fleet hours towed with a single, 30.5 m headrope 

 length net using the formula 



E = (nets * length = 30.5 m) * (min = 60) 



where nets = number of nets towed, 



length = headrope length of a net (meters), 

 min = minutes fished. 



Turtle CPUE (R ) and 95% confidence interval 

 (C.I.) were calculated according to methods de- 

 scribed in Snedecor and Cochran (1967) using the 

 formulae 



R = ^tJ^e, 



1 = 1 



i = l 



95% C.I. on/? =/? + 1.96 (l/S) 



RE,)'^ln(n-l) 



where R = CPUE (turtles/30.5 m net hour), 

 R = estimated CPUE, 

 T, = number of individuals (turtles), 

 E, = effort (30.5 m net hour), 

 n = sample size (number of tows). 



The data were stratified by species, season, 

 depth, and statistical zone (corresponding to those 

 used by NMFS for reporting shrimp landings). 

 For each zone, turtle CPUE, mean depth of cap- 

 ture, mean length of tow, and mortality were 

 computed. In summarizing the data, the Gulf of 

 Mexico was subdivided into eastern (NMFS 

 statistical zones 1-7, corresponding to the Flori- 

 da west coast excluding the panhandle), central 

 (NMFS statistical zones 8-17, corresponding to 

 the Florida panhandle through Louisiana), and 

 western (NMFS statistical zones 18-21, corre- 

 sponding to the Texas coast) areas. The southern 

 North Atlantic area included the east coast of the 

 United States from Florida to North Carolina, 

 statistical zones 24-33. Part of zone 28, the Cape 

 Canaveral ship channel and adjacent shrimping 

 grounds (lat. 28°15'N to 28°30'N) was excluded to 

 avoid positively biasing CPUE estimates. This 

 habitat harbors large concentrations of turtles 

 throughout the year, and high turtle catch rates 

 (0.3643 ± 0.0045 turtles/hour)^ do not reflect 

 those occurring on the shrimping grounds outside 



the Canaveral area. Exclusion of these data is not 

 expected to cause an underestimate of mortalities 

 for the southern North Atlantic because commer- 

 cial shrimping effort near Cape Canaveral is re- 

 stricted to three or four vessels during most of the 

 year. 



Estimates of shrimp fishing effort for the off- 

 shore Gulf of Mexico shrinip fishery were ob- 

 tained from the NMFS Galveston Laboratory (E. 

 Klima^). The shrimp fishing effort was corrected 

 for relative amounts of effort by single rigged, 

 double rigged, and quad rigged vessels and then 

 standardized to 30.5 m net hours. The Atlantic 

 shrimp fishing effort was based on an effort esti- 

 mate developed in 1983 (Anonymous 1983^). Be- 

 cause the data were being updated, more current 

 Atlantic shrimp fishing effort data will be avail- 

 able at a later time. 



Percent mortality of the total catch was esti- 

 mated by a least squares linear regression using 

 percent mortality as dependent upon minutes 

 fished which yielded the relationship of 

 Y = 0.00165X - 0.03. The average mortality 

 over 30-min increments of tow length was calcu- 

 lated, and 10 unweighted means were regressed 

 on minutes fished. Although this approach may 

 violate the assumption of homogeneity in regres- 

 sion, it was assumed to be the most appropriate 

 means of describing this relationship, since the 

 dependence of mortality on tow time is strongly 

 statistically significant (r = 0.98; P< 0.001). 

 Percent mortality was multiplied by turtle cap- 

 tures ±95% upper and lower confidence bounds of 

 turtle captures to estimate the number of turtles 

 killed. 



Results and Discussion 



Turtle captures and mortality by statistical 

 zone and season with associated trawling effort 

 data were analyzed. While the total observer ef- 

 fort in the Gulf of Mexico (16,771 hours) was 

 greater than the southern North Atlantic (9,943 

 hours), 482 turtles were captured in the southern 

 North Atlantic and only 52 were captured in the 



'■^Means ± the 95% confidence interval will be used through- 

 out the paper. 



6E. Klima, Southeast Fisheries Center Galveston Laboratory, 

 National Marine Fisheries Service, NOAA, 4700 Avenue U, 

 Galveston, TX 77550, pers. commun. Summer 1986. 



'^Anonymous. 1983. Environmental assessment of a pro- 

 gram to reduce the incidental take of sea turtles by the commer- 

 cial shrimp fishery in the southeast United States. U.S. De- 

 partment of Commerce, National Marine Fisheries Service, 

 9450 Koger Blvd., St. Petersburg, FL 33702. 



814 



