In recent years a rapidly growing interest in inclusion phenomena has been focused in two major directions. In the first, the binding or complexation of guest species by unimolecular hosts in solution has received much attention, and excellent recent reviews have appeared for two particularly important classes of host, the naturally-occurring cyclodextrinsl-3 and compounds of the synthetic 'crown' type.4 The second equally fascinating aspect of 'host and guest chemistry' relates to the study of crystalline multimolecular inclusion c ~r n p o u n d s , ~-~~ which may be sub-classified as the true clathrate type22 in which the guest molecules are imprisoned in discrete closed cavities or cages; the channel type23 in which the guest species are accommodated in continuous canals running See for example D.

SynopsisIdentifying spawning behavior in Pacific halibut, Hippoglossus stenolepis, is particularly challenging because they occupy a deep, remote environment during the spawning season. To identify spawning events, a method is needed in which direct observation by humans is not employed. Spawning behavior of seven other flatfish species has been directly observed in their natural environment by investigators using SCUBA. All of these flatfish species display almost identical spawning behavior that follows a routine. Therefore, it is reasonable to believe that this spawning behavior occurs in other flatfish species, including Pacific halibut. As part of a larger study, we recaptured two Pacific halibut on which Pop-up Archival Transmitting (PAT) tags had been attached during the winter spawning season. Because the tags were physically retrieved, we were able to collect minute-by-minute depth records for 135 and 155 days. We used these depth data to tentatively identify spawning events. On seven separate occasions between 20 January 2001 and 9 February 2001, one fish displayed a conspicuous routine only seen during the spawning season of Pacific halibut and the routine parallels the actions of other spawning flatfish directly observed by humans using SCUBA. Therefore, we propose this routine represents spawning behavior in Pacific halibut. The second tagged fish did not display the conspicuous routine, thus challenging the assumption that Pacific halibut are annual spawners. PAT tags may prove to be a useful tool for identifying spawning events of Pacific halibut, and that knowledge may be used for improved management in the future.

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