Arctic cod (Boreogadus saida) in fjord and glacial habitats: a collaborative study with Uummannap Kangerlua fishers
Abstract
Arctic cod (Boreogadus saida) (Lepechin, 1774) is often found in front of glaciers, which is the least studied of the species’ habitats. Uummannap Kangerlua and Sullorsuaq in West Greenland provide a unique opportunity to study Arctic cod in the glacial habitat, as they are among the few places with a directed Arctic cod fishery. Inuit fishers from these fjords regularly catch Arctic cod as fresh bait for the Greenland halibut (Reinhardtius hippoglossoides) (Walbaum, 1792) longline fishery, the main economic activity in the region. We collaborated with the fishers to learn about Arctic cod through interviews and collection of fish samples. Ten informants provided information on fishing areas, fishing methods, interannual variability in the catches, relationships with temperature and sea ice, and reported a spawning area near Saattut. One of the two samples collected contained only 21% males, which were longer, heavier, older, and had a higher gonadosomatic index than females. This skewed sex ratio may result from size-selective predation or spawning migration. Collaboration with fishers provided important baseline information on Arctic cod in fjord and glacial habitats. Continued efforts could bring a better understanding of key aspects of Arctic cod that are relevant for all Arctic communities located near glacial fjords.
Graphical Abstract
Eqalugaq (Boreogadus saida) kangerlunni uukkartarfinnilu uumaffilik: aalisartut suleqatigalugit uummannap kangerluani misissuineq
Eqalugaq (Boreogadus saida) (Lepechin, 1774) sermit uukkartarfiini naammattuugassaanerusarpoq, tamaanilu uumaffeqartut misissuiffigineqannginnerpaajusarput. Uummannap Kangerlua aammalu Sullorsuaq Kalaallit Nunaata kitaaniittut sermit uukkarfiini immikkuullarissumik misissuinissamut periarfissagissaartitseqaat, taakkunanimi eqalugarniarnerit qaqutigoortut pisaramik. Kalaallit aalisartut tamaani eqalugarniartaramik, ningittagarsorlutik qaleralinniarnerminni (Reinhardtius hippoglossoides) (Walbaum, 1792) neqitassatut atugassaminnik, qaleralinniarnermi tamaani aningaasarsiorfiit pingaarnersaraat. Aalisartut apersortarlugit suleqatigisarpagut eqalukkat annerusumik ilisimasaqarfiginerulerusukkatsigit misissugassanillu pissarsiffigisarlutigit. Aalisartut qulit sumi eqalugarniartoqartarneranut, qanoq aalisarneqartarnerinut, ukiup qanoq ilinerani pisarineqartarnerisa nikerartarnerinut, immap kissassusianut immallu sikuanut qanoq attuumassuteqarnerannut, Saattullu eqqaani suffisarfeqarnerinut tunngasunik paasissutissanik katersuiffigisarpagut. Eqalukkat tunniunneqartut karsit marluusut aappaani angutivissat amerlassutsimikkut taamaallaat 21%-raat, anginerullutik, oqimaannerullutik, utoqqaanerullutik, arnavissanullu sanilliullutik timaasa angissusaanut sanilliullutik kinguaassiutaasa angissusaat arnavissaninngarnik anginerupput. Eqalukkat taamatut suiaassutsimikkut assigiinngissuteqarnerat uumasut annerit annersiorlutik nerisareqatigiinneraninngaaneersinnaavoq imaluunniit suffiniarlutik ingerlaartoqarneranik isumaqarsinnaalluni. Aalisartunik suleqateqarnerput eqalukkat kangerlummi sermillu uukkartarfiini uummaveqarnerannik tunngaviusumik pingaaruteqartumillu paasisaqarnerulersitsivoq. Suliniutillu ingerlateqqinneratigut eqalukkanut tunngatillugu suut pingaaruteqarluinnartuunersut ilisimaneqarnerulersinnaavoq, issittumilu inuiaqatigiinnut sermit uukkartartut eqqaani najugalinnut attuumassuteqartumik pingaaruteqartumillu paasinninnerulertoqarsinnaassalluni.
1. Introduction
Arctic cod (B. saida, eqalugaq in Greenlandic) is found in a variety of habitats. It can form dense schools near the surface in coastal waters (e.g., Welch et al. 1993, Crawford and Jorgenson 1993), appear directly under or within sea ice (e.g., Gradinger and Bluhm 2004; David et al. 2016), aggregate loosely in deep waters (e.g., Benoit et al. 2008; Geoffroy et al. 2011), and dwell near the bottom of fjords (e.g., Falk-Petersen et al. 1986; Fey and Weslawski 2017; Christiansen et al. 2012). Aggregations of ringed seals (Pusa hispida) (Schreber, 1775) and beluga whales (Delphinapterus leucas) (Pallas, 1776) preying on Arctic cod in front of outlet glaciers suggest the existence of another type of habitat (Hamilton et al. 2019). However, as the presence of icebergs and the risk of ice calving makes accessing and sampling fish in front of glaciers difficult and dangerous, the glacial habitat has been the least studied to date.
Arctic cod is a key species in Arctic marine food webs, channeling energy from zooplankton to higher trophic levels, such as marine mammals and seabirds (e.g., Welch et al. 1992). Climate change is expected to have negative effects on Arctic cod populations, especially in regions at the southern limits of the species range, such as the Bering, Labrador, and Barents seas (Fossheim et al. 2015; Marsh and Mueter 2019). In the West Greenland regions of Upernavik, Uummannaq, and Qeqertarsuup Tunua (Disko Bay), Arctic cod is already coping with sea surface temperatures (SSTs) exceeding the upper thermal tolerance limits of the eggs and the larvae of 2 °C and 5 °C, respectively (Bouchard et al. 2021; Geoffroy et al. In press). A decline in Arctic cod populations could affect the structure and functioning of Arctic food webs, with negative effects on Arctic cod predators. In turn, this could have important societal implications, since predators like marine mammals and seabirds support Arctic communities in many ways, including through hunting, fishing, and ecotourism, as well as by their cultural and spiritual value (e.g., Steiner et al. 2019, 2021; Geoffroy et al. In press).
