Atlantic Sturgeon Habitat Model
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Draft Date:
July 2001

Species:
Atlantic sturgeon, Acipenser oxyrhynchus. Sturgeon are long-lived, late maturing anadromous species which depends on a wide range of estuarine and freshwater habitats for spawning, larval development, and juvenile growth. They are commercially valuable for both flesh and roe. Mature males average 65 pounds and 6-7' in length, while spawning females attain weights up to 250 pounds and 10' in length, with some larger individuals being taken occasionally (Bigelow and Schroeder 1953).

Use of Study Area Resources:
All life stages; Atlantic sturgeon make use of large coastal rivers, estuaries, and offshore areas along eastern North America, from Labrador to Florida. They spawn in fresh water but juveniles and adults typically occur in saline environments.  Juvenile sturgeon are thought to gradually move downstream into brackish waters and remain resident in estuarine waters for months or years. Upon reaching a size of approximately 76-92 cm, the subadults may move to coastal waters where they may undertake long range migrations (Atlantic Sturgeon Status Review Team 1998).  In Maine only the Kennebec/Androscoggin/Sheepscot river system shows evidence of Atlantic sturgeon spawning. However, use of inshore areas by juveniles and some adults is documented for the Penobscot (Maine), Piscataqua/Salmon Falls/Lamprey/Oyster river system (New Hampshire), and the Merrimack River (New Hampshire/Massachusetts; Atlantic Sturgeon Status Review Team 1998).  Occurrences of sturgeon in North Atlantic estuaries also was tabulated by Jury et al. (1994).

Habitat Requirements:

The following summary is taken from the U.S. Fish & Wildlife Service Status Review of Atlantic Sturgeon (Atlantic Sturgeon Status Review Team 1998): “Atlantic sturgeon spawn in fresh water, but spend most of their adult life in the marine environment. Spawning adults migrate upriver in the spring, beginning ... Apr-May in mid-Atlantic rivers and May-July in Canadian waters (Murawski and Pacheco 1977, Smith 1985, Smith and Clugston 1997). Spawning occurs in flowing water between the salt front and fall line of large rivers. Sturgeon eggs, which are highly adhesive, are deposited on the bottom, usually on hard surfaces (i.e. cobble) (Smith and Clugston 1997). Hatching occurs approximately 94-140 hours after egg deposition at temperatures of 20 degrees and 18 degrees C, respectively (Smith et al. 1980).”

“Female Atlantic sturgeon mature....in the Hudson River at 15-30 years (Dovel 1979, Dovel and Berggren 1983; VanEenennaam et al. 1996), and in the St. Lawrence River at 27-28 years (Scott and Crossman 1973). Males mature at younger ages and smaller sizes than females (e.g. ...11-20 years in the Hudson River, 22-34 years in the St. Lawrence River). .... Atlantic sturgeon probably do not spawn every year, though data on spawning intervals do not exist for most populations. ...Insufficient information exists for estimation of age specific emigration rates; however, juveniles are thought to remain in riverine or estuarine habitats for 1-6 years (Smith 1985).”

"...Atlantic sturgeon travel widely once they emigrate from northern natal rivers. Until they mature, juveniles and subadults wander among coastal and estuarine habitats, undergoing rapid growth (Dovel and Berggren 1983, Stevenson 1997). Seasonal movement is north in the late winter and south in the fall and early winter. Subadult Atlantic sturgeon tagged in the Hudson River estuary were recaptured in estuaries and the nearshore ocean from Marblehead, MA to Ocracoke, NC.” (end citation: Atlantic Sturgeon Status Review Team 1998). Trawling surveys in Bath, Maine near Bath Iron Works captured subadults between April and November, but took none from December until the end of the study in February 1998 (Atlantic Sturgeon Status Review Team 1998). This suggests that subadults may move to deeper bottoms during the coldest months, as do other motile marine organisms.

Feeding: Sturgeon are bottom feeders; they root in the sand and mud with their protrusible mouths, taking benthic crustaceans, molluscs, polychaetes, and small fishes (Bigelow and Schroeder 1953).

Depth: Bigelow and Schroeder (1953) reported significant commercial catches in large rivers, such as the Kennebec, and in the Gulf of Maine over Browns and Georges Banks.  Sub-adult sturgeon have been captured at depths down to 85', while adults have been captured to depths of 165' (Taub 1990).

Limiting Factors: Habitat degradation due to pollution and damming of spawning rivers have significantly contributed to population declines. This species has also been overfished, particularly as spawning activities concentrate adults in freshwater habitat. Atlantic sturgeon are believed to require 29 years on average to reach 50% of their maximum egg production Dredging activities in nearshore areas can cause direct mortality on adults drawn into dredge pumps, and may cause indirect mortality of eggs by redistribution of sediments and contaminants. (Atlantic Sturgeon Status Review Team 1998).

