Disk Utility lists same external disk multiple times

On macOS Sierra on a MacBook Air (2013), my 2TB WD My Passport drive keeps creating a new disk device every time I attach it via USB. This Mac was upgraded recently from OS X Yosemite to Sierra, and it seems like this duplication started then. How do I clean this up and prevent it from continuing to happen?

At the command prompt, this is the view:

/dev/disk0 (internal, physical):

#: TYPE NAME SIZE IDENTIFIER

0: GUID_partition_scheme *251.0 GB disk0

1: EFI EFI 209.7 MB disk0s1

2: Apple_CoreStorage Macintosh HD 250.1 GB disk0s2

3: Apple_Boot Recovery HD 650.0 MB disk0s3

/dev/disk1 (internal, virtual):

#: TYPE NAME SIZE IDENTIFIER

0: Apple_HFS Macintosh HD +249.8 GB disk1

Logical Volume on disk0s2

F72A0422-5XXX-49EE-9XXX-4BFCEXXXXXD0

Unencrypted

/dev/disk2 (external, physical):

#: TYPE NAME SIZE IDENTIFIER

0: FDisk_partition_scheme *2.0 TB disk2

1: Apple_HFS 2.0 TB disk2s1

/dev/disk3 (external, physical):

#: TYPE NAME SIZE IDENTIFIER

0: FDisk_partition_scheme *2.0 TB disk3

1: Apple_HFS 2.0 TB disk3s1

/dev/disk4 (external, physical):

#: TYPE NAME SIZE IDENTIFIER

0: FDisk_partition_scheme *2.0 TB disk4

1: Apple_HFS 2.0 TB disk4s1

/dev/disk5 (external, physical):

#: TYPE NAME SIZE IDENTIFIER

0: FDisk_partition_scheme *2.0 TB disk5

1: Apple_HFS 2.0 TB disk5s1

/dev/disk7 (external, physical):

#: TYPE NAME SIZE IDENTIFIER

0: FDisk_partition_scheme *2.0 TB disk7

1: Apple_HFS Portable 2.0 TB disk7s1

/dev/disk8 (external, physical):

#: TYPE NAME SIZE IDENTIFIER

0: FDisk_partition_scheme *2.0 TB disk8

1: Apple_HFS Portable 2.0 TB disk8s1

Thank you!