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Fishery Bulletin 93(2), 1995 



J. S. A 



Figure 1 



Study area (1981-86) located off the mouths of the Piaxtla River and the Teacapan- 

 Agua Brava lagoon complex, Mexico. Twenty-nine stations from the CRIP-INP cruise 

 series are denoted by empty circles. Stations from the BIOCAICT series are indicated 

 with solid circles. 



Seventeen survey cruises were made by the Centro 

 Regional de Investigaciones Pesqueras of the 

 Institute Nacional de la Pesca (CRIP) on board com- 

 mercial shrimp trawlers during the years 1981, 1982, 

 1984, 1985, and 1986, and four cruises were made 

 by the Universidad Nacional Autonoma de Mexico 

 between November 1985 and August 1986 on board 

 the vessel MARSEP XI (BIOCAICT cruises). On all 

 cruises, a pair of 22.9-m otter trawl nets was used. 

 The nets have a progressively reducing mesh size 

 from 6.4 cm on the body of the net to 3.8 cm at the 

 cod end. Eleven sampling stations of the BIOCAICT 

 series were located on four transects perpendicular 

 to the coast line off the mouths of Piaxtla, Presidio, 

 and Baluarte rivers and off the Teacapan-Agua Brava 

 lagoon complex. Sampling depth varied from 9 to 90 

 m. Data from the more extensive CRIP cruises were 

 selected to match the location of the BIOCAICT se- 

 ries (Fig. 1). 



In all BIOCAICT cruises, surface, mid-water, and 

 bottom water samples were taken with 8-L niskin 

 bottles. Temperature was measured in situ with re- 

 versing thermometers to the nearest 0. 1°C. Dissolved 



oxygen (DO) was determined by using a modifica- 

 tion of the Winkler method (Strickland and Parson, 

 1972). At each sampling station, shrimps were sorted, 

 identified, and counted for each catch. Color in fresh 

 animals (Chapa-Saldaha 1 ) proved to be a very reli- 

 able character for species identification. 



CRIP monthly samples from 29 stations within a 

 depth span of 9-80 m were averaged at intervals of 

 18 m (10 fathoms), except for the initial interval of 9 

 m (9-18 m), and pooled across years into four bi- 

 monthly periods. The term sample refers to the num- 

 ber of shrimp per twin net haul divided by the num- 

 ber of hours (ind./h) at each station. The first period 

 (April-May) had a total of 87 samples (April 1985, 

 May 1981, 1982 at 29 stations [Fig. 1], distributed in 

 five depth intervals [9-18 m, 19-36 m, 37-54 m, 55- 

 72 m, and 73-80 m]). June-July had 203 samples 

 (June 1981, 1982; July 1981, 1982, 1984, 1985, and 

 1986) while August-September had 145 samples 

 (August 1981, 1985, 1986; September 1982, 1985), 

 and there were 87 samples for October-December 

 (October 1981; December 1985, 1986). The sampling 

 periods between June and September had higher 



