The depth of towing is of prime importance, 

 and any depth gage available and suitable 

 should be used if possible. Experimentation may 

 be desirable such as the use of explosives or fish 

 poison (a seepage container of rotenone) in 

 front of the net entrance, the use of a half-meter 

 plankton net of coarse mesh in place of the cod- 

 end can, or the installation of several truncated 

 cones of netting within the cod end (similar to 

 a fish weir) to prevent fish from escaping the 

 net. 



0-15 Removal of Specimens. — Carefully and 

 immediately remove all specimens from the net. 

 Small specimens should be kept in addition to 

 larger specimens. Immediately place specimens 

 in containers of sea water for subsequent preser- 

 vation. Color photographs in daylight should be 

 taken of each catch if possible, but must be taken 

 almost immediately, as fish lose their color rap- 

 idly when exposed to air or when preserved. 

 Photography may best be done by placing the 

 specimens in sea water in a shallow tray which 

 has been marked off with painted 1-inch squares 

 or other suitable scale. Print the trawl serial 

 number on a slip of paper and place it in a 

 corner of the tray to be photographed, in order 

 to provide positive identification. 



0-16 Maintenance of Midwater Trawl.— 



After using the net, it is not necessary to rinse 

 it in fresh water, but it should be spread out, 

 thoroughly dried, and then stored. Precaution: 

 Never store the net in a damp condition. 



0-17 Benthos Sampling. — Biological sam- 

 ples of bottom dwelling organisms (benthos) 

 are obtained by towing dredges along the ocean 

 bottom or by means of Van Veen samplers. 

 Clamshell snappers, and Orange Peel bucket 

 samplers. These samplers are described in chap- 

 ter L, Bottom Sediment Sampling. 



0-18 Preservation of Biological Speci- 

 mens. — Specimens taken by plankton tows 

 and small nekton specimens taken by midwater 

 trawls are stored in quart- or pint-size jars in a 

 5-percent solution of formalin (fig. 0-6). Fill 

 the jar only one-third full of specimens drained 

 of excess liquid, placa label shown in figure 0-7 

 in the jar, then add 5 percent buffered formalin 

 to completely fill the jar. 



Directions for preparing 5 percent buffered 

 formalin follow : 



To make 1 pint (460 ml.) of 5 percent buf- 

 fered formalin, place 24.2 ml. of commercial 

 formaldehyde (37 percent) in a pint jar, add 

 0.5 grams of sodiiun bicarbonate, then fill the re- 

 mainder of the jar with sea water. 



Directions for filling out the biological sam- 

 ple labels for plankton tows and nekton and 

 benthos samples are as follows : 



Figure 0-6. 



Preserving plankton and small nekton 

 and benthos specimens. 



Fill out the label with pencil (No. 21/2 or 3H 

 is most desirable) and place inside the container, 

 facing out. If samples are split into more than 

 one container, label each container and explain 

 in the remarks section of the label and indicate 

 on Biological Log Sheet-0. 



Benthos specimens obtained with bottom sedi- 

 ment sampling equipment are stored in quart- 

 and pint-size jars in 70 percent ethyl alcohol. 

 Kill specimens by immersing in fresh water for 

 approximately 3 minutes, and drain specimens 

 of excess liquid. Fill storage jar only one-third 

 full of specimens, place label shown in figure 

 0-7 inside jar, and then add 70 percent ethyl 

 alcohol to coinpletely fll the container. 



Specimens more than 3 inches long should 

 have some of the 5 percent formalin or 70 per- 

 cent ethyl alcohol injected into the body cavity 

 before being stored in the solution. If the speci- 

 men is too large to be stored in a jar, it should 

 be soaked in preservative, wrapped in cheese- 

 cloth, and packaged in a waterproof material. 



Marine plant specimens should be pressed and 

 dried between layers of absorbent paper such 

 as blotting paper or newspaper. Before press- 

 ing, the leaves and fruiting bodies of the plant 

 should be arranged so the plant's identifying 

 morphological characteristics are apparent. The 

 paper should be changed as necessary to insure 

 thorough drying, and a layer of cheesecloth 

 should be placed between the plant and the 

 upper paper to prevent damage to the specimen. 



0-6 



