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Applying Benthic Data: Managing Fisheries Resources

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Summary Batiquitos Lagoon Restoration and Monitoring

Scotian Shelf Habitat Mapping

An example habitat map from the western region of Batiquitos Lagoon. Courtesy: Science Applications International Corporation

Batiquitos Lagoon Restoration and Monitoring

Batiquitos Lagoon, a coastal estuary located in northern San Diego County, California, suffered from tidal restriction caused by roads and railways built during the 20th century. Since the early 1980s, sediment accumulated in the lagoon had obstructed saltwater input from the ocean. These degraded conditions resulted in the need to regularly drain impounded freshwater from the lagoon to lessen impacts to the habitats and species. An environmental restoration project to transform the confined, non-tidal ecosystem back to a fully-tidal saltwater system was implemented in December 1996.

This highly successful restoration project relied substantially on benthic mapping to perform the following:

1. Identify and delineate submerged habitats critical for fisheries species
2. Document declining habitat acreage
3. Identify suitable eelgrass restoration sites (based on bathymetry and substrate type)
4. Monitor spatial and temporal changes in submerged vegetation beds
5. Document sediment accumulation for planning a maintenance dredging schedule

Aerial photographs were used to map submerged and emergent vegetation for long-term trend analysis. These also provided base maps for ongoing field studies (including fish surveys), facilitated biological community and habitat classification, aided in identifying appropriate areas for eelgrass restoration (suitable transplant sites), and helped document spatial and temporal changes in habitat acreage. Aerial mapping of eelgrass in the lagoon was augmented by side-scan sonar data.

Following the opening of the lagoon mouth in December 1996, changes in eelgrass acreage were monitored with these benthic data. Though some eelgrass recruited naturally to the lagoon, transplants were used in suitable areas — identified through sediment and bathymetry mapping. By October 1998, multiple patches of eelgrass had recruited into a central basin and coverage had reached 0.72 acres. Eelgrass coverage continued to increase, reaching approximately 4.46 acres in 1999 and 53.35 acres in 2000.

Since the restoration project began in late 1996, dredging and opening of the lagoon mouth have produced a substantial increase in benthic habitat for coastal fishes. Surveys of fish communities in the lagoon have documented significant increases in the abundance and number of species, including demersal (benthic) fish. The number of species has steadily increased overall, with demersal species having the highest rate of increase. This demonstrates a fundamental change in the lagoon fish communities.

In this restoration effort, benthic mapping was a critical tool in documenting progress towards meeting goals for a healthy estuary. It will also be useful for continued management and maintenance of key resources in the Batiquitos Lagoon.

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