...peculiarities the structure being aged (Kimura and Lyons, 1991). The latter is the primary cause of low precision 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 (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.

[FIGURE 1 OMITTED]

The amphiboreal distribution of Greenland halibut has led to their exploitation by the industrial fisheries 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 (Alton et al., 1988; Witherell (3); Anon. (4); Treble (5)). 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 accomplished 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 of fish) 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. (1); Bowering and Nedreaas, 2001; Alpoim et al. (2)). 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. (1); Kuznetsova et al., 2001; Alpoim et al. (2)). To date these processes have had equivocal effects on the precision of age estimates. International exchanges of Greenland halibut otoliths have yielded mixed results; reported between-reader agreement ([+ or -] year) has ranged from 1% to 69% (Anon. (1)) and from 37% to 51% (CVs ranging from 5.81% to 9.58%) (Alpoim et al. (2)). 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 Center (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 with a general lack of confidence in surface age estimates. This uncertainty, coupled with the observation that otoliths of larger, presumably older, fish tend to grow in thickness rather than in sagittal diameter, led to pilot work for processing and production (large-scale) aging of Greenland halibut sagittae. Various methods reported in the literature and several new techniques were explored. This pilot work converged on a method that involved...

NOTE: All illustrations and photos have been removed from this article.



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