Bochenek et al.: Assessment of Stenotomus chrysops and Centropnstas striata discards in the Mid-Atlantic Bight 



fell between 22.9 cm (25 th percentile) and 25.0 cm (75 th 

 percentile). For the NMFS observer data, the mean size 

 of scup discards was 17.2 cm and ranged from 13.6 to 

 20.6 cm. Fifty percent of the scup discarded fell between 

 16.2 cm (25 th percentile) and 18.2 cm (75 th percentile). 

 For scup landed, the mean size was 22.8 cm and ranged 

 from 19.4 to 28.9 cm. Fifty percent of the scup landed 

 fell between 21.3 cm (25 th percentile) and 23.8 cm (75 th 

 percentile). 



Codend and gear 



Vessels participating in this study and in the NMFS 

 observer program used either millionaire or box nets 

 (Table 1). More tows were made with the box net in both 

 data sets (Table 1). Most tows in our study were made 

 with the composite and 11.43-cm codends because com- 

 parison of these two codends was one focus of our study. 

 Most scup-targeted tows in the NMFS observer database 

 were made with codends <10.16 cm mesh (Table 1). 



Codend mesh size did not have a significant effect 

 on catch length frequencies when data from our study 

 and the NMFS observer data were analyzed separately 

 or combined. We deleted codends with the smallest 

 meshes (meshes slO.16 cm) and re-analyzed the data 

 for the remaining larger codend meshes. Again, catch 

 length frequencies were not significantly different for 

 any of the codend mesh sizes. Finally, we considered 

 the landed and discarded scup separately. For landings, 

 codend mesh size had a moderately significant effect on 

 median length (P=0.0220) and a stronger significant 

 effect on mean length (P=0.0062). Codends with some 

 meshes 212.7 cm caught more of the landed size fraction 

 than the composite and slightly more than the 11.43-cm 

 mesh codend; however, the actual difference in mean 

 length between the three mesh-size groups was small, 

 approximately one cm (Fig. 2). 



The efficiency of the codend may change with the 

 amount of fish caught such that selectivity declines with 

 high catches. Accordingly, scup catches were divided 

 into two groups: those above and those below the me- 

 dian catch for all tows. For catches above the median, 

 codend mesh size had a significant effect (P=0.0441) 

 on the 25 th percentile of size for scup discarded in our 

 study. The 25 th percentile size was largest for codends 

 with some meshes ^12.7 cm and smallest for the com- 

 posite codend. For landed scup, the 25 th percentile sizes 

 were about 22.0 cm regardless of codend mesh size. No 

 significant differences existed between codend mesh 

 sizes for scup length frequency in tows with catches 

 below the median. 



We examined the composition of the catch by weight. 

 Codend mesh size had a limited effect on the ratio 

 of scup discarded to landed, the total catch and to- 

 tal discards of all species, and total scup landed and 

 discarded. Scup discards were greater with codends 

 having some meshes 212.7 cm (P=0.0211). More scup 

 were landed from these tows as well (P=0.0034) and 

 therefore this codend style may contribute to a greater 

 catch rate (Table 2). Very likely, this trend in increased 



I Landed, Composite 

 1 Landed 11.43 cm 



jnik'ii > \11 tin 



Figure 2 



Mean scup {Stenotomus chrysops) length fractions 

 for those tows with landed scup with a composite 

 (10.16 + 11.43 cm) codend, 11.43-cm mesh codend, and 

 a sl2.7-cm mesh codend. l = smallest size. 100 = larg- 

 est size. 



catch is produced by the small number of tows (n=l) in 

 this mesh size category rather than a real improvement 

 in net performance. 



No significant gear effects existed for any of the 

 length-frequency fractions in the combined data set (our 

 study and NMFS observer study). The only significant 

 effect of scope (P= 0.0175) was on total scup discarded 

 in our study. This effect was not present in the NMFS 

 observer data set. 



Discards-to-landings ratio 



Of the 62 tows completed in our study, 39 targeted scup. 

 The NMFS observer program, from 1997-mid 2000, 

 included 35 scup-targeted tows (Table 3). Overall, mean 

 catch per tow for scup-targeted tows was 972.6 kg in 

 our study and 945.3 kg for NMFS observed tows. In 

 our study, the discards-to-landings ratio for all species 

 combined ranged from 1.77 with the composite codend to 

 2.91 with a codend with some meshes al2.7 cm. In the 

 NMFS observer data set, the discards-to-landings ratio 

 for all species combined in scup-targeted tows ranged 

 from 0.47 with codends having meshes of 6.35-10.16 cm 

 to 3.43 with codends with meshes of 11.43 cm (Table 2). 

 The mean discards-to-landings ratio for scup ranged 

 from 1.1 for the NMFS database to 2.4 for our study 

 (Table 3). Ratios varied from a low of 0.35 to a high of 

 5.72 among the various gear and mesh-size combina- 

 tions (Table 4). 



We analyzed cases where scup discards exceeded or 

 were less than landings. When our data and the NMFS 

 observer data were combined, the 25 th (P=0.0219), 50 th 