Arctic cod is regularly fished by Greenlandic Inuit fishers in Uummannap Kangerlua and Sullorsuaq (Uummannaq and Vaigat fjords), to use as fresh bait for the longlines targeting Greenland halibut (R. hippoglossoides, qaleralik in Greenlandic). Although their knowledge of fishing with modern technology is of a more contemporary nature, it is rooted in a rich Indigenous and local context (Government of Greenland 2022). The knowledge of Uummannap Kangerlua and Sullorsuaq fishers is, thus, unique in the Arctic in providing information about Arctic cod in glacial fjords.
The objective of the present study is to document fishers’ knowledge of Arctic cod in West Greenland glacial fjords and to complement this knowledge with preliminary information derived from Western science. Our Two-Eyed Seeing approach (Reid et al. 2021) is well in line with Greenland’s first national research strategy, which emphasizes the value and importance of integrating Indigenous and local knowledge into research projects (Government of Greenland 2022). Here, we present key elements of Arctic cod and its fishery in Uummannap Kangerlua and Sullorsuaq, as shared by fishers during interviews, and biological data from Arctic cod collected by fishers in front of two glaciers.
2. Materials and methods
2.1. Ethics approval
The project was approved by the Greenland Research Council and the Greenland Institute of Natural Resources (GINR). All interviewees gave oral informed consent after the explanation of the project in Greenlandic. All participants gave their consent to be voice-recorded. We did not ask all the participants if they accepted to be named in scientific publications related to the project, and therefore are using numbers to identify the informants. The collection of specimens was conducted in accordance with all laws, guidelines, and regulations applicable in Greenland.
2.2. Study area
The study area comprises Uummannap Kangerlua, one of the largest fjords in Greenland, which hosts 12 outlet glaciers, and Sullorsuaq, which hosts 4 outlet glaciers (Fig. 1; Rignot et al. 2016). Uummannap Kangerlua hosts one town, Uummannaq (1447 inhabitants, Statistics Greenland 2022), five inhabited settlements, and two settlements abandoned after the 2017 tsunami whereas Sullorsuaq hosts two settlements (Fig. 1). The main economic activity of the region is the Greenland halibut (R. hippoglossoides) longline fishery operated from a fleet of individually owned dinghies in the open water season (Fig. 2). Winter fishing for Greenland halibut and harvesting of seals and narwhals (Monodon monoceros Linnaeus, 1758) are other important activities, carried out by snowmobile, dog sled, or dinghy. The marine ecosystem of Uummannap Kangerlua and Sullorsuaq is at the junction of Arctic and boreal realms where both Arctic endemic fish such as Arctic cod (B. saida) and ice cod (Arctogadus glacialis (Peters, 1872), eqalugaasaq in Greenlandic) co-occur with Atlantic fish such as capelin (Mallotus villosus (Müller, 1776), ammassak in Greenlandic), and Atlantic cod (Gadus morhua Linnaeus, 1758, saarullik in Greenlandic). Landfast ice used to cover Uummannap Kangerlua between November/December and June, but nowadays the sea-ice season is much shorter (typically January–May) with increased variability in freeze-up and breakup dates, affecting the travel routines of residents (Baztan et al. 2017; Cooley et al. 2020; Steiro et al. 2021). A shift in ocean temperatures occurred in the mid-1990s as observed in summer SST and mean annual temperature at 150–600 m (Holland et al. 2008; Bouchard et al. 2021).
Fig. 1.
Fig. 2.
2.3. Study design
The interview questions were developed by the first author, reviewed by the other co-authors, and translated into Greenlandic. The questions were grouped by themes or specific research questions as follows: basic background data about the informants, catch of Arctic cod and uses, knowledge about Arctic cod from harvested animals, trends in Arctic cod catches, distribution, seasonal occurrence and local abundance, and biology (spawning). The questions and a short description of the project (in Greenlandic) were sent to the chairman and the CEO of KNAPK (Fishermen and Hunters Association in Greenland) to, first, inform Greenland hunters and fishers about the project, and second, to give them an opportunity to review the project’s outline and the interview questions. We did not receive any feedback at the time but decided to avoid multiple requests out of respect for the organization which was undergoing change in chairmanship (we also sent our documents to the new chair). However, we subsequently made contact and collaborated with two KNAPK board members, who approved the project.
The communities of Uummannap Kangerlua and Sullorsuaq were informed of the project and solicited for collaboration using posters, radio, and newspaper announcements prior to the interview process. The study is part of a larger project aiming at co-producing knowledge on Arctic cod in Greenland. Collecting fish was not part of the original study design for 2022, but samples were obtained opportunistically during our visit, and we decided to include them in the study for two reasons. First, the preliminary data, results, and interpretations derived from the samples provide interesting insights into the population dynamics of Arctic cod in fjord and glacial habitats that are complementary to the fishers’ knowledge. Second, the results and experience gained from this pilot sampling will help in co-designing Arctic cod research with Greenland communities in the future. The final study design has a mixed methods approach, in which qualitative methods (interviews, participatory mapping) and quantitative methods (analyses of fish biological data) are combined (Creswell 2014).
2.4. Interviews
Most informants invited to participate in the study were suggested by the Uummannaq Polar Institute director and employees, who knew many local fishers. Some informants were recommended by other informants during the interviews (snowball sampling). Interviews were conducted individually, but on two occasions were conducted with two individuals from the same household or small community. These pairs were considered as single informants in the framework of the study.
