On fluctuations and spatial distribution of catches in the Yugoslav sardine, sprat, anchovy, mackerel and Spanish mackerel fisheries

Abstract

        Important changes occurred in the Yugoslav pelagic fisheries after the second world war. Amongst these are a higher degree of motorisation of the fishing fleet, more extensive use of purse seines and the use of echo-sounders for fish detection. In spite of these changes and some other influences (among them the economic ones) some regularities appeared in the fluctuations of the annual catches of the sardine, sprat, anchovy, mackerel and Spanish mackerel fisheries and its spatial distribution as shown by an analysis of the official fisheries statistics for the periods 1931-40 and 1947-64.

        The Yugoslav fishing area in the period 1931-40 was smaller than in the period 1947-64 (it did not include the Slovenian Littoral, Istria and some islands). 

       No data on the fishing effort are available. Only data on the catches by weight were collected. The catch was not recorded according to the individual area, but according to the port of registry of the fishing boats, what introduced some error in the data on the spatial distribution of the postwar catch due to a greater mobility of the fishing fleet.

      The individual fishing areas were not the same in the two periods (Fig. 1). However, in two cases two individual areas were taken together when considering the spatial distribution of the catch in order to compensate for this difference.

       The annual catches of the Yugoslav sardine, sprat, anchovy, mackerel and Spanish mackerel fisheries exibited wider fluctuations in the period 1947-64 than in the 1931-40 one. This was partly due to the extension of the Yugoslav fishing area to more offshore grounds in the northern and central Adriatic in recent years (Figs. 2 and 3) *).

      It was only the annual catches of the mackerel fishery in the period 1947-64 which mostly showed some regularity in the fluctuations, a peak occurring every second, third or fourth year (Fig. 3).

      The trend in the annual catch of the sardine fishery was characterized by a marked decrease (b = - 0,17 thousand tons) and a high variability (s = 41.1%), (Table 1, Fig. 4). On the contrary, the catches of the sprat and anchovy fisheries showed a marked increase (for sprat b = 0.20, for anchovy b = 0.19 thousand tons) and a high variability (for sprat s = 35.5, for anchovy s = 45.8%), (Table 1, Figs. 4 and 6). It is significant that the fluctuations in annual catch of the Yugoslav anchovy fishery were similar to those of the quantity of the anchovy recorded in the Chioggia fishmarket (Fig. 7).

     The catch of the mackerel fishery showed a slight upward trend (b = 0.09 thousand tons) and a somewhat lower variability (s = 30.6%), while the catch of the Spanish mackerel fishery remained at about the same average level with a large variability (Table 1, Fig. 8).

     Some coincidence in the annual catch fluctuations of the anchovy and Spanish mackerel fisheries was recorded in the period 1947-64 (Fig. 3). On the contrary, the annual catches of the sardine and anchovy, the anchovy and mackerel, and the mackerel and Spanish mackerel fisheries showed some alternation in their fluctuations. The same coincidence and alternation tendencies were recorded in the annual catch fluctuations of these fisheries during 1931-40 in the East Mid-Adriatic (M u ž i n i ć, 1958). These tendencies continued, thereafter, in spite of the extension of the fishing area offshore and other influences.

      Moreover, in the period 1947-64 a tendency for the catch fluctuations of the sprat and anchovy fisheries to coincide was recorded, as well as a tendency of alternation in the catch fluctuations of the sardine and sprat fisheries (Fig. 3). A more marked alternation was found in the catch fluctuations of the sardine and sprat fisheries in the more northern part of the Yugoslav fishing area (Slovenian Littoral, Pula and Rijeka), (Fig. 5).

      Some dependence of the catch fluctuations of the sprat fishery on the mean annual temperature of the sea surface in the more northern Adriatic was recorded, which might point, at least to some extent, to fluctuations in the availability of the fish (Fig. 5).

      The annual catches of all the species combined showed smaller fluctuations than the annual catch of each species alone (Figs. 2, 3, 9 and 10). This was the consequence of the tendency of the catch fluctuations of the sardine fishery to alternate with those of some of the other species (Figs. 9 and 10). Thus, while there was a tendency for the annual catches of the sardine fishery to decrease (b = - 0.17 thousand tons), these of the sprat, anchovy, mackerel and Spanish mackerel fisheries combined increased (b = 0.47 thousand tons) and showed a variability lower than that of any species alone (s = 26.9%), (Table 1, Fig. 11) *). This increase was probably due for the most part to the extension of the Yugoslav fishing area more offshore.

      The range of the sprat was found to be more northerly and more restricted than that of the sardine, as shown by the distribution of their annual catches and their relative shares in the annual catches of the individual small areas within the Yugoslav fishing area (Figs. 13 and 15). In the Rijeka area the sprat replaced the sardine, to a great extent. These species showed more or less a vicarious character. The sprat was very scarce in the southern part of the Yugoslav fishing area.  

      The range of the anchovy appeared to be more northerly than that of the sardine, but only in the period 1947-64 (Figs. 12, 13, 14 and 15).

       The mackerel showed in both periods a more northerly range than the Spanish mackerel (Figs. 12, 13, 14 and 15). The Spanish mackerel was very scarce in more northerly part of the Yugoslav fishing area, as well as in the most southerly one.

      The sardine was not well-represented in more northerly part of the Yugoslav fishing area (Slovenian Littoral, Pula and Rijeka) in comparison with other species, excluding the Spanish mackerel (Figs. 16 and 17). The opposite was the case in more southerly part.

      In more northerly part of the Yugoslav fishing area the catch was more heterogeneous than in more southerly one (Fig. 15).

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*) The catch of the sprat fishery was recorded only in the period 1947-64.

*) The catch of the Spanish mackerel fishery had no influence.