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3.3 State of resources by oceans

In a review of the state of world fisheries, Garcia and Newton (1994) showed that the annual relative rate of increase of world reported landings had significantly decreased since 1950, indicating that the maximum production from the world’s conventional marine resources under current exploitation regimes was being approached, and that the mean catches of the last few years were probably very close to that potential. Their analysis implicitly used the generalised model shown in Figure 23 where the relative rate of increase in landings during the developing and mature phases is used to estimate where the rate is zero.

The updated relationship for world marine landings is shown in Figure 27. For this world total plot and for those of individual areas and oceans, the annual total landings series (Ct) of fish, crustaceans and molluscs (including aquaculture) was smoothed by a simple three-year running average, and a simple linear trend line fitted to the smoothed values:

(Ct+1 - Ct)/Ct = at + b

Figure 27. Trend in the relative rate of increase of landings in all marine waters

The time series is shorthened to 1951 to 1992 by the processes of calculation and smoothing

The details of these regressions are given in Table 5. Figure 27 shows that for the total marine landings data there are large oscillations around the trend line which intercepts the axis in about 1999, the year in which the rate of increase statistically reaches zero, indicating that the theoretical maximum production of conventional resources has now been reached. The theoretical landings corresponding to each year can be calculated by applying the following equation iteratively, having started with the actual landings at the beginning of the time series:

Ct+1 = Ct (at + b + 1)

The maximum production according to the model is the value corresponding to the year when the rate of increase is zero. In this case the predicted maximum production for world marine fisheries with the present overall fishing regime (generally characterised by small sizes at first capture and significant discards) corresponds to about 82 million tonnes, a value close to the average landings of 1990-94 of about 83 million tonnes.

It is obvious that this crude global estimate of the world potential of conventional resources under the present regime of exploitation, which indicates that the world would be “at MSY” in 1996, is a composite, aggregate result which hides the increasing occurrence of overfishing on a multitude of stocks in many different areas as evidenced during the last half century.

Some disaggregation of the world data by major fishing area, would have the advantage of showing differences in stages of development and could also give some indication as to the fishery potential by area. To this end, the time series of landings totals for the Atlantic, Pacific and Indian Oceans, as well as the Mediterranean Sea (including the Black Sea) have been processed in the same way as the world marine total landings. For comparison, separate plots were made for the North Atlantic and North Pacific regions alone. Finally, the analysis was made for every major fishing area individually. As expected, the quality of the fit decreases with the level of aggregation. The results are summarised in Table 5, and selected plots shown in Figures 28 to 33.

Table 5: Parameters of the trendlines fitted to relative rates of landings increase data, estimated maximum production and first year in which the maximum production is reached. The time series is shortened to 1951-1992 by the processes of calculation and smoothing.

AREA (Years in regression)

Parameters a, b
Y = aX + b

R2

Max. prod.
(106 t)

Fully fished
in:

E.C. Atlantic (63-92)

- 0.0065, 0.15

0.46**

4.3

1984

N.E. Atlantic (51-92)

- 0.0012, 0.04

0.17*

11.6

1983

N.W. Atlantic (51-92)

- 0.0024, 0.05

0.34**

3.9

1971

S.E. Atlantic (51-92)

- 0.0044, 0.12

0.35**

3.2

1978

S.W. Atlantic (65-92)

- 0.0028, 0.10

0.07(1)

0.8

1997(1)

W.C. Atlantic (51-92)

- 0.0016, 0.07

0.14*

2.3

1987

E. Indian (51-92)

- 0.0009, 0.08

0.08(1)

(10.2)

2037(1)

W. Indian (51-92)

- 0.0006, 0.06

0.03(1)

(12.5)

2051(1)

Med. & B. Sea (51-92)

- 0.0003, 0.03

0.01(1)

(2.2)

????

E.C. Pacific (71-92)

- 0.0075, 0.12

0.33**

2.5

1988

N.E. Pacific (60-94)

- 0.0037, 0.12

0.19*

4.1

1990

N.W. Pacific (51-92)

- 0.0015, 0.07

0.32**

26.4

1998

S.E. Pacific (74-92) (.)

- 0.0051, 0,14

0.11*

29.1

2001

S.W. Pacific (70-92)

- 0.0068, 0.17

0.33**

1.1

1991

W.C. Pacific (51-92)

- 0.0019, 0.10

0.34**

10.9

2003

Antarctica (65-77) (.)

- 0.3027, 4.40

0.44**

(0.95)

1980

TOTAL

n.a.

n.a.

125.0

n.a

N. Atlantic (51-92)

- 0.0014, 0.04

0.38**

14.2

1980

Atlantic Total (51-92)

- 0.0018, 0.06

0.51**

21.4

1983

N. Pacific (51-92)

- 0.0016, 0.07

0.38**

29.5

1996

Pacific Total (51-92)

- 0.0020, 0.10

0.29**

54.3

1999

Indian Total (51-92)

- 0.0006, 0.07

0.06(1)

????

????

WORLD (51-92)

- 0.0015, 0.07

0.42**

82.1

1999

(**) Subjective degree of reliability: reasonable

(*) Subjective degree of reliability: less reasonable

(1) This very low slope, probably not significant, indicates a quasi constant, long term increase in landings which may indicate that the maximum has not been reached. The extrapolation largely beyond the observed data to find the intersection date and a value of the potential is highly unreliable.

