AFSC/RACE/GAP/Nichol: Archival tag depth and temperature data from Atka mackerel

Atka mackerel Pleurogrammus monopterygius were captured and tagged with depth and temperature recording devices (archival tags) on 23 July 2000 in Seguam Pass, Aleutian Islands, Alaska. Nine of the 117 tagged fish were recovered in Seguam Pass during September 2000, and an additional 5 fish recovered thereafter (14 total). In addition, 413 tags were released in Tanaga Pass in 2002, with 10 recoveries. Fish were tagged externally just below the dorsal fin. Atka mackerel displayed strong diel behavior, with vertical movements away from the bottom occurring almost exclusively during daylight hours and little to no movement at night. Vertical movements occurred when light levels at 150 m were greater than 7.31 × 10–5 µmol photons m–2 s–1, or approximately between 08:00 and 23:00 h Alaska Daylight Time (ADT; GMT – 8) during August. Daytime vertical movements were correlated with light intensity, time of day and current velocity. The occurrence of vertical movements tended to increase with increasing light during the morning and early afternoon, but then decrease with increasing hour of the day after 13:00 h ADT. The magnitude of surface-directed vertical excursions was reduced during spring tide periods, when current velocities are highest. By comparison, the magnitude of slope-directed excursions was greater during spring tide periods and reduced during neap tide periods. Eight fish were at liberty for 42 to 44 d and 1 for 65 d. Two of the tagged males displayed nest guarding behavior for the majority of their time at liberty. Depths for these 2 males (115 to 117 m) were much deeper than previously observed for Atka mackerel spawning grounds. Given that Atka mackerel are more likely to be on the bottom during the night and less likely during the day, the variance of abundance estimates from bottom trawl surveys may be reduced by accounting for these diel differences.

To examine the vertical migration behavior of Atka mackerel, and relate the behavior to catchability in bottom trawl surveys.

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Publication: Nichol, D.G. and Somerton D.A. 2002. Diurnal vertical migration of the Atka Mackerel Pleurogrammus monopterygius as shown by archival tags. Mar. Ecol. Prog Ser. 239:193-207.

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Atka mackerel were initially captured during two bottom trawl tows made on 23 July 2000 aboard the chartered F/V Morning Star in Seguam Pass, Alaska. Tow durations were kept short (< 15 min) in order to minimize injury to fish. Fish were held briefly in tanks plumbed with a continuous flow of fresh seawater. A total of 117 fish were tagged with archival tags and released on 23 July 2000; 66 fish from the first tow (Haul 4) at 119 m bottom depth and 51 fish from the second (Haul 7) at 110 m bottom depth. Fish were measured to the nearest cm fork length (FL) and released within 3.1 km of the capture location. Archival tags were externally attached just below the anterior section of the dorsal fin. Fish were secured in a V-shaped cradle and paired 18 gauge hypodermic needles were inserted through the fish. Stainless-steel wire (0.02 gauge, 0.5 mm diameter) was fed through the tag and then through the open end of the hypodermic needles. After removing the hypodermic needles, the stainless-steel wire ends were fed through a pink plastic oval and secured with stainless-steel connector sleeves. This procedure took approximately three minutes per fish. A tag reward program was implemented to retrieve tagged fish. This program was conducted in association with an ongoing spaghetti tag project for Atka mackerel in Seguam Pass (See Susanne McDermott).

Publication: Nichol, D.G. and Somerton D.A. Diurnal vertical migration of the Atka Mackerel Pleurogrammus monopterygius as shown by archival tags. Mar. Ecol. Prog Ser. 239:193-207.