Bottom-Up Regulation of Capelin, a Keystone Forage Species

Abstract

The Northwest Atlantic marine ecosystem off Newfoundland and Labrador, Canada, has been commercially exploited for centuries. Although periodic declines in various important commercial fish stocks have been observed in this ecosystem, the most drastic changes took place in the early 1990s when the ecosystem structure changed abruptly and has not returned to its previous configuration. In the Northwest Atlantic, food web dynamics are determined largely by capelin (Mallotus villosus), the focal forage species which links primary and secondary producers with the higher trophic levels. Notwithstanding the importance of capelin, the factors that influence its population dynamics have remained elusive. We found that a regime shift and ocean climate, acting via food availability, have discernible impacts on the regulation of this population. Capelin biomass and timing of spawning were well explained by a regime shift and seasonal sea ice dynamics, a key determinant of the pelagic spring bloom. Our findings are important for the development of ecosystem approaches to fisheries management and raise questions on the potential impacts of climate change on the structure and productivity of this marine ecosystem.

Northern cod comeback

“…The abundance of capelin is likely key, with availability to cod in the Bonavista Corridor increasing since 2006 after almost two decades of low abundance. Capelin biomass has been strongly correlated with rebounding cod biomass, which supports earlier notions that northern cod could not rebuild without them (Rose and O'Driscoll 2002), as well as recent modelling (e.g., Buren et al 2014) and laboratory studies using different approaches and data. It is also possible that immigration of fish occurred, most likely from Smith Sound.…”

“…In recent years, anecdotal evidence suggests capelin have returned to the north, although no surveys have been done. A strong relationship between cod and capelin is in keeping with bottom-up influences on this Northwest Atlantic ecosystem (Greene and Pershing 2007;Buren et al 2014;). On the other hand, there has been no decline in numbers of top predators, harp (Phoca groenlandica) and hooded (Cystophora cristata) seals (DFO 2014), and harvests have been relatively low; hence, it is difficult to postulate how top-down effects (downward trophic cascades) could have been involved in such a rapid increase in the northern cod (e.g., Frank et al 2005).…”

“…Although several additional factors have been put forth in attempts to explain both the lack of rebuilding of the northern cod, including phenotypic or genetic changes in life history characteristics (Hutchings 1999;Olsen et al 2004;Fudge and Rose 2008) and continued overfishing (Shelton et al 2006), the potential importance of a lack of food, in particular capelin, has been repeatedly noted (Rose and O'Driscoll 2002;Davoren and Montevecchi 2003;Obradovich et al 2014;Buren et al 2014).…”

Why timing is everything: Energetic costs and reproductive consequences of resource mismatch for a chick‐rearing seabird

“…Coattendance times, however, were more divergent; with the exception of 2008, durations recorded by Burger & Piatt (1990) during the 1980s were up to 4 h greater than the values reported here (i.e., murres are currently working harder). These differences lend further support to the argument that an abrupt state change in capelin timing and abundance following a regime shift in the early 1990s (Buren et al 2014) caused breeding murres to be more constrained than they were in the 1980s . Capelin biomass and timing are influenced by seasonal sea ice dynamics which are key determinants of the pelagic spring bloom and subsequent emergence of Calanus finmarchicus, capelin's primary prey, from diapause (Buren et al 2014).…”

“…Nevertheless, extreme ice conditions can create profound bottom-up food web effects (Buren et al 2014). In fact, there were peaks in ice area (predictor for capelin timing) when murres and Atlantic puffins Fratercula arctica indicated late arrival of capelin during 2000 and 2009 (Doody et al 2008, Rector et al 2012; this study), and slumps in the timing of ice retreat (predictor of capelin abundance) when murres indicated low capelin abundance during 1984 and 2010 (Burger and Piatt 1990).…”