Semistructured interviews were conducted in Uummannaq and Saattut in July 2022. An additional interview was conducted in Nuuk in November 2022 with a KNAPK representative with expert knowledge on Arctic cod fishery in the Uummannaq region. The interviews were conducted by an English-speaking scientist with the help of a local interpreter fluent in both English and Greenlandic. The interviews addressed the main themes of the interview guide (Supplementary File), but in a fluid dialogue in which participants could follow their ideas and associations, tell relevant stories, and elaborate on different subjects related to the questions. Participants also mapped different features including Arctic cod fishing locations on bathymetric maps of the area (Fig. 1b in Rignot et al. 2016). Other printed materials used during the interviews include a plate with photos of common fishes in the region (with scientific, English, Danish, and Greenlandic names), a schematic of Arctic cod life cycle, a schematic of Arctic marine ecosystems, and a photo of Arctic cod spawners. Each interview lasted between 19 and 73 min (median: 59 min). The interviews were recorded using a smartphone and transcribed in English afterwards. Informants were anonymized and referred hereafter as informant number 1–10.
The interview transcripts were analyzed by manually structuring the data set based on codes generated by the themes of the interview guide and additional themes discussed in individual interviews (Table 1). The thematic coding provided an overview of common information expressed by several informants (common patterns of themes). We regarded each informant as a highly qualified expert on the study subject, and gave high importance to individual responses, stories, and experiences shared by the informants. Detailed and complex accounts from each informant, together with similarities in many statements, ensured the credibility of the interview results (Tracy 2010).
Table 1.
To validate the interviews and inform Uummannap Kangerlua and Sullorsuaq communities about the results, we produced a one-page summary explaining the main findings of the project. The pamphlet presented, in Greenlandic, an early version of Fig. 1, photos, and visual elements. The pamphlet was used as supporting material during in person follow-up interviews with Uummannap Kangerlua fishers and hunters conducted in April 2023. The pamphlet was also printed and distributed to Uummannap Kangerlua fishers, hunters, and other communities’ members. Additionally, the pamphlet was posted on Facebook groups dedicated to Uummannaq residents to reach community members, and on the Facebook pages of the GINR and Oceans North Kalaallit Nunaat to reach a larger public. The in-person validation process was conducted by scientists and interpreters. Weather conditions resulted in a community visit significantly shorter than originally planned. Nonetheless, the three interviewed persons (one informant previously interviewed and two additional knowledge holders) validated the information presented in the pamphlet. Several communities’ members, including one Arctic cod fisher not originally interviewed, approved the Facebook post and agreed to make the project results public.
2.5. Fish samples
Arctic cod samples were collected during our visit in the Uummannaq region in July 2022. A first sample, bought from a factory in collaboration with a fisher, contained fish collected near Sermilik (glacier) in October 2021. The 20 kg frozen block was chopped with an axe and a subsample of about 5 kg was sent to the GINR in Nuuk for analysis. A second sample, provided by informant #9, originated from a recent fishing event near Sermeq Avannarleq (glacier) in Sullorsuaq. Fresh Arctic cod were subsampled from the catch by randomly selecting about 50 fish, frozen, and sent to GINR. Both samples were collected by local fishers using the fishing methods described in the results section.
In the laboratory, fish were thawed and lengths (standard, fork and total, in centimeters), whole body, gonad, liver, and stomach wet weights (in grams), as well as sex, were recorded. Sagittal otoliths were collected, measured (longest diameter, in millimeters) under a stereomicroscope and age was estimated by counting annual increments on cross-sections (Gjøsæter and Ajiad 1994). Gonadosomatic index (GSI) and hepatosomatic index (HSI) were determined according to the equations:
For the October 2021 sample, the sex and standard length of all intact fish were recorded. Weight, GSI, HSI, and age were recorded on randomly selected subsets of fish from that sample (Table 2). For the July 2022 sample, the complete set of measurements was recorded for each fish (Table 2). As three informants mentioned that there are “two types of Arctic cod, the white ones, which are softer, and the black ones, which are harder”, we tentatively attributed the color white or black to each fish before dissection, also trying to consider the skin texture or body firmness in the assessment. However, these characteristics could not be determined with any level of confidence on the thawed fish, and color was not considered further in statistical analysis.
Table 2.
Differences in length, weight, GSI, HSI, and age between samples, or between sexes within a sample, were determined using an analysis of variance (ANOVA) or Student’s t test when the assumptions of normality and homogeneity of variances were met (tested using Shapiro–Wilk and Brown–Forsythe tests, respectively), Welch’s ANOVA or t test when normality was met but not homogeneity of variances, and Kruskal–Wallis or Mann–Whitney test when both assumptions were not met. The significance level of all tests was set to p < 0.05.
3. Results
3.1. Interviews’ results and fishers’ knowledge
3.1.1. Informants
Ten informants participated in the study. The informants resided in Uummannaq (5), Saattut (3), Ikerasak (1), and Nuuk (1) at the time the interviews were conducted. The informants’ average age was 43 years. All informants except #10 (KNAPK representative from Nuuk) fish Greenland halibut commercially in Uummannap Kangerlua using longlines deployed from dinghies in the open water season (Fig. 2). Seven informants occasionally fish Arctic cod. The two other informants living in the Uummannaq region do not fish Arctic cod but buy them to use them as bait for halibut fishing. One informant also mentioned fishing halibut using gill nets along the sea-ice edge between November and April when this practice is allowed. Two informants mentioned they also hunt narwhals, and one mentioned fishing Atlantic cod and hunting seals.
3.1.2. Arctic cod fishing season, areas, methods, and uses
Arctic cod fishing as currently done by fishers in Uummannap Kangerlua and Sullorsuaq is a fairly recent activity rendered possible in the 1990s by the emergence of recreational echosounders (hereafter, referred to as sonar) to detect fish schools. Before that, visual detection, direct or from predators’ aggregations, was possible but not efficient enough to sustain a profitable fishery, as informant #4 mentioned: “We can spot groups of Arctic cod by looking at the birds that are eating, but we really need the sonar.”.
