HIBERNATION OF MAMMALS — MATTHEWS 409 



after the brilliant days of summer the mineral resources of the sea 

 necessary for the growth of plants are temporarily depleted, and with 

 the onset of the shorter days of winter the diatoms die down ; when 

 they decrease in (juantity the exuberance of animal plankton fades 

 away, leaving the filter-feeders short of rations. The teeming shoals 

 of mackerel leave the upper strata of the sea and retire to deeper 

 w^ater where they lie inert waiting for the return of more favorable 

 conditions in the spring. It is then that the fishermen make their 

 great catches of trawled mackerel, sweeping up the shoals that lie 

 torpid near the bottom. 



Even the enormous basking shark, that may weigh up to three or 

 four tons, is entirely dependent on the plankton for its sustenance. 

 Throughout the sunmier months it basks in the sunshine of the upper 

 strata of the sea, cruising along at about two knots and filtering out 

 many tons of plankton from the sea water as it slowly forges ahead 

 with its mouth wide open; thus the planlvton is left stranded in the 

 pharynx on the elaborate arrangement of gill rakers carried on each of 

 the gill arches. But when the summer outburst of plankton dies down 

 there is not enough food for these enormous animals, and they disap- 

 pear from the surface waters. No one knows where they go, but 

 recent research has thrown much light upon their probable where- 

 abouts. 



It was long believed that basking sharks migrated to distant or 

 deeper waters during the winter of the temperate regions, in spite 

 of the fact that specimens are occasionally stranded or sighted even 

 during the depths of winter. Within the last few months new and 

 startling information has been reported upon tliis subject. Careful 

 investigation of a number of winter-caught basking sharks has shown 

 that they do not possess gill rakers — that they are, in fact, without 

 the means of obtaining their characteristic food. It is evident that 

 with the approach of winter the basking shark sheds its gill rakers so 

 that it is thereafter incapable of feeding, and that a new set of rakers 

 slowly develops during the winter to erupt like another dentition in 

 the spring. It is thus almost certain that the basking shark hibernates 

 during the winter, as it cannot feed and is therefore incapable of any 

 sustained activity. At this time of the year it probably retires to 

 deeper water — perhaps seaward of the Continental Shelf — and then, 

 like the mackerel, it proceeds to lie on or near the bottom in a state of 

 torpidity with all its metabolic processes reduced to the absolute 

 minimum ; there it stays until the next year's crop of plankton pro- 

 vides a pabulum which its newly grown gill rakers can collect. 



Parker and Boeseman have recently shown that when the plankton 

 is reduced to its minimum during the winter there is not enough of it 

 in each cubic meter of water to supply the energy necessary to keep 



