live in a bucket of water if possible, and notes added as to its size, colour and behaviour. Photographs are always useful but cannot be relied upon to show up the important features which can be highlighted by a line drawing. A photograph and drawing together is the best combination.

The importance of recording the occurrence of common animals as well as the unusual ones needs to be emphasized. Sightings of Velella or a hammerhead are as treasured as those of rare beasts: it is the common animals that are important, simply by being common. From many observations we can map their distribution and density, and perhaps learn how this distribution may change over the years.

A ship's magnetic compass may show appreciable deviation during the progress of a considerable or severe magnetic storm (see Magnetic Disturbances, page 151).

When an aurora of an active type is seen especially in latitudes lower than those in which aurora is normally seen, the possibility of deflections of the magnetic compass should always be borne in mind. Mere brightness of aurora in a region where aurora frequently occurs is no criterion of the occurrence of a magnetic storm, e.g. a bright, colourless and relatively quiescent aurora seen in August or September in the western Atlantic on the Belle Isle route.

If a ship happens to be struck by lightning, a sudden abnormal deviation of the compass may result. This error may be of a temporary or a permanent nature. Chronometers and other equipment may also be affected.

Abnormal magnetic variation occurs locally in various regions. These variations, if experienced, should always be recorded, particularly if no mention of abnormal variation is made in the appropriate Admiralty Sailing Directions or on Admiralty charts of the region.

Both these phenomena are popularly included in the term 'tidal waves', but neither has any connection with the tides. If either occurs, however, at a coast in conjunction with a high tide, its effect will obviously be greater and more destructive.

Abnormal rises of sea level, on which ordinary sea and swell waves are superimposed, are produced by severe storms. High water levels are thus caused on many coasts, but fortunately the rise is rarely large enough to cause great damage. With strong westerly winds the water level at Cuxhaven, at the mouth of the Elbe, may rise 2¹/₂ metres above the normal. On exceptional occasions the rise has reached 3¹/₂ metres above the normal. Destructive rises mainly occur in connection with tropical storms; rises of as much as 6 and 4¹/₂ metres have been experienced on different sections of the east coast of the United States.

Submarine earthquakes and landslides, and violent volcanic eruptions near a coast or on an island, produce abnormal waves. Sometimes these are visible waves, at other times shock waves, the latter giving the sensation in severe cases of the ship having struck a rock. The visible waves may travel many hundreds of miles, or in very severe disturbances many thousands of miles.

Single high waves in fair weather, with smooth or moderate sea, are almost certainly of seismic origin. Sometimes there may be two or more such waves at intervals. On the other hand, isolated giant waves which have been reported in gale conditions, are probably caused by a synchronism of the larger waves in a sea or swell cycle. Some of these have been estimated to reach or exceed a height of 24 metres.
Abnormal waves

There have been, in recent years, a number of reports of abnormal waves causing considerable damage to quite large ships. There have also been reports of smaller vessels lost without trace possibly as a result of the action of such waves. It has thus become recognized that from time to time, particularly in certain sea areas, there can occur very unusual or 'freak' waves, the causes of which are not yet fully understood and concerning whose frequency we do not know nearly enough.
Freak waves
A 'freak' wave has recently been defined as a wave of very considerable height ahead of which there is a deep trough, so that it is the steepness of the wave which is its outstanding feature and which makes it dangerous to shipping. Many of the reports of 'freak' waves have come from an area off the coast of south-east Africa during the period May to October. It is thought to be very significant that this is an area where a strong current (the Agulhas Current) runs counter to the high seas generated by the rather frequent south-westerly gales of the winter months and also to the unusually heavy swells which spread north-eastwards from the Southern Ocean at that time of the year.

Theory indicates that a counter current opposes the advance of the wave energy through a sea and that when the current speed reaches one-quarter of the speed of the waves the wave energy will be trapped, leading to an area of steep and confused waves beyond which there is a patch of relatively calm water. In practice this is not consistent with the very occasional occurrence of a very high wave, produced by sea and swell waves getting into phase, whose front is much steepened by an opposing current.