Habitat Mapping:
Fresh water habitat was mapped from occurrence data obtained from several sources. Eipper et al. (1982) mapped upstream migratory pathways for anadromous and catadromous fishes throughout New England at a relatively small scale. We coded the corresponding stream segments as suitable habitat on 1:24,000 USGS digital maps (Maine, New Hampshire) and 1:100,000 maps (Massachusetts), supplemented by 1:24,000 for minor features absent from the 1:100,000 data.  Eipper was used for the whole study area. This general information was considerably supplemented state by state with collection data. In Massachusetts we were supplied with point data from Hartel et al. (in press), and from a GIS coverage developed by Massachusetts Department of Fisheries, Wildlife and Environmental Law Enforcement (http://www.state.ma.us/dfwele/gisprog/gisanad.htm). The Atlantic Sturgeon Status Review Team (1998) described Merrimack River habitats. For Maine habitats we also used maps in Squiers and Smith (1979).

Artifacts of grid-cell mapping of riverine themes may in some cases cause habitat omissions, and in others aquatic habitat values in primarily upland areas. Fish habitats were gridded from continuous polygons/arcs derived from USGS hydrology coverages. Single line arcs were necessarily converted into strings of cells, each with a minimum width of 30 m (the cell dimensions).  Even where the dominant land cover of a cell was upland, we retained the habitat value for a stream passing through the cell.  As a result, some upland areas will display habitat value for anadromous fishes.  

The grid process left discontinuities when converting narrow (< 30 m wide) polygon features, such as small rivers, where only part of a cell was crossed by aquatic habitat. Moreover, where National Wetlands Inventory polygons representing wetlands and water bodies differed from those of USGS, the only fish habitat we retained was that which corresponded to aquatic classes in the former. Therefore, fish habitats and migratory pathways may not appear as continuous extents of habitat, or extend to the boundaries of contiguous wetlands in all cases.

Marine habitats were mapped at 2 levels.  Jury et al. (1994) tabulated the relative abundance of Atlantic sturgeon in North Atlantic estuaries by season, life stage, and general salinity zone.  We used Jury et al. to map inshore habitat, identifying the boundaries of those estuaries used by sturgeon from salinity zone maps obtained from NOAA NOS (http://seaserver.nos.noaa.gov/projects/cads/ftp_gis_download.html, downloaded 4/5/01), and adjusted to fit higher resolution coastline data.  All other coastal areas out to a depth of 165' were mapped as habitat, but assigned a lower value than the specific inshore areas.

Habitat Suitability:
Habitat suitability for this model is scored according to our confidence that an area is likely to be used. All freshwater areas mapped from occurrence information were scored 1.0; estuarine/marine areas corresponding to the Jury et al. embayments used by sturgeon were scored 0.5, and deeper habitat (to 165') was scored 0.2

Sources:

Atlantic Sturgeon Status Review Team. 1998. Status Review of the Atlantic sturgeon, Acipenser oxyrhynchus oxyrhynchus. USFWS and NOAA. 125 p.  See at: www.nmfs.noaa.gov/prot_res/readingrm/statrvws/atl_sturgeon.PDF

Bigelow, H.B. and W.C. Schroeder. 1953. Fishes of the Gulf of Maine. U.S. Fish. Wildl. Serv. Fish. Bull. 74(53), 577 p.

Eipper, A., W. Knapp and C. Laffin. 1982. Anadromous fish streams of New England: upstream migratory routes. Portfolio NE-1. USDI Fish and Wildlife Service.

Hartel. K.E., D.B. Halliwell, and A.E. Launer. (in press) Inland Fishes of Massachusetts. Natural Hist. New England Series. Massachusetts Audubon Society, Lincoln, MA.

Jury, S.H., J.D. Field, S.L. Stone, D.M. Nelson and M.E. Monaco. 1994. Distribution an abundance of fishes and invertebrates in North Atlantic Estuaries. ELMR Rep. No. 13. NOAA/NOS Strategic Environmental Assessment Div., Silver Spring, MD. 221pp.

Smith, T.I.J. and J.P. Clugston. 1997. Status and management of Atlantic sturgeon, Acipenser oxyrhynchus, in North America. Environmental Biology of Fishes 48:335-346.

Squiers, T.S. and M. Smith. 1979. Distribution and abundance of shortnose and Atlantic sturgeon in the Kennebec River Estuary. Maine DMR Report, 51 pp.

Taub, S.H. 1990.  Fishery management plan for Atlantic sturgeon. Atlantic States Marine Fisheries Commission Report No. 17. 73pp.