Through cooperative research with fishermen, government, and scientists the ultimate goal of this study is to provide recommendations for strategies to reduce or eliminate depredation on longline gear by sperm whales. As a first step towards this goal, information was collected, in collaboration from the fishing fleet, on the timing of interactions seasonally and diurnally, and identify the sperm whales occurring on the fishing grounds through visual photographic identification and genetic tissue samples. This research helped define the scope of the problem, identify stock structure and the ecology of this endangered species, as well as provided baseline information needed for studying depredation mechanisms, cues and, finally, developing solutions to reducing negative interactions.

The acoustic phase of the project incorporated a passive acoustic component to study how sperm whales might use sound to perform longline depredation. During the deployment of a set of longline gear over a 20 hour period, a set of autonomous acoustic recorders were attached to a buoy anchor line, creating an autonomous vertical array that recorded sounds made in the vicinity of the array. These sounds included noise made by shifting or moving fishing gear that might attract whales, fishing vessel sounds, and distinctive sounds made by sperm whales, called ‘clicks’. The array was also used to track sperm whales in range and depth, within a 2-4 km radius via their acoustic vocalizations, during periods when the longline is on the ocean floor, and during longline recovery.  These passive acoustic measurements provided insights into when and how the animals locate the fishing gear, and whether and how the animals use biosonar to locate individual fish being hauled up on the longline during recovery. Given this information, possible countermeasures to reduce depredation might be surmised.

The fishing fleet out of Sitka, and the Alaska Longline Fishermen’s Association (ALFA), has taken a proactive conservation approach to try and develop a deterrence system before mortalities occur. The use of a longliner communication network allowed the study to maximize the success of the study by limiting fieldwork to days when sperm whales are reported on the grounds. Although this research was conducted in the eastern Gulf of Alaska, the results will be communicated to the fleet elsewhere in the North Pacific where interactions also occur.

Study Area
Sperm whales are often sighted in near coastal waters of Alaska, and the fishing port of Sitka is uniquely situated with ready access to interactions.  Sablefish occur on the continental slope and most commercial longliners fish for sablefish in water depths between 1200’ and 3,000’.  The continental shelf off Kruzof, Baranof and Chichagof islands is very narrow; consequently, the sablefish grounds are only 12-20 miles from shore in this area.  Sitka is an ideal location to launch this project as the fishing grounds are easily accessible and much of the fleet (primarily vessels less than 60 feet) is based out of Sitka.

Study area for the sperm whale deterrent project. The study area is between the two contour lines (100 fm and 1000 fm) with the majority of work occurring in 400 fm off of Kruzof Island (general study area depicted by oval). Sitka is situated at about 570 N latitude and 135020’ W longitude.

Research Goals
We know that sperm whales are taking sablefish off longline hooks, but how?  The questions below are of particular interest, and this study attempted to answer them with the help of acoustics.

1. How do sperm whales locate the longline deployment?  For example, are the animals already present in an area when fishing vessels arrive, or are they attracted by sounds produced by the fishing vessel during deployment, or even attracted by sounds made by shifting fishing gear after deployment?
   
   
2. What strategy do sperm whales use to take fish off, or depredate the line?  Do any whales dive to the bottom to remove fish before the fishing vessel arrives, or do they wait to pick fish off the line as the gear is being hauled in?  At what depths are they taking the fish?
   
   
3. How are whales finding particular fish of interest, particularly at night?  If they are making sounds to locate fish, from how far away can they detect fish, and what is their “hunting” strategy?  How could their “success” rate be reduced?