Comparative Modeling of Cod-Capelin Dynamics in the Newfoundland-Labrador Shelves and Barents Sea Ecosystems

The Atlantic cod (Gadus morhua) stocks in the Newfoundland-Labrador Shelves (NL) and Barents Sea (BS) ecosystems have shown divergent trajectories over the last 40 years. Both stocks experienced either an important decline (BS) or a collapse (NL) in the mid-1980s and early 1990s, respectively. After these population reductions, the BS stock quickly rebounded and it is currently at record high levels, while the NL stock, despite showing some improvement since the mid-2000s, remains at low levels. Fishing and environmental conditions are known to be important drivers of cod dynamics in both ecosystems, especially the availability of high energy prey like capelin (Mallotus villosus), however, the question of how different or similar these two stocks truly are remains. Could, for example, the NL cod stock rebuild if presented to conditions like the ones experienced by BS cod? To explore such questions, we developed a simple biomass dynamic model for cod using a bioenergetic-allometric approach. This model includes fisheries catches and capelin availability as external drivers and was implemented for both ecosystems. Despite the contrasting trends, the model produced very good fits, and showed some remarkably similar estimated parameters in both systems. We explored these similarities by (a) performing the thought experiment of transferring cod stocks between ecosystems by switching estimated key parameters between models and comparing the output, and (b) implementing an integrated model architecture which allowed fitting common parameters for both stocks to evaluate the similarity of key vital rates. Our results indicate that cod trajectories in NL and BS can be reliably described using simple bioenergetic-allometric arguments, fishery catches, and capelin availability. Model parameters that encapsulate intrinsic vital rates were not significantly different between stocks. This indicates that NL and BS cod stocks are biologically similar, and that the differences in their trajectories are driven by the ecosystem context in which these stocks are embedded, and suggests that the NL stock would be expected to rebuild if enough capelin were available. This also indicates that capelin status and trend should be an important consideration for effective management of these cod stocks.publishedVersio

Ringed seal (Pusa hispida) diet on the west coast of Spitsbergen, Svalbard, Norway: during a time of ecosystem change

Global warming is causing Atlantification of water masses and concomitant changes in food webs in the Barents Sea region. To determine whether changes that have been documented at lower trophic levels are impacting the diet of ringed seals (Pusa hispida) gastrointestinal tracts (GITs) from 99 coastal-feeding ringed seals, collected in western Spitsbergen, Svalbard, were analysed via identification of hard-parts. The study animals were shot in spring (n = 30; April–July) or autumn (n = 69; August–October) during four consecutive years (2014–2017). Thirty different prey types were identified, but most seals (55.6%) had consumed between 2 and 4 different types of prey. Polar cod (Boreogadus saida) dominated the diet of the ringed seals in terms of relative biomass (Bi = 60.0%) and frequency of occurrence (FOi = 86.9%), followed by pricklebacks (Stichaeidae; Bi = 23.4%; FOi = 79.8%). Redundancy analysis (RDA) revealed that year was the only significant predictor explaining variance in autumn diet composition (RDA, F3 = 4.96, AIC = − 76.49, p ≤ 0.0050; blubber content and maturity/sex group were not significant). Blue whiting (Micromesistius poutassou) occurred in the diet in small quantities; this Atlantic fish species has not previously been documented in the ringed seals’ diet. Atlantic cod (Gadus morhua) had the highest Bi (9.2%) among Atlantic prey types. However, despite major changes in the last decade in the fish and zooplankton community in western Svalbard, and consumption of a few Atlantic prey types, the ringed seals’ diet in Svalbard continues to be dominated by Arctic prey, especially polar cod.publishedVersio

Studies of minke whale (Balaenoptera acutorostrata) ecology in the northeast Atlantic: Preliminary results from studies of diet and food availability during summer 1992

Stomach content samples from 92 minke whales Balaenoptera acutorostrata, caught during scientific whaling operations in July-August 1992, were collected in five selected areas in Norwegian and adjacent waters. Preliminary results from the stomach analyses indicate a diet almost completely dominated by fish, although there was considerable heterogeneity in species composition between the areas. Capelin dominated the minke whale diets in the two northernmost study areas (Spitsbergen and Bear Island). Further south, in coastal areas of North Norway and Russia, herring was the most important food item, but was accompanied by significant amounts of sand eel, cod, haddock and saithe. A survey aimed to locate and classify fish and plankton resources was conducted simultaneously with the scientific whaling program. The northern areas were particularly dominated by 0-group cod (which was not found in whale stomachs), while capelin abundance was recorded only sporadically. Along the coast of North Norway and Russia, there appeared to be a larger degree of similarity between prey abundance and minke whale diet. Herring was documented to be very abundant both in the resource surveys and in the whale stomach analyses. The similarity in distribution was particularly conspicuous for 0-group herring

Multiple configurations and fluctuating trophic control in the Barents Sea food-web

