W. Don Bowen

QUANTITATIVE FATTY ACID SIGNATURE ANALYSIS: A NEW METHOD OF ESTIMATING PREDATOR DIETS

Accurate estimates of the diets of predators are required in many areas of ecology, but for many species current methods are imprecise, limited to the last meal, and often biased. The diversity of fatty acids and their patterns in organisms, coupled with the narrow limitations on their biosynthesis, properties of digestion in monogastric animals, and the prevalence of large storage reservoirs of lipid in many predators, led us to propose the use of quantitative fatty acid signature analysis (QFASA) to study predator diets. We present a statistical model that provides quantitative estimates of the proportions of prey species in the diets of individual predators using fatty acid signatures. We conducted simulation studies using a database of 28 prey species (n = 954 individuals) from the Scotian Shelf off eastern Canada to investigate properties of the model and to evaluate the reliability with which prey could be distinguished in the model. We then conducted experiments on grey seals (Halichoerus grypus, n = 25) and harp seals (Phoca groenlandica, n = 5) to assess quantitative characteristics of fatty acid deposition and to develop calibration coefficients for individual fatty acids to account for predator lipid metabolism. We then tested the model and calibration coefficients by estimating the diets of experimentally fed captive grey seals (n = 6, switched from herring to a mackerel/capelin diet) and mink kits (Mustela vison, n = 46, switched from milk to one of three oil-supplemented diets). The diets of all experimentally fed animals were generally well estimated using QFASA and were consistent with qualitative and quantitative expectations, provided that appropriate calibration coefficients were used. In a final case, we compared video data of foraging by individual free- ranging harbor seals (Phoca vitulina, n = 23) fitted with Crittercams and QFASA estimates of the diet of those same seals using a complex ecosystem-wide prey database. Among the 28 prey species in the database, QFASA estimated sandlance to be the dominant prey species in the diet of all seals (averaging 62% of diet), followed primarily by flounders, but also capelin and minor amounts of other species, although there was also considerable individual variability among seals. These estimates were consistent with video data showing sandlance to be the predominant prey, followed by flatfish. We conclude that QFASA provides estimates of diets for individuals at time scales that are relevant to the ecological processes affecting survival, and can be used to study diet variability within individuals over time, which will provide important opportunities rarely possible with other indirect methods. We propose that the QFASA model we have set forth will be applicable to a wide range of predators and ecosystems.

The Effect of Maternal Size and Milk Energy Output on Pup Growth in Grey Seals (Halichoerus grypus)

In phocid species in which females fast throughout lactation, maternal energy reserves at parturition must support lactation. Thus, differences in body size and energy stores may influence the magnitude of maternal energy transfer. We examined variation in milk energy transfer and its consequence for pup growth in grey seals over a wide range of maternal body sizes. Milk samples (n = 42) were collected from 28 females over the 16-d lactation period. Milk yields were measured in nine mother-pup pairs by deuterium oxide dilution. Milk fat and energy content increased dramatically over the first half of lactation. At mid-to late lactation milk composition averaged 71.1% dry matter, 59.8% fat, 9.2% protein, and 24.8 kJ/g (bomb calorimetry). Initial maternal mass (149-256 kg) and daily mass loss (3-9 kg/d) were correlated with daily milk output (1.3-4.1 kg/d). Milk energy output (29-92 MJ/d) in turn explained pup mass gain (0.8-2.8 kg/d, r² = 0.997). Pups with greater energy intakes had a greater ratio of fat to protein deposition and thus a greater efficiency of energy storage, increasing from 40% to 79%. Daily milk intake did not change over lactation, but growth rate was greater during the second half of lactation because milk energy intake was greater. Results of this study indicate that large females lose mass more rapidly, produce more milk, and wean larger, fatter pups than do small females. We conclude that differences in maternal mass and available energy stores may have substantial consequences for the pup and may account for much of the reported variation in pup growth both within and between populations of phocids such as the grey seal.