The seasonality of Arctic cod fishing is less determined by the species availability in the region than by accessibility and various socio-economic factors. Informant #1 mentioned that “There are Arctic cod all year round.”, indicating that availability played a minor role in the seasonality of Arctic cod fishing. Accessibility appeared as a major factor. Indeed, as Arctic cod fishing requires open water accessible by dinghy, it is constrained by sea-ice conditions. Informant #3 said that “Fishing for Arctic cod around Uummannaq stops when the sea ice comes.’’. The seasonality of Arctic cod fishing is also strongly determined by accessibility of other species and harvesting priorities in the communities. One informant mentioned that “When it’s no longer the season for spring capelin (in June–July this year), I go for Arctic cod.”, whereas informant #9 explained “In October–November, the narwhals come so we don’t go for Arctic cod.”. Supply and demand on the fresh bait market also regulates the fishing season. For example, when several fishers supply Arctic cod at the same time, others might avoid Arctic cod fishing trips as these would be unprofitable.
Participatory mapping during the interviews showed that the main Arctic cod fishing areas can be categorized into three groups. The first group includes nearshore areas in Karrat Kangerlua (Karrat Fjord), Nuugaatsiap Imaa (Karrat Icefjord), and Illorsuit Imaat (Illorsuit Sound), located in the northern part of Uummannaq Kangerlua (Fig. 1). These areas are not particularly close to any outlet glacier. The second group consists of areas very close to a glacier front, such as Sermilik, Kangilleq, and Sermeq Silarleq (Fig. 1). These locations were specifically mentioned during the interviews but informant #6 said that “At the head of each fjord you find Arctic cod”. Most informants reported on the risky aspect of fishing in these areas, for example, informant #1 mentioned: “We fish Arctic cod near the glacier. It’s dangerous and many people die. But we know. We can see on the sonar when the ice is about to break.”. The third category is an area in Sullorsuaq next to Sermeq Avannarleq, where a polynya allows winter fishing, as informant #9 explained, “Sometimes they go all the way near Qeqertaq just to get fresh Arctic cod in the winter. There is never sea ice over there, because of the strong currents.”. Arctic cod fished in this area (by at least one Qeqertaq fisher) are brought back to Uummannaq and other settlements by snowmobile driven across Nuussuaq (Nuussuaq Peninsula) and on the sea ice of Ikerasaap Sullua (Ikerasak Fjord), or by dinghy around Nuussuaq (Fig. 1).
Arctic cod fishing takes time, fuel, and is not exempt from danger. Benefits might not always balance the costs. At times, personal reasons explain the choice of fishing for Arctic cod in remote areas. For example, a strong family connection between two households in Uummannaq and Qeqertaq has supported the practice of harvesting Arctic cod in Sullorsuaq to sell in Uummannaq. In this case, the cost of travel to find Arctic cod schools is assimilated to the cost of travel to meet family members, and incidentally also bringing together the extra dinghy needed for Arctic cod fishing. Another example comes from an informant who used to live in Illorsuit before the tsunami. In this case, the cost of travel is compensated by the desire to return to preferred fishing grounds.
The fishing method consists of finding a school of Arctic cod using visual observation of predators’ aggregations and sonars, and deploying a net made of “two walls converging in one bag” in the school using two dinghies. The mesh of the net is about 1–1.5 cm. The fishing depth is typically between 10 and 50 m, but can reach up to 200 m. The informants explained: “We use groups of seals and whales to find them, and then we try to find a place where we can have them all together. We need two dinghies. We use stones to make the net dive. We usually catch 4 to 6 tons at once. We fill up the dinghies (about 1.5 tons each) and the rest goes back in the ocean.”.
In general, a small fraction of each Arctic cod catch is kept by the fishers to bait their own longlines, but the majority is sold to other fishers within 1 or 2 days. Part of the catch that is not sold fresh will typically be sold to the factory and frozen. One informant said: “I keep about 30 kilos for myself and I sell the rest to other fishers. If there are some left, I sell them to the factory to freeze.”. As fishing areas can be far and fish hard to find, the frequency of Arctic cod fishing during the season is approximately every 2–4 days, an interval ensuring a continuous supply of fresh bait, as explained by informant #4 “The sail is so long, I don’t go every day. Maybe every other day. It can take 10 to 20 hours to find them. We go out early morning to fish Arctic cod, and they go bad the next evening” and informant #6 “I go maybe every 3–4 days. When we have Arctic cod we can fish halibut for 3–4 days, then on the fourth day we go for Arctic cod.”.
One of the three informants who is also a musher mentioned feeding Arctic cod to his dogs, saying “the dogs love it”. On the contrary, the two other mushers feed little or no Arctic cod to their dogs “because it’s too fatty.”.
3.1.3. Arctic cod as bait
The vast majority of Arctic cod fished is used as bait. Besides Arctic cod, all informants also use capelin as bait, which they either fish themselves, buy fresh from others or frozen from the factory. Fresh bait was unanimously judged as better bait than frozen bait. Informants #2 and #4 mentioned that fresh Arctic cod yields bigger halibut than fresh capelin, whereas informant #3 said that “halibut prefers Arctic cod” without detailing whether he gets more or bigger halibut with that bait. Informants #2 and #6 reported getting more halibut with frozen capelin than with frozen Arctic cod. Frozen capelin is preferred over frozen Arctic cod as their degradation after thawing is slower, as informant #2 explained: “I get more halibut with frozen capelin because their smell doesn’t change as much as Arctic cod does.”.
One informant occasionally fishes ice cod (A. glacialis) with a jig, mentioning this is another good option for bait. Informant #10 detailed the ice cod fishing method used in the region to the North of Uummannap Kangerlua, where Arctic cod fishing is not common: “In Upernavik area they also fish ice cod, that are impossible to catch with nets, so they use very small hooks, maybe 25, on a line and catch them that way. They can be fished year-round and serve as bait.”.
