FISHES OF THE GULF OF MAINE 



323 



temperature of the water. Recent experiments 

 by Worley I3 (which corroborate early hatchery 

 experience) have shown that incubation takes 

 about 150 hours at 54°; 115-95 hours at 57°-61°; 

 about 70 hours at 64°-65°; and about 50 hours 

 at 70°; with normal development limited to 

 temperatures between about 52° (11° C.) and 70° 

 (21° C). 



Newly hatched living larvae are 3.1 to 3.3 mm. 

 long u with large yolk sac, and with numerous 

 black pigment cells scattered over head, trunk, 

 and oil globule which give them a characteristic 

 appearance. The yolk is absorbed and the mouth 

 formed, the teeth are visible, and the first traces 

 of the caudal fin rays have formed by the time the 

 larva is about 6 mm. long. The rays of the 

 second dorsal and anal fins and of the ventrals 

 appear at about 9 mm. (to end of caudal fin); the 

 first dorsal when the total length of the larva is 

 about 14 to 15 mm. The dorsal and anal finlets 

 are distinguishable as such in fry of 22 mm., and 

 the tail fin has begun to assume its lunate shape, 

 but the head and eyes still are much larger than in 

 the adult, the nose blunter, and the teeth longer. 

 At 50 mm. the little mackerel resemble their 

 parents so closely that their identity is evident. 



Rate of growth. — -The sizes of the mackerel fry 

 taken during the mackerel survey carried out by 

 the U. S. Bureau of Fisheries in 1932, 15 added to 

 other available evidence show that our mackerel 

 grow to a length of about 2 inches during the first 

 1 to 2 months after they are hatched, a rate about 

 the same as in British and Norwegian waters. 16 



This size is reached earlier or later in the season, 

 depending on the date when any particular lot of 

 fry was hatched. Thus mackerel fry of IK to 2% 

 inches obviously spawned that spring, have been 

 taken at Woods Hole, both in the first half of 

 June a and in the last 10 days of July, 18 fry of 

 2% to 5 inches in the first half of August, and fish 

 of about 6% inches at the end of that month. 

 Similarly, Captain Atwood found fry of 2 inches 

 and shorter in July in the Massachusetts Bay 



» Jour. Gen. Pliysio]., vol. 16, 1933, pp. 841-857. 



'* They shrink somewhat when preserved. 



'» See Sette (Fish. Bull. U. S. Fish and Wildlife Service, vol. 60, Bull. 38, 

 1943, pp. 173-178) for detailed statistical analysis of these. 



" See Ehrenbaum (Rapp. et Proces Verb., Conseil Perm. Internet. Explor. 

 Mer. vol. 30, 1923, pp. 21, 25) for a discussion of the early growth rate of the 

 European mackerel. 



» Bigelow and Welsh, Bull. U. S. Bur. Fish. vol. 40, 1925, p. 204. 



" Sette, Bull. U. S. Fish and Wildlife Service, vol. 50, Fish. Bull. 38, 

 1943, p. 178, fig. 8. 



region, i. e., about a month after the local mackerel 

 schools had spawned out. 



Fry of 3 % to 4 % inches (obviously of the same 

 season's crop because too small for yearlings) have 

 been taken at Gloucester in August, and Captain 

 Atwood reports them as 6% to 7 inches long, near 

 Provincetown by October. Many of these little 

 fish, up to 7 or 8 inches long (now large enough 

 to be caught in the fish traps and known as tacks 

 or spikes) are caught along the western shores of 

 the Gulf of Maine and along southern New Eng- 

 land during the fall. And measurements of 

 thousands of young mackerel from the Gulf and 

 from southern New England, compiled by the 

 U. S. Bureau of Fisheries, have shown that the 

 fry of the year average 8 to 9 inches, or longer, 

 by the end of their first autumn, before they leave 

 the coast for the winter. But broods produced 

 in different years may grow at different rates, 

 probably depending on feeding conditions, as 

 well as on the dates when they are hatched. 

 Thus fry spawned in the spring of 1927 averaged 

 8% inches in November, but those spawned in 

 1928 averaged 9% inches then. 



Our mackerel run about 10 to 11 inches long 

 in spring and early summer of their second year 

 of growth (they are known now as tinkers) , which 

 agrees closely with Stevens' 19 estimate for mack- 

 erel of the English Channel, based on studies 

 of scales and otoliths. They grow to about 12 

 to 13 inches by that autumn, or to 14 inches in 

 years of especially rapid growth, 20 and the year- 

 lings usually are a little longer in the Gulf of 

 Maine than at Woods Hole, and longer at Woods 

 Hole than off Long Island, N. Y. It remains 

 to be seen whether these differences are due to 

 temperature, to the varying richness of the food 

 supply, or perhaps to crowding. It is also a 

 question for the future whether the differences 

 persist into later life. The brood of 1923, which 

 may perhaps be taken as typical, averaged almost 

 14}£ inches in their third autumn, about 15% 

 inches in their fourth, about 15% inches in their 

 fifth, about 16 inches in their sixth, 16% inches in 

 their seventh, and about 16% inches in their 

 eighth years. Thus the American mackerel, like 

 the European, grows very slowly after its third 



'» Jour. Marine Biol. Assoc. United Kingdom, vol. 30, No. 3, 1952, pp. 

 549-568. 



" Fry spawned in 1927 averaged about 1331 inches but those spawned in 

 1928 averaged only about 12H inches in their second November according 

 to Sette. 



