Image Segmentation: Unable to detect small walrus in images

I am building U-Net Image Segmentation model to detect indvidual walrus in images. The problem I am facing is that the model is detecting groups of walruses as one blob rather than detecting the different indviduals. Example:

How can I get the model to detect individual walrus as in the true mask rather than detecting a blob of walrus as in the predicted mask?

TensorFlow tutorial I’m following: Image segmentation  |  TensorFlow Core