Fish communities across a spectrum of habitats in the western Beaufort Sea and Chukchi Sea

Progress in Oceanography 136 (2015) 115–132

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Fish communities across a spectrum of habitats in the western Beaufort Sea and Chukchi Sea E. Logerwell a,⇑, M. Busby a, C. Carothers b, S. Cotton b, J. Duffy-Anderson a, E. Farley c, P. Goddard a, R. Heintz c, B. Holladay b, J. Horne a,d, S. Johnson c, B. Lauth a, L. Moulton e, D. Neff c, B. Norcross b, S. Parker-Stetter d,f, J. Seigle g, T. Sformo h a

NOAA/NMFS, Alaska Fisheries Science Center, 7600 Sand Point Way, N.E., Seattle, WA 98115, United States School of Fisheries and Ocean Sciences, University of Alaska Fairbanks, 905 N. Koyukuk Dr., Fairbanks, AK 99775, United States NOAA/NMFS, Alaska Fisheries Science Center, Auke Bay Laboratory, Ted Stevens Marine Research Institute, 17109 Pt. Lena Loop Rd., Juneau, AK 99801, United States d School of Aquatic and Fisheries Science, University of Washington, Box 355020, Seattle, WA 98105, United States e MJM Research, LLC, 1012 Shoreland Drive, Lopez Islands, WA 98261, United States f NOAA/NMFS, Northwest Fisheries Science Center, 2725 Montlake Blvd., Seattle, WA 98112, United States g ABR, Inc. – Environmental Research & Services, P.O. Box 240268, Anchorage, AK 99524, United States h North Slope Borough Department of Wildlife Management, P.O. Box 69, Barrow, AK 99723, United States b c

a r t i c l e

i n f o

Article history: Available online 12 May 2015

a b s t r a c t The increased scientific interest in the Arctic due to climate change and potential oil and gas development has resulted in numerous surveys of Arctic marine fish communities since the mid-2000s. Surveys have been conducted in nearly all Arctic marine fish habitats: from lagoons, beaches and across the continental shelf and slope. This provides an opportunity only recently available to study Arctic fish communities across a spectrum of habitats. We examined fish survey data from lagoon, beach, nearshore benthic, shelf pelagic and shelf benthic habitats in the western Beaufort Sea and Chukchi Sea. Specifically, we compare and contrast relative fish abundance and length (a proxy for age) among habitats and seas. We also examined ichthyoplankton presence/absence and abundance of dominant taxa in the shelf habitat. Our synthesis revealed more similarities than differences between the two seas. For example, our results show that the nearshore habitat is utilized by forage fish across age classes, and is also a nursery area for other species. Our results also indicated that some species may be expanding their range to the north, for example, Chinook Salmon. In addition, we documented the presence of commercially important taxa such as Walleye Pollock and flatfishes (Pleuronectidae). Our synthesis of information on relative abundance and age allowed us to propose detailed conceptual models for the life history distribution of key gadids in Arctic food webs: Arctic and Saffron Cod. Finally, we identify research gaps, such as the need for surveys of the surface waters of the Beaufort Sea, surveys of the lagoons of the Chukchi Sea, and winter season surveys in all areas. We recommend field studies on fish life history that sample multiple age classes in multiple habitats throughout the year to confirm, resolve and interpret the patterns in fish habitat use that we observed. Published by Elsevier Ltd.

1. Introduction There are 242 currently known species of benthic and pelagic fishes in Arctic marine waters, distributed among 45 families (Mecklenburg et al., 2010). Fish such as Arctic Cod (Boreogadus saida), salmon and forage fishes (e.g., Capelin Mallotus villosus) play

a key role in the Arctic, as they do in many systems, as prey to seabirds, marine mammals and humans (Bradstreet et al., 1986; Whitehouse et al., 2014). They are also potentially important consumers of secondary production in the Arctic in both benthic and pelagic zones (Frost and Lowry, 1981, 1983; Jarvela and Thorsteinson, 1999). A synthesis of current fish community

⇑ Corresponding author. E-mail addresses: [email protected] (E. Logerwell), [email protected] (M. Busby), [email protected] (C. Carothers), [email protected] (S. Cotton), [email protected] (J. Duffy-Anderson), [email protected] (E. Farley), [email protected] (P. Goddard), [email protected] (R. Heintz), [email protected] (B. Holladay), [email protected] (J. Horne), [email protected] (S. Johnson), [email protected] (B. Lauth), [email protected] (L. Moulton), [email protected] (D. Neff), [email protected] (B. Norcross), [email protected] (S. Parker-Stetter), [email protected] (J. Seigle), todd. [email protected] (T. Sformo). http://dx.doi.org/10.1016/j.pocean.2015.05.013 0079-6611/Published by Elsevier Ltd.

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composition and habitat use supports the goals of SOAR by providing a baseline against which to measure future change. In addition, it provides insight into how climate change might impact Arctic fish communities and the predators that depend on them via changes to their habitat. Surveys have been conducted in nearly all Arctic marine fish habitats during the past decade: from coastal lagoons out to the continental slope. The shallow lagoons inshore of barrier islands of the Beaufort Sea are characterized in the ice-free season by brackish and relatively warm water. This water is formed during spring when floodwaters from North Slope rivers flow to sea and mix with marine waters (Craig, 1984). The nearshore zone is a transition between estuarine waters originating from lagoons and marine waters offshore. The extent of the band of estuarine water in the nearshore depends on the amount of freshwater input, nearshore currents and prevailing winds. By the end of winter the shallow waters of lagoons and the nearshore are frozen solid. Lagoon habitat is less prevalent in the Chukchi Sea and less well-studied, but presumably the lagoons and nearshore habitats in the Chukchi have similar characteristics as those observed in the Beaufort. Beaches in the Beaufort and Chukchi Seas are rarely steep and rocky, but instead are typically sand, gravel, mud or some combination of these (https://alaskafisheries.noaa.gov/shorezone/). The shallow (50 m) and wide Chukchi Sea shelf extends 800 km northward from Bering Strait to the shelfbreak. Water flows north through Bering Strait, bringing heat, nutrients, carbon and organisms that strongly influence the characteristics of the Chukchi Sea ecosystem (Weingartner, 2008). The Alaskan Beaufort Sea shelf is narrower than the Chukchi Sea shelf (80 km wide) and relatively flat; bottom depths increase gradually from the coast to the 80 m isobath and then drop off rapidly along the shelfbreak and slope. Oceanographic characteristics of the Beaufort Sea are influenced by water flowing eastward from the Chukchi Sea, from the westward flowing southern limb of the Beaufort Gyre and discharge from the Mackenzie River (Weingartner, 2008). Increased scientific interest in the Arctic due to climate change, potential oil and gas development and the International Polar Year (IPY 2007–2009) has resulted in the surveys of Arctic fish communities synthesized here. There was a period of large-scale Arctic surveys in the early 1970s to the early 1990s when there was a concerted effort to study areas of potential oil and gas development, the Outer Continental Shelf Environmental Assessment Program (OCSEAP, 1990). There has been a gap in large-scale Arctic research since the OCSEAP era until the 2000s. Our surveys from 2007 to the present provide an opportunity only recently available to study Arctic fish communities across a spectrum of habitats. This project was a collaboration among researchers at a number of agencies, local and federal, and universities providing data in a cooperative fashion from their individual surveys. We compare the fish community composition in lagoon, beach, nearshore benthic, shelf pelagic and shelf benthic habitats. We also use information on age-class of fish along with ichthyoplankton data to compare and contrast how different taxa use these habitats throughout their life history. Finally, we explore similarities and differences in community composition and habitat use of Beaufort and Chukchi Sea fishes. Our synthesis provides a baseline for climate change impacts in the future and suggests directions for future research.

