The role of harp seals, fisheries and food availability in driving the dynamics of northern cod

Buren, Alejandro D.; Koen‐Alonso, Mariano; Stenson, Garry B.

doi:10.3354/meps10897

Cited by 31 publications

(41 citation statements)

References 60 publications

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“…Furthermore, in 1991 there was a major reduction in capelin biomass in the NewfoundlandLabrador shelf area, and to date this stock has not recovered (DFO, 2010). Concomitant increases in the abundance of Northwest Atlantic harp seals has prompted modeling enquiries to assess whether these events were related (Buren et al, 2014): Cod biomass dynamics were best explained by a combination of fisheries removals and capelin availability, whereas seal consumption was found not to be an important driver of the cod stock. Buren et al (2014) did, however, not assess if the currently generally low pressure on common prey species by cod might have some beneficial effects on harp seal growth and condition in the area.…”

Section: Discussion Possible Mechanisms In Predation and Competitionmentioning

confidence: 99%

“…Concomitant increases in the abundance of Northwest Atlantic harp seals has prompted modeling enquiries to assess whether these events were related (Buren et al, 2014): Cod biomass dynamics were best explained by a combination of fisheries removals and capelin availability, whereas seal consumption was found not to be an important driver of the cod stock. Buren et al (2014) did, however, not assess if the currently generally low pressure on common prey species by cod might have some beneficial effects on harp seal growth and condition in the area. Long term fluctuations in body condition have been observed in Northwest Atlantic harp seals where adult seals were in poorer condition in the early 1990s (after the collapse of capelin and with cod on its way down, Buren et al, 2014) than in the mid 1980s before the fish stocks declined (Chabot et al, 1996).…”

Section: Discussion Possible Mechanisms In Predation and Competitionmentioning

confidence: 99%

“…Buren et al (2014) did, however, not assess if the currently generally low pressure on common prey species by cod might have some beneficial effects on harp seal growth and condition in the area. Long term fluctuations in body condition have been observed in Northwest Atlantic harp seals where adult seals were in poorer condition in the early 1990s (after the collapse of capelin and with cod on its way down, Buren et al, 2014) than in the mid 1980s before the fish stocks declined (Chabot et al, 1996).…”

Section: Discussion Possible Mechanisms In Predation and Competitionmentioning

confidence: 99%

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A review of the battle for food in the Barents Sea: cod vs. marine mammals

et al. 2015

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Cod, harp seal and minke whale are the main top predators in the Barents Sea ecosystem. In the last decade, the abundance of cod has increased considerably, and is at a record high level. In spite of this, the growth and condition of cod has remained rather stable, although some decrease is seen in size at age of large, mature cod. During the same period, the abundance of harp seals has declined whereas the minke whale stock has been at a stable level. The body condition (blubber thickness) of these two mammal stocks has, however, decreased, with the strongest decrease observed for harp seals. A possible hypothesis for explaining this is that cod outperform the marine mammal stocks in the competition for food. The main advantages for cod are most likely larger availability of food (mainly capelin) during winter-spring than for marine mammals, as well as a wider range of prey species being available to cod than to marine mammals. Harp seals are more dependent on prey items found close to the ice edge than the other two predator stocks are, which could partly explain why the performance of harp seals is worse than that of the two other main top predators in the area.

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Section: Discussion Possible Mechanisms In Predation and Competitionmentioning

confidence: 99%

Section: Discussion Possible Mechanisms In Predation and Competitionmentioning

confidence: 99%

Section: Discussion Possible Mechanisms In Predation and Competitionmentioning

confidence: 99%

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A review of the battle for food in the Barents Sea: cod vs. marine mammals

et al. 2015

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“…predation) forces are considered major drivers of capelin survival, the collapse of the Newfoundland capelin stock in the early 1990s is hypothesized to have been due to bottom-up processes that affected the recruitment and survival of capelin (Buren et al 2014a, Obradovich et al 2014. In the NW Atlantic, capelin are a key driver in the biomass dynamics of Atlantic cod Gadus morhua (Buren et al 2014b), linked to changes in fecundity of Northwest Atlantic harp seals Pagophilus groenlandicus (Stenson et al 2016), and are key prey for Greenland halibut Reinhardtius hippoglossoides (Dwyer et al 2010), whales (Gulka et al 2017, J. Lawson & G. Stenson unpubl. data), and seabirds (Davoren & Montevecchi 2003, Montevecchi 2007, Buren et al 2012.…”

Section: Introductionmentioning

confidence: 99%

Forecasting capelin Mallotus villosus biomass on the Newfoundland shelf

Lewis¹,

Buren²,

Regular³

et al. 2019

Mar. Ecol. Prog. Ser.

