Pacific halibut is fished by setline (long strings of line with attached hooks) on the continental shelf from northern California to the Bering Sea. The fishery currently operates eight months each year, from mid-March through mid-November. Chalky halibut has been recognized for decades, although until recently the problem was limited to summer fisheries in the southern fishing areas off Washington and Oregon. Until 1995, landings in most areas have occurred during short fisheries in the early and late summer, and most product was frozen. Since 1995, fisheries occur throughout the open period, and a majority of the product is sold fresh. This, combined with an increased awareness of chalkiness by the marketplace, has created the current situation, where as much as two million pounds of the 60-million pound catch is graded as chalky and thus unmarketable as a premium product, constituting a multi-million dollar loss to the industry.
IPHC research, both in the 1960s and in the late 1990s, have shown chalkiness to be directly associated with a buildup of lactic acid and resulting lowered pH in post-mortem flesh. The condition is specifically associated with a denaturation of muscle proteins resulting in an increased drip loss and a sometimes startling loss of translucence in the flesh. In extreme cases, the flesh gapes, and has little use as a food product. Our research has associated chalkiness with two areas of the coast during late summer and early fall, and male halibut tend to be chalkier than females. It is likely that the areas with the highest rate of chalkiness are associated with high bottom temperatures (12-14 degrees C), which are near the upper thermal limit for the species distribution. Most recently, we have facilitated the use of pH meters in 1-2 day post-mortem fish to determine flesh pH, which is predictive of the developing chalky condition.
The condition is reversible in live fish. Flesh which would otherwise likely be chalky does not develop the condition post-mortem if the fish are allowed a 1-2 day resting period after capture, and before killing.
A number of documents regarding chalky fish have been produced by the IPHC, primarily by Stephen Kaimmer.
- An investigation into the occurrence and causes of the chalky condition in Pacific halibut, RARA 1997 [pdf, 301K]
- Continuing the investigation into the occurrence and causes of the chalky condition in Pacific halibut, RARA 1998 [pdf, 293K]
- 1999 Chalky halibut study, RARA 1999 [pdf, 179K]
- Technical Report No. 44 - Chalky halibut investigations, 1997-1999. Stephen M. Kaimmer. 24 p. (2000) [pdf, 504 K]
- Field test of robust pH meter and Summary of 1960s investigations of chalky halibut, RARA 2000 [pdf, 809K]
- Chalky halibut investigations in 2001, RARA 2001 [pdf, 481K]
- Technical Report No. 50 - Investigating the roles of temperature and exercise in the development of chalkiness in Pacific halibut. Robert J. Foy, Charles A. Crapo, and Donald E. Kramer. (2006) [352 KB]