distributions of four common species ( where n >50 

 for fishes for each of the two nets, and n>20 for 

 squid) for: Stenobranchius leucopsarus in two of 

 the three comparisons, Z)/ap/ii/s theta in one of two 

 comparisons, and Tarletonbeania crenularis in two 

 of two comparisons. In all instances where length 

 distributions differed, the pelagic trawl caught an 

 appreciably higher percentage of large animals. 

 Even though the one K-S test for the squid 

 Gonatus pyros was not significant (because of 

 small numbers caught in the IKMT), IB^c of num- 

 bers of this squid from the pelagic trawl were >35 

 mm DML and no animals >35 mm were caught in 

 the IKMT. 



Length-frequency distributions for S. leucop- 

 sarus and T. crenularis from both trawls (Figure 3) 

 show that large lanternfishes are clearly un- 

 dersampled by the IKMT. The modes composed of 

 fishes >45 mm, which are prominent in pelagic 

 trawl catches, are absent in IKMT catches. 



Another notable example of differences between 

 catches of large fish in these collections were cap- 

 tures of Tactostoma macropus. Few large indi- 

 viduals ( >250 mm) have been collected in IKMT 

 tows off Oregon. Three tows with the pelagic trawl 

 at depths of 470-1,070 m in 1978, however, cap- 

 tured many large fish. Twenty-nine percent of the 

 T. macropus caught in these pelagic trawl collec- 

 tions were >250 mm, compared with only 8.2^c in 

 252 IKMT tows to 500 m depth or deeper during 

 previous years. 



Effective Cross-Sectional Area of the Pelagic Trawl 



The cross-sectional area of the pelagic trawl was 

 indirectly estimated from the catches of four 

 species of lanternfishes caught in both the pelagic 

 trawl and IKMT on the three "paired" cruises (Ta- 

 ble 1) to see how it compared with the divers' esti- 

 mates of 50 m^. The following equation was used: 



A = 



CoD 



where A = area in square meters, 



Cj = number of fish caught by pelagic 



trawl, 

 V = volume filtered by the IKMT, in cubic 



meters, 

 Cg = number of fish caught by the IKMT, 

 D = distance trawled by the pelagic trawl 



in meters. 



The volume of water filtered by the IKMT was 



cr 



UJ 

 CD 



3 



600 



400 



200 





 200 



100 



I I I I I I 



I I I I I I 



Stenobrachius 

 leucopsarus 



+"-1— f 



Tarletonbeania 

 crenularis 



40 60 



LENGTH (mm) 



80 



100 



Figure 3. — Length-frequency distribution for Stenobrachius 

 leucopsarus and Tarletonbeania crenularis in pelagic trawl and 

 IKMT collections, July 1976, 0-500 m. 



calculated from a flowmeter mounted in the MPS 

 and monitored aboard ship via electrical cable (see 

 Pearcy et al. 1977). Distances trawled by the 

 pelagic trawl were calculated from ship speed 

 (based on Loran readings) and the duration of the 

 tow. In each comparison, tows and nets selected 

 fished similar depths at the same time of day. The 

 mouth area estimated in this way varied from 19 to 

 3,161 m^ with a median value between 48 and 62 

 m2 (Table 3). The smallest area (19 m^), for D. 

 theta, can be largely explained by the retention of 

 small fish (10-15 mm) in the IKMT but not by the 

 slightly larger mesh of the pelagic trawl. This is 

 the only obvious example of differences in size- 

 frequency distributions that can be explained by 

 escapement of small fish. The large values of 

 mouth area may result from different population 

 densities of two species at the times of sampling 

 during the 1977 cruises. 



The present study indicates that large nets 

 usually catch more individuals, and usually, but 

 not always, more species and larger animals than 

 small IKMT-type nets. Detailed quantitative com- 

 parisons are needed with nets of known cross- 

 sectional areas, with similar mesh size, at the 

 same depths and locations (Roper 1977). Large 

 nets will never replace the smaller IKMT's and 

 rectangular midwater trawls because of the 

 specialized equipment needed to launch and re- 



533 



