chain bridle fastened to eyelets on the front of 

 the sled frame (fig. 27). Because of the weight 

 of the sled, we need a hydraulic or rolling 

 winch to handle it aboard a vessel. The proper 

 ratio of towing line to water depth for normal 

 towing speeds (1-2 knots) is 3:1. 



We made several 10-minute tows at one 

 location to compare catches n-iade with the 

 roller attachment, the digger-bar attachment, 

 and with no attachment. Catches of postlarvae 

 (Penaeus spp.) were largest when the roller 

 attachnnent was used and smallest with no 

 attachment (table 8). We took other animals 

 such as polychaetes, gastropods, pelecypods, 

 coelenterates, echinoderms, and crustaceans 

 in greater numbers when the roller was at- 

 tached. 



The sled with the roller was tested from a 

 12-m. (40-ft.) research vessel under varying 

 sea conditions. We positioned a series of 10 

 numbered buoys at 6-nn. (20-ft.) intervals 

 parallel to the shoreline in 3 m. (10 ft.) of 

 water. The sampling site was one at which 

 white shrimp postlarvae were known to be 

 abundant, A 10-minute sled tow was made in 

 an offshore direction from each buoy on 

 August 8, 1968, when the seas wereOto 0.6 m. 

 high (0-2 ft.), and from seven of the buoys on 

 August 29, 1968, when the seas were 0.6 to 



1.5 m. high (2-5 ft.). Similar catches (table 9) 

 on each day and the uniform ratio of brown 

 shrimp to white shrimp each day indicated 

 that the gear functioned well. 



With this gear, shrimp researchers can 

 collect quantitative samples from bottoms 

 inhabited by the young of commercial species 

 of penaeid shrimp. Further use of this gear 

 could extend existing knowledge of the life 

 histories of other animals which live in the 

 same areas. 



Harold A. Brusher 

 Frank MaruUo 



Table 8. — Average catches of postlarvae 

 (Penaeus spp.) per 1,000 m. ^ during a se- 

 ries of lO-minute tows at the same location 

 with the sampling sled with roller bar, 

 digger bar, and no attachment. 



Table 9. — Catches of postlarval white and brown shrimps per 1,000 m.^ made diiring sets of 



parallel tows, Gulf of Mexico, 1968. 



Tow 



Postlarvae 



Brown 



White 



Tow 



Postlarvae 



Brown 



White 



Number 



Number 



Number 



Number 



1. 

 2. 

 3. 

 4. 

 5. 

 6. 

 7. 

 8. 

 9. 

 ID. 



Average 

 number 



156.7 



1,257.4 



29.1 



3,546.4 



Confidence 

 interval 

 at 0.05 

 level 



+14.4 



+ U4.5 



+19.4 



+1,254.7 



MS. #2015 



39 



GPO 6 9 1-804 



