Sharks of the North Pacific

by Wyatt Fournier from the Northwest Explorer 

Blue shark

As we continue along our Gulf of Alaska survey, catching a wide variety of fish species, we are reminded that this productive ecosystem can support large marine predators. It’s not surprising that our surface trawl intercepts piscivorous sharks that are out hunting for a nutritious meal. Throughout the summer and fall, we’ve been catching salmon sharks, and during this leg we also caught three blue sharks. The salmon shark has a range around the Pacific Rim and has been observed across the GOA and in the Bering Sea. The blue shark’s distribution (see pic) is circumglobal in temperate and tropical waters, with few observations in Southeast and the central Gulf of Alaska. One of the more recent reports in Alaska comes from Yakutat where a blue shark was caught in a commercial net in 1997, which was a strong El Niño year. After we recorded the length and sex of each shark, we released them alive and well.

Pacific Herring

by Wyatt Fournier from the Northwest Explorer

Here the crew begins to sort through a surface tow that caught 47kg of herring.
The next afternoon, we set a tow slightly later in the day and caught 311kg of herring.
These large aggregations of herring have been observed in the inside passage of
Southeast Alaska during the winter months and may provide a prey base for
humpback whales that do not migrate to Hawaii during the cold season.

This component of the Gulf of Alaska Project focuses on the middle trophic level, specifically three forage fish species: Pacific herring, capelin and sandlance. Throughout the Gulf of Alaska ecosystem, these forage fishes provide the critical link between small invertebrates like euphasiids and copepods and species higher on the food chain, including adult predatory fishes, birds, and marine mammals. One of our project goals is to provide a synoptic view, from the shoreline out to beyond the shelf-break, of the distribution and abundance of forage fishes and linkages to the early life stages of the five groundfish species in this study. Our offshore survey will complement the nearshore surveys that assess habitat characteristics and energy content of forage fishes. Gulf of Alaska project researchers will explore interactions among groundfish and forage fish species and their effects on nutritional condition and prey quality. 

Fewer Fish in the Trawls

from the Northwest Explorer by Wyatt Fournier

We do encounter other epipelagic predators, such as this North Pacific daggertooth.  Although this species has been documented up to 146cm, the larger of the two we caught was only 56.2cm.

The catches in our surface trawls this month have been significantly lower than in the cruises in July in the southeast, and in August in the western Gulf of Alaska. Overall, we’ve seen a decline in the number of Pacific salmon we have been intercepting. Previously, all five species of salmon at all maturity levels represented a majority of our catches. As we enter the fall season, juvenile salmon have moved north from this region and the few adults that remain will be spawning soon. Juvenile and adult coho salmon still occur frequently in our catches, while pink salmon catches have decreased considerably. 

Last night, the aurora borealis danced across the night sky in spectacular shades of green. Many of the science and boat crew had not ever witnessed this Alaskan treat, and we all took it as a sign of a safe trip to come.