THE SEA FISHERIES OF EASTERN NORTH AMERICA. 5 



C. Relationships and surroundings — Continued. Page. 



6. Deep-sea fish 53 



Hibernation 54 



Mackerel 54 



Sturgeon 54 



Carp 54 



Migration of fishes: how influenced -. 55 



(a) By physical causes 55 



Temperature of the waters 55 



Currents 57 



Depth 57 



Clearness of water 57 



Condition of air or sky 57 



Winds 57 



(b) Reproductive instinct 57 



(c) By search for food 58 



Relation of herring to copepods 58 



Cod and halibut after capelin and herring 58 



Offshore fish after anadromous fish 58 



Bluefish, &c 58 



(d) Driven by enemies 58 



• Bluefish and menhaden and mackerel 59 



Porpoises, salmon, bluefish 59 



Extent of such actiou , 59 



(e ) Human agencies (exclusive of capture) 59 



Obstructions : 



Dams 59 



Nets 59 



Sounds and concussions 59 



Steamers 59 



Cannon 59 



D. Numbers and abundance Gl 



1. In early days Gl 



Illustrations 61 



From report of U. S. Fish Commission Gl 



From Mr. Martin's notes G^ 



2. At the present time Gl 



3. Variations iu abundance (on large scale, and permanent for a time). .. Gl 



(a) Natural or uncontrollable variations j 



Antagonisms between fish : Bluefish, squeteague, scup, cod, had- 

 dock, balibut, porpoises, sharks, salmon, mackerel, and lobsters 

 in Provincetown 



Climatic conditions 



Causes unknown 



(b) Human agencies 



Direct 



Overfishing 



Pollution of water 



Indirect 



Obstructions 



Disturbance of balance of nature 



Breaking up schools and interfering with spawning 



E. Dangers and fatalities 62 



1. From fellow-inhabitants of the sea 62 



(a) Destruction of eggs and young iish 62 



