Please note the brief summary below each title.  Linked PDF's of full text publications coming soon! 

Prey availability/abundance or diet composition: 

Oceanic factors influencing the distribution of young rockfish (Sebastes) in central California: a predator's perspective.  Ainley, D.G., W.J. Sydeman, R.H. Parrish, and W. Lenarz.  1993.  California Cooperative Oceanic Fisheries Investigation Report 34:133-139.
Used the diet of a seabird, the common murre to assess the abundance of juvenile rockfish (Sebastes spp., mostly S. jordani) in the Gulf of the Farallones, California, 1973-90. On the basis of an exploratory analysis of the data and of several oceanographic factors, we hypothesize that availability of fish in the study area during June-July was a function of advection during the January-February period of rockfish parturition. When upwelling or downwelling was persistent in winter, there were few juveniles in late spring, but when upwelling had been mild or pulsed, juveniles were abundant. Rockfish availability also decreased when turbulence, sea level, and sea-surface temperature were high during winter. Stepwise multiple regression analyses indicated that, among these variables, advective transport significantly affects the distribution of juvenile rockfish.

Ocean climate, euphausiids and auklet nesting: interannual trends and variability in phenology, diet and growth.  Abraham, C.L. and W.J. Sydeman.  2004.  Marine Ecology Progress Series 274:235-250.
Examined interrelationships between mean seasonal oceanographic conditions and prey availability and the timing of breeding, nestling diet, growth and productivity of Cassin’s auklet in the central California Current System.  Breeding phenology and diet composition were positively correlated with seasonal sea-surface temperature and negatively correlated with seasonal upwelling values. As demonstrated by the auklet diet, euphausiids responded to changes in ocean climate on multiple temporal scales. In most years, auklets responded adaptively to variation in oceanographic conditions and prey availability by modifying timing of breeding. However, in years when ocean conditions deteriorated after the initiation of breeding, prey availability was severely reduced beyond the auklet’s adaptive response, resulting in diminished nestling growth and productivity.

Rockfish response to low-frequency ocean climate change as revealed by the diet of a seabird over multiple temporal scales.  Miller, A. and W.J. Sydeman.  2004.  Marine Ecology Progress Series 281:207-216.
Examined the effects of ocean climate variability on juvenile shortbelly rockfish from 1975–2002 in the central California Current by examining the diet of Common Murres on multiple temporal scales. Responses to higher-frequency climate change (interannual El Niño and La Niña events) were strong, with declines in rockfish take in warmwater years. Responses to low-frequency climate events (e.g. shifts of the Pacific Decadal Oscillation, PDO) were less obvious. Inter-annual patterns showed no response to the 1976–1977 regime shift to warmer PDO conditions; instead, rockfish use declined beginning in 1989, corresponding to another suggested regime change, then rebounded shortly after the hypothesized return to a cool phase of the PDO in the late 1990s. Intra-annual diet patterns, however, revealed changes in rockfish use well before 1989. These signals indicate that declines may have corresponded to the 1976–1977 regime shift but were lagged, possibly due to the long lifespan and intermittent recruitment of rockfish. This interpretation is supported by local upwelling patterns that show a lagged correlation between upwelling and juvenile rockfish abundance in the marine bird diet. 

Prey switching by Cassin’s auklet Ptychoramphus aleuticus reveals seasonal climate – related cycles of Euphausia pacifica and Thysanoessa spinifera.  Abraham, C.L. and W.J. Sydeman.  2006.  Marine Ecology Progress Series 313:271-283.
Tested the hypothesis that seasonal patterns of prey use by auklets correspond to within season variation in upwelling and sea surface temperature (SST). We found that the proportion of E. pacifica adults in auklet diet decreased over the chick-rearing period, and increased with increasing UI and decreasing SST; T. spinifera in auklet diet showed an increase over the chick-rearing period, but no relationships were detected with UI or SST. Seasonal changes in the ingestion of euphausiids by auklets appeared to be affected by ocean climate variability; however, prey-selection via a shift in foraging location or competition with other marine predators are alternative valid explanations. 

Planktivorous auklet Ptychoramphus aleuticus responses to ocean climate, 2005: Unusual atmospheric blocking?  Sydeman, W.J., R. W. Bradley, P. Warzybok, C. L. Abraham, J. Jahncke, K. D. Hyrenbach, V. Kousky, J. M. Hipfner, and M. D. Ohman. 2006.  Geophysical Research Letter 33: L22S09, doi:10.1029/2006GL026736.
In spring-summer 2005, anomalous atmospheric-oceanographic coupling caused unprecedented reproductive failures and redistribution of Cassin's Auklet in both central California and southern British Columbia. At SE Farallon Island, CA, the birds abandoned the breeding colony en masse between 10–20 May, a unique behavioral response; for the first time in 35 years, productivity was zero. At Triangle Island, B.C., only 8% of the nesting pairs were successful, the worst year on record. Prey (euphausiid) biomass in the Gulf of the Farallones was also reduced. Results may be explained in part by unusual atmospheric blocking in the Gulf of Alaska in May, which caused the jet stream to shift southwards resulting in poor upwelling-favorable winds and anomalously warm SST. This study demonstrates the deleterious consequences of this climate event for a top marine predator in the central-northern CCS.

