ANDERSON and LINDNER: BIOLOGY OF ROYAL RED SHRIMP 



LATITUDE AND DEPTH DISTRIBUTIONS 



A preliminary examination of our data sug- 

 gested that royal red shrimp tended to be larger 

 in the northern part of the collection area than 

 in the central part, and that size was inversely 

 related to depth. Correlations were significant 

 between median lengths of females and latitude 

 (,• = +0.46; ( = +6.65; 7= 23.39 + 0.09X) 

 and between median lengths of females and depth 

 (,. = —0.46; t = —6.65; 7= 53.78 — O.llX). 

 The data used for these correlations were from 

 the 164 stations at which 20 or more females 

 were measured; the lengths are in Vo-cm units. 

 We did not repeat the calculations for the males 

 because when the smaller size groups of females 

 were caught in a tow, invariably the smaller 

 size groups of males also were caught. 



For the latitude correlation we grouped the 

 median lengths by 10' intervals of latitude. A 

 gi-aph of the data showed that female shrimp 

 tended to be smaller between lat 29°00' and 

 29°39' N than between lat 29°40' and 30°13' N. 

 We had samples fi'om only five stations south of 

 lat 29°00' N, of which four were between lat 

 28°00' and 28°39' N. Although the data sug- 

 gested that large shrimp also tended to inhabit 

 the southern part of the grounds, we are un- 

 willing to draw conclusions for the area south 

 of lat 29°00' N from this small sample. 



The size and latitude relation confirmed re- 

 ports of the fishermen that usually, but not al- 

 ways, they encountered larger shrimp on the 

 northern portion of the grounds than on the 

 central portion. The fishermen rarely fish the 

 southern part of the grounds, and we received 

 conflicting reports on the size of shrimp caught 

 in this area. 



For the depth relation we grouped the data 

 by25-fm (46-m) depth intervals (151-175; 176- 

 200, etc.). The highly significant negative re- 

 lation between size and depth (large shrimp in 

 shallow water and smaller shrimp in deeper 

 water) did not agree with some of our data 

 (Table 2) nor with reports from the fishermen 

 and exploratory fishing personnel; hence we 

 suspected that this relation and perhaps that 

 with latitude were fortuitously caused by the 

 fishing pattern at the times our samples were 



Table 2.— Median length of H. robustus and depth of 

 hauls for eight stations in the same latitude — Silver Bay 

 cruise September 25-28, 1962. 



taken. We therefore re-examined the data and 

 selected only those cruises during which more 

 than one depth class was fished in the same lat- 

 itude zone and those cruises during which the 

 same depth class was fished in the two latitude 

 zones. The depth classes used were 150 to 175 

 fm (274-320 m), 176 to 200 fm (322-366 m), 

 201 to 225 fm (368-411 m). and 226+ fm 

 (413+ m). The latitude zones chosen were lat 

 29°00' to 29°39' N and 29°40' to 30°13' N. We 

 had no stations south of lat 29°00'N that met 

 the requirements. 



After the selection was made, we had 12 

 cruises with 93 stations and 2 depth classes 

 that could be compared by latitude zone for the 

 same depth class; and 18 cruises with 95 sta- 

 tions and 4 depth classes that could be compared 

 by depth class for the same latitude zone. Only 

 those stations were selected from which 20 or 

 more females were measured. The results are 

 shown in Figures 8 and 9 and in Appendix Tables 

 1 and 2. 



In Figure 8 we have plotted the mean median 

 lengths (in ' o-cm units) as scatter diagrams 

 against depth class with latitude zone lat 29°00' 

 to 29°39' N as the abscissa and latitude zone lat 

 29°40' to 30=13' N as the ordinate. If no re- 

 lation existed between the length of the shrimp 

 and the latitude, the dots and crosses would be 

 scattered along and on either side of the 45° 

 lines. All 12 marks fall above the 45° lines, 

 however, showing that shrimp tended to be 

 larger north of lat 29°39' N than in the area 

 between lat 29°00' and 29°39' N. 



In Figure 9 we have plotted the mean median 

 lengths as scatter diagrams separately for each 



319 



