FISHERY BULLETIN: VOL. 76, NO. 1 



MATERIALS AND METHODS 



The Annisquam River is a natural waterway 

 approximately 3 mi long connecting Ipswich Bay 

 on the north side of Cape Ann peninsula with 

 Gloucester Harbor on the south (Figure 1). The 



70°40' 



42°40' 



Figure l. — Map showing locations of the Jones River study site 

 (A) and the University of Massachusetts Marine Station, 

 Hodgkins Cove (B). 



river consists of a dredged channel with extensive 

 tidal mud flats or shallow water on both sides. The 

 mean tidal amplitude at Gloucester Harbor is 3 m. 

 The Annisquam River receives limited freshwater 

 drainage, resulting in salinities of 28-33. 5%o. 

 Water movement is largely dependent on the 

 tides. Average monthly surface water tempera- 

 tures (1 m depth) for the years 1973 and 1974 

 obtained from the University of Massachusetts 

 Marine Station at Hodgkins Cove (Figure 1) indi- 

 cate that monthly temperature fluctuations are 

 great (Figure 2). Temperature data for 1975 were 

 not available. 



The site for this study was located on a mudflat 

 along the west bank of the Jones River, a small 

 tributary opening at the northern end of the An- 

 nisquam River (Figure 1). Historically, this area 

 has been the site of a productive shellfish bed and 

 is known to sustain numerous clams of differing 

 age classes (Mass. Dep. Resour., Div. Mar. Fish, 

 pers. commun.). 



The study began in February 1973 and was 

 completed in October 1975. Clams were collected 

 from the middle of the intertidal zone ( +1 m tidal 

 level) once a month from October 1973 through 

 February 1974 and October 1974 through October 

 1975, and twice a month from March through Sep- 

 tember 1973 and April through August 1974. No 

 samples were taken in September 1974 or in May, 

 June, July, and September 1975. Sample sizes var- 

 ied greatly. Samples collected during the spring 

 and summer months consisted of 30 to 127 clams, 

 21-90 mm shell length. Those collected during the 

 winter months consisted of 15 to 30 clams each in a 

 similar size range. Large numbers of clams were 



20- 



' "T 1 1 1 1 1 1 r 



^ •" M A M J J A S 



FIGURE 2.— Sea-surface (1 m depth) 

 temperatures for Hodgkins Cove, 

 Gloucester, Mass. Monthly means for 

 1973 (••) and 1974 (oo) are plotted. 

 The dashed lines represent 8-yr average 

 maxima, means, and minima for the 

 period 1963-71, based on temperatures 

 for the Portland Lightship (Chase 

 1965-1973) corrected for Hodgkins 

 Cove. 



MONTHS 



156 