Spatio-temporal variability in prey harvest and reproductive ecology of a piscivorous seabird, Cerorhinca monocerata, in an upwelling system.  Thayer, J.A. and W.J. Sydeman.  2007.  Marine Ecology Progress Series 329:253-265.
Tested the hypothesis that upwelling influences forage fish availability and response of a seabird, but that the effects differ spatially within a region. We examined the availability of multiple forage species and the reproductive ecology of rhinoceros auklets relative to ocean climate over 11 yr (1993 to 2003) for 2 colonies off central California: one near the shelf break and another at the coastline. The upwelling index that we used increased through time, while sea surface temperature (SST) generally decreased. Abundance indices of juvenile rockfish fluctuated, while northern anchovy decreased. Diet of the auklet reflected availability of prey in the environment. Auklet reproduction was affected by both marine climate and prey availability. Seabird breeding as well as harvest of anchovy, rockfish and Pacific saury were linked to offspring growth, but growth was not necessarily related to offspring survival. Offspring survival was inversely correlated with SST and positively correlated with mass of prey rather than diet composition. Auklet reproduction was more variable offshore than inshore, possibly reflecting variation in the upwelling cells affecting prey availability within the foraging range of birds from each colony.

Relative contribution of euphausiid prey and timing of breeding to auklet growth: within-season effects.  Abraham, C.L.  2008.  Journal of Avian Biology doi: 10.1111/j.2008.0908-8857.04240.x
Examined the effects of seasonal variation in nestling diet composition and meal mass, and timing of breeding and breeding attempt number (only/first or second breeding attempt) on the growth rate of individual nestlings on Southeast Farallon Island, California. In multivariate models, there were significant and positive effects of the mass proportions of E. pacifica and T. spinifera in the diet, meal mass and breeding attempt number on nestling growth, while the effect of hatching date on growth was negative. The relative influence of T. spinifera on growth was stronger than that of E. pacifica, the effects of hatching date on growth were likely dependent on the effects of breeding attempt, and breeding attempt exerted the strongest effect on nestling growth of all parameters examined. These suggest that the seasonal switch in prey use is advantageous.  Results illustrate the importance of adequate availability of both prey species to auklets in the Gulf of the Farallones. This study represents a unique approach in the investigation of linkages between individual nestling growth rate and diet and breeding phenology parameters by focusing on a fine temporal scale.

Forage fish in the North Pacific as revealed by diet of a piscivorous seabird: synchrony in responses and relationships with SST.  Canadian J. Fisheries Aquatic Sciences. Thayer, J.A., W.J. Sydeman, D.F. Bertram, M.A. Hipfner, L. Slater, S.A. Hatch, and Y. Watanuki.  In press.
Investigated whether take of forage fishes by rhinoceros auklet was related to local marine conditions, throughout the Pacific rim, as indexed by SST. Take of forage fish varied in response to inter-annual 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 inter-annual 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 inter-annual 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.

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Reproductive parameters, survival and populations:
 
Upper  trophic level predators indicate interannual negative and positive anomalies in the California Current food web.  Ainley, D.G., W.J. Sydeman, and J. Norton.  1995.  Marine Ecology Progress Series 118:69-79.
Used a 21 yr time series of productivity for 6 seabird species at the Farallon Islands to assess proximate and remote factors leading to variation in the food supplies available to these predators. A serious lack of food was indicated by negative reproductive anomalies during all warm-water events, some of which were classified as tropical El Niño and others which were not. Equally spectacular but positive anomalies occurred during years adjacent to the negative ones, particularly evident among the most sensitive species. Much of the annual variation, positive or negative, in seabird reproductive success was explained by variation in the Southern Oscillation and/or the Aleutian low pressure system, both of which affect sea-surface temperature and thermocline depth off California. Results indicate that perturbations in the marine food web of the California eastern boundary current system, as indicated by the availability of food to seabirds, are much more complex than is generally appreciated, and are not confined only to negative excursions from normalcy. ENSO is important, but other global atmosphere-ocean phenomena affect the California Current just as dramatically.

