Fishery bulletin of the Fish and Wildlife Service - NOAA

BIOLOGY OF THE ATLANTIC MACKEREL 209
TABLE 13.—Size of mackerel at maturity a» indicated by 1,116 individuals taken by traps in the
vicinity of Woods Hole, Mass., and in Massachusetts Bay during the period, June 24 to July SI,
1986.—Continued.
36.5
37.0
37.6
88.0 - - -
88.Я
39.0
S9.5
40.0
Total
Total
More than 40 + -. ... ... . *. .. .
Grand total. ,
Immature
Number 3
3
1
348
Males
Mature
Number 76222
19
2
2 1
S
23
230
Mature
Percent
86
100
96
Immature
Number
1
METHODS OF COLLECTING EGGS AND LARVAE
2
440
Females
Mature
Number 73422
18
2
2
14
98
Mature
Percent
Mackerel eggs and larvae were collected during the spawning season in the spring
of each year from 1926 to 1932, inclusive. The initial work was exploratory and qualitative
in nature. Tows during the period 1926 to 1929 were drawn horizontally at
the surface, mid-depth, and just above bottom. In 1930 and 1931 oblique hauls were
employed. In 1932, oblique hauls were continued, and a device employed to measure
the quantity of water strained through the nets. The following description refers to
tbe collections made during 1932.
Nets used.—The plankton net used during the first 7 cruises was 1 meter in diameter
at the mouth, and 4 meters long. The first meter of length was cylindrical and
composed of No. 0 millers' gauze with 15 meshes per lineal centimeter, and for the last
3 meters the shape was conical and the material of No. 2 gauze, with 21 meshes per
lineal centimeter. At the end of the cone, attached by a coupling device, was a
"cod-end" 5 inches in diameter and 10 inches long, of No. 12 gauze, in which the catch
collected. During the ninth and tenth cruises, a stramin net was used, which was
2 meters in diameter (at mouth), and of the same proportions as the meter net.
Method oj towing,—To sample uniformly throughout the range of vertical distribution,
of eggs and larvae, the method of oblique towing was used. ' This consisted
of paying out an amount of line appropriate for the maximum depth to be reached by
the particular tow, then hauling back a certain amount of line at fixed intervals of
time, usually 5 meters every 2 minutes or 2 meters every 1 minute, until completion
of the haul. During the period of hauling, the speed of the ship was kept as nearly
uniform as possible.
During the first seven cruises, when 1-meter nets were used, one net was towed
at the shoal stations where the water was nearly uniform from surface to bottom, and
two nets at the deeper stations where thermal stratification of water was prevalent.
At the stations where two nets were used they were attached to the towing cable at
intervals estimated to be appropriate for the upper net to sample down to the thermocline
and the lower net a nearly equal distance below the thermocline. In a typical
instance, with a sounding of 50 meters, the lower net would be attached at the end of
the Line, the upper net 25 meters from the end, and another 25 meters payed out,
making 50 meters of line all told. Towing at the usual speed, the line would stray
90
100
100