(from "Report of the Scientific Committee" of 1968 meeting)

Fin whales
12. The Committee had before it several different analyses of the Antarctic fin whale population as well as the F.A.O. catch analyses. Last year the Committee noted that the new interpretation of growth layers in ear plugs would require reconsideration of the recent estimates of the size, net recruitment rate and sustainable yield of the fin whale stock. Most of the analyses do take into account the revisions necessary and it is now agreed that the original estimates of the Committee of Three, and those based on them in subsequent up-datings, underestimated the size of the total fin whale population. On the other hand the Committee of Three also overestimated the net recruitment rate.

13. Mr. Allen presented an analysis using a method developed and used by him with North Pacific data that estimates the gross recruitment from the age composition of the catch and in turn uses these estimates together with the catch and effort data for the seasons 1945/46 to 1964/65 to calculate stock sizes and yields. The resulting estimate of the gross recruitment rate as based on the total recruited stock in the parent year is 6% leading to a net recruitment rate of 4.5%, since the natural mortality coefficient used here is 0.015. His estimate of the present population size is 60,000 and of the sustainable yield in 1969/70 is from 1,000 to 2,800.

14. Dr. Chapman presented a different method of estimating stock size and present yield which depends on decline in catch per unit of effort and a knowledge of the rate of net recruitment. A rate of net recruitment was calculated from the revised age readings and was found to be about 4%. Using another method and the age data of IWC, 14, pp. 49-54, suitably adjusted, he calculated the gross recruitment rate to be 0.09 and hence, using the Japanese estimate of the natural mortality coefficient which is 0.04, obtained an estimate of the net recruitment rate equal to 0.05. On this basis the present population size is estimated to be 56,000 and the sustainable yield in 1969/70 is 2,900.

15. Dr. Doi and his colleagues reported on the stock assessment using methods and parameters such as age composition for the period 1931/32 to 1967/68 based on new age-length keys, age at recruitment and sexual maturity, marking and sighting. They calculated that the natural mortality coefficient is 0.0415 and derived the population size using calculated catchability coefficients. In this connection they maintained that the catchability coefficient actually is not constant, and that maximum sustainable yield cannot be calculated if net recruitment rate is assumed to be constant. Reproduction curves were obtained from a trial and error method. As a result, they estimated that the maximum sustainable yield was 8,000 - 10,000 and the net recruitment was 4 - 6% at that stock level; and the present net recruitment rate (5 - 7%) is higher than that at the stock level which would give maximum sustainable yield. Using these curves they estimated that the present population size is between 45,000 and 95,000 and that the sustainable yield in 1969/70 is between 3,400 and 5,600.

16. The range of estimates of sustainable yield for 1969/70 in these analyses and by F.A.O. is thus 1,000 to 5,600. Most members believe the best estimate of the sustainable yield for 1969/70 is 3,300 or less. Japanese scientists believe that the best estimate of sustainable yield for 1969/70 is 4,900 to 5,600 and that it is not possible to give a single estimate within this range.

17. As is clearly shown above the scientific groups obtained different estimates of sustainable yield. This is due to the fact that the methods and assumptions used in the analyses are different. The Scientific Committee therefore recommends that to study these questions in greater detail and to obtain more precise estimates, a meeting be held to discuss and review methods of fin whale stock assessment early in 1970.

Sei Whales
18. The methods of assessments of sei whales underwent a thorough review at the Committee's meeting prior to the 20th meeting of the Commission. While there are still problems due to the uncertainty of sei whale biology and the varying emphasis of the expeditions on fin and sei whales there is agreement that the best estimate of sustainable yield of sei whales in the Antarctic at this time is about 5,000.

Blue and Humpback whales
19. Dr. Ohsumi made available an analysis of Japanese sighting data on these species; this analysis suggests a possible increase in pigmy blue whales in Area III but otherwise little evidence of change. Japanese scientists hope to make a complete analysis of all data on blue and humpback whales during the next year at which time the committee will review the prohibition on these species again. At this time it does not suggest any change.

