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Seasonal Migratory Patterns of Pacific Cod (Gadus Macrocephalus) in The

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Seasonal Migratory Patterns of Pacific Cod (Gadus Macrocephalus) in The Bryan et al. Anim Biotelemetry (2021) 9:24 https://doi.org/10.1186/s40317-021-00250-2 Animal Biotelemetry RESEARCH Open Access Seasonal migratory patterns of Pacifc cod (Gadus macrocephalus) in the Aleutian Islands David R. Bryan1,2* , Susanne F. McDermott1, Julie K. Nielsen3, Dave Fraser4 and Kimberly M. Rand5 Abstract Background: Pacifc cod (Gadus macrocephalus) is an ecologically important species that supports a valuable com- mercial fshery throughout Alaska waters. Although its life history includes seasonal movement for spawning and feeding, little is known about its movement ecology. Here, we present results from the frst study to use pop-up satellite archival tags (PSATs) to track the within-year movements of Pacifc cod to understand their potential seasonal movement patterns within the Aleutian Islands. This study was part of a cooperative research project; tagging was conducted onboard commercial vessels during the winter fshing season while Pacifc cod were aggregated to spawn in the central Aleutian Islands. Results: Of the 36 PSATs deployed, we were able to obtain movement data from 13 Pacifc cod that were at liberty between 60 and 360 days. We determined that three tagged Pacifc cod were predated on by marine mammals and three were recaptured by the commercial fshery. Geolocation models were produced for four migrating individuals. Eight Pacifc cod moved to a productive foraging ground near Seguam Island located 64 to 344 km from their release site and presumed spawning ground within a few weeks of their release. These movements indicate that some Pacifc cod in the Aleutian Islands undergo seasonal migration. Three Pacifc cod remained near their release locations (within 50 km) for more than 75 days suggesting the existence of partial migration in the population. Two Pacifc cod under- took larger movements (378 and 394 km) during which they swam over deep passes and crossed several manage- ment boundaries highlighting the potential connectedness of Pacifc cod throughout the Aleutian Islands. Conclusions: This study provided important initial insights into the seasonal movement patterns of Pacifc cod in the Aleutian Islands. Most tracked Pacifc cod (77%) undertook migrations in the middle of March (64–394 km) from their winter spawning areas to summer foraging areas, but a few individuals remained in their capture location suggesting a partial migration strategy. Their ability to cross deep passes that were previously seen as potential barriers to move- ment has expanded our understanding of population connectivity. Keywords: Movement ecology, Pop-up satellite archival tags, Gadidae, Alaska, Spawning aggregation, Geolocation, Partial migration Background Te Aleutian Islands are an 1800-km-long archipelago west of the Alaska Peninsula consisting of hundreds of small, steep submarine volcanoes surrounded by a nar- row shelf with steep drop-ofs. Numerous straits and *Correspondence: [email protected] passes along the island chain connect the North Pacifc 1 National Oceanic and Atmospheric Administration, National Marine Ocean to the Bering Sea and Gulf of Alaska [1]. Te area Fisheries Service, Alaska Fisheries Science Center, 7600 Sand Point Way Northeast, Seattle, WA 98115, USA is largely uninhabited and provides habitat for a tremen- Full list of author information is available at the end of the article dous diversity of fshes, seabirds, and marine mammals © The Author(s) 2021. This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http:// creat iveco mmons. org/ licen ses/ by/4. 0/. The Creative Commons Public Domain Dedication waiver (http:// creat iveco mmons. org/ publi cdoma in/ zero/1. 0/) applies to the data made available in this article, unless otherwise stated in a credit line to the data. Bryan et al. Anim Biotelemetry (2021) 9:24 Page 2 of 18 [2]. It is also a highly productive area and supports a large the summer, yet a large portion (~ 80%) of the commer- abundance of several economically important fsh species cial fshery takes place during the winter (January–April) such as Pacifc ocean perch (Sebastes alutus), Atka mack- when they aggregate to spawn [19]. Potential distribution erel (Pleurogrammus monopterygius), and Pacifc cod changes of the Pacifc cod population between the win- (Gadus macrocephalus) [3, 4]. ter and summer, especially the crossing of management Pacifc cod is a wide-ranging species that can be found boundaries during migrations, has signifcant