On the Movements and Food of the Herring, etc. 399 



in the nets, which were also badly torn. Hence, it would 

 appear that the sharks, when once properly located, remain 

 in or near the same ground, where they have been, and pro- 

 bably are still, abundantly supplied with food ; and the once 

 favourite spawning- ground of the herring is naturally shunned 

 by them for a more quiet and suitable locality. Secondly, 

 for the last three years the fishermen at the Shetland fishing 

 grounds have been sorely tried by loss of time and expense 

 incurred in replacing their nets, owing to the enormous 

 quantity of vegetable matter, which they regard as dirt in 

 the water. This matter is almost exclusively diatom aceous, 

 consisting of the living frustules of Rhizosolenia Shrubsolei 

 and Thallasiosira Nordenskioldii, which we have already re- 

 ferred to, and which, in addition to destroying the fishermen's 

 nets, emit an exceedingly disagreeable odour. 



This was also my experience while on board the " Energy," 

 as we often passed through huge dense banks of it.^ Between 

 these were spaces of clear water, so that the nets were fre- 

 quently stretched across the Rhizosolenia banks and clear 

 spaces together; in every case where the nets were lying 

 among Rhizosolenia not a single herring was caught, while 

 outside of the diatomaceous zones they were found in abund- 

 ance. Many experiments were made to test the exclusive 

 power of the Diatoms, all giving the same results. 



Not being able to account for so much vegetable matter, 

 and little or no animal life in the surface water, I determined 

 to make some experiments as to how deep the alg?e were to 

 be found, and whether the pelagic life was more abundant 

 underneath the algoid material. Accordingly, three nets 

 were worked for an hour simultaneously, one on the surface, 

 one at 10 fathoms, and the other at 20 fathoms ; all three 

 were taken on board with great quantities of algse. The one 

 at 10 fathoms, however, contained the most, showing that it 

 was in greater quantities at 10 fathoms than either at the 

 surface or at 20 fathoms. 



I have never before observed algae to have such a decided 

 effect on the water. In two localities, during the " Challenger " 

 Expedition, viz., Arafura Sea and the Antarctic Sea, algae 



^ The localities are indicated by brown patches on the chart. 



