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Large recent decreases of Cape gannets Morus capensis , Cape cormorants Phalacrocorax capensis and African penguins Spheniscus demersus in South Africa resulted in their being listed as Endangered. These seabirds, endemic to the Benguela upwelling system (BUS), primarily rely on anchovy Engraulis encrasicolus and sardine Sardinops sagax for food, yet decreased during periods of abundance of these prey species. In order to investigate this dichotomy, we examined long-term dietary characteristics for gannets in the region in relation to acoustically-derived biomass of prey. Principal component (PC) analysis of diet composition indicated an alternation in the use of anchovy and sardine (PC1), as well as a marked decrease, after the early 2000s, in the availability of these preferred forage resources (PC2). PC2, which we term the Forage Availability Index, was positively related to numbers of gannets and cormorants breeding each year and to estimates of survival of adult penguins at their two largest colonies in northwest South Africa. This indicates that recent availability of anchovy and sardine was insufficient to support these bird populations. Our results emphasize the need to account not only for overall abundance but also local availability of forage resources, when applying an ecosystem approach to managing fisheries for seabirds. [ABSTRACT FROM AUTHOR]

Understanding aggregation dynamics of forage species is important for evaluating biophysical scaling in marine ecosystems and heterogeneity of trophic interactions. In particular, zooplankton aggregations are fundamental units of many pelagic systems, but are difficult to observe continuously through space and time. Using an established modeling framework that encompasses a coupled regional oceanographic and individual-based modeling system, we test the hypothesis that persistence (duration) of krill aggregations is dependent on their size, intensity, and location of formation within the coastal upwelling region of the California Current. In support of this hypothesis, we found that aggregation size is positively related to intensity, whereas persistence has a parabolic response to aggregation size and intensity, indicating the likelihood that large and highly persistent aggregations are rare. Persistence of krill aggregations also depends on formation location within coastal upwelling areas. We found that krill aggregations were more likely to form near a major seabird colony and that some coastal upwelling areas act as sources of aggregations for other areas. Observations of seabird aggregations were used to evaluate the potential structural realism of predicted krill aggregations. Seabird aggregations displayed marked coherence with predicted krill aggregations in space, providing important criteria on the scaling and availability of krill aggregations to breeding and migratory species. Predicting scales of krill aggregation dynamics will benefit ecosystem assessments, and numerical modeling of predator foraging and marine spatial management aimed at ensuring protection of ecologically important areas. [ABSTRACT FROM AUTHOR]

Climate change may increase both stratification and upwelling in marine ecosystems, but these processes may affect productivity in opposing or complementary ways. For the Southern California region of the California Current Ecosystem (CCE), we hypothesized that changes in stratification and upwelling have affected marine bird populations indirectly through changes in prey availability. To test this hypothesis, we derived trends and associations between stratification and upwelling, the relative abundance of potential prey including krill and forage fish, and seabirds based on the long-term, multi-disciplinary CalCOFI/CCE-LTER program. Over the period 1987 through 2011, spring and summer seabird density (all species combined) declined by ~2% per year, mostly in the northern sector of the study region. Krill showed variable trends with two species increasing and one deceasing, resulting in community reorganization. Nearshore forage fish, dominated by northern anchovy ( Engraulis mordax ) as well as offshore mesopelagic species, show declines in relative abundance over this period. The unidirectional decline in springtime seabird density is largely explained by declining nearshore fish abundance in the previous season (winter). Interannual variability in seabird density, especially in the 2000s, is explained by variability in krill abundance. Changes in the numerical responses of seabirds to prey abundance correspond to a putative ecosystem shift in 1998–1999 and support aspects of optimal foraging (diet) theory. Predator–prey interactions and numerical responses clearly explain aspects of the upper trophic level patterns of change in the pelagic ecosystem off southern California. [ABSTRACT FROM AUTHOR]

