NOTE Garduno-Argueta and Calderon-Perez: Depth distribution of Penaeus brevirostris 



399 



numbers of samples because the CRIP cruises were 

 primarily intended to sample the closed season that, 

 in those years, was imposed for that period. Catch 

 data were averaged by period and depth interval and 

 are reported as mean number of individuals per hour 

 (ind./h ±SE) of trawling. Seasonal abundance data 

 from BIOCAICT cruises, on the other hand, are re- 

 ported for only three depth intervals: 9-15 m, 40-45 

 m, and 70-90 m. Catch figures were averaged for 

 every 2.0°C interval of temperature and 0.5 mL/L 

 interval of dissolved oxygen within the observed 

 ranges and are presented as the average number of 

 individuals per hectare (ind./ha ±SE). 



Nonparametric single factor analysis of variance 

 by ranks (Kruskal-Wallis test for tied ranks) was used 

 to test for differences in shrimp abundance between 

 the five depth intervals in each of the four bimonthly 

 periods and between four dissolved oxygen levels. A 

 nonparametric multiple range test (NMRT) was used 



in cases where Kruskal-Wallis test were significant 

 (<x=0.05, Zar, 1974). 



Results and discussion 



Penaeus brevirostris specimens were collected over 

 a wide depth range, although generally higher 

 catches were taken between 50 and 80 m. The depth 

 distribution varied throughout the sampling period 

 (Fig. 2). Most catches were monospecific, except in 

 August 1986, when both P. brevirostris and P. 

 californiensis were sampled at 80 m on the Piaxtla 

 transect. During the period April-May, shrimp were 

 more abundant between 9 and 18 m (5.8 ±3.6 ind./h) 

 but specimens were also caught at most depth inter- 

 vals except at 73-80 m (Fig. 2A). Differences in mean 

 abundance between the five depth intervals were not 

 significant (Kruskal-Wallis, P>0.05). During June- 



April - May 



10.0 



5.0 



o.o 



40.0 



rh 



9-18 



19-36 37-54 55-72 73-80 



Depth Interval (m) 

 August -September 



N. 



E 20.0 



_r±L 



9-18 19-36 37-54 66-72 73-80 



Depth Interval (m) 



June-July 



30.0 



Q. 



£ 20.0 



B 



10.0 



0.0 



16.0 



12.0 



E 



e- 

 -c 

 if) 



8.0 



4.0 



9-18 19-36 37-54 65-72 73-80 



Depth Interval (m) 

 October- December 



D 



9-18 19-36 37-64 56-72 73-80 



Depth Interval (m) 



Figure 2 



Mean abundance (shrimp/h ±SE) of crystal shrimp, P. brevirostris, at five depth intervals. Data combined 

 from CRIP cruises in 1981, 1982, 1985, and 1986. (A) April-May 1981, 1982, and 1985; (B) June-July 1981, 

 1982, 1984, 1985, and 1986; (C) August-September 1981, 1982, 1985, and 1986; and (D) October-December 

 1981, 1985, and 1986. Abundance refers to mean number of shrimp caught at stations located within each 

 depth interval in one hour trawling (paired 22.86-m otter trawl). 



