PART VIII — AQUATIC ECOSYSTEMS 



of all of the large whales with the 

 possible exception of sperm whales. 

 Sufficient biological and statistical 

 knowledge is now available to put a 

 rational management system into ef- 

 fect. In part, this may have been 

 done. Continued studies are needed, 

 however, to make certain that the 

 quotas already in effect can be sup- 

 ported by the whale stocks (to date, 

 populations of large whales have been 

 measured principally by catch effort) 

 and to help in the establishment of 

 new quotas and regulations. This will 

 require a combination of biological, 

 statistical, and diplomatic effort. 



International Study and Conserva- 

 tion Agreements on the Ice-Seals of 

 the Bering and Chukchi Seas — The 

 expansion of commercial killing of 

 ice-seals (ribbon-, bearded-, and 

 harbor-seals — ringed-seals are little 

 hunted) by the Soviet Union has 

 resulted in depletion of the ribbon- 

 seal population and has put an added 

 strain on the subsistence living of the 

 Alaska Eskimo. There is a need, 

 agreed to in principle by the United 

 States and the U.S.S.R., for rational 

 harvesting of the ice-seals, arranged 

 by an international agreement. Co- 

 operation between countries increases 

 the effectiveness of data collecting 

 and reduces the effort required of 

 each party. 



The knowledge needed to manage 

 ice-seal populations is difficult to col- 

 lect. Harvest quotas set on a trial- 

 and-error basis may be used tem- 

 porarily until more data are available. 



An International Policy on Exploit- 

 ing the Seals of the Antarctic — 

 World whaling and the harp-seal 

 hunting in the North Atlantic yield 

 less and less. As a result, nations 

 such as the U.S.S.R. and Norway 

 have begun to look at the seals of 

 Antarctica as a source of leather and 

 oil. An international policy covering 

 quotas that can be killed, by species 

 and area, is still incompletely formu- 

 lated. Some effort has been devoted 

 toward developing an international 

 plan. This work should be continued 

 even though the basic data for quotas 



is difficult to assemble and provisional 

 quotas will need to be established at 

 first. 



The main protection for antarctic 

 seals is the hostile environment. An 

 opportunity thus exists to exploit 

 marine mammal populations in a 

 rational way. 



The Conservation of Dolphins that 

 are Killed in the Yellow-Fin Tuna In- 

 dustry — The fishermen catching yel- 

 low-fin tuna off Central America with 

 purse seines use schools of dolphins 

 as indicators of tuna. The tuna, for 

 unknown reasons, are under the por- 

 poise schools and follow along with 

 them. The purse seine is set around 

 the dolphins and catches both dol- 

 phins and tuna. (See Figure VIII— 9) 

 Observers estimate that five dolphins 

 are killed for each ton of tuna caught. 

 Fishermen would like to release the 

 dolphins to use again in finding tuna 

 but no effective way of releasing 

 them has been devised. A solution to 

 the problem will require further study 

 of dolphin behavior and experiments 

 in net design. 



Factors Affecting Distribution 



Mechanisms Used by Marine Mam- 

 mals to Guide Migration — Some 

 marine mammals make extensive an- 

 nual migrations. A variety of specu- 

 lative suggestions have been made on 

 how the mammals are able to navi- 

 gate regardless of weather conditions 

 and daylight or darkness. In fact, 

 however, little is known about the 

 mechanisms used to guide migration. 

 The process appears to be more so- 

 phisticated than some of the theories 

 might suggest. Discovery of these 

 mechanisms would be of great bio- 

 logical significance and also important 

 in human navigation and communi- 

 cation. 



The methods of investigation that 

 will explain how accurate navigation 

 over thousands of miles is accom- 

 plished are not well worked out. A 

 combination of approaches will prob- 

 ably be necessary. 



Relation of Oceanographic Con- 

 ditions to the Distribution of 



Figure VIII— 9 — A PURSE SEINE 



Cork Line 



Lead Line 



Purse Line 



Purse Ring & Bridle 



E Purse Weight Line 



F Purse Weight Block 



G Pursing Blocks 



H Purse Weight or Tom 



The sketch shows a purse seine being set. The net is placed in the water. The 

 upper edge is kept afloat with buoys, while the lower edge sinks due to weight. 

 The net is drawn around a large volume of water. It is possible to close off the 

 bottom by pulling the net together, thus enclosing any fish within the volume. The 

 entire seine — and all its contents — can then be picked out of the water. 



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