2. Methods The temporal scope of our synthesis is the ice-free spring to fall season and the years 2007–2012. These years represent our best available data coverage across habitats. In addition, 2007 marks

the first recent historical low in summer sea ice (NCAR, 2007) and can be considered the start of the ‘‘new normal’’ in Arctic climate and ocean conditions (Jeffries et al., 2013). We synthesized data from fish surveys of several habitats in the western Beaufort and Chukchi Seas: coastal lagoon, beach (waters <5 m deep), nearshore benthic (waters <10 m deep), shelf (>20 m deep) surface, shelf midwater (pelagic habitat below the surface and above the bottom) and shelf benthic. We did not have data for the central and eastern Beaufort Sea. We also examine ichthyoplankton data from shelf surveys from both seas. Table 1 summarizes the years, months and habitats for which we had survey data, and Fig. 1 shows the locations of all stations (subsequent figures will show which surveys sampled at which stations). Data were collected from as early as June to as late as October. There were no data from the shelf surface of the Beaufort Sea, nor from the lagoon and shelf midwater of the Chukchi Sea. Fish caught were often identified to species, but not always, so catch by family is reported in some cases. Catch-per-unit effort (CPUE), a measure of fish density, was used to represent relative fish abundance for each habitat. In addition individual length data were summarized for each species or taxonomic group (average and min–max). Virtually no fish age data were available from the surveys, so fish age ranges were based on age-length relationships from other areas (predominantly Alaska region). Finally, three diversity indices were calculated for each habitat in each Sea: Richness (S), Simpson’s Index (D) and Shannon Index (H) (Begon et al., 1990). Because of the different levels of taxonomic resolution in the datasets, diversity indices were calculated at the level of Family. Maps of survey stations were created in ESRI ArcMap 10.0, using Albers projection and the North American Datum 1983.

2.1. Beaufort Sea We synthesized data from fish surveys conducted in five different habitats in the western Beaufort Sea: lagoon, beach, nearshore benthic, shelf midwater and shelf benthic. Data were collected from June through September (depending on the survey). The lagoon habitat of the Beaufort Sea was sampled with two net types, fyke nets and gill nets. The purpose of these on-going surveys is to investigate the subsistence fishery in Elson Lagoon, an important resource for the community of Barrow (Bacon et al., 2009). Fyke nets were maintained by scientists from the North Slope Borough Department of Wildlife Management to estimate species present, size and age distribution and health status of fish. In addition, daily gill net surveys of subsistence fishermen are conducted (http://www.north-slope.org/departments/wildlifemanagement/studies-and-research-projects/fish/fish-surveys). The fyke net had a minimum mesh size of 6.4 mm and was deployed at several locations within the Elson Lagoon system (Figs. 2 and 3). The net was fixed in place and left open to fish for 24 h and sampled each day (with the exception of weekends or before storms) between the months of June and August. Data from 2009–2012 were used for this analysis (Moulton and Seigle, 2012). Catch-per-unit-effort (CPUE) was calculated as No. fish/effort hours, where No. fish was the total number of fish caught in a year and effort hours was the total number of hours the net was open in a year. Total effort hours from 2009–2012 was 2304. The lagoon gill net data were from the 2011 subsistence gill net fishery from the months of June–September. The purpose of the gill net study was to gather information on salmon use, abundance and distribution in the Arctic (Cotton, 2012). Gill nets were deployed by fishermen at several locations spanning the west to east range of the fyke net locations (Fig. 3). The mesh size of the gill nets used in the fishery ranged from 64 to 203 mm. Catches were from daily net observations and fisher’s logbook data of recorded catches. Daily CPUE

Sept Sept Aug–Sept Aug–Sept Aug–Sept

Sept

Aug–Sept July July–Oct

Shelf benthic Shelf surface Nearshore benthic Beach Lagoon

Aug–Sept Aug–Sept Aug–Sept

Chukchi Sea

Sept Aug

Aug Aug

2007 2008 2009 2010 2011 2012

July–Sept July–Sept July–Sept July–Sept

Nearshore benthic Beach

Shelf surface

Aug

Shelf midwater

Aug

Shelf benthic

Aug

Ichthyo-plankton Beaufort Sea

Lagoon

Year

Table 1 Years, months and habitats for which fish and ichthyoplankton survey data were available for the synthesis, for the Beaufort and Chukchi Seas.

Aug–Sept Aug–Sept Aug–Sept

Shelf midwater Aug–Sept

Ichthyo-plankton

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was calculated by dividing No. fish by effort, which was the number of hours the net was fished standardized to a common net length (60 feet). The total number of hours all nets were fished in 2011 was 20,072. The average of daily CPUE was then calculated. The beach and nearshore benthic habitat was sampled as part of a study to update information on fishes of coastal waters of the Alaskan Arctic (Johnson et al., 2010). Fish were captured with a beach seine and bottom trawl on the seaward side of Cooper Island (Figs. 2 and 3). The beach seine stations were in water <5 m deep and were <20 m from shore. The net was a 37 m long variable mesh beach seine with 3.2 mm square mesh in the bunt and was set as a ‘‘round haul’’ (National Marine Fisheries Service (NMFS), 2010). Offshore of each beach seine station, fish were captured with a bottom trawl at two depths: 5 m (about 1.0 km offshore) and 8 m (about 2.5 km offshore). The trawl mouth was 2.6 m wide and 1.2 m deep, the trawl total length was 5.2 m, and the codend was made of 3.2 mm stretch mesh. The trawl was towed from a skiff at about 2.5 knots. Three stations were sampled with beach seines in August 2007 and September 2009. One haul was made at each station. CPUE was No. fish per haul and mean CPUE was calculated for each sampling period (n = 3 hauls). Three stations, each with two depths, were sampled with the bottom trawl in August 2007 and 2009 and September 2009. CPUE was No. fish per haul and mean CPUE was calculated for each sampling period (n = 6 hauls). The shelf midwater and benthic habitats were sampled as part of an August 2008 survey of the Beaufort Sea, the goal of which was to provide baseline information on areas of potential oil and gas development (Logerwell et al., 2010; Rand and Logerwell, 2010; Parker-Stetter et al., 2011). The midwater was sampled with a Marinovich trawl net as part of an acoustic survey (Parker-Stetter et al., 2011), so the net was deployed to identify constituents of the backscatter across the study area (Fig. 2). Net depth ranged from 15 m to 320 m (maximum depth was 10 m off bottom). The fishing dimensions of the Marinovich net were 3–4 m vertical and 6 m horizontal and the mesh of the codend liner was 12 mm. Vessel speed was maintained at 2–4 knots while towing the net. Net position and headrope height were monitored in real-time during the deployment. CPUE was calculated as No. fish per minute (haul duration) and averaged over all hauls (n = 28 hauls). The shelf benthic habitat was sampled with an 83-112 Eastern otter trawl deployed on a depth-stratified grid of stations. Positions were modified from a regular grid by the presence of ice and untrawlable bottom (Fig. 2). The net had a 25.3 m headrope, a 34.1 m footrope and had a 38 mm mesh liner throughout the body and codend. The net was towed at a vessel speed around 3 knots. Net height and width were measured and monitored in real time with acoustic net mensuration equipment and trawl foot rope contact with the seafloor was monitored using a bottom contact sensor. These data were used to estimate area swept by the net. CPUE was calculated as No. fish per area swept and averaged over all hauls (n = 11 hauls). An ichthyoplankton survey was also part of the August 2008 study (Logerwell et al., 2010). A MARMAP 60 cm bongo net fitted with 0.505 mm mesh nets was deployed at oceanographic sampling stations across the range of depths (Fig. 2). The net was towed double-oblique from the surface down to a depth 10 m off bottom and back to the surface. Ichthyoplankton density was calculated as No./10 m2 and then averaged over all stations (n = 28 stations).

