674 



Abstract— The northwest Atlantic pop- 

 ulation of smooth dogfish iMustetus 

 canis) ranges from Cape Cod, Massa- 

 chusetts, to South Carolina. Although 

 M. canis is seasonally abundant in 

 this region, very little is known about 

 important aspects of its biology, such 

 as growth and reproductive rates. In 

 the early 1990s, commercial fishery 

 landings of smooth dogfish dramati- 

 cally increased on the east coast of the 

 United States. This study investigated 

 growth rates of the east coast M. canis 

 population through analysis of growth 

 patterns in vertebral centra. Marginal 

 increment analysis, estimates of preci- 

 sion, and patterns in seasonal growth 

 supported the use of vertebrae to age 

 these sharks. Growth bands in verte- 

 bral samples were used to estimate 

 ages for 894 smooth dogfish. Age-length 

 data were used to determine von Ber- 

 talanffy growth parameters for this 

 population; K = 0.292/yr, L, = 123.57 

 cm. and t^ = -1.94 years for females, 

 and K = 0.440/yr, L„ = 105.17 cm, and t„ 

 = -1.52 years for males. Males matured 

 at two or three years of age and females 

 matured between four and seven years 

 of age. The oldest age estimate for male 

 and female samples was ten and six- 

 teen years, respectively. 



Age and growth of the smooth dogfish 

 (Mustelus canis) in the northwest Atlantic Ocean 



Christina L. Conrath 



Virginia Institute of Marine Science 

 College ol William and Mary 

 1208 Create Road 

 Gloucester Point, Virginia 23062 

 E-mail address conrathig'vims edu 



James Gelsleicliter 



Mote Manne Laboratory 

 1600 Ken Thompson Parkway 

 Sarasota, Flonda 34236 



Jolin A. Musick 



Virginia Institute of Marine Science 

 College of William and Mary 

 1208 Create Road 

 Gloucester Point, Virginia 23062 



Manuscript accepted 14 June 2002. 

 Fish. Bull. 100:674-682 (2002). 



The smooth dogfish, Mustelus canis, is 

 a small shark species found throughout 

 the western Atlantic Ocean from Mas- 

 sachusetts to Florida, and in the north- 

 ern Gulf of Mexico, including Cuba, 

 Jamaica, Barbados, Bermuda, Baha- 

 mas, and southern Brazil to northern 

 Argentina. Smooth dogfish are demer- 

 sal and typically are found in inshore 

 continental shelf and slope waters 

 (Compagno, 1984). Several discrete pop- 

 ulations of smooth dogfish likely exist, 

 separated by large geographic areas; 

 and there appears to be little intermi- 

 gration between the different popula- 

 tions (Bigelow and Schroeder, 1948). 

 The northwest Atlantic population of 

 smooth dogfish ranges from Cape Cod, 

 Massachusetts, to South Carolina and 

 migrates seasonally in response to 

 changing water temperatures (Bigelow 

 and Schroeder, 1948; Castro, 1983). 



Recently, commercial harvest of 

 smooth dogfish has increased on the 

 east coast of the United States. Annual 

 landings were under 80,000 pounds 

 before 1990, over 300,000 pounds in 

 1990, and increased to around 1 million 

 pounds from 1998 to 2000. In one year 

 (1995) landings exceeded 2.5 million 

 pounds (Fig. 1) (NMFS, 2002). Smooth 

 dogfish have been landed in significant 

 amounts (i.e. over 50 metric tons) in 

 Massachusetts, New Jersey, Maryland, 



Virginia, and North Carolina (NMFS, 

 2002). 



Sharks are often highly susceptible 

 to overfishing because of life history 

 traits that include slow growth, large 

 adult size, late reproduction, and the 

 production of a few large well-formed 

 young (Hoenig and Gruber, 1990). Be- 

 cause of these characteristics, shark 

 fisheries tend to decline drastically af- 

 ter a short time and take long periods 

 to recover (Holden, 1974). The determi- 

 nation of how increased exploitation 

 will affect a shark population, like that 

 of M. canis in the northwest Atlantic 

 Ocean, requires information on the 

 growth and reproductive rates of the 

 species targeted by the fishery. The 

 purpose of this study was to determine 

 the growth rates of smooth dogfish 

 from the northwest Atlantic Ocean by 

 using age estimates derived from ver- 

 tebral growth-band counts. 



Materials and methods 



Smooth dogfish were collected from 

 NMFS groundfish and longline surveys, 

 Virginia Institute of Marine Science 

 (VIMS) longline surveys, Grice Marine 

 Laboratory longline surveys, the Massa- 

 chusetts state trawl survey, and by the 

 Massachusetts Division of Marine Fish- 



