Figure 1. — Distribution and some geographical loca- 

 tions of the commercial shrimp, M. vollenhovenii, in 

 Africa. 



a study of the biology of the commercial spe- 

 cies. Because my primary responsibility in 

 Liberia was as the Adviser in Marine Fisheries, 

 my study was a secondary project limited by 

 a lack of time. 



The commercial catch in the lower St. Paul 

 River is composed of two species: Maero- 

 brachium vollenhovenii (Herklots), a large 

 commercial shrimp; and Macrobrachium ma- 

 crobrachion (Herklots), a small shrimp culled 

 from the catch and eaten by the fishermen. 

 Both species are of commercial importance in 

 Dahomey (Monod, 1966). The present report 

 is concerned primarily with the large commer- 

 cial fresh-water shrimp, M. vollenhovenii. 



METHODS AND MEASUREMENTS 



I obtained samples from the commercial 

 fishery at least once a month during the season. 

 Traps used, were tightly woven, and prevented 

 the escapement of small shrimp. The tiny 

 shrimp of the incoming year class were ob- 

 tained from fishermen who collected them in 

 burlap push-nets. Total length, from the base 

 of the eyestalk to the tip of the telson, was 

 measured to the nearest millimeter with a 

 simple measuring board (Pruter and Harry, 

 1952). Shrimp were weighed on a Harvard 



Trip Balance after the major chelipeds had 

 been removed. Specimens 60 mm. long or 

 longer were weighed to the nearest gram ; those 

 less than 60 mm. were weighed to the nearest 

 0.1 g. Salinity samples were taken at stations 

 in the estuaries within 1.6 km. (1 mile) of the 

 mouths of the Mesurado and St. Paul Rivers. 



COMMERCIAL FISHERY 



The commercial fishery for fresh-water 

 shrimp is insignificant compared with the 

 catch and value of other fisheries, but it is 

 significant to the economy of the people of the 

 lower St. Paul River. The fishery for fresh- 

 water shrimp in the lower St. Paul River will 

 be described and the economic value of the 

 fishery estimated. 



Location 



In Monrovia, fresh-water shrimp sold were 

 captured within 3.2 km. (2 miles) upstream 

 from the mouth of the St. Paul River. (The 

 headwaters of the St. Paul River rise in the 

 highlands of Guinea, north of Liberia.) The 

 shoreline, composed of rock-gravel substrate, 

 varied from gradual to steep. Outcrops of 

 large rocks were present along the shore and 

 in the channel (fig. 2). Fishing was carried 

 out within the tidal zone. 



Description of the Fishery 



Traps used in the fishery were made of 6 

 to 13 mm. (14-V2 in.) wide strips peeled from 

 the hard outer layer of a palm frond stem. The 

 strips were tightly interlaced into a fusiform 

 trap, 101 to 152 mm. (4-6 in.) in diameter 

 at the large end and 457 mm. (18 in.) long 

 (fig. 3). The wide end of the trap had an 

 involuted opening 38 to 51 mm. (11/2-2 in.) in 

 diameter, followed (within the trap) by a sec- 

 ond fyke opening of the same size. 



The bait most commonly used was the white 

 core of the cassava root, Manihot utilissima. 

 Three or four 19-mm. (%-in.) square pieces 

 were placed in each trap. When the tide was 

 low, the traps were placed in the intertidal 

 area and partially covered by large rocks; the 

 catch (up to 36 large shrimp per trap) was 

 removed on the next low tide (fig. 4) . Shrimp 

 were sorted by removing the small ones for 