Climate change, reproductive performance, and diet composition of seabirds in the southern California Current ecosystem, 1969-1997.  Sydeman, W.J., M.M. Hester, P. Martin, F. Gress, and J. Buffa.  2001.  Progress in Oceanography 49: 309-329.
Studied the effects of low-frequency climate change on the reproductive performance of 11 species of marine bird in the southern California Current system, 1969–1997. While productivity for some species (Brown Pelican, Double-crested Cormorant, Brandt’s Cormorant) increased, others demonstrated curvilinear patterns of change (Ashy Storm-petrel, Pelagic Cormorant), while all other species (Western Gull, Pigeon Guillemot, Xantus’s Murrelet, Common Murre, Cassin’s Auklet, Rhinoceros Auklet) showed diminishing productivity through time.  Changes in diet composition and in the birds’ abilities to provision young and maintain chick survival during May–July each year appeared most closely related to overall changes in productivity. The decline in productivity and changes in diet composition do not appear directly related to the polarity reversal of the Pacific Decadal Oscillation in 1976/1977; instead, they indicate substantial change in the late 1980s, suggesting another regime-shift at that time.

Xantus’ Murrelet breeding relative to prey abundance and oceanographic conditions in the Southern California Bight.  Roth, J.E., W.J. Sydeman, and P. Martin.  2005.  Marine Ornithology 33: 115-121.
Investigated the effects of temporal variability in prey abundance and oceanographic conditions on Xantus's Murrelet breeding parameters on Santa Barbara Island, California from 1983 - 2001.  Average clutch initiation date was earlier in years with abundant mesozooplankton, stronger upwelling, and lower sea surface temperature. Average clutch size was higher in years with abundant larval saury and mesozooplankton and lower sea surface temperature.
 

Climate and demography of the planktivorous Cassin’s auklet off northern California: implications for population change.  Lee, D.E., N. Nur, and W.J. Sydeman.  2007.  Journal of Animal Ecology 76: 337-347.
Showed how annual variation in ocean climate synchronously affected multiple demographic parameters including survival, breeding propensity, breeding success, and recruitment for Farallon Island Cassin’s auklets.  When demographic parameters positively covary, population fluctuations can be much larger than when parameters vary independently.  This study demonstrates how climate variability has influenced key demographic processes for this diminished marine bird population.

Ecosystem responses to short-term climate variability in the Gulf of the Farallones.  Jahncke, J., B.L. Saenz, C. Rintoul, C.L. Abraham, R.W. Bradley, and W.J. Sydeman.  2008.  Progress in Oceanography XX: XX-XX.
Conducted an integrated study from physics to upper trophic-level predators in the Gulf of the Farallones, California. We hypothesized that decreased zooplankton abundance for upper trophic-level predators in the Gulf of the Farallones during 2004 and 2005 was a response to reduced upwelling-favorable winds and primary production. Based on their trophic ecology, we hypothesized that planktivorous auklets and omnivorous murres will show differential responses to upwelling variability. We examined these hypotheses by analyzing time series on oceanographic variables associated to upwelling and the biological responses at low, mid and high trophic levels. We found that reduced upwelling-favorable wind was correlated with anomalously high SST and low chlorophyll-a concentration from July 2004 to August 2005. During 2005, low chlorophyll concentrations were related to reduced krill abundance in the upper water column and decreased seabird abundance in the vicinity of the breeding colony in the study area. Decreased krill abundance was associated with late timing of nesting and reduced breeding success, with auklets showing a more pronounced response. This study shows how short-term climate variability can affect primary through tertiary productivity, and supports an interpretation of “bottom-up” control of ecosystem dynamics.
 

Adjusting to extreme environments: changing phenology and fluctuating selection in a colonial seabird. Reed, T.E., P. Warzybok, A.J. Wilson, R.W. Bradley, S. Wanless and W.J. Sydeman.  Submitted to Ecology
Examines the individual variation in response to changing environmental conditions for Common Murres at SEFI. The results demonstrated that female murres adjusted breeding phenology (measured as lay date of first egg) in a non-linear fashion to changes in environmental conditions but that there was significant between individual variation in plasticity (different individual response curves). Selection generally favored earlier laying in "average" environments (directional selection), stabilizing selection in "good" environments, and no selection in "poor" environments.  COMU breeding at SEFI experienced greater environmental variation in the CCS system, a stronger correlation between phenology and environment, and greater individual variation in plasticity when compared to COMU breeding in the North Sea. 

