Brown Shrimp Mortality Studies 

 Edward F. Klima 



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A mark-recapture experiment on brown shrimp, Penaeus aztecus, 

 initiated during April 1962 is expected to yield preliminary estimates of fish- 

 ing mortality and information on movement of the stocks of shrimp off the 

 Texas coast. Over 2,400 shrimp were caught, stained with fast green FCF, 

 and released in a 100-square-mile area ranging from 21 to 24 fathoms south- 

 east of Pass Cavallo. Reports from the statistical branch of the Bureau of 

 Commercial Fisheries indicate that this area was the most heavily fished 

 section along the Texas coast in April 1962. 



In addition, about 1,700 shrimp were tagged with Petersen disc tags, 

 and released in the same depth range south of Port Aransas and southeast of 

 Freeport. To obtain reliable estimates of fishing mortality, it is necessary 

 to be able to roughly define the population. Since little is known concerning 

 the movement and the population structure of brown shrimp in the northwestern 

 Gulf, the stained shrimp were released in the area of the heaviest fishing con- 

 centration, and the tagged shrimp were released in adjacent areas. Any 

 movement into or out of the staining area should be evident, and some idea of 

 the population structure will be obtained. 



Because of the nonspecific 

 stain mark and the large area of re- 

 lease, it is not possible to determine 

 the exact distance traveled for any 

 given recovered individual. To min- 

 imize this difficulty, the center of 

 the staining area is considered to 

 be the point of release for all of the 

 stained shrimp. One hundred and 

 twenty -five stained and eight tagged 

 shrimp were recovered through 

 June 6, 1962. Sixty -two percent of 

 all of the recoveries were recap- 

 tured less than 15 miles from the 

 release areas. These shrimp ap- 

 peared to have moved randomly, 

 because approximately equal num.- 

 bers were recovered in all direc- 

 tions from the release position. 

 Fifty marked shrimp traveled more 

 than 15 miles. Of these, 46 moved 

 in an easterly direction, ■while 4 

 Direction and distance of movement of moved in a westerly direction, 



brown shrimp marked in April 1962. 



OFFSHORE MARKING 



AND RELEASE SITE (APR 19621 



RECAPTURE SITES 



ESTUARINE MARKING 



AND RELEASE SITE (MAV 19591 



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