The Barents Sea is a subarctic shelf sea which has experienced major changes during the past decades. From ecological time-series, three different food-web configurations, reflecting successive shifts of dominance of pelagic fish, demersal fish, and zooplankton, as well as varying trophic control have been identified in the last decades. This covers a relatively short time-period as available ecological time-series are often relatively short. As we lack information for prior time-periods, we use a chance and necessity model to investigate if there are other possible configurations of the Barents Sea food-web than those observed in the ecological time-series, and if this food-web is characterized by a persistent trophic control. We perform food-web simulations using the Non-Deterministic Network Dynamic model (NDND) for the Barents Sea, identify food-web configurations and compare those to historical reconstructions of food-web dynamics. Biomass configurations fall into four major types and three trophic pathways. Reconstructed data match one of the major biomass configurations but is characterized by a different trophic pathway than most of the simulated configurations. The simulated biomass displays fluctuations between bottom-up and top-down trophic control over time rather than persistent trophic control. Our results show that the configurations we have reconstructed are strongly overlapping with our simulated configurations, though they represent only a subset of the possible configurations of the Barents Sea food-web.publishedVersio

Combined effects of temperature and fishing mortality on the Barents Sea ecosystem stability

Temporal variability in abundance and composition of species in marine ecosystems results from a combination of internal processes, external drivers, and stochasticity. One way to explore the temporal variability in an ecosystem is through temporal stability, measured using the inverse of the coefficient of variation for biomass of single species. The effect of temperature and fisheries on the variability of the Barents Sea food web is still poorly understood. To address this question, we simulate the possible dynamics of Barents Sea food web under different temperature and fishery scenarios using a simple food-web model (Non-Deterministic Network Dynamic [NDND]). The NDND model, which is based on chance and necessity (CaN), defines the state space of the ecosystem using its structural constraints (necessity) and explores it stochastically (chance). The effects of temperature and fisheries on stability are explored both separately and combined. The simulation results suggest that increasing temperature has a negative effect on species biomass and increasing fisheries triggers compensatory dynamics of fish species. There is a major intra-scenario variability in temporal stability, while individual scenarios of temperature and fisheries display a weak negative impact and no effect on stability, respectively. However, combined scenarios indicate that fisheries amplify the effects of temperature on stability, while increasing temperature leads to a shift from synergistic to antagonistic effects between these two drivers

Arctic Marine Data Collection Using Oceanic Gliders: Providing Ecological Context to Cetacean Vocalizations

To achieve effective management and understanding of risks associated with increasing anthropogenic pressures in the ocean, it is essential to successfully and efficiently collect data with high spatio–temporal resolution and coverage. Autonomous Underwater Vehicles (AUVs) are an example of technological advances with potential to provide improved information on ocean processes. We demonstrate the capabilities of a low-power AUV buoyancy glider for performing long endurance biological and environmental data acquisition in Northern Norway. We deployed a passive acoustic sensor system onboard a SeagliderTM to investigate presence and distribution of cetaceans while concurrently using additional onboard sensors for recording environmental features (temperature, salinity, pressure, dissolved oxygen, and chlorophyll a). The hydrophone recorded over 108.6 h of acoustic data during the spring months of March and April across the continental shelf break and detected both baleen and odontocete species. We observed a change in cetacean detections throughout the survey period, with humpback whale calls dominating the soundscape in the first weeks of deployment, coinciding with the migration toward their breeding grounds. From mid-April, sperm whales and delphinids were the predominant species, which coincided with increasing chlorophyll a fluorescence values associated with the spring phytoplankton blooms. Finally, we report daily variations in background noise associated with fishing activities and traffic in the nearby East Atlantic shipping route. Our results show that gliders provide excellent platforms for collecting information about ecosystems with minimal disturbance to animals, allowing systematic observations of our ocean biodiversity and ecosystem dynamics in response to natural variations and industrial activities.publishedVersio

Humpback Whale (Megaptera novaeangliae) Song on a Subarctic Feeding Ground

Male humpback whales (Megaptera novaeangliae) are known to produce long complex sequences of structured vocalizations called song. Singing behavior has traditionally been associated with low latitude breeding grounds but is increasingly reported outside these areas. This study provides the first report of humpback whale songs in the subarctic waters of Northern Norway using a long-term bottom-moored hydrophone. Data processed included the months January–June 2018 and December 2018–January 2019. Out of 189 days with recordings, humpback whale singing was heard on 79 days. Singing was first detected beginning of January 2018 with a peak in February and was heard until mid-April. No singing activity was found during the summer months and was heard again in December 2018, continuing over January 2019. A total of 131 song sessions, including 35 full sessions, were identified throughout the study period. The longest and shortest complete sessions lasted 815 and 13 min, respectively. The results confirm that singing can be heard over several months in winter and spring on a high latitude feeding ground. This provides additional evidence to the growing literature that singing is not an explicit behavior confined to low latitude breeding grounds. The peak of song occurrence in February appears to coincide with the reproductive cycle of humpback whales. Finally, this study indicates that song occurrence on a subarctic feeding ground likely aids the cultural transmission for the North Atlantic humpback whale population.publishedVersio

