14 



DEPARTMENT OF THE NATAL SERYICE 



6 GEORGE V, A. 1916 



PART ni. 



Conclusion. — ^Halibut is classified for the market according to size: chicken 

 halibut, ranging from 20 to 29 inches in total length from the end of the snont to 

 the middle of the edge of the tail-fin; medium halibut, 30 to 39 inches; large halibut, 

 from 40 inches upwards. They never approach maturity as " chickens." Accepting 

 the principle of the scale-markings as a basis for estimating the age, it is a singular 

 and useful fact, which follows from Professor McMurrich's observations and from 

 my own measurements, that at least up to the twelfth or thirteenth year the age of 

 the halibut is, with sufficient approximation, equal numerically to one-tenth of the 

 total length measured in centimetres. Thus a fish of 28 inches (= 70 centimetres) is 

 7 years old; another of 44 inches (= 110 centimetres) is in its eleventh year. The 

 proportions vary (perhaps by sex) and change as the fish grows. This may be illus- 

 trated by comparing the maximum expanse of the powerful tail-fin, measured across 

 from tip to tip, with the width of the body measured on the white side between the 

 bases of the median fins (see table below). It may be of interest to remark that the 

 great horizontal expanse of the tail-fin, considered in conjunction with the excep- 

 tional swimming powers possessed by the halibut, is paralleled by the horizontal tail- 

 flukes of the Cetacea and by the flattened tail of the beaver. 



Table of Correlated Measurements. 



The halibut is a hardy fish, coming to the surface without showing any reaction 

 to the change of pressure, and continuing to live for some time on deck after being 

 roughly shaken off the hook. Once I saw one disengage itself from the hook as it 

 reached the surface and return rapidly towards the bottom. It would therefore not 

 be difficult to select undamaged individuals and keep them alive in the well of a ship 

 for experimental purposes. The provision of a suitable well such as for many years 

 the Grimsby halibut boats in England have had, should form part of the equipment 

 of any vessel which may be detailed for the scientific branch of the fishery service in 

 the future. It would be a great advantage to observe halibut under experimental con- 

 ditions for a lengthened period so as to be able to test its viability, rate of growth, 

 and discharge of spawn. 



According to Dr. T. W. Wemyss Fulton (on the Eate of Growth of Fishes, 24th 

 Ann. Kep. Scottish Fishery Board, part iii, pp. 179-274, Glasgow, 1906) the approxi- 

 mate size of the female halibut at maturity is 48 inches, that of the male 30 inches. 

 As explained above, a length of 48 inches indicates an age of about twelve years. 

 Professor McMurrich came to the conclusion that the spawning period begins in the 

 eighth year and lasts without any decided interruption throughout the succeeding 

 four or five years. Fulton says that among flatfishes it is a common rule that the 

 male comes to maturity a year earlier than the female; thus the male plaice matures 

 at 4 years old, the female at 5. The female turbot attains maturity at the size of 17 

 to 18 inches, and at the age of 7 years. The turbot and plaice attain the same approxi- 



