A Day in the Life of a
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0800 hours |
It's a cold day in August in the central Aleutian Islands. Three biologists sit at a table in the galley aboard the Great Pacific, gulping down black coffee, and getting ready for their 16-hour work day. The 4-man crew dons raingear, boots, and hard-hats, and heads out onto deck. The vessel, a commercial pollock trawler during the fishing season, has been chartered by the US National Marine Fisheries Service, Alaska Fisheries Science Center, Auke Bay Laboratory, for broad-scale surveys of distribution, growth, bioenergetics, and identification of salmon stocks in the Gulf of Alaska and Aleutian Islands, as part of the US commitment to international cooperative high-seas salmon research under the North Pacific Anadromous Fish Commission (NPAFC). |
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In the wheelhouse, the dark outline of Adak Island barely shows beneath the swirling fog. The skipper runs the vessel in as close as possible to shore. A biologist assists the crew in raising and lowering the small, portable CTD, which measures water temperature and salinity at one-meter increments from the surface to the bottom. The skipper makes a quick, 180° turn, heading the vessel out to sea on a line perpendicular to shore, as the net spools off the stern reel. The crew hooks wire cables to the two big trawl doors, which spread the mouth of the net open. The net, a rope trawl, is specially designed for catching salmon. Long rope leads attached to the net guide fish into the 40-meter horizontal by 13-meter vertical opening, without producing too much drag in the water. The vessel has the horsepower and fuel capacity needed to tow the big net through the water at 5 knots, a speed necessary to catch salmon. The survey design calls for fishing along linear transects, perpendicular to shore over nearshore, slope (200-m bottom contour), and oceanic depths. Adak, one of 19 locations sampled during the survey, is an area of mixing of Asian and N. American salmon, and has been the site of much historical (1955-1978) salmon research. In August, catches are likely to include immature salmon from two of the largest stocks in the North Pacific Ocean: wild sockeye salmon from Bristol Bay, Alaska, and hatchery chum salmon from Hokkaido, Japan. |
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1253 hours |
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1542 hours |
The dramatic warming in water temperature, indicating the influence of the westward moving Alaska Coastal Current, is remarkable. The catch remains small, five sockeye with mostly empty stomachs. Three days earlier catches to to the east at Cape Prominance, Unalaska I., were huge, almost 500 salmon in a one hour tow at surface water temperatures of 12.0°C! What is the difference? The longer tows? Temperatures? Weather or currents? Differences in stock composition and migration routes? Distribution of their food? Likely a combination of these and other factors. |
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1817 hours |
Another small catch (7 sockeye, 2 chum), but now the sockeye stomachs are full of large, bright orange copepods (Calanus christatus) and chum stomachs contain clear, marble-sized gelatinous zooplankton (Salpa). This difference between species could indicate feeding competiton. If so, the sockeye salmon are clearly the winners, because salps have low caloric content compared to copepods. For dinner, the biologists and crew sit down between tows to a delicious pasta and salad dinner, prepared by one of the crew, who does double-duty as cook. |
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2115 hours |
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2355 hours |
Darkness has fallen. Strong currents have altered our tow path. The net brings in four flying (red) squid (Ommastrepes bartramii) and a small, mixed-species catch of salmon (4 sockeye, 4 chum, 1 chinook, and 1 pink salmon). Everyone is exhausted. The biologists quickly sample the catch, and turn in for a restless night of sleep, as the roaring engine moves the vessel, pitching through the swells. The crew takes turns at night watch, running on toward tomorrow's survey line at Amchitka Pass, just beyond the international dateline. |
0857 hours
As the net is rewound onto the reel, the skipper adeptly shakes down fish caught in the top of the net by unwinding and abruptly stopping the reel. Gulls cut the air over the trailing end of net, shrieking for something to eat. A crane lifts the cod end onto a large sorting table, which can hold up to a ton of fish. A crewman unlaces the inner bag, and a small catch, mostly jellyfish, a few Atka mackerel, a rockfish, and a spiny lumpsucker spills out onto the table. No salmon! The disappointing catch is quickly counted and thrown overboard.
