GARTNER ET AL.: FISH ESCAPEMENTS FROM MIDWATER TRAWLS 



Q 30 

 LLI 

 DC 

 fiJ 25 



CO 

 _i 

 < cr 



ziuJ 



ii 



08 



z o 



cr 



UJ 

 CL 



20 



15 



10 



1,6mm MESH 

 4.0mm MESH 



SIZE GROUP (mmSL) 



Figure 1.— Overall numbers of myctophids collected per 10''m^ water filtered for 

 the 1.6 mm mesh and 4.0 mm mesh nets. 



collected over twice as many specimens as the 4 mm 

 mesh net. Overall, the 1.6 mm mesh net was signif- 

 icantly more effective in collecting individuals of 

 smaller than 30 mm SL with a mean calculated 

 abundance ratio for the 6 to 30 mm size groups of 

 2.7:1 between the 1.6 mm and 4 mm meshes. The 

 abundance ratios for the small to large mesh sizes 

 is highest for the smallest size group considered 

 (4.4:1 for the 6 to 10 mm SL group). 



Although the 4 mm mesh captured more fishes at 

 sizes >30 mm SL, the differences, while significant, 

 were not pronounced and never approached the 

 ratios noted for the smaller size groups. The mean 

 ratio for the 1.6 mm to 4 mm meshes for size groups 

 31 to 65 mm SL was 0.9:1 (range 0.8:1 to 1.0:1). At 

 sizes larger than 65 mm SL, the ratios were variable 

 owing to small sample sizes. 



Abundances, Cross-Sectional 



Dimensions and Morphologies of 



Ranking Species 



The same five species made up the ranking mycto- 

 phids from both nets, although the order of abun- 

 dance differed (Table 2). A sixth species, Cerato- 

 swpelus townsendi (formerly C. warmingii, see 

 Badcock and Araujo 1988), was also a dominant 

 myctophid in the 4 mm net catches. Comparisons 

 of internet abundances of ranking species for each 

 size group revealed three basic patterns: 1) Virtual- 

 ly the entire size range was underestimated by the 

 4 mm mesh net {Benthosema suborbitale and Noto- 

 lychnus valdiviae, Fig. 2a, b); 2) only size groups 



up to sexually mature adults (ca. 40 mm SL) were 

 underestimated by the 4 mm mesh net {Lampanyc- 

 tus alatus and Lepidophanes guentheri Fig. 2c, d); 

 and 3) only juveniles smaller than 26 to 30 mm were 

 underestimated by the 4 mm mesh net {Ceratosco- 

 pelus townsendi and Diaphus dumerilii Fig. 2e, f). 

 Of the ranking species, only these last two species 

 were collected in greater numbers by the 4 mm mesh 

 net at sizes larger than 30 mm SL. 



The patterns of net capture vs. size ranges were 

 directly related to the general body dimensions and 

 morphologies of the ranking species. Maximum 

 cross-sectional depths and widths were measured 

 on the body at the pectoral fin base in Benthosema 

 suborbitale, Lampanyctus alatics, Lepidophanes 

 guentheri, and Notolychnus valdiviae, while for 

 Ceratoscopelu^ townsendi and Diaphus dumerilii, 

 the maxima were on the head anterior to the oper- 

 cular openings. Head profiles also differed among 

 species, with the first four species having pointed 

 or wedge shaped outlines, while the latter two had 

 blunt, rounded heads. Both A'^. valdiviae and B. sub- 

 orbitale (Pattern 1) are diminutive species not ex- 

 ceeding 22 mm and 33 mm, respectively, in the 

 eastern Gulf, while the other four species grow much 

 larger (Gartner et al. 1987; Gartner, unpub. data). 

 Mean cross-sectional measurements (Table 3) show 

 that in relation to body length, B. suborbitale is deep 

 bodied, while A^. valdiviae, Lepidophanes guentheri, 

 and Lampanyctus alatus (Pattern 2) are all slender. 

 When compared with the previous species at equi- 

 valent lengths, C. townsendi and D. dumerilii (Pat- 

 tern 3) have generally thick cross-sections. 



215 



