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Chapter 6 - Diadromous FishSturgeons are members of the ancient familyAcipenseridae, large, slow-growing, and late maturinganadromous fish that migrate from the ocean into coastalestuaries and rivers to spawn. Adhesive eggs are attachedto firm substrates in oligohaline (brackish) and tidal freshwaters (Collette and Klein-MacPhee 2002). Juvenilesmay spend several years in fresh water in some rivers, butin others fish move to brackish water in the fall. The lowerportions of rivers and estuaries are important for growth.The distribution and residence times of larval, post-larval,and young juveniles in upstream areas are unknown, butaggregations of juveniles at the freshwater/saltwater interfacesuggest that this is a nursery area. Juveniles remainwithin riverine estuarine systems for periods of about oneto six years before migrating to the coast and onto thecontinental shelf where they grow to maturity. Taggingand genetic data indicate that subadult and adult Atlanticsturgeon may travel widely once they emigrate from rivers,wandering among shallow coastal and estuarine habitats.Coastal features or shorelines where migratory Atlanticsturgeon commonly aggregate include the Bay of Fundy,Massachusetts Bay, Rhode Island, New Jersey, Delaware,Delaware Bay, Chesapeake Bay, and North Carolina(Atlantic Sturgeon Status Review Team 2007).Sturgeons are benthic feeders, with a subterminal mouth(located on the underside of the head) and barbels (fleshyfeelers) well designed for sensing and capturing benthicinvertebrates. Historically, abundant and widely distributed,the combination of slow rates of populationgrowth and high economic demand for flesh and roe madeAtlantic sturgeon especially vulnerable to over-harvesting.Atlantic tomcod (Microgadus tomcod)Atlantic tomcod are distributed in shallow, inshore watersalong the Atlantic coast from southern Labrador toChesapeake Bay, spawning in brackish or fresh areas ofrivers from November to February (Collette and Klein-MacPhee 2002). Atlantic tomcod are not truly anadromousbut amphidromous (utilizing both fresh and marinehabitats but not necessarily requiring both habitats).Tomcod can survive and reproduce with access only tobrackish water. Eggs sink and stick to gravel, stones, orplants, hatching after 24-30 days. Larvae and juveniles eatmostly copepods; as they grow they eat a variety of crustaceans,worms, and larval fishes. Tomcod are benthic, estuarineresidents, and as a result are subject to stress froma variety of pollutants. Detailed studies from the HudsonRiver show elevated levels of PCBs, metals, and pesticidesin tomcod tissues as well as high rates of liver cancer andshortened life spans (Collette and Klein-MacPhee 2002).Data on distribution and abundance of tomcod are limitedbut anecdotal reports indicate that these fish were ubiquitousin coastal waters a century ago and supported somesubstantial fisheries, but today they are less plentiful.Blueback herring (Alosa aestivalis)Blueback herring spawn from Nova Scotia to northernFlorida, but are most numerous in warmer watersfrom Chesapeake Bay south. Blueback herring prefer tospawn in swift flowing sections of freshwater tributaries,channel sections of fresh and brackish tidal rivers,and Atlantic coastal ponds, over gravel and clean sandsubstrates (ASMFC 1999). Similar in appearance, alewifeand blueback herring are collectively known as riverherring. Mature river herring broadcast their eggs andsperm simultaneously into the water column and over thesubstrate. Immediately after spawning, adults migratedownstream. Juveniles remain in freshwater nursery areasin spring and early summer, feeding mainly on zooplankton,but larvae are tolerant of salinity early in life and mayutilize both freshwater and marine nurseries (Collette andKlein-MacPhee 2002). As water temperatures decline inthe fall, juveniles move downstream to more saline waters.Little information is available on the life history of subadultand adult blueback herring after they emigrate to thesea as young-of-year or yearlings, and before they matureand return to spawn. In summer and fall bluebacks areconcentrated in shelf areas north of 40oN latitude, alongGeorges Bank and the perimeter of the Gulf of Maine; inwinter between 40o N and 43o N, and in spring acrossthe continental shelf from Cape Hatteras to Nova Scotiaas migration toward spawning rivers begins (Neves 1981).Recruitment to the spawning population takes placeNorthwest Atlantic Marine Ecoregional Assessment • Phase 1 Report 6-29