Image courtesy of Amanda M. Pippin
This news is extremely disappointing for all who care about this largest of the hammerhead species. It is also a blow to the growing shark ecotourism and dive industry, which currently generates over U.S. $314 million annually, and is expected to double in the next 20 years. Populations of the great hammerhead shark have already declined significantly, and without protection this species risks further decline.
The great hammerhead shark, Sphyrna mokarran, swims in coastal warm temperate and tropical waters in many parts of the world. The U.S. population inhabits waters off the southeastern U.S. and in the Gulf of Mexico, undertaking long annual migrations throughout the region. While this enormous shark, which can grow to 20 feet long and 1200 pounds, shows little interest in humans, we humans have pursued it with a vengeance, in recent years primarily for its fins. Even where there are some restrictions on retention or landings of the fish, like in the U.S., great hammerheads are killed as bycatch when fishermen target other species such as tuna, swordfish or other sharks.
Although I am still sorting through this week’s listing decision documents, the main message of the National Marine Fisheries Service (NMFS), the responsible government agency, seems to be “we don’t know enough” to protect this magnificent species. Time and time again, the conclusion NMFS draws in the listing decision documents is that a piece of information is “inconclusive” or “unclear” as to its implications for the great hammerhead shark.
I disagree. Here’s what we know:
Hammerhead sharks as a complex are in dismal shape. In country after country and region after region, NMFS concedes that hammerhead populations are highly depleted, including in the U.S. (~70-80% decline), Brazil (80% decline in catch rate), Mediterranean (>99.99% decline), N.W. Australia (58%-76% decline from 1996-2005), E. Australia (~83% decline since 1985 in one region and >90% decline since the 1970s in another), and various African nations. Unfortunately, information about great hammerheads specifically is generally lacking, largely because they are naturally rare and species-level reporting has historically been poor. And, in its listing determination, NMFS refuses to impute anything from what’s going with hammerheads as a group to great hammerheads specifically.
The available information indicates that great hammerheads have suffered a significant decline. As NMFS concedes, the one assessment of the U.S. great hammerhead population that is based on a fisheries-independent survey, rather than the less-reliable survey type that is done from commercial fishing boats that can only sample where the fishermen want to go, estimated that the species had suffered a decline of over 90% by 2005. Great hammerheads also now make up a much smaller portion of the overall recorded U.S. hammerhead catch than they did historically (from ~50% in 1982 to <30% in 2005). While there remains uncertainty because of the limited data and a survey done from commercial fishing boats suggests a somewhat more optimistic picture, the best available science says that the U.S. population of great hammerheads has suffered a significant decline. This decline and the ongoing threat from fishing is mirrored in the few places in the world where data about great hammerheads specifically exists, such as South Africa, where great hammerhead catch rates declined by almost 80% from 1978-2003, and the Indian Ocean drift gillnet fishery.
The great hammerhead is innately prone to depletion and slow to recover. The species is slow growing, late to mature, and has low productivity (lower than other hammerheads). Great hammerheads can also live to be over 40 years old, so what happens to them now is of longstanding consequence for the species.
The market for sharks, including or shark parts such as fins, is huge and still growing. According to the U.N. Food and Agriculture Organization (FAO), “global capture production” of hammerheads has increased more than 8000% (!) since 1990 (and FAO numbers are generally considered underestimates). Great hammerhead fins, called “Gu pian”, are particularly desirable in the fin trade—according to NMFS, it’s been calculated that fins from about 375,000 great hammerhead sharks, equivalent to around 21,000 metric tons, are traded in the Hong Kong fin market annually. Shark consumption will also continue to increase as demand for food, and particularly animal protein, mounts in many regions of the globe.
Illegal shark fishing is epidemic. In West African waters, it’s been estimated that illegal fishing accounts for close to 40% of the region’s catch. Closer to home, Mexican fishermen were estimated to be catching up to 56% of total U.S. commercial shark quota, based on data from 2000-2005. We can put more and more shark conservation laws on the books around the world, but if these laws are simply skirted or not enforced then there is no benefit to the sharks.
A hooked great hammerhead is a dead great hammerhead. Great hammerheads suffer extremely high mortality once they are caught: in one study, 94% of great hammerheads caught on commercial longlines were dead when brought onboard. Another recent study found that, out of five shark species, great hammerheads suffered the highest post-release stress, indicating that even if a great hammerhead survives capture it is likely to die after it is released. Such high post-capture mortality means that traditional conservation measures for sharks, such as finning restrictions, prohibitions or limits on landings, prohibitions on retention, catch limits, size limits, and limits on longline soak time, will have limited efficacy for great hammerheads. Once a great hammerhead is caught, whether purposefully or incidentally, whether by a commercial longliner or a recreational fishermen, its chances of survival are dim.
An ESA listing for the great hammerhead shark would have ensured the adoption of management measures to stop the species’ decline. A recovery plan implemented under the law would reduce shark fishing mortality and help establish protection for critical great hammerhead habitat, including coastal breeding and nursery areas, as well as key feeding grounds.
So what’s the future of the great hammerhead? That remains to be seen. But it is very discouraging that the Endangered Species Act will not be a tool available to guarantee that it has one.