Chondrichthyes (cartilaginous fish,
including sharks, rays and chaemeras) >
Fishing of cartilaginous fish
Note: This was written in the late 1980's and some of
the figures are out-of-date.
Cartilaginous fishes are increasingly important
fisheries species in many areas of the world as evidenced by a
three-fold increase in the total catch since 1947. The catch
statistics published by the Food and Agriculture Organization of the
United Nations (FAO) for 1986 show that 627,000 tonnes of
cartilaginous fishes were caught world-wide. This represents about
0.7 % of the total world fisheries catch which was about 92 million
tonnes in 1986. Between 1947 and 1986 over 420 million tonnes of
cartilaginous fishes were taken in fisheries. This does not include
the millions of tonnes taken as a by-catch of other fisheries then
discarded. India, Pakistan, Indonesia, Taiwan, Japan, and China are
among the leading countries that catch and market cartilaginous
fishes. Among African countries, Nigeria has the highest reported
catches of cartilaginous fishes, and landed between 11,000 and
36,000 tonnes of cartilaginous fishes between 1970 and 1986,
according to FAO catch statistics. However, catch statistics for
most African countries either go unreported or the information is so
scattered that an accurate assessment of the fishery is impossible.
In southern Africa cartilaginous fish fisheries
have been slow to develop because of the misconception that
cartilaginous fishes are `inedible'. The flesh of many species is
quite palatable and can be eaten fresh or dry salted as `biltong'
(jerky). Elsewhere than southern Africa, many species of sharks and
rays are the basis of substantial fisheries for food, and relatives
of the St Joseph (family Callorhinchidae) are fished wherever they
occur. A large industry formerly existed for liver oil from various
coastal sharks, which has a high vitamin A content.
Soupfin sharks
(Galeorhinus galeus) and several other species were heavily fished
for liver oil off Australia, the United States, South America, and
southern Africa. Today synthetically produced vitamin A has replaced
the demand for liver oil, except for some countries where shark
liver oil is cheaper to produce than synthetic vitamin A.
Several directed and by-catch fisheries for
cartilaginous fishes operate in southern Africa, but only a small
portion of the catch is utilized as food for the domestic market. In
St. Helena Bay on the west coast dried shark meat or biltong is
exported to several central African countries, most notably DRC.
Gillnetters take a sizable catch of
St Joseph (Callorhinchus
capensis) off the western Cape, some 640 tonnes as reported by FAO
in 1986, which is eaten locally. The fishery for Soupfin shark at
Gans Bay once processed sharks for vitamin A liver oil, but today
their operation is mainly restricted to the biltong (jerky) market,
which is sold domestically.
Another fishery for small sharks, situated on
the east coast, utilizes both the flesh for food and the liver oil
for vitamin A. The flesh is exported to several European countries,
the liver oil is processed and sold locally, fins are dried and
exported for the oriental fin trade, jaws are sold for curios, and
vertebrae and viscera are utilized locally for traditional medicine.
There is some movement to develop a local market for leather from
sharks, which is more durable and commands a higher price than
ordinary leather from cattle. Preparation of hides requires much
time and effort, however.
Probably the best publicized small shark
fishery is that conducted by the Natal Sharks Board (NSB) to protect
the bathing beaches of Natal from shark attack. The NSB catches
about 1,000 large sharks per year, and currently costs about USA
$4,000,000 a year to run. This is not a commercial operation but a
heavily subsidized fishery where the cost to catch each shark
(possibly up to $4000 at present) is considerably more than the
value of the catch. The catch can only be utilized to a limited
extent because of operational constraints with shark netting, which
may leave sharks in the nets for long periods. Meat, hides, and fins
are often unusable and carcasses must be disposed by burying them.
