along the British Columbia coast is probably the main factor accounting for the 

 presence of commercial quantities of albacore in these comparatively far north 

 latitudes. 



The extent of this "pouching effect" seems to be the most important 

 factor governing the possibilities of any quamtity of albacore occurring in Alaska 

 waters. The factors involved in producing the wedge of warm inshore water seem 

 to be controversial and have been attributed to both solar warming and seasonal 

 currents. By employing accurate thermometers and accurate methods for securing 

 temperatures, fishing operations in this region could be confined to the wedge 

 of warm water. The width of the warm water wedge id.ll undoubtedly vary throughout 

 the summer, and its shape will probably be modified from year to year. 



Vertical Distribution 



A series of subsurface temperatures was taken with the bathythermograph 

 in an effort to determine the average depth of warm water during the summer months 

 and any relationship between its depth and the occurrence of albacore. In general, 

 albacore were not found to be concentrated in regions where the warm water ex- 

 tended only a few feet below the surface. The average depth of the thennocline 

 in waters of productive fishing was sixty feet, sometimes extending to 80 or 90 

 feet. Results of the gill-net fishing indicate that the tuna generally stay within 

 the upper regions of the warm surface layer; very few were taken in the lower 

 meshes of the nets (see section on gill-net catches). 



Color of VJater 



The co].or pattern of the water along the Pacific Northwest coast con- 

 sists essentially of a coastal green zone which is adjoined by the deep blue of 

 the open ocean. The coastal green zone is of variable width and is generally 

 several degrees colder than the offshore blue water. The deep-blue color of water 

 is said to be caused by the moleculer scattering of the shorter light-wave lengths 

 from water moleciles. Therefore, the deep blue of the open ocean is characteristic 

 of water essentially free of particulate material or dissolved pigmented substances, 

 and regions of green or colors other than blue in the ocean may be considered as 

 areas of discolored water. These regions of discoloration may be the results of 

 phytoplankton or zooplankton, suspended particles of earth carried to sea by streams 

 and rivers, organic debris, or dissolved organic corapoimds of either marine or 

 terrestrial origin. 



Gunther (1936) attributes the green coastal zone of the Peru current to 

 phytoplankton (mostly diatoms). Ths abundance of nutrient salts brought up by up- 

 welling along the coastal regions of Peru makes possible a rich growth of phyto- 

 plankton, whereas the offshore surface waters are isolated by a well-defined dis- 

 continuity layer which prevents vertical mixing. Offshore waters are thus depleted 

 of nutrient sailts and have orily a small phytoplankton population. A similar con- 

 dition may possibly account for the coastal green zone off the Oregon and the 

 Washington coasts during the tuna season. 



Good tuna fishing is usually fo'ond in the blue water, with occasional 

 catches being made in blue-green or green water. Much of the albacore fishing 

 off the Oregon and the Washington coasts occurs in the blue offshore waters border- 

 ing the cooler, green, coastal zone. The apparent reluctance of albacore to enter 

 this coastal green water probably has little or no relation to the color of the 

 water, but may be attributed to the lower water temperatures, which are generally 

 below those at which albacore are tal<en in this fishery. 



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