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Fishery Bulletin 104(4) 



water, as measured by the depth sensor of the electronic 

 tag, to those predicted by tide models. Unfortunately, 

 we are unable to use this method near Alaska because 

 the water depth is much greater than in the North Sea. 

 Deep water necessitates that the depth sensor of a tag 

 have a greater range, which decreases depth resolution. 

 Thus, tags used off Alaska have a depth resolution that 

 is greater than the tidal range; therefore the tag cannot 

 distinguish tidal fluctuations. 



Another tagging method has been used to geolocate 

 Baltic Sea cod {Gadus morhita) (Neuenfeldt et al.-). This 

 method is based on combined data of depth, tempera- 

 ture, and salinity obtained by electronic tags attached 

 to cod. Hydrographic fields obtained from hydrodynamic 

 modeling are used as a geolocation database to identify 

 daily locations of fish by comparison with the environ- 

 mental data collected by each electronic tag. Unfortu- 

 nately, the tags that we used are not available with a 

 salinity sensor and hydrodynamic models of the area 

 are not accurate on the bottom (Hedstrom'^). 



Ambient light data collected by electronic tags may 

 be used to calculate daily estimates of latitude and 

 longitude of fish. Geolocation by light has been imple- 

 mented successfully on a variety of pelagic species to 

 discern their daily position and movement patterns 

 (Gunn and Block, 2001; Schaefer and Fuller, 2002; Itoh 

 et al., 2003; Sibert et al., 2003). 



However, no studies have been conducted to evaluate 

 light-based geolocation estimates from tags attached to 

 demersal fish, nor from fish inhabiting high latitudes. 

 Unfortunately, light levels in deep and high-latitude 

 waters may be low and if the water is turbid, the light 

 may be attenuated very quickly, thus hindering position 

 estimates. Additionally, many demersal fishes inhabit 

 a depth range where geolocation by light has not been 

 evaluated at any latitude. 



The goal of this study was to examine the feasibility 

 of using ambient light geolocation for estimating de- 

 mersal fish movements in high latitudes. This was ac- 

 complished by the following procedures: 1) by comparing 

 daily latitude and longitude estimates from two propri- 

 etary software types developed by Wildlife Computers, 

 2) by examining latitude and longitude estimates as a 

 function of depth, and 3) by examining in situ latitude 

 and longitude estimates of pop-up archival transmitting 

 (PAT) tags attached to wild Pacific halibut. 



Materials and methods 



The pop-up archival transmitting tag (PAT, Wildlife 

 Computers, Redmond, WA, vers. 2.0) is a miniature 



- Neuenfeldt, S., H.-H. Hinrichsen, and A. Nielsen. 2004. A 

 method to geolocate eastern Baltic cod by using Data Storage 

 Tags (DSTs), 14 p. Int. Coun. Explor.'Sea CM/L:06. Int. 

 Coun. Explor. Sea, H.C. Andersens Boulevard 44-46, 

 DK-1553, Copenhagen V, Denmark. 



^ Hedstrom, K. 2005. Personal commun. Artie Region 

 Supercomputing Center, Univ. Alaska Fairbanks, PO Box 

 756020, Fairbanks, AK 99775. 



computer that is attached externally to a fish. The tag 

 contains a clock and sensors that collect depth, tempera- 

 ture, and ambient light intensity data at user-specified 

 intervals (Sibert, 2001). On a programmed date, the 

 PAT tag disengages from the fish, floats to the surface, 

 and transmits summaries of the recorded temperature, 

 depth, and light data to Argos satellites; the data are 

 then retrieved by the investigator. If the tag is retrieved, 

 the complete archival record of temperature, depth, and 

 ambient light data may be obtained. 



From October 2000 to March 2002, a pilot study was 

 conducted to assess the feasibility of using PAT tags as 

 a tool for identifying critical habitat of demersal fishes 

 in high latitudes (Seitz et al., 2002, 2003). Geoposi- 

 tion estimates were made from light data collected in 

 three experiments in which PAT tags were attached to 

 1) Pacific halibut in outside aquaria, 2) a stationary 

 mooring, and 3) wild Pacific halibut in situ. The tem- 

 perature and depth data from the wild Pacific halibut 

 experiment and their Argos-based final locations have 

 been reported previously (Seitz et al., 2003). 



In the first experiment, two Pacific halibut were cap- 

 tured, transported live to outside aquaria at the Alaska 

 SeaLife Center (Seward, Alaska; 60.099°N. 149.440°W) 

 and tagged on 18 Oct. 2000 with PAT tags programmed 

 to record light intensity every minute. The tags were 

 retrieved on 1 May 2001, and the longitudes and lati- 

 tudes of Pacific halibut estimated from the tag data 

 were compared with the known location of the Pacific 

 halibut in the aquaria. 



A second experiment was conducted by using a 

 fixed mooring to examine latitude and longitude esti- 

 mates as a function of depth. From December 2000 to 

 April 2002, four PAT tags were attached to a station- 

 ary mooring line (the NOAA Alaska Observing Sys- 

 tem's "GAK-l" mooring) in Resurrection Bay, Alaska 

 (59.852^N, 149.330°W) at depths of 27, 57, 96 and 146 

 m. These tags were attached to four different current 

 vanes on the mooring line so that their light sensors 

 faced up. 



In a third experiment, to evaluate the performance 

 of the light sensor and geolocation algorithm /;; situ. 

 fourteen wild Pacific halibut (108-165 cm fork length) 

 were captured, tagged, and released in November 2000, 

 March 2001, and July 2001 from a commercial longlin- 

 ing vessel in Resurrection Bay, AK, and off Cape Aialik, 

 AK (for details, see Seitz et al., 2002, 2003). Light data 

 were recovered from eight tags. PAT tags were tethered 

 externally to each study animal by a piece of monofila- 

 ment fishing line secured to a titanium dart that was 

 inserted into the dorsal musculature of the fish. At a 

 user-specified date and time, the PAT tag corroded the 

 pin to which the tether was attached, thus releasing 

 the tag from the animal. The tag floated to the surface 

 and transmitted summarized data records through the 

 Argos satellite system.^ After the tag popped-up to the 



■• Service Argos, Inc. (http://www.argosinc.com). [Accessed 

 on: 13 December 2005.1 



