Fortier and Villeneuve Cannibalism and predation by Scomber scombrus larvae 



273 



Percent vertical distribution Temperature (°C) 



20 40 60 80 100 20 40 60 80 100 20 40 60 80 100 20 40 60 80 100 5 10 15 20 



n= 43 . 



Atlantic mackerel 

 Scomber scombrus 



Yellowlail flounder 

 Limanda ferruginea 



Redfish 

 SebasTes spp. 



Silver hake 

 Merluccius bdmeans 



Figure 3 



Diel changes in the vertical distribution of the four most abundant species offish larvae captured with the multi-net sampler 

 (24 and 25 July 1991) at the station (52-m depth) of the sampling grid where the greatest density offish larvae was found. 

 Black histograms represent nighttime percent distribution and white histograms, daytime percent distribution. Vertical pro- 

 files of temperature are shown on the right. Sample size (number of larvae) is given with the vertical distribution and sam- 

 pling hour with the temperature profile. 



proportion to their availability in the plankton by 

 larvae of all lengths. Copepods >600 /mi were selected 

 for by larvae >7 mm (Table 5). 



Out of the 710 fish larvae found in the gut of At- 

 lantic mackerel larvae, 36 were identified visually 

 and 38 were identified by discriminant analysis of 

 their otoliths (Table 6). The species composition of 

 the prey identified by either method was similar 

 (Table 6). Assuming that the species composition of 

 the 74 fish larvae identified represented the true com- 

 position of the assemblage ingested, conspecifics made 

 up the majority ( 66 f /r ) of the fish larvae preyed upon by 

 Atlantic mackerel larvae. Selectivity for a given spe- 

 cies of larval fish prey was calculated for stations where 

 >10 larvae were identified in the gut of Atlantic mack- 

 erel larvae. The results indicated little selection by 

 mackerel larvae for any species of fish larvae (a=l/ 

 AT=0.25, where N=A species) (Table 6). 



Atlantic mackerel larvae preyed primarily on 

 newly hatched larvae despite the availability of larger 

 larvae in the plankton (Fig. 6). Only one conspecific 

 prey >5 mm was found in the gut of mackerel larvae 

 despite the availability of conspecifics in the plank- 

 ton. Except for one larva 9 mm long, yellowtail floun- 

 der prey were <6.5 mm. The three redfish prey for 

 which measurements are available were <5.5 mm. 

 Atlantic mackerel apparently did not capture silver 

 hakes >2.5 mm. The lengths of conspecifics, redfish, 

 and silver hake prey corresponded to the range of 

 lengths at hatching for these species (Fig. 6). 



Predation by Atlantic mackerel larvae in 

 relation to prey density 



There was no consistent relationship between pre- 

 dation on invertebrates by Atlantic mackerel larvae 