(.) Regression excluded years when major fisheries were not in operation

Figure 28. Trend in the relative rate of increase of landings from the North Atlantic Ocean
The time series is shorthened to 1951 to 1992 by the processes of calculation and smoothing

Figure 29. Trend in the relative rate of increase of landings from the Atlantic Ocean

The time series is shorthened to 1951 to 1992 by the processes of calculation and smoothing

Figure 30. Trend in the relative rate of increase of landings from the Mediterranean and Black Sea

The time series is shorthened to 1951 to 1992 by the processes of calculation and smoothing

Figure 31. Trend in the relative rate of increase of landings from the North Pacific Ocean

The time series is shorthened to 1951 to 1992 by the processes of calculation and smoothing

Figure 32. Trend in the relative rate of increase of landings from the Pacific Ocean

The time series is shorthened to 1951 to 1992 by the processes of calculation and smoothing

Figure 33. Trend in the relative rate of increase of landings from the Indian Ocean

The time series is shorthened to 1951 to 1992 by the processes of calculation and smoothing

The coefficients of determination (R2) are generally not very high and some are really low, and so the results of this analysis must be considered with much caution. For the Indian Ocean the slope is extremely small and does not lead to any usable estimate of potential. In the following analysis, therefore, the total potential for the Indian Ocean has been taken as the sum of the separate estimates obtained for the Eastern and Western Indian Ocean (Table 5).

The potential for the world marine production has been estimated in three different ways producing very different results (Table 6):

(1) Directly from data aggregated to world totals (Potential = 82 million tonnes);
(2) Summing estimates made for each Ocean (Potential = 100 million tonnes)
(3) Summing estimates made for each FAO major fishing area (Potential = 125 million tonnes).
Table 6: Comparison between estimated potentials and average landings of the last 5 years (1990-1994) (all figures have been rounded)

AREAS

Potential
(A)

Landings
1990-94 (B)

Difference
(A-B)

Status2

E.C. Atlantic

4

3

1

O

N.E. Atlantic

12

10

2

O

N.W. Atlantic

4

3

1

O

S.E. Atlantic

3

1

2

O

S.W. Atlantic

1

2

-1

I

W.C. Atlantic

2

2

0

O

E. Indian

10

3

7

I

W. Indian

13

4

9

I

Med. & B. Sea

2

2

0

F

E.C. Pacific

3

1

1

O

N.E. Pacific

4

3

1

O

N.W. Pacific

26

24

2

I

S.E. Pacific

29

15

14

I

S.W. Pacific

1

1

0

O

W.C. Pacific

11

8

3

I

Antarctica

0.2

0.3

0.1

O

SUM OF AREAS

125

83

42


N. Atlantic

14

13

1

O

N. Pacific

30

27

3

F

Atlantic Total

21

21

0

I-F

Pacific Total

54

53

1

I-F

Indian Total

231

7

16

I

Med. & B. Sea

2

2

0

F

SUM OF OCEANS

100

83

17


WORLD

82

83

-1


1 Sum of the separate estimates for the Eastern and Western Indian Ocean
2 Overfished, Increasing, Fully fished (based on date when rate of increase = zero, Table 5)
The difference between the aggregate potential (in case 1 above) and the potentials estimated with somewhat disaggregated data (in cases 2 and 3 above), which amounts to 18 and 43 million tonnes respectively, could be interpreted as the potential improvement to total world production if all Oceans or major fishing areas were fished to their maximum, avoiding overfishing in all of them.

If a comparison is made, region by region, between the average landings of the last 5 years and the maximum potential production shown in Tables 5 and 6, and if we take into account the subjective degree of reliability of the trendlines (indicated by the number of asterisks on Table 5) it would appear that, relative to the present situation:

- an increase of 10 million tonnes might be possible (**),
- an additional increase of 17 million tonnes is less certain (*),
- an additional increase of 15 million tonnes is highly uncertain.
These possible increases, however, have to be considered with prudence for the following reasons.

First, there is a large difference between the present levels of production of the Indian Ocean (Eastern and Western areas together) of around 7 million tonnes, and the potential of about 23 million tonnes estimated from a regression with an extremely low coefficient of determination (Table 5). The slope is not significantly different from zero, but the intercept is, indicating a positive and relatively constant rate of increase of about 5% per year, reflecting the fact that the landings from the Indian Ocean are still growing exponentially despite the high variability observed. Some external validation may assist in determining the potential for Indian Ocean fisheries (see below).

Second, the same difficulty pertains to the Mediterranean which also shows a very weak, non-significant slope but a (smaller) positive intercept, indicating that the Mediterranean Sea production keeps increasing. This is, however, one of the longest exploited seas in the world and most of its resources have been declared fully fished or overfished for years, and sometimes decades. Caddy et al. (1995) noted that despite such assessments, Mediterranean landings continued to increase slowly but steadily and hypothesised that such increase might be due to an increase in productivity due to eutrophication. A possible interpretation is that this sea is fully fished (in terms of the present fishing regime) even though its productivity might be growing, in effect displacing upwards the entire fishery development model shown in Figure 23. Given the uncertainty as to whether eutrophication will continue to increase production, it is assumed for this analysis that the potential production corresponds to present production.

Third, the Southeast Pacific also represents a major uncertainty with an estimated potential of 29 million tonnes when actual production has only reached 15 million tonnes (Table 6). This is an area with a long history of large fluctuations in landings and of fishery collapses (Peruvian anchoveta). It is also an area where major fisheries developed since 1970 on new species such as Chilean jack mackerel and South American pilchard and, for this reason, the smoothed time series used in the analysis was shortened to 1974-1992 (Table 5). Thus, with highly variable landings and a truncated series, the estimated potential for this area is uncertain and may well be unrealistically high. It is not believed that there are large under-exploited demersal resources and, although cephalopod fisheries can be developed further, their potential is unlikely to provide anything like the extra 14 million tonnes indicated by this analysis.


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