Ocean climate and seal condition

The mean annual weaning weight of pups declined from 1975 to the late 1990s, a period characterized by a large-scale, basin-wide warm decadal regime that included multiple strong or long-duration El Ni？os; and increased with a return to a cool decadal regime from about 1999 to 2004. Increased foraging effort and decreased mass gain of adult females, indicative of reduced foraging success and nutritional stress, were associated with high ocean temperatures.Despite ranging widely and foraging deeply in cold waters beyond coastal thermoclines in the northeastern Pacific, elephant seals are impacted significantly by ocean thermal dynamics. Ocean warming redistributes prey decreasing foraging success of females, which in turn leads to lower weaning mass of pups. Annual fluctuations in weaning mass, in turn, reflect the foraging success of females during the year prior to giving birth and signals changes in ocean temperature cycles.Multidecadal fluctuations, or biological regime shifts, have basin-wide effects on sea surface temperature (SST) and upwelling that are associated with large-scale changes in biological productivity [1,2]. They are similar to the 3–4 year cycles of the El Ni？o Southern Oscillation (ENSO) but on longer time scales, and as background states, may amplify ENSO effects [3]. The Pacific Decadal Oscillation (PDO), which addresses the North Pacific/North American sector, comprises events that persist for 20 to 30 years [4,5]. In the 20th century, "cool" PDOs prevailed from 1947 to 1976 while "warm" PDOs were recorded from 1925 to 1946 and from 1977 through at least the mid-1990s. Chavez and colleagues [6], focusing on the last two regimes, report that in the mid-1970s the Pacific changed from a cool "anchovy regime" (ocean temperatures colder than normal, shallow thermocline and strong upwelling, increased nutrient supply and zooplankton and overall productivity, high catches of anchovies and salmon, low sardine abundance) to a warm "sardine regime" (o