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Habitat Assessment & Marine Chemistry Program

Pacific Sandfish (Trichodon trichodon) in Southeastern Alaska

adult Pacific sandfish
Figure 1.  An adult Pacific sandfish captured in southeastern Alaska.  Photo by Mandy Lindeberg.

Forage fish are an important component in Alaska’s marine ecosystems and coastal areas. Forage fish are a critical food source for numerous groundfish, marine mammals, and seabirds. Little is known, however, about the life history characteristics or habitat of many forage fish species in Alaska, including Pacific sandfish (Trichodon trichodon) (Fig. 1). Sandfish are thought to spawn on rocky intertidal shorelines, and their larvae are thought to develop in shallow nearshore areas. Adults burrow into sand, usually at depths shallower than 150 m, and can reach a maximum size of about 300 mm.

Pacific sandfish are commonly found in nearshore waters of the southeastern Bering Sea and the Gulf of Alaska. There is no commercial fishery for sandfish in Alaska, but sailfin sandfish (Arctoscopus japonicus) are commercially fished and cultured in Japan and Korea. In particular, information is scarce on the biology and habitat of sandfish, especially for southeastern Alaska. Shoreline development and global climate change (e.g., increased water temperature and sea level) may adversely affect sandfish populations because of their relatively specialized nearshore spawning sites and 1-year incubation period.

map, see caption
Figure 2.  Location of sites sampled for Pacific sandfish (Trichodon trichodon) near The Brothers Islands, southeastern Alaska, 2001-04.  (click map to enlarge)

To provide new information on the general biology of Pacific sandfish including habitat preference, age, size, and diet, we captured sandfish with a beach seine in July and March and with a midwater trawl in May near The Brothers Islands in southeastern Alaska (Fig. 2). We seined 10 sites in summer (July 2001-03) and in winter (March 2002-04) in a variety of nearshore habitat types, including steep bedrock outcroppings, rocky bottoms with understory kelps (e.g., Laminaria), eelgrass, and sand beaches. We also captured sandfish with a midwater rope trawl in Frederick Sound and in Pybus Bay. We aged fish with otoliths and analyzed stomach contents to describe their diet.

We captured a total of 15,431 sandfish of a variety of ages. During spring we captured subadult and adult sandfish (age 4, 5, and 6); during summer we captured mostly juveniles (98% age 1), and during winter we caught only larval sandfish. We captured most (99%) fish with a seine, including 1,027 fish in July (mean fork length (FL) = 86 mm) and 14,231 larvae in March (mean total length = 16.2 mm). Most of these fish were adjacent to steep bedrock outcroppings with attached kelp.

We also observed large schools of juvenile sandfish actively feeding near the surface during the day near these areas. We caught juvenile sandfish along with young of the year (YOY) walleye pollock, YOY Pacific cod, YOY Pacific herring, and juvenile chum salmon. Apparently, sandfish exhibit schooling behavior as larvae and juveniles and co-occur with a variety of forage species, sometimes preying on those that are of consumable size. The few adult sandfish captured with a seine were found exclusively in low gradient, sandy habitat.

We caught 173 adult and subadult fish with a trawl. Mean FL of the trawl-caught fish was 150 mm and most were at depths between 14 and 64 m and at least 400 m offshore. Notably absent in any of our catches were age-2 and age-3 fish. Sandfish may segregate into different habitat types depending on age and size, which may explain the absence of some age groups in our catches.

Diet of sandfish differed by fish size. Adult and subadult sandfish ate mostly fish, whereas juvenile sandfish ate mostly decapods. For juvenile sandfish, fish (mostly gadids) made up 50% of the stomach content weight in 2001, but only 7% in 2002. The annual difference may be explained by the relative abundance of YOY gadids—gadid abundance was over six times greater in 2001 than in 2002.

Because of the relative high abundance of larval and juvenile sandfish in the shallow nearshore waters of The Brothers Islands, this area appears to be an important spawning and nursery area for sandfish. The length of time that larvae remain in shallow nearshore areas, however, appears to be limited because we captured no age-0 fish in July.

The dependence of sandfish upon nearshore areas for spawning, egg incubation, and larval rearing, coupled with the greater sensitivity to pollutants of early life stages than of adults, warrant the protection of nearshore areas from shoreline development and pollutants to maintain healthy sandfish populations.

By John Thedinga

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