Full report - Conservation Gateway

Chapter 7 - Demersal FishGeorges Bank, Southern New England, and the Mid-Atlantic to Cape Hatteras.Of the elasmobranchs included in this assessment, spinydogfish and clearnose skate have the most distinct seasonalmigration patterns. Spiny dogfish are known to makedistinct north and south migrations along the ContinentalShelf, as well as moving inshore and offshore seasonallyin response to changes in water temperature. Theyprimarily occur north of Cape Cod in summer, movesouthward to Long Island in the fall, and go as far south asNorth Carolina in the winter. In the spring, they migrateback north, reaching Georges Bank in March and April(Stehlik 2007). Clearnose skate also make distinct seasonalmigrations north of Cape Hatteras, moving inshoreand northward along the Continental Shelf during springand early summer and offshore and southward during autumnand early winter when temperatures drop to 13-16 oC (Packer et al 2003b).Little skate are not known to migrate extensively, but theydo make seasonal onshore and offshore migrations cuedby temperature changes, generally moving into shallowerwaters in the spring and deeper waters in the winter. Theyalso move north and south with seasonal temperaturechanges along the southern fringe of their range (Colletteand MacPhee 2002). While several reports indicate thatthorny skate undertake seasonal migrations in the summerand winter, others suggest they are a sedentary species. Noseasonal migration patterns have been reported for rosetteskate, although shoreward migrations during the summerhave been suggested.Adult and juvenile life stages of elasmobranchs includedin this assessment generally utilize similar habitatswithin the region, but habitat preference varies withspecies. Adult and juvenile barndoor skate generally occupysimilar habitats across the range. Adults are widelydistributed on benthic habitats composed of soft muds,sand, and gravel. Adult and juvenile clearnose skates arefound predominantly on soft bottom substrates along theContinental Shelf at depths less than 30 m. They havealso been found on rocky and gravelly substrates (Packeret al. 2003b; Stevenson 2008). Adult and juvenile littleskate are widely distributed across benthic habitats incoastal bays and estuaries along the Continental Shelf,generally on sandy or gravelly mud bottoms, but are alsofound in predominantly mud substrates (Packer et al.2003c; Stevenson 2008). Adult and juvenile rosette skateoccur on the outer Continental Shelf on benthic substratesof mud and sand, and also on substrates of mud andsand mixed with gravel (Packer et al. 2003d; Stevenson2008). Adult and juvenile thorny skate occur on a varietyof benthic substrates across the Continental Shelf andSlope, including sand, gravel, broken shells, pebbles, andsoft mud (Packer et al. 2003e; Stevenson 2008). Spinydogfish distributions are heavily influenced by depth, watertemperature, and prey availability (Stehlik 2007).All of the elasmobranchs included in this assessmentshare a similar life history, characterized by relatively slowgrowth rates, late age at maturity, and production of fewoffspring. The skate species reach sexual maturity at 5-7years, while spiny dogfish do not reach sexual maturity until10-12 years. Elasmobranchs mate throughout much ofthe year, with clearnose, thorny, and rosette skate havinghighest egg production in the summer, little skate producingeggs twice a year (spring and fall), barndoor skate matingin late-fall and winter, and spiny dogfish mating in thefall. Spiny dogfish are unique in that their egg fertilizationand development is oviparous. Fertilized eggs developwithin a tough, leathery egg casing which is deposited overa variety of substrates. Egg development is slow, lasting 2-3years before hatching occurs on the sea floor (Packer et al.2003 a, b, c, d, and e; Stehlik 2007).Elasmobranchs are omnivorous, feeding on a variety ofbenthic prey species including crustaceans, amphipods,and a variety of small fishes. The skate species display similardietary preferences, feeding primarily on polychaetes,decapods, copepods, bivalves, and shrimp but also on avariety of small fishes. Spiny dogfish are more piscivorous,feeding on a variety of fish species including capelin, cod,haddock, herring, mackerel, sand lance, and several speciesof flatfish. Elasmobranch eggs are preyed on by a varietyof fish species, while adults have relatively few predators.7-78Northwest Atlantic Marine Ecoregional Assessment • Phase 1 Report