Occurrence of Commercially Important and Endangered Fishes in Delaware Wind Energy Areas Using Acoustic Telemetry

Haulsee, D.; Oliver, M.; Fox, D. (2020). Occurrence of Commercially Important and Endangered Fishes in Delaware Wind Energy Areas Using Acoustic Telemetry (Report No. OCS Study BOEM 2020-020). Report by University of Delaware. Report for Bureau of Ocean Energy Management (BOEM).

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Abstract

The Mid-Atlantic Bight has been identified as an area with great offshore wind potential, creating interest in the development of offshore wind energy projects in Wind Energy Lease Areas (WEAs). The Delaware (DE) WEA starts approximately 11 km off the coast, but little information about the distribution and occurrence of marine species in this area is known. Between 2017-2019, an extensive acoustic telemetry project monitored the timing and location of Atlantic sturgeon, winter skate, and other acoustically telemetered species in the DE WEA (Figure 1). This study was conducted to better understand the potential of encountering these species during future development in the DE WEA, as well as address potential impacts to commercial fisheries. The primary objectives of this study were: (1) Acoustically tag additional Atlantic sturgeon (n=50) and winter skate (n=50) in the DE coastal ocean (2) Deploy an acoustic receiver array for two years in the DE WEA (3) Determine seasonal usage of Atlantic sturgeon, winter skate and other acoustically telemetered species as provided by the ACT Network in the DE WEA (4) Develop environmentally driven models of Atlantic sturgeon and winter skate in the DE WEA (5) Determine transit times of acoustically telemetered species in the DE WEA and nearby coastal ocean (6) Deliver acoustic detection data to acoustic telemetry networks (ACT, MATOS, OTN) (7) Compare the recovery efficiency of standard and acoustic release receivers. Our key findings are highlighted below:

Acoustic detections from all receivers in the array documented the presence of 26 different marine fish and mammals, which creates a baseline to inform future monitoring efforts.
Atlantic sturgeon occurred in the DE WEA nearly year-round, however distribution shifted from the shallow northwestern corner in the spring-summer, to the deeper offshore waters in the fall and winter. Atlantic sturgeon detections were highest in November and December, with far fewer Atlantic sturgeon detections during the summer, especially August. These observations expand upon previous studies for Atlantic sturgeon which characterized their occurrence as much more seasonal than documented in our study. Patterns in the timing and distribution of Atlantic sturgeon were consistent between years.
Using detections from collaborators monitoring the Maryland (MD) WEA and our detections in the DE WEA, we estimated the transit rates for Atlantic sturgeon migrating north in the spring, and south in the fall. Transit rates were consistent with those reported by other studies in the MidAtlantic. In addition, we quantified residency behavior in the DE WEA, which was highest in November and December. This provides further evidence that these months are likely when there is the greatest risk of encountering Atlantic sturgeon in the DE WEA.
A generalized additive model (GAM) was created to predict the occurrence and distribution of Atlantic sturgeon using remotely sensed ocean surface parameters (temperature, color), modeled ocean bottom temperature, and seafloor characteristics (bathymetry, sediment grain size, and bottom temperature). This model expands upon similar models produced for Atlantic sturgeon in the area but captures the distribution of Atlantic sturgeon further offshore than previously observed. Model outputs reflect the seasonality of the distribution and occurrence of Atlantic sturgeon in the DE WEA. We also show selection for coarse sand by Atlantic sturgeon for the first time in this region.
Few tagged winter skate were detected in the DE WEA, indicating that there is a low risk of impacting the commercial stock of winter skate due to offshore wind development in this WEA. The few winter skate that briefly entered the DE WEA did so in the spring and fall. Based on the acoustic detections of all tagged species detected, it appears the spring and fall are important seasons in the study region, with high numbers of species occurring in the DE WEA. This is presumably related to the seasonal migrations of these species.
We observed a large variety of elasmobranch species occurring in the DE WEA, mostly during the summer months. In addition, we detected two marine mammals (seals), which entered the DE WEA in the spring. Further research is needed to better understand the occurrence and distribution of these species in this region, and to establish baselines for their abundance predevelopment.
While not a focal species, we noted a high number of detections of striped bass; a species which supports a large commercial and recreational fishery. Striped bass occurrence was highly seasonal, with fish occurring in high numbers in November through January slightly more inshore and in March through May slightly more offshore.
Our study demonstrated the utility of acoustic-release transceivers, which minimized gear loss and enabled more reliable data collection of acoustic detections for tagged marine animals in this region. In addition, acoustic-release receivers allowed us to quantify excess ambient noise in the study region due to seafloor mapping efforts being conducted in anticipation for offshore wind energy development in the DE WEA.