428
Chapter 11: The Pacific Ocean
the earliest of which I have a record was performed by the Singapore fisheries department
in 1926. The well-documented survey by Ommaney (1961) of the Gulf of Thailand gives
us an invaluable record of the nearly pristine structure of the demersal fish populations.
More recent surveys record a dismal decline of the once-dominant species and of overall
fish biomass that has attracted much attention internationally, so much so that the Gulf
of Thailand served as the exemplar for Pauly’s paradigm of “fishing down the food web”
(e.g., Pauly and Chuenpagdee, 2003). However, the problems of maintaining sustainable
fisheries are not what we are about here, and more to the point is that a massive alteration
of the entire shelf ecosystem has occurred. Attempting to model how this ecosystem might
function (e.g., Pauly and Christensen, 1993) has, as elsewhere, become like trying to hit a
moving target: to understand its pristine state is now very difficult and perhaps impossible.
It will be sufficient here to draw attention to some features of the pristine state of the
benthic ecosystem as far as it can now be discerned; the general arrangement of ecotypes
apparently followed the same pattern as on other tropical shelves. The near-permanence of
thermal stratification in the tropics at least doubles the number of characteristics ecotypes,
by permitting the development of warm-water and cool-water faunas of both invertebrates
and fish. Elsewhere, the cool-water fauna has many elements that are enabled to penetrate
from higher latitudes into the tropical zone, and the same is undoubtedly true here.
The overall pattern is very like that described for the eastern Atlantic (see GUIN) except
that here the depth at which the thermocline intercepts the shelf is much deeper. The
pristine fauna was dominated by the same families (Ariidae, Drepanidae, Polynemidae,
Sciaenidae) as occur everywhere on tropical shelves that are not invested with coral reefs,
together with some Indo-West Pacific endemics (Leiognathidae, Lactaridae). Between
1963 and 1982, this fauna in the Gulf of Thailand was reduced to 17% of its original
biomass, so that squid (Loligo spp.) have replaced leiognathids as the dominant group
in terms of biomass. A more recent review suggests that demersal biomass of fish in
the Gulf of Thailand has progressively declined from around a standing stock of around
700,000 tons in 1960 to less than 50,000 in 1995; similar declines are recorded on the
NW Borneo shelf and on the Phillipine coasts (Stobutzki, 2006).
The demersal fish fauna of the Timor Sea, the Gulf of Carpentaria, and the Arafura
Sea were surveyed (266 standard trawl hauls) by Okera (1982), who used recurrent group
analysis to specify the characteristic fauna of six habitats: neritic mud (15–20 m), inner
shelf muddy sand (10–50 m), offshore sands (80–90 m), midshelf mixed deposits (60–
110 m), shelf break mixed deposits (120–220 m), hard bottoms of boulders at all depths.
With each of these habitats is associated a characteristic group of 10–20 species, such
that the genera associated with each resemble genera on similar deposits elsewhere in the
tropics. A very similar result was obtained in the Ragay Gulf, in the Philippines, by Jamir
(1999), who applied statistical procedures, including cluster analysis, to describe three
depth zones (warm < 90 m, cool 90–150 m, and cold >150 m) depths of mixed layer,
thermocline, and subthermocline water. There is some rearrangement of this distribution
during major ENSO events, as in 1982–83. Within each zone, the important determinants
of fish population structure is bottom type, benthic food biomass, and effects of river
effluents. A very similar arrangement has been described for the shelf of the South
China Sea, partitioned at 40, 100, and 200 m; here, the shallow partition is dominated
by lizardfish (Saurida) and the middle zone by snappers and bream (Pagrus, Dentex,
Lutjanus, et al.) and ponyfish (Leignathidae).
Synopsis
Case 4—Small-amplitude response to trade-wind seasonality—The SUND province has a
very shoal pycnocline because of the extent of the surface brackish layer of river water.
