594 



Fishery Bulletin 98(3) 



million lbs. (Table 4, Fig. 6). Total finfish bycatch estimates 

 from the delta lognormal model were consistently lower for 

 all years, and overall followed the same trend as the esti- 

 mates from the current general linear model. The normal- 

 ized plot of total finfish bycatch (i.e. year estimate minus 

 the mean divided by the standard deviation of the time 

 period) shows that the trends are identical between the 

 two models up to 1990, but in 1991-95 some discrepan- 

 cies were observed (Fig. 7). However, both models show 

 a decreasing trend in the total finfish bycatch estimates 

 from about 1,100 million lbs. (1972-84) to less than 700 

 million lbs. during the last 10 years ( 1985-95). This decline 

 can be attributed to improvements in the selectivity of the 

 shrimp trawl gear to retain less bycatch (i.e. introduction 

 of TEDs and BRDs) or to an overall reduction of the traw- 

 lable fish stock biomass in the U.S. Gulf of Mexico. 



For Atlantic croaker, bycatch estimates from the delta 

 lognormal model were on average 4.5 billion fish for the 

 1972-95 period, 74.57. lower than estimates of 17.7 billion 

 fish from the general linear model (Table 4, Fig. 61. Once 

 more, the normalized plot shows a similar decreasing trend 

 in bycatch estimates from both models in the 1972-95 

 period (Fig. 7). Atlantic croaker, together with longspine 

 porgy iStenotomus caprintis), are the most common fin- 

 fish bycatch species in the Gulf of Mexico shrimp fishery. 



therefore a significant reduction in bycatch estimates of 

 Atlantic croaker most likely correlates with a reduction in 

 total estimated finfish bycatch. 



Bycatch estimates of red snapper from the delta lognor- 

 mal model were slightly greater in general from 1972 to 

 1982, and much lower from 1987 to 1995 compared with 

 estimates yielded with the general linear model (Fig. 6). 

 On average, the delta lognormal model bycatch estimates 

 were 22.1 million fish for the years 1987-95, 40*^ lower 

 than the equivalent average of 36.8 million fish estimated 

 with the general linear model (Table 4). The normalized 

 plot shows that since 1987, there has been an overall 

 increasing trend in red snapper bycatch according to both 

 the general linear model and delta model estimates, a 

 peak in bycatch in 1990, subsequent low in 1992, and an 

 increasing trend since then (Fig. 7). Prior to 1987, red 

 snapper bycatch was relatively lower, with an exception of 

 the highest bycatch peak in 1972 and some above average 

 bycatch in 1980-82. 



Delta lognormal estimates of Spanish mackerel bycatch 

 were 97'/; higher on average than those from the general 

 linear model (Fig. 6, Table 4) for the time period 1972-95. 

 Spanish mackerel bycatch estimated by the delta lognor- 

 mal model was on average 6.5 million fish, compared with 

 3.2 million fish estimated by the general linear model. In 



