Ecosystem structure in the Iceland Sea and recent changes to the capelin (Mallotus villosus) population

Abstract

Pálsson, Ó. K., Gislason, A., Guðfinnsson, H. G., Gunnarsson, B., Ólafsdóttir, S. R., Petursdottir, H., Sveinbjörnsson, S., Thorisson, K., and Valdimarsson, H. 2012. Ecosystem structure in the Iceland Sea and recent changes to the capelin (Mallotus villosus) population. – ICES Journal of Marine Science, 69: . The objective of the Iceland Sea Ecosystem Project was to analyse principal ecosystem patterns, including the life history of capelin. Ten surveys were conducted for this purpose between 2006 and 2008, and hydrographic data from 1970 to 2011 were analysed. Long-term temporal patterns indicate an increase in the temperature of surface and intermediate waters during recent years in the Iceland Sea. The phytoplankton consisted mainly of diatoms in spring, with flagellates and dinoflagellates appearing later in the year. Zooplankton and fish were dominated by a few species. In late summer, the pelagic foodweb ranged between trophic levels 2.4 and 3.6. Trends in nutrients and primary production showed a clear seasonal pattern with a spring bloom in late May, followed by a peak in secondary production in July/August. The spatial structure of the lower ecosystem levels in summer was stable across the 3 years, determined mainly by the structure of the water masses. The pelagic fish fauna consisted primarily of adult pelagic fish and transient numbers of larval species. The spatial pattern of capelin indicated northward displacement of 0-group capelin and westward displacement of older capelin in recent years. The annual biomass was estimated at 3.8 million tonnes of phytoplankton, ∼21 million tonnes of zooplankton, and 1.0 million tonnes of fish.

Improved transport estimate of the East Icelandic Current 2002–2012

“…From the north, the Iceland Sea receives fresh and cold waters which are branching off from the East Greenland Current (EGC) (Figure ) [ Swift and Aagaard , ; Dickson et al ., ; Pálsson et al ., ]. The main water masses are Polar Surface Water (PSW, σ Θ ≤ 27.70 kg m −3 ) [ Rudels et al ., ], in the Iceland Sea also termed Arctic Surface Water (ASW) [ Swift and Aagaard , ].…”

“… Schematic map of the surface circulation in the Iceland Sea, based on surface drifter trajectories; figure adapted from Pálsson et al . []. Red dots denote the standard stations LN1–LN6 on the LanganesNE section, and the black cross marks the position of the EIC mooring.…”

Fluxes of carbon and nutrients to the Iceland Sea surface layer and inferred primary productivity and stoichiometry

“…Gudfinnsson (2012) found, from his data of daily productivity, an average annual phytoplankton productivity of 65 g C m −2 yr −1 , and Thordardottir (1984) presented an average annual primary production in the Arctic domain, in the vicinity of the time series station, of 75 g C m −2 yr −1 , based on measured 14 C uptake at light saturation. A modelling study (Skogen et al, 2007), suggests a mean annual production in the Iceland Sea at 70 g C m −2 yr −1 , with an f ratio of ∼ 0.7.…”

“…The Iceland Sea ( Fig. 1) is most often defined as the waters delimited by Greenland in the west; the Denmark Strait and the continental shelf break south of Iceland to the south; by Jan Mayen and the Jan Mayen Fracture Zone to the north and by the Jan Mayen Ridge to the east (Pálsson et al, 2012). The hydrographic properties of the Iceland Sea can generally be described as Arctic Intermediate Water overlying Arctic Deep Water (e.g.…”

Harvest control rules in modern fisheries management

“…Recent research suggests that changes in the distribution, which were related to climate changes, affected the results from the autumn surveys (Palsson et al, 2012;Carscadden et al, 2013). Not until 2010, when the survey area was increased and the autumn surveys covered the full distribution of the stock, was it again possible to set a preliminary TAC.…”