247 



Abstract — Thu population structure 

 and abundance of the American lob- 

 ster {Homarus americanus) stock in 

 the Gulf of Maine are defined by data 

 derived from a fishery-independent 

 trawl survey program conducted by 

 the National Marine Fisheries Service 

 (NMFS). Few sampling stations in 

 the survey area are located inshore, 

 in particular along coastal Maine. 

 According to statistics, however, more 

 than two thirds of the lobster land- 

 ings come from inshore waters within 

 three miles off the coast of Maine. In 

 order to include an inshore survey 

 program, complementary to the NMFS 

 survey, the Maine Department of 

 Marine Resources iDMR) initialized 

 an inshore survey program in 2000. 

 The survey was modeled on the NMFS 

 survey program, making these two 

 survey programs comparable. Using 

 data from both survey programs, we 

 evaluated the population structure 

 of the American lobster in the Gulf 

 of Maine. Our findings indicate that 

 lobsters in the Gulf of Maine tend 

 to have a size-dependent inshore-off- 

 shore distribution; smaller lobsters 

 are more likely to stay inshore and 

 larger lobsters are more likely to 

 stay offshore. The DMR inshore and 

 NMFS survey programs focused on 

 different areas in the Gulf of Maine 

 and likely targeted different seg- 

 ments of the stock. We suggest that 

 data from both survey programs be 

 used to assess the lobster stock and 

 to describe the dynamics of the stock 

 in the Gulf of Maine. 



A comparison of two fishery-independent 

 survey programs used to define the population 

 structure of American lobster 

 (Homarus americanus) in the Gulf of Maine 



Yong Chen 



School ol Marine Sciences 

 218 LibbyHall 

 University ol Maine 

 Orono, Maine 04469 

 E-mail address ycheniaTnaineedu 



Sally Sherman 



Carl Wilson 



John Sowles 



Department ol Marine Resources 

 West Boothbay Harbor, Maine 04575 



Minoru Kanaiwa 



School of Marine Sciences 

 218 LibbyHall 

 University of Maine 

 Orono, Maine 04469 



Manuscript submitted 6 August '2004 

 to the Scientific Editor's Office. 



Manuscript approved for publication 

 22 August 2005 by the Scientific Editor. 



Fish. Bull. 104:247-255 (2006). 



Many fish species experience size- 

 dependent inshore-offshore move- 

 ment at a certain stage (or stages) of 

 their lives, resulting in size-depen- 

 dent distribution. Shallow inshore 

 waters along coasts in many parts 

 of the world are primary nursery or 

 spawning grounds (or both) for many 

 commercially and recreationally 

 important fish species (Taylor, 1953; 

 Caddy, 1975). Juveniles of many fish 

 species inhabit shallow inshore waters 

 but migrate to deeper waters with 

 increasing size (Chen et al., 1997). 

 This size-dependent movement can 

 also be observed in other life his- 

 tory stages such as when mature fish 

 migrate to spawning grounds (Rowl- 

 ing, 1994). One consequence of such 

 a size-dependent movement is that 

 spatial distribution of fish becomes 

 size-specific. Many ocean fish aggre- 

 gate in their habitats according to size 

 (Paloheimo and Dickie, 1964; Caddy, 

 1975; Hilborn and Walters, 1992). 



The American lobster {Homarus 

 americanus) is distributed through- 

 out the northwest Atlantic from the 



Straight of Belle Isle, Newfoundland, 

 to Cape Hatteras, North Carolina. It 

 supports the most valuable commer- 

 cial fishery in the Northeast United 

 States (ASMFC, 2000). This lobster 

 is most abundant in shallow coastal 

 waters but can also be found in wa- 

 ter depths of 700 meters (Cooper and 

 Uzmann, 1980; Lawton and Lavalli, 

 1995). Various surveys and studies 

 have indicated that there are large 

 differences in lobster density among 

 different areas and different water 

 depths (Wahle and Steneck, 1992; 

 Wilson. 1998; Palma et al., 1999). 



Lobsters tend to move little during 

 their first year on the bottom (Wahle, 

 1992; Palma et al., 1999). The daily 

 and annual movement range increas- 

 es with their sizes. After they reach 

 harvestable size, their annual range 

 of movement is about 2 to 3 kilome- 

 ters (Krouse, 1980). Sublegal-size lob- 

 sters generally have small seasonal 

 movements (<1 km/year) and are 

 largely found near shore. Larger lob- 

 sters are more mobile (<20 km/year) 

 and show progressively offshore deep 



