I don't want to catch mackerel or ling , I like catching ling , but no one wants to eat them when there is cod on the go and they don't go back very well with the swim bladder blowing so I try to avoid them , I don't use bait on the wrecks , it attracts ling every time , specially a big lump of mackerel.
If I'm fishing hard ground I'll use daylights and hokkais and such and bait them with chunks of mackerel and squid and catch most anything thats down there , sometimes a ling as well , but they go back ok on the hard with it generally being shallower.
On the wrecks in the deeper water I usually start off with a 200g or 300g pirk depending on how fast the drift is and I let it drop fast , sometimes a mackerel will get hooked on the way down ,but give it a slack line and it generally comes off , if there are cod on the wreck they will usually take a pirk , once I know they are there I switch to shads , because I prefer to fish with shads and rather than mackerel , I'm often plagued by coalies , even with a BIG pirk.
99% of the fish I catch on shads are cod , pollock like them , but they are usually higher up in the water and I fish hard on the bottom , I still catch the odd ling and hate it every time one comes up with it's swimm bladder sticking out of it's mouth
I will fish for ling at some stage , because I want to catch a biggun

, but I'm told the best time is later on in the season , so until then I'll try to avoid them , I want a few mackerel next time out also , a friend has asked me to bring some , I like catching mackerel as well , but not if they are going to be wasted , I like to catch them one at a time on a little spinning rod , but I might chuck a fly at them next time we get a calm sea ......... if we ever get another calm sea
Ray