Another bait option for the fishers is to buy frozen squids from the factory, which is imported, for example, from Argentina. However, it seems to be used only as a last resort, as informant #7 explained: “Fish only eat squid if they are very hungry. Maybe before capelin comes (in May), there’s nothing to eat yet so they eat anything, but when there are capelin or Arctic cod in the water they don’t care for squid. I only use squid if I don’t have anything else.”.
Finally, informant #9 reported on Northern sand lance (Ammodytes dubius Reinhardt, 1837) and their uselessness as bait: “You can see sand lance in the sand, with just the head coming out. Everywhere in the harbor. In summer and also maybe winter. But nobody fishes them. We have no use for them. Once we tried putting them on the hook but the halibut didn’t like it.”.
3.1.4. Morphological differences
The existence of different morphotypes was not the subject of an interview question but has been mentioned spontaneously during the interviews on two occasions. Informants #9 and #10 noticed morphological differences in Arctic cod from different locations: “There are two types of Arctic cod, white and black. Near the glacier they are lighter, and softer; near Illorsuit and Nuugaatsiaq they are darker and a little bit hard. The white ones are very good to fish halibut. Halibut loves the white ones.”. Contrary to this information that the white morphotype is found in glacial habitats whereas the black morphotype is found in coastal habitats, informant #9 identified both morphotypes in the sample he collected near Sermeq Avannarleq in Sullorsuaq (Fig. 3).
Fig. 3.
3.1.5. Vertical distribution, ice association, and spawning area
Some informants provided information about the species’ vertical distribution, for example, that “Arctic cod move between the surface down to 100 meters” and that “The smaller ones stay at shallower places, the bigger ones go deeper.’’. Informant #7 reported that “Sometimes when ice is coming down (glacier calving), Arctic cod are pushed upwards because the water is so powerful.”. Two informants (#4 and #7) mentioned positive relationships with ice: “Arctic cod follow the sea ice.”. On the contrary, informant #1 said that “The presence or absence of ice doesn’t really influence the presence of Arctic cod.”. We were informed about a spawning area by informant #9: “Arctic cod come around Saattut in the winter to lay eggs. Last December, just around Christmas, my father caught many pregnant Arctic cod just around Saattut.”.
3.1.6. Arctic cod predators
Seals were reported as Arctic cod predators from several informants, including #7: “The seals we catch just outside Saattut all year round have Arctic cod in their stomachs.”. Informant #2 described the diet of Greenland halibut including some seasonal variations: “In the stomachs we find squid, small Greenland halibut, small Atlantic cod, Arctic cod, shrimps, etc. In April–May–June I see more Arctic cod in Greenland halibut stomachs.”. As mentioned by informant #8, Greenland halibut seems to prey on Arctic cod schools targeted by fishers: “Sometimes you even get Greenland halibut in the net with Arctic cod.”. According to informants #2, #8, and #10, the diet of narwhals includes Greenland halibut, squid, and Arctic cod. Informant #7 mentioned a minke whale (Balaenoptera acutorostrata Lacépède, 1804) hunted in October, 5 or 6 years ago, with a stomach full of Arctic cod. Finally, two informants mentioned they often observed seabirds eating small Arctic cod.
3.1.7. Changes in Arctic cod distribution and abundance
In general, the informants did not report temporal trends in the abundance of Arctic cod or other animals, but some mentioned interannual variation. For example, to the question “Do you see change now compared to 10 or 20 years ago for Arctic cod?”, informant #1 answered “There’s always seasons where there’s a lot of them, and seasons where there’s very few. I think it will continue like this.’’ informant #8 answered “It changes all the time, it can be more or less every year.”, and informant #9 answered “Sometimes there are good years, sometimes bad years.”.
However, informant #7 observed a connection between climate change and Arctic cod habitat: “Since the climate has started to change, there has been a lot more fresh water melting from under the glaciers, and Arctic cod follows the fresh water. They used to live under the big iceberg (the ice sheet), but now they’re coming everywhere, although they still prefer to stay under the ice.”.
Three informants interviewed in July 2022 noted that Arctic cod abundance and distribution were unusual that year so far. Informant #1 said “We’ve seen less Arctic cod this year compared to last year.”, informant #2 mentioned that “This year we haven’t had Arctic cod yet. Maybe because it took so long to warm up because the ice stayed for a long time.’’ and informant #4 reported that “This year there’s nothing near Illorsuit. There’s some here and there but no schools. Maybe they (the fishers) did not look hard enough. When capelin is no longer around, they will look harder.”.
As reported by informant #10 in November 2022 and by informant #9 in a follow-up interview in March 2023, the summer of 2022 was characterized by very high abundance of capelin and a low number of Arctic cod caught. Informant #10 also reported a scarcity of ringed seals in Uummannap Kangerlua in 2022 and suggested a relationship between Arctic cod, temperature, and ringed seals: “There were no Arctic cod this year in Uummannaq, maybe because the water was warmer, because there were a lot of capelin and the season was very long, until October. It was the first time capelin were so numerous and stayed for so long near the coast in the region. We can see that Arctic cod is very important for the ecosystem because this year there was no Arctic cod and there was no seal either.”. Informant #9 said that when the surface water is warmer than usual, Arctic cod can stay in deeper water, move North, or stay close to the glacier.
3.2. Fish samples
The sample collected near Sermilik in October 2021 contained 48% females, 21% males, and 30% immature fish whereas the sample collected near Sermeq Avannarleq in July 2022 contained 44% females, 56% males, and no immature fish (Fig. 4). Fish from October 2021 were shorter, weighed less, and had lower HSI than fish from July 2022 when taken together, as well as when separated by sex (Student’s t, Welch’s t, Mann–Whitney, p < 0.001, Table 3, Fig. 4). Males from October 2021 had a much higher GSI than males from July 2022 (Mann–Whitney, p < 0.001) whereas for the females, there was no significant difference in GSI between samples (Mann–Whitney, p = 0.628, Table 3, Fig. 4).