There are probably other ocean areas where conditions favourable for these 'freak' waves occur from time to time, e.g. in the vicinity of the Gulf Stream in a period of north-easterly gale. More information is greatly needed. Whenever these abnormal wave conditions are met with they should be reported in as much detail as possible. Besides the exact time and position, weather conditions and the course and speed of the ship, information is needed about wind and wave conditions, both before and after the encounter, about any other factors which may influence the state of the sea, and of course a full description of the 'freak' wave itself together with a brief note about any damage sustained. This information should be entered in the 'Freak Wave Report' or 'Additional Remarks' sections of the meteorological logbook.

BIRDWATCHING AT SEA
Mariners have a unique opportunity to observe many species of birds, which most of us can only read about.

Seabirds. Some species such as shearwaters, albatrosses and petrels, are pelagic and roam the oceans of the world, where they are seen following in the ship's wake, or feeding in areas rich in plankton and other small invertebrates. But they come to land only on remote islands. Ashore, many are heard rather more often than seen, because they nest in deep burrows, and move only by night. Gulls, terns and skuas are mainly coastal, although many make long journeys on migration; the Arctic Tern makes a 25 000-mile annual journey from its breeding areas, often within the Arctic Circle, to winter in the Antarctic.

Landbirds. Vast numbers of landbirds also migrate across the sea, for example across the Bay of Biscay, eastern Atlantic and the Mediterranean from Europe to Africa and back. There are many similar areas of high density: the western Atlantic, Caribbean and Gulf of Mexico, the Gulf of Aden and Arabian Sea, and many areas in the Pacific. Most of these landbirds travel by night, at heights of about 5000 feet, unseen except on aero-radar. But when disoriented by fog or clouds obscuring the star patterns, or when tired by headwinds, they descend to rest aboard anything in sight. Ships can provide a haven of rest, and in adverse migration weather these 'falls' of birds can be spectacular, involving several hundreds of many species. Most often reported are the large, extrovert or multicoloured species such as ospreys and hoopoes, and many species of herons and egrets, kingfishers, and birds of prey such as falcons, hawks and owls. Some of these will hitchhike aboard ships for hundreds of miles, often in the 'wrong' direction, preying on the much more numerous and smaller warblers, finches, wagtails, robins, swallows and like species.
Royal Naval Birdwatching Society

Thus the identification of birds at sea can become an absorbing pastime as well as a fascinating hobby. The Royal Naval Birdwatching Society (RNBWS) was founded in 1946 to co-ordinate the activities of RN bird-watchers at sea, but has progressively widened its membership to include all who share a common interest in birds and the sea itself. Up to 100 Merchant Navy officers and ratings are members of the RNBWS, sending in contributions from many of the world's oceans, using specially designed reporting and census forms. Identification is greatly assisted by accurate descriptions, sketches and photographs, together with details of geographical positions, dates, wind and weather conditions. Such observations can have a unique scientific value, and analyses of these and extracts of meteorological logbooks from weather reporting ships, are published in the society's annual journal Sea Swallow, to provide a unique source of data, built up over 44 years. The UK Met. Office can put would-be members in touch with the RNBWS.
Seabirds under threat

Some seabird species are under threat of extinction because of the combined effect of damage to their breeding areas and feeding grounds. The culprit in both cases is often Man himself, either due to perdition by introduced cats and rats or by direct damage to the fragile ecology of the breeding islands; over fishing and pollution can upset the balance of food available in their feeding grounds. There is thus a growing worldwide interest in these phenomena and scientists need to know much more about their distribution, their feeding methods and their movements in the non-breeding season. Seafarers can therefore play an important role in establishing the facts.

DOLPHIN AND WHALE OBSERVATIONS
Identification of cetaceans (Latin: cetus, whale) at sea is not easy, as most of the animal cannot be seen and even when on occasion they leap clear of the surface it is only momentary. However, observing and recording sightings of cetacea can be a very rewarding experience.

