they move in either a northerly or north- 

 westerly direction. There is no distinct 

 seasonal pattern in the size -depth rela- 

 tion. Small shrimp predonninate on the 

 grounds during the months of September 

 through May. 



Using as an index of abundance the 

 number of shrimp caught per hour in 

 the standard try net, additional infor- 

 mation on shrimp movements was ob- 

 tained. Catches are charted on the fol- 

 lowing graphs, and the diameter of the 

 circles denote the number of shrimp 

 taken per try -net hour (figs. 14 to 16). 

 The greatest abundance occurred from 

 December 1957 to January 1958 and from 

 March to June 1958. Catches during these 

 periods were made in shallow water on 

 the southern and eastern sectors of the 

 grounds. This evidence indicates a period 

 of recruitment during the winter, with 

 shrimp entering the grounds from the 

 south and east, much as was shown by 

 the size -depth relation. 



FLEET CONCENTRATIONS 



Most of the data on fleet concentra- 

 tions were obtained from observations 

 made on the charter vessel. These ob- 

 servations were made on every cruise 

 and hence are more complete than those 

 made from airplanes. Airplane flights 

 over the grounds at night provide spatial 

 distribution and estimates of the total 

 number of vessels trawling. Seven air- 

 plane flights were made (table 4, p. 21). 



The number of boats observed from 

 the charter vessel are totaled for 5-mile 

 squares and are represented by symbols 

 denoting the various concentrations (figs. 

 17-19). These figures can only be con- 

 sidered as rough estimates since the 

 diagram for each cruise usually repre- 

 sents a total of three nights' observations. 

 Boats moving from one location on the 

 grounds to another during the cruise 

 could have been nnissed altogether. Vary- 

 ing visibility on the fishing grounds also 

 produces errors. 



While observations on the distribution 

 of fishing effort are incomplete, some 

 general seasonal trends in fishing effort 

 can be seen. During the period December 



to June the largest concentrations of 

 vessels were observed and were located 

 on the eastern and southeastern portions 

 of the grounds. An exception to this 

 occurred during October when concen- 

 trations of over 35 vessels per 5 -mile 

 square were noted on the southwestern 

 portion of the grounds. During the re- 

 mainder of the year the vessels generally 

 covered the entire grounds, their distri- 

 bution being restricted by the State con- 

 servation area and by the occurrence of 

 algae. 



The distribution of fleet concentrations 

 agrees well with the abundance indices 

 of pink shrimp in time and space. The 

 largest catches of shrimp and the largest 

 number of vessels were found on the 

 eastern and southern portions of the 

 grounds, and these values were also 

 highest during the months from December 

 to June. 



SHRIMP DISCARDING 



Since small shrimp bring a lower price 

 than large shrimp, fishermen sometimes 

 discard the small ones. This practice is 

 important in the analysis of the fishery 

 because shrimp which are caught and 

 then discarded are not included in catch 

 records. This lowers the catch per unit 

 of effort of a vessel and introduces an 

 error in the average size of shrimp 

 caught. Estimates of discard in this study 

 have come only from the research vessel 

 for reasons discussed earlier. Observa- 

 tions were made on (1) the sizes of 

 shrimp discarded compared to those re- 

 tained, (2) the ratio of times fishermen 

 discarded shrimp to the times that they 

 did not discard shrimp, and (3) the possi- 

 ble influence of different size distribu- 

 tions causing fishermen to discard. 



To obtain information on the sizes of 

 shrimp discarded compared to those re- 

 tained, heads from shrimp that had been 

 retained and whole discarded shrimp 

 were measured during five cruises (fig- 

 ure 20). When discarding occurred, vir- 

 tually all shrimp as large as 19 mm. 

 (smaller than 100 count, heads off) were 

 discarded and about 80 percent of 22 

 mm. and about 60 percent of 25 mm. 

 were discarded. Practically no shrimp 

 larger than 28 mm. carapace length (60 



16 



