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| Trends in Vessel Tonnage
Tonnage, like most other definitions used in Fisheries Statistics, is not a straightforward concept. The Fleet Register contains a mixture of both Gross Tonnage (GT) and Gross Registered Tonnage (GRT) although neither is clearly defined in the Merchant Shipping Acts. Tonnage is also measured in a slightly different way for vessels over and under 25m in registered length. Tonnage is a volumetric measurement of vessel capacity. Table 6 shows that the total recorded tonnage of the vessels in the Scottish fleet increased by 26-28 per cent between 1986 and 1992, depending on whether or not there was actually any increase in the number of under 10m boats. After showing little change between 1993 and 1995 the tonnage suddenly increased by 13 per cent in 1996. The overall increase in tonnage since 1986 reflects an increase in the average size of vessel rather than in the number of vessels. Problems with the figures for the under 10m fleet mean that trends in overall vessel numbers are unclear. Table 6: Tonnage of the Scottish Fishing Fleet by Length Class, 1986-96
Since 1986 the average tonnage of a vessel has increased by about 3 per cent pa. However, the trends differ radically between the different vessel length classes. The under 10m sector has shown relatively little growth in average tonnage (0.6 per cent pa). In 1996, the average size was 3.3 tonnes per boat. The large reduction shown in Table 6 for 1993 seems more likely to be a statistical aberration than any genuine change. If, as seems likely, those under 10m vessels, which were incorporated into the register for the first time in 1993, were predominantly the smallest boats then their inclusion will inevitably have reduced the average tonnage from that year. The medium sized vessels also experienced little change in average tonnage over the 1986-96 period as a whole, as a decrease of -1.1 per cent pa prior to 1991 has been offset by an increase of 1.2 per cent pa since then. In 1996, these boats each averaged 35 tonnes. It is amongst the largest vessels of 25+m where the most rapid growth in average tonnage has occurred. After 1986, the average size of the 25+m vessels grew by 6.9 per cent pa to 291 tonnes in 1996. This represented an increase of 90 per cent for the ten year period as a whole. There was a particularly dramatic jump of 27 per cent in 1996. The growth in average tonnage has been most pronounced amongst the very large vessels of over 35m. Their average size grew by 4 per cent pa up until 1993, but has accelerated by 19 per cent pa since then. This, no doubt, reflects the aggregation of licences from medium sized boats onto fewer but much larger and heavier'super trawlers', although it is possible that the scale of the recent increase may have been exaggerated as a result of more vessels being measured on the basis of GT rather than GRT. The former gives rise to higher tonnage figures. It is apparent, therefore, that not only has the fleet been dividing into large and small vessel segments but that the former has seen a disproportionate increase in the average tonnage of its vessels, which have become both longer, wider and deeper. The smallest vessels have seen their total tonnage increase because of the growth in their recorded numbers rather than in the average size of such boats. An increase in average tonnage has been evident in the last two years. This is because the smallest vessels have to remain under 10m in length if their owners are to take advantage of the less stringent licensing conditions and this provides an incentive for them to increase capacity by investing in deeper draughted, broader and heavier boats rather than in longer ones. Trends in Vessel Power As vessels have increased in both length and tonnage, it might be expected that they would need to become ever more powerful in order to move them through the water, especially as the speed of many of the newer vessels is greater than that of their predecessors. Engine power is measured in kilowatts (kW). Table 7 shows that total recorded engine power has increased by 33 per cent since 1986, although the increasing coverage of under 10m vessels prior to 1993, as well as the inclusion of all such boats in 1993, have distorted this figure upwards. If the 1993 break in series is ignored, total engine power has increased, on average, by about 2 per cent pa since 1986. Table 7: Power (kilowatts) of the Scottish Fishing Fleet by Length Class, 1986-96
The overall figure for average power per vessel has been artificially dragged down in those years when additional under 10m boats suddenly appear in the statistics. The most obvious example of this occurred in 1993 when an extra 400 or so small boats entered the fleet register, leading to a 6.4 per cent fall in the overall average power per vessel in that year. A clear upward trend in average power per vessel is evident for all three length class groupings, ranging from 2.0 per cent pa for the medium and large vessels to 3.3 per cent pa for the small ones. These data are not without their problems. The small boat series is likely to have been distorted by the changes in coverage since 1986 whereas, for reasons explained below, the average power figures for large vessels appear to have become less reliable since 1993. In 1996, the figures for average power per vessel were 42 kW, 231 kW and 806 kW for small, medium and large vessels, respectively. Trends in Both Vessel Power and Tonnage Although all sectors of the fleet have seen an increase in both the average gross tonnage and power (kW) of vessels, as shown in Charts 1, 2 and 3, there are interesting differences between them. The small and medium sized vessels experienced a faster increase in average power than in average tonnage but the converse was the case for the large vessels. The more rapid growth in kilowatts than in tonnage probably reflects the need for additional power to work the extra gear and equipment now being carried on small and medium fishing vessels. However, such an explanation might also be expected to have applied to the larger vessels. In this latter case, it seems much