Assessment of Propeller Scarring in Seagrass Beds of the South Texas Coast

Dunton, Kenneth; Schonberg, Susan

Distribution and intensity of scaning in approximately 5,700 ha of seagrass beds were quantified using high resolution (1:2,400) aerial photography taken in January 1997 in the Corpus Christi Bay National Estuary Program (CCBNEP) study area along the south Texas coast. Scarring levels were defined as light (less than 57a), moderate (5-201o), ot heaw (greater than 209a) based on the percentage of area covered by propeller scars within each of eight distinct regions. Suneys by boat and aircraft were used to verifu aerial photogaphy and collect Differential Global Positioning System (DGPS) coordinates for rectification and registration procedures. Distribution and Ievels ofscaning were digitally rransfened onto USGS topographical charts and analyzed using Geographic Infomation System (GIS) techniques. Within the suryey area, 2,200 ha (39%) of seagrass meadows were identified as either moderately or severely scaned. Scaning ofgrassbeds was great€st in Estes Flats, where over 97E ofthe grassbed was scarred, with 75% rated as severe. Moderate and severe scaning was also prevalent in the Dast Flats (497a), Shamrck Island (35%), and Redfish Bay (237d regions. Propeller scaring of seagrasses by boating activity is caused by misjudgment ofwater depth or channel locatioq, taking shoftcuts across shallow flats, maintenance ofchannels through grassbeds using illegal navigational aids, and ignorance with respect to the damage caused by propellers. Management priorities should focus on public education and the marking of secondary chmnels to minimize damage to adjacent gtassbeds. Future reseach efforts should be directed toward understanding the long-tem elfects of seagrass scaring in an effort to develop local management strategies to minimize continued damage to this valuable resource.

Assessment of Propeller Scarring in Seagrass Beds of the South Texas Coast

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