Juvenile red rockfish, Sebastes sp., associations with sponges in the Gulf of Alaska

Marine Fisheries Review, Summer, 2003 by J. Lincoln Freese, Bruce L. Wing

Introduction

Sponge-fish associations have been documented for a variety of species in both cold-water and tropical habitats. Eastman and Eakin (1999) found that fishes of the genus Artedidroco (Artedidraconidae) are associated with sponge beds in the Ross Sea of Antarctica. Likewise, Tokranov (1998) described the association of sponge sculpin, Thyriscus anoplus (Cottidae), with sponge beds in the northern Kuril Islands.

Konecki and Targett (1989) found that cod icefish, Lepidonotothen larseni (Nototheniidae), in waters adjacent to the Antarctic Peninsula utilize the spongocoel of the hexactinellid (glass) sponge Rossella nuda as a substrate on which to deposit their eggs. Notothenioid fishes known to utilize sponges as spawning and nesting sites include emerald rock-cod, Notothenia bernacchii (Moreno, 1980) and Antarctic spiny plunderfish, Harpagifer antarcticus (Daniels, 1978). Antarctic fishes that utilize sponges for predator avoidance include sharp-spined notothen, Trematomus pennellii, and spotted notothen, T. nicolai, as well as the crocodile icefish, Pagetopsis macropterus. Dayton et al. (1974) state that glass sponges provide almost all of the vertical structure on the sea floor in the Ross Sea of Antarctica.

Finally, Munehara (1991) established that the silverspotted sculpin, Blepsias cirrhosus (Cottidae), uses the sponge Mycale adhaerens as a spawning bed, stating that the eggs benefit from this association through predator avoidance, oxygen supply, and the natural antibacterial and antifungal properties of the sponge. Konecki and Targett (1989) note that glass sponges serve as important nesting and refuge sites for Antarctic fishes, and destruction of sponge communities by bottom trawling could have an impact on fish ecology in the region.

The 1996 amendments to the Magnuson-Stevens Fishery Conservation and Management Act require that increased emphasis be placed on "essential" fish habitat (USDOC, 1996). One type of marine habitat that fishery managers must consider during decision-making is living substrate. In Alaska waters, living substrate is often provided by a variety of epibenthic fauna, such as deepwater corals (e.g. Primnoa spp., Paragoria spp.), sea whips (Pennatulacea), and a number of large, erect sponges (Heifetz, 2002: Malecha et al., In press). These taxa form a high-relief, complex habitat that is generally thought to foster increased biological diversity and productivity by providing abundant cover and food aggregations for fish in various stages of their life history (Collie et al., 1997).

Studies conducted in the Gulf of Alaska (GOA) have shown that the aforementioned organisms are heavily impacted by even one pass of a commercial bottom trawl (Freese et al., 1999; Krieger, 2001). These findings generally agree with those of studies conducted in other parts of the world (Wafting and Norse, 1998; Auster and Langton, 1999: Moran and Stephenson, 2000). Trawl impacts can result from direct removal or damage to the megabenthos as well as changes in species composition over time (Wassenberg et al., 2002). Research in the GOA and elsewhere has shown that sponge communities and gorgonian coral colonies in boreal waters may be very slow to recover from trawl damage (Freese, 2003; Krieger, 2001).

An association between large Primnoa spp. colonies and six species of adult rockfish has been documented by Krieger and Wing (2002) in the GOA. Although it has been assumed that sponges at northern latitudes provide important habitat for fish in early stages of their life cycle in the GOA, there has heretofore been only anecdotal information available to support this assumption. This paper describes in situ observations made from a research submersible of an association between juvenile red rockfish, Sebastes spp., and one species of sponge in the GOA.

Materials and Methods

In June 2001, researchers from the NMFS Alaska Fisheries Science Center's Auke Bay Laboratory conducted a series of biological surveys in the eastern GOA, using the research submersible Delta. The Delta is a 4.7 m long, battery-powered underwater vehicle able to dive to depths of 345 m with a pilot and an observer. It is outfitted with video cameras, halogen lights, a laser scaling device, gyro compass, voice communications equipment, and a transponder. The transponder allows tracking of the vehicle by the submersible's surface support vessel, which has GPS capability. During the survey dives, positional fixes were taken at 30-second intervals.

The video equipment consisted of an externally mounted Hi-8 video camera pointed downward at an angle of 45[degrees] and an internal video camera positioned parallel to the seafloor. The cameras were used to record images of the seafloor and associated benthos, while an audio track was used to record observer comments. A digital camera was used by the observer to take still photographs.

The primary purpose of the surveys was to collect information on red tree coral, Primnoa sp., abundance, distribution, and habitat associations at locations where past NMFS trawl surveys had brought up the species as bycatch. Survey sites ranged from waters along the southeast part of the Kenai Peninsula, southeastward to the Fairweather Grounds in the vicinity of Yakutat, Alaska.