Persistence of avian carcasses on sandy beaches and marsh edges in the northern Gulf of Mexico

Veronica W Varela,Guthrie S Zimmerman

doi:10.1007/s10661-019-7920-3

Veronica W Varela, Guthrie S Zimmerman

Open Access

https://doi.org/10.1007/s10661-019-7920-3

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Abstract

As part of the natural resource damage assessment for the Deepwater Horizon oil spill, a mathematical model was used to estimate the total number of bird carcasses deposited on shorelines based on the number of carcasses collected and adjustment factors such as detection probability and carcass persistence. Studies of carcass persistence occurred along sandy beaches and marsh edges in the northern Gulf of Mexico to obtain site-specific inputs for the model. We estimated persistence rates for these habitat types and evaluated the influence on persistence of carcass size, location of the carcass on the beach, dominant vegetation type in the marsh, carcass distance into marsh vegetation, and length of time a carcass was stranded on a shoreline. The length of time stranded had the greatest influence on persistence in both habitat types, with persistence initially relatively low and increasing logarithmically. Carcass size and position were weakly influential on sandy beaches. Carcass size had stronger influences along marsh edges, and marsh habitat type also affected persistence. We found evidence of a positive relationship between distance into the marsh and persistence during the first 24 h after carcass deployment.

Highlights

During an oil spill in coastal environments, the number of bird carcasses found on shorelines can be used as an indicator of the magnitude of environmental harm
We examined the potential influence of these factors on carcass persistence on sandy beaches and marsh edges in the northern Gulf of Mexico to provide information for consideration by future investigators of carcass persistence
Accounting for overdispersion in the marsh edge analysis could have resulted in less support for size and habitat given the observed uncertainty associated with confidence intervals for the fitted values. These field studies and our analyses provide the first estimates of avian carcass persistence on sandy beaches and along estuarine marsh edges in the northern Gulf of Mexico

Summary

Introduction

During an oil spill in coastal environments, the number of bird carcasses found on shorelines can be used as an indicator of the magnitude of environmental harm. A mathematical model is commonly used during oil spill natural resource damage assessments to estimate the total number of bird carcasses that deposit on shorelines based on the number of carcasses collected and adjustment factors for at least detection probability and carcass persistence (Ford et al 1996, 2001, 2006, 2009). As part of the process to quantify harm to birds, the Trustees counted and collected carcasses from shorelines in the vicinity of the oil spill and conducted several field studies to develop inputs for a mathematical model that would estimate total bird carcass deposition on shorelines (Amend et al 2020). To estimate the carcass persistence inputs for the model, the Trustees evaluated how long deployed study carcasses remained on shorelines of sandy beaches and marsh edges in the northern Gulf of Mexico. The investigators focused on developing carcass persistence estimates for different shoreline types (i.e., sandy beaches vs marsh edges, which may indicate different types of scavengers or other carcass removal activities) as a function of time and carcass size

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