¿ What Por qué is the ocurren cause of sea los lion varamientos strandings ? de lobos marinos ?
By Alejandro Arias del Razo , M . S .
Photo : José “ El Güero ” Arce Smith .
Fotografía Photo : José : José “ El Güero “ El Güero ” Arce ” Arce Smith Smith . .
Strandings of several marine mammals along the Pacific coasts have reached a record level in the last two years . In 2015 , over 3,000 sea lion strandings were registered along California ’ s coasts . This number is equivalent to the sum of the previous five years , which leads to the following question : Why are so many sea lions dying in our coasts ?
The biologists and physics ’ studies have showed us that there are at least three factors that when combined have caused this unfortunate phenomenon .
The first factor is that climate phenomenon “ El Niño ”, common name given to the Southern oscillation related to a rise in sea surface temperature due to a mass of water that comes from the equator near Asia , has been one of the strongest on record this year ( 2015-2016 ).
This rise of sea temperatures causes different effects in the ocean and the atmosphere , which is the reason why we hear about “ El Niño ” on the news . At a biological level , usually colder waters of our coasts sink due to the arrival of these warmer waters . It is important to recall that warmer fluids rise and cooler fluids sink . This is why hot air balloons rise by using a burner to heat the air . Concerning sea water , colder sinking waters often carry the nutrients that phytoplankton ( what we could consider to be little sea plants , but are actually bacteria ) needs in order to grow .
This loss of resources has a cascade effect . If there is a lack of phytoplankton , there will be less food for fish . Therefore , less food for the sea ’ s large predators , such as sea lions , dolphins , sharks , among others . As a result , they need to invest more time and energy finding their food ; and in most cases , they need to dive at great depths to reach the cold water column .
The second cause of marine mammal strandings is “ the blob ”, another oceanic phenomenon that was discovered in 2013 . It is a 1,000 mile long and 300 feet deep warm water mass located between Alaska and Baja California . In addition to causing similar effects as those attributed to “ El Niño ” ( causing the immersion of the colder waters ), researchers of the University of British Columbia in Canada discovered that this phenomenon supports the growth of toxic algae blooms ( such as diatom Pseudo-nitzschia ), that produce a neurotoxin called domoic acid .
The excessive growth of these algae also affects mammals that eat toxin-contaminated prey . This has caused a massive poisoning and stranding of California ’ s sea lions in our coasts .
At last , the third factor is the decrease in their major prey population : sardines and anchoveta . While population growth of these two species is cyclical , which means that they tend to dramatically increase and decrease through time , the population has decreased in recent years . As a result , sea lions have had to consume other prey such as squid .
Nevertheless , these animals provide fewer calories and fat , which causes nutritional stress in sea lions , hence the malnourishment of their pups .
In regular conditions , the female sea lion goes through a cycle of foraging at sea and returns every three days to feed their pups . However , under the previously stated circumstances , these trips might take longer , leaving the sea lion pups starving or malnourished . This is the cause why most of the stranded sea lions at our beaches are pups that died of starvation .
4 JUNE 2016