4. PRODUCTION MODELS

4.1 Catches
4.2 Present level and recent trends of nominal effort
4.3 Catch per unit effort
4.4 Potential yields and present levels of exploitation

4.1 Catches

Catch statistics broken down by years, species groups, countries, CECAF statistical divisions and, as far as possible, main fishing grounds are given in tables 3 and 4. Among the countries fishing appreciable quantities of cephalopods, Greece, Korea, Portugal and USSR still fail to report - at least for all years - their catch statistics according to the breakdown (species groups/statistical divisions) adopted by CECAF. Therefore, some assumptions or guesses had to be made when preparing these tables. Some misidentifications are also likely. For instance, USSR has reported catches of squids only. As, according to all evidence, this country also takes some quantities of octopus and cuttlefishes, one wonders whether such amounts are included in the reported squid catches or remain unreported.

However, as more appropriate statistics are available for two major fishing countries (namely Japan and Spain), the catch tables prepared by the Group shall give a fairly good picture of the respective role of the main species groups, countries and fishing areas. As an example, the origin of the production by CECAF statistical areas is presently known for about 80% of the total catch.

By species, octopus is contributing some 60-70% of the total catches, squids 20-25% and cuttlefishes 10-20% (table 3). By countries, Spain has been on the average fishing more than half of the overall catch (52%) during the last three years. It is followed by Korea (20%), Japan (16%), USSR (5%) and Italy (4%).

The Group also attempted to estimate the contribution of the main fishing grounds indicated on maps 1 to 3. This was made more speculative because only Japan collects its data by small statistical squares (30'). Fortunately, until 1976 Spain restricted its operations within the northernmost grounds (Cape Garnett/Cape Barbas). Therefore, some reasonable indications can be derived from the existing data. Assuming that the Korean operations have a similar area distribution as the Japanese ones, the following percentages are obtained (table 4):

Main fishing grounds	Contribution (% of the total production of the area)
Cape Garnett/Cape Barbas	@ 75%
Cape Blanc	> 20%
Nouakchott	1%
Cape Verde (south)	2%

The contribution of the last fishing ground (Cape Verde, south) is, however, likely to increase in the future since, as it has been noted above, the development of a cephalopod fishery in this sector is very recent.

Finally, it should be observed that the overall production has notably decreased in recent years, from around 200 000 tons in the period 1972-75 down to 166 000 tons in 1977. This decline affects all the three species groups. However, it is less marked for squids.

4.2 Present level and recent trends of nominal effort

Table 5 gives available information on fleet sizes for the last few years. Recently, Japan has appreciably reduced its operations; most of its largest vessels have now left the area. Only the smaller boats have maintained their level of activity (Appendix 3, table 2). Many of the latter now operate under various fishing agreements with coastal countries. In addition, since 1976, a shift in the geographical distribution of effort has been observed: many vessels operating previously in the Cape Garnett - Cape Barbas sector have moved south of Cape Blanc.

Spain has steadily increased its effort until 19751 progressively replacing Japan as the first producer in the area. Its effort has tended to stabilize in recent years. Until 1977, Spanish vessels have been operating only north of Cape Blanc but, since that date, a growing proportion have moved south.

Little detailed information is available on the activities of Korea, the production of which has also passed recently before the Japanese catch. Its fleet has regularly grown until 1976 and has probably stabilized (at a size of about 100 trawlers) since. This development has to some extent counterbalanced the decline of Japanese operations. For Korea as well, a shift from the northernmost grounds to the south ones is reported.

4.3 Catch per unit effort

Catch per unit effort covering the whole period of exploitation is available from Japan, Portugal and Spain. Japanese indices of abundance (Appendix 3) are given separately for octopus, cuttlefishes and squids. They all refer to the Sahara Division, i.e. to the Cape Garnett - Cape Barbas and Cape Blanc grounds combined, with one exception: one additional series refers to the cuttlefish in the Cape Verde Division, i.e. essentially from the Nouakchott ground.

Spanish cpue's correspond to the fishing activities in the area north of Cape Blanc. Until 1974 data have been collected in tons per trawling hours from that part of the fleet supplying the factory vessel "Galicia". After that date, data are given in tons/day fished by trawlers belonging to the same fleet. After 1975, the quality of these data has dropped. However, since the same date, cpue are collected from the other part of the fleet, i.e. from the freezer trawlers which represent about 95% of the total Spanish fleet. These three cpue series have been combined in a single one (tables 6, 7, 8 and 9). Generally, the Japanese and Spanish cpue's fit well together in the sense that they show a parallel rate of decline in stock abundance over time.

