The effect of timing of tagging on streamer-tag recapture rates for American lobster - Homarus americanus

Fishery Bulletin, July, 2003 by Michel Comeau, Manon Mallet

Discussion

Our results suggest that streamer tag loss for the American lobster depended upon the molt stage of the lobster at the time of tagging. Tag-induced mortality without molting was observed mainly within four days of tagging for lobsters tagged in late premolt and postmolt stages; whereas lobsters tagged in early premolt and intermolt stages seemed to be less affected by tagging trauma because none died following the tagging process. Autopsies revealed that the length of time between tagging and death was related to a specific tagging trauma and depended upon the molt stage. Perforation of the pericardial sac caused massive bleeding and resulted in death within 30 min of tagging. The rupture of the dorsal thoraco-abdominal membrane, which also caused bleeding, killed the lobsters within days. Perforation of the hepato-pancreas killed the lobsters within weeks. These types of tagging trauma that caused death were reported by Krouse and Nutting (1990) for American lobsters tagged with Australian western rock lobster (Panulirus longipes cygnus) insertion tags. With more careful tagging manipulations, these types of trauma could possibly be reduced. However, even with extreme care during tagging manipulations, the rupture of the dorsal thoraco-abdominal membrane for lobsters tagged in the postmolt stage might be difficult to avoid. Tagging postmolt lobsters was sometimes difficult because the abdominal muscles of some lobsters were thin, and insuring the insertion of the tag through these muscles was a delicate operation. Thus, streamer tags not completely embedded into well-developed abdominal muscles could be a serious problem for tag retention. Tag shedding without molting was observed only for one lobster tagged in the postmolt stage. In general, lobsters tagged with streamer tags during intermolt and postmolt stages had a lower level of tag loss than lobsters tagged in the premolt stage. The level of streamer tag loss was the highest for lobsters tagged in the late premolt stage.

Tag-induced mortality observed during or shortly after molting was almost exclusively observed for lobsters tagged in the late premolt stage. Although lobsters tagged in the early premolt stage did not die from tagging trauma, they shed proportionately more tags during molting than lobsters tagged in the late premolt stage. Unlike tag loss for lobsters that did not molt, tag loss at molting was not the result of the perforation of internal organs or a questionable tag insertion during tagging but was caused by the tag being firmly attached to the old thoraco-abdomincal membrane and being shed, still attached to the exuvia. For tagged lobsters that died during molting, which were almost exclusively lobsters tagged in the late premolt stage, tag loss was caused by massive bleeding resulting from the rupture of the entire new thoraco-abdominal membrance by the tag that was still firmly attached to the old thoraco-abdominal membrane. In addition, we observed a high level (21%) of tag misalignment due to the partial attachment of the tag to the old carapace for lobsters that did not have tag loss during molting. For these lobsters, incorrect insertion of the streamer tag was not an issue. Hence, firm tag attachment of the tag to the dorsal thoraco-abdominal membrane of the old carapace (which causes tag-induced mortality or tag shedding) is a serious problem.