NOTES ON THE FAUNA ABOVE MUD BOTTOMS IN DEEP WATER IN THE GULF OF MAINE

¹ From the Woods Hole Oceanographic Institution, Woods Hole, Massachusetts

Findings from 22 trawl-hauls, at 20 stations on mud bottoms in the western and northern parts of the Gulf of Maine, in depths between 120 and 228 meters, August, 1936, are:

1. The faunal community of the water just above these deep mud bottoms is so monotonous that the catch consisted, in every case, almost wholly of five species of fish (Sebastes marinus, Merluccius bilinearis, Urophycis tenuis, Hippoglossoides platessoides, Glyptocephalus cynoglossus) and of the shrimp, Pandalus borealis, in varying combinations of relative abundance. The only exception was at one station where a larger catch was made of crabs (Geryon) than of shrimp.

2. The only other fishes taken were odd examples of the 19 species listed on page 309. The total number of species to be expected in such situations (except as accidental strays) is probably not more than 35.

3. As the nets were arranged to fish off bottom, benthonic invertebrates were not sampled.

4. The most significant faunal contrast, from the regional standpoint, is that Pandalus has a well-marked center of population, at least in summer, in the deep bowl west of Jeffrey's Ledge where bottom currents are weak. A positive correlation was also shown between the amounts of shrimps caught at different stations and the percentage of organic matter in the mud, corroborating Hjort and Ruud's (1938) earlier conclusion that Pandalus is abundant only where the supply of organic debris on the bottom is relatively large.

5. Merluccius was also most plentiful in this bowl, probably in pursuit of shrimp. But the catches do not support any prevailing contrast between this locality and the open basin of the Gulf, in the abundance of any one of the other four fishes of which large catches were made. Neither is any regional contrast suggested in the qualitative composition of the fish fauna over mud bottoms in different parts of the Gulf at the depths in question.

6. The stock of Merluccius, in the localities and depths studied, was strongly dominated by the yearlings, an age group the habitat of which in the Gulf of Maine was previously unknown, though the older fish are extremely plentiful there in shoaler water. But the catches of Sebastes, of Hippoglossoides, of Glyptocephalus, and of Urophycis tenuis consisted chiefly, or (in the last case) wholly of fish of two years and upwards. The few cod that have been taken in the bowl from time to time have all been very large, though smaller cod as well find their way down into the deeps of the open basin of the Gulf.

7. Length-frequency distribution of the catches added to previous information, indicates that Sebastes, in the Gulf of Maine, attains an average length of about 7.5 cm. at one year of age and of about 18 cm. at two years. But subsequent growth is so slow that age-analysis of larger sizes would require a larger series of measurements than are yet available. Yearlings of Merluccius average about 17 cm. by late summer in the deep waters of the Gulf, the two-year-olds about 25 cm.

8. It is estimated that the combined weight of shrimp and fish of all species, in the bowl west of Jeffrey's Ledge, at depths greater than 150 meters, would have averaged at least 576 lb. per haul of 1.5 sea miles with an 82-foot trawl, or 55 lb. per acre of bottom, had the 6-inch stratum next the sea floor been included.