2.2. Chukchi Sea We synthesized data from fish surveys conducted in five different habitats in the Chukchi Sea: beach, nearshore benthic, shelf

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Fig. 1. Stations sampled by fish and ichthyoplankton surveys of the Beaufort and Chukchi Seas, 2007–2012 (total number of stations = 467). Dashed line indicates longitudinal boundary between Beaufort and Chukchi Seas.

Fig. 2. Beaufort Sea study area. Stations sampled in the lagoon (fyke net), beach (seine), nearshore benthic (bottom trawl), shelf benthic (bottom trawl), and shelf midwater (trawl). Stations sampled by ichthyoplankton survey are also shown.

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Fig. 3. Detail of lagoon and nearshore study areas of the Beaufort Sea. Stations sampled by the fyke net, beach seine and nearshore bottom trawl are shown. Gill nets were set near the most northern fyke net and spanning the shore westward towards the other fuke net locations shown in Elson Lagoon (indicated by shaded area).

surface, shelf midwater and shelf benthic. Data were collected from July through September (depending on the survey). The beach and nearshore benthic habitats were sampled as part of the Coastal Assessments research program of NOAA Alaska Fisheries Science Center Auke Bay Laboratory (http://www.afsc. noaa.gov/ABL/Habitat/ablhab_coastal.htm). Fish were captured with a beach seine and bottom trawl on the coast near Barrow (Figs. 4 and 5). The gear and deployment methods were the same as those used to survey the Beaufort beach and nearshore habitats (Thedinga et al., 2013). The beach seine stations were in water <5 m deep. Offshore of each beach seine station, fish were captured with a bottom trawl at two depths: 5 m and 8 m. Six stations were sampled with beach seines in August 2007–2009 and September 2009. One haul was made at each station. CPUE was No. fish per haul and mean CPUE was calculated for each sampling period (n = 6 hauls). Six stations, each with two depths, were sampled with the bottom trawl in August 2007–2009 and September 2009. CPUE was No. fish per haul and mean CPUE was calculated for each sampling period (n = 12 hauls). The shelf surface waters were sampled as part of the Bering Sea-Aleutian Salmon International Survey (BASIS; http://www. npafc.org/science_basis.html) and the Arctic Ecosystem Integrated Survey (EIS; https://web.sfos.uaf.edu/wordpress/arcticeis/). BASIS was a coordinated program of cooperative research on Pacific salmon in the Bering Sea designed to investigate the response of salmon to climate change. The survey typically extended from the Alaska Peninsula to just north of St. Lawrence Island, but in 2007 it included the Bering Strait and northeastern Chukchi Sea. Arctic EIS was a multi-disciplinary study of the oceanography, lower trophic levels, crab and fish communities of the northeastern Bering Sea and eastern Chukchi Sea. Station

spacing was 36–55 km. 25 stations were sampled in September 2007 and 81 were sampled in August-September 2012 (Fig. 4). Pelagic fish were captured with a Cantrawl 300 midwater trawl with a mean horizontal spread of 54 m, mesh size of 12 mm, rigged to sample the top 12 m of the water column. CPUE was No. fish/km2 and mean CPUE was calculated for each survey. The shelf benthic habitat was sampled with a large bottom trawl as part of the Arctic EIS. Sampling design was based on a 55.6 km (30 nmi) square grid pattern with the trawl stations located at the approximate center of each grid cell, resulting in a total of 71 sampling locations (Fig. 4). The survey was conducted during August-September 2012. The bottom trawl was an 83-112 Eastern otter trawl, the same net used to sample the Beaufort shelf benthic habitat. The codend of the net had a liner of 3.2 cm mesh. CPUE was calculated as No. fish/area swept (ha; derived from net mensuration data) and averaged over all hauls. The shelf benthic habitat was also sampled with a smaller net, the 3 m plumb-staff beam trawl (Gunderson and Ellis, 1986). This gear was deployed at stations throughout the Chukchi Sea over the course of seven multi-disciplinary surveys (Fig. 6). Table 2 provides a summary of the years, months, vessel/cruise name and acronym, and number of stations sampled for each survey. Stations were selected by two methods, coincident with other disciplines (2009-RUSALCA and two CSESP surveys), or opportunistic samples when time was made available by the host cruise, usually at night or along a set cruise track (BASIS, COMIDA, 2007 Oshoro Maru and 2008 Oshoro Maru). During all surveys, a 3 m plumb staff beam trawl with a 4 mm mesh codend liner and an effective mouth opening of 2.26 width and 1.2 m height was used to collect benthic fishes. The net was towed at 1–1.5 knots on the bottom for 2–5 minutes, typically, and distance was calculated

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Fig. 4. Chukchi Sea study area. Stations sampling the nearshore (nearshore bottom trawl and beach seine), shelf benthic (bottom trawl), and shelf surface (trawl) are shown.

Fig. 5. Detail of the nearshore study area of the Chukchi Sea. Stations sampled by beach seine and nearshore bottom trawl are shown.

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Fig. 6. Chukchi Sea study area. Stations sampled by plumb staff beam trawl on several surveys are shown.

Table 2 Summary of shelf beam trawl surveys.

Table 3 Summary of ichthyoplankton surveys.

Year

Month(s)

Vessel/Cruise name

No. stations

Year

Month(s)

Vessel/ Gear Cruise name

2007

September

27

2007 2008 2009

August July August

2007 2009 2010 2011

September September August–September August–September

BASIS RUSALCA CHAOZ CHAOZ

2009 2009

September–October July–August

2009

September

Bering Sea-Aleutian Salmon International Survey (BASIS)a Oshoro Marub Oshoro Marub August Chukchi Sea Environmental Studies Program (CSESP)c September CSESPc Chukchi Sea Offshore Monitoring in Drilling Area (COMIDA)d Russian-American Long-term Census of the Arctic (RUSALCA)e

9 15 25

26 30 21

a

http://www.npafc.org/science_basis.html. Norcross et al. (2013a,b). c Day et al. (2013) and Norcross et al. (2013b). d http://www.comidacab.org/Default.aspx, Holladay et al. unpublished data. e http://www.arctic.noaa.gov/aro/russian-american, Holladay et al. unpublished data. b

between positions of the vessel when towing cable was fully deployed and haul back began. CPUE was No. fish/1000 m2 and mean CPUE was calculated for each survey. Fish catch composition for each habitat type was calculated as % CPUE by number averaged over all surveys for that net type/habitat with the exception of the surface trawl surveys. Catch composition for the surface trawl surveys of 2007 and 2012 was very different, so data for each year are presented separately. Even though the beam trawl surveys conducted in 2007, 2008 and 2009 only had

No. stations

60-cm bongo 47 60-cm bongo 31 2 1-m epibenthic sled 56 1-m2 epibenthic sled 84

partial spatial and temporal overlap, the catch compositions among surveys were not dissimilar. The top ten taxa in terms of relative CPUE were similar among all beam trawl surveys, thus the CPUEs from all surveys were averaged and catch composition was calculated. Ichthyoplankton data were collected during four cruises in the Chukchi Sea (Table 3 and Fig. 7). Ichthyoplankton was sampled during the 2007 BASIS and 2009 RUSALCA cruises described above using a standard MARMAP 60 cm bongo net (Posgay and Marak, 1980) fitted with 0.505 mm mesh nets. The net was towed double-obliquely from the surface down to a depth 10 m off bottom and back to the surface. Ichthyoplankton was collected during the BOEM Chukchi Acoustics, Oceanography, and Zooplankton (CHAOZ) surveys in 2010 and 2011 with a 1 m2 epibenthic sled trawl (Tabery et al., 1977) fitted with 0.333 mm mesh nets. In 2010, a single net was fitted on the sled and fished obliquely from the bottom to surface. In 2011, two nets were used with the first net being fished for approximately 5 minutes with the sled in contact with the bottom and the second fished obliquely from the bottom to surface. Presence/absence of all taxa was tabulated and density (No./10 m2) was calculated for the most abundant taxa. The mean density across surveys was then calculated, with one

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Fig. 7. Chukchi Sea study area. Stations sampled by ichthyoplankton nets on several surveys are shown.

exception. Because there was virtually no spatial overlap between the 2009 and the 2007, 2010 and 2011 surveys, the data from the 2009 survey were treated separately.

