"I thought 'something's not right'."
He saw more muddy ewes at the bottom of the hill. He realised the mud was concealing horrific injuries - throats ripped out, jaws torn off, scalps slashed.
"There were broken fence batons and posts lying around. These things didn't give up easy."
He found the rest of the small flock spread through the paddock.
Most were still alive but terribly injured.
He had to shoot 10 in total to put them out of their misery - 9 ewes and one lamb.
He found two lambs injured but alive under the bodies of their dying mothers. They survived, with stitches.
Mr Anderson said a vet confirmed, based on bite marks, that the attack had been carried out by at least two large-mouthed dogs.
In the pouring rain, Mr Anderson did his best to make sure the living animals had shelter. Twice in the night, he got up with a spotlight to make sure the dogs had not returned.
Animal services came the next day, and word of the attack was spread around the neighbourhood via Facebook.
Mr Anderson was looking for witnesses to the daylight attack.
"I can't believe this has happened in the middle of the day and no one saw it."
The ewes were worth about $250 each, and Mr Anderson was sure a big vet bill was on the way. He wants the owner of the dogs to come forward and take responsibility.
He said he moved to the Western Bay from Auckland in June last year.
"I left Auckland because I didn't think I would run into things like this here...and within a year this has happened."
The Western Bay of Council has confirmed its animal services staff attended the incident.
A spokesman said they were investigating, "but as there were no eye witnesses it is very difficult to identify the dogs in question".
"We would like to remind dog owners that if you are leaving your property, it is your responsibility to make sure your dogs are confined. This is the best way to ensure they do not roam."
