486 BULLETIN OF THE BUREAU OF FISHERIES 



mollusks, worms and ascidians ("sea squirts") — in fact, practically any animals 

 living on bottom that are small enough for them to devour. Occasionally they 

 catch small fish. Plaice do not bite a baited hook very readily, partly, no doubt, 

 because they are sluggish fish, but partly, we believe, because the clams, cockles, 

 and herring usually employed for bait are not their favorite food. 



All the large predaceous fish that feed near bottom probably prey more or less 

 upon the plaice, and halibut no doubt destroyed great numbers of them in the Gulf 

 of Maine formerly, for flatfish of one sort or another bulk large in their diet. How- 

 ever, the adult plaice can have no serious enemy in the Gulf to-day except the cod 

 and perhaps the spiny dogfish. In more northern seas Greenland sharks prey 

 regularly on them. Smitt " and Huntsman both speak of the numbers of round 

 worms to be found in the intestines and body cavity of plaice, and its gills are 

 sometimes attacked by parasitic copepods. 



Habits. — Plaice are bottom fish like other flounders, usually lying flat on the 



ground, but they must rise some distance from the mud on occasion and move about 



to a considerable extent to account for the capture of so many in gill nets, while 



we once caught one a foot long in a tow net at least 5 to 10 fathoms above the 



bottom off Ipswich Bay, where the water was about 50 fathoms deep. 



Rate of growth. — The young plaice seeks bottom when about an inch and a 

 half long, after which its rate of growth depends on the temperature of the water 

 and probably on the length of the growing season, for growth practically stops 

 during the winter. Thus Huntsman (1918) has found that it takes 3 to 5 years 

 for a plaice to grow to a length of 12 inches in Passamaquoddy Bay where the 

 temperature of the bottom water in 15 to 18 fathoms warms to about 49 to 51° in 

 August, 58 4 to 6 years in the open Bay of Fundy where the bottom temperature is 

 somewhat lower (45 to 48°) ; 6 to 9 years in the cooler water (about 38°) of Cheda- 

 bucto Bay in the Straits of Canso; and upward of 8 years in the still lower tem- 

 peratures (colder than 35°) of the Gulf of St. Lawrence. Plaice living in the deeper 

 parts of the Gulf of Maine may be expected to grow at about the same rate as the 

 Bay of Fundy fish, while those living on Georges Bank and in the coastal zone 

 from Cape Cod to Cape Elizabeth probably do so as fast as the Passamaquoddy 

 Bay fish — that is, they may reach a length of 15 inches in 5 years or even sooner, and by 

 that age, according to Huntsman, they may gain 1 1 ounces in weight yearly. Some 

 plaice become sexually mature when only 6 inches long, probably all of them do so 

 by their third year, and they may live to an age of 24 to 30 years. 



Although plaice grow so much more rapidly in the comparatively warm water 

 of Passamaquoddy Bay than in lower temperatures, large ones are far less common 

 there or in the Bay of Fundy than in the Gulf of St. Lawrence, where fish 10 to 12 

 years old and of corresponding size form a considerable proportion of the stock, 

 a discrepancy which Huntsman explains by assuming a higher death rate in warm 

 waters than in cold. However, a study of the composition of the stock in other 

 parts of the Gulf of Maine and especially that of its southwest part, where plaice 

 spawn freely (p. 487), may show that the older fish simply move out of the Bay of 

 Fundy. 



" Scandinavian Fishes, 1892. « Craigie, Contributions to Canadian Biology, 1914-15 (1916), pp. 151-161. 