Changes in variance are infrequently examined in climate change ecology. We tested the hypothesis that recent high variability in demographic attributes of salmon and seabirds off California is related to increasing variability in remote, large-scale forcing in the North Pacific operating through changes in local food webs. Linear, indirect numerical responses between krill (primarily Thysanoessa spinifera) and juvenile rockfish abundance (catch per unit effort ( CPUE)) explained >80% of the recent variability in the demography of these pelagic predators. We found no relationships between krill and regional upwelling, though a strong connection to the North Pacific Gyre Oscillation ( NPGO) index was established. Variance in NPGO and related central Pacific warming index increased after 1985, whereas variance in the canonical ENSO and Pacific Decadal Oscillation did not change. Anthropogenic global warming or natural climate variability may explain recent intensification of the NPGO and its increasing ecological significance. Assessing non-stationarity in atmospheric-environmental interactions and placing greater emphasis on documenting changes in variance of bio-physical systems will enable insight into complex climate-marine ecosystem dynamics. [ABSTRACT FROM AUTHOR]

Santora, J. A., Ralston, S., and Sydeman, W. J. 2011. Spatial organization of krill and seabirds in the central California Current. – ICES Journal of Marine Science, 68: 1391–1402. The hypothesis that krill and krill–predator spatial organization and abundance co-vary interannually was tested by investigating the spatial organization of krill and planktivorous seabirds in the central California Current ecosystem over 5 years of varying oceanographic conditions, 2002–2006. To measure the abundance and distribution of krill, data were integrated from large-scale hydroacoustic surveys and station-based net samples, and these data linked to concurrent shipboard visual surveys of seabirds. Acoustically based estimates of the relative abundance of krill were correlated with net samples of Euphausia pacifica, suggesting that acoustic signals mainly reflected the distribution of this numerically dominant species. The distribution and abundance of krill displayed marked changes over years, but the characteristic spatial scale of krill and seabirds remained similar (1–4 nautical miles), confirming the hypothesis of covariance in spatial structure. Krill and the seabird species investigated showed similar habitat associations, i.e. the outer shelf and shelf–slope region, showing that the at-sea distributions of seabirds can provide information on the presence/absence of krill patches. The results also underscore the importance of measuring spatial organization as well as relative abundance in promoting better understanding of predator–prey and marine ecosystem dynamics. [ABSTRACT FROM PUBLISHER]

In conjunction with the North Pacific Continuous Plankton Recorder program, we conducted surveys of seabirds from June 2002 to June 2007. Here, we tested the hypotheses of (i) east–west variations in coupled plankton and seabird abundance, and (ii) that surface-feeding and diving seabirds vary in their relationships to primary productivity and mesozooplankton species abundance and diversity. To test these hypotheses, we developed statistical models for 20 species of seabirds and 12 zooplankton taxonomic groups. Seabird density was highly variable between seasons, but was consistently higher in the western than eastern North Pacific. Seabird diversity was greater in the east. Zooplankton abundance did not differ between regions. We found associations at the “bulk” level between seabird density and net primary productivity, but only one association between seabirds and total zooplankton abundance or diversity. However, we found many relationships between seabird species and the abundance of different zooplankton summarized at the genus or family level. Some of these taxonomic relationships reflect direct predator–prey interactions, while others may reflect zooplankton that serve as ecological indicators of other prey, such as micronekton, upon which the birds may feed. Surface or near-surface feeding, mostly piscivorous seabirds, did not differ systematically from diving, mainly planktivorous seabirds in their zooplankton associations. Seabirds apparently respond to zooplankton taxonomic groupings more so than bulk zooplankton characteristics, such as abundance or diversity. Macro-ecological studies of remote marine ecosystems using zooplankton and seabirds as ecological indicators provide a framework for understanding and assessing spatial and temporal variations in these difficult-to-study pelagic environments. [ABSTRACT FROM PUBLISHER]