3. Results and discussion 3.1. Beaufort Sea Salmonids (Salmonidae) made up a large portion of the catch in the lagoon, in both the fyke net and gill net surveys (Table 4). The gill net catches were particularly dominated by salmonids, but these data were from subsistence fishers and were thus biased because salmonids such as Broad Whitefish (Coregonus nasus) and Least Cisco (Coregonus sardinella) were target species. Least Cisco, Chum Salmon (Oncorhynchus keta) and Pink Salmon (Oncorhynchus gorbuscha) dominated the catches. Least Cisco, Chum Salmon and Pink Salmon are Arctic residents so this result is expected. However, a few Sockeye Salmon (Oncorhynchus nerka) and one Chinook Salmon (Oncorhynchus tshawytscha) also were caught. Sockeye Salmon are known to spawn in the Mackenzie River, so the potential for capturing adult Sockeye returning to their natal river is high, however Chinook Salmon have rarely been found in the Arctic, so this result is highly unusual (Stephenson, 2006; Irvine et al., 2009). The size range of the salmonids (426– 775 mm) indicates that these fishes were immature and maturing (Table 5; Farley et al., 2009; Moss et al., 2009; E. Farley, unpubl.). Forage fishes (Smelts (Osmeridae), Pacific Herring (Clupea pallasii) and Pacific Sand Lance (Ammodytes hexapterus)) seemed to have a greater tendency to use habitats close to shore (Table 4). The lagoon, beach and nearshore benthic habitats were characterized by a greater number of forage fish species than the shelf

midwater and benthic. Capelin were found in all habitats and dominated the beach seine catch. Arctic Cod dominated the nearshore bottom trawl, shelf midwater trawl and shelf bottom trawl catch (Table 4). The size range of Arctic Cod in all habitats was similar and fairly broad (26–230 mm; Table 5), and likely spans several age classes from age-0 to age-3 and greater (Norcross et al., 2015). In the three habitats outside the lagoon, Arctic Cod were largest in the shelf benthic, although smaller (age-0) fish were present on the shelf benthic along with the large fish. Arctic Cod eggs, larvae and juveniles were found in the shelf ichthyoplankton (Table 6). Furthermore, catch density of Arctic Cod larvae was greatest of all ichthyoplankton taxa (Table 7). This suggests that Arctic Cod use the Beaufort Sea shelf for spawning and larval development, development of age-0 fish occurs throughout the nearshore and shelf and fish move/stay offshore as they age. Saffron Cod (Eleginus gracilis) was present in the lagoon, beach and nearshore habitats (Table 4). Saffron Cod were also present in the shelf benthic habitat but at low relative CPUE (0.005%). Saffron Cod were largest in length in the lagoon (74–394 mm; Table 5). Results from the ichthyoplankton survey on the shelf showed that Saffron Cod were the second most abundant taxa in the catch (Table 7). Length range of Saffron Cod in the nearshore and beach (22–78 mm) indicates these fish were juveniles (Table 5 (Norcross et al., 2015)). These patterns in larval, juvenile and adult distribution suggest that Saffron Cod spawn on the shelf and move into nearshore and the lagoon as they age. This hypothesis could be addressed by seasonal sampling of multiple life stages of Saffron Cod, including sampling the surface waters (our surface trawl data from the Chukchi Sea have shown relatively high densities of Saffron Cod). In addition, ichthyoplankton sampling in the lagoon would reveal whether they also spawn in that habitat.

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Table 4 Catch composition in the Beaufort Sea, % CPUE. Mesh size of the net is shown at the top, along with the months and years that sampling took place. Sample sizes are reported as hours fished for the fyke and gill net data, and as number of stations across all years for the other data. Catch composition is % CPUE by number averaged over all surveys for that net type/habitat. Cells are coded such that darkest cells represent species/families with the greatest% CPUE for that net type/habitat. Richness (S), Simpson’s Index (D) and Shannon Index (H) for each habitat are shown at the bottom.

a

b

a b

Number of hours the net was fished standardized to a common net length (60 feet). Most of the sculpin in the shelf midwater trawl catch were unidentified.

Three species that are commercially important outside the Arctic, Walleye Pollock (Gadus chalcogrammus), Pacific Cod (Gadus macrocephalus) and Greenland Halibut (Reinhardtius hippoglossoides), were only present in shelf demersal habitat (Table 4). Walleye Pollock ranged in size 80–320 mm (Table 5). These fish were 1–3 years old, and smaller at age than Bering Sea Pollock (Rand and Logerwell, 2010) and thus not likely to be large enough to be of commercial value. Pacific Cod were 240–330 mm (Table 5), likely age 1–3 (Matta and Kimura, 2012). Greenland Halibut specimens have been found across the Beaufort Sea previous to this

work (Chiperzak et al., 1995). Greenland Halibut reported here were 130–400 mm (Table 5), age 1–6 (Matta and Kimura, 2012) younger and smaller than those that recruit to the fishery in the Bering Sea (Barbeaux et al., 2013). None of these three species were present in the shelf ichthyoplankton (Table 6), indicating that they are likely not yet spawning at Arctic latitudes, but were transported from the Bering Sea after being spawned there. The lagoon habitat appears to play a role in the life history of salmonids, forage fishes, and Saffron Cod. Furthermore, there were two species that appeared to use the lagoon habitat to an extent

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Table 5 Fish length in mm (mean and range) in the Beaufort Sea. Mesh size of the net is shown at the top, along with the months and years that sampling took place and the number of fish measured (all species combined). ‘‘ND’’ stands for ‘‘no data’’. The cells are coded the same as Table 1, and thus indicate relative % CPUE.

a

a

a

a

Sample size = 1.

Table 6 Presence/absence of taxa in the ichthyoplankton, in the Beaufort Sea August 2008 (n = 28 stations). Family

Common name

Scientific name

AMMODYTIDEA

Pacific Sand Lance

Ammodytes hexapterus

GADIDAE

Unidentified cod Arctic Cod Saffron Cod

Boreogadus saida Eleginus gracilis

COTTIDAE

Arctic Staghorn Sculpin Shorthorn Sculpin

Gymnocanthus tricuspis Myoxocephalus scorpius

X X

STICHAEIDAE

Unidentified pricklebacks Slender Eelblenny Daubed Shanny

Lumpenus fabricii Leptoclinus maculatus

X X X

LIPARIDAE

Kelp Snailfish Unidentified snailfish

PLEURONECTIDAE

Unidentified flounder Longhead Dab Bering Flounder

Eggs

Larvae

Juveniles

X X

Liparis tunicatus

X X X

X X

X X X

Limanda proboscidea Hippoglossoides robustus

not usual for their taxa, a sculpin and a flatfish (Table 4). Fourhorn Sculpin (Myoxocephalus quadricornis) was one of the dominant species in the lagoon and was not present in shelf midwater and

X

X X

benthic habitats. In contrast, the other sculpin species were found only outside the lagoon from the beach to the shelf. Arctic Flounder (Pleuronectes glacialis) were only caught in the lagoon. Other

E. Logerwell et al. / Progress in Oceanography 136 (2015) 115–132 Table 7 Mean density (No./10 m2) of most abundant taxa in the ichthyoplankton, in the Beaufort Sea August 2008 (n = 28 stations). Most of the catch was larval fish, with a few juvenile Arctic and Saffron Cod. Common name

Scientifica name

Mean density (No./10 m2)

