280 



Fishery Bulletin 94(2), 1996 



Kendall and Gordon (1981) calculated an average 

 mortality rate of 35%/d (SD=20*7r/d) for larvae <13 

 mm, whereas Ware and Lambert (1985) reported a 

 rate of 42%/d for larvae <8 mm. Thus, according to 

 our conservative estimate of digestion time, preda- 

 tion by Atlantic mackerel larvae (average 31%/d) 

 would represent a sizable fraction (>38%) of the to- 

 tal mortality typically experienced by newly hatched 

 larvae in the sea. This is consistent with an estimate 

 of 41% for the fraction of the total mortality of newly 

 hatched bay anchovy that could be attributed to pre- 

 dation by medusae (Purcell et al., 1994). According 

 to our highest estimate (average 93%/d), predation 

 by Atlantic mackerel larvae could wipe out popula- 

 tions of newly hatched co-occurring species in a few 

 days, and all the mortality of newly hatched Atlan- 

 tic mackerel could be attributed to cannibalism. 



Atlantic mackerel larvae can dominate the larval 

 fish assemblage over large areas in spring and early 

 summer. For example, the species represented from 

 62.2% to 76.9% of the ichthyoplankton in the neritic, 

 transitional, and oceanic zones of the Celtic Sea in 

 the spring of 1980 (Horstman and Fives, 1994). We 

 conclude that, in these areas, predation by Atlantic 

 mackerel larvae could represent a significant sur- 

 vival bottleneck for co-occurring species in the days 

 after hatching. 



Acknowledgments 



Funding for this research was provided by OPEN 

 (Ocean Production Enhancement Network), one of 

 the 15 networks of Centres of Excellence supported 

 by the Government of Canada through the Natural 

 Sciences and Engineering Research Council of 

 Canada (NSERC). Additional grants from NSERC 

 and Employment and Immigration Canada to L. 

 Fortier were instrumental in completing laboratory 

 analyses. The field work could not have been con- 

 ducted without the assistance of our colleagues from 

 McGill and Dalhousie Universities. Special thanks 

 are given to L. Natanson for her contribution to this 

 study and T. Miller for videotape measurements of 

 unpreserved larvae. G. Bergeron, G. Chaumillon, L. 

 Michaud, L. Mousseau, A. Potvin, M.-A. Remillard, 

 M. Simard, and C. Quinonez-Velazquez assisted in 

 the field or the laboratory, or both. 



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