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



tives of this research were to 1) test whether shrimp 

 movement (measured in terms of distance travelled, 

 days at large, speed, direction, or recapture depth) 

 varied according to species, sex, or release location 

 (state), and 2) test for directional movement after 

 recaptures were adjusted by patterns in fishing 

 effort. 



MATERIALS AND METHODS 



Collection and Tagging of Shrimp 



Shrimp were collected by trawl at night off the 

 Texas and Tamaulipas coasts. All collections were 

 made in 16-20 m waters within 5 km of release sites. 

 Shrimp were held in flow-through tanks before and 

 after tagging and until released. 



Shrimp were marked with colored, numbered 

 polyethylene streamer tags as described by Marullo 

 et al. (1976). Shrimp between 80 and 140 mm total 

 length were selected because these sizes represented 

 recent recruits. Tagged shrimp were released at 18 

 m depths within 12 hours of collection using expend- 

 able, delayed-release canisters (Emiliani 1971). Each 

 plastic canister was weighted, filled with 50-75 

 tagged shrimp, sealed with a salt block, and released 

 overboard. The salt block dissolves after 10-15 

 minutes under water and the canister springs open, 

 releasing the shrimp on the sea floor. 



Ten releases of tagged shrimp were made at eight 

 sites between 24°44'N, 97°31'W and 25°57'N, 

 97°04'W off Tamaulipas (Fig. 1). These releases 

 were made during 30 May-8 June 1986 from the 

 INP ship BIP-IX. Twelve releases were made at six 

 sites between 26°05'N, 97°05'W and 26°55'N, 

 97° 17'W off Texas (Fig. 1). The Texas releases were 

 made during 21-28 June 1986 and 7-11 July 1986 

 from the NOAA ships Chapman and Oregon II. The 

 order of release sites was randomized given the 

 following restrictions: 1) the 21 June release site 

 was fixed due to vessel cruising speed, and 2) each 

 Texas site was visited once before repeating any site 

 (this was not possible off Tamaulipas). Releases were 

 confined to sites within 150 km of the U.S. -Mexico 

 border (25°57'N) based on shrimp movement speeds 

 that averaged 2.5 km/d during 1978-80 (NMFS, 

 unpubl. data) over a maximum closure of 60 days. 

 In fact, 90% of all transborder recaptures after 

 1978-80 experiments resulted from releases within 

 120 km of the border (Sheridan et al. 1987). 



No predetermined number of shrimp was set for 

 each night's tagging due to natural variabilities in 

 abundance and catchabUity. Species composition and 

 size range of released shrimp were estimated by 



identification and measurement of up to 300 shrimp 

 for each day's release. Identification and measure- 

 ment of all tagged shrimp was not conducted be- 

 cause such handling could have increased stress and 

 thus influenced behavior or survival of tagged 

 shrimp. Only brown shrimp and pink shrimp were 

 marked and released. Periodic lottery rewards of 

 $50-$500 were offered as incentives to fishermen 

 on both sides of the border to report capture of 

 tagged shrimp with information on location, depth, 

 and date of recapture (Cody and Fuls 1981). 



Collection of Recaptures and 

 Fishing Information 



Port agents employed by NMFS and INP inter- 

 viewed fishermen and processors in American and 

 Mexican ports to collect recaptured tagged shrimp 

 and information on fishing locations, landings, and 

 effort. All recaptures during the period 30 May-31 

 August 1986 were checked for accuracy of date and 

 location and were identified to species when possi- 

 ble. Although recaptures were made after 31 Aug- 

 ust, only recaptures during the 94 d period were 

 chosen to best reflect summer environments. Recap- 

 tures returned with the following inconsistencies 

 were omitted from analyses of movement (although 

 they are included in a general summary of recap- 

 tures. Table 1): 1) not identified as brown shrimp 

 or pink shrimp, 2) recapture dates after 31 August 

 1986, 3) recapture dates prior to or the same as 

 release dates, 4) incomplete latitude and longitude, 

 5) depth not specified, 6) sex not specified, and 7) 

 recaptured in trawl tows over distances exceeding 

 9 km. These restrictions reduced the number of 

 usable recaptures from 5,639 (as of the date of last 

 recapture, 5 December 1986) to 3,032 (Table 2). 



Port agent interviews of fishermen throughout the 

 U.S. Gulf of Mexico were used to estimate total 

 brown shrimp and pink shrimp fishing effort off 

 Texas during the period 1 June-31 August 1986. 

 These data are collected by specific 9 m depth zones 

 paralleling the coast within quadrangles of one 

 degree latitude and longitude and, as such, are too 

 coarse to examine shrimp movements in detail. Log- 

 books were voluntarily kept by the captains of 47 

 Texas shrimp vessels for the duration of the recap- 

 ture period to collect precise information on start- 

 ing and stopping points and times, depths, tow dura- 

 tions, and landings. Logbook data were assumed to 

 reflect fishing activities of all vessels off Texas and 

 were used to estimate the amount of total brown 

 shrimp fishing effort (which includes pink shrimp) 

 within 10 minute quadrangles of latitude and longi- 



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