Dataset: Species surveys at defined tides on the exposed rocky shores of Tatoosh Island, Makah Reservation, Washington 2014-2017

Samples were taken at four sites of relatively uniform rock bench of at least 30 meters (m) in length at Tatoosh Island, Makah Reservation, Washington, USA, known by investigators as: East Strawberry (48.39144N, -124.73839W), The Finger (48.39387N, -124.73841), The Glacier (48.39145N, -124.74098), and Simon's Landing (48.39121N, -124.73271W). Sampling occurred on days with low spring tides to sample the broadest stretch of shoreline exposed at low tide. At each site, once per year, we set a Dewalt rotating, self-leveling laser level on a tripod just above the upper limit of the barnacle zone, set the laser detector to a specified level on the transit and moved along the shore from south to north choosing 10 spots along the bench at the selected transit height spaced as evenly as possible along the entire rock bench while avoiding topographic irregularities such as tide pools or large cracks in the rock bench. This sampling pattern resulted in 10 general sampling bands extending down each rock bench. Within each band, sampling points were selected by moving the transit to a point in the band at a generally appropriate height as assessed by moving the transit upward or angling it sideways until the laser detector on the transit beeped, then slowly moving the base of the transit up or down the shore while holding the transit vertical until the laser beam was detected. At each point, a 50 x 50 centimeter (cm) quadrat, divided into 121 sub-squares defined with monofilament cross lines to aid in estimating percent cover was centered on the identified sample point and oriented to be perpendicular to the slope of the rock, and was photographed from below (seaward side at the bottom), with the quadrat frame spanning nearly the entire vertical (short) frame of the photograph to maximize detail. Upon completion of sampling at one tide height, the detector on the transit would be moved by the selected vertical tidal sampling increment, usually 0.2 m but occasionally 0.1 m at some sites/years, and the process was repeated until the lowest point that could be reached at low tide was surveyed. Sampling was initiated 3-3.5 hours before predicted low tide to follow the tide out to its lowest level.