Lauth et al.: Timing and duration of mating and brooding periods of Pleurogrammus monopterygius 



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either establishing nesting territories before spawning 

 or in brooding eggs afterwards. Only from the western 

 North Pacific Ocean is there published information on 

 the nesting period from beginning to end, but methods 

 and results have been vague and have relied on catch 

 data from various nonstandardized fishing gears and 

 methods (Gorbunova, 1962; Zolotov, 1993). Egg incuba- 

 tion times are useful for approximating the end of the 

 male nest brooding period (Gorbunova, 1962; Lauth and 

 Blood, 2007), however, controlled rearing experiments 

 at a wider range of water temperatures are needed to 

 accurately determine how the rate of embryonic develop- 

 ment is affected (Lauth and Blood, 2007). 



The objective of this study was to clarify Atka mack- 

 erel's temporal use of breeding habitat by investigat- 

 ing the timing and duration of nesting, spawning, and 

 brooding phases in the North Pacific Ocean. This study 

 makes use of in situ visual and behavioral observations 

 of male Atka mackerel and an incubation model that 

 synthesizes data from laboratory incubation experi- 

 ments, egg mass collections from three different nesting 

 sites, and descriptions of embryonic development from a 

 companion manuscript (Lauth and Blood, 2007). 



Materials and methods 



Direct observation of nesting behavior 



Visual and behavioral observations from time-lapse 

 video and data from archival tags were used for deter- 

 mining the beginning and end of the nesting period (i.e., 

 the duration of male territoriality), and to document 

 nesting behaviors before the onset of spawning. Sexual 

 dichromatism (Medveditsyna, 1962; Rutenberg, 1962) 

 and behavioral changes in males (Nichol and Somerton, 

 2002; Lauth et al., in press) are primary indications of 

 nesting activity. Nest guarding males are distinguished 

 by their bright yellow or orange color and dark black 

 vertical stripes. When males are breeding, they defend 

 a nesting territory for long periods and refrain from 

 vertical migrations. Sexually mature females or non- 

 spawning Atka mackerel of both sexes are bluish-green 

 or gray and typically undergo dial vertical migrations 

 year round (Nichol and Somerton, 2002). 



Time-lapse camera Diving operations to deploy and 

 retrieve underwater camera equipment were conducted 

 from the National Atmospheric and Oceanic Administra- 

 tion (NOAA) National Marine Fisheries Service (NMFS) 

 charter vessels FV Morning Star (May 2002), FV Sea 

 Storm (July 2002), and the United States Fish and 

 Wildlife Service RV Tiglax (August 2002). A Sony Hi8 

 (Sony Electronics, Inc., San Diego, CA) video camera was 

 placed inside a Plexiglas housing and secured to a moor- 

 ing on the seafloor at 23 m by a diver at a known nesting 

 site at Seguam Island, Alaska (52 22.10°N, 172 20.26°W) 

 on 31 May 2002. The video camera had a time-lapse 

 controller that could be set by the user to record video 

 images at periodic intervals. The camera was attached 



to a tripod frame made of welded steel. On the initial 

 deployment, the time-lapse controller was set to record 

 1 minute of video each day. It was recovered on 28 July 

 2002 (60 days later) and reset at the same location to 

 record 1 minute of video every hour until 7 August 2002 

 (a 10-day period). The camera was recovered and reset 

 a final time to record 15 sec/h until 31 August 2002 (a 

 24-day period) when the camera was recovered. 



Archival tags Archival tag data from a previously pub- 

 lished study on Atka mackerel diel behavior (Nichol 

 and Somerton, 2002) were used to infer nest-guarding 

 behavior and to corroborate nesting periods. In July 

 2000, 117 Atka mackerel were captured by trawl, tagged, 

 and released in Seguam Pass with archival tags that 

 recorded the time, depth, and temperature once each 

 minute (Nichol and Somerton, 2002). Commercial trawl- 

 ers recovered 14 Atka mackerel with tags. Data from 

 four of the tags were from males that showed no verti- 

 cal movement for extended periods, which is consistent 

 with nesting. Data from two of the four tags were also 

 reported in Nichol and Somerton (2002). 



Laboratory incubation experiments 



Results from laboratory rearing experiments were used to 

 develop parameters for an incubation model to determine 

 how Atka mackerel incubation time varies between nest- 

 ing sites. Laboratory experiments were conducted at the 

 Alaska Sealife Center (ASLC) with egg masses spawned 

 by captive Atka mackerel. In October 2002, a commercial 

 fishing vessel with a bottom trawl collected 20 live Atka 

 mackerel from Seguam and Tanaga Passes. The fish 

 were kept live in tanks on board the fishing vessel and 

 transported to the ASLC. After acclimation, antibiotic 

 treatment, and a one-month quarantine at the ASLC, 

 14 Atka mackerel were transferred to ASLC exhibit 

 tanks equipped with a submersible video camera for 

 documenting spawning and nesting behavior. Each time 

 an egg mass was discovered, the videotape was reviewed 

 to determine the time of egg mass deposition. Fertilized 

 egg masses were transferred to one of four closed-system 

 incubation tanks consisting of a 150-L tank, recircula- 

 tion pump, and a 1/3 hp inline chiller controlled by an 

 electronic thermostat. The configuration of the system 

 provided stable temperatures with very little fluctuation. 

 Temperatures for the incubation chambers were chosen 

 on the basis of (>; situ observations at nesting sites in 

 the Aleutian Islands (Lauth et al., in press). Ten incuba- 

 tion experiments were conducted at four different water 

 temperatures: three each at 4°, 5°, and 7°C, and two at 

 10°C. The light cycle in the aquaria was regulated with 

 an electronic timer set at 12 h light and 12 h dark. 



For all incubation experiments, hatching day for an 

 egg mass was defined as the first day larvae hatched 

 from the egg mass. A scatter plot of incubation tempera- 

 ture versus total days to first hatching was constructed 

 for all incubation temperature trial data, and regression 

 analysis (Zar, 1999) was used to determine how total 

 days to hatching varied as a function of temperature. 



