Forecasting capelin Mallotus villosus biomass on the Newfoundland shelf

Abstract

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.

Accounting for a nonlinear functional response when estimating prey dynamics using predator diet data

“…sea surface temperature), chlorophyll and zooplankton biomass have all had oscillatory dynamics in the last 20 years (Colbourne et al, 2018;NAFO, 2019) which may have driven some of the variability in sand lance population dynamics. In fact, the oscillatory pattern observed here for sand lance loosely matches the patterns that have been estimated for 2J3KL capelin (Lewis et al, 2019),…”

Harp Seals: Monitors of Change in Differing Ecosystems

“…Stenson et al (2016) found that while the general decline in fecundity is a reflection of densitydependent processes associated with increased population size, the large inter-annual variability is due to varying rates of late term abortions which are related to changes in capelin abundance and mid-winter ice coverage. Capelin biomass on the Newfoundland Shelf has been shown to be impacted by changes in the timing of ice retreat which influences the timing of the primary productivity bloom and, as a result, the amount of zooplankton available as prey for capelin (Buren et al, 2014;Lewis et al, 2019). This suggests that mid-winter ice extent reflects environmental conditions that influence a variety of harp seal prey species.…”

Distribution and Life History of Spawning Capelin in Subarctic Alaska

“…In contrast, Capelin biomass on the Newfoundland Shelf was estimated at 22,000 metric tons in 2010 and typically ranged from 98,000 to 200,000 metric tons during 2003–2017 based on acoustic surveys (Lewis et al. ).…”