Arctic Cod Saffron Cod Bering Flounder Longhead Dab

Boreogadus saida Eleginus gracilis Hippoglossoides robustus Limanda proboscidea

4.7 0.7 0.3 0.4

flatfishes were only present outside the lagoon from the nearshore to shelf. Another indication that the lagoon habitat may be unique is that taxonomic diversity (D and H) in the fyke net catch was the highest of the habitats examined (Table 4). Perhaps some fish taxa prefer the shallow, warmer and brackish waters of lagoon habitats compared to other habitats offshore (Craig et al., 1982). For example, it has been noted that the abundances of most anadromous species in nearshore and lagoon waters of the Beaufort Sea are correlated with warm temperatures and low salinities (Craig, 1984). There may also be a benefit from greater availability of terrestrial-based nutrients (Dunton et al., 2006) and abundant food resources, predominantly epibenthic mysids and amphipods (Craig and Haldorson, 1981; Griffiths and Dillinger, 1981; Craig, 1984). In addition, anadromous fishes may use lagoons as migration corridors during spring and fall migration (Craig, 1984). Alternatively, there may be conditions in the lagoon that exclude other fishes, such as high seasonal variability in temperature and salinity. For example, in North Salt Lagoon, surface salinity in late June is 0–4 and rises to 27–29 over the course of the summer (T. Sformo, unpubl.) and lagoon temperatures can fluctuate between 0 and 14 °C (Craig et al., 1982). Our data on fish distribution and size across habitats, combined with ichthyoplankton data generates ideas about the spawning and ontogenetic movements of several taxa. As discussed above, Arctic Cod appears to use all habitats for most life history functions, with the largest fish staying/moving offshore to the shelf benthic habitat. Whereas Saffron Cod appear to spawn on the shelf and move into nearshore and the lagoon as they age. Pricklebacks and eelblennies (Stichaeidae) were larger away from the beach (Table 5) and were present as larvae over the shelf (Table 6), suggesting that spawning occurs on the shelf, larvae are transported inshore, and fish move offshore as they age. Snailfish (Liparidae) larvae were present on the shelf (Table 6), suggesting they spawn there. In contrast, eelpouts (Zoarcidae) and poachers (Agonidae), were not found in the ichthyoplankton on the shelf (Table 6), suggesting they spawn elsewhere or at an early season. Several species that were dominant or restricted to the lagoon and/or beach habitats were not found in the shelf ichthyoplankton: Fourhorn Sculpin, Arctic Flounder, sticklebacks (Gasterosteidae), and Capelin (Tables 4 and 6). We hypothesize that they spawn in the lagoon and beach habitats where the adult stages were found. In contrast, Pacific Sand Lance, which was found only in the beach habitat as adults (Table 4) was present in the shelf ichthyoplankton (Table 6). Pacific Sand Lance spawn in subtidal or intertidal sand substrates (Robards et al., 1999) and our data suggest that the larvae (and perhaps the eggs) are then transported offshore. Seasonal surveys of multiple life stages of fish in all habitats would address the hypotheses and unknowns about the life history of these taxa discussed here. Smaller, presumably younger, fish were found in the beach and nearshore benthic habitats, consistent with the hypothesis that these are nursery areas. For example age-0 Arctic Cod (Gallaway and Norcross, 2011), Saffron Cod (Norcross et al., 2015), Slender Eelblenny (Lumpenus fabricii; Norcross et al., 2015), Capelin (Doyle et al., 2002), and sculpin (Cottidae; Gallaway and

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Norcross, 2011), were present in these habitats closer to shore (Table 5). However, age-0 fish were also present further offshore along with older fish. For example, Arctic Cod up to age 3+ were caught in the shelf midwater and shelf benthic habitats along with age-0 fish. Thus the beach and nearshore habitats do not appear to be the only habitats used as nursery areas; although older fish may prefer offshore habitats. 3.2. Chukchi Sea Salmonids (Salmonidae) were found almost exclusively in the surface waters of the shelf, with the exception of a relatively low catch of Arctic Cisco (Coregonus autumnalis) and Pink Salmon in the beach habitat (Table 8). This is not surprising, given that the surface trawl survey was designed to assess the distribution of juvenile salmonids. Pink and Chum Salmon were the dominant species in 2007 and Chum were in 2009. Chinook, Coho and Sockeye Salmon were caught at relatively low % CPUE. As discussed above for the Beaufort Sea results, it is unusual to catch Chinook Salmon in the Arctic (Stephenson, 2006; Irvine et al., 2009). Salmonids ranged from 170 to 331 mm (Table 9) and were thus age-0 (Chinook) to juveniles or maturing (Farley et al., 2009; Moss et al., 2009). The relatively high CPUE of juvenile Pink and Chum Salmon during 2007 (Table 8) provided some evidence that increased warming in the Arctic, evidenced by the 2007 sea ice minimum (Woodgate et al., 2010), may be beneficial for future salmonid productivity in the region. For instance, adult Pink Salmon were captured in anomalously high numbers within subsistence nets off Barrow, Alaska during 2008 (E. Farley, unpubl.). Perhaps not surprisingly, Pink Salmon catch made up 22% of total CPUE in the lagoon gill net survey in the Beaufort Sea (this study). Juvenile Pink Salmon return to their natal spawning streams after one year in the ocean, suggesting that the high CPUE of juvenile Pink Salmon during 2007 was linked to increased catches the following year. Similarly, anomalously high numbers of adult Chum Salmon were captured off Barrow in subsistence nets during 2009 and 2010 (E. Farley, unpubl.), following the typical 2–3 year marine life history for these fish. The summer sea temperatures in the Chukchi Sea were very warm during 2007 (Woodgate et al., 2010), potentially contributing to the success of juvenile Pink and Chum Salmon during that year. Thus future warming in the Arctic, particularly during summer months, may contribute to better early marine growth for juvenile salmonids and increased returns to spawning habitat (Andrews et al., 2009; Moss et al., 2009). Forage fishes (Smelts (Osmeridae), Pacific Herring and Pacific Sand Lance) were found in all habitats, although Pacific Sand Lance was the only forage species caught in the beam trawl (Table 8). The greatest relative densities of forage fishes were found in the beach and shelf surface habitats, in particular Capelin. Capelin were caught in a somewhat similar range of lengths in all habitats, although the smallest fish (29 mm) were found in the beach habitat and the largest (180 mm) in the shelf surface waters (Table 9). This range of lengths likely corresponds to post flexion larvae (Doyle et al., 2002) to age 3+ (Brown, 2002). The length of Rainbow Smelt (Osmerus dentex) increased from the nearshore to the shelf from a minimum size of 72 mm to a maximum of 300 mm (Table 9). Pacific Herring were caught in a similar range of lengths in the shelf surface and benthic habitats. The largest range of Herring sizes occurred in the shelf surface habitat (in 2012), 78–313 mm (Table 9), likely ages <1 to 9+ (Lassuy, 1989). Capelin and Pacific Sand Lance spawn on or near the beach (Brown, 2002; Robards et al., 1999), thus the catches of larval and age-0 forage fishes suggests that after spawning, juvenile fishes spend some amount of time in the nearshore before moving offshore into deeper waters. Large spawning events of

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Table 8 Catch composition (% CPUE) from each net type/habitat in the Chukchi Sea. Mesh size of the net and survey months are shown at the top. Sample size is the number of stations sampled summed over all years. Cells are coded such that darkest cells represent species/families with the greatest% CPUE for that net type/habitat. Richness (S), Simpson’s Index (D) and Shannon Index (H) for each habitat are shown at the bottom.

