Swimming Crabs and a Sea Lion, Oh My!
Swimming Crabs
On July 9, 2026, the IEP San Francisco Bay Study Study collected an arched swimming crab (Callinectes arcuatus), in the otter trawl at a Carquinez Strait station. This crab is subtropical and tropical, normally ranging from south of Los Angeles, CA to Peru. During periods of high ocean temperatures, such as the current marine heat wave or strong El Niño events, it may be found as far north as San Francisco. The Bay Study previously collected one C. arcuatus in 1997 (Table 1), a year with a strong El Niño event.
Table 1. San Francisco Bay Study collections of Callinectes arcuatus from 1980 to July 2026. Size is carapace width in mm. For 1980-2025 data: SF Bay Study EDI
| Year |
Month |
Station |
Sex |
Size |
| 1997 |
11 |
428 |
Male |
86 |
| 2026 |
7 |
447 |
Female |
69 |
Kathy Hieb, Senior Environmental Scientist (Supervisory) with the Bay Study, remembers that a small C. arcuatus was also collected in Suisun Marsh by another study and that commercial Bay shrimp trawlers were collecting them in 1997-1998.
Figure: Callinectes arcuatus collected by the San Francisco Bay Study, July 2026. CDFW photo by America Negrete Luna.
In addition to Callinectes arcuatus, Bay Study has collected the Xantus swimming crab (Portunus xantusii), especially during the extreme marine heat wave of 2015-2016 (Table 2).
Table 2. San Francisco Bay Study Portunus xantussi catch data.
SF Bay Study EDI
| Year |
Total Catch |
| 1984 |
1 |
| 2015 |
62 |
| 2016 |
117 |
| 2017 |
8 |
Portunus xantusii normally ranges from Southern California to Baja California. The 2017 short communication Temperature-induced range expansion of subtropical crab along the California coast (PDF) by Sadowski et al. in the journal Marine Ecology describes the range expansion and first occurrence of P. xantusii to northern California in 2016. However, this paper did not use Bay Study data, as Bay Study’s first collection of P. xantusii was in 1984 during an El Niño event. In addition, Bay Study collected 187 P. xantusii from November 2015 to April 2017.
Sea Lion at Skinner Fish Facility
On June 15, 2026, the California Department of Water Resources notified the California Department of Fish and Wildlife that a sea lion had made its way between the trash racks and wing gates at the Skinner Fish Facility. While staff were brainstorming ideas on how to get the trapped sea lion out, the sea lion found its own escape route the next day by making a 5-foot jump on the wing walls. With assistance from Skinner staff, the sea lion was given an escape route and was able to swim back into the normal environment.
As we question what tempted the sea lion to that spot, Skinner staff are working on some preventive measures to be more prepared for next time. Although rare, it has happened before and will most likely happen again!
A wayward sea lion basking on the wing wall at the Skinner Fish Facility. Photo by DWR staff, Trent Schaffer.