Background
DEPREDATION
Depredation, or the removal of fish from a longline, by sperm whales has created economic loss to fishermen, incurring added costs of fuel, crew, and gear. Entanglement in fishing gear is a risk to the whales and hazardous to boat crews. Additionally, depredation on the Alaska Fisheries Science Center’s (AFSC) sablefish longline survey in the Gulf of Alaska is becoming frequent enough that it may be affecting population indices derived from the survey. Through cooperative research with fishermen, government fisheries managers, and scientists, our ultimate goal is to work to understand this complex relationship between sperm whales and the longline fishery, and to provide recommendations for strategies to reduce or eliminate depredation on longline gear by sperm whales.
Government agencies, scientists and fishermen are working together to find a way to reduce sperm whales/longline interactions. The first step was collecting information: When do these interactions happen? Is it seasonal? Does it happen at a particular time of day? Which whales are hanging around the fishing grounds? Researchers identified sperm whales using photography and genetic tissue samples. This information has helped define the scope of the problem and provided baseline information. Our next step used acoustical recording instruments to study how the whales remove the hooked fish and what cues the whales use to find the gear. This information is being used to develop and test solutions to decrease interactions. These actions will maintain both healthy whale populations and commercial fisheries.
Longlining is a commercial fishing method that uses hooks and line. It is used to catch halibut and groundfish, an overall name to describe fish that spend most of their lives near the ocean floor. Groundfish include sablefish, Pacific cod, and many species of rockfish. Ground lines – averaging two to four miles long – are laid along the ocean bottom. At intervals along this length, shorter lines, about 1-foot long are attached to the groundline and have a baited hook at the end. One longline may have 3,200 baited hooks. Each end of the longline is anchored to sink it to the ocean floor and also marked with buoys on the surface for retrieving the line. This unit of gear is called a longline “set”. Fishermen let the gear “soak:” for several hours or overnight before hauling the line back in. This fishery is a very important fishery for coastal communities in Alaska, where many longliners are homeported. Vessels targeting sablefish tend to be small; 78% are less than 60ft (18m), while 21% are between 60-125ft (18-38m) in length. Vessels usually fish two or three sets of gear concurrently, alternating between sets (i.e., hauling in the gear, deploying the gear and then moving on to the next set).
During the 1980s and 1990sthe halibut and sablefish fisheries became “derby style” fisheries, with short, intense openings of 1 day to two weeks when the entire year’s quota was harvested.. Longline vessels then crowded together for the best areas and crews scrambled to fish as much gear as possible to maximize their catch before the fishery closed. Vessels fished regardless of weather, and prices were often low because markets were flooded at the close of the fishery. In the mid 1990’s, management of the halibut and sablefish fisheries changed to a quota system, where the annual quota is divided among license holders who were allocated an allowable percentage of the total quota. This is known as the IFQ fishery (Individual Fishing Quotas). Each fisherman may fish until his or her quota is met during an elongated season from March to November.
The IFQ fishery is a safer fishery and results in less wastage of fish, less lost gear and a better consumer product. The increased season length, while reducing interactions between vessels, may increase the possibility of interactions with whales because gear is available to the whales for a longer season.
Sablefish (Anoplopoma fimbria) are large, robust fishes with a sleek profile. They are dark brown to black on their sides and top, and a pale color on their belly. They are commonly called blackcod, however, they do not belong to the codfish family. They range from Japan, north into the Bering Sea and south through Alaska and British Columbia to Mexico, with the highest concentrations in Alaska.
Adult sablefish grow to 100 cm or more, live primarily in water deeper than 200 m, and have been found as deep as 3000 m. Sablefish observed from an occupied submersible were found on or within 1 m of the bottom. They are amongst the top predators on the continental slope, eating a wide variety of fish, octopus, squid, crab, and shrimp, and even carrion. They are long-lived, with some individuals estimated to live longer than 90 years. Sablefish spawn in deep water (300-700 m) along the continental slope with exact depth and season depending upon location. In Alaska, maximum spawning occurs in March through April. Eggs and larvae collect primarily in deep water, but young-of-the-year (<8 cm) are found in near-surface waters. The smallest individuals eat zooplankton in their first weeks of life. The juveniles grow rapidly, and move to deeper water.
Due to its rich oil content, sablefish is exceptionally flavorful and an excellent fish for smoking. Sablefish is the highest valued finfish per pound in Alaska commercial fisheries. The major fishery for sablefish in Alaska uses longlines; however sablefish are a valuable bycatch in the trawl fishery as well. Sablefish enter the longline fishery at 4-5 years of age, perhaps slightly younger in the trawl fishery. Commercial fishing for sablefish occurs annually from approximately. March to November on the upper continental slope at depths averaging 250-600 fathoms (500-1200m). The ex-vessel value of sablefish in Alaska in 2012 was $109 million.
Interactions between sperm whales and fishing operations, particularly longline operations, occur in the higher latitudes of the world’s oceans. In the Gulf of Alaska depredation by sperm whales of longline gear set for sablefish has been occurring for over three decades. In 1995 a change in management resulted in an expanded fishing season. This change allowed increased opportunities for sperm whales to depredate longline fishing gear and by 1997 reports of depredation had increased substantially.
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