Fin whales
20. The Committee had before it assessments by Japan based on a continuation of last year's methods, and by U.S.S.R. The latter country submitted a mathematical document which requires additional study. The Committee will review it at a later meeting. Japanese scientists noted that present assessments of the fin whale stock in the North Pacific pose some problems. The assessments indicate that stocks are below the level giving maximum sustainable yield in the Eastern North Pacific Ocean.

21. The sustainable yield of fin whales in the total North Pacific, excluding the East China Sea, is estimated to be 1,640.

Sei whales
22. The present sustainable yield of sei whales is estimated to be between 1,200 and 2,200 (average 1,700) but the maximum sustainable yield is probably somewhat higher than this, 2,300 to 2,700 (average 2,500). There is no doubt that the 1968 catch of 5,739 sei whales was much above the present sustainable catch and also above the maximum sustainable catch. The assessments suggest there is still a surplus available but this surplus will be used in a few years and at this time there will need to be a substantial reduction of catches if the population is not to be depleted. Since the size of the surplus is uncertain and higher levels of catch reduce the surplus more rapidly, the Commission is urged to take steps to ensure that the sei whale stocks are not reduced to the level below that giving maximum sustainable yield. The danger of this can be reduced if the level of catch is reduced from the present high level.

Blue and humpback whales
23. The Committee received an analysis of Japanese sighting data from Dr. Ohsumi. This shows a slight increase of blue whales but no increase is evident in the humpback population. The Committee will review the data again next year with a view to making a recommendation to the Commission relative to the present ban on killing these species. This ban for both of these species terminates at the end of 1970.

Gray whales
24. The Committee expressed its appreciation of the full reports received from the United States on results obtained under previous special permits for studies of gray whales. It urged continuation of these studies according to the plans indicated. It suggests that the work to develop a satisfactory mark for whale calves should be carried on. It also notes that a scientific collection of gray whales in their feeding area would be very useful and hopes that some national group will undertake this.

North Atlantic baleen whales
25. The Committee had before it a paper by Mr. Allen and Dr. Mitchell on the Northwest Atlantic summarizing not only recent fin whale catches but also earlier catches of baleen whales. The Committee noted that Canada has a quota on its fin whale catches based on the best scientific evidence available on the status of the stocks. The Committee discussed the status of fin whale stocks in other areas of the North Atlantic but found no evidence upon which to base any recommendations. All the data seem to suggest that the blue and humpback whale stocks in the Northwest Atlantic were originally quite small and that under exploitation prior to closure they were seriously depleted. There has perhaps been some rebuilding of humpback stocks in the Northwest Atlantic but evidence is limited. Such sightings data as are available do not suggest any substantial increase of blue and humpback whales elsewhere in the North Atlantic. In these circumstances the Committee recommends that the present ban on killing humpback whales in the North Atlantic (which terminates 8th November, 1969) and on killing blue whales in the North Atlantic (which terminates 24th February, 1970) be extended three more years at present. It is urged that companies operating in this area provide sighting data on prohibited species in the interim.

26. The only new information available on sperm whales in the southern hemisphere is the paper by Mr. P. Best. His conclusion is that "the present level of exploitation of male sperm whales in the south-east Atlantic, and particularly of mature males, must be viewed with concern". Unfortunately, for most of the southern oceans the sperm whale stock situation is still unclear and hence the Committee can give no new advice on management of these sperm whale stocks.

In view of our continuing lack of assessment of sperm whales except in the North Pacific, it is recommended that a meeting to study sperm whale biology and methods of assessments and if possible to make assessments for all stocks be held, early in 1970.

27. The Committee had available to it a very thorough analysis by Dr. Doi and Dr. Ohsumi on North Pacific sperm whale stocks. These support the conclusions stated in our report last year that the present catches of males exceed the sustainable yield. While there is still a surplus of males to support such catches, when this surplus is exhausted there will have to be a sharp reduction of catches. The Committee noted the recent increase in catches of female sperm whales and that total catches of females remain slightly below the level of sustainable yield. Considering the North Pacific sperm whale catch as a whole the Committee recommends that there be no further increase.

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