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The Abundant—But Not So Tasty—Giant Grenadier

View slideshow Recently retired Alaska Fisheries Science Center scientist Dave Clausen from NOAA's Auke Bay Laboratory holds a giant grenadier. Credit: NOAA Fisheries grenadiers02.jpg grenadiers03.jpg grenadiers04.jpg

Great gross gobs of…giant grenadier—and me without my spoon. If only giant grenadier were tasty, you’d probably find it on the menu at your favorite seafood restaurant. But instead, you’d likely turn your nose up if presented with this prolific deep-water fish on your dinner plate. A NOAA Fisheries sensory analysis panel has categorized giant grenadier as “unpalatable” because of its soft texture and high moisture content. It also rates low in protein content.

Because of their great abundance, there have been several attempts to develop a fishery for giant grenadier, however, because of their low flesh quality, there has been little success. There have also been endeavors to develop treatment processes to make the fish palatable, but so far these efforts have not proven successful. While they are not marketable at present, giant grenadier have an important ecological role in their environment as an apex predator. Apex predators have few to no predators of their own, residing at the top of their food chain.

Most people are unaware giant grenadier even exist. However, Alaska fishermen are very familiar with giant grenadier because they are incidentally caught in fisheries such as sablefish, Pacific halibut, and Greenland turbot.

Currently, grenadier are not managed in the Exclusive Economic Zone (3 to 200 nautical miles from shore) off Alaska, meaning that there are no catch limits and no required monitoring of catch. That might change as early as February 2014 when the North Pacific Fishery Management Council will take final action to manage grenadier species in federal waters off Alaska. At its December meeting in Anchorage, the Council selected a preliminary preferred alternative of adding grenadiers to the “ecosystem component” of the fishery management plans for both the Bering Sea and Gulf of Alaska groundfish fisheries. The preliminary preferred alternative includes prohibiting directed fishing for grenadiers, establishing a maximum retainable amount, establishing a separate management category for grenadiers in the fishery management plans separate from the forage fish category, and requiring record keeping and reporting.

In bottom trawl surveys conducted by NOAA Fisheries in the Bering Sea and the Gulf of Alaska, this species is the most abundant fish, in terms of weight, in depths from 600 to 3,000 feet (200-1,000 meters). Giant grenadier extend much deeper than 3,000 feet (1,000 meters). There are reports that they have been caught deeper than 6,000 feet (2,000 meters), but little is known about their abundance in waters deeper than 3,000 feet because neither the NOAA surveys nor fishing effort  presently extend below this depth. 

NOAA tracks their abundance and estimated catch via observer records and works on research to better understand the biology of this species. In a recent maturity and aging study conducted by the NOAA Auke Bay Laboratories and the NOAA Age and Growth Laboratory in Seattle, scientists discovered that female giant grenadier do not start to reproduce until they are 20 years old. The maximum age found in the study was 58 years, which is older than the vast majority of fish species. Both of these laboratories are part of the Alaska Fisheries Science Center.

Most giant grenadier caught in surveys and incidentally in other fisheries are female. NOAA scientists think most males reside in even deeper depths.

During the ageing study scientists discovered that the otoliths, the ear bones in fish that are used for aging, were variable in shape. This is unheard of within a species. 

In 2013, NOAA Fisheries launched another cooperative study, this time with the addition of the genetics laboratory at Auke Bay Laboratories in Juneau, Alaska. The goals are to describe the otolith shape differences of fish sampled from the Bering Sea and throughout the Gulf of Alaska and to conduct a genetic analysis to determine if the shape differences indicate that these are different stocks.  There is even the possibility that what we call giant grenadier are actually more than one species.

The North Pacific Fishery Management Council is expected to take final action on managing grenadier species in federal waters off Alaska at their meeting February 3-11, 2014, in Seattle.