9. EVALUATION OF THE FINDINGS

Critical analysis of the findings of large-scale acoustic surveys should be attempted after the completion of the processing/tabulation of the results of the main surveys. In this phase, the calculated estimates can be examined to throw light on the underlying relationship and effects of various factors. The computations required for such analysis are considerably more involved than those required for the preparation of straightforward detailed summary tables. The main topics to be covered during the critical analysis of the results of an acoustic research programme can be summarized as follows.

1. Temporal and spatial comparison of the calculated estimates; estimation of biomass seasonality pattern and for the various varieties of fish, estimation of biomass trends, estimation of the migratory pattern of pelagic stocks.
2. Existing relationship between the survey magnitudes and testing hypothesis.
3. Estimation of the existing relationship, if any, between total landings and biomass estimates over time.
4. Estimation of the existing relationship of the spatial distribution of the survey biomass with observed environmental conditions (temperature, upwelling, nutrients, primary production, currents, etc.)
5. Existing relationship of spatial distribution of the survey biomass with the distribution of eggs and larvae.
6. Estimation of the statistical availability of the target biomass (= is defined as the portion (percentage) of the target biomass which is accessible to the efforts of local fisheries) and statistical apparent density of the survey biomass (= is defined as the part (absolute) of the target biomass which is accessible to local fisheries).
7. Validation of the calculated biomass estimates, e.g., by using the results of related stock assessment studies;

As an illustration, we present below part of the results attained at the critical analysis of the findings of the conducted large-scale acoustic surveys off the south-west coast of India (IND/75/038). The prepared graphs (Fig. 9a, b, c, d, e, f) are charts in axonometric projection portraying, on an oblique projection, variations in the statistical availability and statistical apparent availability of the surveyed stocks (see above item 6):

Figure 9a:

The individual segments of the chart provide the temporal variations in the relative distribution of the target yearly average biomass between the inshore depth domain (0-50 m) and offshore depth domain (50-200 m), as well as the temporal variations of the yearly total landings expressed as a percentage of the target yearly average biomass.

Figure 9b:

The individual segments of the chart show the temporal variations in the relative distribution of the yearly average biomass of whitebait between the inshore depth domain (0-50 m) and the offshore domain (50-200 m), as well as the temporal variations of the yearly total landings of whitebait expressed as a percentage of the yearly average biomass of whitebait.

Figure 9c.

The individual segments of the chart portray the temporal variations in the relative distribution of the yearly average biomass of other varieties of fish between the inshore depth domain (0-50 m) and the offshore domain (50-200 m), as well as the temporal variations of the respective yearly total landings expressed as a percentage of the yearly average biomass of other varieties of fish.

Figure 9d:

The first segment of the trimetric drawing portrays variation of the offshore variation of the offshore target yearly average biomass over time (50 - 200 m) The second segment of the drawing portrays variation of the inshore target yearly average biomass (0-50 m) over time. The third segment of the drawing portrays variations of the yearly total landings over time.

Figure 9e:

The three segments of the trimetric drawing portray temporal variations of the yearly biomass of whitebait and estimated whitebait landings over time (see above Fig. 9d.).

Figure 9f:

The three segments of the trimetric drawing portray temporal variations of the yearly average biomass of other varieties of fish and observed landings over time (see above Fig. 9d.). Three segments of the trimetric drawing portray temporal variations of the yearly average biomass of other varieties of fish and observed, landings over time (see above Fig. 9d).

Among other things there were two important points which became apparent at the critical analysis of the findings¹ (IND/75/038):

1. There was an obvious lack of relationship between total landings and estimated biomass of target species (this is also confirmed by the low values of the estimated linear correlation coefficients), and
2. As the estimated biomass increases the shift in biomass occurs offshore, away from existing fishing effort (0-50 m), therefore fishing effort does not reflect these changes, or benefit from them directly.
¹ See: Bazigos, G.P. et al., 1980, Biomass estimates in the southwest coast of India (IND/75/038). Consolidation of the results of the Acoustic Programme of the Project. Vol. 1. Summary biomass estimates, methodology, Vol. 2. Detailed results, regional estimates, Vol. 3. Atlas of the resources. Cochin, FIRM-IND/75/038, Report 16, pag.var.

Figure 9a Target biomass: variations in statistical availability over time

Figure 9b White bait: variations in statistical availability over time

Figure 9c Other varieties of fish: variations in statistical availability over time

Figure 9d Target biomass: variations in statistical apparent densities over time

Figure 9e White bait: variations in statistical apparent densities over time

Figure 9f Other varieties of fish: variations in statistical apparent densities over time

Figure 9a:	The individual segments of the chart provide the temporal variations in the relative distribution of the target yearly average biomass between the inshore depth domain (0-50 m) and offshore depth domain (50-200 m), as well as the temporal variations of the yearly total landings expressed as a percentage of the target yearly average biomass.

Figure 9b:	The individual segments of the chart show the temporal variations in the relative distribution of the yearly average biomass of whitebait between the inshore depth domain (0-50 m) and the offshore domain (50-200 m), as well as the temporal variations of the yearly total landings of whitebait expressed as a percentage of the yearly average biomass of whitebait.

Figure 9c.	The individual segments of the chart portray the temporal variations in the relative distribution of the yearly average biomass of other varieties of fish between the inshore depth domain (0-50 m) and the offshore domain (50-200 m), as well as the temporal variations of the respective yearly total landings expressed as a percentage of the yearly average biomass of other varieties of fish.

Figure 9d:	The first segment of the trimetric drawing portrays variation of the offshore variation of the offshore target yearly average biomass over time (50 - 200 m) The second segment of the drawing portrays variation of the inshore target yearly average biomass (0-50 m) over time. The third segment of the drawing portrays variations of the yearly total landings over time.

Figure 9e:	The three segments of the trimetric drawing portray temporal variations of the yearly biomass of whitebait and estimated whitebait landings over time (see above Fig. 9d.).

Figure 9f:	The three segments of the trimetric drawing portray temporal variations of the yearly average biomass of other varieties of fish and observed landings over time (see above Fig. 9d.). Three segments of the trimetric drawing portray temporal variations of the yearly average biomass of other varieties of fish and observed, landings over time (see above Fig. 9d).