more likely that the way in which the power figures have been recorded is different. The discrepancy between trends in average tonnage and average power for the large vessels has increased over time. Between 1986 and 1990 average tonnage grew at a rate that was 1.5 times higher than average power but since 1992 this rate has jumped to 10 times higher. The larger vessels have started to incorporate auxiliary power sources to work the increasingly varied and complex gear and electronic equipment which they carry. Since these are generally separate from the main engine driving the propeller they are not included in the declared figures for vessel power. In addition, the actual power figures can be under-recorded as a result of derating (limiting) the engine. This is a widespread practice and it is very difficult to ensure that such a reduction in power is permanently maintained. In practice, it is not difficult subsequently to change the rating of an engine simply by altering the fuel flow to the engine. Charts 4, 5 and 6 plot the growth in both total tonnage and power and show that the growth trends for tonnage and power in the large vessel sector are very similar between 1986 and 1993. After 1993 the trends suddenly diverge. If the 1986-1993 statistical relationship between power and tonnage is projected forward, based on regression analysis, it can be used to derive expected power figures for subsequent years on the basis of the actual tonnage figures in those years. These expected power levels can be compared with the actual ones to obtain an estimate of the total level of power that appears to have been under-recorded. Up until 1993, the power level in the 25+m fleet increased, on average, by 289 kW for every 100 tonnes of increase in fleet tonnage. On the basis of the regression relationship the projected level of power in 1993 would have been 169,200 kW which is very similar to the recorded level of 170,700 kW. However, since then the projected level has exceeded the recorded level by a rapidly increasing amount. Whilst this, no doubt, reflects the growing practice of derating engines, the previous tonnage/power relationship will have been distorted to the extent that there has been a shift from GRT to GT as the basis for measuring tonnage. Since power is an integral part of the VCU formula that is used to measure catching capacity this estimate suggests that VCUs are becoming a less meaningful measure of such capacity. Hence the impact of policies that seek to reduce effective catching capacity are likely to be over-stated if they continue to use VCUs as the basis for measuring their success. Conclusion Since 1986 there have been notable changes in the size and ownership location of vessels in the Scottish fishing fleet. It is more difficult to say anything about trends in the number of vessels because of the various data problems. The fleet structure has become increasingly polarised into large numbers of small vessels (under 10m) and a much smaller but growing number of big vessels (25+m) that are steadily increasing in average length, tonnage and power. The medium sized vessels have shown a steady decrease in numbers. The smaller vessels work close to the shore and mostly use creels to target shellfish, whilst the largest boats target pelagic species or engage in trawling for whitefish. The changing geographical distribution of the ports at which the ownership of the fleet is based reflects these trends. Those ports that are close to shellfish grounds, where creel fishing methods can be used by under 10m vessels, and those that provide both important markets, either for fresh fish or because of local processors, and can also accommodate the new generation of large demersal trawlers and pelagic vessels, have benefited from these trends and seen their share of the fleet ownership increase. The local availability of shellfish stocks in the Highlands and Islands explains why 71 per cent of the owners of small vessels are based in that area. In contrast, only 45 per cent of the owners of medium size and 20 per cent of the large vessels are located in the region. The ownership of the latter size of vessel has become increasingly concentrated into the larger ports of North East Scotland, Troon and into Shetland. There are a number of possible policy implications that arise from these trends. The increasing segregation of the fleet into small and large vessels suggests that there may be scope to build further on the differences in the management regimes applied to the small boat sector. Such vessels mostly fish close inshore, within the 12 mile limit for territorial waters, and predominantly target shellfish. This sector seems particularly well placed to experiment with ways of introducing some form of local/regional management of the stocks which they target. There is evidence to suggest that the power figures being declared by the large vessel sector have become less reliable since 1993. Since power is an integral part of the VCU formula that is used to measure catching capacity, this suggests that VCUs are becoming a less meaningful measure of such capacity. Hence the impact of policies such as licence aggregations and decommissioning fishing boats, which seek to reduce effective catching capacity, are likely to be over-stated if they continue to use VCUs as the basis for measuring their success. This suggests that it is desirable to try and find ways of making any VCU based definition of capacity more robust. The trends also have implications for harbour development policy. The wide spread of small shellfish boats around the coast suggests that there is a need for a large number of small but safe anchorages and basic landing facilities. In contrast the shift to ever larger vessels suggests that there is a requirement for a limited number of strategically located deep water ports to accommodate such vessels. There seems little point in investing in poorly located ports that, in the past, have depended on medium size boats to support their local infrastructure. Annex 1 Table 2A: The Number of Vessels by District and Length Class, 1986-96
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