The Air Operational Watch Report for the day, CX/MSS/OPD 1121 (in National Archives HW 13/38) says:
Heavy fighter patrols in the Bay [of Biscay] were flown in considerable strength, at least 15 Ju 88s being operated from Lorient and Vannes. Contact was made with Coastal Command a/c and a Sunderland was shot down about 1400 [BST]
Intentions:
1) 5 Ju 88s to leave Vannes at 1145 for operation, flying out and in over 14W 486 and landing at 1645
2) 15 Ju 88s tobe airborne in Lorient for Vannes at 1150 (proceeding thence to) Square 4869. A/c to land in Lorient and Vannes.
The interpretation of this second intention is conjectural, and it is not clear whether the 15 Ju 88s are meant to include the 5 up from Vannes or not
In all 4 a/c of the first Staffel (E, N, M and V) were heard in W/T, as well as L of the second. CHVL FM [factory marking] identified as I./ZG 1) contacted Kerlin 12591317 and presumably belings to the second Staffel while PLOX (Ju 88) was called by both Kerlin and Vannes at different times during the operation.
Note: In addition to the above it is known that 6 Ju 88s w
to fly from Bordeaux to 14W 551, crossing Cap Ferr
1420. This perhaps refers to a training flight by 7
Some words at the edge of the page were lost when the reports were bound into the file. All those flights took place later than your crash, reinforcing what Chris said about a training flight (or a test flight prior to the day's operation, perhaps?).
On 20 March I./ZG 1 had 40 (20) Ju 88s with 18 crews ready for operations; III./ZG 1 had 16 (10) Ju 88s and 11 crews ready. (Bundesarchiv RL 2-III/729b)