EARLY LIFE HISTORY 



Larval fish, often called fry, are particularly vulnerable to predation and 

 environmental stress. The larvae of most fishes are planktonic for some time, 

 have limited powers of locomotion and drift freely in the water column. The 

 period of larval life varies for different species and may last from a few 

 days to several years. The larvae of the winter flounder are planktonic for 

 about 50 days. Atlantic herring remain in the larval stage for 5 to 7 months 

 (Graham et al. 1972). Sea lamprey larvae require 5 or more years before 

 undergoing metamorphosis (Lagler et al. 1962). The average duration of larval 

 stages in the Gulf of Maine is about 3 to 5 months. Water temperature also 

 influences the duration of the larval stage; that is, the higher the 

 temperature, the faster the development of the eggs and larvae. 



The larval stage in fishes is terminated at metamorphosis, when the fishes 

 develop adult features and habits. At this point they are considered 

 juveniles. Final development and maturation of the gonads signals the onset 

 of sexual maturity. The time required to attain sexual maturity varies among 

 species and with water temperatures. For example, Atlantic silverside and 

 sticklebacks reach maturity within one year after hatching, whereas freshwater 

 eels require 6 to 12 years. The Atlantic sturgeon may take 15 or more years 

 (Lagler et al. 1962). 



Larval Populations 



Planktonic eggs and larvae are seasonally important components of the plankton 

 communities (TRIGOM 1974). Detailed data are available for the midcoast 

 region (lower Sheepscot-Damariscotta estuaries), offshore Gulf of Maine, and 

 the Bay of Fundy. The species compositon and seasonal abundance of the 

 estuarine larval populations have been described for the Sheepscot/Back River 

 estuaries by Maine Yankee Atomic Power Company surveys (1970 to 1976), for the 

 lower Sheepscot estuary by Chenoweth (1973), and for the mid-coast region by 

 Graham and Boyar (1965) and Graham and coworkers (1972). The offshore marine 

 larvae in the Gulf of Maine and Georges Bank were sampled by Marak and Colton 

 (1961) and Marak and coworkers (1962a and 1962b). Fish and Johnson (1937) 

 surveyed the marine larvae in the Bay of Fundy and northern Gulf of Maine 

 waters. Some of these data are given in table 11-4. Complete lists of all 

 larval species found in the marine and estuarine surveys are given in appendix 

 tables 8 and 9. 



Fish larvae in the offshore waters are dominated by the larvae of resident 

 fishes (cod, haddock, sand lance, and flounder). Silver hake larvae dominate 

 the larvae of summer migrant fishes. Larval populations in the Bay of Fundy 

 are dominated by the larvae of Atlantic herring and redfish, which are typical 

 northern resident species. In the Sheepscot estuary, larval abundance is 

 greatest from late winter through spring, with greatest concentrations in the 

 upper estuaries (figure 11-2). These estuarine larvae are composed of both 

 marine and estuarine fishes. Species that utilize the estuaries as primary 

 spawning and/or nursery areas (as indicated by the abundance of larvae) 

 include the wrymouth, rock gunnel, sculpins , sea snails and snakeblenny 

 (Chenoweth 1973), Atlantic herring, winter flounder, and Atlantic tomcod 

 (Maine Yankee Atomic Power Co. 1976). 



11-20 



