Incorporating Uncertainty into Management Models for Marine Mammals

Abstract: Good management models and good models for understanding biology differ in basic philosophy. Management models must facilitate management decisions despite large amounts of uncertainty about the managed populations. Such models must be based on parameters that can be estimated readily, must explicitly account for uncertainty, and should be simple to understand and implement. In contrast, biological models are designed to elucidate the workings of biology and should not be constrained by management concerns. We illustrate the need to incorporate uncertainty in management models by reviewing the inadequacy of using standard biological models to manage marine mammals in the United States. Past management was based on a simple model that, although it may have represented population dynamics adequately, failed as a management tool because the parameter that triggered management action was extremely difficult to estimate for the majority of populations. Uncertainty in parameter estimation resulted in few conservation actions. We describe a recently adopted management scheme that incorporates uncertainty and its resulting implementation. The approach used in this simple management scheme, which was tested by using simulation models, incorporates uncertainty and mandates monitoring abundance and human-caused mortality. Although the entire scheme may be suitable for application to some terrestrial and marine problems, two features are broadly applicable: the incorporation of uncertainty through simulations of management and the use of quantitative management criteria to translate verbal objectives into levels of acceptable risk.     

Analysis of fatty acids and fatty alcohols reveals seasonal and sex-specific changes in the diets of seabirds

A key challenge in ecology is to find ways to obtain complete and accurate information about the diets of animals. To respond to this challenge in seabirds, traditional methods (usually stomach content analysis or observations of prey at nests) have been supplemented with indirect methods or molecular trophic markers. These techniques have the potential to extend the period of investigation outside the few short months of breeding and avoid biases. Here, we use an analysis of fatty acids (FAs) and fatty alcohols (FALs) from blood, adipose tissue and stomach oil to investigate how the diets of male and female common guillemots (Uria aalge), black-legged kittiwakes (Rissa tridactyla) and northern fulmars (Fulmarus glacialis) differed through the sampling period (prelaying and breeding season) and by sex. Diets of both sexes of all three species generally varied across the season, but sex differences were apparent only in fulmars during prelaying. Our study shows that FA/FAL analysis can provide significant insights into diets of seabirds, in particular periods of the annual cycle which are not readily studied using traditional methods.     

Pre-migratory life history stages of juvenile Arctic birds: costs, constraints, and trade-offs

Many young birds on the Arctic tundra are confronted by a challenging task: they must molt their feathers and accumulate fat stores for the autumn migration before climatic conditions deteriorate. Our understanding of the costs and constraints associated with these stages is extremely limited. We investigated post-juvenal molt and premigratory fattening in free-ranging juvenile White-crowned Sparrows (Zonotrichia leucophrys gambelii) on the Arctic tundra. We found evidence for trade-offs between premigratory fat accumulation and molt: heavily molting birds had significantly less fat. Birds increased the rate of fat accumulation as the season progressed, but we found no evidence of a similar increase in rate of molt. Using a controlled captive study to isolate the energetic costs of body feather replacement, we found no difference in fat or size-corrected mass of birds actively growing body feathers as compared to controls. Molting birds, however, consumed 17% more food than controls, suggesting a significant cost of body feather growth. Our results provide evidence of significant costs, constraints, and trade-offs associated with post-juvenal molt and premigratory fat accumulation in young Arctic birds.     

Studying dispersal at the landscape scale: efficient combination of population surveys and capture-recapture data

Researchers often rely on capture-mark-recapture (CMR) data to study animal dispersal in the wild. Yet their spatial coverage often does not encompass the entire dispersal range of the study individuals, sometimes producing misleading results. Information contained in population surveys and variation in population spatial structure can be used to overcome this issue. We build an integrated model in a multisite context in which CMR data are only collected at a subset of sites, but numbers of breeding pairs are counted at all sites. In a Black-headed Gull Chroicocephalus ridibundus population, the integrated-modeling approach induces an increase in precision for the demographic parameters of interest (variances, on average, were decreased by 20%) and provides a more precise extrapolation of results from the CMR data to the whole population. Patterns of condition-dependent dispersal are therefore made easier to detect, and we obtain evidence for colony-size dependence in recruitment, dispersal, and breeding success. These results suggest that first-time breeders disperse to small colonies in order to recruit earlier. The exchange of experienced breeders between colonies appears as a main determinant of the observed variation in colony sizes.     

