Movement, Growth, and Mortality of American Lobsters, Homarus 

 americanus, Tagged Along the Coast of Maine 1 



JAY S. KROUSE 2 



ABSTRACT 



During the spring of 1975, 2,882 American lobsters, Homarus americanus, were tagged at three locations off 

 Maine. Four months after release 65% of the lobsters had been returned and by the completion of the study in 

 September 1977, 2,188 (75.9%) lobsters had been recaptured. Most returns (88%) occurred within a 5 n.mi. (9.3 

 km) radius of the release site and only about 1% of the recaptured lobsters had moved more than 10 n.mi. (18.5 

 km). Movement and catchability did not vary significantly by sex nor size. The majority of lobsters traveled 

 shoreward or along the coast on a west to southwesterly course with minimal easterly movement. All long 

 distance migrants O20 n.mi. or 37.0 km) followed a south to southwesterly course. Extremely high annual 

 instantaneous fishing mortality rates (4.0-7.3) estimated for each release area confirm the overexploitation of the 

 Maine inshore lobster fishery. 



INTRODUCTION 



METHODS 



During the past decade concern for the future well-being of 

 the Maine American lobster fishery has intensified as levels of 

 fishing effort have increased and catches have generally 

 declined. In response to this interest in Maine's most valuable 

 commercial fishery, the Lobster Research Project of the Maine 

 Department of Marine Resources (DMR), initiated in 1966 

 extensive studies of various facets of the fishery (Thomas 1973; 

 Krouse and Thomas 1975; Krouse 1978) and biology of the 

 lobster (Krouse 1973). Even though information from these 

 studies has provided some basis for scientific management of the 

 lobster fishery, additional research is required in many areas. 

 One important area with a paucity of information is that of 

 lobster movement along the Maine coast. To date there have 

 been three tagging studies with Maine lobsters. Harriman 3 and 

 Cooper (1970) tagged lobsters at Monhegan Island [about 10 

 n.mi. (nautical miles), 18.5 km offshore] and determined that 

 those lobsters were nonmigratory since most recaptures were 

 recovered within a 2 n.mi. (3.7 km) radius of the island. In con- 

 trast, Dow (1974) reported that 5 of 162 lobsters (23 returns in 

 all) tagged by commercial fishermen off the Maine coast 

 traveled 75-138 n.mi. (138.9-255.6 km) toward Cape Cod. Four 

 of these migrant lobsters were larger than the Maine maximum 

 legal size of 127 mm CL (carapace length) when tagged, 

 indicating a positive relationship between a lobster's size and 

 movement. 



In view of the limited size and scope of these lobster tagging 

 studies conducted previously in Maine waters, we decided to 

 undertake a coastwise tagging project. Objectives of this present 

 study were to provide new information on growth, mortality, 

 and movement or migration patterns of legal-sized lobsters 

 (81-127 mm CL). 



'This study was conducted in cooperation with the Department of Commerce, 

 National Marine Fisheries Service, under Public Law 88-309 as amended, Com- 

 mercial Fisheries Research and Development Act, Project 3-228-R. 



2 Marine Resources Laboratory, Maine Department of Marine Resources, 

 West Boothbay Harbor, ME 04575. 



'Harriman, D. M. 1952. Progress report on Monhegan tagging 

 1951-52. Unpubl. manuscr., 8 p. Maine Dep. Mar. Resour., W. Boothbay 

 Harbor, ME 04575. 



Tagging Areas 



Three tagging sites, Kennebunkport, Boothbay Harbor, and 

 Jonesport, representing the western, central, and eastern 

 sections of the Maine coast (Fig. 1), were selected on the basis of 

 geographical location and local availability of lobsters. 



Well in advance of the scheduled dates for tagging, certain 

 lobster dealers were contacted at each tagging area, and 

 arrangements were made to purchase about 1 ,000 lobsters from 

 each area. It was specified that these lobsters be locally caught 

 and not sorted by size. These requirements would ensure that 

 the tagged lobsters were characteristic of the area studied in 

 terms of size, movement, and catchability. 



To determine whether the tagged lobsters were representative 

 in size of those lobsters caught commercially, length- frequencies 

 were plotted by 1 mm increments for lobsters tagged at each tag- 

 ging site (Fig. 2). Because of the likeness between size composi- 

 tion data of this present study and data obtained from Maine's 

 Commercial Sampling Program (Thomas 1973), we are confi- 

 dent that the lobsters tagged were typical of the legal size range 

 of lobsters along the Maine coast. 



Tagging 



The sphyrion tag developed by Scarratt and Elson (1965) and 

 later modified by Cooper (1970) was selected as the primary 1 

 mark as it can be retained through a molt. The model we used in 

 this study consisted of a supple yellow PVC (polyvinylchloride) 

 tube (2 mm diameter x 55 mm long) attached by a thin 

 polyethylene thread to a 7 mm long stainless steel anchor. Tags 

 were attached according to the technique described by Cooper 

 (1970). 



In order that the magnitude of tag loss could be evaluated a 

 secondary tag was used. The tag selected was the Floy cinch-up 

 which was secured to the pincer claw by either fastening it 

 around the proximal end of the propodus or around the carpus 

 of lobsters > 100 mm CL. Although this tag would be lost after 

 ecdysis, we anticipated that a sufficient number of lobsters 

 would be recaptured prior to molting, to enable estimation of 



