C30 REPORT OF COMMISSIONER OF FISH AND FISHERIES. 



establislif'd than could have been hoped. IJiavo nh-eady shown that 

 this I'undaniental premise, is entirely wrong. The iiiaxs of plo.nlton in 

 the ocean is not perennial and constant, hut ofhi(/hIi/ variahle and oseil- 

 latinfj size. The biological conipo.sition is very diverse, dependent upon 

 temporal variations — year, season, weatlier, time of day, upon climatic 

 conditions and especially upon the complicated ciirrentic conditions of 

 the streams of the sea, of the oceanic and littoral currents, the deep 

 currents, and the local zoocurrents. 



A comprehensive and fair estimation of all these cecological condi- 

 tions must a in'iori lead to the conviction that the distribution of the 

 ])lanldon in the ocean mvst he extremely irreefular, and we find this 

 "purely theoretical view comi)letely established'' a posteriori by the 

 compaia.tive consideration and comparison of all the earlier above- 

 mentioned observations. These can not be regarded as refuted by the 

 opposing view of Hensen ; for the empirical basis of the latter is, in 

 regard to its time and i)lace, much too scanty and incomplete. 



One might perhaps object that the technical methods of plankton 

 capture which Hensen employed gave more complete results than the 

 methods hitherto used: but this is not the case. The recent descrip- 

 tion which Hensen gives of his technical methods for obtaining plankton 

 (or pelagic fishery) is A^ery praiseworthy (9, pp. 8 to 14). The construc- 

 tion of the net (material, structure of the net, size of filtration), the 

 management of the catch and of the craft, are there carefully described. 

 The advance of the new teehniciue there realized may indeed serve to 

 carry on the pelagic fishery or i)]ankt()n cai)turemore productively and 

 more completely than Avas possible with the previous simjder technical 

 ai)paratus of i>lanktol()gy ; but 1 can not find that one of the proposed 

 improvements of this pelagic technique shows a great advance in prin- 

 ciple and is at all conqtarable to the great advance which Palumbo 

 and Chierchia made in 1884 by the invention of the closible net. 

 Besides, I can not understand how the new "■plankton net" constructed 

 by Hensen could give more ac<'urate results than the siini)le "Miiller 

 net" hitherto emidoyed, and the "toNv net^' used by the Challenger. 

 Such a A'crtical net will always bring up only a part of the plankton 

 contained in the volume of water going through it, an<l by no means, 

 as Hensen and lirandt believe, is a column of water whose height and 

 base area can be measured with sufficient accuracy perfectly filtered. 

 In this sup]>osition the incalculable disturbances by conditions of cur- 

 rents, es])e(;ially of concealed deep streams, are left out of account, as 

 already mentioned. Besides, Chierchia has lately shown how unreliable 

 and li(tle ])r()duetive is the fishery with the vertical net on account of 

 the consideral)U^ hoiizontal swimming movements of the pelagic animals 

 (Sj p. 79). At any rate, the improvements Hensen has introduced into 

 the technical m<'fhods of ])lankton capture are not so important that 

 the i-emarkable ditference between his and the earlier results can 

 thereby be explained. 



