The phrase "northern elephant" refers to a type of elephant that is found in the northern part of a certain region. It is a way to specify that the elephant being talked about is from the northern area. Full definition
For instance, in one study of northern elephant seals, four percent of all males — the winners of bloody dominance battles — did 85 percent of the mating. (discovermagazine.com)
Since then, the population of northern elephant seals has recovered at an average rate of six percent per year. (nps.gov)
The longest life expectancy of a male northern elephant seal is approximately 14 years. (en.wikipedia.org)