William J. Sydeman

Climate change, reproductive performance and diet composition of marine birds in the southern California Current system, 1969-1997

We 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. Reproductive performance of Brown Pelican (Pelecanus occidentalis) and Double-crested Cormorant (Phalacrocrax auritus) in southern California demonstrated an increase in the 1970s and early 1980s, attributable to recovery from organochlorine contamination (primarily DDE). Brandt’s Cormorant (Phalacrocorax penicillatus) in central California was the only species to demonstrate a secular increase in performance through time, a pattern that remains unexplained. Ashy Storm-petrel (Oceanodroma homochroa ) and Pelagic Cormorant (Phalacrocorax pelagicus) demonstrated curvilinear patterns of change, with decreasing reproductive performance in the past decade. All other species including Western Gull (Larus occidentalis), Pigeon Guillemot (Cepphus columba), Xantus’s Murrelet (Synthiloboramphus hypoleucus ), Common Murre (Uria aalge), Cassin’s Auklet (Ptychoramphus aleuticus) and Rhinoceros Auklet (Cerorhinca monocerata ) showed diminishing reproductive performance through time. Patterns of change for the murre and auklets were not significant, presumably because of a lack of reproductive variation for these species, which display a conservative breeding effort (i.e. single-egg clutches). Changes in the birds’ abilities to provision young and maintain chick survival during May–July each year appeared most closely related to overall changes in reproductive performance. Dietary change indicated a decline in use of juvenile rockfish ( Sebastes spp.) by marine birds in central California. There was also significant interannual variability in consumption of juvenile rockfish and the euphausiid Thysanoessa spinifera. Patterns of change in marine bird reproductive performance were generally concordant between southern and central California after considering the period of recovery for Brown Pelican and Double-crested Cormorant. The decline in reproductive performance and changes in diet composition do not appear directly related to the polarity reversal of the Pacific Decadal Oscillation

Age‐Specific Weaning Success of Northern Elephant Seals in Relation to Previous Breeding Experience

We studied the effect of age and previous breeding experience on the probability of successful reproduction in female northern elephant seals (Mirounga angustirostris). Reproductive data, collected over a 12—yr period, were analyzed by multiple logistic regression to describe the functional relationships among the variables. We also examined the relationships among age, experience, date of breeding, and reproductive success to determine if differences in timing explain age—specific productivity. Finally, we investigated the relationship among age, experience, and maternal behavior to determine if correlates of reproductive effort could be related to age— and experience—specific patterns of reproductive success. Reproductive success increased between the maternal ages of 3 and 7 yr and then levelled off, demonstrating an asymptotic relationship. However, the relationship between reproductive success and age, after statistically controlling for previous experience, showed instead that success increased linearly throughout an animals lifetime. In contrast, after statistically controlling for age, reproductive success was related to experience in a parabolic fashion; success increased with experience for the first few breeding attempts, but declined later in an animals reproductive lifetime. The effects of experience depended on age: among young animals experience was apparently beneficial, but among old animals greater experience was deleterious. These results suggest experience—related senescence. Timing of breeding was related to experience, rather than age, in a curvilinear fashion; arrival and parturition dates were later for inexperienced and very experienced females, and were earliest for moderately experienced animals. Young animals that gave birth later in the season experienced reduced reproductive success; we observed no such decline in older animals. Thus, among young females, arriving and giving birth earlier each year was adaptive. Aggressiveness and dominance increased with age and experience, but we were unable to separate the effects of age and experience. We contend that the experience—related drop in reproductive success reflects the cost of reproduction. Breeding at a young age and/or continuously appears to result in lower reproductive success later in life. Furthermore, curvature in age—specific reproductive success can be explained by experience—related senescence. This result has general applicability, suggesting that age—related senescence instead may be due to reproductive burn—out. These results indicate that previous breeding experience and differences in individual quality do not explain the pattern of increasing reproductive success with age in northern elephant seals, and provide indirect support for the hypothesis that animals increase reproductive effort as they age to offset a concomitant decrease in residual reproductive value.

Range-wide reproductive consequences of ocean climate variability for the seabird Cassin's Auklet

We examine how ocean climate variability influences the reproductive phenology and demography of the seabird Cassins Auklet (Ptychoramphus aleuticus) across approximately 2500 km of its breeding range in the oceanographically dynamic California Current System along the west coast of North America. Specifically, we determine the extent to which ocean climate conditions and Cassins Auklet timing of breeding and breeding success covary across populations in British Columbia, central California, and northern Mexico over six years (2000-2005) and test whether auklet timing of breeding and breeding success are similarly related to local and large-scale ocean climate indices across populations. Local ocean foraging environments ranged from seasonally variable, high-productivity environments in the north to aseasonal, low-productivity environments to the south, but covaried similarly due to the synchronizing effects of large-scale climate processes. Auklet timing of breeding in the southern population did not covary with populations to the north and was not significantly related to local oceanographic conditions, in contrast to northern populations, where timing of breeding appears to be influenced by oceanographic cues that signal peaks in prey availability. Annual breeding success covaried similarly across populations and was consistently related to local ocean climate conditions across this system. Overall, local ocean climate indices, particularly sea surface height, better explained timing of breeding and breeding success than a large-scale climate index by better representing heterogeneity in physical processes important to auklets and their prey. The significant, consistent relationships we detected between Cassins Auklet breeding success and ocean climate conditions across widely spaced populations indicate that Cassins Auklets are susceptible to climate change across the California Current System, especially by the strengthening of climate processes that synchronize oceanographic conditions. Auklet populations in the northern and central regions of this ecosystem may be more sensitive to changes in the timing and variability of ocean climate conditions since they appear to time breeding to take advantage of seasonal productivity peaks.

