Habitat-based submersible assessment of macro-invertebrate and groundfish assemblages at Heceta Bank, Oregon, from 1988 to 1990

Exploitation of groundfish off the U.S. Pacific coast reached maximum levels during the 1990s, resulting in severe declines in at least nine species of groundfish. From 1988 to 1990, we used the 2-man submersible Delta to make 42 dives and run replicate visual belt transects at six stations ranging from 67-360 m in depth at Heceta Bank on the outer continental shelf of Oregon. We identified four major habitats and associated benthic macroinvertebrate and groundfish assemblages: (1) shallow rock ridges and large boulders (< 100 m deep) dominated by basket stars, juvenile rockfishes, yelloweye rockfish, and lingcod; (2) mid-depth small boulder-cobbles (100-150 m) dominated by crinoids, brittle stars, rosethorn, pygmy/Puget sound, and canary rockfishes; (3) deep cobble (150-200 m) dominated by crinoids, brittle stars and various small rockfish species, and (4) deep mud slope (> 200 m) dominated by fragile urchins, sea cucumbers, shortspine thornyhead, and flatfishes. Although substantial interannual variation in groundfish abundance among seafloor types was evident in the 12 most abundant and/or commercially important fish taxa sampled, high variance resulted in statistically significant differences among years only in juvenile rockfishes. These data provide a baseline for future comparisons exploring long-term change this continental-shelf ecosystem.     

Effects of excluding bottom-disturbing mobile fishing gear on abundance and biomass of groundfishes in the Stellwagen Bank National Marine Sanctuary, USA

The Stellwagen Bank National Marine Sanctuary (southern Gulf of Maine, northwest Atlantic) is partially overlapped by the Western Gulf of Maine Closure Area (WGMCA). This is a region in which mobile, bottom-disturbing fishing gear has been banned by the New England Fishery Management Council to facilitate the rebuilding of depleted groundfish populations. We assessed the effects and effectiveness of the WGMCA on groundfish assemblages using habitat-stratified (gravel, sand, mixed benthic habitats) sampling by means of a commercial trawler, inside and outside of the WGMCA. Sampling occurred over three month-long sampling periods in 2004-2005, two during the spring seasons and one during the fall season. A total of 18 species were analyzed for protection effects. After controlling for substratum, location and sampling season, eight groundfish species exhibited higher mean proportional abundance inside than outside the WGMCA while two were proportionally more abundant on average outside of the closure. Four species had higher mean proportional biomasses on average inside the closure and three outside. We conclude that the WGMCA may be achieving its goal of rebuilding abundance and biomass for some commercially targeted groundfishes but not all. This study, six to seven years post-closure establishment, reveals fine-scale spatial and taxonomic complexity which will require a very different monitoring protocol than the one currently in place if adaptive management is to be successful in the region [Current Zoology 56 (1): 134-143, 2010].