The predicted relationship between nitrogen stable isotope discrimination between predator and prey consumed (∆¹⁵N) and the prey stable nitrogen isotope composition (dietary-δ¹⁵N) estimates for each shark species based on the widely reported ∆¹⁵N-dietary δ¹⁵N relationship

<p>[<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0077567#B7" target="_blank">7</a>,<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0077567#B8" target="_blank">8</a>,<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0077567#B40" target="_blank">40</a>,<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0077567#B67" target="_blank">67</a>]. </p

Genepop Input File

Microsatellite allele sizes formatted for Genepop

Dual-plot of individual predator (■) and mean (± SD) δ¹³C and δ¹⁵N values of the PP for each predator ((a), (f), (k), (p); see Table 1).

<p>Standard ellipse areas corrected for sample size (SEA_c) of sharks (solid black) and PP functional prey groups (Crustacean, dashed light gray; Mollusk, dotted light gray; Teleost, dashed dark gray; Elasmobranch, solid dark gray; Mammal solid light gray), and the broader diet (dotted black) following Jackson et al. [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0077567#B29" target="_blank">29</a>]. Note different scales on the x- and y-axes in each species.</p

Illustration of the expected relationship between stable isotope values of a predator and its’ prey in mixing space [27,28], employing the Bayesian approach of Jackson et al. [29], centered on multivariate ellipse based metrics.

<p>In choosing discrimination factor (∆¹⁵N and ∆¹³C) values, it would be expected that the δ¹⁵N and δ¹³C values of the predator after adjustment to specific ∆¹⁵N and ∆¹³C values should overlay or fall within the range of δ¹⁵N values of the PP it consumes (see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0077567#pone-0077567-t002" target="_blank">Table 2</a>), indicating a best-fit scenario between predator and prey [ellipses represent prey (black) and predator (gray) respectively]. Black points represent δ¹³C and δ¹⁵N values of a predator, gray points (light and dark) represent adjusted-δ¹³C and adjusted-δ¹⁵N values with two different ∆¹⁵N and ∆¹³C values. White shapes represent mean (± variance) of prey species. </p

Box plots representing the δ¹⁵N values of all of the PP derived from stomach content data of the bonnethead <i>Sphyrna tiburo</i>, Atlantic sharpnose <i>Rhizoprionodon terraenovae</i>, bull <i>Carcharhinus leucas</i>, and white <i>Carcharodon carcharias</i> shark.

<p>Box plots representing the δ¹⁵N values of all of the PP derived from stomach content data of the bonnethead <i>Sphyrna tiburo</i>, Atlantic sharpnose <i>Rhizoprionodon terraenovae</i>, bull <i>Carcharhinus leucas</i>, and white <i>Carcharodon carcharias</i> shark.</p

Metric multidimensional scaling (<i>m</i>MDS) ordinations of size class 2 (medium) <i>G</i>. <i>cuvier</i> dietary samples with approximate 95% region estimates fitted to bootstrap averages for decades 1 (1983–1992), 2 (1993–2003) and 3 (2004–2014).

<p>(a) Percentage frequency of occurrence (%F), (b) Percentage mass (%M), (c) Percentage number (%N) and d) Percentage index of relative importance (%IRI). <i>R</i>, ANOSIM global <i>R</i> statistic and associated <i>p</i> value. Significant pairwise tests (with <i>p</i> value in brackets) are detailed in each figure.</p

Randomized cumulative prey curves derived from the stomach contents of <i>G</i>. <i>cuvier</i> caught in the KwaZulu-Natal shark nets and drumlines, 1983–2014.

<p>a) Small, b) medium, c) large size classes and d) all sharks combined. The order in which the stomachs were analysed was randomised 500 times and the means (solid lines) and 95% confidence levels (dashed lines) presented.</p

Netted beaches on the KwaZulu-Natal coast and, in parenthesis, the length of nets in kilometres and number of drumlines as of December 2014.

<p>Several net installations (*) were removed permanently during the study period 1983–2014. Insert shows the locality of the netted region in relation to the South African coast.</p

Metric multidimensional scaling (<i>m</i>MDS) ordinations of dietary samples with approximate 95% region estimates fitted to bootstrap averages for small (< 150 cm), medium (150–220 cm) and large (> 220 cm) <i>G</i>. <i>cuvier</i>.

<p>(a) Percentage frequency of occurrence (%F), (b) Percentage mass (%M), (c) Percentage number (%N) and (d) Percentage index of relative importance (%IRI). <i>R</i>, ANOSIM global <i>R</i> statistic and associated <i>p</i> value. Significant pairwise tests (with <i>p</i> value in brackets) are detailed in each figure.</p

Variance component analysis from linear mixed-model analysis for <i>G</i>. <i>cuvier</i> δ¹³C and δ¹⁵N for two tissue (muscle and liver) and three tissue (muscle, liver and skin) models.

<p>The between-individual component (BIC) represents the total intercept variance and the within-individual component (WIC) represents the residual variance. Total niche width (TNW) is the sum of the intercept and residual variances for δ¹³C and δ¹⁵N. Total BIC and total WIC are calculated by combining the intercept variances for δ¹³C and δ¹⁵N and then dividing by TNW. Proportion of WIC and BIC that explained TNW is in parentheses.</p