Chronologies developed from annual growth-increment widths of splitnose rockfish (Sebastes pinniger) and yelloweye rockfish (Sebastes ruberrimus) otoliths were compared with time series of lay date and fledgling success for the common murre (Uria aalge) and Cassin’s auklet (Ptychoramphus aleuticus) in the north-central California Current. All time series were exactly dated and spanned 1972 through 1994. In a principal components analysis, the leading principal component (PC1bio) accounted for 64% of the variance in the data set. By entering the upwelling index, the Northern Oscillation index, sea surface temperatures, and the multivariate ENSO (El Niño Southern Oscillation) index into principal components analysis, a time series of environmental variability PC1env was developed for each month of the year. Over the interval 1972 through 1994, PC1bio most strongly correlated with PC1env for February and, to a lesser extent, January and March. Moreover, when each of the six biological time series was related to the 12 PC1env through stepwise multiple regression, February was always the most significant (p < 0.01). The same was true if upwelling index was substituted for PC1env. As upper-trophic predators, rockfish and seabirds independently corroborate that wintertime ocean conditions are critical for productivity in the California Current ecosystem. Nous avons comparé les chronologies obtenues à partir des largeurs des incréments de croissance annuelle sur les otolithes du sébaste canari (Sebastes pinniger) et du sébaste aux yeux jaunes (Sebastes ruberrimus) et les séries chronologiques des dates de ponte et du succès de l’envol chez le guillemot marmette (Uria aalge) et le starique de Cassin (Ptychoramphus aleuticus) dans le centre nord du courant de Californie. Toutes les séries chronologiques portent des dates précises et couvrent la période de 1972 à 1994. Dans une analyse des composantes principales, la première composante principale (PC1bio) explique 64 % de la variance de l’ensemble de données. Nous avons produit une série chronologique de la variabilité de l’environnement PC1env pour chaque mois de l’année en incluant l’indice de résurgence, l’indice d’oscillation boréale, les températures superficielles de la mer et l’indice multidimensionnel ENSO (oscillation australe d’El Niño) dans l’analyse des composantes principales. Dans l’intervalle de 1972 jusqu’à la fin de 1994, la PC1bio est le plus fortement corrélée avec PC1env en février et, à un degré moindre, en janvier et en mars. De plus, lorsque chacune des six séries chronologiques biologiques est mise en relation avec les 12 PC1env par une régression multiple pas à pas, février est toujours le mois le plus significatif (p < 0,01). Il en est de même si on substitue l’indice de résurgence à PC1env. En tant que prédateurs de haut niveau trophique, les sébastes et les oiseaux marins confirment de manière indépendante que les conditions de l’océan en hiver sont déterminantes pour la productivité de l’écosystème du courant de la Californie. [ABSTRACT FROM AUTHOR]

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We investigated the aggregative response of marine birds and cetaceans to bathymetric features in central California over 4 years, 1996–1997 and 2001–2002. A total of 1700 km2 of ocean habitat was surveyed over six cruises. We considered the distribution of the most abundant marine birds and mammals in relation to bathymetry. We focused our analyses on eight focal taxa: Cassin''s auklet (Ptychoramphus aleuticus), common murre (Uria aalge), sooty shearwater (Puffinus grieus), phalarope species (red, and red-necked: Phalaropus fulicaria, Phalaropus lobatus), Dall''s porpoise (Phocoenoides dalli), Pacific white-sided dolphin (Lagenorhynchus obliquidens), humpback whale (Megaptera novaeangliae), and Risso''s dolphin (Grampus griseus). We evaluated associations of top predators with seven bathymetric indices and three distance measurements to shallow-water topographies. The bathymetric descriptors included (1) median depth, (2) depth coefficient of variation, (3) contour index, and shortest distance to (4) the mainland, (5) the continental shelf-break (200-m isobath), (6) the continental slope (1000-m isobath), and (7) pelagic waters (3000-m isobath). The measurements of shallow water topographies included the shortest distance to: (8) the Cordell Bank seamount, (9) the Farallon Island Archipelago (a breeding colony for auklets and murres), and (10) Monterey Canyon. We documented two instances of spatial autocorrelation (for Cassin''s auklet and common murre) at lags (distances) of 0–3 and 3–9 km, respectively, and accounted for this spatial pattern in analyses of habitat associations. We found similar relationships between cetaceans and bathymetric features at both interannual and weekly time scales. Seabirds revealed both persistent and variable relationships through time. For the resident breeding murres, we detected an interannual trend in habitat use, with these birds shifting their distribution offshore over time. Our study demonstrates that resident and migrant marine birds and cetaceans are associated with bathymetric features and shallow-water topographies, though responses varied across species and time. In spite of this variability, we contend that bathymetric associations of upper trophic-level predators can help delineate sites of elevated trophic transfer. An understanding of marine productivity and predator aggregation patterns is essential to design ecosystem-level conservation plans for protecting marine habitats and species. [Copyright &y& Elsevier]