Abstract
Avangrid LLC, in collaboration with the University of Massachusetts Dartmouth’s School for Marine Science and Technology (SMAST), has developed a monitoring plan to assess the potential environmental impact of future offshore renewable energy development on marine fish and invertebrate communities in the Lease Area OCS-A 0534. One component of the monitoring plan is a demersal trawl survey. The trawl survey is modeled after the Northeast Area Monitoring and Assessment Program (NEAMAP), a regional survey used to assess near-shore fish communities. The data collected from this survey is intended to provide baseline information on species abundance distribution, population structure and community composition to be used in a future impact analysis. Similar fisheries studies are being conducted within Lease Area OCS-A 0501 (the “Vineyard Wind 1 Study Area”) and within Lease Area OCS- A 0522 (the “522 Study Area”); these studies are reported separately.
Two seasonal trawl surveys were conducted from the fall of 2021 through the winter of 2022 using a commercial fishing vessel. Ten tows were conducted each season in the 534 Study Area. Tow locations were randomly selected using a systematic unaligned sampling design. A standardized bottom trawl with a 1” knotless liner was towed behind the vessel for 20 minutes at 3 knots. Acoustic sensors were used to ensure the net’s performance by monitoring the trawl geometry. The catch was sorted by species. Aggregated weight as well as individual fish lengths and weights were collected.
A total of 20 tows were completed throughout the year. The catch data obtained shows a dynamic area with a diversity of marine species. A total of 36 species were collected; however, the majority of the catch was comprised of a small subset of the observed species. The five most abundant species (spiny dogfish, scup, butterfish, little skate, and Atlantic longfin squid) accounted for 90.2% of the total catch weight in the 534 Study Area. All species caught displayed seasonal variations in distribution and abundance. The data indicate a unique assemblage of species and abundance in each season. The fall and winter surveys appeared to be relatively unique in the species assemblage.
Interannual changes in abundance varied amongst species and communities. For example, butterfish, Atlantic herring, Atlantic cod, scup, and Atlantic longfin squid exhibited increases in seasonal catch rates. Conversely, red hake, silver hake, monkfish, and little skate exhibited decreased annual catch rates. The seasonal changes were largely in line with those observed in 2019/2020 and 2020/2021. Winter tows were primarily associated with little skates, alewife, Atlantic herring, Atlantic mackerel, and blueback herring. Fall tows were associated with spiny dogfish, scup, butterfish, little skate, and longfin squid. The winter and fall surveys had similarity to the previous survey year. The interannual similarities may be due to consistent bottom water temperatures across the fall and winter surveys between survey years.
An updated power analysis was conducted using data aggregated from three survey years. The results indicate that the current bottom trawl survey effort would provide reasonable “power” to detect small to medium scales of change in abundance for the most common species, if changes in abundance do occur. Providing the additional year of survey data caused small changes to the CVs for most species, the changes observed serve to provide a more realistic assessment of the variability in the data and therefore a better understanding of the statistical power to detect changes.