Study looks at climate impact on Pollock

Older, more age-diverse stocks tend to spawn earlier

Larvel Pollock are the subject of a NOAA Fisheries study on the impact of climate change on reproductive health. (Photo courtesy of the Alaska Fisheries Science Center)

A federal fisheries study on the impact of climate change on Pollock has found that spawning times have varied in the Gulf of Alaska by over three weeks throughout the last three decades.

Researchers with the NOAA Fisheries’ Alaska Fisheries Science Center concluded that climate clearly drives variation in spawn timing, with warmer temperatures leading to an earlier and more protracted spawning period, consistent with expectations of advanced spring phenology under warming. Phenology is the study of cyclic and seasonal natural phenomena, especially in relation to climate and plant and animal life.

Thirty-two years of data from ichthyoplankton surveys was used in this study, published in mid-November, to reconstruct timing of pollock reproduction in the Gulf of Alaska.

Researchers also noted that an older and more age-diverse spawning stock tended to spawn earlier and over a longer duration that a younger stock.

Models designed for the study suggested that demographic shifts associated with sustainable harvest rates could shift the mean spawning date seven days later and shorten the spawning season by nine days relative to an unfished population, independent of thermal conditions. While projections under climate change suggest that spawn timing will become more stable for these Pollock in the future, researchers said they still don’t know what the consequences of this stabilization will be for the development of first-feeding larvae with production of zooplankton prey in spring.

Still, having knowledge of the mechanisms underlying reproductive cyclical and seasonal patterns will improve biologists’ ability to monitor and manage species under changing climate conditions, the study concluded.

Changes in the timing of reproductive events can be critically important, since they determine what conditions will be encountered by Pollock during early life stages. Variation in spawning time relative to spring conditions can impact chances of survival, and alter the predator-prey dynamics, and this is critical since the majority of lifetime mortality often occurs in the first weeks of life.

If larvae arrive too early there may be insufficient zooplankton prey or if they arrive too late, larvae will be small relative to predators and competitors, researchers noted.

Researchers also noted that in general warmer temperatures speed the rate of ovarian development and result in earlier onset of spawning in laboratory fish. Still warmer than optimal temperatures may also delay spawning through delayed ovarian development.

Also, patterns and presumed mechanisms linking changing temperatures to spawn timing appear to differ among species and stocks, precluding any general conclusions about thermal effects on spawn timing, the study said.

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Margaret Bauman is a veteran Alaska journalist focused on covering fisheries and environmental issues. Bauman has been writing for The Cordova Times since 2010. You can reach her at mbauman@thecordovatimes.com.