Fig. 4.
Table 3.
In the October 2021 sample, the males were longer than the females, which were longer than the immatures (Kruskal–Wallis with Dunn’s multiple comparison, p < 0.042). The males were heavier than the females and the immatures (Kruskal–Wallis with Dunn’s multiple comparison, p < 0.001), with the latter two groups being of similar weight (Dunn’s, p = 0.101). Males, females, and immatures had similar HSI (Kruskal–Wallis, p = 0.524). Males had much higher GSI than females (Mann–Whitney, p < 0.001, Table 3, Fig. 4).
In the July 2022 sample, males and females had similar length (Mann–Whitney, p = 0.059), weight (Student’s t, p = 0.254), and HSI (Student’s t, p = 0.420) but males had a higher GSI than females (Welch’s t, p < 0.001).
Standard, fork, and total lengths were linked by strong linear relationships (Table 4). A single weight–standard length relationship was fitted for males, females, and immatures from the 2021 and 2022 samples (Fig. 5). Similar relationships linked weight (W) and fork length (FL): W = 0.0035*(FL)3.28 (r² = 0.96, p < 0.001, n = 84) and weight and total length (TL): W = 0.0041*(TL)3.17, r² = 0.95, p < 0.001, n = 84).
Fig. 5.
Table 4.
A significant linear relationship linked fish standard length (SL, in cm) and otolith length (OL, in mm): SL = 2.39*(OL) + 1.90 (r² = 0.86, n = 84, p < 0.001). In October 2021, 71% of the females were aged 1, the others were aged 2. The males from that sample were mostly aged 2 (75%). In July 2022, the majority of the males and females were aged 3 (83% and 74%, respectively). Length-at-age regressions differed between sex (ANCOVA, p = 0.007) but not between samples within a sex (ANCOVAs, p > 0.60); hence data were pooled (Fig. 6). The females had a growth rate of 2.9 cm·year−1 between years 1 and 2, increasing to 3.3 cm·year−1 between years 2 and 3 (Table 5). The males had a growth rate of 2.4 cm·year−1 between years 1 and 2, decreasing to 1.4 cm·year−1 between years 2 and 3 (Table 5).
Fig. 6.
Table 5.
4. Discussion
4.1. Use of glacial fronts by Arctic cod
Our results show that Arctic cod are found in dense schools near glacial fronts. Foraging hotspots are created at the fronts of outlet glaciers by subsurface plumes of freshwater discharged from the glacier that aggregate zooplankton, which is often stunned or killed from osmotic shock, hence becoming easy prey (Lydersen et al. 2014). It is unclear whether Arctic cod aggregate at glacial fronts voluntarily to feed on zooplankton, or if they are being aggregated by the same mechanism as the plankton, or a combination of both. The information from fishers that Arctic cod follow the glacial meltwater (or are pushed upwards by it), along with the visual observation of a lethargic Arctic cod near a glacier front in Kangertittivaq (Scoresby Sound, Caroline Bouchard, personal observation) suggests that the latter mechanism is plausible.
Glacier fronts appear as an essential habitat for some Arctic cod predators including black-legged kittiwake (Rissa tridactyla) (Linnaeus, 1758), northern fulmar (Fulmarus glacialis) (Linnaeus, 1761), Greenland halibut, ringed seal, beluga, and narwhal (Lydersen et al. 2014; Laidre et al. 2016; Hamilton et al. 2019; Schiøtt et al. 2022). In Svalbard two decades ago, ringed seals and belugas were spending approximately half of their time near glacier fronts foraging on Arctic cod (Hamilton et al. 2019). After changes in sea-ice conditions and fish assemblages, the belugas now favor boreal fish away from glacier fronts, but the ringed seals did not switch prey and now spend more time foraging near glacial fronts, a habitat serving as Arctic refugia (Hamilton et al. 2019). The low numbers of both Arctic cod and ringed seal in Uummannap Kangerlua in 2022 reported by informant #10 suggests a strong association between the two species in coastal West Greenland as well. Fishers in Uummannap Kangerlua and Sullorsuaq have observed Greenland halibut in Arctic cod schools and reported catching larger halibut when using Arctic cod as bait. In Ilulissat Kangerlua (Ilulissat Icefjord), Greenland halibut increase in size towards the glacier front (Schiøtt et al. 2022 ). As on northwest Atlantic shelves, Greenland halibut in Uummannap Kangerlua appeared as an opportunistic feeder preying on a large range of taxa including Arctic cod (Chumakov and Podrazhanskaya 1986; this study; Caroline Bouchard, personal observation). As no other typical Greenland halibut prey (e.g., capelin, squids, shrimps) were reported from glacier fronts, it seems that Greenland halibut could benefit from targeting Arctic cod in these areas.
The October 2021 sample collected near Sermilik contained only 21% males, which were longer, heavier, older, and had a higher GSI than the females. This skewed sex ratio could have resulted from females being selectively exploited by the fishing method; however, size selectivity of the gear is unlikely considering the small mesh size used (1–1.5 cm). More likely, high frequency of females in the fall was related to higher male mortality during summer (Bain and Sekerak 1978). We hypothesize that the extreme female-skewed sex ratio in our sample is related to ringed seals preferentially eating the largest fish in subsurface schools at glacial fronts. In Baffin Bay, thick-billed murre (Uria lomvia) (Linnaeus, 1758), northern fulmar and black-legged kittiwake preferentially capture age-1 Arctic cod (LeBlanc et al. 2019). Such a size-selective predation from seabirds could counterbalance some of the effect of seals’ predation on the sex ratio if both types of predators were feeding on the school, but the effect of seals could dominate. The sample collected in July 2022 was composed of 56% males, which were similar sized as females. In this sample, a potential gradual depletion of one sex relative to the other during the summer would have had less time to occur but was also less likely because of the similar size of both sexes.
