Small-scale community structure and trophic ecology of groundfishes in the Stellwagen Bank National Marine sanctuary under two anthropogenic disturbance regimes

Abstract

A combination of overexploitation and destructive fishing practices, such as bottom trawling, have depleted native populations of groundfishes in coastal New England and reduced benthic community diversity. The Stellwagen Bank National Marine Sanctuary (SBNMS) in the southern Gulf of Maine is partially overlapped by the Western Gulf of Maine Closed Area (WGMCA). The WGMCA is closed to commercial fishing for groundfishes managed under the Northeast Multispecies complex and the use of bottom trawling fishing gear is prohibited to protect essential fish habitat. This has reduced fishing pressure and benthic disturbance levels. The area of the SBNMS outside of the WGMCA is still disturbed by intensive commercial fishing for much of the year. Key questions for this area are (1) How does the higher level of disturbance in areas outside of the WGMCA affect SBNMS groundfish communities?, (2) Is the WGMCA effective at increasing the diversity, abundance, and biomass of groundfishes in the SBNMS?, and (3) How does the decrease in disturbance impact groundfish trophic ecology? A comparison of the groundfish communities inside and outside of the WGMCA within the SBNMS was carried out via trawl sampling. Results show that groundfish communities are more diverse inside the WGMCA than outside. Additionally, several commercial groundfish species had higher abundance and/or biomass inside the WGMCA. Stable isotope analyses showed that prey items differed for some species inside and outside of the WGMCA, but trophic levels were unaffected. Finally, stable isotope analyses of five groundfish species provide evidence that groundfishes may display a high level of foraging area fidelity. Primary conclusions include: (1) the protection of groundfish habitats from trawling disturbances paired with reduced fishing pressure will result in increases in community diversity and abundances of groundfishes, (2) groundfish ecology should be considered on a small geographic scale due to apparent site fidelity, and (3) if the entire SBNMS were closed to bottom trawling and commercial fishing, it could help to rebuild overexploited groundfish populations in the southern Gulf of Maine and serve as a source population for the remainder of the Gulf of Maine and adjacent shelf environs.