Why do marine shipping companies have a so good P/E ratio?

Here is a list of 10 marine shipping companies with low P/E ratio:

1   ZIM ZIM Integrated Shipping Services Ltd.
2   NMM Navios Maritime Partners L.P.
3   DAC Danaos Corporation
4   SBLK    Star Bulk Carriers Corp.
5   MATX    Matson, Inc.
6   CMRE    Costamare Inc.
7   GSL Global Ship Lease, Inc.
8   SB  Safe Bulkers, Inc.
9   DSX Diana Shipping Inc.
10  EGLE    Eagle Bulk Shipping Inc.

What is the catch?