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

Tag shedding was observed during molting for 21% (29) of the lobsters tagged in the premolt stage (Table 1). Tag shedding was observed for lobsters tagged in both early and late premolt stages (Table 1) but was significantly higher ([chi square]=5.9; P=0.014) for lobsters tagged in the early premolt stage. Twenty-one percent (28) of lobsters tagged in the premolt stage that molted had a misaligned tag (pulled to one side).

Only 4% (8) of the lobsters tagged in the postmolt stage died during the second experiment, and only one individual (<1%) shed a tag (Table 1). The autopsies revealed that tags were not well embedded in the muscle tissue and large scars were observed on the dorsal thoraco-abdominal membrane of seven individuals (Table 2). These lobsters died within 11 days of tagging. The death of the other individual was not related to tagging for there was no sign of tagging trauma. Three percent (5) of the lobsters had a misaligned tag at the end of the experiment.

From a total of 229 lobsters initially tagged for the first experiment, 17% (38) were in the intermolt stage. Although the sample number was small, none of these lobsters shed their tag, died from the tagging procedure, or molted. This finding indicates that these small male lobsters (67-78 mm CL) skipped an entire molting season (July-August) in 1998 and retained their tags without risk. Only one (3%) lobster had a misaligned tag at the end of the experiment. No lobster that was returned to the sea after the experiments had infected wounds from the tag insertion procedure.

Reid studies

Tag-induced mortality was observed within 30 min in every tagging study conducted between 1994 and 1996, varying in rate between 0.4% to 3.5%. The majority of the lobsters tagged in early July 1994, 1995, and 1996 were in the premolt stage because 94% to 99% had molted before being recaptured the following fishing season. Except for two lobsters (1.1%) tagged in 1994 that were recaptured the following fishing season with a size increase, all of lobsters tagged in September-October were in the postmolt stage. Recapture rates based on the first recapture period for lobsters tagged in early July (premolt) were significantly lower than the recapture rates for lobsters tagged in September-Octeber (postmolt) for the 1994 ([chi square]=10.6; P=0.0Ol) and 1995 ([chi square]=11.4.; P=0.0O07) tagging, but not for the 1996 ([chi square]=2.0; P=0.156) tagging (Table 3). Although lobsters were recaptured for up to three years following their tagging, the recapture rate was drastically reduced between the first and second recapture period (Table 3). No lobsters were recaptured after four years.

Based on the information from our aquarium observations, the adjusted recapture rates of the field tagging studies showed no difference between lobsters tagged in the premolt and postmolt stages (Table 3). Because the 1995 July tagging was carried out one week later and the molting season was early that year (Comeau and Savoie, 2001), the adjusted recapture rate, based only on late premolt lobsters, was 35.2% (CI 30.8, 42.1). The confidence intervals calculated from Monte-Carlo simulations were always wider for lobsters tagged in the premolt stage (Table 3).