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Forage fish play a central role in marine ecosystems, acting as a trophic link between plankton and larger marine species. They also contribute to global economies by directly and indirectly supporting commercial and recreational fisheries. Managing forage fish is problematic due to their high spatial-temporal variation in biomass and strong responses to environmental variability. A variety of mechanisms have been proposed to explain variation in capelin Mallotus villosus biomass, a keystone forage fish in the Northwest Atlantic, including factors influencing cohort strength such as larval abundance and larval food (i.e. Pseudocalanus spp.) availability. Alternately, pre-spawning mortality of capelin may be regulated by the timing of the retreat of sea ice (t ice) via its effects on the spring bloom and the availability of food (e.g. Calanus spp.) for adult capelin, or by the condition of adult capelin the previous fall. Here, we used a Bayesian approach in a multimodel inference framework to assess support for a series of hypotheses explaining the population dynamics of capelin. The most parsimonious model included larval abundance, t ice , and capelin condition in the fall, and explained 68% of the variance in capelin biomass. These results are consistent with much of the literature that suggests capelin in the Northwest Atlantic are driven by bottom-up forces. This model allows us to produce forecasts of capelin biomass 1−2 management cycles in advance, which will be a valuable contribution to the management of this forage fish species.

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“…This ontogenetic diet shift is coincidental with the aforementioned spatial ontogenetic shift at early ages. That we observed the relationship between temperature and growth to become increasingly positive in sizes of fish expected to become increasingly reliant on capelin as a diet staple further suggests that many of the benefits [detriments] of warming [cooling] operate through the food web (Buren, Koen‐Alonso, & Stenson, ; Buren, Koen‐Alonso, Pepin, et al, ; Mullowney et al, ).…”

Section: Discussionmentioning

confidence: 65%

Temperature influences on growth of unfished juvenile Northern cod (Gadus morhua) during stock collapse

Mullowney

Rose

Dawe

et al. 2019

Fisheries Oceanography

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This study examined growth of unfished juvenile Northern cod (Gadus morhua) off Newfoundland concomitant with stock collapse in the cold early 1990s. Two unpublished data sets were examined, one from collapse‐period trapping sites along the northeast coast of Newfoundland and one from a post‐collapse inshore trawl survey. Cumulative surface and bottom temperatures were significant predictors of growth rates of the young fish with year‐classes born during collapse experiencing slower growth than those born during subsequent warming. Relationships between accrued temperature and growth were consistent across periods, with slow growth of collapse‐period fish reflecting slower accumulation of temperature‐at‐age. Temperature influences were spatially broad‐based with no significant differences in growth rates for fish captured along the entire northeast coast of Newfoundland. Predicted differences in growth rates for collapse versus recovery year‐classes were proportional to cumulative surface temperatures but not cumulative bottom temperatures. Although significant, temperature effects on growth were relatively unimportant at youngest ages. Overall, growth differences between periods were small but large differences occurred between slowest and fastest growing year‐classes. The results suggest initial responses to increasing temperatures were delayed following collapse. We conclude that although temperature was an important determinant of dampened productivity that it alone cannot account for the collapse and slow recovery of the stock. This is the first known study to directly quantitatively link temperature impacts to an unfished component of the Northern cod stock complex during collapse, removing need for implicit assumptions about whether or not cold conditions contributed to the collapse of this iconic fish stock.

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The role of harp seals, fisheries and food availability in driving the dynamics of northern cod

Cited by 31 publications

References 60 publications

A review of the battle for food in the Barents Sea: cod vs. marine mammals

A review of the battle for food in the Barents Sea: cod vs. marine mammals

Forecasting capelin Mallotus villosus biomass on the Newfoundland shelf

Temperature influences on growth of unfished juvenile Northern cod (Gadus morhua) during stock collapse

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