Comedu and Mdllet Effect of timing of tagging on tag recapture rates for Homarus americanus 



477 



death from natural causes (Beverton and Holt, 1957). In 

 the present article, "tag shedding" refers to the physical 

 detachment of the tag from a lobster and "tag-induced 

 mortality" refers to the actual death of a lobster caused by 

 the tagging process. 



In the southwestern Gulf of St. Lawrence, lobsters are 

 harvested either in the spring prior to the July-August 

 molting season, or in late summer and early fall (early- 

 August to early October, partially during and shortly after 

 molting) (Comeau and Savoie, 2001). The purpose of our 

 study was to estimate the level of streamer tag loss for 

 the American lobster tagged before and after the summer 

 (July- August) molting season by using aquarium observa- 

 tions. From the results of our aquarium study, we deter- 

 mined adjustments of the recapture rate in relation to the 

 molt stage at the time of tagging. 



Materials and methods 



Aquarium observations 



Two experiments were carried out at the "Aquarium et centre 

 marin" (New Brunswick Department of Agriculture, Fisher- 

 ies and Aquaculture) in Shippagan, New Bi-unswick, with 

 lobsters captured in Baie des Chaleurs 147°52'N; 64°52'W). 

 Because the main focus of our study was to investigate tag 

 loss in relation to the molting stage, only males were con- 

 sidered because they have a higher probability of molting 

 annually compared to sexually mature females (Comeau 

 and Savoie, 2001). All lobsters caught were brought to the 

 laboratory where carapace length (CD and shell rigidity 

 were recorded (the latter with a durometer) (Comeau and 

 Savoie, 2001 ). In both experiments, lobsters were tagged by 

 the same person to avoid variability in tagging procedure 

 following the technique described by Moriyasu et al. (1995). 

 Streamer tags manufactured by Hallprint Pty. Ltd. (15 

 Crozier Rd, Victor Harbor, South Australia, 5211 Australia) 

 were used. As is routinely done in our tagging studies in 

 the field (Comeau et al., 1998, 1999), tagged lobsters were 

 kept in a holding tank for a minimum of 30 min following 

 tagging, and dead lobsters were removed from the experi- 

 ment. Tagged lobsters were then transferred to large tanks 

 partitioned with 25 x 25 cm individual compartments. These 

 tanks were supplied with running seawater at ambient 

 temperature. Lobsters were fed rainbow smelt (Osmerus 

 mordax) twice a week. Lobsters were examined three times 

 a day in July and August, and on a daily basis for the rest 

 of the experiment. The date of tag shedding, of molting, or 

 of death was recorded for each lobster. 



Limited aquarium space prevented the use of a control 

 group of untagged lobsters. However, autopsies were per- 

 formed on all lobsters that died in the course of the experi- 

 ments in order to identify the cause of death. The following 

 tagging traumas, causing death, were identified (Krouse 

 and Nutting, 1990): 1) perforation of vital organs, such as 

 the pericardial sac and the hepato-pancreas; 2) rupture 

 of the thoraco-abdominal membrane; and 3) necrosis or 

 infection of lobster tissue at both the point of entry emd 

 exit of the tag. 



The first experiment began on 23 June 1998 before the 

 summer molting season with the tagging of 229 hard-shell 

 male lobsters ranging between 66 and 78 mm CL. To avoid 

 unnecessary manipulation of the lobsters, the molt stage 

 at tagging was estimated by the number of days between 

 tagging and molting. Individuals that molted within 30 

 days of and 30 days after tagging were considered lobsters 

 tagged in late premolt and early premolt stages (Aiken, 

 1980), respectively. The molt stage of lobsters that died dur- 

 ing the experiment was determined by observations of the 

 pleopods (Aiken, 1980). A total of 191 male lobsters were 

 tagged in premolt stage (56 in early and 135 in late premolt 

 stage) and 38 in the intermolt stage (lobsters that did not 

 molt over the entire experiments). Observations of premolt 

 tagged lobsters that molted in June and July ended on 8 

 September 1998. Observations of the remaining lobsters 

 tagged on 23 June 1998 ended on 30 October 1998. Before 

 releasing the lobsters in the water, their wounds from the 

 tag insertion were examined for infection. 



The second experiment began 9 September 1998 with the 

 tagging of 187 soft-shell male lobsters in the postmolt stage 

 based on shell condition criteria (Aiken, 1980; Comeau and 

 Savoie, 2001). They ranged in size between 66 and 83 mm 

 CL. Observations of postmolt tagged lobsters ended on 30 

 October 1998. 



Field studies 



Comparison of recapture rates from field studies Six 



tagging studies were carried out after the fishing season 

 (May-June) in Caraquet, New Brunswick, between 1994 

 and 1996. Male and female lobsters were captured, tagged, 

 and released on the commercial fishing grounds. For each 

 year, tagging was done before (in early July with hard- 

 shell lobsters) and after (in mid-September with soft-shell 

 lobsters) the molting season. In 1995, the July tagging was 

 delayed one week because the lobster fishing season ended 

 on 7 July instead of 30 June. In 1996, tagging was carried 

 out in early October instead of mid-September because of 

 bad weather. As with the aquarium experiments, the same 

 person performed the tagging procedure. Tagged lobsters 

 were kept in a holding tank for a minimum of 30 min 

 following tagging and any dead lobsters were removed. 

 Finally, an awareness campaign described in Comeau et 

 al. (1998) was conducted to maximize the participation 

 of fishermen in reporting tagged lobsters as tag recovery 

 took place during the fishing seasons following the year of 

 tagging. 



Adjustment of the recapture rate Recapture rates ob- 

 served during the fishing season following tagging were ad- 

 justed by using the information from the aquarium obser- 

 vations. In contrast to tag misreporting that biases the 

 estimated number of recaptured lobsters, tag loss affects 

 the number of tagged animals (AT) in the population avail- 

 able to the fishery. To account for possible tag loss in our 

 field studies, AT was adjusted as follows. Letp represent the 

 tag-retention rate parameter estimate based on aquarium 

 observations with variance p(7-p;n"', where n is the total 

 number of animals observed in each aquarium experiment. 



