18 ? Museum Notes

3,500 in the open sea—off Alaska this rich belt extended about 30 miles from shore; we have no knowledge of its breadth on the B. C. coast, except that it extends beyond 20 miles seaward off the entrance to Barkley Sound.

In estimating the amount of “plankton” in the sea, we have not only to deal with areas but also with depths; for instance, at depths of ten or fifteen fathoms diatoms may be more numerous than at the surface, or we may have to descend one or two hundred fathoms before finding copepods or schizopods in abundance.

The abundance of diatoms near the coast is due to the enrichment of the water by fertilizing materials derived from rivers and streams or substances dissolved by the sea on the beaches; they increase exuberently during April and May, then decrease un- til autumn, when a lesser increase is usual, and during the winter the summer species are replaced largely by other species in very much fewer numbers.

As to their food value, recently (Vide “Nature,’ October 15th, 1927) Prof. H. H. Gran has published the results he obtained in a European area; by finding the amount of oxygen dissolved in the-water, he estimated the amount of useful food they produced (in terms of glucose), this amounted to 5.2 grammes per cubic metre for a depth of ten metres; put into our units, this is 470 Ibs. per acre, during 20 days in the spring while they were attaining their vernal maximum.*

It is by this conversion of chemical elements into food products by plants (Bac- teria, Diatoms, Algae, etc.) that the total amount of animal life in the sea is main- tained in spite of the quantities of animal products that are being continually with- drawn by man and by natural causes.

Plants are also necessary for the purification of the water, the oxygen, which they liberate oxidizing decaying animal matter.

The chemistry of the sea, however, is very complicated; the advances made in molecular physics of recent years showing that the chemical actions and reactions taking place there are much more complicated than had been supposed.

The animal life in the “plankton” is bewildering in its variety of species, and its immense numbers are almost beyond belief.

For instance, herrings or pilchards may be feeding on a medium-sized species of copepod (2 mm. in length) ; each fish may eat a fifth of an ounce, as it takes 75,000 such copepods to weigh an ounce; this means 15,000 are required for each fish: one shoal of these fish may number two or three million individuals (about 1,200,000 herrings weigh 100 tons).

If the feed is a large species of copepod (4-5 mm. in length), some 2,000 could be eaten by each fish; and this daily consumption may continue over lengthy periods. An important constituent of the “plankton” are the pelagic shrimps (Schizopoda, pl. IV., fig. 6), of which there are numerous species; about 500 to 600 of these weigh an ounce; they are called by fishermen “pink feed’? and by whalers ‘whale feed.’ They are a favorite food of many fishes, including salmon and pilchards.

The writer is informed by an authority on whaling that five species of whales off the B. C. coast feed on these shrimps, the feeding grounds being some forty miles off shore, and that 1,500 Ibs. would be a moderate estimate of the weight of these small crustaceans with which the stomach and digestive tract of a whale measuring 50 to 60 feet in length would be packed; this quantity representing the daily consumption.

The whales now are greatly reduced in numbers and it would be interesting to know if these shrimps have correspondingly increased.

* In chemical notation: 6H,O+ 6CO,=C,H,,0, (glucose) + 30,.