75 



operating to reduce and destroy Teredo in Carquinez Strait in the win- 

 ter months. 



Examinations of piling at several localities along Carquinez Strait 

 during the period from January to April, 1921, have shown no living 

 Teredo above Crockett. These borers were apparently all dead at local- 

 ities above Crockett by about the middle of February, whereas in the 

 preceding November they had extended upstream for twenty-two miles 

 to Antioch with the invasion of sea water. By midwinter they were 

 apparently exterminated, not only in the expanded region of Suisun 

 Bay, including its lower end near Martinez, where the influence of the 

 fresh water run-off dominates, but also well down the narrower Car- 

 quinez Strait where tidal flow from San Pablo Bay brings periodically, 

 at spring and midtides, considerably increased contributions of sea- 

 water. There was, however, a sufficient amount of sea-water at Croc- 

 kett, and at the Carquinez Strait Light on the opposite side of the 

 Strait, to permit a small number of Teredo to survive at this point, 

 which is thus established as the winter or flood survival barrier in 1921. 



At the Carquinez Strait Light Station, on April 25, 1921, a living 

 Teredo was found in a pile in shallow water near low tide level, which 

 was doubtless a survivor from the previous autumn. As only one pile 

 was pulled for examination here, it seems extremely probable that this 

 solitary speciment was a representative of others which had lived 

 through the winter in neighboring piles. In the Mare Island dyke, near 

 Carquinez Light, which is more directly exposed to the influx of fresh 

 water from Napa Creek, all Teredo were found to be killed off and a 

 subsequent inspection of a number of piles pulled for the Committee at 

 various points along the Mare Island Channel failed to show any living 

 specimens. 



At Crockett, on June 10 and 11, numerous healthy Teredo were 

 found in two piles pulled at different points along the waterfront of the 

 California and Hawaiian Sugar Refinery. These specimens averaged 

 rather more than 4 inches in length and must certainly have repre- 

 sented an infection of the previous autumn, as test timbers planted here 

 in March had up to that date showed no infection. No evidence of 

 breeding activity, as shown by larvae in parent adults and by attacks 

 of young Teredo on test timbers, were detected anywhere in the bay 

 until some time later than this. It should be mentioned that nine other 

 piles pulled at Crockett at this time contained only the shells and occa- 

 sional pallets of specimens some time dead, indicating that only a small 

 minority of the many Teredo present in November had survived the 

 lowered salinities prevailing in this region during the winter months. 

 The living Teredo at Crockett were all found within six feet of the mud 

 line in twenty feet of water. 



Above Crockett, as has been indicated, no living Teredo were found, 

 although field work was carried on as far up as Avon. In the upper 



