536 



Abstract— The thorny skate (Ambly- 

 raja radiata) is a large species of 

 skate that is endemic to the waters 

 of the western north Atlantic in the 

 Gulf of Maine. Because the biomass 

 of thorny skates has recently declined 

 below threshold levels mandated by 

 the Sustainable Fisheries Act, com- 

 mercial harvests from this region 

 are prohibited. We have undertaken 

 a comprehensive study to gain insight 

 into the life history of this skate. 

 The present study describes and 

 characterizes the reproductive cycle 

 of female and male thorny skates, 

 based on monthly samples taken off 

 the coast of New Hampshire, from 

 May 2001 to May 2003. Gonadoso- 

 matic index (GSI), shell gland weight, 

 follicle size, and egg case formation, 

 were assessed for 48 female skates. 

 In general, these reproductive para- 

 meters remained relatively constant 

 throughout most of the year. However, 

 transient but significant increases 

 in shell gland weight and GSI were 

 observed during certain months. 

 Within the cohort of specimens sam- 

 pled monthly throughout the year, a 

 subset of females always had large 

 preovulatory follicles present in their 

 ovaries. With the exception of June 

 and September specimens, egg cases 

 undergoing various stages of develop- 

 ment were observed in the uteri of 

 specimens captured during all other 

 months of the year. For males (n = 48), 

 histological stages III through VI 

 (SIII-SVI) of spermatogenesis, GSI, 

 and hepatosomatic index (HSI) were 

 examined. Although there appeared to 

 be monthly fluctuations in spermato- 

 genesis, GSI, and HSI, no significant 

 differences were found. The produc- 

 tion and maintenance of mature sper- 

 matocysts (SVI) within the testes was 

 observed throughout the year. These 

 findings collectively indicate that the 

 thorny skate is reproductively active 

 year round. 



The reproductive cycle of the thorny skate 

 (Amblyraja radiate) in the western Gulf of Maine 



James A. Sulikowski 



Jeff Kneebone 



Scott Elzey 



Zoology Department 



University ol New Hampshire 



Durham, New Hampshire 03824 



Present address: Florida Program for Shark Research, 



Florida Museum of Natural History 



University of Florida 



P.O.Box 117800 



Gainesville, Florida 32611 

 E-mail address (for J A Sulikowski) |sulikow(&hotmail com 



Joe Jurek 



Yankee Fishing Coop 



Route 1A 



Seabrook, New Hampshire 03874 



Patrick D. Danley 



Deparment of Biology 

 University of Maryland 

 College Park, Maryland 20742 



W. Huntting Howell 



Zoology Department 

 University of New Hampshire 

 Durham, New Hampshire 03824 



Paul C. W. Tsang 



Department of Animal and 



Nutritional Sciences, 

 University of New Hampshire 

 Kendall Hall, 129 Main St 

 Durham, New Hampshire 03824 



Manuscript submitted 28 June 2004 

 to the Scientific Editor's Office. 



Manuscript approved for publication 

 29 March 2005 by the Scientific Editor. 



Fish. Bull. 103:536-543 (2005). 



The thorny skate (Amblyraja radi- 

 ata) is a member of the family Rajidae 

 (Robins and Ray, 1986; Collette and 

 Klein-MacPhee, 2002). It is a cosmo- 

 politan species, endemic to both sides 

 of the Atlantic Ocean, from Greenland 

 and Iceland to the English Channel 

 in the eastern Atlantic (Compagno et 

 al., 1989), and from Greenland and 

 Hudson Bay, Canada, to South Caro- 

 lina, in the western Atlantic (Robins 

 and Ray, 1986; Collette and Klein- 

 MacPhee, 2002). Despite such a wide 

 distribution, knowledge pertaining to 

 the reproductive biology of this species 

 is limited. Templeman (1982) reported 

 the occurrence of egg capsules in A. 

 radiata, and Templeman (1987), Del 

 Rio (2002), and Sosebee 1 examined 

 size at sexual maturity. 



In the Gulf of Maine, these skates 

 were generally discarded as bycatch 

 because of their low commercial value 

 NEFMC. 2 ' 3 Recently, the rapidly ex- 

 panding markets for skate wing has 

 made this species commercially more 

 viable, especially because A. radiata 

 meets the minimum VA pound-cut 

 pectoral fin size sought by proces- 

 sors (Sosebee 1 ; NEFMC 2 ). Although 

 no comprehensive published data for 

 reproductive cycles currently exist for 

 thorny skates in the Gulf of Maine, 



information from the few skate spe- 

 cies studied so far indicates that 

 sexual maturity at a late age, low 

 fecundity, and a relatively long life 

 span may also be characteristics of A. 

 radiata's life history (Winemiller and 

 Rose, 1992; Zeiner and Wolf, 1993; 

 Francis et al., 2001; Frisk et el., 

 2001; Sulikowski et al., 2003). When 

 these characteristics are coupled with 

 the practice of selective removal of 

 large individuals, the thorny skate 

 population in the Gulf of Maine may 

 be highly susceptible to over-exploita- 

 tion by commercial fisheries (Brander 

 1981; Hoenig and Gruber, 1990; Casey 

 and Myers 1998; Dulvy et al., 2000; 

 Frisk et al., 2001). Because of an in- 



1 Sosebee, K. 2002. Maturity of skates 

 in northeast United States waters. Sci- 

 entific Council Research Document 

 NAFO. no. 02/134. 17 p. [Available 

 from the Northwest Atlantic Fisheries 

 Organ., Dartmouth, NS.) 



2 New England Fishery Management 

 Council (NEFMC). January 2001. 2000 

 stock assessment and fishery evaluation 

 (SAFE) report for the northeast skate 

 complex, 179 p. NEFMC, 50 Water 

 Street, Mill 2 Newburyport, MA 01950. 



:! New England Fishery Management Coun- 

 cil (NEFMC). 2003. Skate fisheries 

 management plan, 142 p. 50 Water St., 

 Mill 2 Newburyport, MA 01950. 



