208 BULLETIN OF THE BUREAU OF FISHERIES 



dous production of mackerel eggs or practically none at all, corresponding to the 

 fluctuations in the stock of fish, and this generalization applies equally to all other 

 parts of the breeding range. In this respect conditions may vary widely in differ- 

 ent regions in any given year. In 1915, for example (the only year when we towed 

 consistently throughout the spawning season) , small egg catches combined with a 

 poor commercial catch of adult mackerel (p. 199) to suggest but little reproduction 

 for the Gulf of Maine, but this must have been a very productive year in the Gulf 

 of St. Lawrence, judging from the abundance of mackerel eggs the Canadian Fish- 

 eries Expedition found there. 



Mackerel spawn over a wide range of temperature and, schooling and spawning 

 near the surface as they often do, the eggs are produced in temperatures closer to 

 those in which they are to develop than are the eggs of most ground fish. We 

 have foimd odd eggs in the Gulf of Maine in water as cold as about 39° and as warm 

 as 64°, while the Canadian Fisheries Expedition towed a few in temperatures as 

 low as 38.8° and 40° off Halifax, but the chief production takes place between 46° 

 and 61°. This applies equally to the Gulf of St. Lawrence where Dannevig records 

 eggs in extremes of 42.6° and 61.7°, but where it seems they are produced in greatest 

 number when the surface water is between 46.5° and 59°."^ Mackerel spawn in the 

 whole range of salinity proper to the open surface waters of the Gulf of Maine in 

 summer, that is, from about 31.9 per cent to about 33 per cent, but never in brack- 

 ish water. 



The mackerel is a moderately prolific fish, females of medium size producing 

 360,000 to 450,000 eggs, but only a small part of these (40,000 to 50,000 on the 

 average) are spawned at any one time (p. 207). Mackerel spawn chiefly at night. 



The egg is buoyant, from 0.97 to 1.38 mm. in diameter, and with one large 

 oil globule. A large series of Gulf of Maine eggs measured by Welsh were 

 about 1.1 to 1.2 mm. in diameter with an oil globule of 0.3 mm. At a temperature 

 of 60 to 62°, incubation occupies about 96 hours; about 120 hours at 55° in the 

 hatchery. Newly hatched larvae are 3.1 to 3.3 mm. long with very large yolk sac 

 and numerous black pigment cells scattered over head, trunk, and oil globule. By 

 the time the larva is 6 mm. long the yolk has been resorbed, the mouth is formed, 

 and the teeth are to be seen. The eye is very large and the first traces of the caudal 

 fin rays have formed. The rays of the second dorsal and anal fins and the vcntrals 

 appear at about 9 mm.; the first dorsal when the larva is about 14 to 15 mm. long. 

 In fry of 22 mm. the dorsal and anal finlets are distinguishable as such and the 

 tail has begun to assume the characteristic lunate form, but the head and eye are 

 still much larger, the nose blunter, and the teeth longer than in the adult. At 

 50 mm. the little mackerel resemble their parents so closely that their identity as 

 such is clearly apparent. 



" Dannevig does not list the temperatures for the rich egg catches. 



