δ¹⁵N values versus growth increment number (age) for 15 white sharks.

<p>A) Individuals modeled with a VBGF curve. B) Individuals showing a significant linearly increasing trend. C) Individuals showing no significant pattern. Average pre-parturition δ¹⁵N values (n = 3) are indicated as grey filled circles for individuals with relatively high juvenile δ¹⁵N values (>17‰).</p

The niche overlap between each individual and the population.

<p>A) The 90% confidence limit for the population (black ellipse) and for individual sharks (colored ellipses). B) The distribution of the proportional similarity index, <i>w_ij</i><a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0045068#pone.0045068-Lu1" target="_blank">[66]</a>, within the sampled population of California white sharks, which exhibits strong individuality with both specialists and generalists.</p

Ontogenetic and Among-Individual Variation in Foraging Strategies of Northeast Pacific White Sharks Based on Stable Isotope Analysis

<div><p>There is growing evidence for individuality in dietary preferences and foraging behaviors within populations of various species. This is especially important for apex predators, since they can potentially have wide dietary niches and a large impact on trophic dynamics within ecosystems. We evaluate the diet of an apex predator, the white shark (<em>Carcharodon carcharias</em>), by measuring the stable carbon and nitrogen isotope composition of vertebral growth bands to create lifetime records for 15 individuals from California. Isotopic variations in white shark diets can reflect within-region differences among prey (most importantly related to trophic level), as well as differences in baseline values among the regions in which sharks forage, and both prey and habitat preferences may shift with age. The magnitude of isotopic variation among sharks in our study (>5‰ for both elements) is too great to be explained solely by geographic differences, and so must reflect differences in prey choice that may vary with sex, size, age and location. Ontogenetic patterns in δ¹⁵N values vary considerably among individuals, and one third of the population fit each of these descriptions: 1) δ¹⁵N values increased throughout life, 2) δ¹⁵N values increased to a plateau at ∼5 years of age, and 3) δ¹⁵N values remained roughly constant values throughout life. Isotopic data for the population span more than one trophic level, and we offer a qualitative evaluation of diet using shark-specific collagen discrimination factors estimated from a 3+ year captive feeding experiment (Δ¹³C_shark-diet and Δ¹⁵N_shark-diet equal 4.2‰ and 2.5‰, respectively). We assess the degree of individuality with a proportional similarity index that distinguishes specialists and generalists. The isotopic variance is partitioned among differences between-individual (48%), within-individuals (40%), and by calendar year of sub-adulthood (12%). Our data reveal substantial ontogenetic and individual dietary variation within a white shark population.</p> </div

Summary of biological and collection data and proportional similarity index (<i>w_ij</i>) for white sharks.

<p>Abbreviations are as follows: California Academy of Sciences (CAS), Natural History Museum of Los Angeles County (LACM), G. Chan (GC), Moss Landing Marine Lab (MLML), K. Goldman (KG), S. Anderson (SA), and Long Marine Lab (LML).</p

Carbon and nitrogen isotope values from sub-adult to adult growth bands (≥6 years old).

<p>The colored symbols are from white sharks; open symbols represent years ≤1986 and closed symbols represent years >1986. Isotopic values for potential prey data are the grey boxes and are as follows: 1) northern elephant seal, 2) California sea lion, 3) harbor seal, 4) dolphin, 5) harbor porpoise, 6) tuna, 7) neritic fish, 8) offshore cephalopod, 9) nearshore cephalopod, 10) blue shark, 11) hammerhead shark. The mean prey isotope values were corrected for trophic enrichment (Δ¹³C = 4.2‰ and Δ¹⁵N = 2.5‰) and collagen-to-muscle (Δ¹³C = 2.0‰ and Δ¹⁵N = 0‰), if necessary (prey data and citations are listed in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0045068#pone.0045068.s002" target="_blank">File S2</a>).</p

Average width of last 6 growth bands and average isotopic values from outer-12 mm of vertebrae from leopard sharks fed a constant diet of squid over 1250 days.

<p>Average width of last 6 growth bands and average isotopic values from outer-12 mm of vertebrae from leopard sharks fed a constant diet of squid over 1250 days.</p

Using Stable Isotope Analysis to Understand the Migration and Trophic Ecology of Northeastern Pacific White Sharks (<em>Carcharodon carcharias</em>)

<div><p>The white shark (<em>Carcharodon carcharias</em>) is a wide-ranging apex predator in the northeastern Pacific (NEP). Electronic tagging has demonstrated that white sharks exhibit a regular migratory pattern, occurring at coastal sites during the late summer, autumn and early winter and moving offshore to oceanic habitats during the remainder of the year, although the purpose of these migrations remains unclear. The purpose of this study was to use stable isotope analysis (SIA) to provide insight into the trophic ecology and migratory behaviors of white sharks in the NEP. Between 2006 and 2009, 53 white sharks were biopsied in central California to obtain dermal and muscle tissues, which were analyzed for stable isotope values of carbon (δ¹³C) and nitrogen (δ¹⁵N). We developed a mixing model that directly incorporates movement data and tissue incorporation (turnover) rates to better estimate the relative importance of different focal areas to white shark diet and elucidate their migratory behavior. Mixing model results for muscle showed a relatively equal dietary contribution from coastal and offshore regions, indicating that white sharks forage in both areas. However, model results indicated that sharks foraged at a higher relative rate in coastal habitats. There was a negative relationship between shark length and muscle δ¹³C and δ¹⁵N values, which may indicate ontogenetic changes in habitat use related to onset of maturity. The isotopic composition of dermal tissue was consistent with a more rapid incorporation rate than muscle and may represent more recent foraging. Low offshore consumption rates suggest that it is unlikely that foraging is the primary purpose of the offshore migrations. These results demonstrate how SIA can provide insight into the trophic ecology and migratory behavior of marine predators, especially when coupled with electronic tagging data.</p> </div

Rate of consumption in offshore focal areas (PEL: Pelagic, HI: Hawaii) relative to California (CA) estimated using the spatially explicit Bayesian mixing model.

<p>Results show posterior model estimates (median, interquartile range and max/min values). The green dashed line designates the relative consumption rate in the California focal area. Consumption rate is estimated using three different tissue incorporation rates for both offshore focal areas (SB: juvenile sandbar shark, BA: allometrically scaled bird, FA: allometrically scaled fish, see text for details).</p

Relationship between white shark length (TL) and δ¹³C and δ¹⁵N of white shark muscle.

<p>The two ellipses contain the δ¹³C and δ¹⁵N values of two of the smallest sharks that had the highest δ¹³C and δ¹⁵N values.</p

White shark focal areas from satellite tag data from Jorgensen et al. [<b>4</b>].

<p>Regions used in the mixing model are indicated (California, Pelagic, Hawaii), see text for details. White shark aggregation sites in central California where tissue collection occurred are designated with the star. Mean chlorophyll-<i>a</i> concentration for 2006 (Aqua MODIS, <a href="http://oceanwatch.pfeg.noaa.gov" target="_blank">http://oceanwatch.pfeg.noaa.gov</a>) showing productivity gradients which isotopic gradients generally follow. Inset shows conceptual diagram showing how the seasonal migration of white sharks take them between regions with isotopically distinct prey.</p