drainages). The resident American eel, a catadromous fish, is perhaps the most 

 ubiquitous fish in Maine. It is found in almost every major drainage and 

 aquatic system (see atlas map 4) . 



Two of the summer migrants, American shad and blueback herring, are anadromous 

 fishes, spending part of their life cycle in marine waters and swimming up 

 estuaries and rivers to spawn in fresh water. Striped bass are anadromous in 

 the southern part of their range but they do not commonly spawn in Maine. 



Maine's historically rich populations of anadromous fishes declined near the 

 turn of the century through the 1960s as a result of dams that blocked 

 pathways to spawning areas. Altered water flow and river pollution by 

 municipal and industrial wastes also were factors. The status of recovery, 

 problems remaining, and management strategy for the enhancement of anadromous 

 fish resources are discussed under "Management," in this chapter. 



REPRODUCTION 



Spawning habits are known for most of Maine's resident marine and estuarine 

 fishes, notably the anadromous fishes, and sport and commercial fishes. 

 Detailed life history information by species is available in Bigelow and 

 Schroeder (1953), Everhart (1958), Clayton and coworkers (1976), Scarola 

 (1973), TRIGOM (1974), and Scott and Crossman (1973). 



Spawning adults and the eggs and larvae of fishes are particularly sensitive 

 to changes in their environments. Many species require specific habitats, 

 migratory pathways, and environmental conditions (e.g., temperature and 

 salinity) for successful spawning. Anadromous fishes, such as salmon, 

 alewife, smelt, and blueback herring, require unobstructed passage through 

 estuarine and riverine systems to suitable freshwater spawning grounds; some 

 of these fish negotiate obstructions better than others. 



Many species that spawn offshore, such as the Atlantic cod and Atlantic 

 herring, migrate to certain open water areas to spawn. Spawning activity is 

 synchronized for many species. This usually results in greater than normal 

 concentrations of a species in a spawning area. As a result the whole 

 population of a species is vulnerable to a single adverse event (e.g., fishing 

 and oil spills). The eggs and larvae of most fishes are generally vulnerable 

 to predation and environmental changes. They are relatively concentrated in 

 numbers and have limited or no powers of locomotion by which to leave an 

 unfavorable area. 



Fecundity 



The success of reproduction is determined largely by the survival of the year 

 classes during their early life stages. Natural mortality usually is very 

 high during that time. The reproductive strategy of most fishes involves the 

 external fertilization of great numbers of eggs. A small percentage survive 

 to adulthood. Fishes that show a higher degree of parental care usually lay 

 fewer eggs. There usually is a trade-off effect between the number of eggs 

 laid and the rate of survival of the young to maturity; that is, the energy 

 that goes into producing large quantities of eggs is not available to provide 

 care for the young. 



11-15 



10-80 



