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

The Portuguese Ledge State Marine Conservation Area (SMCA) lies four miles offshore of the Monterey peninsula. It 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. Of California’s 124 MPAs, the Portuguese Ledge State Marine Conservation Area is one of 14 MPAs which provide ecosystem protections for deep water, submarine canyon habitat. It covers about 11 square miles of offshore habitat, is composed of approximately 95 percent soft bottom and 5 percent hard bottom, and contains about 1.5 square miles of the Monterey Canyon. The Portuguese Ledge SMCA has the greatest depth range of California’s MPAs. Depths within the SMCA range from 302 to 4793 feet, while the deepest portion of the Monterey Canyon exists in federal waters just outside the SMCA at depths near 13123 feet.

Monterey Canyon and nearby MPA Locations. Map by CDFW Marine Region GIS Lab

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, with depth, and distance from shore, among other factors. Deepwater flow in the canyon constantly moves resources, frequently changes direction and speed, and reaches velocities up to 1.1 yards/second. Turbidity currents also flow through the canyon. These underwater currents carry large amounts of sediment at velocities up to 2 yards/second and are thought to move around 654,000 yards3 of sediment annually. The constant shift of resources and structure in the canyon creates a varied and complex environment producing an area with high species diversity.

Until the early 1990s, the Monterey Canyon was considered to be one of the primary contributors to coastal upwelling in the Monterey Bay. Coastal upwelling is one of the most important processes in the bay and occurs when warm, nutrient poor water is blown offshore by coastal winds and cold, nutrient rich water rises to the surface. This influx of nutrient rich water is thought to be responsible for Monterey Bay’s high productivity and species diversity. While studies have identified Año Nuevo as the primary source of this cold, nutrient rich water, the Monterey Canyon may be an auxiliary source that helps retain the upwelled water in the bay for a longer period of time. The peak in primary productivity (the total amount of energy produced by photosynthesis) in the Monterey Bay typically occurs during spring and summer upwelling events. Around this time of year 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. The photosynthetic energy that promotes this diversity comes from algae and phytoplankton converting sunlight into chemical energy.

Because this area has historically been a commercial and recreational fishing hotspot, when drafting the boundaries and regulations for the Portuguese Ledge SMCA, the preservation and protection of marine species was balanced with fishing industry concerns and needs. While this 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 improve the status of depleted and at risk species. As such, the primary goals of this SMCA include protections focused mainly on the deep water reef and the valuable habitat and species found there. The result of this is that the Portuguese Ledge SMCA allows the recreational and commercial fishing of pelagic finfish, and provides protection for more demersal (seafloor) species such as groundfish. By allowing conditional fishing in this protected area, fishermen are still able to catch certain valuable fish species (sardines, anchovies, mackerel, and salmon are some of the most important commercial fisheries in the central coast) and the SMCA continues functioning as an effective part of the MPA network for other managed species. Although changes in observed species composition/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 Coast MPAs in 2007, long-term monitoring efforts by the California Department of Fish and Wildlife and associated researchers may better help understand these changes over time. If you are interested in seeing more commercial landings data follow this link.

Because the Portuguese Ledge SMCA is too deep for a dive on SCUBA, footage from surveys conducted via remotely operated vehicle offer a rare glimpse into 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!


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