FISHERY BULLETIN: VOL, 77, NO, 4 



r BROWN SHRIMP 



MISSISSIPPI RIVER TO TEXAS 



I 1 [ ] 1 1 1 I 1 I I 1 [ I I 1 1 ' 



1959 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 



Figure 2. — Trends in slope (fc) of regressions of transformed 

 cumulative percentage (Inf ) on size category (C) for brown 

 shrimp in Mississippi River to Texas (solid line, circles) and 

 Texas coast (dashed line, dots) 1959-76 (data from Tables 1,2). 



WHITE SHRIMP 



MISSISSIPPI RIVER 10 TEXAS 



, -r TEXAS COAST 



I I I I I I I I I ^ I I I 1 I I I I 

 1959 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 



VEAR. x 



Figure 3. — Trends in slope (6) of regressions of transformed 

 cumulative percentage (InF) on size category (C) for white 

 shrimp in Mississippi River to Texas (solid line, circles) and 

 Texas coast (dashed line, dots), 1959-76 (data from Tables 1,2). 



shown by positive trends that were significantly 

 different from zero at the 95% level of confidence 

 (Table 3; Figures 2,3). This change in b with time 

 indicated that the size composition of the reported 

 annual catches of brown and white shrimp shifted 

 during 1959-76 toward greater proportions of 

 shrimp of smaller size in the catches. This shift 

 was more pronounced in Texas, but the Louisiana 

 catches contained considerably greater propor- 

 tions of small shrimp than did those of Texas. 

 Points for 1959 and 1960 may be less reliable 

 than those for later years because the Gulf Coast 

 Shrimp Data reports were released for the first 

 time in 1956, and by 1961 the data collection 

 methods had been greatly refined. Elimination of 

 data points for 1959 and 1960 decreased all the 



Table l. — Linear regressions of trtinsformed cumulative 

 percentage (Inf) on size category (C) for brown and white 

 shrimp, Mississippi River to Texas (based on U.S. Fish and 

 Wildlife Service 1960-69; National Marine Fisheries Service 

 1970-78).' 



Brown shrimp 



White shrimp 



of determination 



Table 2 — Linear regressions of transformed cumulative per- 

 centage (In Fl on size category (C) for brown and white shrimp, 

 Texas coast (based on U.S. Fish and Wildlife Service 1960-69; 

 National Marine Fisheries Service 1970-78.1.' 



^F = Cumulative percentage of weight caught in each of seven size 

 categories. C = lower limit of each of seven size categories, all b's were 

 significantly differentfromzeroatthe 99 9% level of confidence. r^ - coefficient 

 of determination. 



trends in b, and the trend for brown shrimp from 

 Mississippi River to Texas was no longer different 

 from zero at the 95% level of confidence (Table 3). 

 However, elimination of points for the first 2 yr 

 from the trends also reduced the degrees of free- 

 dom from 16 to 14 for the test of significance of 

 trends, so the test was less sensitive in this case. 

 Whether or not the apparent trend was real for 

 brown shrimp from Mississippi River to Texas 

 could be determined by examination of data for 

 years beyond 1976, as they become available. 



988 



