Keeping pace with change: An evaluation of the Maine-New Hampshire bottom trawl survey in a warming Gulf of Maine

The Maine-New Hampshire Bottom Trawl Survey (MENHBTS) plays a crucial role in monitoring the inshore marine ecosystem of the Gulf of Maine (GOM). However, climate-driven shifts in species distribution, phenology, and diversity may change the ability of the survey to consistently track managed populations and gather representative data to inform regional fisheries stock assessments. This study leveraged the standardized protocols and long-term data series of the MENHBTS to assess environmental, structural, and functional shifts in inshore waters of the GOM and determine if species availability to the survey changed during the time period of 2000–2023. Change point analysis identified thermal regime shifts in bottom water and sea surface temperatures occurred during 2010 and 2012, respectively, dividing the time series into two periods. Distribution shifts were assessed using a center of gravity (CG) analysis, with the survey boundaries serving as a fixed reference frame. While over 12 species of finfish and invertebrates (e.g., American lobster, Homarus americanus ,White hake, Urophycis tenuis ) exhibited shifts in their CG either northeastward, offshore, or to deeper waters, the catchability of most species remained relatively stable, changing by less than 10% within the survey’s original spatiotemporal boundaries. Biological data suggested possible changes in spawning seasons and size structure may be occurring in several species; however, due to the limited seasonal window of the survey, conclusions concerning shifts in phenology should be considered preliminary and require further investigation. Seasonal species diversity in the MENHBTS exhibited opposing trends depending on the index used; however, biomass-based catch diversity, which characterizes dominant species, decreased significantly in both seasons during the warm regime. Outcomes provide new insights into how inshore habitats and communities, which are often underrepresented in broader regional assessments, have changed over the last two decades, and support the development of climate resilient fisheries management strategies in the GOM.