. Report for ... on the Lancashire Sea-Fisheries Laboratory at the University of Liverpool, and the Sea-Fish Hatchery at Piel. ificant difference. If we take the average lengthsfor the years 1913-1909 we shall find that the plaice of 1920are, on the whole, bigger than in the years immediately pre-ceding the war ; but it would be wrong to associate the increaseso indicated with the restrictions on fishing of the years is necessary to consider also the deviations from the averageof 1909-1913, and we see that the good year 1920 is not anybetter than the best of the pre-war years with w
. Report for ... on the Lancashire Sea-Fisheries Laboratory at the University of Liverpool, and the Sea-Fish Hatchery at Piel. ificant difference. If we take the average lengthsfor the years 1913-1909 we shall find that the plaice of 1920are, on the whole, bigger than in the years immediately pre-ceding the war ; but it would be wrong to associate the increaseso indicated with the restrictions on fishing of the years is necessary to consider also the deviations from the averageof 1909-1913, and we see that the good year 1920 is not anybetter than the best of the pre-war years with which it iscontrasted. The fact is that these length-frequency data arevery difficult to interpret in some cases : to make the bestuse of the information that they give requires also a knowledgeof the migrations. We should want to know, rather closely,in what months the crises of the migrations occurred, because 145 we are comparing a definite period (August-September) in allthe years, and it may be the case that large plaice had leftLiverpool Bay, in greater proportion, and in a certain month,in one year than in Fig 18. Graph representing the lengths of plaice caught by the 6-inchtrawl-net on the Liverpool Bay grounds in the months August-Septemberduring the period 1909-13,1920. Summational curves, from Tables.), 23, 24. The Northern Plaice Grounds in 1920 and 1921. There is material for an interesting comparison in thedata obtained on the northern grounds in 1920-1921, wheninvestigations into the spawning of the fish were made, andwhen we were able (by permission of the Fishery Board forScotland) to trawl in Luce Bay. The Table 17 gives thelength-frequencies tor the months of January to April, and forthe Shoals and Slaughter grounds (the latter being thaton which spawning fish were found). Fig. 19 is a graph of thesedata, and also the results of the hauls made in Luce Bay in1920-21. 146 Table XVII. Northern Grounds, 1920-21. Length Frequencies. Shoals. Slatjghter. SO
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectfisheries, bookyear18
