Interannual and regional variability in settlement of groundfishes to protected and fished nearshore waters of Oregon, USA

For most benthic marine organisms, settlement of pelagic offspring to bottom-associated habitats is a necessary step in the replenishment of adult populations. Quantifying spatial and temporal variation in settlement is therefore important to fully understand population dynamics, inform fisheries management targets, and design effective spatial management strategies. Data on nearshore patterns of fish settlement are lacking for the northern California Current System (CCS), which is characterized by complex oceanographic currents and a seasonal, intermittent upwelling regime. Thus, to quantify spatial and temporal patterns of fish settlement in the northern CCS in relation to oceanographic conditions, we measured settlement of 5 fish taxa to 2 regions of the Oregon coast over 5 settlement seasons (late spring to early fall, 2012-2016). Temporal patterns of settlement reflected taxon-specific degrees of episodic settlement, with cabezon Scorpaenichthys marmoratus exhibiting the most uniform settlement across each season, and splitnose Sebastes diploproa and redbanded S. babcocki rockfishes exhibiting the most episodic settlement. Fish settlement tended to be greater during short periods of downwelling (upwelling relaxation events) for all but the largest fish taxa. Within settlement season, variation in size-at-settlement tracked taxon-specific temporal patterns of arrival but was unrelated to water temperature. Differences in fish settlement between small marine reserves and nearby unprotected areas was region- and taxon-specific, highlighting the fact that size and habitat heterogeneity should be considered in the design of marine reserves. These findings provide a deeper understanding of settlement patterns across the mosaic of environmental variability in eastern boundary currents such as the CCS.