6o Cruise of the "Alert." 



a " trammel" net across the outlet while the tide was ebbing, and 

 in this way entrapped great quantities of mullet and mackerel ; 

 sometimes upwards of eighty, ranging in weight from two to 

 eleven pounds per fish, being taken at one haul. 



I collected some green flocculent matter from the surface of 

 one of these lagoons, and found it to consist almost entirely of 

 diatoms. 



One fine day in April we noticed a great concourse of gulls 

 and shags, attracted by a shoal of fish, in the pursuit of which 

 they ventured unusually close to the ship. This gave us an 

 opportunity of observing that the common brown gull of the 

 channels, the female of L. Dominicanus, behaves towards the male 

 bird in many respects like a skua. No sooner would one of the 

 "black-backed" (male) birds capture a fish, and rise from the 

 surface, than he would be attacked by one of the brown birds, 

 and chased vigorously about the harbour ; the predatory bird not 

 desisting from the pursuit until the coveted prize had been dropped 

 by its rightful owner. This I noticed on more occasions than one. 

 As a rule, however, the female was content to fish for herself. 

 Several Dominican gulls in immature plumage were seen amongst 

 the crowd, and were easily distinguished from the adults by the 

 mottled brown plumage, and by the colour of the mandibles being 

 green instead of orange, as in the males, and black as in the 

 females. Now and then the whole flock of gulls and shags would 

 rise on the wing, as they lost the run of the shoal of fish. 

 They would then be directed to the new position of the shoal by 

 the success of some straggling bird, when a general rush would 

 be made to the new hunting ground. It was most amusing to 

 witness the widely different fishing powers of the shags and gulls, 

 and the consequently unequal competition in the struggle for food. 

 The shag in flight, on observing a fish beneath him, at once 

 checks himself by presenting the concave side of his wings to the 

 direction in which he has been moving, and then, flapping legs 

 foremost into the water, turns and dives ; whereas the gull has 



