Dungeness Crab Zoea Distributions in the Northern California Current

Dungeness crab (Cancer magister) is an important commercial species along the west coast of North America, and its population dynamics are highly influenced by processes occurring during its planktonic early life history. However, little is known about this stage, including offshore distributions of the early larval stages. To begin to fill this knowledge gap, we examined the cross-shelf and vertical distribution of development stages of Dungeness crab zoea off the coast of central Oregon during late winter. Based on the crab life cycle, we hypothesized that 1) late stage zoea would be most abundant offshore and with a maximum at the shelf break, and 2) more variation in concentrations between day and night in later stage zoea than early stage zoea. We conducted depth discrete sampling between 0-100 m in March 2019 on the continental shelf, shelf break, and 80 km offshore off Newport, OR, during both day and night. Overall concentrations of zoea were significantly higher over the continental shelf and shelf break than offshore, especially Stage V zoea, which was the most abundant stage found. Vertical distribution patterns varied by station. Zoea were not uniformly distributed in the water column and remained in the upper 50 m of the water column regardless of diel period over the continental shelf and shelf break. Significantly more zoea were captured at night in the offshore station. Back-calculated birth dates based on average larval stage durations indicated that most larvae were hatched in mid-December, but some were hatched continuously through to mid-February. These data will contribute to a more thorough understanding of Dungeness crab early life history, providing empirical data to parameterize biophysical models and inform management of this highly valuable fishery.