Influence of the frontal zones on ichthyoplankton and mesopelagic fish assemblages in the Crozet Basin (Indian sector of the Southern Ocean)

102

131

The distribution of southern elephant seal Mirounga leonina prey encounter events (PEEs) was investigated from the foraging behaviour of 29 post-breeding females simultaneously equipped with a satellite tag, a time−depth recorder and a head-mounted accelerometer. Seal diving depth and PEE were related to water temperature at 200 m (T 200 ), and light level at the surface (L 0 ) and at depth. Approximately half (49%) of all dives were located in waters encompassed between the southern Antarctic Circumpolar Current Front and the Polar Front. Seals dived significantly deeper during the day than at night. Diving and PEE depth increased with increasing T 200 and for a given T 200 according to L 0 and the percentage of surface light reaching 150 m. On average, 540 PEEs per day were recorded. Seals exhibited more PEEs per unit of time spent diving during the twilight period compared with at night, and were least successful during daylight hours. Elephant seals forage in T 200 ranging between −1 and 13°C; however, few PEEs were recorded at depths shallower than 400−500 m at night when the T 200 exceeded 8°C. The diet of female Kerguelen elephant seals appears to be dominated by myctophids (lanternfish), and according to the average mass of their most likely myctophid prey (9 g, Electrona calsbergi and E. antarctica; 30 g Gymnoscopelus nicholsi and G. piabilis), we estimate that seals consumed 4.8−16.1 kg of fish daily. Despite lower catch rates in warmer waters, no relationship was found between the mean T 200 at the scale of the foraging trip and daily or absolute mass gain, suggesting that elephant seals are compensating for lower catch rates by consuming larger/richer prey items in those waters.

Section: Discussionsupporting

confidence: 91%

Southern elephant seal foraging success in relation to temperature and light conditions: insight into prey distribution

Guinet¹,

Vacquié‐Garcia²,

Picard³

et al. 2014

102

131

“…at the northern limit of the Polar Front. This confirms data obtained through oceanlc campai.gns in this area (Koubbi 1993). The average temperature at 200 m extrapolated from sea-surface temperature data in this latitudinal band (i.e.…”

Section: Foraging Areas and Hydrographic Featuressupporting

confidence: 89%

“…For these 2 sectors, bathymetric data indicates depths ranging between 2000 and 4000 m, without any noticeable discontinuity (Koubbi 1993). High foraging success for king penguins in the sector 47"-48" S was observed for brooding as well a s incubating birds.…”

Section: Foraging Areas and Hydrographic Featuresmentioning

confidence: 87%

Foraging habitat and food intake of satellite-tracked king penguins during the austral summer at Crozet Archipelago

Bost¹,

Georges²,

Guinet³

et al. 1997

152

108

ABSTRACT. The relationsh~ps between the foraging strategy of seabirds, hydrographic features and food availability are poorly understood. We investigated the movements at sea, time spent per oceanic sector, food intake, and d~e t of king pengulns Aptenodytespatagonicus in the Crozet Islands (Southern Indian Ocean) during summer, as a function of the position of major frontal zones. Fifteen trips at sea were monitored using satelhte transmitters over 3 austral summers (1992 to 1994). During each season, satellite transmitters were used in conjunction with stomach temperature recorders in order to investigate feeding activity. The at-sea distribution of klng penguins was closely related to the localisation of major hydrographic frontal systems. Intense prospecting areas were observed mainly in zones corresponding to the northern h i t of the Polar Front (50" to 51°S), southern limit of the Sub-Antarctic Front (44.50' to 45O S], and a zone between 47' and 48" S. During trips directed south, 2 distinct phases based on travelling speed were detected. The myctophids Electrons carlsbergi, Krefftichtys anderssoni and Protomyctophurn tenisoni dominated the diet. The est~mated average amount of food ingested per day at sea was 2.4 kg. Between 17 and 64 kg of food was captured during 7 to 25 d at sea. Approximately 80% of the food intake occurred during the first phase of the trip. Food intake was related to trip duration and relative amount of time spent in particular oceanic sectors. The sections 47' to 48" S and 48.5" to 50.50" S appeared particularly favorable for food intake, the latter coinciding with the northern limit of the Polar Front. King penguins fed ~ntensively on several distinct patches when traveling towards the Polar Front. The foraging range seems to be related to the foraging success during the first phase of the trip. The foraging strategy of king penguins during the summer favors displacements toward frontal zones where food availability is optimal.

“…Mesoscale fronts are common in coastal areas, but are still poorly understood in terms of their oceanography and how they structure bio logical communities (Landry et al 2012). While studies on the complex plankton community dynamics at a front have included mid-trophic level organisms, most have focused on fish and crustaceans (Backus et al 1969, Angel 1989, Koubbi 1993, Pakhomov et al 1994, Lara-Lopez et al 2012. Gelatinous zooplankton, as iono-and osmo-conformers that adjust slowly to even small salinity gradients, also tend to aggregate at density discontinuities (Mills 1984).…”

Section: Introductionmentioning

confidence: 99%

Environmental drivers of the fine-scale distribution of a gelatinous zooplankton community across a mesoscale front

Luo¹,

Grassian²,

Tang³

et al. 2014

Mesoscale fronts occur frequently in many coastal areas and often are sites of elevated productivity; however, knowledge of the fine-scale distribution of zooplankton at these fronts is lacking, particularly within the mid-trophic levels. Furthermore, small (<13 cm) gelatinous zooplankton are ubiquitous, but are under-studied, and their abundances underestimated due to inadequate sampling technology. Using the In Situ Ichthyoplankton Imaging System (ISIIS), we describe the fine-scale distribution of small gelatinous zooplankton at a sharp salinitydriven front in the Southern California Bight. Between 15 and 17 October 2010, over 129 000 hydromedusae, ctenophores, and siphonophores within 44 taxa, and nearly 650 000 pelagic tunicates were imaged in 5450 m 3 of water. Organisms were separated into 4 major assemblages which were largely associated with depth-related factors. Species distribution modeling using boosted regression trees revealed that hydromedusae and tunicates were primarily associated with temperature and depth, siphonophores with dissolved oxygen (DO) and chlorophyll a fluorescence, and ctenophores with DO. The front was the least influential out of all environmental variables modeled. Additionally, except for 6 taxa, all other taxa were not aggregated at the front. Results provide new insights into the biophysical drivers of gelatinous zooplankton distributions and the varying influence of mesoscale fronts in structuring zooplankton communities.