SIMoN
Archives
Mola die off in Monterey Bay (Fall 2009)
Mola mola
The giant ocean sunfish, Mola mola, is found in all tropical and temperate ocean basins. Common visitors to the California coast, giant ocean sunfish are often found in large numbers off southern California during the summer months and in Monterey Bay during the fall (September-November).

In October 2009, citizen scientists, beachCOMBERS and divers reported a peak in the number of finless, eyeless Mola mola carcasses washing up on the beaches of Monterey Bay. Early sightings on Pescadero Beach were reported to oceansunfish.org on September 18. Numerous additional sightings were reported during the week of October 21 including: one on Marina State Beach, six near the coastguard pier on Oct 22 and 19 carcasses on Monterey State Beach between Seaside and Wharf 2 found on October 24th.
Mola carcass

Bottlenose dolphin
Finless and eyeless Mola mola carcasses found on a beach. Photos: Thys, Oceansunfish.org.
On October 26, seven more were reported off Point Pinos. Reports waned the following weeks with one carcass being reported off Hopkins marine station on Nov 9, one on Sunset beach, Nov 11, two on Del Monte beach, November 11, and three on Asilomar beach, Nov 18. On January 1 another carcass was reported on Monastery Beach just north of Point Lobos.

All Mola mola were of similar length (between 30-60 cm) and believed to be young of the year. Most were missing dorsal and anal fins as well as eyes. Reports of similar die-offs occurred in 1959 and 1960 (Gotshall 1961). These die-offs are due to a combination of oceanic conditions that deliver young Mola mola to nearshore waters and in contact with California sea lions. The sea lions tear off the dorsal and anal fins, toss the body across the surface of the water and then frequently abandon the fish. Although sea lions are able to puncture the intestinal cavity, the thick semi-impenetrable skin of the Mola mola often causes the sea lions to abandon the incapacitated fish--leaving it to slowly sink to the seafloor where it is consumed by seastars and other benthic scavengers.

Dr. Tierney Thys, director and founder of oceansunfish.org, is working with scientists from the Monterey Bay Aquarium Research Institute (MBARI) to determine what combination of oceanographic conditions contributes to such large die-offs off the California coast and beyond.

Reference:

Gotshall, D. W. 1961. Observations on a die-off of molas (Mola mola) in Monterey Bay. California Fish and Game 47(4):339-341.

Related Links:


Top of page ]