Identification. The various cetacean species often appear very similar to one another and must be carefully examined before they can be identified with any degree of certainty. Every species has one or more characteristic similar to those of another and by systematically working through a set of characteristics there is a greater chance of identifying any particular species. The behaviour of any species often changes according to the circumstances and although helpful this behaviour may not always be as reliable as the morphological characteristics.

Whales In the case of the large whales, the larger the whale, generally the smaller and further back is the dorsal fin. The ways in which the whale surfaces, blows and dives are, when added to size and colour characteristics, useful to know before attempting an identification. In the case of smaller whales and dolphins, especially where known distribution patterns overlap, identification becomes even more difficult because there are many more options to consider. In addition to making general descriptions, observers at sea can aid identification by experts, as well as adding to their knowledge of these intelligent creatures, by answering all or some of the following questions:

Many marine organisms have the ability to produce light. This phenomenon is known as bioluminescence and it occurs in many different visible forms. Most bioluminescence observed from a ship at sea is induced by the turbulence of the wake or bow wave, and is usually made up of the responses of many different organisms. Nevertheless this visible bioluminescence is frequently dominated by the contribution of certain microscopic forms which are present in abundance in the surface waters.

Types of bioluminescence. Although the most frequently encountered phenomenon is a relatively uniform glow, interspersed with occasional flashes from larger animals, there are also a number of more remarkable manifestations reported by observers at sea. These include:

e) Great systems of bands rotating round a central hub like the spokes of a wheel. These often develop from moving parallel bands and are known as phosphorescent wheels'. More than one wheel may be visible at once, rotating in the same or opposite directions.

Most of our knowledge of the varied forms of bioluminescent phenomena has been derived from the observations recorded in ships' meteorological logbooks and these will continue to be of the greatest value. The accumulation of eyewitness reports, together with the research by marine biologists on particular species, will provide the means for better interpretation of the causes of the phenomena and their significance in the ecology of the oceans.

Observations should always be as precise and as detailed as possible and should include quantitative estimations wherever practicable. Examples of these are the size of what appear to be individual organisms, or the direction, rate, length and width of luminous bands. A water sample is always very helpful if it can be treated with a convenient preservative. Ideally, the addition of formaldehyde to give a 5 per cent solution will leave the contents of the water easily identifiable. If formaldehyde is not available, alcohol can be used, even in the form of branded spirits, but the alcohol content of the diluted sample should be at least 10 per cent. Tincture of iodine can also be used to good effect. In any case a record of whether the water sample was luminous when shaken or stirred would be useful, and whether any organisms were visible in the sample.

It is important to recognize that the degree to which the observer is dark adapted can make a great difference to his ability to see bioluminescence, and particularly to his estimate of its colour. The colour of a weak light is very difficult to assess unless the observer is adequately dark adapted because the colour sensitivity of the human eye changes with the light conditions. Whenever the bioluminescence is bright enough an estimate of its colour can be very useful in its interpretation.

It is now possible to classify the various forms of bioluminescent phenomena and to interpret the causes of some of them with reasonable confidence. However, there are still many cases where we do not know either the organisms involved or the stimulus producing the light emission. For example, many of the apparent rates of movement of luminous patches, bands or wheels are too great to be caused by movements of the organisms themselves. A particularly puzzling phenomenon is the appearance of luminescence in the air a few feet above the surface of the sea when there is no obvious light in the water.

Those fortunate enough to observe moving parallel bands or a phosphorescent wheel should in particular try to give an estimate of the time interval between successive bands or spokes and the direction of rotation. How far from the ship was it, and did the pattern change? It is often possible to conduct simple experiments which can add substantially to the value of the report:

The normal colour of the sea in the open ocean in middle and low latitudes is an intense blue or ultramarine. The following modifications occur elsewhere:

It is desirable to record all cases of unusual sea coloration. To determine the cause, microscopic examination of a sample may be necessary, and whenever possible a sample should be taken for subsequent examination at the Institute of Oceanographic Sciences Deacon Laboratory. The sample can be preserved for a considerable time if a few drops of 40 per cent formalin or of a strong solution of mercuric chloride are adde