CHAPTER 



BIOLOGICAL SAMPLING 



0-1 GeneraL — Biological organisms can be 

 obtained from the ocean in several ways. Drift- 

 ing micro-organisms such as zooplankton and 

 phytoplankton are collected by towing nets 

 through the water. Swimming animals (nekton) 

 are obtained by towing trawls at various depths 

 in the ocean. Bottom dwelling animals 

 (benthos) are collected by towing dredges along 

 the ocean bottom. And specialized attaching and 

 boring orgaiiisms are obtained by exposing ar- 

 rays of fouling panels. 



0-2 Biological Sampling Nets. — Biological 

 sampling nets are designed for various pur- 

 poses. Some nets can be used only when the 

 ship is stopped or at anchor, and other nets are 

 designed to take samjjles while the ship is drift- 

 ing or underway. Certain nets can be used to ob- 

 tain samples only at tlie surface, and still others 

 can be used to collect samples from any depth 

 desired. Net mesh sizes vary. The selection of 

 the mesh size depends on the organisms sought. 

 Qualitative samplers sieve organisms from the 

 water, but they do not measure the volume of 

 water that passes through the net. On the other 

 hand, quantitative samplers not only sieve 

 organisms, they also measure the volume of 

 water filtered. Biological sampling nets used by 

 the U.S. Naval Oceanographic OiRce are de- 

 scribed below. Biological towing observations 

 are recorded on Biological Log Sheet-0 (fig. 



0-3 Qualitative Plankton Sampling Net.— 



A qualitative plankton sampling net is shown 

 in figure 0-2. The net is cone shaped, and its 

 opening at the large end is fitted with reinforced 

 eyes and lashed to a metal ring. The small, or 

 cod, end of the net is attached to the sample 

 bucket. Qualitative plankton sampling nets 

 used by the U.S. Naval Oceanographic Office 

 have one-meter, half-meter, and 30 centimeter 

 metal rings, and are approximately 5 meters, 3 

 meters, and one meter long, respectively. 



0-4 How to Operate the Qualitative Plank- 

 ton Sampling Net.— The qualitative plankton 

 sampling net is simple to operate, and the only 

 tool required is a medium sized .screwdriver. The 

 qualitative plankton net may be towed either 

 vertically, obliquely, or horizontally. 



Step 1. Bridle the net to the towline with 

 three lines attached at equidistant points on the 

 metal ring. For a horizontal tow, use any line or 

 wire available for the towline ; for a vertical or 

 oblique tow, use the oceanographic winch and 

 %2" or %6"ii^'^h wire. 



Step 2. Check to assure that the mesh size 

 of the net agrees with the mesh size number on 

 the bottom of the sample bucket, and tighten 

 the screw-type base clamp to secure the sample 

 bucket to the small end of the net. 



Step 3. Lower the net over the weather side 

 of the ship if the ship is drifting or moving, or 

 stream tlie net to leeward if the ship is anchored. 



Step 4. When the net is open and streaming, 

 towing can commence. In some instances, it may 

 be necessary to add weights to the sampler 

 bucket or towing line to attain the desired depth. 

 Recommended towing speeds are 2 to •! knots. 



Step 5. Stream the net for 30 to 60 minutes 

 if takmg a horizontal tow, or lower it from sur- 

 face to the desired depth and back to surface if 

 obtaining an oblique or vertical plankton 

 sample. 



Step 6. To retrieve the net, haul it in by a 

 slow steady pull on the line, and in bringing it 

 aboard, avoid turning the net inside out. 



Step 7. Wlien retrieved, any plankton cling- 

 ing to the side of the net should be rinsed into 

 the bucket with sea water. Then, detach the 

 bucket and empty its contents into a sample jar. 

 If the bucket is full of specimens, reduce towing 

 time on next tow. If less than one-fourth full 

 increase towing time. 



0-5 Maintenance of the Qualitative Plank- 

 ton Net. — After the operation is completed, 

 rinse the net and bucket in fresh water to remove 

 any plankton that may have adhered to the 

 sampler; then, dry the net in the shade. (Keep 

 oil and grease oif net.) 



0-6 The Clarke- Bumpus Quantitative 

 Plankton Sampler. — The Clarke-Bumpus 

 quantitative plankton sampler is shown in fig- 

 ure 0-3. It is designed to be opened and closed 

 at a desired depth, and it is equipped with a 

 fiow meter that measures the volume of water 

 passing through the net. Thus, a quantitative 

 plankton sample can be taken at a desired depth 

 by means of this sampler without contamina- 

 tion from plankton in overlying water strata. 



0-1 



