In Search of the Golden Hammerhead
Responding to a question about the Golden Hammerhead and a statement by another subscriber that it is actually a Scalloped Hammerhead, I wrote:
The Golden Hammerhead (Sphyrna tudes) is a valid species, quite distinct from the Scalloped Hammerhead (S. lewini).
Although the Golden Hammerhead is an abundant, widely distributed shark, it is relatively poorly known. Until recently, this species was known as the Smalleye Hammerhead, in reference to — you guessed it! — its relatively small eyes. During 1985 and 1986, Dr. Jose Castro of Clemson University conducted a survey of shark species found off Trinidad and Tobago for the FAO (the Food and Agriculture Organisation of the United Nations), in order to determine the feasibility of shark fisheries in the area. He discovered that living and fresh-caught S. tudes are a striking bright yellow or orange and that the species is economically important in Trinidad, as it is one of the most abundant sharks in market catches; it also is part of the by-catch of shrimp trawlers and of various small gill net fisheries. Due to its remarkable coloration, this species is known to local fishermen as the Yellow or Golden Hammerhead, a name which is more descriptive and preferable to the older, duller name of Smalleye Hammerhead. Every day, Dr. Castro was able to examine dozens of specimens at the Port of Spain fish market. Castro also used mesh bottom gill nets to catch these sharks throughout most of the year (except December through February, when seas were too rough), thereby filling in many gaps in our knowledge of the basic life history this remarkably pigmented shark. What follows is a brief overview of the life history of this species, mostly synopsized from Castro's 1989 paper, "Biology of the Golden Hammerhead, Sphyrna tudes, off Trinidad" (Environmental Biology of Fishes, Vol. 24, No. 1, pp 3-11):
The Golden Hammerhead Shark inhabits the northeastern coast of South America, from Venezuela to Uruguay. It is found in coastal waters at depths of 30 to 130 feet (9 to 40 metres) over muddy bottoms. The Golden Hammerhead is a small species which attains a maximum size of about 4 feet and 20 pounds (1.22 metres and 9 kilograms). The most distinctive characteristic of this species is its striking bright orange or yellow color. Juveniles less than 2.5 feet (80 centimetres) long are bright yellow or orange; adults are pale yellow. The color is apparently due to pigments present in this species' diet; juveniles feed primarily on penaeid shrimp (especially Xiphopenaeus kroyeri), while adults feed on marine catfishes (family Ariidae) and their eggs. Two pigments have been isolated and, at the time of Castro's 1989 report, their biochemical characterization was being ascertained (one of these pigments is almost certainly a form of carotene, a class of unsaturated hydrocarbons which gives ariid catfish eggs their rich golden/orange color). Male Golden Hammerheads mature at a length of about 2.5 feet (80 centimetres); females of this species at a length of about 3.2 feet (98 centimetres). Off Trinidad, female Golden Hammerheads ovulate and mate during the month of August. Developing pups of this species — like those most other members of the family Carcharhinidae (the one exception is the Tiger Shark, Galeocerdo cuvier, which relies on yolk reserves throughout its 13- to 16-month gestation period) — are nourished at late stages of gestation via a yolk-sac placenta. Gestation of the Golden Hammerhead appears to last about 10 months; off Trinidad, birth occurs in shallow waters from late May to June. Broods of this species consist of 5 to 12 pups, which at birth measure about 1 foot (30 centimetres) long. In female Golden Hammerheads, the ovarian cycle runs concurrently with the gestation cycle, so it seems likely that females of this species are fertilized shortly after giving birth and that the species reproduces every year (rather than having a two-year reproductive cycle as in many larger carcharhinids, in which females take a year off after giving birth, recovering and building up energy stores for a year before mating again).
Sporting a bright orange or yellow color with metallic or iridescent hues, the Golden Hammerhead must surely rank as among the most beautiful and easy-to-recognize of elasmobranchs. These colors and hues fade rapidly after death, reducing this once-colorful, graceful little shark to a dull grey shadow of its former glory. When jammed into a specimen bottle of alcohol preservative, the shark is further distorted and leached of the last of its colors, becoming a warped grey-brown grotesque under glass that silently gathers dust on a museum shelf. Since the pigments which give the Golden Hammerhead its striking coloration are soluble in alcohol, it comes as no surprise that this species was once known by the deathly dull name of Smalleye Hammerhead.
While there is a great deal of valuable information that can be obtained from examination of preserved specimens, many aspects of the former animal's life history, behavior, and coloration in life are lost forever. Museum docents and backroom boffins who never venture into the field are missing crucial — and, I think, many of the most fascinating — parts of an species' life story. Dead fish — like dead men — tell few tales.
Cheers,
— R. Aidan Martin
Posted to SHARK-L August 4, 1998
