a giant piranha

• 0, 0, -1941 (seen once) (3 of 31 spawns here)
• 1856, 1446, -83 (1 of 4 spawns here)
• -742, 1305, -104 (2 of 4 spawns here)
• -839, 1277, -70 (seen once)
• 1473, 2203, -65 (seen once) (1 of 2 spawns here)
• -510, 1659, -90 (seen once) (1 of 3 spawns here)
• -1145, 2203, -83 (seen once)
• -785, 2203, -98 (seen once) (1 of 3 spawns here)
• 820, 1443, -91 (seen once) (1 of 2 spawns here)
• -1986, 1394, -74 (seen once) (1 of 2 spawns here)
• -1590, 1602, -77 (seen once) (1 of 3 spawns here)
• -1990, 1364, -64 (seen once) (1 of 2 spawns here)
• -1609, 1593, -77 (seen once)
• 124, 1605, -84 (seen once) (1 of 2 spawns here)
• 645, 1634, -92 (seen once) (1 of 8 spawns here)
• 1934, 2130, -84 (seen once) (1 of 4 spawns here)
• 1919, 2113, -84 (seen once)
• 810, 2316, -62 (seen once)
• 0, 0, -2010 (seen once) (1 of 60 spawns here)

As /loc gives them: Y, X, Z, the most used first; nearby spawns share a spot, and one seen in a single visit may be where the mob had been pulled to.