38 



creasing its catch has become one of the classic examples of the practical value 

 of planktonic research. 



The Hardy plankton recorder gives a continuous line of ecological obser- 

 vation across an area being investigated. Patchiness in the distribution of 

 plankton can be effectively investigated with this instrument. However, every 

 method of plankton collection has its limitations, and the most serious disad- 

 vantages of this instrument are (1) it is designed for towing at a single depth 

 only, and this near the surface, and (Z) the organisms are crushed when rolled 

 up in the filtering band, making identification difficult. 



Clarke-Bumpus Sampler - Another plankton sannpler that has received wide 

 acceptance during the past few years is the Clarke-Bumpus net. It is a small- 

 sized net, designed to be towed at slow speeds, which contains both a closing 

 device and a flow meter. The instrument consists essentially of a brass tube, 

 five inches in diameter and about six inches long, to which may be attached 

 small silk or nylon nets of any desired mesh. The Clarke-Bumpus sampler 

 can be used for either oblique or horizontal hauls, and it can be modified to take 

 vertical hauls. It can be used singly or in series of several nets attached to 

 the same cable at any desired interval. 



This sampler is a small net, designed to collect moderate amounts of 

 plankton. It can be used in freshwater as well as marine habitats. It has def- 

 inite advantages over standard plankton nets in problems that do not require 

 large volumes of plankton. Wiborg (1948) compared the performance of the 

 Clarke-Bumpus sampler with both a centrifugal plankton pump and a standard 

 Nansen closing net, and found the Clarke-Bumpus sampler more satisfactory in 

 most respects. The Clarke-Bumpus sampler has the limitations inherent in 

 any sampler towed at relatively slow speeds and used for short distance rather 

 than continuous sampling. It is described by Clarke and Bumpus (1950). 



Hi-Speed Samplers - For some years I have been concerned with the problem 

 of the quantitative sampling of fish eggs and larvae. The patchiness character- 

 istic of the distribution of holoplankton is accentuated in the distribution of fish 

 eggs and larvae. Furthermore, the quantitative sampling of fish larvae pre- 

 sents several perplexing problems, not the least of which is the ability of many 

 of the large larvae to "dodge" a slow moving net during daylight hours. Stand- 

 ard plankton nets are attached to a towing wire by a bridle about 5 meters long, 

 and it is quite likely that both the towing wire and the bridle act as scares. 

 Hence, to prevent dodging it was desirable to devise a net that would precede 

 the towing wire rather than follow it, and one that could be towed at high speeds. 

 To obtain a more representative sample, it was necessary to devise a sampler 

 which could be hauled over considerable distances. To take depth distribution 

 as well as horizontal distribution into account, the samplers should be usable 

 in series, and a suitable depressing force applied to maintain the instruments 

 at the desired depths. Furthermore, it was necessary to have some means of 

 metering the water entering the net, and desirable to have a method of recording 

 the depth at which the net fished. We constructed a pilot model of a hi-speed 

 net which fulfilled about half of the above requirements. It had a flow meter, 

 but no depth meter. By using the expedient of attaching the net to the end of 

 the wire it was possible to have the mouth opening (1" in diameter) precede the 

 wire. The net could not be used in series, nor could it be sunk to any depth. 

 It was limited to horizontal tows near the surface. Within its limitations it per- 

 formed exceedingly well. Nothing iniitsppath dodged it. Slender fish, 8 or 10 

 inches, were taken on several occasions when met head-on by the net. This 

 type of hi-speed net would still be valuable for reconnaissance work. 