The jaws and teeth are sold as jewelry and curios, and some fins are
marketed locally. Official NSB figures are not available, but the
actual catch weight is small compared to other fisheries. If the
average shark caught weighs about 68 kg (about as much as a human
being), multiplying this by the average annual shark catch of the
NSB between 1978 and 1984 (1151 individuals), the annual catch of
the NSB is about 78 tonnes. This small fishery is ecologically
significant, however, because it targets sharks near or at the apex
of the food web and has steadily operated for over three decades.
There are buyers of dried shark fins for the
oriental fin market in major cities in southern Africa, which export
them to Taiwan and Hong Kong. The value of shark fins, which are
used to make the gelatinous base for shark-fin soup, has soared in
the past few years: prices of USA $100.00 per kg for large fins and
$25.00 per kg for small fins were recently quoted to us. This has
stimulated sport anglers as well as commercial fishermen to collect
and save shark fins from otherwise unwanted sharks. Offshore foreign
longliners targeting billfish and tuna also collect shark fins as a
major low-volume, high-value bycatch, and the effects of this
largely unstudied but world-wide and pervasive fishery is virtually
unknown. Local blue-water anglers and trawlermen in the western Cape
suspect that blue sharks have been heavily depleted by the longline
fishery in the past twenty years.
The post-JAWS media publicity on sharks has
helped to stimulate a market for the jaws and teeth of sharks, which
are locally sold as curios, decorations, and as jewelry or shipped
overseas. Large shark jaws are valuable, and the jaws of large
Great
white sharks command an inordinately high value, particularly in the
United States. Spot commercial fisheries for large white sharks,
targeting their jaws or entire frozen carcasses for display have
occured in the western Cape.
The sport angling community of southern Africa,
including rock and surf and skiboat anglers, comprises another
directed but largely non-utilized fishery. Up to seven tonnes of
sharks and rays are sometimes landed in a single day in major
angling competitions. Competitive anglers target specifically for
cartilaginous fishes since points are awarded based on the total
weight and sharks and rays on the average weigh more than bony fish.
Unfortunately most of this catch is usually discarded or processed
into fish meal. However, there is an increasing tendency for anglers
to release sharks and rays after weighing and tagging them. There
are specialist anglers in Natal who seek large rays for the sport
they give when hooked, but release them afterwards. Many of the
angling clubs maintain detailed records on their catches for the
purposes of scoring in local and regional competitions. This
represents an ideal database for scientists to study the long-term
effects of fishing pressure for a given area and hence assist
anglers in helping to maintain and manage their fishing stocks. It
is essential, however, that the species being caught are accurately
identified to increase the value of the information.
Trawler fleets operating off the southwest and
west coast of southern Africa from Cape Agulhas to Namibia conduct
the single largest fishery for cartilaginous fishes in the area. In
addition to trawling vast quantities of hake and other bony fishes
they catch substantial amounts of cartilaginous fishes as an
untargeted bycatch.
Dogfish (family
Squalidae), skates (family
Rajidae), houndsharks (family Triakidae),
catsharks (family
Scyliorhinidae), and
St Joseph are the most important components of
this bycatch. Most of these cartilaginous fishes are wasted because
they have a low value in the trawlfish market and are generally
discarded to make room for commercially valuable bony fish. A small
quantity of Biscuit skates (Raja straeleni) are processed for skate
wings and utilized locally. Probably most if not all of the
cartilaginous fishes that are discarded are dead after being in the
trawl for several hours, so these animals are essentially being
exploited without being used. The catch weight of cartilaginous
fishes discarded from this by-catch fishery is uncertain since no
statistics are kept, and the impact of this fishery on the demersal
community is presently unknown.
Using data from a research cruise of RV
Africana (046) off the western Cape, we derived a weight ratio of
hake to cartilaginous fishes caught on the cruise. By multiplying
the ratio by the total hake catch in southern African waters, we
obtained a rough estimate of about 22,000 tonnes of cartilaginous
fishes caught per year in the trawl fishery. This represents about
11 million individuals assuming a weight of about 2 kg per shark,
ray, or chimaera.
Text by Leonard J.V. Compagno, David A. Ebert
and Malcolm J. Smale
|