824 



NATURE 



[August 26, 1920 



are fairly evenly distributed. This method gives us 

 what has been called "the fishing coefficient, " and 

 this has been estimated for the North Sea to have a 

 probable value of about 033 for those sizes of fish 

 which are caught by the trawl. Heincke," from iin 

 actual examination of samples of the stock on the 

 ground obtained by experimental trawling (" the catch 

 coefficient "), supplemented by the market returns of 

 the various countries, estimates the adult plaice at 

 about 1,500,000,000, of which about 500,000,000 are 

 caught or destroyed by the fishermen annually. 



It is difficult to imagine any further method which 

 will enable us to estimate any such case as, say, the 

 number of plaice in the North Sea, where the indi- 

 viduals are so far beyond our direct observation and 

 are liable to change their positions at any moment. 

 But a beginning can be made on more accessible 

 ground with more sedentary animals, and Dr. C. G. 

 J oh. Petersen, of the Danish Biological Station, has 

 for some years been pursuing the subject in a series 

 of interesting reports on "The Evaluation of the 

 Sea." " He uses a bottom-sampler or grab, which 

 can be lowered down open and then closed on the 

 bottom so as to bring up a sample square foot or 

 square metre (or in deep wat^r one-tenth of a square 

 metre) of the sand or mud and its inhabitants. With 

 this apparatus, modified in size and weight for 

 different depths and bottoms, Petersen and his fellow- 

 workers have made a very thorough examination of 

 the Danish waters, and especially of the Kattegat and 

 the Limfjord, have described a series of "animal 

 communities " characteristic of different zones and 

 regions of shallow water, and have arrived at certain 

 numerical results as to the quantity of animals in 

 the Kattegat expressed in tons — such as 5000 tons of 

 plaice requiring as food 50,000 tons of " useful 

 animals " (moUusca and polychaet worms), and 

 25,000 tons of starfish using up 200,000 tons of useful 

 animals which might otherwise serve as food for 

 fishes, and the dependence of all these animals 

 directly or indirectly upon the great Beds of Zostera, 

 which make up 24,000,000 tons in the Kattegat. Such 

 estimates are obviously of great biological interest, 

 and, even if only rough approximations, are a valu- 

 able contribution to our understanding of the meta- 

 bolism of the sea and of the possibility of increasing 

 the yield of local fisheries. 



But on studying these Danish results in the light 

 of what we know of our own marine fauna, although 

 none of our seas have been examined in the same 

 detail by the bottom-sampler method, it seems prob- 

 able that the animal communities as defined by 

 Petersen are not exactly applicable on our coasts, and 

 that the estimates of relative and absolute abundance 

 may be very different in different seas under different 

 conditions. The work will have to be done in each 

 great area, such as the North Sea, the English 

 Channel, and the Irish Sea, independently. This is 

 a necessary investigation, both biological and physical, 

 which lies before the oceanographers of the future, 

 upon the results of which the future preservation and 

 further cultivation of our national sea-fisheries may 

 depend. 



It has been shown by Johnstone and others that the 

 common edible animals of the shore may exist in such 

 abundance that an area of the sea may be more pro- 

 ductive of food for man than a similar area of pasture 

 or crops on land. A Lancashire mussel-bed has been 

 shown to have as many as 16,000 young mussels per 

 square foot, and it is estimated that in the shallow 



26 F. Heirxcke, Cons. Per. Internat. Explor. de la Mer, " Investigations 

 on the Plaice," Copenhagen, 1913. 



*7 See Reports of the Danish Biological Station, and especially the 

 Report for 1918, "The Sea Bottom and its Production of Fish Fooi. 



XO. 2652, VOL. 105] 



waters of Liverpool Bay there are from 20 to 200 

 animals of sizes varying from an amphipod to a 

 plaice on each square metre of the bottom.*" 



From these and similar data which can be readily 

 obtained it is not difficult to calculate totals by esti- 

 mating the number of square yards in areas of 

 similar character between tide-marks or in shallow 

 water. And from weighings of samples some ap- 

 proximation to the number of tons of available food 

 may be computed. But one must not go too far. 

 Let all the figures be based upon actual observation. 

 Imagination is necessary in science, but in calculating 

 a population of even a very limited area it is best to 

 believe only what one can see and measure. 



Countings and weighings, however, do not give us 

 all the information we need. It is something to know 

 even approximately the number of millions of animals 

 on a mile of shore and the number of millions of 

 tons of possible food in a sea area, but that is not 

 sufficient. All food-fishes are not equally nourishing 

 to man, and all plankton and bottom invertebrata are 

 not equally nourishing to a fish. At this point the 

 biologist requires the assistance of the physiologist 

 and the biochemist. We want to know next the 

 value of our food-matters in proteids, carbohydrates, 

 and fats, and the resulting Calories. Dr. Johnstone, 

 of the oceanography department of the University of 

 Liverpool, has already shown us how markedly a 

 fat summer herring differs in essential constitution 

 from the ordinary white fish, such as the cod, which 

 is almost destitute of fat. 



Prof. Brandt at Kiel, Prof. Benjamin Moore at 

 Port Erin, and others have similarly shown that 

 plankton gatherings may vary greatly in their nutrient 

 value according as they are composed mainly of 

 Diatoms, of Dinoflagellates, or of Copepoda. And, no 

 doubt, the animals of the "benthos," the common 

 invertebrates of our shores, will show similar differ- 

 ences in analysis.*' It is obvious that some contain 

 more solid flesh, others more water in their tissues, 

 others more calcareous matter in the exoskeleton, and 

 that therefore, weight for weight, we may be sure 

 that some are more nutritious than others ; and 

 this is probably at least one cause of that preference 

 we see in some of our bottom-feeding fish for certain 

 kinds of food, such as polychaet worms, in which there 

 is relatively little waste, and thin-shelled lamellibranch 

 molluscs, such as young mussels, which have a highly 

 nutrient body in a comparatively thin and brittle shell. 



My object in referring to these still incomplete 

 investigations is to direct attention to what seems a 

 natural and useful extension of faunistic work for 

 the purpose of obtaining some approximation to a 

 quantitative estimate of the more important animals 

 of our shores and shallow water and their relative 

 values as either the immediate or the ultimate food 

 of marketable fishes. 



Each such fish has its "food-chain" or series of 

 alternative chains, leading back from the food of man 

 to the invertebrates upon which it preys, and then to 

 the food of these, and so down to the smallest and 

 simplest organisms in the sea, and each such chain 

 must have all its links fully worked out as to seasonal 

 and quantitative occurrence back to the Diatoms and 

 Flagellates, which depend upon physical conditions, 

 and take us beyond the range of biology, but not 

 bevond that of oceanography. The Diatoms and the 

 Flagellates are probably more important than the 

 more obvious seaweeds not only as food, but also in 



28 "Conditions of Life in the Sea," Cambridge Ut iversity Pres.s, ipo8. 



29 Moore and others have made analyses of the protein, fet, etc., ni the 

 soft parts of Sponge, Ascidian, Aplysia, Fusus, Echinus, and Cancer at 

 Port Erin, and find considerable differences— the protein ranging, for 

 example, from 8 to 51 per cent., and the fat from 2 to 14 per cent, (see 

 li io-Cknnical Jouru.,- voi. vi., p. 291) 



