Movement of American lobster in the southwestern Gulf of St. Lawrence - Homarus americanus

Fishery Bulletin, April, 2002 by Michel Comeau, Fernand Savoie

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Lobster movements in the Northumberland Strait were related to whether the site was located toward the center or at either extremity (either end) of the Strait. Lobsters at sites close to the external boundaries (Fig. 1, sites 17, 18, 20, 21, 26, and 27) traveled on average shorter distances (5.4-8.6 km) than those located in the center of the Strait (Fig. 1, 12.2-19.4 km, sites 19, 22, and 23). Although tags were recovered in the western portion of Northumberland Strait (LFA 25) at a different time (a different fishing season) compared with tag recoveries at the other LFAs, movements seemed to be related to the extent of shallow waters (<20 m) rather than the time of the recovery period.

Discussion

Lobster movements in the southwestern GSL are related to the local bottom topography and are depth-dependent, i.e. lobsters traveled on average longer distances in areas where the shallow waters (<20 m) extended farther from shore. We observed that on the narrow coastal shelf of western Cape Breton and in some areas in Baie des Chaleurs, lobsters traveled on average less than 5 km compared with distances ranging from 9.3 to 19.4 km in the gradually sloping bottom of the Northumberland Strait and some shallow bays. Similarly, Templeman (1935) reported that the average distance traveled by lobsters from sites located on the north side of Prince Edward Island and the western part of the Northumberland Strait ranged from 7 to 10 km. As with our results, longer movements were reported in the Egmont Bay area (central Northumberland Strait); lobsters traveled an average distance of approximately 14 km (Wilder, 1963) on lobster habitat in shallow (<20 m) waters. In other sites within the GSL, lobsters also traveled on average small distances. Lobsters in the Magdelan Islands (Templeman, 1935; Bergeron, 1967) and on the northern shore of Baie des Chaleurs (Corrivault, 1948) traveled average distances ranging from 3 to 16 km and 12 km or less, respectively. On the west coast of Newfoundland, Templeman (1940) reported that lobsters traveled an average of 3.2 km in St. George's Bay and 8.2 km in Portau-Port Bay; hence, lobsters disperse within the GSL, in general, over small distances in inshore waters.

Most of the lobster movements observed in the southwestern GSL were oriented along the coast in inshore waters. Although the shallow (<20 m) gradually sloping bottom of the central Northumberland Strait, the Malpeque Bay, and Miramichi Bay areas allows for longer and more broader dispersions, lobsters remain close to either the New Brunswick, Nova Scotia, or Prince. Edward Island coastline, or confined to a bay environment. However, dispersions along the coast might not be the only types of lobster movements in southwestern GSL. Movements per pendicular to the coast have been documented in the Magdalen Islands (Templeman, 1936; Bergeron, 1967; Munro and Therriault, 1983), Bonavista Bay in Newfoundland (Ennis, 1984), and on the north shore of Baie des Chaleurs (Corrivault, 1948) because a migration of lobsters moving inshore in the spring and offshore in the fall was observed. Recently, a trawl survey conducted at a depth of 40 m in the Caraquet area (Baie des Chaleurs) over a 7-month period produced lobsters in mid-May, late-October, and November, but not between June and early-October (Comeau, personal obs.). Further, the recapture positions during the fishing season showed that lobsters tagged during these trawl surveys were recaptured along the coast at depths less than 20 m from Stonehaven to Miscou (Comeau, personal obs.). This finding suggests that there is an inshore-offshore movement on the south shore of Baie des Chaleurs similar to the one observed by Corrivault (1948) on the north shore of that bay. Unfortunately, our tagging projects were not designed to study this type of movement and did not allow us to speculate more on inshore-offshore movements.