Portuguese data were not used for they correspond to vessels fishing mainly for hake, i.e. in average on deeper grounds. In fact, the percentage of "molluscs" (no smaller breakdown is given in the data reported by Portugal, but this category was assumed to consist mainly of cephalopods) never represented more than 10$ of the total Portuguese catch. In addition, this percentage has declined over the last 15 years, suggesting that a change in target species and area of operations has occurred.

Although the Japanese and Spanish cpue should, to a large extent, be referred to specific fishing grounds, there are no separate catch statistics for each fishing ground and species group which would cover also the whole period of exploitation. Only the catches coming from south of Cape Verde could be identified. They were eliminated from these assessments, as exploitation there has started only recently. Assessments were essentially made for each cephalopod species groups corresponding to the entire area north of Cape Verde. Considering the respective contribution of the various fishing grounds to the overall production, it is clear that these assessments correspond essentially to the Cape Garnett/Cape Barbas and Cape Blanc stocks.

As Japan has been for a long time almost alone to exploit the Nouakchott ground, an assessment based only on Japanese cpue and catches has been also attempted for the cuttle-fish in this sector.

For the production models, Japanese and Spanish cpue series have been combined - proportionally to the respective national catches - each time cpue's from the two sources of data were available. In addition, to estimate the total annual catches for each major species groups (octopus, cuttlefishes, squids) the unallocated quantities (few percents) have been broken down proportionally to the quantities reported by species groups.

4.4 Potential yields and present levels of exploitation

The data finally used for assessing the stocks a given in the tables 6 to 9. In the application of the production model, the indices of abundance and the total effort of the same years were correlated for octopus, cuttlefishes and total cephalopods. It is only for the squids (fig. 6), which are supposed to live longer, that the average of the current effort and that of the previous year was used. The change in cpue vs effort was represented by a semi-logarithmic equation, utilizing a functional regression to adjust the curve to the observed values.

Generally speaking the correlations are good for octopus (fig. 4, cuttlefishes (fig. 5) and total cephalopods (fig. 7). The observed values are more scattered for squids (fig. 6); this is probably due to the erratic distribution of squid concentrations and the resulting sporadic nature of their exploitation.

It should be observed that the distribution of effort over the various species components is likely to change with time and that such variations can slightly modify the precise shape of the various yield curves. In fact, it seems that in recent years relatively more attention has been given to the squids. With this change in the pattern of fishing a higher rate of exploitation has resulted for that species category and, now, squids appear to be as intensively exploited as octopus and cuttlefishes ^1/. Such shift in target species is also reflected in the species composition of the Spanish catches where the proportion of squids has increased in recent years.

^1/The third session of the CECAF Working Party on Resource Evaluation (Rome, February 1976) concluded that in 1974, while the octopus and cuttlefishes stocks were over-exploited, the average production of squids could still be slightly increased by more intensive fishing

These computations lead to the conclusion that all cephalopod stocks located north of Cape Verde were overexploited in 1977, the last year for which data are available. Depending on the species group, the efforts exerted were apparently between 30 and 95% higher than those corresponding to the theoretical average máximum yield (table 10). This conclusion is in agreement with the one reached by the CECAF Working Party on Resource Evaluation at its Third Session (Rome, February 1976). It is also in accordance with the observations made on natural and total mortalities of octopus (section 3.2). With the apparent full exploitation of squids, the last opportunity for expansion has disappeared.

It should be noted that the effort exerted on the various species groups (with the exception of squids) has tended to stabilize in recent years, probably partly because of the decline in catch rates down to unprofitable levels and partly because of the difficulties, related with the changes in the ocean regime, encountered by some fleets to have access to their traditional grounds. The decrease in total yield observed since 1972-75 for the sector as a whole has therefore probably two causes: an excessive exploitation of the stocks combined, for the last few years, with a moderate reduction in fishing effort. The last column in table 10 shows, however, that such reduction remains insufficient.

Because of the lack of appropriate data, no assessment of the stocks south of Cape Verde could be made.