Survival, breeding probability and reproductive success in relation to population dynamics of Brandt's Cormorants Phalacrocorax penicillatus

The size of the breeding population of Brandts Cormorants Phalacrocorax penicillatus on Southeast Farallon Island, off the coast of central California, USA, shows large annual fluctuations and has declined by 50% since the 1970s. We investigated patterns of variation in adult survival, breeding probability, resighting probability, juvenile survival and reproductive success, to determine the extent to which variation in demographic processes reflected variation in environmental conditions (e.g. food availability) versus densitydependence, using observations of breeders and non-breeders from 1976 to 1995. Resighting and breeding probabilities varied significantly among years, and both were positively correlated with an annual index of prey availability — the abundance of juvenile rockfish. Adult survival between years was significantly correlated with changes in juvenile rockfish abundance and differed between sexes (0.77, males; 0.71, females). Female, but not male, survival appeared age-specific: older f...

Trace metals in seabirds, Steller sea lion, and forage fish and zooplankton from central California

We studied concentrations of the trace metals, aluminum (Al), chromium (Cr), iron (Fe), copper (Cu), zinc (Zn), arsenic (As), selenium (Se), silver (Ag), cadmium (Cd), and mercury (Hg), in krill (Euphausia pacifica and Thysanoessa spinifera), two species of fish (short-bellied rockfish Sebastes jordani and northern anchovy Engraulis mordax), four species of marine bird (Common Murre Uria aalge, Brandts Cormorant Phalacrocorax penicillatus, Rhinoceros Auklet Cerorhinca monocerata, and Pigeon Guillemot Cepphus columba) and a pinniped, (Steller sea lion Eumetopias jubatus) from the Gulf of the Farallones, central California in 1993. Geometric mean levels of some trace elements in Steller sea lions were elevated (Cu, 91.0 mg/kg dry weight; Hg, 19.0 mg/kg; Se, 4.1 mg/kg). Levels of Hg in Pigeon Guillemot (3.5 mg/kg) were also elevated. Mercury increased whereas Pb decreased with increasing trophic level in the Gulf of the Farallones food web. Selenium levels were highest for krill and sea lions, and intermediate for fish and birds occupying mid trophic levels. Results indicate little to relatively high trace metal contamination of upper trophic level marine wildlife in the central California coastal marine ecosystem.

Forage fish of the Pacific Rim as revealed by diet of a piscivorous seabird: synchrony and relationships with sea surface temperature

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 mono- cerata), 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. Resume´ : Nous testons lhypothese qui veut quil y ait des changements interannuels synchrones dans les dynamiques des poissons fourrage autour de la bordure du Pacifique Nord. Cest pourquoi nous avons echantillonneles peuplements de poissons fourrage alaide dun oiseau marin predateur, le macareux rhinoceros (Cerorhinca monocerata), asix sites detude cotiers du Japon ala Californie. Nous avons verifiesi les captures de poissons fourrage sont reliees aux conditions

Demographic Processes and Population Dynamic Models of Seabirds

Seabirds, like many taxa of birds in the 19905, face numerous conservation challenges. The primary challenge is to maintain or restore populations in the face of destruction of habitat, introduction of non-native predators, human disturbance (including hunting and collecting),.oil spills, and the like. The low reproductive rates and deferred maturity of seabirds exacerbate the problems (Buckley and Downer, 1992; Croxall and Rothery, 1991), which makes recovery from catastrophic events difficult or even impossible. Seen in this light, nearly all seabird populations can be categorized as “vulnerable,” if not “threatened” or “endangered”; hardly any can be categorized as “not vulnerable” (cf. Mace and Lande, 1991). Over the past decade a multitude of disturbances has affected seabirds, including several major oil spills, of which the Exxon Valdez oil spill is surely the most prominent (Rice et al., 1996; Piatt et al.,1990). Events such as these oil spills have focused the attention of the public, government agencies, and the scientific community on the doubled-headed question: What are the long-term effects of such disturbance, and can seabirds recover from the assault? Interest in answering questions like these is heightened by concern about major oceanographic perturbations, including El Nino events, and activities of commercial fisheries, which could very well undermine the prey base for many seabirds.