Capelin on beaches near Barrow have been reported (S. Johnson, unpubl.), whereas spawning areas of Pacific Sand Lance and other forage fishes in the Arctic are largely unknown. Arctic Cod were present in all habitats. They made up relatively large portions of the catch in the nearshore and shelf benthic habitats (Table 8). The minimum size of Arctic Cod was somewhat similar across habitats, 30–40 mm (Table 9), age-0 (Gallaway and Norcross, 2011). However, the maximum length of Arctic Cod increased from the beach to the benthic shelf from 66 mm to 260 mm (age-0/1 to age-3+ (Gallaway and Norcross, 2011)).

Arctic Cod larvae were one of the top four most abundant taxa in the ichthyoplankton catch (Table 11), suggesting that they use the shelf habitat for larval development and possibly spawning. The pattern in fish lengths and ichthyoplankton catch suggests that Arctic Cod use nearshore and shelf habitats for multiple life history functions, with the older Cod staying/moving offshore to the shelf benthic habitat. Saffron Cod were likewise found in all habitats, making up a large portion of the catch in the shelf surface habitat (Table 8). Saffron Cod had a similar size distribution as Arctic Cod across

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Table 9 Fish length in mm (mean and range) in the Chukchi Sea. Mesh size of the net is shown at the top, along with the months and years that sampling took place and the number of fish measured (all species combined). ‘‘ND’’ stands for ‘‘no data’’. The cells are coded the same as Table 8, and thus indicate relative % CPUE.

a

a

If no min–max shown, only one fish was measured.

habitats. The smallest fish were 26–40 mm (Table 9), age-0 (Norcross et al., 2015). The maximum lengths increased from 50 mm in the beach habitat to 360 mm on the shelf, likely spanning at least 3 age classes (Table 9). This suggests that their use of different habitats through development is similar to that of Arctic Cod. Pacific Cod and Walleye Pollock, important commercial cod (Gadidae) species in the Bering Sea, were found in the nearshore and shelf benthic habitats, at low relative CPUE (0.5% or less; Table 8). Walleye Pollock were also found in the shelf surface habitat at low % CPUE (Table 8). Walleye Pollock ranged in size from 58 to 160 mm (Table 9). These fish were likely mostly age-1 to age-2 (Brown et al., 2001; Hinckley, 1984) and thus were not commercially valuable (Walleye Pollock recruit to the Bering Sea fishery at age-3 or-4 (Ianelli et al., 2013)). Although no adult Walleye Pollock were caught, their eggs, larvae and juveniles were found in the shelf ichthyoplankton survey (Table 10). These could have been transported into the Chukchi Sea from the Bering Sea, or could have been spawned and reared in the north.

Documentation of mature adult Walleye Pollock in the Chukchi is needed to confirm spawning activity for this species in the Arctic. In addition, determining the developmental stage of eggs caught in the Arctic could help reveal whether eggs may have been transported from the south or were spawned locally. Pacific Cod, another important commercial cod in the Bering Sea, ranged in size from 100 to 254 mm (Table 9), likely age 1–2 (Matta and Kimura, 2012). Pacific Cod larvae were not found in the ichthyoplankton (Table 10) so we hypothesize that these fish were spawned in the Bering Sea and transported north. Flatfishes (Pleuronectidae) were found in all habitats. The greatest number of flatfish species and the greatest relative CPUE occurred in the shelf benthic habitat (Table 8). Bering Flounder (Hippoglossoides robustus) and Yellowfin Sole (Limanda aspera) dominated the shelf benthic flatfish catch, although the % CPUE was not very large (around 5%). Species that are commercially important in the Bering Sea, Yellowfin Sole, Greenland Halibut and Alaska Plaice (Pleuronectes quadrituberculatus), ranged in average size from 45 to 191 mm (Table 9). This corresponds to ages 0–2

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Table 10 Presence/absence of taxa in the ichthyoplankton, in the Chukchi Sea September 2007–2011 (n = 218 stations, all years). Family

Common name

Scientific name

2007, 2010, 2011

OSMERIDAE

Capelin Unidentified smelts

Mallotus villosus

AMMODYTIDAE

Pacific Sand Lance

Ammodytes hexapterus

GADIDAE

Arctic Cod Walleye Pollock Unidentified cod

Boreogadus saida Gadus chalcogrammus

COTTIDAE

Butterfly Sculpin Arctic Staghorn Sculpin Spatulate Sculpin Shorthorn Sculpin Hamecon Unidentified Myoxocephalus

Hemilepidotus papilio Gymnocanthus tricuspis Icelus spatula Myoxocephalus scorpius Artediellus scaber

STICHAEIDAE

Slender Eelblenny Daubed Shanny Blackline Prickleback Fourline Snakeblenny Stout Eelblenny Arctic Shanny Unidentified Lumpenus

Lumpenus fabricii Leptoclinus maculatus Acantholumpenus mackayi Eumesogrammus praecisus Anisarchus medius Stichaeus punctatus

LIPARIDAE

Unidentified Liparis Variegated Snailfish Kelp Snailfish

Liparis gibbus Liparis tunicatus

X X X

AGONIDAE

Arctic Alligatorfish Gray Starsnout Alligatorfish

Aspidophoroides olrikii Bathyagonus alascanus Aspidophoroides monopterygius

X X X

PLEURONECTIDAE

Bering Flounder Unidentified Limanda Yellowfin Sole Longhead Dab Sakhalin Sole Alaska Plaice

Hippoglossoides robustus Limanda aspera Limanda proboscidea Limanda sakhalinensis Pleuronectes quadrituberculatus

X X X X

Whitespotted Greenling Masked Greenling

Hexagrammos stelleri Hexagrammos octogrammus

X X

Eggs

HEXAGRAMMIDAE

Scientific name

Arctic Cod Bering Flounder Yellowfin Sole Longhead Dab

Boreogadus saida Hippoglossoides robustus Limanda aspera Limanda proboscidea

Juveniles

Eggs

X X

Larvae X

X X X X

X X

X X

X X

X X

X X X X X

X

X

Table 11 Mean density (No./10 m2) of most abundant taxa in the ichthyoplankton, in the Chukchi Sea September 2007–2011 (n = 218 stations, all years). Common name

Larvae

2009

Mean density (No./10 m2) 2007, 2010, 2011

2009

0.02 2.5 80.2 0.8

1.3 0.2

for Greenland Halibut and ages 0–6 for Yellowfin Sole (Matta and Kimura, 2012), younger and smaller than those that recruit to the fishery in the Bering Sea (Barbeaux et al., 2013; Wilderbuer et al., 2013). Alaska Plaice was not found in the shelf ichthyoplankton (Table 10), suggesting they are not spawning in the Arctic. Greenland Halibut were similarly not found in the ichthyoplankton (Table 10), but Greenland Halibut larvae grow to large sizes in the plankton (80 mm in the Bering Sea, Duffy-Anderson, unpubl.) and may be too large to be sampled effectively by the zooplankton nets used in these surveys. In fact, Greenland Halibut ranging in size from 63 to 80 mm were caught in the shelf surface trawl (Table 9) so it appears that this species may spawn in the Arctic. Yellowfin Sole was one of the top four species in the ichthyoplankton, dominating the catch by two orders of magnitude in some surveys (Table 11). Although Greenland Halibut and Yellowfin Sole larvae were found in the Chukchi, the fish caught in the bottom

