224 U. S. BUREAU OP FISHERIES 



satisfaction are frequently traced to these causes. Copper oleate, 

 however, has proved to be an excellent preservative ancl antifouling 

 agent for fish nets wherever used properly. Usually a fisherman con- 

 siders only the first cost and does not consider whether it might not 

 be much cheaper in the long run to frequently treat his nets with 

 copper oleate rather than to buy new netting. 



Tlie full value of cooper oleate as a net preservative can not be 

 determined until accurate data are available upon the costs of treating 

 netting with different preservatives, including copper oleate, and the 

 length of life of the twine so treated. Practical tests of this nature 

 have been arranged in cooperation with fishermen at several points on 

 the Atlantic seaboard ancl on the Great Lakes. These tests will also 

 show the advantages and disadvantages of using copper oleate under 

 practical conditions and indicate what modifications in its use are 

 necessary for different kinds of gear under the widely varying 

 conditions to which they are subjected. 



Cordage manufacturers are finding copper oleate to be a good 

 preservative and antifouling agent for manila rope. At least one 

 company now sells for marine use a line of rope treated with this 

 material. 



IODINE CONTENT OF PRESERVED SEA FOODS 



In a paper published during 1924 (Bureau of Fisheries Document 

 No. 967) it was shown that fresh sea foods contain a higher per- 

 centage of iodine than other common foods. It was pointed out 

 that since goiter and other thyroid disorders are caused by a lack of 

 iodine being ingested, the liberal use of sea foods in the diet should be 

 an efi'ective preventive of these disorders, especially in so-called 

 goiterous belts where the iodine content of the water and foods is 

 below normal. The amount of iodine necessary to prevent goiter is 

 very small — only about one part in 3,000,000 parts of the body 

 weight — but it is important that this balance be maintained. 



Many of these goiterous belts are so located that it is rather 

 difficult for the inhabitants to obtain marine fish in the fresh con- 

 dition. Much of the marine fish which they consume has been 

 preserved in some manner, such as canning, salting, and smoking. 

 The question naturally arises as to whether these preserved products 

 contain iodine in quantities comparable to that in fresh fish. A 

 series of analyses was made which indicates that such products do 

 contain comparable quantities of iodine. The results of these 

 analyses were published in Bureau of Fisheries Document No. 979. 



CRAB FISHERY OF CHESAPEAKE BAY 



Due to the alarming decline in the crab production of Chesapeake 

 Bay, particularly along the eastern shore, the bureau was strongly 

 urged to investigate this industry. Very little information was 

 available upon which to base a determination of the character or 

 reasons for the decline, and it was therefore first necessary to make 

 a statistical survey in which particular attention was directed to the 

 discovery of such statistics on catches during previous years as could 

 be found in the records of crab houses. An analysis of such statistics 

 as were found indicated that the decline in abundance of crabs took 

 place well in advance of a decline in total catch. The total catch 

 did not decline seriously until sometime between 1915 and 1920, 