Effects of ocean temperature on the southern range limits of two understory kelps, <Emphasis Type="Italic">Pterygophora californica</Emphasis> and <Emphasis Type="Italic">Eisenia arborea</Emphasis>, at multiple life-stages

Environmental factors have long been shown to influence species distributions, with range limits often resulting from environmental stressors exceeding organism tolerances. However, these abiotic factors may differentially affect species with multiple life-history stages. Between September 2004 and January 2006, the roles of temperature and nutrient availability in explaining the southern distributions of two understory kelps, Pterygophora californica and Eisenia arborea (Phaeophyceae, Laminariales), were investigated along the coast of California, USA and the Baja California Peninsula, Mexico, by limiting either: (a) tissue nitrogen uptake and storage by adult sporophytes during periods of elevated temperature, and/or (b) production of embryonic sporophytes by microscopic gametophytes. Results suggest that while adult sporophytes of both species are tolerant of high temperatures and low nutrients, reproduction by their microscopic stages is not. Specifically, while E. arborea produced embryonic sporophytes at both 12 and 18°C, temperatures commonly observed throughout the southern portion of its range, P. californica produced sporophytes at 12 but not at 18°C. As a result, it appears that the southern distribution of P. californica, which ends in northern Baja California, Mexico, may be limited by temperature acting on its microscopic stages. In contrast, the ability of E. arborea’s microscopic and adult stages to tolerate elevated temperatures allows it to persist in the warmer southern waters of Baja California, as well as to the north along the California coast where both species co-occur.     

Developmental arrest in Japanese medaka (Oryzias latipes) embryos exposed to sublethal concentrations of atrazine and arsenic trioxide

Embryos of the Japanese medaka (Oryzias latipes) were exposed to serial concentrations of atrazine (0, 25, 50, and 100 ppm) and arsenic trioxide (0, 0.025, 0.05, 0.1 ppm) until hatching. Stasis of circulation, blood islands, titanic convulsions, tube heart and mortality were observed in atrazine-treated embryos. Each endpoint exhibited a concentration-response relationship. Only 4% of the embryos hatched in the 25 ppm, and none in the 50 and 100 ppm, probably due to cell death attributed to the embryos' inability to break from the chorion. With arsenic exposure, hatching was inversely correlated to chemical concentration: 86%, 75% and 54% for 0.025, 0.05 and 0.1 ppm, respectively. Hatching periods were also reduced from 7-13 days in controls to 7-11 days in arsenic-treated embryos. This observation was more pronounced with the 0.05 ppm concentration, showing a reduction of about 4 days. Despite this shortage in hatching time, there were no observable morphological abnormalities, as seen with atrazine. The ecological significance of these findings and implications for the development of sublethal toxicity tests using Japanese medaka embryos are important.     

Carbon, nitrogen and phosphorus elemental stoichiometry in aquacultured and wild-caught fish and consequences for pelagic nutrient dynamics

The elemental carbon (C), nitrogen (N) and phosphorus (P) compositions of the whole-body and gut content of wild marine fish inhabiting the Bay of Biscay (Northeast Atlantic) were studied. Furthermore, the literature was examined for studies of aquacultured fish, reporting the elemental composition of the whole-body fish, that of their food, and nutrient assimilation and gross growth efficiencies (GGE). In both wild-caught and aquacultured fish, significant differences in C, N and P elemental composition were found between species, with P being the most variable component. Differences among species in terms of C, N and P content could be explained by varying proportions of storage compounds in whole-body fish, and varying degrees of ossification. Aquacultured fish feces were found to be P-rich, because of a lower P assimilation efficiency, compared to C or N assimilation efficiencies. Examination of aquacultured fish literature also revealed that C, N and P GGE and nutrient resupply ratios agreed with basic principles of homeostatic regulation of whole-body fish elemental composition. Extrapolation of the results to broader marine systems indicated that fish may be important for conveying nutrients toward the ocean interior.