Lewis, R. M., and C. M. Roithmayr. 



1981. Spawning and sexual maturity of gulf menhaden, 

 Brevoortia patronus. Fish. Bull., U.S. 78:947-951. 

 McGurk, W. D. 



1984. Effects of delayed feeding and temperature on the age 

 of irreversible starvation and on the rates of growth and 

 mortality of Pacific herring larvae. Mar. Biol. 84:13-26. 

 Murphy, G. I. 



1968. Pattern in life history and the environment. Am. Nat. 

 102:391-403. 



Nicholson, W. R. 



1975. Age and size composition of the Atlantic menhaden, 

 Brevoortia tyrannus, purse seine catch, 1963-71, with a brief 

 discussion of the fishery. U.S. Dep. Commer., NOAA Tech. 

 Rep. NMFS SSRF-684, 28 p. 



1978. Movements and population structure of Atlantic men- 

 haden indicated by tag returns. Estuaries 1:141-150. 

 Reintjes, J. 



1969. Synopsis of biological data on the Atlantic menhaden, 

 Brevoortia tyrannus. U.S. Fish Wildl. Serv., Circ. 320, 30 



P- 

 Stearns, S. C. 



1976. Life-history tactics: a review of the ideas. Q. Rev. Biol. 

 51:3-47. 



Allyn B. Powell 



Southeast Fisheries Center Beaufort Laboratory 

 National Marine Fisheries Service, NOAA 

 Beaufort, NC 28516 USA 



Germano Phonlor 



Fundacao Universidade do Rio Grande 

 Departamento de Oceanografia 

 Caixa postal k7k 

 96200 Rio Grande - RS, BRAZIL 



SEASONALITY OF BLUE MUSSEL, 



MYTILUS EDULIS L., LARVAE IN 



THE DAMARISCOTTA RIVER ESTUARY, 



MAINE, 1969-77 1 



(Engle and Loosanoff 1944; Stubbings 1954; Baird 

 1966; Bohle 1971; Rasmussen 1973; Jorgensen 1981; 

 Kautsky 1982). 



Seed (1975) summarized reproduction in Euro- 

 pean mussel populations and found that spawning 

 in M. edulis varies with latitude, occurring earlier 

 in warm waters and progressively later in cooler, 

 northern waters. However, Newell et al. (1982) 

 reported no latitudinal variation of spawning among 

 mussel populations along the northwestern Atlan- 

 tic coast. Such geographic variation has been attrib- 

 uted to the existence of physiological races (Stauber 

 1950; Loosanoff and Nomejko 1951). Newell et al. 

 (1982) and Fell and Belsamo (1985) also found that 

 mussel populations at the same latitude in Long 

 Island Sound spawn at different temperatures and 

 times of the year. They surmised that food avail- 

 ability, rather than temperature, dictates when 

 spawning occurs. 



Factors which are important in the timing and 

 intensity of spawning can be determined by moni- 

 toring spawning activity. This may be achieved 

 directly, by examination of gonad development in 

 seasonally collected samples, or indirectly, by ob- 

 serving the presence or absence of M. edulis larvae 

 in plankton samples (Chipperfield 1953). While the 

 direct method is preferable, the indirect method 

 does allow one to use long-term plankton records. 

 These provide an estimate of the variation in both 

 the timing and intensity of spawning. Since the 

 source of the larvae is not certain, some caution 

 should be used in the interpretation of the results 

 (Seed 1975). 



An 8-yr plankton record of Mytilus larval abun- 

 dance presents an unusual opportunity to observe 

 long-term variability in spawning and larval occur- 

 rence. Specifically, the data were examined with the 

 following goals: 



The spawning of the blue mussel, Mytilus edulis L., 

 has been the subject of many studies (see Bayne 

 1976 for partial review). In an early paper Field 

 (1922) reported that gametogenesis and spawning 

 were influenced by water temperature, though he 

 provided no data. Chipperfield (1953) found that 

 mussels spawn over a specific range of water tem- 

 perature (9.5°-12.5°C). In addition, Chipperfield 

 noted that the rate of temperature change prior to 

 spawning influences intensity. Other investigators 

 have found that mussels spawn over a specific tem- 

 perature range, which may vary among locales 



Contribution No. 183, Ira C. Darling Center, University of 

 Maine, Orono, ME. 



1) Determination of the initiation and the dura- 

 tion of the spawning season and degree of tem- 

 poral variation between years; 



2) Determination of the variation in larval abun- 

 dances within and between seasons; 



3) Examination of the possible correlation of en- 

 vironmental variables (temperature, phyto- 

 plankton abundance, degree days, calendar 

 date, and lunar cycles) with spawning activity. 



Materials and Methods 



The study site was the Damariscotta River estuary 

 (Fig. 1), a narrow embayment, 29 km long, which 

 receives a limited amount of freshwater. The estu- 



FISHERY BULLETIN: VOL. 84, NO. 4, 1986. 



995 



