296 



Natural mortality rate^ annual fecundity, 

 and maturity at length for Greenland halibut 

 {Reinhardtius hippoglossoides) 

 from the northeastern Pacific Ocean 



Daniel W. Cooper (contact author)' 

 Katherine P. Maslenikov^ 

 Donald R. Gunderson^ 



Email address (for D. W, Cooper): dan.cooper@noaa.gov 



' Alaska Fisheries Science Center F/AKC 2 

 7600 Sand Point Way NE 

 Seattle, Washington 98115-0700. 



^ University of Washington 

 School of Aquatic and Fishery Sciences 

 1122 NE Boat Street 

 Seattle, Washington 98195. 



Mortality, fecundity, and size at 

 maturity are important life his- 

 tory traits, and their interactions 

 determine the evolution of life his- 

 tory strategies (Roff, 1992; Stearns, 

 1992; Charnov, 2002). These same 

 traits are also important for popula- 

 tion dynamics models (Hunter et al., 

 1992; Clark, 1999). It is increasingly 

 important to accurately determine 

 Greenland halibut (Reinhardtius hip- 

 poglossoides) life history traits and 

 to correctly assess the status of its 

 stocks because low recruitment or low 

 biomass estimates have led to catch 

 restrictions in the Bering Sea and 

 Aleutian Islands (lanelli et al.M, the 

 Northeastern Arctic (Adlandsvik et 

 al., 2004), and the Northwest Atlantic 

 (Bowering and Nedreaas, 2000). 



Mortality has been estimated for 

 stocks of Greenland halibut from the 

 Northwest Atlantic (Bowering, 1983) 

 and from the Bering Sea (lanelli et 

 al.^J from population age structures 

 where a maximum age near 20 years 

 has been assumed. However, recent 

 age validation (Treble et. al-) and a 



new aging technique (Gregg et al., 

 2006) indicate that Greenland hali- 

 but may have a lower mortality rate 

 and live longer. Fecundity estimates 

 (Gundersen et al., 2000) and length 

 at maturity estimates (Morgan et al., 

 2003) vary by geographic area and 

 year for Greenland halibut in the At- 

 lantic. Fecundity of Greenland hali- 

 but from the Bering Sea has been 

 estimated once (D'yakov, 1982), and 

 no estimates for Greenland halibut 

 maturity at length have been report- 

 ed from Alaskan waters. 



A significant and positive relation- 

 ship between natural mortality rate 

 (M) and annual reproductive effort, 

 as measured by gonadosomatic in- 

 dex (GSI=ovary weight /somatic body 

 weight), was found for 28 fish stocks 

 of a variety of species (M=1.79xGSI, 

 r2 = 0.75) (Gunderson, 1997). This 

 GSI-M relationship can provide an 

 estimate of M independent of age 

 data, and is desirable for Greenland 

 halibut because age data are still 



1 lanelli, J. N., T. K. Wilderbuer, and D, 

 Nichol. 2005. Stock assessment and 

 fishery evaluation: Bering Sea and Aleu- 

 tian Islands Greenland turbot. Website: 

 http:www.afsc.noaa.gov/refm/docs/2005/ 

 BSAIGturbot.pdf (accessed on 28 June 

 2006). 



2 Treble, M. A., S. E. Campana, R. J. Wastle, 

 C. M. Jones, and J. Boje. 2005. An 

 assessment of age determination meth- 

 ods, with age validation of Greenland 

 halibut from the Northwest Atlantic. 

 NAFO SCR Doc. 05/43, 22 p. Northwest 

 Atlantic Fisheries Organization, P.O Box 

 638, Dartmouth, Nova Scotia, Canada 

 B2Y 3Y9. 



controversial for this species. The ob- 

 jectives of this study are to estimate 

 annual fecundity, length at 50% ma- 

 turity, and the rate of instantaneous 

 natural mortality (M) by using GSI 

 for Greenland halibut from the Ber- 

 ing Sea and Aleutian Islands. 



Materials and methods 



Ovaries were collected by fishery 

 observers and scientists from the 

 National Marine Fisheries Service 

 (NMFS) in the Bering Sea and Aleu- 

 tian Islands (Table 1, Fig. 1). Fork 

 length (cm) and somatic weight 

 (kg) (ovaries and stomach contents 

 removed) were recorded at sea. Total 

 weight was approximated by adding 

 somatic weight and the estimated 

 fresh ovary weight. 



Ovaries were removed and placed 

 in a 10% formalin solution buffered 

 with sodium bicarbonate. Twenty- 

 eight ovaries were weighed (±2 g) 

 before being placed in formalin. The 

 fresh weight was later compared to 

 formalin weight to determine a con- 

 version factor when fresh weight was 

 not available. Ovaries were removed 

 from the 10% buffered formalin, 

 blotted dry, and weighed (±0.001 g). 

 When possible, a whole cross section 

 was removed from one lobe of an 

 ovary for histological analysis. If the 

 ovary cross section was too large to 

 fit on a slide, a wedge-shaped sample 

 was removed which included tissue 

 from the center of the ovary to the 

 ovarian wall. Ovary tissue samples 

 were embedded in paraffin, sectioned 

 at 4 fim, and stained with hema- 

 toxylin and eosin. All 56 specimens 

 smaller than 40 cm were obviously 

 immature because of their very small 

 ovaries; therefore histological exami- 

 nation was completed on only six of 

 these specimens to verify that they 

 were immature. 



Manuscript submitted 18 March 2005 

 to the Scientific Editors Office. 



Manuscript approved for publication 



8 September 2006 by the Scientific Editor. 



Fish. Bull. 105:296-304 (2007). 



