The marine copepod Pseudocalanus sp. exhibits an unusual reverse diel vertical migration in Dabob Bay, Washington, concurrently with a normal vertical migration by nocturnal invertebrate predators. Reduced spatial overlap with predators appears to decrease mortality rate of adult female Pseudocalanus. A life table analysis suggests that the demographic disadvantage associated with daily migration across a thermal gradient can be overcome if mortality is reduced by as little as 16 percent.

No abstract

1991. Local-scale versus large-scale factors affecting recruitment. Can. ). Fish. Aquat. Sci. 48: 1003-1 006.Recent analyses of Atlantic cod (Gadus morhua) and haddock (Melanogrammus aeglefinus) stocks in the northwest Atlantic have indicated that large-scale factors (several hundred to thousands s f kilometres) dominate over effects operating on more local scales (10 to a few hundred kilometres) in determining recruitment patterns for these stocks. Adding additional years and additional stocks to the data set, the recruitment time series for cod and haddock have been reexamined. A first differencing technique was used to remove trends in the data. The results indicate that while large-scale effects probably do affect recruitment, the dominant factors are operating on more local scales and correlations are strongest for neighboring stocks.Les rksultats de rkcentes analyses des stocks de morue de I'Atlantique (Gadus msrhua) et d"ig8efin (Melanogrammus aeglefinus) peuplant les eaux de Iltlantique nord-ouest rkv$lent que des facteurs 3 grande kchelle (de plusieurs centaines A plusieurs milliers de kilom$tres) affaiblissent Bes incidences de facteurs locaux (de 10 21 quelques centaines de kilomgtres) dans la determination des regimes de recrutement. On a reevalue la s6rie temporelle de donnkes sur le recrutement de %a morue et de I2iglefin en y ajoutant des donnkes resueil8ies pendant dfautres annkes et des donnkes sur d'autres stocks. ha mkthode des diffkrences premibes a permis dfeliminer les tendances dans les donnkes. Les rksultats rkvglent que meme si les incidences A grande kchelle agissent sur le recrutement, les facteurs dominants agissent sur une echelle plus locale et les corr6iations sont plus marqukes entre des stocks voisins.