IRVINE — Now that Erik Karlsson is signed for the next eight years to the tune of $92 million, the Sharks’ blue line has three important — and expensive — pieces locked up for more than a half-decade. Karlsson’s deal carries a salary-cap hit of $11.5 million, while Brent Burns has six years left at an $8-million hit and Marc-Edouard Vlasic seven more at a $7-million annual hit.



Add it all up and that’s $26.5 million of annual salary-cap space committed to just three defensemen through 2024-25, when Burns’ contract expires.



While the blue line looks set for the 2019-20 campaign with that three-headed monster along with Brenden Dillon, Radim Simek and either Dalton Prout or Tim Heed filling out the top six, the Sharks are going to need some young and inexpensive talent on defense soon.



As it turns out, two of the more promising prospects taking part in this weekend’s rookie tournament in Southern California are...