Untangling the relationships between climate, prey and top predators in an ocean ecosystem.  Wells, B.K., J.C. Field, J.A. Thayer, C.B. Grimes, S.J. Bograd, W.J. Sydeman, F.B. Schwing, and R. Hewitt.  In press.  Marine Ecology Progress Series.
Used path analysis and partial least squares regression to visualize and quantify links between biological and physical components in the California Current ecosystem and to predict reproductive success at three trophic levels. We examined the applicability of this approach using a hierarchical pattern of environmental indices and relationships previously described in the literature, and quantitative measures of zooplankton, fish, and seabird productivity. We show that each trophic level and community production can be described using environmental and biological data in a manner that provides a comprehensive evaluation of physical and biological connectivity and mechanisms. Importantly, our approach to modeling an ecosystem represents a practical middle ground between simple correlative methods typically employed and a perhaps unattainable complete mechanistic understanding of all physical and biological mechanisms regulating variability in reproductive success.

Population consequences of oceanographic variability across the range of a top predator, Cassin’s auklet Ptychoramphus aleuticus.  Wolf, S., W.J. Sydeman, C.L. Abraham, J.M. Hipfner, B. Tershy, and D. Croll.  In press.   Ecology.
Investigated the relationships between ocean climate conditions and the breeding ecology of the Cassin’s auklet over nearly 2,500 km of its breeding range in the CCS.  Local auklet breeding environments ranged from seasonally variable, high-productivity environments in the northern and central CCS to aseasonal, low-productivity environments to the south. Auklet timing of breeding for the southern population was highly asynchronous within and across years, did not covary with northern populations, and was not significantly related to local oceanographic conditions in contrast to northern populations. Annual breeding success covaried more strongly across populations and was consistently related to local oceanographic conditions, although total chick production differed among populations. We suggest that auklet timing of breeding in northern and central populations is tied to seasonal oceanographic cues that signal peaks in prey availability unlike in the southern population that experiences no distinct cues.

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Distribution and abundance:
 
Ocean warming and long-term change in pelagic bird abundance within the California Current system.  Veit, R.R., P Pyle and J.A. McGowan.  1996.  Marine Ecology Progress Series 139:11-18
Report that seabird abundance within the California Current system has declined by 40% over the period 1987 to 1994. This decline has accompanied a concurrent, long-term increase in sea surface temperature. The decline in overall bird abundance is largely but not entirely, a consequence of the 90% decline of sooty shearwaters, the numerically dominant species of the California Current.

Apex marine predator declines ninety percent in association with changing oceanic climate. Veit, R. R., J. A. McGowan, D. G. Ainley, T. R. Wahls, and P. Pyle. 1997.  Global Change Biology 3: 23-28.
Three time series of pelagic bird abundance collected in disparate portions of the California Current reveal a 90% decline in Sooty Shearwater abundance between 1987 and 1994. This decline is negatively correlated with a concurrent rise in sea-surface temperatures; Sooty Shearwaters have declined while sea temperatures have risen. There is a nine-month lag in the response by shearwaters to changing temperatures.
The geographical scale of our study demonstrates that the decline of Sooty Shearwaters is not a localized phenomenon, nor can it be ascribed to a short-term distributional shift.
 

Spring-time distributions of migratory birds in the southern California Current: oceanic eddy associations and coastal habitat hotspots over 17 years.  Yen, P.P.W., W.J. Sydeman, S.J. Bograd, K.D. Hyrenbach, and.  2006.  Deep Sea Research II 53:399-418.
Used a 17-year time series of shipboard observations to address the hypothesis that marine birds associate with persistent hydrographic features in the southern (CCS). We explored associations (presence/absence and density relationships) of marine birds with mesoscale features (eddies, current jet) and metrics of primary productivity (chlorophyll a and nitrate concentrations). Mesoscale eddies were consistently identified in the study region, but were spatially and temporally variable. Although there were species-specific differences, of the hydrographic habitats considered, the upwelling region of Point Conception appears to be an important ‘‘hotspot’’ of sustained primary production and marine bird concentrations. Point Conception and other similar coastal locations (upwelling cells) may warrant protection as key foraging grounds for seabirds.

Habitat or location: Why Brown Pelicans use different roost selection strategies during different times of year. Robinette, DR, J Howar, and N Collier. In Review.  Studies in Avian Biology XX: XX-XX
Describes seasonal differences in roost selection by endangered Brown Pelicans (Pelecanus occidentalis californicus) in central California.  As local sea surface temperatures increase and anchovies move nearshore in summer and early fall to spawn, pelicans spread out over many locations of various habitat types and foraging flocks are more common.  Roost selection at this point appears to be driven by proximity to local prey.  As sea surface temperatures subside and nearshore anchovy availability decreases in late fall and winter, pelicans shift roosting strategies and mainly select elevated habitats that provide shelter against adverse environmental conditions.


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