RAPPORTS. XIII C2: THOMPSON 



24 - 



shores of the Firth. It will be seen that the characters of the Cod at the two former 

 stations, Burghead Bay and Smith Bank, are not very different; and indeed as regards 

 the inter-quartile zone they are practically identical at these two stations. It is, however, 

 apparent that the Smith's Bank station contains a very considerably greater number of the 

 larger fish, for we see that while in both cases 25 % are over about 35 centimetres, yet 

 10 % of the whole are over 94 centimetres at Station XII, while only 10 % are over 52 

 centimetres on the other station. In the case of the curve for Station VII we have a 

 very different condition of things, for we now see that while the median point corresponds 

 to 40 centimetres, the two quartiles, instead of being near together, are far apart, the one 



at 24 centimetres and the 

 other at 92. The reason of 

 course is that, as has been 

 explained, on page 9, we 

 have here both the smaller 

 fish and the larger fish pre- 

 sent in numbers, while the 

 intermediate sizes are scarce 

 or almost absent; in other 

 words, the median point is 

 now difficult to strike, and 

 gives us an uncertain and 

 unreliable figure. A very 

 small difference in the rela- 

 tive proportions of the two 

 separate groups of smaller 

 and larger fishes might set 

 the median within the one 

 group, or far away from it 

 within the other. Howewer, 

 so far the median will be of 

 service in showing roughly 

 which of the two separate 

 groups predominates upon 

 the various stations. Thus in figure 28, where we have charted the median sizes of 

 Cod, we see that comparatively small Cod, with a median size of from 27 to 45 centi- 

 metres, predominate upon all the inshore stations, with the exception of the outer fringe 

 of Burghead Bay, and also upon the Smith Bank region; in other words, they are char- 

 acteristic of that area of the Moray Firth below the 30 fathom line. An exception is 

 found at Station XVI, where the median size is about 40 centimetres. This happens to be 

 a case where the two groups are pretty equally divided, and where a very small additional 

 catch of large Cod would have set the median among the larger figures. At Station VII, 

 which lies outside the 30 fathom line, but in water of little less depth, and whei'e more- 

 over the actual trawlings have often extended eastward to a depth of 30 fathoms, we 

 again find the large median size of over 90 centimetres. In the chart of the upper de- 

 ciles (figure 29), we see that in the majority of the stations at a distance from shore the 



Fig. 28. Median sizes of Cod on the stations in the Moray Firth. 



