690 



Fishery Bulletin 88(4), 1990 



Figure 2 



Stratified mean number of sandlance (■) per tow (log transforma- 

 tion) on left, and the number of copepods Calanusfiyonarchicxa ( + ) 

 per m^ (log transformation) on right. Note: the scale for sandlance 

 is different from that of copepods. 



Results 



Changes in abundance of sandlance 

 and copepods 



The mean number of sandlance per tow (log transfor- 

 mation) collected during spring bottom-trawl surveys 

 ranged between years (Fig. 2) from a minimum 0.000 

 (in 1986) to a maximum 4.06(3 per tow (in 1988). Two 

 trends were apparent. The data show a decline in 

 catches from 1982 to the zero value of 1986. Catches 

 increased in 1987, peaking in 1988 to 4.066 sandlance 

 per tow (log value). The number of sandlance caught 

 in 1988 was a regional abundance maximum for spring 

 surveys, 1968-88 (from information presented in 

 Nelson and Ross 1989). 



The log-transformed values of C. finmarchicuslm^ 

 of water collected in the CPR ranged from 3.270 (in 

 1984) to 4.988 (in 1986), and generally increased on 

 Stellwagen Bank between 1982 and 1986 (Fig. 2). The 

 increase was most apparent between 1984 and 1986. 

 The number of C. finmarchicus collected in 1986 was 

 one order of magnitude greater than that collected dur- 

 ing any other year of the study. Following 1986 the 

 number of C. finmarchicus declined rapidly to 3.640 

 (log value) in 1987, then to 3.070 (log value) in 1988 

 (Fig. 2). 



The abundance of sandlance on Stellwagen Bank was 

 inversely related to the abundance of C. finmarchicus 

 (r, = -0.883, P<0.05, N=7). The three years when 

 the spring tow values for sandlance were the lowest 

 (1983, 1985, and 1986) were the three peak years for 

 C. finmarchicus (Fig. 2). Conversely, the number of 

 C. finmarchicus recorded on Stellwagen Bank during 

 1988 was one of the lowest throughout the study 



period. This is the year when the sandlance reached 

 its maximum peak of abundance. 



Changes in whale abundance 



Humpback and fin whales showed a similar trend in 

 abundance (r, = 0.3338, P<0.074, Table 2), although 

 the variation in the observed number of humpbacks 

 between years was much more pronounced than for fin 

 whales. The number of humpbacks/year increased from 

 3.59 whales/effort in 1982 to 9.00 whales/effort in 1985 

 (Table 1, Fig. 3). During 1986 humpback abundance 

 declined to the minimum value recorded during the 

 study period of 0.23 whales/effort. A small increase in 

 1987 was followed by a much larger increase in 1988 

 to 6.98 whales/effort (Fig. 3). 



Less dramatic fluctuations between years were evi- 

 dent in the number of fin whales from 1982 to 1988. 

 The abundance of fin whales declined from the max- 

 imum value of 3.71 whales/effort in 1984 to the low 

 values of 1.9 and 1.4 whales/effort recorded in 1986 

 and 1987, respectively (Fig. 3). Although the numbers 

 of fin whales/effort were lower in 1986-87 than in 

 previous years, they did not change by more than an 

 order of magnitude, as did other whale species. The 

 number of fin whales increased to 3.61 whales/effort 

 in 1988. 



The strongest positive correlation occurred between 

 right and sei whales (r, = 0.6842, P<0.()001, Table 2). 

 The right whale is a rare but regularly occurring spe- 

 cies whose temporal occurrence in the study area has 

 been generally restricted to the months of late-winter 

 through early-spring (Winn et al. 1986, Brown and 

 Winn 1989, Hamilton and Mayo 1990). This pattern 

 was generally repeated in all years of the study period 

 except 1986. Excluding 1986, there were only 12 right 

 whale sightings from 1982 to 1988, and during most 

 years there were no sightings (Table 1). However, in 

 1986, 174 right whale sightings (0.95 whales/effort) 

 were recorded, and right whales were observed vir- 

 tually every day throughout the summer (Hamilton and 

 Mayo 1990). 



Sightings of sei whales on Stellwagen Bank, and in 

 Cape Cod Bay, are very rare in any season (CeTAP 

 1982, Mayo et al. 1988). We did not observe sei whales 

 in the study area between 1982 and 1985 (Table 1). 

 However, their numbers increased significantly in 1986 

 (when they were commonly observed) to 0.26 whales/ 

 effort (Table 1, Fig. 3). The occurrence of sei whales in 

 1986 was followed by an equally dramatic decline dur- 

 ing 1987 (2 sightings, 0.01 sei whales/effort) and 1988 

 (no sightings). Between 1982 and 1988, the sei whale 

 and right whale were abundant only during 1986 (Fig. 

 3), when the abundance of C. finmarchicus also reached 

 a recorded regional maximum (Wishner et al. 1988). 



