Management of Pacific halibut (Hippoglossus stenolepis), a long-lived flatfish, is complicated by possible ontogenic and sex-specific variation in migration. Archival tags promise the ability to help uncover long-term movement patterns at the individual level, if the tags can be retained and recovered from healthy fish. We examined fifteen individuals (69–90 cm fork length) for long-term physiological response to intracoelomic implantation of three types of archival tags: fully internal, internal with right angle protruding light stalk, and internal with straight protruding light stalk. Tags represented 0.05–0.16% of initial fish weights. Fish were reared at 10.8 ± 1.1°C for 59 weeks post-surgery. One fish died after 39 weeks from thermal stress unrelated to the surgical procedure. Temporal variation in behavior of tagged fish was indistinguishable from that of controls (n = 15 tagged, 5 controls). Treatment and control-group fish grew at similar rates. No tag expulsion or physiological response was evident in the individual that died at 39 weeks, but nine of eleven individuals dissected at the end of 59 weeks had developed internal responses. These responses ranged from deposition of fibrous protein and/or calcitic material on tag surfaces to partial or full tag encapsulation in either the visceral peritoneal layer (fully-internal tags) or the intestinal mesenteries (stalk-bearing tags). The responses were within the range reported for other pleuronectids implanted with tags of similar configuration and may have implications for design and interpretation of long-term tagging studies. Encapsulation may reduce the probability of tag recoveries even in the absence of tag expulsion, especially in species eviscerated at sea.
