FISHERY BULLETIN: VOL. 87. NO. 2, 1989 



used to test the hypothesis that there were no 

 detectable differences in shrimp recapture patterns 

 for each species off each state as indicated by R/f 

 values. This was a randomized complete blocks 

 design for paired comparisons of R/f values as fixed 

 treatments (north or south) and releases of tagged 

 shrimp (10 off Tamaulipas, 12 off Texas) as ran- 

 domly chosen blocks (Sokal and Rohlf 1969; Under- 

 wood 1981). 



RESULTS 



Releases and Recaptures 



A total of 42,223 shrimp was marked and released 

 between 30 May and 11 July 1986, with an overall 

 recapture of 5,639 shrimp (13.4%) by 5 December 

 1986, the date of last recapture (Table 1). Over the 

 entire recapture period, 50 brown shrimp and 62 

 pink shrimp marked off Tamaulipas were recaptured 

 across the border in Texas waters, while 5 brown 

 shrimp and 2 pink shrimp marked off Texas were 

 recaptured off Tamaulipas. General mortality 

 among tagged shrimp prior to daily releases totalled 

 2.48%. For no apparent reason, prerelease mortality 

 was higher for the June releases off Texas (5.24%) 

 than for those off Tamaulipas (0.48%) or off Texas 

 in July (0.86%). 



Brown shrimp represented 59.2% of the overall 

 estimated species composition at release, while pink 

 shrimp formed 40.8% (Table 2). There was consider- 

 able variation in species composition on a daily basis 

 at any given site as well as among sites. The largest 

 within-site differences were between 1 June and 7 

 June releases near 25°25'N off Tamaulipas (brown 

 shrimp comprised 92% and 31%, respectively) and 



between 21 June and 11 July releases at 26°55'N 

 off Texas (brown shrimp comprised 21% and 97%, 

 respectively). 



Species compositions at release and after recap- 

 ture (excluding unknowris; Table 2) were significant- 

 ly different for 12 of 22 release dates and over all 

 releases in each state (i-test for equality of propor- 

 tions, a = 0.05; Sokal and Rohlf 1969). This is like- 

 ly a reflection of differences in fishing effort: experi- 

 mental shrimp were collected in 16-20 m waters 

 while commercial shrimpers fished 5-90 m waters. 

 Other factors could act and interact to cause these 

 proportional changes in species composition includ- 

 ing differential natural and tag-induced mortality, 

 depth and substrate preferences, or catchability. 



A total of 2,607 recaptures was excluded due to 

 inconsistencies in recapture information cited pre- 

 viously. The remaining 3,032 "best" recaptures 

 (Table 2) were used for all remaining analyses. 



Components of Movement 



Species, sex, and state had variable effects on the 

 movements of recaptured shrimp, as indicated by 

 distances travelled before recapture, days at large, 

 speed, direction, and recapture depth. Distance 

 travelled before recapture was significantly affected 

 by both species and state (Table 3). The species x 

 state interaction was also significant. Pink shrimp 

 moved both the greatest and least mean distances 

 of all eight groups, depending upon where they were 

 released. Pink shrimp released off Tamaulipas 

 moved an average of 29.5 km (males) or 29.0 km 

 (females), distances that were significantly greater 

 than those of pink shrimp released off Texas (males 

 = 9.2 km, females = 9.8 km). Brown shrimp re- 



Table 3. — Distances travelled by recaptured brown shrimp and pink shrimp. A. Three- 

 factor, model I ANOVA using log (x -^ 1)  transformed data. B. Mean distances travelled. 

 Underlined means are not significantly different (Fisher's LSD, o = 0.05). B = brown 

 shrimp, P = pink shrimp, F = female, M = male, Ta = Tamaulipas, Tx = Texas. 



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