Clearing the Way for the California Crossing Bridge on the Elm Fork
Project Location:
Elm Fork of the Trinity River
Dallas, Texas
Project Partners:
TxDOT
Blanton & Associates, Inc
Services:
Freshwater Survey Mussel and Relocation
Scientific SCUBA
PIT Tagging
Post Relocation Monitoring
Survival and Recapture Analysis
Project Type:
Transportation / Bridge
Freshwater Mussel Relocation and Monitoring, California Crossing Bridge Replacement
Project Overview and Objectives
Zara provided freshwater mussel relocation and long-term monitoring for the California Crossing Bridge Replacement Project on the Elm Fork of the Trinity River in Dallas County, Texas. The project involved a dense, established mussel community that included rare and state-listed species within the construction impact area.
Survey and relocation work presented unusual field challenges. The Elm Fork is deep and turbid, with essentially zero underwater visibility, entanglement hazards, heavy silt, flood debris, and changing conditions associated with frequent flooding. Zara's scientific dive team developed specialized underwater survey and relocation methods to safely work within these conditions while collecting the data needed to evaluate the effectiveness of mussel relocation over time.
Services Provided
Freshwater mussel surveys and relocation
Scientific SCUBA and zero-visibility tactile surveys
Relocation site selection
PIT tagging and individual identification
Multi-year post-relocation monitoring
Rare and state-listed species documentation
Survival, recapture, and recovery analysis
Technical reporting
Working entirely by touch in zero-visibility conditions, Zara divers used specialized SCUBA equipment and underwater communications to locate and collect mussels from the bridge construction impact area. In total, 448 mussels were collected and relocated to carefully selected habitat outside the impact area. Of those, 143 mussels were individually marked with PIT tags and redundant color-coded identifiers to support long-term tracking.
Study Results
Zara returned to the relocation site for five monitoring events over a 39-month period. Despite the formidable challenges, the project demonstrated remarkable success:
The project achieved a cumulative recapture rate of 66%, with 94 of 143 tagged animals re-encountered over five survey events. This rate is notably higher than the average 43% rate reported in 21 other studies.
The monthly survival probability of tagged mussels was estimated at 0.98 ± 0.004 over a 39-month monitoring period. This high survival rate strongly suggests that the tagging and relocation methods employed had little to no negative impact on the mussels' survival.
This project provides compelling evidence that the relocation of freshwater mussels from impacted areas is an effective strategy for preventing direct construction-related mortality in individual mussels.
Our Impact
Findings from the project contributed valuable ecological data to the understanding of mussel populations in a previously understudied stretch of river and allowed for the refinement of sample and relocation techniques, establishing industry baseline expectations for recapture and survival.
This project underscores Zara’s expertise in executing complex environmental conservation efforts under extreme conditions, setting new benchmarks for freshwater mussel relocation success.
