DIFFERENCE IN SEX RATIOS OF THE 



ANADROMOUS ALEWIFE, ALOSA 



PSEUDOHARENGUS, BETWEEN THE TOP AND 



BOTTOM OF A FISHWAY AT 



DAMARISCOTTA LAKE, MAINE' 



The Damariscotta River alewife, Alosa pseu- 

 doharengus, fishery has been monitored by the 

 Maine Department of Marine Resources every 

 year since 1971 for abundance offish, length and 

 weight frequencies, age distribution, and sex 

 ratios. From 1977 through 1979, sampling plans 

 were also devised to estimate numbers, size, and 

 sex composition of ripe alewives escaping the 

 fishery and entering the lake to spawn. (Through- 

 out this paper they will be collectively referred to 

 as escapements.) 



While sampling the 1977 escapement rim it be- 

 came evident that a greater number of males than 

 females were entering the lake to spawn. This 

 male dominance was not unusual as it was re- 

 ported in other alewife runs, as well. Bigelow and 

 Schroeder (1953) stated that as a rule males 

 greatly outnumber females on the spawning 

 grounds. What prompted this investigation was 

 the fact that while the escapement runs had sig- 

 nificantly more males than females, the samples 

 from the commercial catch revealed a consistent 

 sex ratio of 1:1. Similar disproportionate ratios 

 were observed in the 1978 and 1979 escapement 

 runs, while the commercial catch ratios were 1:1 

 each year. In this paper I will examine these vary- 

 ing sex ratios and offer considerations for further 

 investigation. 



Study Area 



The Damariscotta River fishery is located in the 

 adjoining towns of Nobleboro and Newcastle and is 

 one of the largest alewife fisheries in the state, 

 composing about 30% of the annual total landings 

 (Gating 1958). This area was selected for study 

 because of the easy access to sampling both the 

 commercial catch and the escapement run. The 

 objectives of the study were: 1) to estimate the 

 abundance of spawning adults, 2) to determine the 

 escapement level which will maximize subsequent 

 recruitment, and 3) to determine population 



'This study was conducted in cooperation with the U.S. De- 

 partment of Commerce, National Marine Fisheries Service, 

 under Public Law 89-304, as amended, Commercial Fisheries 

 Research and Development Act, Projects AFC-18-(2,3) and 

 AFC-21-L 



characteristics of the Damariscotta River alewife 

 stock such as stock size, age, distribution, and 

 growth rates. 



Damariscotta Lake, in Lincoln County, Maine, 

 is a narrow, north-south oriented body of water 17 

 km long and 1,806 ha in area. There are three 

 major outlets in a dam at the southeastern end of 

 the lake: the first supplies water to a hydroelectric 

 power station, the second is the main outflow con- 

 trolled by two spillways, and the third is a man- 

 made fishway. In 1803, the start of a commercial 

 run was created (Atkins 1887), and a fishway made 

 of stones set to form a series of irregular pools and 

 raceways was constructed beside the main outflow. 

 The fishway is about 150 m long with a 16 m verti- 

 cal rise. 



The spawning migration of this fishery's ale- 

 wives consists of a 29 km swim up the Damaris- 

 cotta River to head of tide at Great Salt Bay The 

 fish then enter the outflow of Damariscotta Lake 

 via a tidal stream about 50 m long. The stream 

 divides in two and the right branch becomes the 

 entrance to the fishway. The left branch leads past 

 two dipping bins used by the commercial fishery 

 and then to the spillways. The spillways are 

 opened to allow a sufficient amount of water into 

 the stream to attract alewives into the bins. The 

 alewives in this stream have a choice of swimming 

 either into the left branch and the dipping bins or 

 into the right branch and into Damariscotta Lake 

 via the fishway. 



Due to the type of construction and the lay of the 

 embankment, the fishway is not consistent in its 

 rise from pool to pool. The bottom and top sections 

 are steepest, while the middle levels out, moderat- 

 ing the waterflow The resting pools are of varying 

 sizes and some of them appear to be too small, 

 causing overcrowding of the alewives. Some of the 

 connecting raceways are long and narrow, allow- 

 ing for a faster current than is present in other 

 raceways. The combination of a small pool and a 

 difficult raceway lowers the efficiency of this fish- 

 way. From the appearance of alewives passing 

 through the fishway, it is a difficult and exhaust- 

 ing run. 



Methods 



From 1977 to 1979, when escapement counts 

 were made, a wood and wire mesh trap, 3 m long by 

 1.2 m wide by 0.8 m deep, was placed in the lake 

 side of the dam at the top of the fishway The trap's 

 entrance covered the dam opening, where the es- 



FISHERY BULLETIN: VOL. 79, NO. 1. 1981. 



207 