Alternatively or concomitantly, the skewed sex ratio could be associated with spawning migration and behavior. For Atlantic cod (G. morhua), a spatiotemporal analysis of sex ratios suggested that males arrive at the spawning area first, with females moving into the area when ready to spawn (Morgan and Trippel 1996). The GSI values in this study showed that male gonads develop between August and October, while female gonads do not develop before October. This is concordant with other studies from the Canadian Arctic suggesting an onset of gonadal development in August for the males, and in December for the females (Bain and Sekerak 1978; Hop et al. 1995, 1997; Matley et al. 2013). The sex ratio we observed in October might result from a spawning migration pattern similar to that of Atlantic cod. Males with fully developed gonads may migrate from the glacial habitats to the spawning areas during the fall, leaving mostly females in the schools near the glacier. The spawning season of Arctic cod varies among regions and years, but overall ranges between September and April (Aune et al. 2021; Geoffroy et al. In press). In the Barents Sea, Arctic cod spawning migration begins in August–September and the spawning period can last between 1 and >4 months (Aune et al. 2021). Considering the December spawning event described by an informant, it seems possible that spawning migration had affected the sex ratio observed in October.
Considering our low sample size, our interpretations are only speculative at this point, but continued collaboration with fishers to expand the sampling, both spatially and temporally, would allow us to achieve stronger conclusions. Our preliminary results and interpretations from the fish samples can also help in designing future sampling programs aiming at better understanding the role of different processes in determining the population structure observed. For example, we could further investigate the roles of size-selective predation and spawning migration on the sex ratios, by asking fishers to sample spawning aggregations and to note about the predators feeding on each school they sample.
4.2. Climate change and the uncertain future of Arctic cod in Uummannap Kangerlua
The fishers mentioned interannual variability in Arctic cod catches. As reported first by the fishers interviewed in July 2022 and later by fishers interviewed in November 2022 and March 2023, there were low catches of Arctic cod in Uummannap Kangerlua in 2022. Concomitantly, official Arctic cod landings (fish that end up in factories) in the Uummannaq region were relatively low in 2022: 4.6 t compared with 38 t in 2021 and 21 t in 2020 (Greenland’s Fisheries License Control Authority, unpublished data). Some of the interannual variation in Arctic cod fishery may result from fishers’ behavior, priorities, and accessibility. For example, in 2022, the very high abundance of capelin associated with difficult access to Arctic cod due to sea-ice conditions, may have resulted in less interest in Arctic cod fishing that year. However, some of the interannual variability in the catches likely results from biological variability in Arctic cod abundance, which might be linked with environmental conditions.
An informant hypothesized that a delay in the vernal warming of the surface waters caused by a late ice breakup might explain the absence of Arctic cod schools at their usual locations in the summer of 2022. According to in situ and satellite measurements, June–August SST in Uummannap Kangerlua were colder in 2022 than the 1991–2020 mean for the respective months (Timmermans and Labe 2022). A more extensive sea-ice cover in March 2022 than the 1991–2020 median in adjacent Baffin Bay (Meier et al. 2022) also correlates with the late ice breakup observed by the fishers.
In Pikialasorsuaq (North Water Polynya) and Northwest Baffin Bay, the biomass of adult Arctic cod has been correlated with the timing of ice breakup and the North Atlantic Oscillation (NAO) during early life stages (Herbig et al. In press). If a similar relationship exists in eastern Baffin Bay and coastal west Greenland, parameters linked to the NAO such as changing temperatures, precipitation patterns, and wind direction and strength, could be important determinants of Arctic cod population size in Uummannap Kangerlua. The relationships between environmental conditions and the biomass of adult Arctic cod lagged 1 year (Herbig et al. In press). Hence the mechanisms potentially linking the low abundance of Arctic cod in 2022 with local conditions of SST and sea ice that same year remains to be described. The low abundance of adult Arctic cod in Uummannap Kangerlua in 2022 could be a result of failed or low recruitment in the previous years. Indeed, June and July SST in Uummannap Kangerlua in 2019 were much higher than the upper thermal limit of Arctic cod eggs and larvae and likely caused high mortality and low recruitment in the region, except in Ukkusissat Sulluat (Ukkusissat Fjord) where a glacial meltwater refuge potentially protected the eggs and larvae against high SST (Bouchard et al. 2021). Low recruitment in 2019 could have resulted in low biomass of Arctic cod age-1 in 2020, age-2 in 2021, and age-3 in 2022. However, the fishers found plenty of adult (age 1+) Arctic cod in 2020 and 2021 and our limited data contain no indications of a failed recruitment in 2019. Clearly, more complex environmental conditions than SST alone are at play in determining Arctic cod recruitment in Uummannap Kangerlua.
Independent of the underlying causes, the low biomass of Arctic cod in Uummannap Kangerlua in 2022 might have impacted the population of ringed seals in the region. In addition to the account of informant #10 and a hunter interviewed as part of the validation process who said that 2022 was a very bad year for seals hunting in Uummannaq area, the official catch statistics collected by the Government of Greenland show that ringed seals catch in 2022 was the third lowest over the past 30 years (Fig. 7). A total of 1060 ringed seals were harvested in 2022, representing a third of the number in 2009 (3229 seals), the highest year. In particular, the catch in May 2022 (90 seals) was the lowest on record for May, historically the month with the highest catch, although the peak seems to be progressively shifting from May to April (Fig. 7). In the Amundsen Gulf, declines in ringed seals’ body condition and reproduction between the 1971–1979 and 1992–2014 periods have been associated with a potential decrease in the seals’ preferred prey, Arctic cod (Harwood et al. 2015). As Arctic cod is an important prey in the diet of ringed seals in Uummannaq (Siegstad et al. 1998; this study), a similar trophic cascade could occur in the area. However, the low abundance of ringed seals in Uummannap Kangerlua in summer 2022, as reported by informant #10 interviewed in November 2022, suggests the seals moved to different locations in search of prey. Our current level of knowledge precludes any prediction on whether a situation like 2022 is likely to re-occur in the coming years, but it certainly would impact the communities, particularly fishing and hunting activities.
