Mesoscale Eddies Are Oases for Higher Trophic Marine Life

Mesoscale eddies stimulate biological production in the ocean, but knowledge of energy transfers to higher trophic levels within eddies remains fragmented and not quantified. Increasing the knowledge base is constrained by the inability of traditional sampling methods to adequately sample biological processes at the spatio-temporal scales at which they occur

Density dependent catchability in bottom trawl surveys

Fish form schools, layer or patches in which the individual fish's behaviour is not independent of its neighbours movements. On the other hand, at low densities fish may have the freedom to act as single individuals independently of what other fish are doing. Potentially, if these contrasts occur in nature, they may give rise to behavioural differences of fish in front of the trawl at high and low densities with successive effects on catchability and bottom trawl indices of stock abundance. We explore in this paper the hypothesis that the density of fish has a significant effect on catchability of the survey trawl. Data from Norwegian and Canadian video observation recorded during trawling are studied, and related to bag trawl experiments which measured escapement underneath the survey trawls in both regions

Silent research vessels are not quiet

Behavior of herring Clupea harengus stimulated by two ocean-going research vessels; respectively designed with and without regard to radiated-noise-standards. Both vessels generate a reaction pattern, but, contrary to expectations, the reaction initiated by the silent vessel is stronger and more prolonged than the one initiated by the conventional vessel. The recommendations from the scientific community on noise-reduced designs were motivated by the expectation of minimizing bias on survey results caused by vessel-induced fish behavior. In conclusion, the candidate stimuli for vessel avoidance remain obscure. Noise reduction might be necessary but is insufficient to obtain stealth vessel assets during surveys

Detecting Atlantic herring by parametric sonar

The difference-frequency band of the Kongsberg TOPAS PS18 parametric sub-bottom profiling sonar, nominally 1–6 kHz, is being used to observe Atlantic herring. Representative TOPAS echograms of herring layers and schools observed in situ in December 2008 and November 2009 are presented. These agree well with echograms of volume backscattering strength derived simultaneously with the narrowband Simrad EK60/18- and 38-kHz scientific echo sounder, also giving insight into herring avoidance behavior in relation to survey vessel passage. Progress in rendering the TOPAS echograms quantitative is described

Varying FML

Varying FM

Number and weight of fish species caught at three trawl stations in the Norwegian Sea.

<p>Catch (numbers, n and weight, w) composition from the Norwegian Sea eddy interior (station positions are indicated in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0030161#pone-0030161-g002" target="_blank">Figure 2</a>) as a result of targeted trawling on high acoustic densities in the DSL (#1) and on surface concentration (#2 and 3).</p

Acoustic, satellite, and ADCP comparisons from a transect through the Iceland Basin eddy.

<p>Panel A: ship track (black line) through multiple eddies as detected by satellite altimetry anomalies (colour scale in cm) in June 2004. Panels B and C: co-occurrence between the satellite altimetry anomalies (cm) of two of the eddies and the wheel structured acoustic record (panel F and G, showing S_V at 18 kHz, colour scale in dB) of two anticyclonic eddies. Water current velocity vectors (m/s, 0–600 m) along the cruise track are indicated by the blue arrows (panels B and C). Panels D and E illustrate the variation in biomass density (s_V) in the upper depth layer (150–450 m, red), intermediate depths (451–850 m, green), deep water (>850 m, blue), and entire water column (black). Vertical line in D, F indicate sunset. Sunrise is taking place prior to the start of the horizontal axis in E, G.</p

Comparison of acoustic biomass densities (s_V) related to distance from eddy centre and depth.

<p>The three panels show data for the three depth categories; A. surface layer (0–100 m), B. mid water (101–600 m) and C. deep water (Deep, ≥600 m). In each panel distance from centre are categorized in R1<9 km, 9≤R2<37 km, R3≥37 and day (D) and night (N) data are presented.</p