Problems with Case statement and grouping.

Hi I need to display my data as per the following table:

Port_Description   Vessel_Name      LobstersKG      Crabs (KG)      Velvets(KG)
Aberdaron           Mary Rose                     3.5                      0                      0
                           Boy Paul                     2.3                    4.5                      0
Aberdeen                   Lady Eleanor             4.5                    2.3                      0
Aberffraw           Saorsa                             4.6                    2.5                      0
                        

I think I’m part of the way there but the following statement doesn’t give me the above table:

SELECT Port_Description, Vessel_Name, Common_Name,
      case
      when Common_Name = 'Lobsters' then ProductKiloQty
    end
    AS LobstersKG
      FROM FormData
      GROUP BY Port_Description, Vessel_Name, Common_Name, ProductKiloQty

It gives me this:

Port_Description      Vessel_Name      Common_Name      LobstersKG
Aberdaron                 Mary Rose            Lobsters                    3.5
                                 Boy Paul            Crabs                           NULL
                                 Boy Paul            Lobsters                    2.3
Aberdeen                         Lady Eleanor            Crabs                           NULL
                                 Lady Eleanor            Lobsters                    4.5
Aberffraw                 Saorsa                    Crabs                           NULL
                                 Saorsa                    Lobsters                    4.6

I tried adding to the case statement as follows:

SELECT Port_Description, Vessel_Name, Common_Name,
      case
      when Common_Name = 'Lobsters' then ProductKiloQty
    end AS LobstersKG
    case
      when Common_Name = 'Crabs' then ProductKiloQty
    end AS CrabsKG
      FROM FormData
      GROUP BY Port_Description, Vessel_Name, Common_Name, ProductKiloQty

But it didn’t work.  Please can someone tell me how I can achieve this?