Marking Rate 



Observations based on several field experi- 

 ments indicate that an inexperienced person 

 can mark 200 to 240 shrimp per hour; ex- 

 perienced workers can often mark 300 or 

 more shrimp per hour. Marking shrimp by 

 injection is tedious work, so in spite of the 

 rate-per-hour given, one person may be ex- 

 pected to mark no more than 2,000 shrimp 

 a day. 



Field experiments require that the number 

 of marked shrimp be counted prior to release. 

 This is best done as the shrimp are being 

 injected. A set of 10 colored beads strung 

 on a small wire serves this purpose very 

 nicely. One bead is moved when 10 shrimp 

 are marked and a 100-tally mark made as 

 the set is completed. Losses due to marking 

 can be determined as the shrimp are released 

 and then subtracted from the total number 

 marked. 



RELEASE OF MARKED SHRIMP 



marked shrimp should be released a few 

 hundred at a time during daylight hours and 

 observed until they have safely burrowed into 

 the bottom. Rough estimates of immediate 

 losses due to predation may be obtained 

 accordingly. In deep water, releases should 

 be made by use of an underwater release 

 box (fig, 7). The illustrated box has been 

 used successfully to release shrimp on the 

 bottom in water depths to 25 fathoms. In use, 

 the box is attached to a suitable line or cable 

 preferably wound off a power winch. Shrimp 

 are placed in the box after marking, lowered 

 to the bottom slowly, and allowed to escape 

 at or near the bottom when the box-opening 

 device is activated by a weighted messenger. 



Marked shrimp being released in the general 

 area where recapture may occur should be 

 liberated in small groups at random so they 

 may mix well with the standing crop. They 

 should ordinarily be released as near as 

 possible to the site of original capture. Rocky 

 bottom areas should be avoided since they 

 frequently contain excessive numbers of pre- 

 daceous fish. 



The manner of handling shrimp after the 

 dye is injected and until they are safely 

 returned to the water is important. Since 

 shrimp suffer temporary impairment of swim- 

 ming ability and some loss of equilibrium 

 upon injection, they should not ordinarily be 

 released for at least 4 hours following stain- 

 ing. Because during this period they are also 

 less agile than unmarked animals and react 

 slowly to external stimuli, they are more 

 prone to predation. 



In experiments designed to provide an esti- 

 mate of fishing mortality, it is essential that 

 we know within rather narrow limits the 

 actual number of stained shrimp released 

 alive and in good condition. It is suggested, 

 therefore, that whenever it is feasible to do 

 so, each group of stained shrimp be held for 

 24 hours following injection. Due to handling 

 and marking there is always a small mor- 

 tality that will not be apparent in the first 

 4 hours. 



In areas characterized by relatively clear 

 shallow water and active predator populations. 



STAINS AND STAINING 

 SOLUTIONS 



Kinds and Quality 



Of the four vital dyes reported most useful 

 for marking shrimp (Dawson, 1957), three 

 have been subjected to extensive field and 

 laboratory tests. These are fast green FCF, 

 Trypan blue, and Trypan red. The fourth, 

 Niagara sky blue 6B, has not been field 

 tested. Experience with these dyes indicates 

 that properties of a given dye (color) vary 

 with the manufacturer, which may be due to 

 differences in the mordant characteristic of 

 each product. Culling (1957) points out that 

 difficulty In achieving a satisfactory stain 

 may be experienced when using too pure a 

 form of certain dyes; that is, some impurities 

 are necessary components in many staining 

 compounds. 



The fast green FCF manufactured by Na- 

 tional Aniline and the Trypan blue and Trypan 

 red manufactured by Harleco proved satis- 

 factory. Trypan blue and fast green FCF both 



