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How Many Fish in the Sea?
Georgina McGill
Science, Technology, Environment and Resources Group
Since 1950 growing world demand for fish has meant increased exploitation
of wild stocks of fish, crustaceans and molluscs. Between 1950 and 1970
total reported marine capture landings rose from 18.5 million tons to
59 million tons. (1) Since the late 1980s marine capture fisheries have
remained at about 83 million tons, although the overall production figure
disguises changes in the composition of the catch and the fishing effort
expended to maintain it.
At the Twentieth Session of the FAO Committee on Fisheries in 1993,
it was reported that 69 percent of the world's marine stocks for which
data are available were either fully to heavily exploited (44 percent),
overexploited (16 percent), depleted (6 percent) or very slowly recovering
from overfishing (3 percent), and therefore were in need of urgent corrective
conservation and management measures. (2) The purpose of this Research
Note is to provide a brief overview of the current state of Australia's
wild fish resources.
Australian Fish Catch
Australia has the world's third largest fishing zone which, at 8.94 million
square kilometres, is bigger than our land area and extends 200 nautical
miles out to sea. However, it is only ranked fifty-fourth in world fishery
production tonnage, as our waters are relatively nutrient poor and unable
to sustain large fish populations. (3) Fishing is Australia's fourth largest
primary industry, with a gross production of 218273 tonnes in 1994-95 and
a gross value of production (GVP) of $1744 million. (4) (See also Research
Note No. 55 On High Seas?-Australia's Fishing Industry). The GVP
is high because a significant portion of the commercial catch is highly
priced species such as prawns, rock lobsters, scallops and abalone.
Fisheries Management
Fisheries resources are usually managed in units termed ' a fishery'. A
fishery may be variously defined by (i) the area (e.g., the South East Fishery,
which extends from New South Wales down to and around Tasmania to South
Australia) or (ii) a combination of the area with a species (e.g., Northern
Prawn Fishery or East Coast Tuna Fishery) or (iii) a combination of the
area and the fishing gear/methods used (e.g., Western Deepwater Trawl Fishery).
By 1991 Commonwealth and State legislation had defined about seventy fisheries.
Concerns over exploitation levels of Australia's fisheries resources
have existed for over a century. A variety of fisheries management tools
has been used to conserve fish stocks. These include area closures during
spawning, minimum legal sizes, season closures, limited entry (only licence
holders with specific endorsement) and catch quotas. The Commonwealth
is currently emphasising 'output controls' such as 'total allowable catch'
(TAC) to restrict the catch to sustainable levels. An annual TAC is applied
to some species. The TAC is divided into 'individual transferable quotas'
(ITQs) within the fishery.
Status of Fish Stocks
Despite these efforts, nine of our species have been assessed as overexploited.
(5) About twenty-two of the one hundred-odd commercially fished species
are 'considered heavily or fully exploited to the extent that any higher
average catches could start to affect the stock replacement (recruitment)
potential of their populations.' (6) The Bureau of Resource Sciences says
that although nine species have been assessed as underexploited, there is
probably not much room for expansion of the total landed catch. (7)
Table 1. Status of Commercial Fisheries Resources under Commonwealth or Joint Jurisdiction
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Fishery Status Catch trend
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Northern Prawn Fully exploited Variable
Torres Strait Prawn Fully exploited Variable
Torres Strait Lobster Underexploited Variable
Northern Fish Trawl Underexploited by domestic fishers Unavailable
Northern Shark Underexploited by domestic fishers Stable
East Coast Tuna (Yellowfin) Uncertain Variable
East Coast Tuna (Skipjack) Uncertain: probably underexploited Declining
Southern Bluefin Tuna Overexploited Limited by quotas
Southern Shark School overexploited School declining
Gummy fully exploited Gummy stable
South East Fishery: 14 quota species 7 fully exploited Limited by quotas
1 underexploited
6 uncertain
South East Fishery: Eastern Gemfish Overexploited Limited by quotas
South East Fishery: Orange Roughy At or near full exploitation Declining, limited by quotas
Great Australian Bight: Uncertain Shelf stable, slopes declining
Shelf and Slope
Jack Mackerel Uncertain Variable
Squid Probably underexploited Stable
North West Slope Trawl Fully exploited Declining
Western Deepwater Trawl Underexploited Variable
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Source: Bureau of Resource Sciences, Fishery Status Reports 1994
For at least half of the commercially fished species there is insufficient
knowledge to determine the effects of fishing on stock levels. Table 1 illustrates
the status of fisheries under some form of Commonwealth management.
Sustainable fishing
Substantial knowledge is required to predict sustainable fishing levels
of our fisheries resources. The life history of each species is unique and
a great deal of biological information is required on factors such as growth,
reproduction, recruitment and mortality. Other factors such as interactions
with other species; the effects of changing oceanic conditions; the effects
of trawling (dragging a net across the sea floor) and pollution on habitats
and nurseries; the effects of fishing, not only on a target species but
also on its predators or prey; and patterns of behaviour, should also be
understood.
Orange Roughy
The orange roughy is an example of a species which was intensively fished
before key knowledge of its breeding cycle (it doesn't become sexually mature
until it is over 27 years old) and longevity (it can live to over 100 years)
became widely available. Commercial fishing began in earnest for this high
value species in 1986 with a recorded landed catch of 4200 tonnes (see above).
The catch peaked in 1990 at 45000 tonnes. The first TAC for the Eastern
area of this fishery of 24000 tonnes was introduced in May 1990. Improved
knowledge of the population dynamics of the orange roughy have seen the
TACs dramatically reduced. The most recent TAC (for 1996) was for 6500 tonnes.
A recent estimate of the long-term sustainable yield for orange roughy was
around 3000 tonnes for the whole South East Fishery. (8)
Uncertainty
Many of our fisheries resources are still not well known as most of the
research has been directed to the more valuable species (such as prawns
and southern bluefin tuna). Hence the large number of species (fifty-nine
out of one hundred) whose status is categorised as 'uncertain' or 'unknown'.
Endnotes
- FAO, The State of World Fisheries and Aquaculture, Rome 1995, p.47
- FAO, ibid. p.8
- FAO, ibid. p.52
- ABARE, Australian Fisheries Statistics 1995, Canberra 1995
- Kailola, Patricia J. et al, Australian Fisheries Resources, Canberra
1993, pp.404-7
- Kailola, P. et al., ibid. p.2
- Kailola, P. et al., ibid. p.2
- Tilzey, R. (ed), The South East Fishery, Canberra 1994, p.113
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