PROGRESS IN BIOLOGICAL INQUIRIES, 1931 451 



On one trip to Western Bank a commercial trawl with this type 

 of cod-end Avas fished alternately with a similar trawl using a com- 

 mercial cod-end. It was found that with an equal catch of large 

 haddock but one-fifth as many undersized ones were taken. The 

 numbers of undersized fish of other species were reduced in propor- 

 tion. Tests of this type of cod-end are being continued, and several 

 improvements are being developed. 



The gear experiments conducted by the bureau have been greatly 

 facilitated through the cooperation of a number of commercial con- 

 cerns. The Linen Thread Co., of Boston, Mass., and the Plymouth 

 Cordage Co., of Plymouth, Mass., furnished much of the material 

 and made up most of the experimental gear. Lloyd Runkle, of the 

 former company, assisted on several field trips and had charge of 

 constructing the experimental gear. Later in the work several com- 

 mercial models were constructed by the Portland Trawling Co. in 

 their net loft at Groton, Conn. Except for some preliminary work 

 on the Albatross II, the field trials were conducted on the schooner 

 Exeter and steamer Kingfisher through the generous cooperation of 

 the General Sea Foods Corporation and Portland Trawding Co. 



Early-life history. — Material has been collected during the past 

 year concerning the location and extent of spawning areas and the 

 movements of the eggs and larvae during the period when they drift 

 passively with the current. This material is used for the study of the 

 interdependence of the various banks for their replacement of small 

 haddock, and the causes of success or failure in the production of the 

 different year classes. 



During the haddock-spawning season in the spring of 1931 three 

 trips were made on the Albatross II, each of about two weeks' dura- 

 tion, and covering a grid of 40 stations, spaced at 32-mile intervals 

 each way, extending over the area from west of Nantucket Shoals to 

 Browns Bank. At each station from one to four tow-net hauls were 

 made, depending on the depth, using 1-meter silk nets and a Welsh 

 trawl. The sorting and analysis of the collections have not pro- 

 gressed far enough to report results, 



Hydrographic data, such as water samples and temperatures, were 

 obtained at each station for the various depths, and on the last two 

 trips 800 drift bottles were released, 10 to each station on each trip. 

 The drift bottles were colored a brilliant yellow, a color which tests 

 had shown to be most conspicuous under the conditions encountered. 

 The returns from this work have been exceptionally numerous and 

 have given us a much better conception of the surface currents in the 

 Georges Bank region. 



MACKEREL 



The mackerel is prominent among the important food fishes of 

 the Atlantic coast, not only for the magnitude of the annual catch, 

 which in recent years has averaged around 40,000,000 pounds an- 

 nually, but also for the extreme fluctuations in abundance which 

 have characterized this species ever since records on this fishery 

 were first kept, early in the nineteenth century. The objective of 

 the bureau's investigations of this species is to ascertain the nature 

 and causes of these changes in abundance, to determine whether they 

 may be affected by man's inroads on the stock in the sea, or whether 