Sex-specific, seasonal foraging tactics of adult grey seals (Halichoerus grypus) revealed by state-space analysis

In many large pelagic animals, observing behavior is limited to observation by radio or satellite telemetry. In many cases, discriminating different behaviors from telemetry data has been a key, but often elusive, goal. Here we use state-space models (SSMs) to fit a correlated random walk (CRW) model that switches between two unobserved behavioral states (nominally foraging and traveling) to 41 male and 43 female adult grey seal (Halichoerus grypus) satellite telemetry tracks. The SSM results reveal markedly different spatial behavior between the sexes, fitting well with sexual size dimorphism and known dietary differences, suggesting that the sexes deal with seasonal prey availability and reproductive costs differently. From these results we were also able to produce behaviorally informed habitat use maps, showing a complex and dynamic network of small, intensely used foraging areas. Our flexible SSM approach clearly demonstrates sex-related behavioral differences, fine scale spatial and temporal foraging patterns, and a clearer picture of grey seal ecology and role in the Scotian Shelf ecosystem.

Mass and Energy Transfer during Lactation in a Small Phocid, the Harbor Seal (Phoca vitulina)

In true seals (family Phocidae), the large energetic costs of lactation are supported primarily by mobilization of stored fat. We studied the magnitude of fat and energy depletion in lactating harbor seals (n = 17) on Sable Island, and fat and energy storage in their pups, using cross-sectional morphometric and isotopic methods. Initial mass of mothers studied ranged from 87 to 94 kg. Maternal mass declined by 33% over the first 19 d of the 24-d lactation period. Most of this loss (68.8%) was from the sculp (i.e., skin and attached blubber). Estimated maternal body fat, derived from dilution of deuterium oxide, decreased from 24% at parturition to about 7% at 19 d postpartum. Mothers lost 163 kg (78.7%) of their stored fat and 3.1 kg (20.0%) of stored protein, representing 713.8 MJ (169 Mcal) or 60.5% of stored energy. Newborn pups contained 93.0 MJ (22.1 Mcal) of energy, divided similarly between fat (46 4%) and protein (53.6%). Pup body mass increased from 10.6 kg to 25.8 kg. Sculp mass accounted for 62. 7% of mass gained by the pup. Total body fat of pups increased from 11% at birth to 35% at 19 d. Pups deposited 346 8 MJ (82.2 Mcal) or 48. 7% of energy withdrawn by females from body stores. Unlike large phocid species, lactating harbor seals initiate feeding during lactation apparently because energy reserves are insufficient to cover the combined costs of lactation and maternal metabolism.

Variation in Milk Production and Lactation Performance in Grey Seals and Consequences for Pup Growth and Weaning Characteristics

Phocid seals are one of the few groups of mammals capable of sustaining the energetic demands of lactation entirely through body nutrient stores while fasting. Lactation performance of the female in turn influences the rate and pattern of pup growth. We examined variation in and patterns of milk composition and production, maternal energy output, and pup growth and energy deposition over the entire lactation period in 18 grey seal mother‐pup pairs using hydrogen isotope (3H2O and D2O) dilution. Milk composition was independent of maternal mass and nutrient stores, indicating dependence on other physiological and genetic factors. Heavier females lactated longer ( \documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \usepackage[OT2,OT1]{fontenc} \newcommand\cyr{ \renewcommand\rmdefault{wncyr} \renewcommand\sfdefault{wncyss} \renewcommand\encodingdefault{OT2} \normalfont \selectfont} \DeclareTextFontCommand{\textcyr}{\cyr} \pagestyle{empty} \DeclareMathSizes{10}{9}{7}{6} \begin{document} \landscape

LINKING MOVEMENT, DIVING, AND HABITAT TO FORAGING SUCCESS IN A LARGE MARINE PREDATOR

r^{2}=0.653

Sex differences in the diving behaviour of a size-dimorphic capital breeder: the grey seal

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