Malibu Creek - Ecology

Ecology

It is estimated that the Steelhead trout (Oncorhyncus mykiss) populations within the Southern California Coast Steelhead Distinct population segment (DPS) have declined dramatically from annual runs totaling 32,000-46,000 adults to less than 500 returning adult fish. This estimate is based largely on the four major steelhead-bearing watersheds, Santa Ynez River, Ventura River, Santa Clara River, and Malibu Creek. Genetic analysis of the steelhead in all four of these watersheds has shown them to be of native and not hatchery stocks. A sand berm across the mouth of the Malibu Creek Lagoon blocks the stream to ocean-based steelhead except during the rainy winter season when high flows breach the berm and opens access to the estuary. The fish quickly reach an impassable barrier presented by the 30 m (98 ft) high Rindge Dam, restricting them to the lowest 3.2 km (2.0 mi) of more than 112 km (70 mi) of historic steelhead habitat. The dam, originally built for water storage and flood control in 1926, no longer functions as the reservoir is completely filled with sediment. Over the past decade several government agencies and non-profit organizations have been trying to remove the dam to restore access to upstream spawning habitat. In 1997, the southern Evolutionarily Significant Unit (ESU) of steelhead trout was added to the federal list of endangered species, with Malibu Creek as the southernmost boundary. Since 1997, the protected range of this ESU has been extended to the U.S./Mexican border. The National Marine Fisheries Service (NMFS) estimates that only 500 anadromous adults remain within this ESU (NMFS 2007). In summer, 2006, there was a massive die off of native and exotic fish and invertebrates in Malibu Creek, thought to be due to a combination of pollution, high temperatures and low oxygen. The steelhead trout population fell to zero by November, 2006. Fortunately, surveys in summer 2008 documented five returning adult steelhead over 50 cm (20 in), and over 2,200 smolts under 10 cm (3.9 in) were also recorded.

The rare plant Malibu baccharis (Baccharis malibuensis) is endemic to the Malibu Creek drainage.