Douglas F. Bertram

The seasonal cycle revisited: interannual variation and ecosystem consequences

The annual seasonal cycle accounts for much of the total temporal variability of mid- and high-latitude marine ecosystems. Although the general pattern of the seasons repeats each year, climatic variability of the atmosphere and the ocean produce detectable changes in intensity and onset timing. We use a combination of time series data from oceanographic, zooplankton and seabird breeding data to ask if and how these variations in the timing of the spring growing season affect marine populations. For the physical environment, we develop an annual index of spring timing by fitting a non-linear 2-parameter periodic function to the average weekly SST data observed in British Columbia from 1 January to the end of August each year. For each year, the phase parameter describes the timing of seasonal warming (the timing index) and the amplitude parameter describes the magnitude of the temperature increase between the fitted winter minimum and summer maximum. For the zooplankton, which have annual and strongly synchronous cycles of biomass, productivity, and developmental sequence, we use copepodite stage composition to index the timing of the annual maximum. For seabirds, we examine (1975–1999) the timing of hatching, nestling growth performance, and diet for four species of alcids at Triangle Island, British Columbia’s largest seabird colony and the world’s largest population of the planktivorous Cassin’s auklet. Temperature, zooplankton, and seabirds have all shown recent decadal trends toward ‘earlier spring’, but the magnitudes of the timing perturbations have differed from variable to variable and from year to year. Recent (1996–1999) extreme interannual variation in spring timing and April SST helped to facilitate a mechanistic investigation of oceanographic features that affect the reproductive performance of seabirds. Our results demonstrate a significant negative relationship between the annual spring timing index (and April mean SST) and nestling growth rates for both Cassin’s auklet and rhinoceros auklet. Nestling growth rates were significantly lower in early, warm years. We demonstrate that low growth rates of Cassin’s auklet occurred when copepod

EFFECTS OF MATERNAL AND LARVAL NUTRITION ON GROWTH AND FORM OF PLANKTOTROPHIC LARVAE

Maternal nutritional stress lowers the organic content of eggs and slows the initial growth of larvae of sea urchins and bivalves. Also, larval nutritional stress changes the form and developmental sequence of larvae as an adjustment to scarce food. If effects of nutrient supplies in eggs were like those of nutrient supplies in planktonic food, then maternal nutrition would affect larval form and developmental plasticity in the same way as larval nutrition. We used natural variation in maternal habitat to test this hypothesis, using laboratory growth experiments. In the sea urchin Strongylocentrotus droebachiensis, mothers from greater depth (100 m) had smaller ovaries and smaller eggs than mothers from shallower depth (<6 m), which indicated poorer maternal nutrition at depth. Effects of maternal habitat, gonad size, and egg size on larval growth rate were significant but small compared to the effect of abundance of larval food. The growth of larvae was little affected by differences in maternal habitat that had a large effect on fecundity and some effect on egg size. There were no effects on larval body or juvenile rudiment that resembled the developmental plasticity in response to larval food. Food-limited mothers did not produce larvae with larger larval feeding apparatus or retarded development of juvenile rudiments. Uncoupled morphogenetic effects of endogenous and exogenous nutrients should be advantageous where benthic and planktonic food supplies vary independently. Finely tuned responses to stimuli may restrict the evolutionary consequences of developmental plasticity. Because maternal nutrition did not affect form of the larvae, larval form can be used as an index of planktonic conditions affecting feeding larvae.

Changes in Canadian seabird populations and ecology since 1970 in relation to changes in oceanography and food webs.

Systematic monitoring of seabird populations in Canada has been ongoing since the 1920s and the monitoring of diets and other biological indicators of ecosystem change started in the 1970s. Long-te...

SURVIVAL RATES OF CASSIN'S AND RHINOCEROS AUKLETS AT TRIANGLE ISLAND, BRITISH COLUMBIA

Abstract We estimated survival of Cassins Auklet (Ptychoramphus aleuticus) and Rhinoceros Auklet (Cerorhinca monocerata) from recapture rates during 1994–1997. For both species, a two “age”-class model provided the best fit. Estimates of local adult survival were significantly lower for Cassins Auklet (0.672 ± 0.047) than for Rhinoceros Auklet (0.829 ± 0.095). Our estimate of survival appears lower than that required for the maintenance of a stable population of Cassins Auklets. The available information indicates that a low survival rate and a declining population at Triangle Island are plausible, particularly given the recent large scale oceanographic changes which have occurred in the North Pacific Ocean. Nevertheless, additional mark-recapture data and indexes of population size are required to rigorously demonstrate population declines at the worlds largest Cassins Auklet colony.

Plastic ingestion in marine-associated bird species from the eastern North Pacific

In addition to monitoring trends in plastic pollution, multi-species surveys are needed to fully understand the pervasiveness of plastic ingestion. We examined the stomach contents of 20 bird species collected from the coastal waters of the eastern North Pacific, a region known to have high levels of plastic pollution. We observed no evidence of plastic ingestion in Rhinoceros Auklet, Marbled Murrelet, Ancient Murrelet or Pigeon Guillemot, and low levels in Common Murre (2.7% incidence rate). Small sample sizes limit our ability to draw conclusions about population level trends for the remaining fifteen species, though evidence of plastic ingestion was found in Glaucous-Winged Gull and Sooty Shearwater. Documenting levels of plastic ingestion in a wide array of species is necessary to gain a comprehensive understanding about the impacts of plastic pollution. We propose that those working with bird carcasses follow standard protocols to assess the levels of plastic ingestion whenever possible.

