Graph of the Day: N. Carolina Great Shark Abundance, 1972-2007

The eastern seaboard’s longest continuous shark-targeted survey (UNC), conducted annually since 1972 off North Carolina, demonstrates sufficiently large declines in great sharks to imply their likely functional elimination. Declines in seven species range from 87% for sandbar sharks (Carcharhinus plumbeus); 93% for blacktip sharks (C. limbatus); up to 97% for tiger sharks (Galeocerdo cuvier); 98% for scalloped hammerheads (Sphyrna lewini); and 99% or more for bull (C. leucas), dusky (C. obscurus), and smooth hammerhead (S. zygaena) sharks (Fig. 1 and table S5). Because this survey is situated where it intercepts sharks on their seasonal migrations, these trends in abundance may be indicative of coastwide population changes. The UNC survey also showed the loss of the largest individuals, with declines in mean lengths of blacktip, bull, dusky, sandbar, and tiger sharks of 17 to 47% (fig. S3), suggesting that overexploitation has left few mature individuals in these populations. The remaining four elasmobranch-consuming great sharks were caught too rarely to detect trends from this survey. Two of those, great white (Carcharodon carcharias) and sand tiger (Carcharias taurus) sharks, were each caught only once and early in the UNC survey (in 1974 and 1978, respectively). The only survey that has caught enough sand tigers to note a trend targets sharks in Chesapeake Bay and suggests a decline of over 99% between 1974 and 2004 (15, 16). …

Cascading effects of the loss of apex predatory sharks from a coastal ocean