Alaska Angler

Christopher Batin

Pacific Halibut Feeding Habits

I like to spend the winter months reading about the sportfish species to be pursued in the upcoming season. I feel such research allows me to be a more effective and successful angler.

In one report, USGS biologists examined the stomach contents of 947 sport-caught halibut in one study entitled, Pacific Halibut in Glacier Bay National Park that is of interest to sport anglers wanting to brush up on halibut behavior. Their report is as follows, and while it is an older report, it is a baseline study of the type that can provide insights as to where to find these flatfish, and what anglers should use for bait when pursuing them.

According to biologists Hooge and Taggart, analysis of stomach contents revealed an ontogenetic shift in diet from small crustaceans to fish as halibut mature. There is also a dichotomy in the co-occurrence of stomach content items; individuals often either exhibit only items that can be found during active foraging (e.g. large numbers of juvenile crabs) or only items that are associated with sit-and-wait predation (e.g. walleye pollock).

Movement Patterns

Long distance movements of Pacific halibut have been emphasized in previous studies and most population models developed for this species assume relatively unrestricted movements between areas (long-life sonic tags were internally implanted in 97 halibut in Glacier Bay and more than 1,500 were individually wire tagged). Results from these two studies indicate an ontogenetic shift in home range patterns; juvenile fish move widely but often still within the Glacier Bay area, whereas large sexually mature individuals exhibit much smaller home ranges. Many of these mature individuals have home ranges, which are half a square kilometer, and exhibit both within-year and between-year site fidelity. These home ranges often have little simultaneous spatial overlap. Larger individuals have been observed occasionally to alter their pattern of small home ranges and to travel more widely before returning to a relatively sedentary pattern; a few larger individuals appear never to establish home ranges.

Wire-tagging data provide a separate corroborating line of evidence for site fidelity of adult Pacific halibut. Of the halibut originally wire-tagged in Glacier Bay and then recaptured at a later time, more than 95 percent were recaptured within Glacier Bay with an additional three percent caught in the adjoining Icy Strait area. Individuals have been recaptured five years after tagging within a few hundred yards of their original capture and release location.

Sonic-tracking data also indicate that some individuals leave during the winter, but many appear to remain within Glacier Bay. Spawning of halibut has been hypothesized to occur only at spawning areas off the outer coast during the winter. The presence of reproductively mature individuals within the Bay during this time may indicate either that Pacific halibut do not spawn every year or that spawning can occur within the Bay.

Biologists sampled halibut by setting 149 research long-lines with 400 hooks each throughout Glacier Bay. They write: “Results of these studies and from sonic-tracking individuals suggest that there are two broad patterns of habitat choice and dispersion. The first pattern appears to be ontogenetic, with larger individuals exhibiting a relatively uniform distribution pattern and a preference for deeper water; smaller individuals seem to prefer shallow water and areas of steep topographical relief in a much more aggregated distribution pattern. The second observed pattern reflects changes in distribution along the length of Glacier Bay’s recently deglaciated fjord system. This pattern is characterized by decreased halibut abundance with greater proximity to glacial termini. Initial indications from sampling salinity, temperature, and the amount of silt and phytoplankton (indicated by chlorophyll) in the water are that this pattern is due to oceanographic conditions rather than successional processes.”

In other words, this may help explain why halibut fishing deteriorates as the summer progresses and water silts up in saltwater bays that are fed by glacial runoff, such as Valdez Arm, and many bays in Prince William Sound. Most anglers know, halibut fishing generally deteriorates in these inshore waters as the summer progresses.

Ecological Relationships

Biologists have hypothesized that halibut at Glacier Bay exhibit two foraging modes that underlie movement patterns, distribution and catchability. These modes are active foraging and sit-and-wait predation.

“Juveniles probably establish wide-ranging movement patterns, actively searching for areas of high prey abundance where they are easily caught on long-lines,” the report indicates. “Many adults probably establish small non-overlapping home ranges where they wait for large fish or invertebrates; rarely does a long-line come within enough proximity for these sit-and-wait individuals to be captured.”

Halibut Diets

Prey Species Found in Halibut Stomachs

( * Indicates common prey species in seabird diets)

Chart courtesy USGS

Chris Batin is editor of The Alaska Angler, a contributing editor for Outdoor Life, and author of numerous books, journals and DVDs on Alaska fishing and hunting, available at www.AlaskaAngler.com.

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