Then why is there no genetic link between Northern Somalis and Socotrans? Aren't they all j1?
Haplogroup T does not have a marked presence in Yemen either even though the assumption is that it is the most probable passageway used by the supposed ancestor/ancestors of T Somalis.
Bulliet asserted that Socotra was a conduit for the introduction of certain domesticated animals commonly associated with Somalis. It is within the realm of possibility that Bulliet's assertion can be linked to the presence of the Somali T lineage in Northern Somalia. Socotra is much closer to Northern Somalia than Yemen, hence, it would have been easier to transport livestock. Moreover, the date proposed by Bulliet compliments the current TMRCA of the Somali T lineage.
I am not saying that the above theory is watertight. Nonetheless, the fact that Somali clans were historically concentrated in the North-Eastern Horn than areas closer to Bab El Mandeb may indicate that the migration route taken was not necessarily the shortest crossing point between the Horn and Arabia. If Semites established themselves in Socotra, who is to say that a similar migration by sea did not directly bring the Somali T lineage to the North-Eastern horn?