ESTIMATING ABUNDANCE OF GROUNDFISH ON GEORGES BANK 



273 



method, the proportion of days fished in eacli zone 

 was 2.3.4 percent for shallow, 5.3.0 percent for 

 medium, and 23.6 percent for deep, which ao;reed 

 very closely with the proportions derived from 

 the first roufjh estimate. 



TOTAL AREA AND PRODUCTIVE AREA OF BANK IN 

 EACH DEPTH ZONE AND SUBAREA 



On Georges Bank and South Channel, each unit 

 area (10' of latitude by 10' of longitude) averages 

 10 by 7.5 miles, or 75 square miles in area. On 

 this basis, using our own 60- and 125-fatiiom con- 

 tour lines, the whole of Area XXII South contains 

 22,153.5 square miles of bank ranging between 

 and 125 fathoms in depth. Of this total, 29.5 

 percent is in the shallow zone, 41.2 percent is in 

 the medium-depth zone, and 29.3 percent is in 

 the deep zone (not considering depths of more 

 than 125 fathoms). 



Table 1 shows the square miles of bank at each 

 depth in each subarea. The right-hand section of 

 tlie table shows the area of productive bank, as 

 measured by the intensity of the otter-trawl 

 fishery. The productive area is interpreted to in- 

 clude the portions of the bank enclosed by the 

 fishing-intensity contour of 50 days per unit area 

 out of a total of more than 32,000 fishing days. 

 Studies on the haddock (Herrington 1948) show 

 that the area occupied by the schools of large 

 haddock expands in years when the population is 

 large and contracts when the population shrinks. 

 Therefore, there are large areas (especially in 

 Subareas M, X, and O) that are potentially pro- 

 ductive, as shown by the abundance of haddock 

 taken in former years, that have been fished less 

 in recent years. However, such portions of the 

 banks must be included in any estimate of the 

 productive area. 



In figure 5, the areas of bank in each depth zone 

 are shown graphically. It is noteworthy that 

 subareas G and H on the west and east sides of 

 the South Channel contain less than 20 percent 

 of medium-depth water although they have ap- 

 pro.ximately twice as much shallow water and three 

 to four times as much deep water. Thus, the 

 medium-depth zone is a narrow, rapidly shelving 

 band between the shallow bank and a deep-water 

 plateau that occupies the center of the South 

 Channel. The deep water in the other four sub- 

 areas, instead of forming a plateau, is a narrow 

 shelving rim surrounding Georges Bank. 



The deep-water zone of G and H on the plateau 

 (chiefly about 70 to 95 fatlioms) is fished inten- 

 sively for ocean perch, gray sole, and haddock. 

 The narrow band of deep water comprising the 

 northern portion of J, and sometimes extending 

 slightly into M, has practically no ocean perch but 

 is fished intensively for haddock and other ground- 

 fish. 



The deep zone on tlie eastern and southern edge 

 of Georges Bank in M, N, and O is seldom fished. 

 The reason for the lack of fish in this area may be 

 the influence of the Gulf Stream, which comes 

 close to this edge of the bank and causes a rise in 

 temperature. 



Except for G and H, all of the subareas contain 

 more medium water than either shallow or deep. 

 Practically all of the medium-depth water in J and 

 the western portion of M is heavily fished for had- 

 dock, cod, and flounders. Subareas N and O were 

 not so heavily fished because of the lack of suffi- 

 cient population pressure in the haddock in recent 

 years (as explained above), but both subareas con- 

 tain large areas of potentially productive bank in 

 the medium-depth zone. 



Table 1. — Approximate area and fishing intensity by otter trawlers in each depth zone and subarea of Area XXII South 



'Areas enclosed hy fishine-intcnsity contour of 50 duys of fishinc per unit iircu of 75 sqimn- rnili'S, out of a total of over 32,000 days of fishing. 



