643 



Improving the precision of otolith-based 

 age estimates for Greenland halibut 

 {Reinhardtius hippoglossoides) with 

 preparation methods adapted for fragile sagittae 



Jacob L. Gregg 



Western Fisheries Research Center 

 Marrowstone Marine Field Station 

 United States Geological Survey 

 616 Marrowstone Pt Road 

 Nordland, Washington 98358-9633 



Delsa M. Anderl (contact author) 

 Daniel K. Kimura 



National Oceanic and Atmosphenc Administration 



National Marine Fishenes Service 



Alaska Fisheries Science Center 



7600 Sand Point Way NE 



Seattle, Washington 98115-6349 



Email address for D, M. Anderl; Delsa. Anderla noaagov 



Otolith-based age estimates for 

 Greenland halibut {Reinhardtius hip- 

 poglossoides) have low precision, and 

 there is general uncertainty about 

 their accuracy in older fish (Anon.'; 

 Alpoim et al.-). Low precision can 

 result from inadequate training of 

 age readers, poor aging criteria, or 

 peculiarities of the structure being 

 aged (Kimura and Lyons, 1991). The 

 latter is the primary cause of low pre- 

 cision with Greenland halibut, and 

 it confounds attempts to improve the 

 former two. Sagittae of Greenland 

 halibut are irregular in shape and 

 exhibit marked bilateral asymmetry 



' Anonymous. 1997. Report of the 

 ICES/NAFO workshop on Greenland 

 halibut age determination, Reykjavik, 

 Iceland, 26-29 November 1996. ICES 

 CM 1997/0:1, 53 p. Palaegrade 2-4 

 DK-1261 Copenhagen K Denmark. 



2 Alpoim, R., E. Roman, B. Greene, R. 

 Burry, and W. R. Bowering. 2002. Re- 

 sults of the Greenland halibut iRein- 

 hardtiiis hippoglosoides ) otolith 

 exchange between Spain, Canada, and 

 Portugal. /;; NAFO Scientific Council 

 Meeting, June 2002. NAFO SCR Doc. 

 02/141, 14 p. P.O. Box 638, Dartmouth, 

 Nova Scotia, Canada B2Y 3Y9. 



(Fig. 1). Much of this irregularity is 

 due to finger-like projections, which 

 begin as small, marginal tubercles in 

 4- to 6-year-old fish, and can develop 

 into convoluted, fragile structures in 

 older fish. The variable deposition 

 rate of aragonite and protein that 

 produces these structures makes 

 interpretation of growth patterns 

 difficult and results in age estimates 

 that vary depending on which region 

 of the otolith is examined. 



The amphiboreal distribution of 

 Greenland halibut has led to their 

 exploitation by the industrial fisher- 

 ies of more than ten nations in the 

 North Atlantic and North Pacific 

 Oceans and by several aboriginal 

 fisheries in the near shore regions of 

 Greenland and northern Canada (Al- 

 ton et al., 1988; Witherell^; Anon.^; 

 Treble''). Age determination (aging) 

 and age structure analysis have 

 been undertaken primarily for North 



Atlantic and Barents Sea stocks. 

 Methods vary between laboratories 

 but the majority of aging is accom- 

 plished by examining the surface 

 patterns of whole sagittae. For the 

 purposes of this note, "surface" (or 

 "surface aging") will refer to the 

 surface pattern of the whole sagitta. 

 Generally, only the left (i.e., blind 

 side offish) sagitta is aged because it 

 has a more centric nucleus, resulting 

 in more evenly spaced annuli (Lear 

 and Pitt, 1975; Bowering, 1978. 1982; 

 Haug and Gulliksen, 1982; Anon.'; 

 Bowering and Nedreaas, 2001; Al- 

 poim et al.'-'). Attempts to improve 

 the resolution of growth patterns 

 have included baking both sagittae, 

 clearing them with oil, grinding the 

 distal surface of the left sagitta, and 

 breaking and burning the left sagitta 

 (Anon.'; Kuznetsova et al., 2001; Al- 

 poim et al.-). To date these processes 

 have had equivocal effects on the pre- 

 cision of age estimates. Internation- 

 al exchanges of Greenland halibut 

 otoliths have yielded mixed results; 

 reported between-reader agreement 

 (±0 year) has ranged from 1% to 69% 

 (Anon.') and from 37% to 51% (CVs 

 ranging from 5.81% to 9.58%) (Alpo- 

 im et al.-). Despite these exchanges, 

 concern about precision still exists 

 and a consensus on preferred aging 

 methods for Greenland halibut has 

 not been reached. 



The Alaska Fisheries Science Cen- 

 ter (AFSC) has collected Greenland 

 halibut otoliths from the Bering Sea 

 and Aleutian Islands for over 20 

 years, but little aging was attempted 

 prior to 2003. Initial examination of 

 the otoliths left AFSC age readers 



3 Witherell, D. 2000. Groundfish of the 

 Bering Sea and Aleutian Islands area: 

 species profiles 2001. North Pacific 

 Fisheries Managements Council. 60.5 

 W. 4"' Ave. Ste. 306 Anchorage, AK 

 99501-2252. 



^ Anonymous. 2004. Annual quota table 

 for 2005. In 2004 Annual report of the 

 Northwest Atlantic Fisheries Organiza- 

 tion, P.O. Box 638, Dartmouth, Nova 

 Scotia Canada B2Y 3Y9. 



^ Treble, M. 2005 Personal, commun. 

 Arctic stock assessment biologist. Fish- 

 eries and Oceans Canada, 501 University 

 Crescent, Winnipeg, Manitoba Canada 

 R3T 2N6 



Manuscript submitted 12 May 2005 

 to the Scientific Editor's Office. 



Manuscript approved for publication 

 6 January 2006 by the Scientific Editor. 

 Fish. Bull. 104:643-648 12006). 



