Fishery, Climate, and Ecological Effects on Pacific Halibut Size-at-age

Project Description

Pacific halibut are an iconic fish in the northeast Pacific due to their enormous size. They are the largest flatfish in the world, reaching lengths up to 8 feet and weighing up to 500 pounds. They are also one of the longest-lived flatfish, attaining maximum ages over fifty years old. Despite their reputation as a large and long-lived fish, the size-at-age of halibut has experienced significant declines in recent decades. For instance, the average weight of a 20-year-old halibut has declined from more than 120 pounds in 1988 to less than 45 pounds in 2013. Interestingly, the current small sizes-at-age are comparable to sizes-at-age experienced by Pacific halibut in the 1920s. Maximum size-at-age of halibut was observed in the 1970s and 1980s. There are a host of potential reasons for this recent decline in body size. Observed reductions in halibut size-at-age could be the result of more competition among halibut or between halibut and growing populations of arrowtooth flounder, changes in prey composition or availability, response to climate variability, such as increased ocean temperatures that may have affected metabolic processes including respiration rates, or genetic selection by fisheries that prefer larger fish, leaving stunted ones to reproduce. Together with our collaborators at the International Pacific Halibut Commission and National Marine Fisheries Service, we are undertaking a thorough investigation into various possible causes for changes in halibut size-at-age. The UAF contribution to this project is being conducted by master's student, Jane Sullivan, and involves three facets. First, she will describe temporal and spatial variability in size-at-age over the last 100 years. Then she will examine multiple environmental and ecological covariates that may be influencing growth and size-at-age of Pacific halibut. Finally, she will use an age- and size-structured equilibrium model developed by Dr. Steve Martell at the IPHC to examine the cumulative effects of fishery removals, size-selective fishing, and bycatch on size-at-age.




Research Team

Principal Investigator

picture of Gordon Kruse

Gordon Kruse

  • Marine fish and invertebrate ecology
  • Marine fish and invertebrate biology
  • Fisheries oceanography
  • Population dynamics
  • Fisheries management
(907) 796-5458
Full Profile

Co-Principal Investigators

Steven Martell, International Pacific Halibut Commission, 206-552-7683,

Bruce Leaman, International Pacific Halibut Commission, 206-634-1838,

Kerim Aydin, National Marine Fisheries Service, 206-526-4225,

Kirstin Holsman, National Marine Fisheries Service, 206-526-4691,



Project Funding

North Pacific Research Board and Pollock Conservation Cooperative Research Center
Amount: Total budget: $467,675 (UAF portion: $264,644)
Start Date: 2015-09-13 End Date: 2015-08-31

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