Evaluation of Atlantic Cod Predation on American Lobster in the Southern Gulf of St. Lawrence, with Comments on Other Potential Fish Predators

Demersal fishes are widely thought to be an important source of natural mortality for juvenile American lobster Homarus americanus. There were no significant relationships between abundance indices of American lobster and the dominant demersal fish species, Atlantic cod Gadus morhua , in the southern Gulf of St. Lawrence. American lobster was found in only one of 22,625 Atlantic cod stomachs collected between 1955 and 1980—a period of low American lobster abundance. Only six of 12,008 Atlantic cod collected between July 1990 and October 1996 (a period of high American lobster abundance) had eaten American lobster. Most size‐classes of the two species were spatially separate from early July to early September and November to May. American plaice Hippoglossoides platessoides , the second most abundant demersal fish species, did not eat American lobster ( n = 1,800 stomachs). Again, the two species were spatially isolated for most of the year. More limited studies (in terms of spatial or seasonal coverage) on the diets of eight shallow‐water fish species ( n = 4,674 stomachs) detected consumption of American lobster by shorthorn sculpin Myoxocephalus scorpius , cunner Tautogolabrus adspersus , and white hake Urophysis tenuis but not by winter flounder Pleuronectes americanus , yellowtail flounder P. ferruginea , thorny skate Raja radiata , spiny dogfish Squalus acanthias , or Greenland cod Gadus ogac. This study eliminated Atlantic cod, Greenland cod, American plaice, yellowtail flounder, winter flounder, and thorny skate as important predators of American lobster in the southern Gulf of St. Lawrence; however, the question of which of the remaining demersal fish species are important predators of American lobster remains largely unresolved.