FISHERY BULLETIN: VOL. 75. NO. 4 



FIGURE 9.— Distribution by month and 

 fishing zone of the mean catch rate of 

 shrimp for U.S. vessels fishing in the 

 Guianas-Brazil fishery, July 1972 to 

 December 1974. See Figure 1 for loca- 

 tion of fishing zones. Catch rate is ex- 

 pressed as pounds (and kilograms) of 

 shrimp (heads-off weight) per hour of 

 fishing. 



depth. The average catch rates were: 35.4 lb/h 

 (0-5 fm), 25.0 lb/h (6-10 fm), 21.5 lb/h (11-15 fm), 

 20.5 lb/h (16-20 fm), 21.1 lb/h (21-25 fm), 20.7 

 lb/h (26-30 fm), 21.1 lb/h (31-35 fm), 23.2 lb/h 

 (36-40 fm), 22.7 lb/h (41-45 fm), and 24.5 lb/h 

 (46-60 fm). Off Guyana, Surinam, and French 

 Guiana (zones 69-77), average catches were lower 

 at the intermediate depths (16-35 fm) than in 

 shallower or deeper water (Figure 10). Off Brazil 

 the average catch did not vary with depth in zones 

 78 and 79, but in zones 80 and 81 average catches 

 were higher at the intermediate depths than in 

 shallower or deeper water. 



We also examined the distribution of fishing 

 effort in relation to depth. Fishing effort was con- 

 centrated primarily in intermediate depths. Sixty 

 percent of the fishing effort reported in logbooks 

 occurred between 21 and 35 fm, 189c in <20 fm, 

 and 22% in >36 fm. Off Guyana, Surinam, and 

 French Guiana most fishing was between 16 and 

 30 fm; off Brazil, it was in deeper water (Figure 

 11). While the highest catch rates were usually in 

 the shallow and deep zones at the edge of the 

 fishing grounds, these areas supported only a 

 small percentage of the total fishing effort. Shal- 

 low and deep zones probably were fished only 

 when good catches could be made, whereas the 

 intermediate depths were fished during times of 

 both good and poor fishing. 



The availability of shrimp to the fishermen in 

 relation to time of day varies for each area, species, 

 and time of the year. Most fishing for shrimp was 

 done at night, some during the day, and some on a 



24-h/day basis (Figures 12 and 13). The time spent 

 fishing at night was three times that spent during 

 the day. White shrimp were caught primarily dur- 

 ing daylight hours off the Guianas and fishing in 

 the East Gullies (zone 79) was usually done during 

 the day. In the Drop-Off and Steeples (zones 80- 

 81), fishing on a 24-h/day basis made up nearly 

 half the total fishing time. The average catch rates 

 for the entire fishery were 29.6 lb/h (day fishing), 

 18.9 lb/h (night fishing), and 22.1 lb/h (day and 

 night fishing). The mean catch rates were higher 

 for day fishing than night in all zones and at all 

 depth intervals. We conclude that the usual 

 strategy is to fish at night, except for certain 

 species (e.g., white shrimp) or in certain areas 

 (e.g., East Gullies) where day fishing is more suc- 

 cessful. During periods of high catches, fishing is 

 usually carried out on a 24-h/day basis until a full 

 catch is made or until the fishermen are 

 exhausted. 



APPRAISAL OF THE FISHERY 



The fishery for shrimp in the Guianas-Brazil 

 area reached a historical maximum annual pro- 

 duction of 27.3 million pounds heads-off in 1973. 

 We used a surplus yield model to estimate the 

 maximum sustainable yield of the resource (Fox 

 1970). We also compared predicted annual equi- 

 librium yields with actual annual yields attained 

 to measure the expected variation from equilib- 

 rium conditions. 



An exponential surplus yield model suggested 



710 