Citizen Science Reveals an Extensive Shift in the Winter Distribution of Migratory Western Grebes

Marine waterbirds have shown variable trends in abundance over the past four decades with some species displaying steep declines along the Pacific coast from British Columbia through California. One of the most dramatic changes has been that of western grebes (Aechmophorus occidentalis) in the Salish Sea. This region was a former core of the species wintering distribution but they have become increasingly rare prompting calls for conservation action. A more thorough understanding of this situation requires the analysis of trends at broader geographic scales as well as a consideration of mechanisms that might have led to a change in abundance. We used hierarchical modeling with a Bayesian framework applied to 36 years of Audubon Christmas Bird Count data to assess continent-wide and regional population trends in western and Clark’s grebes (A. clarkii) from 1975 to 2010. Our results show that the North American wintering population of Aechmophorus grebes decreased by ∼52% after 1975, but also that western grebes displayed strongly opposing regional patterns. Abundance decreased by about 95% over 36 years in the Salish Sea but increased by over 300% along coastal California. As a result, the mean centre of the species distribution shifted south by an estimated 895 km between 1980 and 2010. Mechanisms underlying this shift require further study but we hypothesize that it may be related to a change in the abundance and availability of their forage fish prey base. Since the mid-1980s, the Pacific sardine stock off the California coast increased from a few thousand metric tonnes to over two million. At the same time both the abundance and availability of Pacific herring declined in the Salish Sea. Studies are needed to examine this hypothesis further and additional consideration should be directed at other changes in the marine environment that may have contributed to a range shift.

Estimation of Coast-Wide Population Trends of Marbled Murrelets in Canada Using a Bayesian Hierarchical Model

Species at risk with secretive breeding behaviours, low densities, and wide geographic range pose a significant challenge to conservation actions because population trends are difficult to detect. Such is the case with the Marbled Murrelet (Brachyramphus marmoratus), a seabird listed as ‘Threatened’ by the Species at Risk Act in Canada largely due to the loss of its old growth forest nesting habitat. We report the first estimates of population trend of Marbled Murrelets in Canada derived from a monitoring program that uses marine radar to detect birds as they enter forest watersheds during 923 dawn surveys at 58 radar monitoring stations within the six Marbled Murrelet Conservation Regions on coastal British Columbia, Canada, 1996–2013. Temporal trends in radar counts were analyzed with a hierarchical Bayesian multivariate modeling approach that controlled for variation in tilt of the radar unit and day of year, included year-specific deviations from the overall trend (‘year effects’), and allowed for trends to be estimated at three spatial scales. A negative overall trend of -1.6%/yr (95% credibility interval: -3.2%, 0.01%) indicated moderate evidence for a coast-wide decline, although trends varied strongly among the six conservation regions. Negative annual trends were detected in East Vancouver Island (-9%/yr) and South Mainland Coast (-3%/yr) Conservation Regions. Over a quarter of the year effects were significantly different from zero, and the estimated standard deviation in common-shared year effects between sites within each region was about 50% per year. This large common-shared interannual variation in counts may have been caused by regional movements of birds related to changes in marine conditions that affect the availability of prey.

Seasonal variability in vulnerability for Cassin's auklets (Ptychoramphus aleuticus) exposed to microplastic pollution in the Canadian Pacific region

Marine plastic pollution is an emerging global conservation challenge, potentially impacting organisms at all trophic levels. However, currently it is unclear to what extent plastic pollution is impacting marine organisms at the population, species or multispecies level. In this study, we explore seasonal exposure (i.e., vulnerability) of Cassins Auklet (Ptychoramphus aleuticus) to plastic pollution with exposure models during boreal summer and winter seasons. Based on these models, we infer exposure at the population level for this species, in the Canadian Pacific region where approximately 75% of the global population of this species breeds. The models quantify plastic exposure by determining seasonal core foraging areas and plastic concentrations found in those same areas. Core foraging areas were determined using a Generalized Additive Model based on at-sea observation data (collected year round: 1990-2010) and 50% Home Range Kernels based on aerial telemetry data (May and June 1999-2001). Plastic concentrations within these core areas were interpolated based on seawater microplastic concentrations from the summer of 2012. We found that during the boreal summer, Cassins Auklets were exposed to relatively low concentrations of plastics. During the winter, auklet distribution shifted towards the coast where plastic concentrations are considerably higher. Model derived seasonal variability in exposure was consistent with necropsy results from bird carcasses recovered during the winter of 2014, and from a multiyear study on chick provisioning during the summer. Local oceanography likely plays a role in determining seasonal shifts in both marine bird as well microplastic concentrations, and hence exposure. As well, individual sensitivity (i.e., dose-dependent effect) may vary with annual cycles. Currently, research is focusing on determining how sensitive individual birds are to microplastic concentrations, and our models will help translate sensitivity found at the individual level to potential impacts at population or species level.