74 



Fishery Bulletin 88(1), 1990 



100 150 200 250 300 350 400 450 500 



TOTAL LENGTH (mm) 



Figure 6 



I'lTcent frequency of* 'liiiihidi/ilcrux Jdhrr witliin 

 Kl-mni TL size classes. 



composed 25% of total volume in stratum 3. Percent 

 number was low for hydroids in stratum 3, but they 

 could only be counted as one individual per stomach 

 each time they were encountered, whereas there were 

 usually many amphipods per stomach. The IRI ranked 

 hydroids as the second-most important food source, 

 followed by polychaetes (feeding tentacles) and 

 sponges. TheMZ ranked polychaetes second, followed 

 by sponges and amphipods. Although Scyphozoa 

 ranked as one of the top seven food items in stratum 

 3, it occurred in only one stomach, which was distended 

 with 16 mL (after blotting) of jellyfish. Most stomachs 

 from stratum 3 that were considered full contained 3-6 

 mL of food. 



The MI indicated that hydroids were the dominant 

 food for all size classes oiC.faber. being found in over 

 75% of the stomachs from each size class and accoun- 

 ting for approximately 25% of the volume in each of 

 the groups (Fig. 5). The MI also showed that antho- 

 zoans were nearly as important as hydroids for fish up 

 to 200 mm SL, but were not important to fish >2()0 

 mm SL. The second-ranking prey for fish >200 mm SL 

 was polychaete-feeding tentacles according to the MI. 

 The IRI denoted amphipods as a major source of food 

 for fish of all sizes (dominant, by far, for fish > 100 mm 

 SL), but this was certainly due to the numerical bias 

 of the IRI. The MI indicated amphipods were a minor 

 dietary component except for fish 100-200 mm SL, 

 where they were the third-most important prey. Un- 

 identified egg masses, probably gastropod eggs, were 

 found in 4% of the stomachs from fish up to 100 mm, 

 but were a relatively minor component of the diet from 

 fish this size. Sponges were observed in 26% of the 

 stomachs from fish >200 mm SL and accounted for 

 21% of total volume of prey for these fish, making it 



the third-ranked food item for fisli in this grouji accord- 

 ing to the MI. 



Age and growth 



All but 6 of the 643 pairs of otoliths obtained were used 

 in age analysis, since 6 pairs were deemed unreadal)le 

 due to deformities in otolith structure. Discernment of 

 check marks on whole otoliths oiCfaber was relatively 

 easy in either reflected or transmitted light, and there 

 was 93% agreement between the two series of counts 

 and measurements. The differences between the re- 

 maining 7% (attributable to measurement and record- 

 ing errors) were satisfactorily resolved, allowing all 637 

 otolith pairs to be utilized in ageing analysis. The pat- 

 tern of alternating opaque and translucent l)ands which 

 were observed on the sagittae were believed to be 

 permanent records of the physiological growth of the 

 Atlantic spadefish from which they had been obtained. 



Length-frequency distributions are often used to 

 separate fish of different lengths into age groups and 

 are also utilized to validate ageing techniques, particu- 

 larly for younger age groups (Lagler 1956, MacDonald 

 1987). Good agreement was seen between the TLs of 

 fish determined to be age and age 1 by counting 

 opaque zones on otoliths and the range of TLs for the 

 first and second groups in a length-frequency distribu- 

 tion (Fig. 6). Consequently, the innermost opaque zone 

 on each sagitta was believed to be the first annulus. 



Since marginal increments on the otoliths should 

 approach zero during the time of annulus formation, 

 the monthly means were calculated to determine if one 

 opaque band was laid down on the sagittae during each 

 year. Generally, the mean marginal increment was low- 

 est in May and ijicreased steadily, by month, through 



