PROGRESS IN BIOLOGICAL INQUIRIES, 1926 611 
Should our year-class theories be verified by subsequent study, we shall 
have an explanation of the tremendous fluctuations that occur in the American 
mackerel fishery; for if, in any one year, we depend mostly or wholly on 
mackerel of a single year class, it means that the stock of mackerel in the 
ocean is augmented principally by the offspring in unusual abundance in 
certain years, with one or a number of years intervening when very few young 
mackerel survive to enter the commercial fishery. Not only would the estab- 
lishment of this fact explain the fluctuating abundance of mackerel, but it 
would also make possible the foretelling of years of abundance and years of 
scarcity, which would be a service of no little importance to the mackerel 
fishermen and fish dealers. 
The establishment of this fact may also have tremendous importance in the 
conservation of the species. Each successful season leads fishermen to outfit 
in excessive numbers for the following season, and, having incurred heavy 
outlay in outfitting, they are obliged to continue even after it is evident that 
the season is a poor one. Were it known in advance that the season would 
be a failure, the fishermen would, in large part, turn their attention to other 
fisheries, avoiding a profitless investment in outfitting for the mackerel fishery 
and thus relieving the species of undue strain during critical periods in its. 
survival. 
In addition to the large secular fluctuations of the fishery, which may be 
traced to the dominant-age classes, there are the fluctuations within the season. 
These raise a number of questions of utmost importance to the fishing industry, 
questions that a greater knowledge of the biclogy and ecology of the species 
should answer. Why are mackerel caught abundantly on some days and not 
on others? What causes the appearance of mackerel at certain times at cer- 
tain places? Why were the medium mackerel taken in the southern and 
summer fisheries, and why were the large and very large mackerel taken only 
during the cape shore and the autumn fisheries? In an attempt to answer 
these questions eventually we are compiling data of the catches and tempera- 
tures at various points along the coast; and as the contributions of the ocean- 
ographers provide additional knowledge of the physical and ecological condi- 
tions in the north Atlantic, we may ultimately be successful in understanding 
the causes of the intraseason fluctuations. 
There are many other problems that also must be undertaken along with 
the major part of the investigation. These are being carried on in so far as our 
resources will permit. We have done some townetting for mackerel eggs and 
larvee and have established the fact that in 1926 there was a great abundance 
of these forms in Massachusetts Bay. It is hoped to continue this work in order 
to correlate, if possible, the years of successful spawning with the years of 
subsequent successful commercial fishery. It is also necessary to know whether 
the stock of mackerel found along the American coast is a homogeneous popula- 
tion, or whether it is composed of several distinct races, which might individu- 
ally be affected by unequal birth rates and thus produce differing size domi- 
nance in various regions. Tagging experiments, which might throw light on 
this point, were initiated in 1925, but due to the technical difficulties in finding 
a suitable tag these were discontinued for the time being without results that 
we can consider significant. It is hoped to develop a suitable tag and continue 
these experiments, and also to examine mackerel in the various regions from a 
morphological standpoint to determine whether racial characters are present. 
Meanwhile, our data are being collected in a manner that will permit of 
segregation according to such localities as may be designated for separate 
analysis in future migration and racial studies. 
Doctor BieeLtow. I would like to ask one question—why the growth 
of the mackerel is so extraordinarily slow after they get to a con- 
siderable size ? 
Mr. Serre. That we will have to ascertain. 
Doctor Brcretow. In fact it does not grow at all. 
Mr. Serre. The growth is very slow; but the material we had was 
not very extensive. 
Captain Watuace. Is the temperature of the water taken into 
consideration in the matter of scarcity? 
