222 BULLETIN OF THE BUREAU OP FISHERIES. 



eastward and a little north from the northern end of Fairy Island to the mainland. 

 There are similar areas south and west of Fairy Island. The slope, the middle ground, 

 and similar areas lie in the open lake and are subjected to severe wave action. The 

 water is usually in motion and the conditions are not in this respect unlike those found 

 in a stream. Among the fish is at least one characteristic stream form, Notropis cornutus, 

 the common shiner. This habitat may be called the unprotected vegetation habitat. 



The vegetation is not emergent and is characterized by absence of water hlies. On 

 the slope the plants are found on the less steep portions and there form a discontinuous 

 fringe or zone. On a still, bright day one may see that the plant growth of the slope 

 consists of little groups of Poiamogeton naians, millfoil, and perhaps other plants which 

 are i or 2 feet apart and in most places do not make dense masses. There are consid- 

 erable stretches of the slope that are without vegetation. One of these lies opposite 

 the laboratory on South Fishtail Bay. There are a few places in which the vegetation is 

 more dense. On the whole, it occurs in patches or islands and within these it is sparse. 



Where the shoals are protected from the wave action vegetation gets a foothold, 

 muck accumulates, and the conditions approach those of a pond with relatively quiet 

 waters. This is the case on the east and west sides of North Fishtail Bay, in the bay 

 directly south of Fairy Island, and at the mouth of Bessie Creek. Water lilies occur in 

 such situations and the large-mouthed black bass is the characteristic but not abundant 

 fish. The common sunfish is more abundant here than elsewhere. This habitat of 

 bays and estuaries may be referred to as the protected vegetation habitat. It contains 

 most of the species of fish to be found in the lake. It merges into the unprotected 

 vegetation habitat. For the present it seems best to treat the vegetation habitat as a 

 unit, although in the future it may be advisable to subdivide it. 



. THE DEEP-WATER HABITAT. 



Beyond the slope near the bottom is the abysmal or deep-water region, where the 

 bottom is of a soft, black ooze and where there are no large water plants. It extends 

 from a depth of 25 feet (probably somewhat less) to 89 feet, the extreme depth of the 

 lake, and comprises the bottom and the layer of water i or 2 meters thick above it. 

 Above the thermocline this layer of water is agitated by the wind, is relatively warm 

 and well lighted, and contains in summer an abundance of oxygen. Passing downward 

 along the bottom through the thermocline we encounter within a vertical distance of 7 

 feet a drop in temperature of some 10° F. As we descend the temperature near the 

 bottom continues to drop from about 54° F. at the thermocline (July 10) to between 

 43° and 50°, depending on the depth reached. The water below the thermocline is not 

 only cold but relatively quiet, unaffected by wave action, and relatively dark. In mid- 

 summer it contains little oxygen at any level and none at all at a depth of 63 feet or 

 more. We have taken no fish below the thermocline in midsummer. They are then to 

 be found only in those parts of the abysmal region that lie above the thermocline 

 between the lakeward border of the vegetation zone and a depth of about 45 feet. 



THE FISHES. 



Our data concerning the fishes are given below under each species. The locality 

 numbers in the tables refer to the map on page 220. The numbers in the column headed 

 "Water depth " give the distances below the surface at which the fish were taken. They 



