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  • Canadian Science Publishing  (3)
  • 1
    In: Canadian Journal of Fisheries and Aquatic Sciences, Canadian Science Publishing, Vol. 66, No. 5 ( 2009-05), p. 869-872
    Abstract: In the paper “Does the fall phytoplankton bloom control recruitment of Georges Bank haddock, Melanogrammus aeglefinus , through parental condition?”, Friedland et al. (Can. J. Fish. Aquat. Sci. 65(6): 1076–1086, 2008) examine a sizable number of hypotheses aiming to explain the recruitment patterns observed in Georges Bank haddock. The authors focus on a correlation between the size of the autumnal phytoplankton bloom and the survivor ratio (recruitment), concluding this to be the main factor determining recruitment, via the mechanism of adult condition at the time of spawning. Here we examine this result in close detail and re-analyse some of the data presented in the paper. We show that the recruitment metric upon which Friedland et al. base their conclusions inadvertently biases the analysis in favour of high recruitment events and against low recruitments. As a consequence, Friedland et al. disregard correlations that are, in fact, significant. Furthermore, we show that the parental condition hypothesis hinges upon a single, highly uncertain data point, without which the correlation is no longer significant. We find that evidence for the parental condition hypothesis is weak, and that in performing the analysis in the chosen manner, Friedland et al. have overlooked alternative hypotheses.
    Type of Medium: Online Resource
    ISSN: 0706-652X , 1205-7533
    Language: English
    Publisher: Canadian Science Publishing
    Publication Date: 2009
    detail.hit.zdb_id: 7966-2
    detail.hit.zdb_id: 1473089-3
    SSG: 21,3
    SSG: 12
    Location Call Number Limitation Availability
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  • 2
    Online Resource
    Online Resource
    Canadian Science Publishing ; 2008
    In:  Canadian Journal of Fisheries and Aquatic Sciences Vol. 65, No. 7 ( 2008-07), p. 1297-1306
    In: Canadian Journal of Fisheries and Aquatic Sciences, Canadian Science Publishing, Vol. 65, No. 7 ( 2008-07), p. 1297-1306
    Abstract: Copepods in the genus Calanus are usually considered to be the preferred prey of gadoid larvae in many areas; however, in the Irish Sea, the abundances of these Calanus species are low and highly variable. We use this situation to test whether Calanus species are still actively selected by gadoid larvae in Calanus -poor environments. Diets of Irish Sea cod ( Gadus morhua ), haddock ( Melanogrammus aeglefinus ), and whiting ( Merlangius merlangus ) were studied from the yolk-sac stage to the juvenile stage. Prey from stomach contents were compared with in situ abundance via an index of prey preference. As expected, all larvae selected copepod nauplii at the onset of feeding. As the larvae developed, their prey preferences changed and varied with species. Cod and whiting showed a similar transition of prey species preference, with a clear preference for Calanus species after metamorphosis, even in this area of low abundance of these Calanus species. The diet composition of haddock differed from that of cod and whiting, as nauplii remained in their diet later into development and there was little preference for individual copepod species detected. The differences in prey selectivity suggested between these gadoids may be attributed to their population variability through the known variability of their preferred prey items.
    Type of Medium: Online Resource
    ISSN: 0706-652X , 1205-7533
    Language: English
    Publisher: Canadian Science Publishing
    Publication Date: 2008
    detail.hit.zdb_id: 7966-2
    detail.hit.zdb_id: 1473089-3
    SSG: 21,3
    SSG: 12
    Location Call Number Limitation Availability
    BibTip Others were also interested in ...
  • 3
    Online Resource
    Online Resource
    Canadian Science Publishing ; 2009
    In:  Canadian Journal of Fisheries and Aquatic Sciences Vol. 66, No. 12 ( 2009-12), p. 2130-2141
    In: Canadian Journal of Fisheries and Aquatic Sciences, Canadian Science Publishing, Vol. 66, No. 12 ( 2009-12), p. 2130-2141
    Abstract: Atlantic herring ( Clupea harengus ) have contrasting spawning strategies, with apparently genetically similar fish “choosing” different spawning seasons, different egg sizes, and different spawning areas. In the North Sea, both autumn- and winter-spawning herring share the same summer feeding area but have different spawning areas. Females of both spawning types start their oocyte development in April–May. Oocyte development is influenced by the body energy content; during the maturation cycle, fecundity is down-regulated through atresia in relation to the actual body condition. Hence, fecundity estimates must account for the relative time of sampling. The down-regulation over the whole maturation period is approximately 20% in autumn- and 50% in winter-spawning herring. The development of the oocytes is the same for both spawning strategies until autumn when autumn spawners spawn a larger number of small eggs. In winter spawners, oocyte development and down-regulation of fecundity continues, resulting in larger eggs and lower number spawned. In theory, autumn and winter spawners could therefore switch spawning strategies, indicating a high level of reproductive plasticity.
    Type of Medium: Online Resource
    ISSN: 0706-652X , 1205-7533
    Language: English
    Publisher: Canadian Science Publishing
    Publication Date: 2009
    detail.hit.zdb_id: 7966-2
    detail.hit.zdb_id: 1473089-3
    SSG: 21,3
    SSG: 12
    Location Call Number Limitation Availability
    BibTip Others were also interested in ...
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