The mixed layer is 15–25 m in all months, the photic depth being deeper at about 40 m;
Chapter 11: The Pacific Ocean
the earliest of which I have a record was performed by the Singapore fisheries department
in 1926. The well-documented survey by Ommaney (1961) of the Gulf of Thailand gives
us an invaluable record of the nearly pristine structure of the demersal fish populations.
More recent surveys record a dismal decline of the once-dominant species and of overall
fish biomass that has attracted much attention internationally, so much so that the Gulf
of Thailand served as the exemplar for Pauly’s paradigm of “fishing down the food web”
(e.g., Pauly and Chuenpagdee, 2003). However, the problems of maintaining sustainable
fisheries are not what we are about here, and more to the point is that a massive alteration
of the entire shelf ecosystem has occurred. Attempting to model how this ecosystem might
function (e.g., Pauly and Christensen, 1993) has, as elsewhere, become like trying to hit a
moving target: to understand its pristine state is now very difficult and perhaps impossible.
It will be sufficient here to draw attention to some features of the pristine state of the
benthic ecosystem as far as it can now be discerned; the general arrangement of ecotypes
apparently followed the same pattern as on other tropical shelves. The near-permanence of
thermal stratification in the tropics at least doubles the number of characteristics ecotypes,
by permitting the development of warm-water and cool-water faunas of both invertebrates
and fish. Elsewhere, the cool-water fauna has many elements that are enabled to penetrate
from higher latitudes into the tropical zone, and the same is undoubtedly true here.
The overall pattern is very like that described for the eastern Atlantic (see GUIN) except
that here the depth at which the thermocline intercepts the shelf is much deeper. The
pristine fauna was dominated by the same families (Ariidae, Drepanidae, Polynemidae,
Sciaenidae) as occur everywhere on tropical shelves that are not invested with coral reefs,
together with some Indo-West Pacific endemics (Leiognathidae, Lactaridae). Between
1963 and 1982, this fauna in the Gulf of Thailand was reduced to 17% of its original
biomass, so that squid (Loligo spp.) have replaced leiognathids as the dominant group
in terms of biomass. A more recent review suggests that demersal biomass of fish in
the Gulf of Thailand has progressively declined from around a standing stock of around
700,000 tons in 1960 to less than 50,000 in 1995; similar declines are recorded on the
NW Borneo shelf and on the Phillipine coasts (Stobutzki, 2006).
The demersal fish fauna of the Timor Sea, the Gulf of Carpentaria, and the Arafura
Sea were surveyed (266 standard trawl hauls) by Okera (1982), who used recurrent group
analysis to specify the characteristic fauna of six habitats: neritic mud (15–20 m), inner
shelf muddy sand (10–50 m), offshore sands (80–90 m), midshelf mixed deposits (60–
110 m), shelf break mixed deposits (120–220 m), hard bottoms of boulders at all depths.
With each of these habitats is associated a characteristic group of 10–20 species, such
that the genera associated with each resemble genera on similar deposits elsewhere in the
tropics. A very similar result was obtained in the Ragay Gulf, in the Philippines, by Jamir
(1999), who applied statistical procedures, including cluster analysis, to describe three
depth zones (warm < 90 m, cool 90–150 m, and cold >150 m) depths of mixed layer,
thermocline, and subthermocline water. There is some rearrangement of this distribution
during major ENSO events, as in 1982–83. Within each zone, the important determinants
of fish population structure is bottom type, benthic food biomass, and effects of river
effluents. A very similar arrangement has been described for the shelf of the South
China Sea, partitioned at 40, 100, and 200 m; here, the shallow partition is dominated
by lizardfish (Saurida) and the middle zone by snappers and bream (Pagrus, Dentex,
Lutjanus, et al.) and ponyfish (Leignathidae).
Synopsis
Case 4—Small-amplitude response to trade-wind seasonality—The SUND province has a
very shoal pycnocline because of the extent of the surface brackish layer of river water.
The mixed layer is 15–25 m in all months, the photic depth being deeper at about 40 m;