174 



Fishery Bulletin 94(1). 1996 



rate during each of the three years for which we ob- 

 tained samples (1986, 1988, and 1992). Likewise, fish 

 collected during July-September grew at similar 

 rates during 1990 and 1992. An average growth rate 

 of 1.01 mm/day for the first 200 days was estimated 

 from the equation. When the data were analyzed by 

 time of collection (and consequently by separating 

 smaller, younger fish from larger, older fish), the 

 equation for the June 1986 samples was 



LEN = i67.193<r 626U< '- 00184,AG£ '. 



[r 2 =0.588, n=22] 



with an estimated growth rate of 0.71 mm/day, and 

 the equation for July-September ( 1992 ) samples was 



LEN = 206.980e- 17 - 7158e ^ 2299(AG£ \ [r 2 =0.877, «=89] 



with an estimated growth rate of 0.99 mm/day. 



Discussion 



A hyaline zone, or check, can form on fish otoliths in 

 response to a significant change in environmental 

 conditions such as temperature or food availability, 

 or both (i.e. by the transition from a pelagic to a de- 

 mersal lifestyle). Our samples of juvenile white hake 

 reflect the dramatic change in habitat experienced 

 by this species because the smallest, youngest fish 

 (pelagic juveniles) were collected from deep offshore 

 areas and the largest, oldest fish (demersal juveniles) 

 were collected from shallow inshore locations. 



The juveniles collected in Woods Hole, Massachu- 

 setts, in August, 1992 (70-104 mm TL) had hyaline 

 edges on their sagittal otoliths which would have ap- 

 peared as a check on adult otoliths. Previous studies 

 suggest that juvenile white hake "settle out" from a 

 pelagic to demersal lifestyle at about 50 to 80 mm 

 TL (Musick, 1974; Markle et al., 1982). They may 

 also actively migrate to inshore areas at this time 

 because juvenile hake in this size range have often 

 been collected from shallow inshore areas (Bigelow 

 and Schroeder, 1953; Musick, 1969; Markle et al., 

 1982; Comyns and Grant, 1993). The ages of the ju- 

 veniles collected in Woods Hole (59-73 days) confirm 

 that this hyaline zone was a check rather than the 

 first annulus. 



Daily ages were also used to calculate growth rates 

 for the juvenile hake. We found that juveniles grew 

 about 0.99 mm/day in June and September I 1992 I, a 

 rate that coincides with Fahay and Abie's I 1989 i es- 

 timate of 1.02 mm/day for demersal juveniles col- 

 lected during June-October 1986, which they calcu- 

 lated by means of length-frequency progression. This 



relatively fast growth rate may reflect the benefit to 

 juvenile fish of moving into warm, shallow areas 

 where prey abundance can be high. 



Our results also support Fahay and Abie's ( 1989) 

 hypothesis that juvenile white hake are recruited 

 northward along the east coast of the United States. 

 As mentioned above, only smaller, younger individu- 

 als were collected from southern locations (in the mid- 

 Atlantic Bight) and only larger, older fish were col- 

 lected from areas farther north ( in the Gulf of Maine ). 

 Whereas only cruises with positive catches of white 

 hake were utilized for this study, Fahay and Able 

 (1989) obtained similar results after an extensive 

 series of surveys conducted during 1984-87, using 

 various sampling gear and covering areas from Cape 

 Fear, North Carolina, to the Scotian Shelf (Tables 1 

 and 2 in Fahay and Able, 1989). Fahay and Able 

 ( 1989) also reviewed the results of other researchers 

 which documented the absence of eggs and larvae in 

 Georges Bank-Gulf of Maine waters and the north- 

 ward progression of juvenile stages in the study area 

 (Chenowith, 1973; Colton and St. Onge, 1974; Bolz 

 et al., 1981; Laroche, 1982; Townsend, 1984). 



In light of the northward recruitment theory, and 

 given the northward progression of sizes and ages, 

 all of the fish in this study probably came from one 

 spawning population located offshore from the mid- 

 Atlantic Bight and Georges Bank region. Our collec- 

 tions from the Gulf of Maine in July and August 1992 

 may indicate that there were two successful spawn- 

 ing periods (or one very protracted spawning period) 

 that year because they included two size classes of 

 juvenile hake. We found no evidence of a summer- 

 spawning Scotian Shelf stock, possibly because of the 

 timing of our sampling of the northernmost stations 

 (in July-August 1992). These results again support 

 Fahay and Abie's ( 1989) hypothesis that there is no 

 significant spawning within the Gulf of Maine. 



In summary, our results confirm details of the early 

 life history of white hake. Pelagic juveniles settle into 

 a demersal existence at 50 to 80 mm TL, when they 

 are approximately 50 to 60 days old. Many individu- 

 als settle in shallow estuarine nursery areas which 

 results in the formation of a hyaline check on their 

 sagittal otoliths. We therefore support previous age- 

 ing studies in which the check on adult otoliths was 

 not counted in ageing. We also confirm with daily 

 ageing a growth rate of about 1 mm/day for juvenile 

 white hake. Finally, we provide additional evidence 

 that there is apparently a major spawning popula- 

 tion of adults located offshore of the mid-Atlantic 

 Bight-Georges Bank region, and that juvenile hake 

 spawned from this group are recruited northward 

 into the Gulf of Maine. 