implica- from the southern tip of the Korean Peninsula (Yel- tions in our understanding of their population dynamics low Sea) in the western North Pacifc Ocean across the and stock structure and thus their stock assessment. Aleutian Islands and as far north as the Chukchi Sea and south to the California coast in the eastern North Pacifc Methods Ocean. Genetic research has shown that there is lim- Fish capture and release ited connectivity among spawning groups of Pacifc cod, A total of 36 Pacifc cod were captured and released dur- as well as a strong isolation by distance signal across its ing a cooperative venture on both bottom trawl and pot North American range [5–9]. Genetic work has shown fshing vessels during commercial fshing operations strong support for signifcant diferences between Bering targeting Pacifc cod in the Aleutian Islands near Adak Sea and Aleutian Islands cod, as well as the possibility for Island, Alaska (Fig. 1). Due to diferences in the vessels additional diferentiation within spawning stocks found and the gear deployed, the methods used to capture and along the Aleutian Archipelago [5, 6]. In the United release Pacifc cod difered. However, the procedures for States, Pacifc cod is the ffth most valuable fnfsh spe- attaching the satellite tags to the Pacifc cod were the cies with almost all of the commercial catch coming from same. Alaskan waters [10]. In Alaska, Pacifc cod is currently managed as three separate stocks: Gulf of Alaska, Aleu- Trawl vessel operations tian Islands, and Bering Sea. We captured, tagged, and released 21 Pacifc cod from In the eastern Bering Sea, Pacifc cod undertake the FV Ocean Explorer on 18–20 February 2019, in large seasonal migrations from annual summer feeding Nazan Bay near Atka Island (Fig. 1). Nazan Bay is a grounds to winter spawning sites [11, 12]. Persistent win- known spawning site for Pacifc cod and tagging eforts ter spawning locations have been observed, and genet- coincided with time of peak spawning time. Te FV ics and tagging research suggest that individuals display Ocean Explorer is a 185-foot (56.4 m) bottom trawl ves- homing tendencies and site fdelity during their spawn- sel that conducted two, 6-h tows during daylight hours ing season [11, 13]. In the Gulf of Alaska (Prince William targeting Pacifc cod. We retained and tagged Pacifc Sound), Pacifc cod have high site fdelity to small fords cod opportunistically from each tow. After the net was with limited partial migration (i.e., some tagged fsh brought on deck, the crew hand selected the most vig- migrated after spawning season) [14]. Te fndings from orous Pacifc cod from the top of the trawl net (most these limited studies on Pacifc cod appear to be similar recently captured) and immediately placed them into to the larger body of research into the movement ecol- one of two large holding tanks, 1000 L each, that had a ogy of its congener, Atlantic cod, Gadus morhua, which constant supply of untreated seawater. Once in the tanks, has been shown to display both partial and long-distance we further examined the Pacifc cod for external signs of migratory patterns including high site fdelity [15, 16]. barotrauma and removed individuals that showed signs Tere are regional diferences in the migratory behaviors of injury. Pacifc cod that were caught during the frst of Atlantic cod, thus it is likely that Pacifc cod may also haul were tagged within 2 h of capture and retained in exhibit varying regional migration strategies [17, 18]. the tank until fshing operations were completed for the In this study, we used pop-up satellite archival tags day. Te time between capture and release ranged from (PSATs) to examine the seasonal movement of Pacifc 6 to 8 h. Pacifc cod that were captured during the sec- cod in the Aleutian Islands from a winter spawning ond haul were tagged and released within 1.5 h. Water ground to its feeding distribution in the summer and fall. temperatures in the tank were within 1 °C of bottom tem- Tis was the frst study to use PSATs to track Pacifc cod peratures as recorded by net mounted instruments. We in the Aleutian Islands and two goals of the study were to carefully lowered tagged Pacifc cod to the sea surface test the feasibility of using commercial vessels as tagging with a sling and then returned them to 50 m depth with platforms and determine the methodology of tagging a SeaQualizer™ descending device attached to a weighted these medium-bodied fsh and evaluate success rates. line. Te device included of a spring-loaded clamp that Seasonal movement patterns of Pacifc cod are especially on the surface gripped the lower lip of the Pacifc cod.
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