FISHERY BULLETIN: VOL. 84, NO. 1 



75*00' 74*30' 74*00' 



Figure 1— Map of the Norfolk Canyon study area with station 



73*30' 



locations indicated. 



73*00' 



Sampling Design 



Norfolk Canyon and an adjacent open slope were 

 divided into five sampling strata: 75-150 m, 151-400 

 m, 401-1,000 m, 1,001-2,000 m, and 2,001-3,000 m. 

 Six stations were then randomly assigned in each 

 depth stratum. The duration of all tows in depths 

 of <2,000 m was 0.5 h (bottom time). Where the 

 depth exceeded 2,000 m, the tow times were ex- 

 tended to 1 h. Station depth was determined from 

 a sonic precision depth recorder when the net was 

 set and then every 3 min for the duration of the 0.5 

 h tows (every 6 min for the 1-h tows). Mean station 

 depth was then determined by averaging the 11 

 resultant values. 



Data Collection and Analysis 



Head lengths instead of total lengths were 

 measured because macrourids have slender whiplike 

 tails that are easily damaged during trawling. The 

 head length (HL) was measured to the closest 

 millimeter, from the tip of the snout to the posterior 

 edge of the opercle using Helios 4 dial calipers. The 

 fish were weighed with an Ohaus dial-a-gram scale 

 Calibration showed the scale to be accurate within 



■•Reference to trade names does not imply endorsement by the 

 National Marine Fisheries Service, NOAA. 



1.0-1.5 g under all typical shipboard conditions. 



The sex and gonadal conditions of freshly captured 

 specimens were noted. Gonadal samples for histo- 

 logical processing were stored in Davidson's preser- 

 vative and later mounted using standard paraffin 

 techniques. Sections (5 mm) were stained with 

 Mayer's hematoxylin and eosin counterstain. 



Saccular otoliths and a scale sample were removed 

 from all Nezumia bairdii and stored dry. Represen- 

 tative otolith samples were chosen randomly from 

 individuals over the entire size range of fish 

 captured. 



The length-weight relationships for Nezumia bair- 

 dii, Coryphaenoides armatus, and C. rupestris were 

 analyzed using log transformed weights regressed 

 against head length (Fig. 2). 



Regression analysis of head length on depth of cap- 

 ture was performed for each species to determine 

 any significant change in head length with change 

 in depth. Testing of the hypothesis that fi = for 

 the regression line ascertained whether there was 

 a significant change of size with changing depth. The 

 coefficient of determination (r 2 ) was also calculated 

 to determine what proportion of the variance of head 

 length could be attributed to change in depth. 



The a posteriori Student-Newman-Keuls analysis 

 of means was used as a second method for inter- 

 preting the size/depth relationship. This method 

 calculated the mean depth of capture of each head- 



36 



