Exploring California’s Marine Protected Areas: Portuguese Ledge State Marine Conservation Area

Portuguese Ledge State Marine Conservation Area (SMCA) lies four miles offshore of the Monterey peninsula in central California. The SMCA was established following the passage of the Marine Life Protection Act in 1999, which mandated the redesign of California’s marine protected area (MPA) system into a cohesive network. Currently, only 14 of the 124 state MPAs protect deepwater, submarine canyon habitat; Portuguese Ledge SMCA was one of the first such MPAs to be established.

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Monterey Canyon, Portuguese Ledge SMCA (lower center), and other nearby MPAs  map by CDFW Marine Region GIS Lab

The SMCA covers about 11 square miles of offshore habitat composed of approximately 95 percent soft bottom and 5 percent hard bottom habitat, including roughly 1.5 square miles of the Monterey Canyon. Portuguese Ledge SMCA has the greatest depth range of any California MPA, ranging from 302 to 4,793 feet deep. The deepest portion of Monterey Canyon, at nearly 13,123 feet deep, can be found just outside of the SMCA in federal waters.

The Monterey Canyon is an ever-changing environment carved out by erosion, tectonic deformation, and water flow. Resources and nutrients within the canyon can fluctuate seasonally; they can also change with depth, distance from shore, and other factors. Deepwater flow in the canyon, which can reach velocities of up to 1.1 yards/second, constantly moves resources and frequently changes direction and speed.

Turbidity currents also flow through the canyon. These underwater currents carry large amounts of sediment at velocities of up to 2 yards/second and are thought to move around 654,000 cubic yards of sediment annually. The constant shift of resources and structure in the canyon creates a varied and complex environment with high species diversity.

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Humpback whales frequent the bay during spring and summer. CDFW photo by P. Serpa

Coastal upwelling is one of the most important processes in Monterey Bay. It occurs when warmer, nutrient-poor surface water is blown offshore by coastal winds, and cold, nutrient-rich water rises to the surface. This influx of nutrient-rich water also supports the bay’s high productivity and species diversity. Until the early 1990s, the Monterey Canyon was considered one of the primary contributors to coastal upwelling in Monterey Bay. While studies have actually identified Año Nuevo as the primary source of cold, upwelled water in the bay, the Monterey Canyon may help to retain the nutrient-rich water in the bay for a longer period of time.

Nutrients drive primary productivity (the total energy produced by photosynthesis in algae and tiny, plant-like organisms called phytoplankton), which typically peaks during the spring and summer in Monterey Bay, and supports a food web that extends from the smallest microscopic plankton to the largest of whales. During the spring and summer, a diverse assemblage of marine mammals, including humpback whales, Pacific white-sided dolphins, Risso’s dolphins, and common dolphins are readily observed throughout the bay.

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Rosy rockfish (hiding) and starry rockfish (left) on a deepwater reef in Portuguese Ledge SMCA  CDFW/MARE photo

While a single MPA on its own cannot facilitate the recovery of any single species on a statewide scale, the MPA network, completed in 2012, aims to create a large group of ecologically connected MPAs that together help to improve the status of depleted and at-risk species. The primary goals of Portuguese Ledge SMCA include protections that focus mainly on the deepwater reef and the valuable habitat and species found there. However, preserving and protecting marine species within the SMCA had to be balanced with fishing industry concerns and needs when drafting the area’s boundaries and regulations, due to its history as a commercial and recreational fishing hotspot. The result was regulations that permitted recreational and commercial fishing for pelagic finfish, while protecting species such as groundfish that live on the sea floor. Fishermen still catch valuable fish species on this historic fishing ground, such as sardines, anchovies, mackerel, and salmon (to name a few of the more important commercial fisheries along the central coast) while the SMCA continues to function as an effective part of the MPA network by protecting other species (check out California’s commercial landings data).

Although changes in species composition and density – like noticing more or less fish, different types of fish, or larger fish in a given area – cannot currently be attributed solely to the implementation of central California MPAs in 2007, long-term monitoring efforts by the California Department of Fish and Wildlife and associated researchers may help to better understand these changes over time.

Although the sea floor within Portuguese Ledge SMCA is out of reach for scuba divers, footage from surveys conducted via remotely operated vehicle offer a rare glimpse of this dynamic, rich environment!


logopost by Jose Ayala, CDFW Scientific Aid

Learn more about MPAs by diving into the
Exploring California’s Marine Protected Areas series!