The staining technique was first employed 

 at the field level in 1956 by the Bureau of 

 Commercial Fisheries (Costello, 1959). Re- 

 sults were encouraging. A series of experi- 

 ments that began in 1959 and terminated in 

 1962 provided basic information on the geo- 

 graphical range of stocks that support the 

 valuable pink shrimp (Penaeus duoramm) fish- 

 ery on the Tortugas grounds (Costello and 

 Allen, 1960). 



Based on nearly 4 years' field experience, 

 the present report describes means for cir- 

 cumventing or mitigating difficulties that may 

 be encountered in shrimp staining experi- 

 ments. It is offered primarily as a guide for 

 agencies contemplating shrimp research in 

 which the staining technique might be incor- 

 porated as a tool. 



FIELD OPERATIONS 



The nature of preparations for an experi- 

 ment in which vital stains are to be used to 

 mark shrimp depends in large measure on 

 the status of knowledge regarding shrimp 

 populations in the study area as well as on 

 the scope of work to be accomplished. Shrimp 

 populations supporting well-established fish- 

 eries lend themselves readily to mark- 

 recapture experiments. If fishery statistics 

 and certain hydrographic data (especially 

 sea-temperature measurements) are also 

 available, their incorporation in analysis of 

 experimental results may be expected to 

 increase the amount of useful information 

 obtained. 



(ocneral 



Staining sites where shrimp can be held 

 under conditions conducive to their survival 

 should be selected. This may require a series 

 of water-quality observations which include 

 checks on dissolved oxygen, turbidity, salinity 

 range, and prevailing daytime and nighttime 

 water temperature. When working with pink 

 shrimp we found that low-salinity (<10 p.p.t.) 

 water should be avoided since they became 

 particularly delicate in such an environment. 

 We also encountered high mortality in these 

 shrimp when the water temperature (surface 



or bottom) exceeded 75° F. The foregoing does 

 not infer that successful marking experiments 

 are impossible outside the temperature and 

 salinity limits indicated; however, these limits 

 indicate points at which mortality due to 

 handling and marking will rise rapidly. Effec- 

 tive handling of large numbers of pink shrimp 

 outside these limits will require considerably 

 larger holding facilities than are recom- 

 mended herein. 



Marking experiments in offshore areas re- 

 quire that the shrimp be raised rapidly to the 

 surface, marked, and returned to the bottom 

 with minimum injury. This treatment subjects 

 them to a series of physical stresses not yet 

 fully understood. Minimizing exposure to pre- 

 dation upon release also poses a problem. 

 Experience gained by initiating and carrying 

 out mark-recapture experiments under a va- 

 riety of conditions (for example, in, near, or 

 at some distance from areas at heavy fishing 

 activity; at different seasons; etc.) has indi- 

 cated that greatest success when using the 

 staining method to estimate mortality will be 

 achieved when releases are made just prior 

 to peak shrimp abundance in the study area. 



Other factors to be considered include the 

 expected number and distribution of commer- 

 cial fishing vessels in the study area and 

 special conditions such as closed seasons. 

 Where regulations restrict shrimp trawling 

 during certain periods, completion of the 

 mark and release phase a short time before 

 the season reopens may be advantageous in 

 allowing desired dispersal before marked 

 shrimp are subject to recapture. 



Obtaining Experimental Material 



The techniques of catching, transporting, 

 and holding live juvenile shrimp have been 

 well developed by commercial bait fishermen 

 around the Gulf of Mexico (De Sylva, 1954; 

 Woodbum, Eldred, Clark, Hutton, and Ingle, 

 1957; Inglis and Chin, 1959). When under- 

 taking a marking experiment involving juvenile 

 shrimp, it is convenient to hire an experienced 

 fisherman to obtain suitable quantities of live 

 specimens in good condition and arrange for 

 their transportation to the marking site. Where 

 this is not possible, it will be necessary to 



