Annual instantaneous rates of fishing mortality (F) and 

 apparent total mortality (Z') which ranged from 4.14 to 7.31 

 and 5.89 to 8.73 (Table 7), respectively, were extremely high as 



Table I. — Annual instanlaneous rales of nppfent total (Z') and 

 f ish!ng (/") mortality on American lobsters estimated from returns 

 grouped by different time intervals. Annual mortality rates expressed as 

 - j s are in parentheses. 





Kennebunkpc t 

 Z' F 



Boothbay Harbor 

 Z' F 



Jot 



lesport 



T .e 

 interval 



Z' 



F 



Weekly 



7.10 



4.14 



6.36 



4.13 



8.73 



7.22 





(99.9) 



(98.4) 



(99.8) 



(98.4) 



(99.9) 



(99.9) 



Biweekly 



7.08 



4.89 



6.16 



4.11 



8.39 



7.31 





(99.9) 



(99.2) 



(99.8) 



(98.4) 



(99.9) 



(99.9) 



Monthlv 



7.12 



4.93 



5.89 



3.98 



8.72 



7.27 





(99.9) 



(99.3) 



(99.7) 



(98.1) 



(99.9) 



(99.9) 



the result of the actual return rates which were, I believe, not 

 fully representative of general conditions; the fact that annual 

 mortality rates were calculated from tag return data collected 

 when the catches of the seasonal lobster fishery were highest, 

 and systematic errors inherent in most tagging studies. Gulland 

 (1969) has classified these errors according to their effects on 

 the various estimates. Types A and B errors result from tag 

 loss and systematically bias mortality rates causing an 

 underestimate of fishing mortality and an overestimate of the 

 true total mortality (Z), respectively. Type A error, which is 

 caused by death of fish shortly after tagging and incomplete 

 reporting of recaptures, affects F but not Z. Type A errors 

 appeared minimal except at Boothbay Harbor where trawlers 

 were suspected of unreported catches of tagged lobsters. In 

 fact, the relatively lower estimates of F at Boothbay Harbor 

 may be attributable, in part, to this error. Of the Type B 

 errors, which include natural mortality, emigration, and tag 

 detachment, only the latter was of significant magnitude in 

 this study to warrant consideration. 



Quantitative estimates of tag loss were obtained by follow- 

 ing Gulland's (1963) methodology for estimating tag retention 

 rates with data from double tagging experiments. Due to 

 problems that we encountered initially with this procedure, 

 Russell (1980) analyzed this method and corrected some of 

 Gulland's basic equations. 



In all cases, estimated losses of the sphyrion tag were higher 

 than those of the cinch tag (Table 8). Considering differences 

 in modes of attachment, higher losses of sphyrion tags were 

 expected; however, cinch tag losses were greater than antici- 

 pated. Evidently some of the cinch tags became loose and 

 subsequently slipped off the chela (claw). In retrospect, this 

 type of loss would have been minimized had the tag been 

 secured around the carpus (section proximal to the propodus) 

 of the pincer claw. 



A comparison of the relatively high annual loss rates of indi- 

 vidual tags (range of 39.4-51.5%) with those of both tags (range 

 of 15.0-24.0%) clearly indicates how tag returns would have been 

 reduced if only one tag rather than two had been used. Never- 

 theless, in view of these estimates, we feel that tag loss was of 

 sufficient magnitude to bias mortality estimates. This error, 

 termed Type B, is an additional cause of mortality ("X") and 

 results in an overestimate of Z but has no effect on F. Unfor- 

 tunately, if we convert the highest annual tag loss rates 

 (39.4-51.5%) (Table 8) to instantaneous rates (0.50-0.72) and 

 then subtract these values from estimates of Z' (5.89-8.73) 

 (Table 7), this only results in an insignificant reduction in Z'. 

 Thus it is apparent that other factors besides tag loss have 

 caused overestimates of Z. When these errors are operative 

 only F is estimated from tagging data; thus Z is derived from 

 some independent estimate and M is the difference between F 

 and Z. 



Undoubtedly, the most meaningful mortality estimates 

 derived from data of this study are those of F and even these 

 values as well as estimates of Z are inflated as the result of 

 incomplete mixing of tagged lobsters with the untagged popu- 

 lation [Gulland's (1969) Type C error] along with other factors 

 previously stated. Despite this bias, estimates of F do indeed 

 reflect the Maine lobster fishery's extremely high rate of 

 exploitation. 



SUMMARY 



1 . Of 2,882 lobsters tagged in the spring of 1975, 2,188 (75.9%) 

 were recaptured through September 1977. Lobsters 

 released at Jonesport had the highest return (85.2%) follow- 

 ed by Kennebunkport (74.8%) and Boothbay Harbor 

 (67.4%). 



2. Catchability of legal-sized lobsters did not vary by sex nor 

 size. 



3. Twenty-four ovigerous females ranging from 82 to 109 

 mm CL were recaptured. 



4. Sixty-six (3.0%) of the lobsters recaptured had molted while 

 at large. Percentage of increases in carapace length varied 

 from 7.3 to 18.1% (12.7% mean) at Boothbay Harbor, 1 1.5 to 

 16.0% (13.1% mean) at Kennebunkport, and 10.6 to 18.5% 

 (15.1% mean) at Jonesport. 



5. The majority of returns from Kennebunkport (98.0%), 

 Boothbay Harbor (73.6%), and Jonesport (91.5%) were 

 caught within a 5 n.mi. (9.3 km) radius of the release sites. 

 Recaptured lobsters moved on the average more at 

 Boothbay Harbor (4.45 n.mi., 8.2 km) and less at 

 Kennebunkport (2. 16 n.mi., 4.0 km). Only about 1% of the 

 returns wandered >10 n.mi. (18.5 km). 



6. Most movement was shoreward with a westerly drift from 

 the point of release. Few lobsters traveled in an easterly 



Table 8. — Estimated percentage of tag loss after various time intervals for American lobsters 

 released at Kennebunkport, Boothbay Harbor, and Jonesport, Maine. 





Kennebunkport 





Boothbay Harbo 



r 



Jonesport 











Both 







Both 







Both 



Week 



Sphyrion 



Cinch 



tags 



Sphyrion 



Cinch 



tags 



Sphyrion 



Cinch 



tags 



1 



2.0 



1.6 



0.03 



1.2 



1.2 



0.01 



1.8 



1.2 



0.02 



4 



7.6 



6.3 



0.5 



4.8 



4.5 



0.2 



6.7 



4.9 



0.3 



16 



24.7 



21.1 



5.2 



16.7 



16.0 



2.7 



22.3 



17.0 



3.8 



52 



51.5 



46.5 



24.0 



39.4 



38.2 



15.0 



48.3 



39.9 



19.3 



