400 



Fishery Bulletin 93(2). 1995 



July, higher catches were obtained between 55 and 

 72 m (22.1 ±8.855), but abundance was also consid- 

 erable at 37-54 m (6.9 ±3.3) (Fig. 2B, Kruskal-Wallis 

 test, P<0.001). Mean abundance was significantly 

 different between depth interval 55-72 m and all 

 other intervals (NMRT, P<0.01), between depth in- 

 terval 37-54 m and the remaining three intervals 

 (NMRT, P<0.01), and was not significantly different 

 between depth intervals 9-18, 19-36, and 73-80. In 

 August-September, red shrimp was found only at 

 depths beyond 55 m (Fig. 2C, Kruskal-Wallis, 

 P<0.025). Mean abundance was significantly differ- 

 ent between depth interval 55-72 m and all other 

 depth intervals (only three categories were consid- 

 ered, as three intervals with zero abundance were 

 regarded as one; NMRT, P<0.005). Abundance be- 

 tween depth intervals 9-18 m, 19-36 m, 37-54 m, 

 and 73-80 m was not significantly different. During 

 the October-December period, P. brevirostris catches 

 were taken mainly at depth intervals 31—40 and 41- 

 50 m (Fig 2D, Kruskal-Wallis, P>0.05). Although 



there appears to be a distinct difference in abundance 

 between depth intervals, the test was not significant 

 because the number of zero catches was high (79 

 cases out of 84), making the sum of ranks very simi- 

 lar in all intervals. The high standard error indicates 

 the extent of data dispersion. 



These results suggest that although P. brevirostris 

 is generally found at greater depth intervals in the 

 summer and autumn, its presence at mid-depths and 

 shallower waters in spring may be an indication of 

 seasonal changes in bathymetric distribution, i.e. 

 onshore in spring and offshore in summer and autumn. 



The distribution and abundance of P. brevirostris 

 observed during the BIOCAICT cruises (Fig. 3) were 

 very similar to those described earlier, i.e. the shrimp 

 were mostly distributed in deeper waters except for 

 the capture of some individuals at a depth of 10 m in 

 June 1986 (Presidio and Baluarte transects). In No- 

 vember 1985 (Fig. 3A) and January 1986 (Fig. 3B), 

 most individuals were caught at the deepest stations 

 (70-90 m; 11.47 ±3.99 and 53.07 ±18.01 ind./ha, 



20.0 



15.0 



ro 



X 



10.0 



E 

 e_ 

 JZ 



C 5.0 

 0.0 



2.0 



1.5 



ro 



X 



Q. 1.0 



e 



November 1985 



9-15 40-45 70-90 



Depth Interval (m) 



June 1986 



9-15 40-45 70-90 



Depth Interval (m) 



January 1986 



ro 



X 



80.0 



60.0 



40.0 



E 



L. 



$1 20.0 

 0.0 



B 



9-15 40-45 70-90 



Depth Interval (m) 



4.0 



August 1986 



ro 

 X 

 X 



3.0 



2.0 



1.0 



0.0 



D 



9-15 40-46 70-90 



Depth Interval (m) 



Figure 3 



Mean abundance (shrimp/ha ±SE) of crystal shrimp, Penaeus brevirostris, at depth intervals observed during 

 the BIOCAICT cruises in (A) November 1985, and (B) January, (C) June, and (D) August 1986. 