Later, experts at the Alaska Department of Fish and Game Lab in Juneau, will examine the otolith samples for thermal marks, artificially induced to identify individual stocks of hatchery fish. Auke Bay Lab experts will use the tissue samples to identify stocks. One biologist spends the time between tows working in a makeshift laboratory on deck, examining salmon stomachs, which are mostly empty or contain well-digested contents. No salmon feeding going on here, and where are the sockeye? For lunch, the biologists make sandwiches, as the hungry crew devours a huge meal of sausage, eggs, and hashbrowns.
The catch is two immature chum and, finally, two sockeye (1 immature, 1 adult). A daggertooth, has a stomach full of juvenile greenling, sandlance, and rockfish. The immature sockeye has a stomach full of small, grey hyperiid amphipods (Parathermisto), notable for their big black eyes, but the other salmon stomachs are almost empty.
Our largest salmon catch on this transect (72 sockeye, 3 chum). The net also comes up with hundreds of small, gonatid squid. The sockeye salmon stomachs are nearly full of a mix of euphausiids, copepods, pteropods, and amphipods. Good feeding, but lots of individual variation indicates patchy prey distribution.
Aboard the F/V Kaiyo Maru
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0400 hours |
The bulk of the 93-meter stern trawler, Kaiyo maru, the flagship of the Fisheries Agency of Japan, drifts lazily in the northern area of the central Bering Sea. Interest in determining the wintertime distribution and temperature habitats of high-seas salmon (Oncorhynchus spp.) has brought the Kaiyo maru to this distant location. After leaving Tokyo, the ship fished along the 165°E meridian moving northwards. South of 46° N latitude, young sockeye (O. nerka), chum (O. keta), pink (O. gorbuscha), and chinook (O. tshawytscha) salmon, spending their first winter at sea, had been abundant in the catches (N=1954). In the coming days, as she continued her operations first to the northwards, and then to the northeastward around the western end of the Aleutian Islands, the salmon catch had dwindled to a sprinkling of young sockeye, chum, pink, and chinook, and a few older sockeye and chum salmon that were spending their second winter at sea (n=12) . Only the day before, the Kaiyo maru had arrived in the international waters of the central Bering Sea basin known as the donut hole. 
The Kaiyo maru is a large vessel, easily accommodating a crew of 47 with 10 additional scientists, including specialists of salmon biology, ecology, and distribution, and, physical and biological oceanographers. Five scientists are from the Far Seas Laboratory in Shimizu, Japan, three students come from Hokkaido and Shimizu, and another two scientists come from Russia and the USA. This is the first opportunity for these scientists to fish for salmon in the Bering Sea in winter. For the moment, the researchers are sleeping, but outside the icy waters are 1.2°C, and the air temperature is hovering at -8°C. In an hour, they will don their protective clothing, drink some coffee and head out on deck to start the morning's work.
Meanwhile, on the side of the trawl deck the 2-m long Norpac zooplankton net is recovered from 150 m depth and the zooplankton clinging to the mesh are rinsed into a collecting bottle. This plankton net recovers some, but not all of the planktonic animals fed upon by salmon. This morning's collection contains small jellyfish, arrow worms, and copepods, but it is not rich in food for salmon. A preservative is added so that the sample can be later sorted, identified, and weighed into its plankton components. The winch is then used to deploy the 30-l Go-Flo water sampler. Water samples are collected from several depths to determine the levels of photosynthetic pigments contained in the phytoplankton, which is an indicator of the capacity for photosynthesis in the water column. Additional surface water samples are collected for determination of the rate of primary production. By now, the small group on deck can smell the comforting indications that breakfast is nearly ready. The crew dashes out of the cold to eat a hot meal of miso soup, rice, and grilled mackerel. Contemplating the results of the previous evening's XBT (expendable bathythermograph), which measures temperature and depth, the salmon scientists have decided to make two trawl operations, one to immediately follow the other based on the thermal structure of the water column. The XBT profile shows that the water temperature from the surface to 150 m differs only by 9 hundredths of a degree, from 1.66° to 1.75°C, indicating a deeply mixed surface layer. Deeper, however, between 150 and 170 m, the water temperature warms from 1.75°C to 3.90°C. This