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



13 



reduce scup discards, yet permit the majority of scup 

 to attain sexual maturity. Kilograms discarded might 

 be reduced by more than half. Fishermen would reach 

 their trip limit sooner and thus stop fishing earlier. 

 As a result, fishing mortality rate even on larger scup 

 would be reduced. This single change would reduce 

 discards more than any change in net or codend design 

 tested to date and would not result in any increase in 

 fishing-induced mortality for scup. 



the percentage in scup-targeted tows. This finding indi- 

 cates that there is considerable discrimination between 

 the two species at the level of the fishery. The black sea 

 bass fishery is currently regulated under the small- 

 mesh fishery GRA plan in which fishing is prohibited in 

 some areas to reduce scup mortality. This investigation 

 finds no evidence to support the efficacy of this manage- 

 ment approach. Scup discards do not appear to be an 

 important attribute of the black sea bass fishery. 



Black sea bass 



Estimates of discards of black sea bass are low in 

 the black-sea-bass-targeted fishery, based on the few 

 observed tows in our study and data from the NMFS 

 observer database. Regardless of which codends were 

 used, the same size fractions of black sea bass were 

 caught. The composite codend (10.16+11.43 cm mesh) 

 caught more black sea bass than were landed. Discards 

 was also higher. As with scup, mesh size and gear type 

 had minor effects on the size frequency, the discards- 

 to-landings ratio, and the kilograms of black sea bass 

 caught. The majority of tows where black sea bass were 

 caught had ratios of black sea bass discarded to landed of 

 less than 0.3, indicating that few discards occur in this 

 fishery. In contrast, most of the scup tows were charac- 

 terized by discards-to-landings ratios greater than one. 

 The differences in discards-to-landings ratios between 

 black sea bass and scup may be due to a combination of 

 biological factors controlling the average size of scup in 

 the larger schools and to regulatory factors that do not 

 match well with the size range of scup in schools. 



Unlike scup, black sea bass size frequencies and total 

 weight caught were similar in tows taken during the 

 first and last half of the trip. Trip limits are in effect 

 for both black sea bass and scup. The difference between 

 the two species in the distribution of catch through the 

 time course of the trip may be the result of biological 

 effects in that the schooling of scup would tend to pro- 

 duce higher catches during the middle or latter part of 

 the trip as the captain finds schools of fish. 



Powell et al. 3 showed that black sea bass and scup are 

 caught simultaneously more frequently than expected 

 by chance in tows in the Atlantic mackerel (Sco?nber 

 sco?nbrus), Loligo squid, scup, and silver hake fisheries 

 and suggested that they should be regulated together. 

 Our analysis also showed this pattern in that the two 

 species were frequently caught in the same tows (39 

 out of 40 scup-targeted tows and seven out of 10 black- 

 sea-bass-targeted tows caught both scup and black sea 

 bass). In addition, Shepherd and Terceiro (1994), Musick 

 et al., (1985), and Musick and Mercer (1977) also found 

 that both scup and black sea bass were caught in the 

 same tow. Use of a common codend mesh size regulation 

 for both fisheries may prove useful. The failure to find 

 significant differences between mesh sizes suggests that 

 the 10.16+11.43 cm composite bag might be a reasonable 

 choice for both fisheries. However, scup discards were a 

 small fraction of black sea bass landings in black-sea- 

 bass-targeted tows (0.4%) — very small in comparison to 



Conclusions 



Because fishermen catch both scup and black sea bass 

 in the same tow and because the current regulations 

 require fishermen to use an 11.43-cm mesh codend when 

 targeting scup, and, a 10.16-cm mesh codend when tar- 

 geting black sea bass, two different codend mesh sizes 

 are used on the same trip. The composite codend was 

 designed to retain the smaller black sea bass catches 

 and some scup when catch rates are low but permits 

 more scup to escape at higher catch rates. The composite 

 codend (10.16+11.43 cm mesh) performed as well as the 

 other codends used in our study, including the 11.43-cm 

 legal-size codend. The composite codend with 10.16-cm 

 mesh followed by the 11.43-cm or 12.7-cm mesh codends 

 should be further evaluated on both black sea bass 

 and scup-directed tows. If this composite codend works 

 equally as well as the legal 11.43-cm mesh codend cur- 

 rently in place for scup (and the data presented here sug- 

 gest that it does), consideration should be given to using 

 this codend because it permits the retention of smaller 

 black sea bass without negatively influencing scup. This 

 change would eliminate the need to carry two codends 

 onboard and thus would reduce overall trip costs without 

 impacting the number of scup discards. However, neither 

 codend successfully addresses the need to significantly 

 reduce scup discarding in the scup-directed fishery. 



Codends with some 12.7-cm meshes tended to reduce 

 discards by reducing the catchability of smaller scup, 

 but the trends were often not significant, possibly due 

 to the small sample size, but possibly also because nets 

 were clogged by schools of smaller-size scup. The data 

 indicate that further studies with 12.7-cm or greater 

 mesh composites may identify codend configurations 

 that will produce fewer discards. DeAlteris and La 

 Valley (1999) have documented that scup can survive 

 capture in a trawl net and subsequent escapement. 

 Therefore, optimizing codend mesh size could reduce 

 discard mortality. 



Larger scup were caught in tows where the total catch 

 weight was low. Large catches tended to accompany the 

 interception of scup schools. These large catches can 

 clog the nets and thus reduce size selection even at 

 larger mesh sizes. Alternatively, larger scup may not 

 be associated with smaller scup in schools. We cannot 

 discriminate between the two explanations. Regard- 

 less of the reason, the tendency of the largest catches 

 to contain proportionately more smaller fish will likely 

 minimize the positive influence of net management in 