X X X X X X X

X X

X X

X X

X X

X X

trawls were sub-adults. Age data and collection of spawning females would clarify whether, when and where these species are spawning in the Chukchi Sea. We examined the shelf surface trawl data for each year (2007 and 2012) separately because of striking between-year differences in catch composition. In 2007 Saffron Cod dominated the catch whereas in 2012 Capelin were dominant (Table 8). 2007 was an anomalous year due to warm water advected to the Chukchi (Woodgate et al., 2010), coincident with the first new record ice minima (NCAR, 2007). Cooler summer water temperatures prevailed in the Chukchi Sea during years after 2007 (Proshutinsky et al., 2011; Timmermans et al., 2012). Capelin are thought to prefer cooler water temperatures (Anderson and Piatt, 1999), so this difference between 2007 and 2012 ocean conditions may explain the difference in species composition in the surface waters. We examined data from two different gear types deployed in the same habitat, the benthic shelf, and not surprisingly the catch composition was different. The shelf plumb staff beam trawl catch was dominated by sculpins (Arctic Staghorn (Gymnocanthus tricuspis) and Shorthorn (Myoxocephalus scorpius)) and by Slender Eelblenny. In contrast, the catch of the larger mesh shelf 83-112 Eastern otter bottom trawl was dominated by Arctic Cod (Table 8). Arctic Cod were present in the beam trawl catch, but at lower relative density. Similarly, Saffron Cod were caught in both nets, but at a lower relative density in the beam trawl. Differences in net size and speed of deployment likely contributed to this pattern. A paired trawl experiment in the Chukchi Sea during the 2012 Arctic EIS survey allowed for a comparison of the

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catch of the beam trawl and the 83-112 trawl data (Britt et al., 2013). Although the two trawls caught a similar number of fish taxa per haul, a station-by-station comparison showed that the catch composition was very different: 33% of the fish species caught were gear-specific. The beam trawl was more effective at catching juvenile fishes, whereas the 83-112 trawl was more efficient at capturing larger and more mobile organisms. Britt et al. (2013) conclude that the two trawls are complementary sampling tools and used together provide a more inclusive catalog of species composition than either gear used alone. Our data on fish distribution and size across habitats in the Chukchi Sea, combined with ichthyoplankton data generate hypotheses regarding life history and habitat use of several taxa. As discussed above, it appears that Arctic and Saffron Cod use multiple habitats for multiple life history functions, with the older fish staying/moving offshore. A similar pattern was observed for other taxa. Sculpins (Cottidae) were present in all habitats, with greatest % CPUE in the shelf surface and benthic habitats (Table 8). The largest fish were in the shelf benthic, likely age-4 or higher (Table 9). Although fish were smaller and likely younger towards shore (age-0 to age-3), smaller, presumably age-0 sculpins were found offshore with the larger sculpins (Gallaway and Norcross, 2011). Pricklebacks (Stichaeidae) were likewise present in all habitats, with greatest relative CPUE in the nearshore benthic and shelf benthic habitats (Table 8). Fish increased in size from the beach out to the offshore shelf habitat being as large as 205 mm in the shelf surface habitat and as large as 390 mm in the shelf benthic habitat (Table 9), likely greater than age-3 (Gallaway and Norcross, 2011). Similar to the cods (Gadidae) and sculpins, age-0 pricklebacks (30–50 mm) were also caught in the shelf benthic habitat along with the older, larger fish (Table 9). Snailfishes (Liparidae) and poachers (Agonidae) were found in all habitats but at relatively low% CPUE (2% or less; Table 8). Eelpouts (Zoarcidae) were found in all habitats, except the beach, at 4% CPUE or less (Table 8). Snailfishes, eelpouts and poachers all increased in size from the beach through the nearshore and to the offshore surface and bottom habitats (Table 9). Similar to the species discussed above, smaller and presumably younger fishes were also present in the offshore habitats along with the bigger, older fishes. Smaller, presumably younger, fishes were found in the beach and nearshore benthic habitats, suggesting these are nursery areas. For example age-0 Arctic Cod (Gallaway and Norcross, 2011), Saffron Cod (Gallaway and Norcross, 2011), Slender Eelblenny (Gallaway and Norcross, 2011), Capelin (Doyle et al., 2002) and sculpins (Gallaway and Norcross, 2011) were present in these habitats closer to shore. However, age-0 fishes were also present further offshore along with older fishes, age 3 and higher. 3.3. Overall patterns The sampling effort differed among the two seas, particularly on the shelf, with fewer surveys occurring during fewer years in the Beaufort Sea compared to the Chukchi Sea. This could lead to bias in fish community composition or distribution due to different sample sizes and/or different oceanographic conditions among years. Nonetheless, there were numerous similarities between the patterns observed in the two seas. Salmon (Oncorhynchus sp.) were most prevalent in the lagoon habitat in the Beaufort Sea and the shelf surface habitat in the Chukchi Sea. However, no shelf surface surveys have been conducted in the Beaufort, so it is as yet unknown if salmon use the surface waters as they do in the Chukchi. Conversely, no surveys of Chukchi lagoons have been conducted, so it is unknown if salmon use lagoons as they do in the Beaufort. Lagoon habitat is less prevalent in the Chukchi than the Beaufort, so it is possible that the salmon found in the Chukchi Sea are restricted to the shelf during

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their marine phase. Surveys of the surface waters of the Beaufort and the lagoons of the Chukchi are needed to resolve this apparent difference in habitat use of salmon. Pink and Chum Salmon were common salmon species in both Seas, not surprisingly, given that they are Arctic residents. Chinook Salmon were also caught, albeit at relatively low abundance, in both Seas. Chinook Salmon are rarely seen in the Arctic leading to speculation that their range may be expanding due to climate change (Moss et al., 2009), but more evidence is needed to confirm this hypothesis (Stephenson, 2006). Forage fishes (Pacific Sand Lance, Pacific Herring, Capelin, Rainbow Smelt) in both Seas seem to prefer habitats relatively close to shore such as the lagoon, beach and nearshore. As discussed above (in the Beaufort Sea section), lagoon habitat may be preferred due to the relatively warm and low salinity waters, abundant food resources and proximity to natal streams for anadromous fishes. The brackish water characteristic of lagoons can extend out to the beach and nearshore depths (<10 m), is distinct from adjacent marine waters and provides important feeding habitat for anadromous and marine fishes in summer (Craig, 1984). During winter this estuarine band is absent and most anadromous fishes return to North Slope rivers and marine fishes move offshore as nearshore waters freeze. The nearshore of the Chukchi Sea coast is similarly warm and low salinity during summer due to solar heating and freshwater inputs (R. Heinz, unpubl.). Capelin and Pacific Sand Lance use beach and intertidal habitats for spawning in summer (Robards et al., 1999). Mass spawning of Capelin has been observed on beaches near Barrow in previous studies (George et al., 2009). Forage fishes also occurred in the surface waters of the Chukchi Sea shelf with some species, such as Capelin, dominating the catch. A surface trawl survey in the Beaufort Sea is needed to determine whether this distribution is unique to the Chukchi Sea or typical of Arctic forage fishes. Arctic Cod dominated the benthic habitats of the nearshore and shelf in both Seas. Arctic Cod were also relatively abundant in the shelf midwater of the Beaufort Sea. Although we present no survey data from the Chukchi midwater habitat, preliminary results from the 2012 and 2013 acoustic-trawl surveys of the Arctic Ecosystem Integrate Survey (EIS) show that the one of the primary acoustic targets observed in the midwater of the Chukchi Sea were age-0 Arctic Cod (https://web.sfos.uaf.edu/wordpress/arcticeis/). We hypothesize that the life history distribution of Arctic Cod is similar for the Beaufort and Chukchi Seas: spawning and larval development takes place on the shelf, development of age-0 fish occurs throughout the nearshore and shelf and fish move/stay offshore as they age. The life history distribution of Arctic Cod in the Chukchi and Beaufort Seas has not been documented in detail. It is known that they spawn under sea ice during winter, between November and March (Rass, 1968; Craig et al., 1982). The eggs are buoyant and remain at the surface through hatching (Graham and Hop, 1995). Larvae remain at the surface for several months after hatching, until September when they settle to the bottom (Baranenkova et al., 1966; Sekerak, 1982). Age-0 fish are known to be planktonic and found in bays, fjords and offshore. Juveniles and adults are understood to be found either dispersed throughout the water column of concentrated in schools at the ice edge, along shorelines in summer and in deep offshore waters (Bradstreet et al., 1986). Our synthesis of Arctic Cod distribution based on the limited large scale survey data available provides a more current and more detailed state of understanding of how Arctic Cod may use different habitats throughout their life history. Field studies focusing on Arctic Cod life history that would sample multiple age classes in multiple habitats throughout the year are needed to confirm and refine our ideas. We suggest that the distribution and habitat use of Saffron Cod was different between the two Seas. In the Beaufort, the data are

