Trends in Oyster Populations in the Northeastern Gulf of Mexico: An Assessment of River Discharge and Fishing Effects over Time and Space

Abstract

Within the Big Bend region of the northeastern Gulf of Mexico, one of the least developed coastlines in the continental USA, intertidal and subtidal populations of eastern oyster Crassostrea virginica (hereafter referred to as "oyster") are a critical ecosystem and important economic constituent. We assessed trends in intertidal oyster populations, river discharge, and commercial fishing activity in the Suwannee River estuary within the Big Bend region using fisheries-independent data from irregular monitoring efforts and publicly available environmental data. We used generalized linear models to evaluate counts of oysters from line-transect surveys over time and space. We assessed model performance using simulation to understand potential bias and then evaluated whether these counts were related to freshwater inputs from the Suwannee River and commercial oyster fishing effort and landings at different time lags. We found that intertidal oyster counts have declined over time and that most of these declines are found in inshore intertidal oyster bars, which are becoming degraded. We also found a significant relationship between oyster counts and a 1-year lag on mean daily Suwannee River discharge, but including commercial fishery trips or landings did not improve model fit. It is unclear whether declines in intertidal oyster bars are offset by formation of new oyster reefs elsewhere. These results quantify rapid declines in intertidal oyster reefs in a region of coastline with high conservation value that can be used to inform ongoing and proposed restoration projects in the region.

Bootstrap methods can help evaluate monitoring program performance to inform restoration as part of an adaptive management program

“…Oyster reefs in this region commonly form linear chains parallel to the shoreline and provide multiple ecosystem services ranging from fisheries, protection of shoreline features, and promotion of estuarine conditions ( Kaplan et al, 2016 ). In recent decades, Lone Cabbage Reef has degraded in terms of oyster coverage and elevation of the reef surface ( Frederick et al, 2016 ; Moore et al, 2020 ; Seavey et al, 2011 ), potentially reducing the effectiveness of this reef complex in providing both local (e.g., oyster habitat for fish and wildlife) and large-scale (e.g., promotion of estuarine conditions; Kaplan et al, 2016 ) ecosystem benefits and fishery harvests. Since multiple lines of evidence have identified substrate as a limiting resource ( Frederick et al, 2016 ), our restoration approach uses large, quarried limestone rock (average size 52 × 34 × 33 cm) to rebuild the elevation and historic footprint of Lone Cabbage reef identified from surveys completed in the 1800’s ( Raabe, Streck & Stumpf, 2004 ).…”

“…Since multiple lines of evidence have identified substrate as a limiting resource ( Frederick et al, 2016 ), our restoration approach uses large, quarried limestone rock (average size 52 × 34 × 33 cm) to rebuild the elevation and historic footprint of Lone Cabbage reef identified from surveys completed in the 1800’s ( Raabe, Streck & Stumpf, 2004 ). Oyster monitoring efforts focus on assessing restoration goals of increases in Lone Cabbage oyster population (counts from transects) on restored oyster bars compared to adjacent extant unrestored (wild) oyster bars, which may be declining ( Moore et al, 2020 ).…”

“…For our GLM, we fit a model with live oyster counts as the response variable and a dummy variable for restored/unrestored reefs as the predictor variable. We included transect length as an offset to account for the differences in transect length between sites ( Moore et al, 2020 ). We compared these results for each of our post-construction monitoring periods.…”

A Synthesis of Deepwater Horizon Impacts on Coastal and Nearshore Living Marine Resources

“…Several factors affect inter-and sub-tidal oyster populations. A series of natural disasters and especially hurricanes (e.g., Katrina in 2005) as well as flooding events (and especially in 2019) have negatively affected local populations (Moore et al, 2020). Oysters are filter feeding invertebrates, and as such have limited capacity to metabolize organic pollutants such as polycyclic aromatic hydrocarbons (PAHs) resulting in their bioaccumulation within tissues.…”

“…Landings in Alabama and especially Mississippi were among the time series lows in 2018, with the latter likely affected by freshwater flooding of Mississippi Sound from heavy rains and the opening of the Bonnet Carré Spillway. For Florida, most landings occurred east of the area affected by the DWH spill, and long-term declines there are likely related to hydrological changes (Moore et al, 2020).…”