2016 Assessment of the Pacific Cod Stock in the Gulf of Alaska

February 14, 2016

Pacific cod (Gadus macrocephalus) is a transoceanic species, occurring at depths from shoreline to 500 m. The southern limit of the species’ distribution is about 34° N latitude, with a northern limit of about 63° N latitude. Pacific cod is distributed widely over Gulf of Alaska (GOA), as well as the eastern Bering Sea (EBS)  and  the  Aleutian  Islands  (AI)  area.  Tagging  studies  (e.g.,  Shimada  and  Kimura  1994)  have  demonstrated  significant  migration  both  within  and  between  the  EBS,  AI,  and  GOA.  Recent  research  indicates the existence of discrete stocks in the EBS and AI (Canino et al. 2005, Cunningham et al. 2009, Canino et al. 2010, Spies 2012). Pacific cod is not known to exhibit any special life history characteristics that would require it to be assessed or managed differently from other groundfish stocks in the GOA. The Pacific cod stock in the GOA is managed as one stock.

Pacific cod eggs are demersal and adhesive. Eggs hatch in about 15 to 20 days. Spawning takes place in the sublittoral-bathyal  zone  (40  to  290  m)  near  bottom. Eggs  sink  to  the  bottom  after  fertilization  and  are  somewhat adhesive. Optimal temperature for incubation is 3° to 6°C, optimal salinity is 13 to 23 parts per thousand (ppt), and optimal oxygen concentration is from 2 to 3 ppm to saturation. Little is known about the optimal substrate type for egg incubation.

Little is known about the distribution of Pacific cod larvae, which undergo metamorphosis at about 25 to 35  mm. Larvae  are  epipelagic,  occurring  primarily  in  the  upper  45  m  of  the  water  column  shortly  after  hatching, moving downward in the water column as they grow.

Juveniles occur mostly over the inner continental shelf at depths of 60 to 150 m. Adults occur in depths from  the  shoreline  to  500  m,  although  occurrence  in  depths  greater  than  300  m  is  fairly  rare. Preferred substrate is soft sediment, from mud and clay to sand. Average depth of occurrence tends to vary directly with  age  for  at  least  the  first  few  years  of  life,  going  deeper  with  age.  In  the  GOA  trawl  survey,  the  percentage of fish residing in waters less than 100 m tends to decreases with length. The GOA trawl survey also indicates that fish occupying depths greater than 200 m are typically in the 40-90 cm range.

It  is  conceivable  that  mortality  rates,  both  fishing  and  natural,  may  vary  with  age  in  Pacific  cod.  In particular, very young fish likely have higher natural mortality rates than older fish (note that this may not be particularly important from the perspective of single-species stock assessment, so long as these higher natural mortality rates do not occur at ages or sizes that are present in substantial numbers in the data). For example,  Leslie  matrix  analysis  of  a  Pacific  cod  stock  occurring  off  Korea  estimated  the  instantaneous natural mortality rate of 0-year-olds at 9.10 yr-1 (Jung et al. 2009). This may be compared to a mean estimate for age 0 Atlantic cod (Gadus morhua) in Newfoundland of 4.17% per day, with a 95% confidence interval ranging from about 3.31% to 5.03% (Gregory et al. in prep.); and age 0 Greenland cod (Gadus ogac)  of  2.12% per day, with a 95% confidence interval ranging from about 1.56% to 2.68% (Robert Gregory and Corey Morris, pers. commun.).

Last updated by Alaska Fisheries Science Center on 04/22/2019

Pacific Cod Research in Alaska North Pacific Groundfish Stock Assessments