f» 



David Starr Jordan -taking live plankton sample for ship- 

 board physiology studies. 



operating condition and found to be a valuable tool for 

 sea-going laboratory investigations. 



By use of a temperature block, a time-temperature 

 curve vi'as obtained for the development and hatching of 

 jack mackerel eggs: a sea-going respirometer was tested 

 and functioned successfully in a gimbal arrangement; and 

 experiments with the oxygen electrode and an activity 

 meter were done in David Starr Jordan s laboratory. 



R. Laskf 



David Starr Jordan -(/.?/«^ temperature hloek for larvat 

 development studies at sea. 



FEEDING BEHAVIOR PROJECT 



C.P. O'Connell has brought his studies of the mech- 

 anism of feeding in the northern anchovy to completion 

 during this year. Using experimental tanks, with nauplii 

 and adults of brine shrimp (Artemia salinaj as food, he 

 has analyzed the two kinds of feeding: biting and filter- 

 ing. He has shown that even at extremely high densities 

 of both kinds of food the biting attack on adult Artemia 

 is much more efficient. He has extended his laboratory 

 observations to an analysis of the likely efficiency of fil- 

 tration at varying concentrations of zooplankton orga- 

 nisms above 100 microns, basing his estimates on his pre- 

 vious work with towed zooplankton pumps in the Cali- 

 fornia Current. From his pump samples, he concludes 

 that only rather limited areas have a sufficient biomass of 

 G. Mattson zooplankton organisms forthe nutritional requirements of 



anchovy that feed by filtration alone. He therefore con- 

 cludes that the biting attack is a necessary and usual com- 

 plement to filtration. 



He has also investigated other relations between 

 biting and filter feeding in schools of anchovy when pre- 

 sented with different mixtures of adult and larval 

 Artemia. He has shown that even in the presence of 

 dense concentrations of nauplii some individuals will bite 

 preferentially at the sparse adult Artemia. and he con- 

 cludes that this behavior indicates that the biting attack 

 normally operates so that anchovy graze preferentially 

 on large organisms. 



C.P. O'Connell is now beginning comparable work 

 on the feeding of the Pacific mackerel, which he finds 

 will not respond to Artemia nauplii at any density but 

 will change from biting to filtration in the presence of 

 great enough densities of adult -4/-rew/a. 



— FISH SCHOOLING BEHAVIOR 



Many commercially important marine fish live in 

 schools, and indeed the harvesting of these fishes may be 

 economically practicable only because of this habit. 

 Schooling infiuences all aspects of the life of pelagic 

 marine fish: their migration, feeding habits, availability 

 to the fishery, and even their reaction to fishing gear. 

 Thus, knowledge of the behavior of schools is essential 

 for improvement of fishing techniques, understanding 

 life histories, and prediction of the availability of fish. 



22 