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consistent with fish spawning on the shelf and moving into the nearshore and lagoon as they age. In the Chukchi it appears that, similar to Arctic Cod, they use nearshore and shelf habitats for multiple life history functions with older fish staying or moving offshore. As discussed above, no surveys have been conducted in Chukchi lagoons, so the use of lagoons by Saffron Cod in this area cannot be ruled out. However, given the relative paucity of lagoon habitat in the Chukchi, it is possible that this habitat use behavior is unique to the Beaufort Sea. The little published information on Saffron Cod life history indicates that they spawn in winter, December–February, in relatively cold and shallow waters close to shore. The eggs are demersal and non-adhesive. Larvae and juveniles have been caught in surveys of Norton Sound, Bering Strait and eastern Bering Sea (Dunn and Matarese, 1987); and recently as an ‘‘invader’’ of nearshore habitats of Prince William Sound, Alaska (Johnson et al., 2009). As suggested above, for Arctic Cod, our synthesis provides the most current and detailed conceptual models for the life history distribution of Saffron Cod and further surveys of multiple life history stages of Saffron Cod across seasons are needed. Species of cod and flatfish that are commercially important elsewhere were found in both Seas: Walleye Pollock, Pacific Cod, and Greenland Halibut. Yellowfin Sole were also found in the Chukchi Sea. None of these species were found in the ichthyoplankton in the Beaufort Sea suggesting they are not yet spawning that far north. In contrast, Walleye Pollock and Greenland Halibut larvae were present in the Chukchi Sea, as were high abundances of Yellowfin Sole larvae. Larvae were present; however, adult fish of these species were not. Continued monitoring of multiple life stages of Walleye Pollock and flatfishes in the Arctic, including spawning adults, if present, will determine whether the ranges of these valuable species are shifting north with climate change. However, the current perspective is that bottom water temperatures in the Arctic are too cold to support spawning Walleye Pollock and that the sub-adult fish that are caught at high latitudes were advected by currents from spawning locations in the Bering Sea (Hollowed et al., 2013). In contrast, Greenland Halibut are found in Arctic latitudes in the Atlantic and it is thought that there is potential for the spawning range of Greenland Halibut to extend into the Pacific Arctic given appropriate temperature and feeding conditions (Hollowed et al., 2013). Similarly, there is a potential for the range of Yellowfin Sole to extend into the Arctic given its presence at high latitudes and eclectic diet (Hollowed et al., 2013). Regardless of whether any of these species are spawning in the Arctic at this time, none of the fish caught in our surveys were large enough to be commercially valuable. Patterns in taxonomic diversity across habitats differed between the Beaufort and Chukchi Seas. The dominance of Capelin in the beach and shelf surface habitats of the Chukchi Sea resulted in the lowest taxonomic diversity (D and H indices) compared to other Chukchi habitats. This is in contrast to the Beaufort Sea where the nearshore benthic, shelf midwater and shelf benthic habitats had low diversity scores due to the dominance of Arctic Cod. The Chukchi Sea shelf beam trawl catch data had the highest indices of taxonomic diversity, due to the distribution of catch among gadid, sculpins, pricklebacks, eelpouts, and flatfish. No one species made up more the 30% of the total CPUE in the shelf beam trawl catch. The highest taxonomic diversity in the Beaufort Sea was observed in the lagoon, due to the distribution of catch among salmonids, smelts, sticklebacks, cod, sculpins and flatfishes. Nearshore habitats have been shown to be nursery areas in Northeast Pacific marine systems, such as Southeast Alaska (Johnson et al., 2005), Bering Sea-Aleutian Islands (Thedinga et al., 2008), Prince William Sound, Alaska (Norcross et al., 2001) and the Gulf of Alaska (Norcross et al., 1995; Brown, 2002). Species groups using the nearshore in these systems for juvenile

development include cod, forage fishes and salmonids. For many taxa in our datasets age-0 fishes were found nearshore and older fishes were further offshore consistent with the idea that the nearshore provides nursery habitat. However, this does not appear to be a straightforward ontogenetic offshore migration because at least some age-0 fishes were present offshore with the older fishes. Again, field studies of multiple ages classes in multiple habitats throughout the year would help resolve and interpret these patterns. Arctic nursery habitat may not be typical, compared to other temperate and tropical areas (Beck et al., 2001). In temperate and tropical areas, nursery habitat often includes physical structure such as eel grass beds or kelp patches. Much of the nearshore areas of the Arctic are overlaid with shorefast ice for most of the year. Ice keels, extending as deep as 20–30 m, can cause significant bottom scouring as the ice deforms in mid-winter and moves out in summer. Consequently, there are few physical features or vegetation to provide juvenile fish with cover in the nearshore. Instead of physical cover, oceanographic conditions (i.e. temperature and salinity) in nearshore waters during the Arctic summer may provide age-0 fish with a predator refuge that simultaneously traps prey and offers temperatures that optimize growing conditions (Jarvela and Thorsteinson, 1999). The relative abundance estimates of small fishes near shore could have been influenced by differences in gear type. The nets fished on the beach and in the nearshore benthic habitat had smaller mesh than the shelf surface trawl and shelf bottom trawl. The beach and nearshore nets were also smaller in overall dimensions. There is a possibility that bigger fish were able to avoid the smaller mesh inshore nets, because they were towed at slower speeds than the larger shelf bottom trawl. Another concern might be that the larger mesh offshore nets were not capable of catching small fish. However small fishes of many taxa were caught in the nets fished offshore, so this bias does not appear to be a problem at the resolution of the analyses discussed above. All the surveys that contributed to the synthesis of fish distribution and habitat use across habitats were conducted in spring-fall, ice-free seasons. This highlights the need for surveys of fishes in their overwinter habitats, which would need to be conducted under the ice and in polynyas such as those near Wrangell and St. Lawrence Islands. 4. Summary In summary, our synthesis of fish survey data across a spectrum of habitats in the Beaufort and Chukchi Seas revealed more similarities than differences. Some highlights are that Chinook Salmon may be moving into the Arctic; and that the nearshore is a habitat for forage fish across age classes and also a nursery area for other species. In addition, we document the presence of commercially important Walleye Pollock and flatfishes and although they are not likely spawning in the Arctic now, the flatfishes have potential to expand their range into the Arctic. Finally, we provide the most current and detailed conceptual models for the life history distribution of key gadids in Arctic food webs: Arctic and Saffron Cod. We also identify research gaps, such as the need for surveys of the surface waters of the Beaufort Sea, surveys of the lagoons of the Chukchi Sea, and winter season surveys in all areas. We recommend field studies on fish life history that sample multiple age classes in multiple habitats throughout the year to confirm, resolve and interpret the patterns in fish habitat use that we observed. Acknowledgements The authors thank 3 anonymous reviewers for their constructive comments. This study is part of the Synthesis of Arctic

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Research (SOAR) and was funded in part by the U.S. Department of the Interior, Bureau of Ocean Energy Management, Environmental Studies Program through Interagency Agreement No. M11PG00034 with the U.S. Department of Commerce, National Oceanic and Atmospheric Administration (NOAA), Office of Oceanic and Atmospheric Research (OAR), Pacific Marine Environmental Laboratory (PMEL). This research is contribution EcoFOCI-0835 to NOAA’s Ecosystems and Fisheries-Oceanography Coordinated Investigations.

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