. Discovery reports. Discovery (Ship); Scientific expeditions. 284 DISCOVERY REPORTS knots. Nevertheless it was never possible to keep the ship's speed absolutely constant during any one towing or to be sure that the speed of the ship was exactly the same at successive towings, and with small variations in the speed the depth of the nets varied widelyâthe nets rising towards the surface with increased speed and falling with de- creased speed. Thus the shallowest surface haul was at St. 735, where the net fished from 62 to o m., and the deepest was at St. 748, where the net fished from 180 to o
. Discovery reports. Discovery (Ship); Scientific expeditions. 284 DISCOVERY REPORTS knots. Nevertheless it was never possible to keep the ship's speed absolutely constant during any one towing or to be sure that the speed of the ship was exactly the same at successive towings, and with small variations in the speed the depth of the nets varied widelyâthe nets rising towards the surface with increased speed and falling with de- creased speed. Thus the shallowest surface haul was at St. 735, where the net fished from 62 to o m., and the deepest was at St. 748, where the net fished from 180 to o m. There were many gradations between these two extremes. The deep net also frequently fished through depths which varied widely from those aimed at. The following stations may be quoted as instances of the kind of variation which occurred: St. 727: 310-170 m. 733: 300-140 m. 746: 306-124 m. 748: 204-138 m. 757: 320-126 m. St. 769: 342-150 m. 776: 356-170111. 802: 320- 70 m. 815: 314-188 m. 830: 356-140111. Similar figures may be found throughout the tables. The question of applying some correction to these hauls so as to standardize the catches should therefore be given consideration. In spite of the somewhat wide variations in the depths at which the surface net began towing it can be shown diagrammatically (Fig. 4) that the oblique path of the SURFACE HAUL TRACK OF SHIP STEAMING AT 5 KNOTS [ MINUTE], I£00m APPROX I395mAPPR0X OUT ZOOM, A' DEEP HAUL â TRACK OF SHIP STEAMING AT g KNOTS [60m PER MINUTE] . IgOOM APPROX outsoom. b. closing depth. 00 M '-200 m IOOm 200 m -300m Fig. 4. Diagram illustrating the variations in the length of the oblique tow with variations in the com- mencing depth of the surface and deep hauls and in the closing depth of the deep net. net to the surface was in reality not widely different at every haul. In Fig. 4 a number of surface hauls have been plotted which begin at depths varying from 50 to 180 m., the widest limi
Size: 3356px × 745px
Photo credit: © Paul Fearn / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookdecade1920, booksubjectscientificexpedition