location of quickly changing temperature is the thermocline depth. The salmon scientists wonder if the surface mixed layer is too cold for salmon and whether the salmon could be holding just below the thermocline to take advantage of the warmer water found there. The decision is made to set the first trawl of the day in the surface layer (0-50 m depth) and a second trawl operation at the thermocline depth (175-210 m). Their expectations for the catch of salmon run the gamut: bag full, to bag empty. The Kaiyo maru is slowly making headway, and first the codend, then gradually the whole trawl net slips off the end of the stern ramp. The midwater trawl is huge: the mesh bag alone is 222 m long. The cables and bridles are slowly unwound off the large winch until more than 100 m of cable has been let out and the trawl disappears behind the boat. The 9-m2 trawl doors, each weighing 1450 kg, swing and bounce as the crew deftly attaches them between the trawl and the main warp cables from which the trawl is towed. The doors spread the mouth of the trawl into an oval 50-m tall and 70-m wide. The warp cable is quickly run out to 400 m and the trawl slowly comes back up to the surface where its own bow wave is visible from the bridge. The ship is now trawling to the westward at 5.8 kts, and any salmon swimming in front of the net's mouth are likely to tire eventually, and drift back into the lined codend from where there is no escape, even for much smaller myctophids, or juvenile fishes.
Processing the salmon catch includes collection of scales for determination of the fish's age. Scales from the preferred area on the midbody are not to be found due to the abrasive action of the trawl, so scales are removed from protected areas under the fins, usually the pectorals. The fork length is measured to the nearest mm and the fish is weighed to nearest gram. Judging from their size, these young chinook salmon were likely to be spending their first winter at sea. A blood sample is removed to determine the serum levels of a growth hormone, (IGF-1) insulin-like growth factor 1, The announcement is made that it is time for lunch and the ship's complement is grateful to be served a hot noodle soup. Lunch is eaten quickly because soon it will be time to retrieve the second tow. The scientists are wordlessly wondering, will there be more salmon in this deep tow? Will there be any? Gradually the net is brought back onboard and the codend is opened. Three more young chinook salmon reveal themselves in the mesh among the squid (Gonatidae sp. and Gonatus midendorfii) and the lumpfish (Aptocyclus ventricosus). The process begins again, the catch is brought below, the salmon are measured, weighed, a scale, and blood sample removed. Obviously, chinook salmon are adapted to the extreme cold water of the central Bering Sea. But are there other species of salmon overwintering in the surface waters of the Bering Sea? Maybe the next trawl will reveal these secrets. The scientists retreat to their rooms to read, write, analyze, sleep, or perhaps play the guitar. Meanwhile, the Kaiyo maru steams south 90 nm to the next station and prepares to set her net. |
On deck, the crew shovels and washes the inch-thick slush ice that has formed on the trawl deck. A few make heavy wet snowballs from the snow that has gathered on the trawl net. On the starboard side, a winch hoists the 2-m tall CTD sensor and rosette of Niskin bottles up and into the water. Over the next hour and 10 minutes, depth, temperature, and salinity sensors continuously transmit data to the ship's computer as the CTD descends from the surface to 1500 m providing the data oceanographers require to describe the ocean environment in which salmon live, and probe the intermediate depths that contribute to dynamics of ocean circulation. As the CTD rosette is slowly brought back from the depths, the Niskin bottles are tripped electronically to capture water from 23 depths as the cable rewinds the CTD rosette back to the surface.
After an hour, the warp cable is hauled back and the process is repeated in reverse. Eventually the codend is back on deck, unraveled, and the codend liner thrown open. The catch is five young chinook salmon. The salmon and by-catch of squid (Gonatidae) and jellyfish are removed from the netting and put into trays and taken below for processing. The crew busily prepares to set the trawl immediately back in the water.
which changes seasonally and precedes rapid growth in salmon. The salmon are individually labeled and frozen for later detailed examination at Shimizu, where individual organs will be weighed, stomach contents will be identified, and tissue samples for condition factor and stock identification will be collected.
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