Fig. 7.
4.3. Arctic cod fishery provides unique scientific opportunities
Studying Arctic cod in the field is generally a complex and expensive scientific endeavor, often performed from large vessels or icebreakers in the most remote Arctic seas. Arctic cod scientists can rarely rely on fishery surveys or bycatch data, and an important part of our current knowledge of this key species emerged from studies of its predators (e.g., Harwood et al. 2015; Hamilton et al. 2019). The fishers in Uummannap Kangerlua and Sullorsuaq have been fishing Arctic cod for almost 30 years. Here for the first time, scientists collaborate with them to learn more about the species. Our approach provides unique insights into some aspects of Arctic cod ecology.
Spawning migrations and locations have been identified as a key knowledge gap in Arctic cod research (Geoffroy et al. In press). The identification of a spawning area near Saattut is, thus, a very important finding. The occurrence of subsurface Arctic cod schools in a winter polynya at a glacier front is another novel and unique information provided by the fishers. Polynyas are important for Arctic cod during early life (e.g., Fortier et al. 2006; Bouchard et al. 2008; Bouchard and Fortier 2011; Vestfals et al. 2019) but to our knowledge no subsurface school has yet been reported from a winter polynya. Further collaborative sampling with fishers would help determine the relative roles of glaciers, polynyas, and other factors in explaining these annually recurring aggregations.
One informant observed that Arctic cod segregate vertically by size in Uummannap Kangerlua, with smaller fish occupying shallower depths. The informant might have been referring to the smaller size of the fish in subsurface schools compared with the fish eaten by Greenland halibut in deep water (the fishers often assess the stomach content of the halibut they fish). This would be consistent with similar large-scale patterns (hundreds of meters) documented in Svalbard fjords and other Arctic seas (e.g., Falk-Petersen et al. 1986; Geoffroy et al. 2016; Wathne et al. 2000). Alternatively, the informant might have been referring to a vertical segregation by size occurring within the subsurface schools. In this case, it might be somewhat similar to a small-scale pattern (tens of meters) documented in Arctic cod schools near Resolute (Nunavut). There, fish in satellite schools (groups of dispersed fish found at the surface) were smaller than fish from the main schools near the bottom at 10–20 m (Matley et al. 2012).
Two morphotypes were described by Uummannap Kangerlua fishers and visible on fresh fish (Fig. 3). Arctic cod seems to display a range of coloration and morphologies, but the differences have not been associated with any biological, environmental, or geographical parameters (Chernova 2018). The underlying causes of these two morphotypes could include habitat, age, physiological condition, reproductive activity, food, and genotype. Many species of fishes can change color rapidly to match the background, thanks to a mechanism of rapid intracellular transport of pigment organelles within chromatophores: organelles aggregated at the cell centers result in the fish appearing paler, while organelles evenly distributed throughout the cells result in the fish appearing darker (Wallin 2002). As the fishers generally find the white morphotype near glaciers, this common mechanism might be the main cause behind the observed morphotypes. In this study, the morphotypes could no longer be distinguished after freezing and thawing, hence a different sampling protocol should be used if this parameter is to be investigated in the future.
The two fish samples collected opportunistically for this study provided the first biological data on Arctic cod at glacial fronts in Greenland. A continued collaboration with fishers in Uummannap Kangerlua and Sullorsuaq would allow us to expand and optimize the sampling and better document the use of glacial fronts by Arctic cod, the relationships with their predators and potential implications for the communities.
Acknowledgements
First and foremost, Qujanarsuaq to the fishers in Uummannap Kangerlua and Sullorsuaq who shared their invaluable knowledge with us. Our warmest thanks to Ann Andreasen, the Uummannaq Children’s Home for exceptional support in terms of local coordination, logistical support, and general advice. We also express our gratitude to Heidi Andreasen from the Uummannaq Polar Institute for her precious help in connecting with local fishers, and Pipaluk Hammeken, Helene Kristiansen, Else Marie Nikolajsen, and Else Løvstrøm for facilitating and translating the interviews. We are thankful to Hannah Felicitas Kuhn and Lars Heilmann for assistance with laboratory work, and Aqqalu Rosing-Asvid for help with the ringed seal data.
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Published In
Arctic Science
Volume 9 • Number 4 • December 2023
Pages: 781 - 795
History
Received: 3 March 2023
Accepted: 30 May 2023
Accepted manuscript online: 22 June 2023
Version of record online: 23 August 2023
Copyright
© 2023 The Authors. This work is licensed under a Creative Commons Attribution 4.0 International License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author(s) and source are credited.
Data Availability Statement
Data are available upon reasonable request to the corresponding author. Access to interview transcripts or recordings will require informants’ approval.
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Author Contributions
Conceptualization: CB, PF, KL, PED, HC
Formal analysis: CB, PF, KL, PED, HC
Funding acquisition: CB, PF, KL, PED
Investigation: CB, PF, KL, PED, HC
Project administration: CB
Visualization: CB, PF
Writing – original draft: CB
Writing – review & editing: CB, PF, KL, PED, HC
Competing Interests
Caroline Bouchard served as Associate Editor at the time of manuscript review and acceptance and did not handle peer-review and editorial decisions regarding this manuscript.
Funding Information
The project received funding from the Greenland Research Council and the Danish Environmental Protection Agency as well as in-kind contribution from Oceans North Kalaallit Nunaat.
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Caroline Bouchard, Patrick Farnole, Kristine Lynge-Pedersen, Parnuna Egede Dahl, and Henrik Christiansen. 2023. Arctic cod (Boreogadus saida) in fjord and glacial habitats: a collaborative study with Uummannap Kangerlua fishers. Arctic Science.
9(4): 781-795. https://doi.org/10.1139/as-2023-0014
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