Abstract:We tested the hypothesis of synchronous interannual changes in forage fish dynamics around the North Pacific Rim. To do this, we sampled forage fish communities using a seabird predator, the rhinoceros auklet (Cerorhinca monocerata), at six coastal study sites from Japan to California. We investigated whether take of forage fishes was related to local marine conditions as indexed by sea surface temperature (SST). SST was concordant across sites in the eastern Pacific, but inversely correlated between east and west. Forage fish communities consisted of anchovy (Engraulis spp.), sandlance (Ammodytes spp.), capelin (Mallotus spp.), and juvenile rockfish (Sebastes spp.), among others, and take of forage fish varied in response to interannual and possibly lower-frequency oceanographic variability. Take of primary forage species were significantly related to changes in SST only at the eastern sites. We found synchrony in interannual variation of primary forage fishes across several regions in the eastern Pacific, but no significant east-west correlations. Specifically in the Japan Sea, factors other than local SST or interannual variability may more strongly influence forage fishes. Predator diet sampling offers a fishery-independent, large-scale perspective on forage fish dynamics that may be difficult to obtain using conventional means of study. Résumé :Nous testons l'hypothèse qui veut qu'il y ait des changements interannuels synchrones dans les dynamiques des poissons fourrage autour de la bordure du Pacifique Nord. C'est pourquoi nous avons échantillonné les peuplements de poissons fourrage à l'aide d'un oiseau marin prédateur, le macareux rhinocéros (Cerorhinca monocerata), à six sites d'étude côtiers du Japon à la Californie. Nous avons vérifié si les captures de poissons fourrage sont reliées aux conditions marines locales, telles que représentées par la température de surface de la mer (SST). Les SST s'accordent d'un site à l'autre dans l'est du Pacifique, mais il y a une corrélation inverse entre l'est et l'ouest. Les peuplements de poissons fourrage consistent, entre autres, d'anchois (Engraulis spp.), de lançons (Ammodytes spp.), de capelans (Mallotus spp.) et de jeunes sébastes (Sebastes spp.) et la capture de poissons fourrage varie en réaction à la variabilité océanographique interannuelle ou aussi peut-être de fréquence moins élevée. La capture de poissons fourrage principaux est en corrélation significative avec SST seulement dans les sites de l'est. Nous observons un synchronisme dans la variation interannuelle des poissons fourrage principaux entre plusieurs régions de l'est du Pacifique, mais aucune corrélation significative entre l'est et l'ouest. Tout particulièrement dans la mer du Japon, des facteurs autres que la SST locale et la variabilité interannuelle peuvent influencer plus fortement les poissons fourrage. L'échantillonnage du régime alimentaire des prédateurs permet d'obtenir, indépendamment de la pêche commerciale, une perspective à grande échelle de la dynamique des poissons f...

We compared annual indices of breeding by Thick-billed Murres, Uria lomvia, at a colony in northern Hudson Bay with annual variation in the extent of sea-ice cover during May and June, the period when birds arrive and initiate breeding. Greater ice cover was associated with delayed breeding and lower attendance rates at the colony during the early incubation period (late June). We detected no effect on egg size, reproductive success, or adult body mass. The extent of ice cover in May was positively correlated with the proportion of Arctic cod fed to nestlings, and in June with the proportion of capelin in the rest of the diet. There was a positive correlation between the proportion of capelin in the chick diet and chick body mass at 14 days of age. We attribute the delay in laying during years of heavy ice cover to the reduced area available for foraging close to the colony. Prolonged persistence of ice, though delaying the onset of laying, may benefit the birds later in the season, as they forage preferentially in the vicinity of ice. We suggest that the strong relationships we observed between the extent of ice cover and aspects of the breeding biology of Thick-billed Murres may apply to other Arctic-nesting seabirds and may reflect conditions affecting the entire marine food web.