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Chapter 6 - Diadromous FishSea-run trout typically remain near the mouth of theirnatal stream, but have been found up to 45 km away inopen ocean habitats or in other estuaries (Collette andKlein-MacPhee 2002). Technically most of these fish areamphidromous, spending substantial time feeding andgrowing in freshwater but frequently visiting saltwater.Few authors agree on the specific mechanism that initiatesanadromy or on the relatedness of resident and sea-runbrook trout in mixed populations; possible factors includeenvironmental conditions, food availability, and densitydependentbehavior (Doucet et al. 1999).Shortnose sturgeon (Acipenser brevirostrum)Shortnose sturgeon are found in rivers and estuaries fromthe Saint John River in New Brunswick to the SaintJohn’s River in Florida (Collette and Klein-Macphee2002). There are currently 19 spawning populations thatare considered to be viable; the largest known populationis the Hudson River with 38,000 individuals, the secondlargest is 18,000 in the Saint John River (NMFS 1998).Adult shortnose sturgeon exhibit freshwater amphidromy(i.e., adults spawn in freshwater but regularly enter saltwaterhabitats) in some rivers in the northern part of theirrange but are generally estuarine anadromous in southernrivers (Kieffer and Kynard 1993). At least one population,in the Connecticut River, is landlocked above theHolyoke Dam 128.7 km upstream and never enters saltwater (Hartel et al. 2002). Fish move upriver to spawninggrounds in the spring, then return to lower freshwater orbrackish reaches. Spawning occurs in deep, fast currentsover rocky substrate at or above the fall line (Collette andKlein-Macphee 2002). Shortnose sturgeon have recentlybeen found to travel moderate distances between riversystems; in 2006 a sturgeon tagged in the Savannah Riverin Georgia was found 300 miles (483 km) away in theSantee-Cooper River system in South Carolina (AmandaWrona, personal communication).Shortnose sturgeon reach maturity at progressively laterages from south to north, and females mature two to threeyears later than males. In Georgia, males mature at age2-3, while females in New Brunswick may not reproduceuntil age 13. After maturity, males spawn every one to twoyears and females every three years. Shortnose sturgeonare opportunistic benthic foragers, feeding on crustaceans,mollusks, insects, and worms (Collette and Klein-Macphee 2002).Northwest Atlantic Marine Ecoregional Assessment • Phase 1 Report 6-31