Do the estuary and watershed support a healthy population of steelhead?

No, the local steelhead population continues to be threatened even with some habitat improvement.

The Morro Bay watershed is home to steelhead trout (Oncorhynchus mykiss), which are born in freshwater streams like Chorro Creek. Some of these fish, known as resident or rainbow trout, spend their entire lives in the creek. Others, known as steelhead, spend a few years in fresh water and estuarine environments before journeying to the ocean. Whether a fish becomes a steelhead trout or remains a resident rainbow trout depends on genetic and environmental factors.

Steelhead are very sensitive to water and habitat quality in both freshwater and the ocean. The Estuary Program works to protect creek habitat, water quantity, and water quality to benefit this threatened fish population.

Protecting Steelhead from Predators

Sacramento pikeminnow (Ptychlocheilus grandis, pictured below) are invasive fish that compete with the steelhead in our watershed for habitat and food. Adult pikeminnow also consume juvenile steelhead. In 2017, we began pikeminnow management efforts to remove them from our creeks to support steelhead recovery. Our early work indicated that removing one pikeminnow can protect around 150 to 200 juvenile steelhead annually.

One method of pikeminnow management involves electrofishing (pictured above), where fish in the vicinity are temporarily stunned by an electric current put into the water using an electrofishing backpack. The fish are scooped up to be identified and measured, and all but the pikeminnow are returned to the creek.

Tracking Steelhead Growth and Movement

We recently completed a steelhead tracking study over two years of spawning seasons to monitor the growth and movement of steelhead to support our understanding of how and when these fish migrate between our creeks, the estuary, and the ocean. This helps us identify times of year when fish need enough water flowing through creeks to migrate and when we should avoid certain activities that might interfere with their movement.

The method used to track fish for the project is called mark-recapture. Backpack electrofishers are used to temporarily stun and capture fish to be weighed and measured (left). Then, steelhead of sufficient size are anesthetized, implanted with a Passive Integrated Transponder (PIT) tag (right), and returned to the creek. These tags are small microchips that uniquely identify each fish, similar to the microchips used for dogs and cats. The PIT tags are detected by an antenna in the creek as the fish swim past it.

A total of 1,225 steelhead trout were captured during the study, and 870 were large enough to tag. Of the 201 tagged fish detected at the antennae, nearly 60% were likely resident trout that would spend their entire lifespan in the creeks. The remaining 81 were fish that moved into the estuary to smolt (transition from freshwater to saltwater habitat), a process that occurred primarily between January and April. Most of these smolts left the creeks and did not return, while a handful moved back and forth between Chorro Creek and the estuary.

This study provided fascinating new information, and we hope to expand the effort to better understand how steelhead utilize other freshwater tributaries like San Bernardo, Pennington, and Dairy Creeks.