San Ignacio Lagoon is one of the four breeding lagoons of the Northeastern Pacific gray whale population that remains relatively undeveloped. It is located on the Pacific coast of Baja California Sur, Mexico, adjacent to Bahía Ballenas, approximately 680 km south of the International border between coordinates 26⁰ 42′ and 27⁰ 00′ N and, 113⁰ 7′ and 113⁰ 18′ W. San Ignacio Lagoon is situated in the southern part of the El Vizcaíno Biosphere Reserve, the largest refuge in Latin America, which is managed by the Secretariat of Environment and Natural Resources of Mexico (SEMARNAT).
Geology and climate
This lagoon borders gently sloping coastal alluvial plains, composed of sediments dating from the Cretaceous and Tertiary periods, covered by Pleistocene alluvium. The climate is arid with an annual precipitation of 56 mm, which occurs mainly during the winter months. There is no water input to the lagoon from rivers, lakes, etc. The interior of the lagoon consists of a series of narrow, relatively deep channels, surrounded by intertidal sand and marshes.
Dimensions and topography
The lagoon lies on a north-south axis, extends inland approximately 32 km, is between 1.8 and 6.5 km wide, and has an area of 152 km2, of which only approximately 57% or 87 km2 have sufficient depth (> 2m) to be used by gray whales. The semi-diurnal tides range from 0.9 m to 2.4 m, and the strong currents keep the interior channels open.
San Ignacio Lagoon has a distinctive topography characteristic of lagoons with a large tidal range, and can be divided into five areas: The mouth, the east channel, the lower, middle, and upper lagoons.
Areas of San Ignacio Lagoon
- The mouth: It is 3.5 km wide and is defined by a line of shallow sandbars with a 1 km entrance channel with a maximum depth of 17 m. This steep-walled channel runs northward, parallel to the west coast of the barrier island, Isla Ana.
- Lower lagoon: It consists of a steep-walled channel with a maximum depth of 26 m. It starts 3 km wide near the Mouth and ends 1.8 km wide at Punta Piedra.
- East channel: To the west of Isla Ana, the east channel deviates from the main lagoon, turns southwest behind Isla Ana, and runs 5 km to the Estero Pitahaya, which is very shallow.
- Middle lagoon: It is characterized by a system of three channels ranging from eight to 21 m deep, which becomes shallower and more irregular west of the La Freidera ranch.
- Upper lagoon: It is a slightly inclined basin with an average depth of 5 m. Two islands, Isla Garzas and Isla Pelícano, are located approximately in the middle of the lagoon, separated by a shallow isthmus at low tide. The area north of the islands and the northern part of the lagoon is a shallow basin that averages 2 m in depth.
Regulations and use of the lagoon
The Biosphere Reserve regulations restrict whale watching to the lower part of the lagoon, near the entrance, between December 15 and April 15 of each winter and spring. Therefore, approximately two-thirds of the lagoon (the Middle and Upper areas) are a sanctuary for the exclusive use of small fishing and research vessels.
