According to the passage there has been two main theories about the reasons why sea otter population started declining. The first theory is environmental pollution and the second theory is attacks by predators. Three main reasons to support the first theory where discussed in the passage and also based on the lecture, answers have been provided for each reason and all of aformentioned reasons and responses will be addressed in next paragraphs.
The first mentioned reason based on the first theory for atter declining was that there has been water samples that shows the polluted water in the area. The professor provides a solid example that if that was true then dead bodies of animal should've been found by the shore, while there was never anything found, on the other hand the fact that no dead bodies were found supports the second theory that states that the predators are the reason for population decline.
The second reason is that even if the predators were the reason of this trajedy, the effect should've been on other sea mammals as well, but the facts say otherwise. According to the professor the change of diet in orca actually may cause this phenamenon since the whales were in danger because of humans they left and then the orca needed to feed on sea otters.
Finally the third reason states that because the pollution is more concentrated on some areas and not on others, it explains that why the population density is lower in that areas. This claime is answered easily, since the predators tend to hunt where they can easily go and hunt, therefore the sea otter population in deep waters has declined but not in shallow waters where they can not go easily. 
According to the passage there has been two main  
theories
 about the  
reasons
 why  
sea
 otter  
population
  started
 declining. The  
first
  theory
 is environmental pollution and the second  
theory
 is attacks by predators. Three main  
reasons
 to support the  
first
  theory
 where discussed in the passage and  
also
 based on the lecture, answers have  
been provided
 for each  
reason
 and all of  
aformentioned
  reasons
 and responses will  
be addressed
 in  
next
 paragraphs.
The  
first
 mentioned  
reason
 based on the  
first
  theory
 for  
atter
 declining was that there has been  
water
 samples that  
shows
 the polluted  
water
 in the area. The professor provides a solid example that if that was true then dead bodies of animal should've  
been found
 by the shore, while there was never anything found,  
on the other hand
 the fact that no dead bodies  
were found
 supports the second  
theory
 that states that the predators are the  
reason
 for  
population
 decline. 
The
 second  
reason
 is that even if the predators were the  
reason
 of this  
trajedy
, the effect should've been on other  
sea
 mammals  
as well
,  
but
 the facts say  
otherwise
. According to the professor the  
change
 of diet in orca actually may cause this  
phenamenon
 since the whales were in  
danger
  because
 of humans they  
left
 and then the orca needed to feed on  
sea
 otters. 
Finally
 the third  
reason
 states that  
because
 the pollution is more concentrated on  
some
 areas and not on others, it  
explains
 that why the  
population
 density is lower in that areas. This  
claime
  is answered
  easily
, since the predators tend to hunt where they can  
easily
 go and hunt,  
therefore
 the  
sea
 otter  
population
 in deep  
waters
 has declined  
but
 not in shallow  
waters
 where they can not go  
easily
.