Changes in humpback whale song structure and complexity reveal a rapid evolution on a feeding ground in Northern Norway

Singing behaviour by male humpback whales (Megaptera novaeangliae) has traditionally been associated with low-latitude breeding grounds. However, in recent years, this vocal behaviour has been increasingly reported outside these areas. All singers in a given population sing the same version of a song and this song is continually evolving over time with modifications on different levels within the song structure. Tracing changes in whale song will help to undercover the drivers underlying this vocal display and contribute to the understanding of animal culture and its evolution. To determine the progressive changes in songs found on a subarctic feeding ground and migratory stopover, a detailed analysis of humpback whale song recordings from Northern Norway was conducted. Passive acoustic data from the Lofoten-Vesterålen Ocean Observatory (LoVe), collected using a bottom-moored underwater hydrophone, were used from January - April 2018 and January 2019. Two measures of the song structure were examined: (1) sequence similarities using the Levenshtein distance and (2) song complexity using a principal component analysis (PCA). In total, 21 distinct themes were identified which presented highly directional, structural changes over time. Two themes from 2018 reoccurred in 2019, whereas all other themes in 2019 appeared to be evolved versions of 2018 themes. All songs grouped into three general clusters, reflecting the rapid evolution over the study period. With all sampled animals singing the same version of the song, this might indicate that the singers are either from the same breeding population or that song learning occurred before the study period. Song complexity appeared to follow the trend of song progression; songs became more complex as they evolved over the months in 2018 and decreased in complexity between the years, returning to a more simplified song in 2019. The results confirm that humpback whale song exhibits a rapid progression on a shared subarctic feeding ground, with strong potential for song exchange and opportunities for cultural transmission between populations in the North Atlantic

Changes in humpback whale song structure and complexity reveal a rapid evolution on a feeding ground in Northern Norway

Singing behaviour by male humpback whales (Megaptera novaeangliae) has traditionally been associated with low-latitude breeding grounds. However, in recent years, this vocal behaviour has been increasingly reported outside these areas. All singers in a given population sing the same version of a song and this song is continually evolving over time with modifications on different levels within the song structure. Tracing changes in whale song will help to undercover the drivers underlying this vocal display and contribute to the understanding of animal culture and its evolution. To determine the progressive changes in songs found on a subarctic feeding ground and migratory stopover, a detailed analysis of humpback whale song recordings from Northern Norway was conducted. Passive acoustic data from the Lofoten-Vesterålen Ocean Observatory (LoVe), collected using a bottom-moored underwater hydrophone, were used from January - April 2018 and January 2019. Two measures of the song structure were examined: (1) sequence similarities using the Levenshtein distance and (2) song complexity using a principal component analysis (PCA). In total, 21 distinct themes were identified which presented highly directional, structural changes over time. Two themes from 2018 reoccurred in 2019, whereas all other themes in 2019 appeared to be evolved versions of 2018 themes. All songs grouped into three general clusters, reflecting the rapid evolution over the study period. With all sampled animals singing the same version of the song, this might indicate that the singers are either from the same breeding population or that song learning occurred before the study period. Song complexity appeared to follow the trend of song progression; songs became more complex as they evolved over the months in 2018 and decreased in complexity between the years, returning to a more simplified song in 2019. The results confirm that humpback whale song exhibits a rapid progression on a shared subarctic feeding ground, with strong potential for song exchange and opportunities for cultural transmission between populations in the North Atlantic.publishedVersio

Distribution of rorquals and Atlantic cod in relation to their prey in the Norwegian high Arctic

Recent warming in the Barents Sea has led to changes in the spatial distribution of both zooplankton and fish, with boreal communities expanding northwards. A similar northward expansion has been observed in several rorqual species that migrate into northern waters to take advantage of high summer productivity, hence feeding opportunities. Based on ecosystem surveys conducted during August–September in 2014–2017, we investigated the spatial associations among the three rorqual species of blue, fin, and common minke whales, the predatory fish Atlantic cod, and their main prey groups (zooplankton, 0-group fish, Atlantic cod, and capelin) in Arctic Ocean waters to the west and north of Svalbard. During the surveys, whale sightings were recorded by dedicated whale observers on the bridge of the vessel, whereas the distribution and abundance of cod and prey species were assessed using trawling and acoustic methods. Based on existing knowledge on the dive habits of these rorquals, we divided our analyses into two depth regions: the upper 200 m of the water column and waters below 200 m. Since humpback whales were absent in the area in 2016 and 2017, they were not included in the subsequent analyses of spatial association. No association or spatial overlap between fin and blue whales and any of the prey species investigated was found, while associations and overlaps were found between minke whales and zooplankton/0-group fish in the upper 200 m and between minke whales and Atlantic cod at depths below 200 m. A prey detection range of more than 10 km was suggested for minke whales in the upper water layers.publishedVersio