Shark Problems (from a human’s viewpoint) 183
Sharks also contain high burdens of polychlorinated compounds (PCBs,
dioxins). These compounds are known to cause “immunosuppression, em-
bryonic abnormalities, reproductive dysfunction, carcinogenesis, and a se-
vere loss of body mass” in vertebrates. Concentrations of these chemicals
in the livers of Greenland Sharks were higher than in those of polar bears.
Other sharks found to contain high levels of PCBs in liver and muscle in-
clude Common Thresher Shark, Bull Shark, Leafscale Gulper Shark, Ti-
ger Shark, Blue Shark, Atlantic Sharpnose, and Smooth Hammerhead
(Sphyrna zygaena).
Given these levels of contaminants in shark livers, it should be a matter
of concern that shark liver oil is a source of vitamin A and a component in
several pharmaceuticals. Liver oil from Nurse Sharks, Oceanic Whitetips,
and Silky Sharks near Cuba showed PCB levels of over 14 parts per billion
(ppb). A Japanese study also found PCBs and related polybrominated di-
phenyl ethers (PBDEs) in shark liver oil supplements. Canadian research-
ers also found PCBs and DDT in shark liver oil. Some health standards
in the United States allow no detectable PCB concentrations of any level.
PCB concentrations in Bull and Greenland Sleeper sharks at some locales
are so high that a dead Bull or Sleeper shark found on a beach would have
to disposed of as “hazardous waste.” Just more reasons to not eat shark or
ingest shark products.
We know that these pollutant concentrations can affect human health.
What we don’t understand is what they might be doing to the health of the
sharks. The level of pollutants in Greenland Sleeper Sharks and Smooth
Hammerhead Sharks greatly exceed the threshold amounts known to cause
reproductive malfunction in aquatic mammals. We don’t know what the
critical levels of these toxins are in sharks, whether they are higher or lower
than in humans.
In Iceland, a traditional food for social gatherings, called Hákarl, is
made from Greenland sharks, a tradition that started long before the era
of chemical analyses. The meat of these large sharks, which grow to over
6 m long and weigh 1,000 kg (21 ft and 2200 lb), is prepared by ferment-
ing it (letting it rot) for several months. The dish is served in (fortunately
small) bite-size chunks. Sleeper Shark muscle is very high in two nitrogen-
rich chemicals, urea and trimethylamine oxide (TMAO). Eating a piece of
Hákarl is like chewing on a sponge soaked in household ammonia (impres-
sion of first author, GH). The dish is made more palatable albeit still ined-
ible by following each bite with a shot of a highly distilled vodka-like drink
called Brennivín, or “black death,” often accompanied by much singing.
Without fermentation (accomplished by burying the meat for several
months), the nitrogen by-products in Greenland shark meat can be not