Thirty -three shrimp were recaptured in water shallower (16 to 19 fathoms) 

 than in the release areas; no shrimp were recaptured in deeper water. 



The information obtained from the return of marked shrimp indi- 

 cates no immigration into and little long-distance movement out of the staining 

 area. The stocks of shrimp off Pass Cavallo appear to have made a short- 

 distance nnovement in an easterly direction. Since marked shrimp are still 

 being returned, and the catch and effort data are not yet available, no attempt 

 has been made to estimate fishing mortality. 



Nautical miles 



15 or less 



16 - 30 

 31 - 45 

 46 - 60 

 61 - 75 



84 



49 



133 



Seabed drifters, which indicate the direction of bottonn currents, were 

 released along with marked shrimp. The return of these drifters indicates that 

 there was a slow westerly current in the staining area. 



At present, there are only two stains. Trypan blue and fast green 

 FCF, that are suitable marking agents to use on shrimp for growth and mor- 

 tality studies. To increase the versatility of the staining technique, laboratory 

 experiments are being made to find additional stains. 



Primary marks such as fast green FCF are now used exclusively. 

 These stains are obvious and, with familiarization, are easily seen by fisher- 

 men. Secondary marks are not so obvious and are identified by visual, chemical, 

 or fluoronnetric examination in the laboratory. The use of a series of secondary 

 marks with primary marks increases the number of possible experiments that 

 can be carried on at one time. 



To date, 34 stains, dyes, and inks have been tested for use as either 

 primary or secondary marks. Of these, only certain nunnbering machine inks, 

 blue and green, show promise as primary marks for short-term experiments 

 of no more than 50 days. 



Preliminary results indicate that several fluorescent pigments might 

 prove suitable as secondary marks when used with one of the biological stains. 

 These fluorescent pigments do not fade, nor are they shed from the shrimp 

 during molting and were easily detected under ultraviolet light 61 days after 

 marking. Two other materials which might be useful as secondary marks are 

 red and blue checkwriter inks. The inks were also visible at the site of injec- 

 tion 61 days after marking. A clear solvent which fluoresces white under 

 ultraviolet light and mixes readily with fast green shows promise as a poten- 

 tially good secondary mark. 



Further experiments are presently being made to deternnine the 

 suitability of these pigments and inks as secondary marks. 



34 



