170 



The use of otolith microstructure in 

 resolving issues of first year growth 

 and spawning seasonality of white 

 hake, Urophycis tenuis, In the Gulf 

 of Maine-Georges Bank region 



Kathy L. Lang 

 Frank P. Almeida 

 George R. Bolz 



Woods Hole Laboratory. Northeast Fisheries Science Center 

 National Marine Fisheries Service, NOAA 

 Woods Hole, Massachusetts 02543 



Michael P. Fahay 



J. J Howard Laboratory, Northeast Fisheries Science Center 

 National Marine Fisheries Service, NOAA 

 Highlands, New Jersey 07732 



White hake, Urophycis tenuis, has 

 become an increasingly important 

 commercial species in the north- 

 eastern United States. Landings 

 from the Gulf of Maine-Georges 

 Bank region steadily increased 

 from less than 1,000 metric tons (t) 

 in the late 1960's to approximately 

 7,500 t in 1984, averaged about 

 5,800 t during 1986-91, and in- 

 creased to an average of 9,300 t 

 during 1992-93 (NEFSC, 1995; 

 Burnett et al. 1 ). An assessment of 

 white hake conducted in 1984 indi- 

 cated that landings above 6,000 t 

 would probably not be sustainable. 

 However, a lack of information re- 

 garding the biology of the species 

 and the fishery (e.g. catch-at-age 

 data) left the evaluation uncertain 

 (Burnett et al. 1 ). Recent analyses 

 have estimated the long-term po- 

 tential catch to be about 6,500 t 

 (NEFSC, 1995). 



The stock structure of white hake 

 in the Gulf of Maine— Georges Bank 

 region is uncertain. While previous 

 assessments of the population in 

 U.S. waters have assumed a single 



stock inhabiting the waters of the 

 Gulf of Maine south to the mid-At- 

 lantic Bight (Burnett et al. 1 ), the 

 existence of two reproductively iso- 

 lated stocks in the northwest Atlan- 

 tic has been revealed, and their 

 spawning seasonality determined 

 by Fahay and Able ( 1989). 



Fahay and Able ( 1989 ) concluded 

 that the southern stock of white 

 hake spawns along the continental 

 slope, primarily south of Georges 

 Bank, but also on the Scotian Shelf 

 and off southern New England in 

 the spring. The northern stock re- 

 portedly spawns in the shallow 

 waters of the southern Gulf of St. 

 Lawrence and Scotian Shelf in the 

 summer (Fahay and Able, 1989). 

 These conclusions were based on 

 the distribution and abundance of 

 early life history stages as well as 

 known circulation patterns through- 

 out the region. Their results also in- 

 dicated that there is negligible suc- 

 cessful spawning of the species 

 within the Gulf of Maine (Fahay 

 and Able, 1989). Further, on the 

 basis of circulation patterns be- 



tween the Gulf of St. Lawrence and 

 southern New England waters, 

 Fahay and Able (1989) provided 

 support for the hypothesis of Musick 

 (1969) that pelagic juveniles ac- 

 tively migrate across Georges Bank 

 into the Gulf of Maine. 



Accurate age data on the adult 

 component of the stock greatly en- 

 hance estimates of spawning stock 

 size and predictions of future catch 

 and abundance. Several ageing 

 studies have been conducted for 

 white hake (Nepzky, 1968; Beach- 

 am and Nepzky, 1980; Hunt, 1982; 

 Clay and Clay, 1991). Ages deter- 

 mined by counting the number of 

 hyaline zones visible on transverse 

 sections of the sagittal otoliths have 

 been validated for white hake in- 

 habiting the Gulf of St. Lawrence 

 by comparing mean lengths at age 

 with observed length-frequency 

 modes (Hunt, 1982). However, the 

 results of a preliminary analysis of 

 age data collected from the Gulf of 

 Maine-Georges Bank region indi- 

 cated that there is still uncertainty 

 about the first hyaline zone and 

 therefore the location of the first 

 annulus. 



Researchers ageing white hake 

 have noted the presence of a hya- 

 line zone between the nucleus and 

 what has been regarded as the first 

 annulus (Hunt, 1982; Clay and 

 Clay, 1991). This hyaline zone var- 

 ies in intensity and in distance from 

 the nucleus. Most experienced age 

 readers believe that this zone is lo- 

 cated too close to the nucleus to be 

 the first annulus and have assumed 

 that it is a check formed either 

 when pelagic larvae settle into a 



1 Burnett, J., S. H. Clark, and L. O'Brien. 



1984. A preliminary assessment of white 

 hake in the Gulf of Maine— Georges Bank 

 area. Natl. Mar. Fish. Serv., Northeast 

 Fisheries Science Center, Woods Hole Lab. 

 Ref. Doc. 84-31. 33 p. 



Manuscript accepted 14 September 1995. 

 Fishery Bulletin 94:170-175 ( 1996). 



