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State of marine fishery resources

As pointed out by Grainger and Garcia (FAO, 1996), when a sufficiently long time series is available and marked changes in landings have occurred, the model described above may allow the present state of the fishery to be diagnosed, based on the development phase that it has reached.

In accordance with Grainger and Garcia (FAO, 1996), to compare each of the different time series, the data were first standardized by rescaling each time series so that the averages equalled zero and standard deviation (SD) equalled 1. Then, by comparing the data available in every two consecutive years of each time series, each resource-year element in the data was placed in one of three categories - increasing, little change or decreasing landings - depending on whether the slope of the series between the two years considered was more than 0.05, between + 0.05 and - 0.05, or less than - 0.05, respectively.

FIGURE 3: Percentage of major marine resources showing increases, little change and decreases in landings

The results of this classification are illustrated in Figure 3, which shows the percentages of the 21 species or species groups that fall into each of the three categories in a particular year. In spite of the oscillations observed, it can be noted that the percentage of the resources in the increasing category, which was about 35 percent at the beginning of the series, surpassed 70 percent at the end of the 1950s and oscillated around the 50 percent level until the mid-1980s. In the last ten years of the series, the percentage of resources in this category returned to its original level. The percentage of the resources showing little change diminished considerably over the entire period (from about 30 to only 2 to 3 percent). This category of stable landings corresponds to a latent undeveloped phase of a fishery before it starts to grow (Phase I), to stabilization at mature exploitation (Phase III) or, in a few cases, to a lower level after a fishery has collapsed (Phase IV). In any case, the decreased percentage of resources showing little change indicates that there has been a reduction in the number of developing or mature fisheries (Phase II or III) and confirms the tendency (similar to that of world fisheries) for the majority of fisheries to fall into one of two main categories: in expansion or in decline.

The standardized landings of each of the series were then fitted with a third-degree polynomial function calculating the slope of the fitted line for every successive pair of years, and the curves were sliced into segments corresponding to the phases of increasing, little change or decreasing. It was assumed that the phases of increase or decrease correspond to the developing (Phase II) or senescent (Phase IV) stages of fishery development, respectively. The phase of little change was subdivided into high-exploitation mature (Phase III) or undeveloped (Phase I) phases, depending on whether the observed period of little change was followed by a period of increase or not. Once the resources matching each profile had been identified, the percentage of resources in each phase was calculated for each year separately and for the whole data set. The overall pattern is illustrated in Figure 4. It clearly shows that in the mid-1950s most of the fisheries were undeveloped (Phase I) while, in the mid-1960s, they were nearly all in the developing phase (Phase II).

FIGURE 4: Percentage of major marine resources in various phases of fishery development

From the mid-1970s, most of the species or species groups were in the mature phase (Phase III) and the first cases of overfishing in the Cuban fishery sector were beginning to appear. The figure also shows that, in 1995, about 38.9 percent of the fisheries were in the senescent phase, 48.7 percent were in the mature phase with a high level of exploitation, and only 12.4 percent were in the developing phase with some possibility for growth.

FIGURE 5: Average standardized landings of shrimps, lane snapper and mangrove oyster1

1 The curve represents the fitted third-degree polynomial.

Landings trend profiles and fitted polynomials for several selected species or species groups are presented in Figures 5, 6 and 7.

FIGURE 6: Average standardized landings of Nassau grouper, gray snappers and mullets1

1 The curve represents the fitted third-degree polynomial.

Although some of the most important fisheries (i.e. those in Figure 5) exhibited the general trend predicted by the generalized fishery model (Figure 1, on page 6), marked decreases in landings of Nassau grouper, gray snappers and mullets are noticeable during the last 20 years (Figure 6). Only the landings of thread herring, mojarras (Figure 7) and turkey wing clam show a positive trend.

FIGURE 7: Average standardized landings of thread herring and mojarras1

1 The curve represents the fitted third-degree polynomial.

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