Comeau and Mallet: Effect of timing of tagging on tag recapture rates for Homarus americanus 



481 



The level of streamer tag shedding in nature seems to be 

 higher than that observed in our aquarium observations 

 and could provide additional information for adjusting 

 streamer-tag recapture rates. From a field study, Rowe and 

 Haedrich (2001) observed that 119c of nonmolted lobsters 

 shed their tags in a one-year period. If we assumed that 

 these lobsters were tagged in the intermolt and postmolt 

 stages, their estimate for streamer-tag shedding is higher 

 than our estimate of less than 1%. Different tagging tech- 

 niques could explain this difference because Rowe and Hae- 

 drich (2001) tagged larger lobsters (>100 mm) differently 

 (with the tag inserted in only one abdominal muscle) than 

 did Moriyasu et al. (1995) for smaller lobsters. The differ- 

 ence could also be explained by the artificial conditions of 

 our aquarium experiment. Under natural conditions tagged 

 lobsters could shed their tags through interspecific interac- 

 tions (Rowe and Haedrich, 2001), intraspecific interactions, 

 and by being dislodged by obstacles in their habitat (Ennis, 

 1986; Krouse and Nutting, 1990). Streamer tag loss related 

 to inter- and intraspecific interactions and the habitat has 

 already been reported for the brown shrimp (Howe and 

 Hoyt, 1982; P. aztecus) and the tiger prawn (Hill and Was- 

 senberg, 1985;P. esculentus). However, more research would 

 be needed to identify the cause of tag shedding in nature 

 and assess its variability in relation to different lobster 

 habitat before the recapture rate could be adjusted based 

 on inter- and intraspecific interactions and the habitat. 



The overall level of streamer tag loss compared to sphy- 

 rion tag loss seems to be lower, but also depends upon the 

 molt stage of the lobster at tagging and molting. In their 

 study, Moriyasu et al. (1995), suggested that sphyrion tag 

 loss mainly occurs within days after tagging or during 

 molting and is related to the lobster molt stage at tagging. 

 We observed lower levels of tag loss compared to those of 

 Moriyasu et al. ( 1995), except for the tag shedding during 

 molting for early premolt lobsters and tag-induced mor- 

 tality for lobsters tagged in late premolt. They observed 

 3% and 11% of tag shedding without molting for lobsters 

 tagged in early and late premolt stages, respectively, com- 

 pared to none in our study. Furthermore, the most striking 

 difference is the level of tag loss that reached 10% and 

 30% for lobsters tagged in intermolt and postmolt stages 

 compared to 0% and <1%, respectively, in our study. The 

 difference in tag loss for lobsters tagged in the postmolt 

 stage could be explained by the physical nature of the 

 tags themselves and the tagging techniques. Compared to 

 the streamer tag that is threaded through two abdominal 

 muscles, the sphyrion tag is anchored to only one muscle by 

 means of a hypodermic needle (Moriyasu et al., 1995). Be- 

 cause the muscles of postmolt lobsters (in the early stages) 

 are not well formed, it is difficult to firmly embed an object, 

 such as a tag, and the probability of tag loss for a tag em- 

 bedded into only one thin muscle is greater than that for 

 a tag treaded through two muscles. Hence, it seems that 

 streamer tags are more effective in terms of tag retention 

 compared to sphyrion tags for lobsters tagged in intermolt 

 and postmolt stages, but equally so for lobsters tagged in 

 the premolt stage. 



In field tagging studies, streamer tags yielded a good re- 

 capture rate within the first year following tagging for lob- 



sters tagged immediately before or after the molting sea- 

 son. The efficiency of streamer tags compared to sphyrion 

 tags had already been established (.Moriyasu et al., 1995; 

 Comeau et al., 1999). Moriyasu et al. (1995) reported that 

 there was a significantly greater recapture rate for lob- 

 sters tagged with streamer tags (44%) compared to those 

 tagged with sphyrion tags (19%). Based on the results of 

 Comeau et al. (1999), the recapture rate of lobsters tagged 

 with sphyrion tags is 22% and 16% for lobsters tagged 

 in premolt and postmolt stages, respectively, compared 

 to 33% and 45% for lobsters tagged with streamer tags. 

 These recapture rates corroborate aquarium observations 

 by Moriyasu et al. (1995) on the tag retention of sphyrion 

 tags and ours on the tag retention of streamer tags for 

 lobster tagged at various molt stages. 



Knowledge of the level of tag loss is paramount for ad- 

 justing the recovery rate to estimate population character- 

 istics and fishery parameters for the American lobster. We 

 observed that the recapture rate dropped significantly in 

 the second and third years at large; this finding suggests 

 a high level of tag loss. A similar multiple-years recapture 

 rate pattern was observed for six other sites within the 

 southwestern Gulf of St. Lawrence (Comeau and Savoie, 

 2002). Rowe and Haedrich (2001) indicated that the 

 streamer tag shedding level for lobsters that molted almost 

 a year later reached 40%. This high level of tag shedding, 

 probably related to the streamer tag remaining firmly 

 attached to the old dorsal thoraco-abdominal membrane 

 during molting, might explain the drastic decrease of tag 

 recaptures observed between the first and the second tag- 

 recapture periods in our field study. We believe that the 

 adjustment of the recapture rate due to tag loss should 

 be limited to lobsters recaptured within the first year at 

 large and prior to the molting season for lobsters tagged 

 in intermolt and postmolt stages. 



The multiple-years recapture pattern of a high recapture 

 rate within the first year at large followed by low recapture 

 rates in subsequent years could have a significant impact 

 on multiyear tagging models. These models that were pro- 

 posed by Sober ( 1970) could be used to estimate population 

 characteristics and fishery parameters if underlying as- 

 sumptions are followed. Based on these multiyear models 

 originally developed for birds (Seber, 1970; Brownie et al., 

 1985), a suite of models adapted for fishery data and ad- 

 justments, mainly by reparameterization, were proposed 

 to address underlying assumption violations (Pollock et 

 al., 1991, 2001; Heam et al., 1998, 1999; Hoenig et al., 

 1998a, 1998b; Frusher and Hoenig, 2001; Latour et al., 

 2001a, 2001b). Some of these models were developed to 

 take into account fishing effort, incomplete mixing, and 

 tag recovery rate. The latter is a composite parameter 

 involving tag retention and tag-induced mortality (tag 

 loss), exploitation rate, and tag reporting rate. There is no 

 argument that the participation of fishermen in returning 

 tags (tag reporting rate) is very important; however, for 

 crustacean fisheries, underlying assumptions dealing with 

 tag loss (see assumptions 2 and 3 in Pollock, 1991, 2001) 

 are equally important and have to be addressed. In general. 

 Pollock et al. (2001) indicated that the assumptions of no 

 tag loss could be violated in two ways; by tag loss in the first 



