Harp Seals: Monitors of Change in Differing Ecosystems

Stenson, Garry B.; Haug, Tore; Hammill, Mike O.

doi:10.3389/fmars.2020.569258

Cited by 25 publications

(50 citation statements)

References 94 publications

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“…Reconstructed data displayed higher demersal fish biomass and lower mammals biomass than the majority of simulated biomass in the NDND simulations ( Fig 3 ). These results are consistent with the hypothesized competition between mammals and demersal fish in the Barents Sea [ 41 ] and with the lower levels of estimated marine mammals abundance during the last three decades in the Barents Sea [ 42 ]. The simulated pelagic fish biomass displayed a bimodal distribution with many high and low values of biomass, and few intermediate biomass values ( Fig 3 ).…”

Section: Discussionsupporting

confidence: 89%

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

et al. 2021

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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.

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Section: Discussionsupporting

confidence: 89%

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

et al. 2021

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“…In the Arctic specifically, some of the organic carbon of their prey can be traced back to sea-ice primary production (Kohlbach et al 2017), an early-season energy source that fuels food webs within the Arctic (Ji et al 2013). Arctic sea-ice declines have already resulted in breeding and foraging habitat reductions for harp and ringed seals (Hamilton et al 2017, 2019, Stenson et al 2020). These pinnipeds will likely encounter increased competition in the remaining sea-ice areas from boreal species shifting northward (Kovacs et al 2011(Kovacs et al , Øigård et al 2013 and from each other, given that they are increasingly overlapping in some areas of their Barents Sea distributions (Bengtsson et al 2020).…”

Section: Introductionmentioning

confidence: 99%

“…These pinnipeds will likely encounter increased competition in the remaining sea-ice areas from boreal species shifting northward (Kovacs et al 2011(Kovacs et al , Øigård et al 2013 and from each other, given that they are increasingly overlapping in some areas of their Barents Sea distributions (Bengtsson et al 2020). The overall reduction or loss of sea-ice primary production and its cumulative effects on food webs are currently unknown, though harp seals are showing declining body condition that is thought to be due to competition with other predators, including the large standing stock of Atlantic cod Gadus morhua, which has shifted northward in the Barents Sea region (Stenson et al 2020).…”

Section: Introductionmentioning

confidence: 99%

Ice-algal carbon supports harp and ringed seal diets in the European Arctic: evidence from fatty acid and stable isotope markers

Kunisch

Graeve

Gradinger

et al. 2021

Mar. Ecol. Prog. Ser.

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Sea-ice declines in the European Arctic have led to substantial changes in marine food webs. To better understand the biological implications of these changes, we quantified the contributions of ice-associated and pelagic carbon sources to the diets of Arctic harp and ringed seals using compound-specific stable isotope ratios of fatty acids in specific primary producer biomarkers derived from sea-ice algae and phytoplankton. Comparison of fatty acid patterns between these 2 seal species indicated clear dietary separation, while the compound-specific stable isotope ratios of the same fatty acids showed partial overlap. These findings suggest that harp and ringed seals target different prey sources, yet their prey rely on ice and pelagic primary production in similar ways. From Bayesian stable isotope mixing models, we estimated that relative contributions of sympagic and pelagic carbon in seal blubber was an average of 69% and 31% for harp seals, and 72% and 28% for ringed seals, respectively. The similarity in the Bayesian estimations also indicates overlapping carbon sourcing by these 2 species. Our findings demonstrate that the seasonal ice-associated carbon pathway contributes substantially to the diets of both harp and ringed seals.

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“…Several species of marine mammals, seabirds and fish are also known consumers of some of the forage species targeted by fin whales 19 . Species such as harp seals and grey seals have substantially increased in abundance over the past decades 23 , 24 .However, the degree of interspecific competition for prey resources during the study period remains largely unknown, and may require further consideration in future studies.…”

Section: Discussionmentioning

confidence: 99%

“…Additionally, oceanographic conditions, characterized by below-average seawater temperatures, changed around year 2000 towards above-average sea temperatures and below-average ice conditions, which have continued to prevail since 20 . Populations of potential competitors of baleen whales, such as harp seals ( Pagophilus groenlandicus ) and grey seals ( Halichoerus grypus ), increased during this period 23 , 24 . It was suggested that these ecosystem changes caused a reduction in prey availability for baleen whales, leading to a decrease in whale abundance at some foraging sites 25 .…”

Section: Introductionmentioning

confidence: 98%

Individual and population dietary specialization decline in fin whales during a period of ecosystem shift

Cabrol

Lesage

Leclerc

et al. 2021

Sci Rep

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This study sought to estimate the effect of an anthropogenic and climate-driven change in prey availability on the degree of individual and population specialization of a large marine predator, the fin whale (Balaenoptera physalus). We examined skin biopsies from 99 fin whales sampled in the St. Lawrence Estuary (Canada) over a nine year period (1998–2006) during which environmental change was documented. We analyzed stable isotope ratios in skin and fatty acid signatures in blubber samples of whales, as well as in seven potential prey species, and diet was quantitatively assessed using Bayesian isotopic models. An abrupt change in fin whale dietary niche coincided with a decrease in biomass of their predominant prey, Arctic krill (Thysanoessa spp.). This dietary niche widening toward generalist diets occurred in nearly 60% of sampled individuals. The fin whale population, typically composed of specialists of either krill or lipid-rich pelagic fishes, shifted toward one composed either of krill specialists or true generalists feeding on various zooplankton and fish prey. This change likely reduced intraspecific competition. In the context of the current “Atlantification” of northern water masses, our findings emphasize the importance of considering individual-specific foraging tactics and not only population or group average responses when assessing population resilience or when implementing conservation measures.

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Harp Seals: Monitors of Change in Differing Ecosystems

Cited by 25 publications

References 94 publications

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

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

Ice-algal carbon supports harp and ringed seal diets in the European Arctic: evidence from fatty acid and stable isotope markers

Individual and population dietary specialization decline in fin whales during a period of ecosystem shift

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