Dataset: Lengths of organisms recorded during emergent and rapid emergent surveys conducted in the subtidal zone of northern California, Sonoma and Mendocino counties, from 1999 to 2023

Data were collected during day-trips aboard California Department of Fish and Wildlife or NOAA patrol boats, generally 2-5 days at select survey locations in 1999, 2000, 2001, 2003-2020, 2022, 2023.

All surveys were done using SCUBA along 30x2 meter (m) transects (60 square meters total area) randomly placed in the subtidal zone in rocky habitats dominated by bull kelp (Nereocystis luetkeana) forests. These randomly placed band transect surveys were stratified by depth (A=0-15, B=16-30, C=31-45, D=46-60 ft) as we know sea urchin and abalone populations differ by depth. Two divers (a dive team) work together to count and measure organisms.

Divers were deployed as teams to randomly-selected GPS waypoints within designated depth strata (A, B, C, D). As with other surveys, the patrol boats provide support to the small boats and logistical support to divers. Divers typically complete multiple transects within each of the four depth strata ranging from 0-60 feet at each site. Divers swim along transect tapes measuring 30 x 2m in area across the rocky reef. All transects are in habitat which is dominated (>70% rock) by rocky reef. Two divers (a dive team) work together to count and measure organisms.

Emergent Surveys:
Emergent sampling focused on emergent, exposed, or cryptic animals in rock crevices or under rock ledges but visible without turning rocks or the use of a flashlight. Organisms were identified and measured on the longest axis to the nearest millimeter by the divers as time allowed. Size data (and other physical and biological data) from each dive are recorded on waterproof datasheets which the divers fill out along the transect. Upon return to the boat, data sheets are checked by the lead diver to ensure accuracy and readability for the first quality control check.

Rapid Emergent Surveys:
In response to the extreme purple sea urchin population increase and abalone mortality event in 2016-18, divers conducted a rapid assessment sampling technique: Rapid Emergent Abalone Surveys (REAS). REAS are similar to standard emergent surveys but focus on purple sea urchin and red abalone counts, allowing divers to survey more area. Measurements of organisms are recorded as time allows. Divers conduct two to four rapid emergent transects per dive.

The data specific to this dataset are the lengths (mm) of red abalone, flat abalone, pinto abalone, red sea urchin, and purple sea urchin along each transect.