Seabird segregation at Gulf Stream frontal eddies

Abstract

Eddies along the western frontal boundary of the Gulf Stream result in the episodic formation of physically and biologically distinct water masses at the continental shelf break (ca 200 m lsobath) off the southeastern United States. Standardized counts of seabirds were made simultaneously with ship-board and satellite-derived (VHRR) hydrographic measurements in 3 eddy-assoc~ated water masses during July 1983, and in 4 water masses during August 1984. Two statistical models were used to test for significant relations between seabird species composition and these water masses. Contingency analyses of abundance data from both cruises revealed that seabird specles were not distributed independently of water mass type (p < ,005). Tested against the null hypothesis of homogeneous species' abundances, 85 % of common (densities 2 0 5 birds km-2) seabird species exhibited significant affinities for a single water mass. The aerially foraging and feeding black-capped petrel Pterodroma hasitata and bridled tern Sterna anaethetus were most abundant in oligotrophic Gulf Stream and warm filament water, respectively. Species foraging on the ocean surface and feeding for more prolonged periods, shearwaters Puffinus gravis and Calonectrjs diornedea and storm-petrels Oceanites oceanicus and Oceanodroma castro, were most abundant in the upwelled cold core of the eddy. Interspecific variation in seabird affinities for meso-scale (50 to 150 km) water masses can be attributed to trophic segregation originating from species-specific foraging behaviors, and oceanographic processes that dlrectly or indirectly influence prey availability. These patterns indicate that apex marine consumers parallel other taxa and trophic groups in their responses to environmental heterogeneity induced by western boundary currents. Gulf Stream frontal eddies persist at 'event' time scales (2 to 14 d ) , thereby further suggesting that some s e a b~r d s are functionally integrated with marine communities affiliated with relatively small, ephemeral, and kinetic physical features.

Predator diversity hotspots in the blue ocean

“…Oceanographically, these features are characterized by increased turbulence, mixing, and mesoscale eddies, which can enhance local production by transporting nutrients into the euphotic zone (28,29). In addition, they also tend to concentrate food supply and have been shown to provide key feeding areas for pelagic species (30)(31)(32). Diversity hotspots in the northwest Atlantic as well as Hawaii coincide conspicu- Fig.…”

Impact of El Niño on the foraging behavior of female northern elephant seals

“…2) revealed typical wide coverage of the northeast Pacific Ocean. Mean maximum distance traveled was not significantly different in 1998 (1841 ± 827 km) than in data pooled from 1995 to 1996 and 1999 (2270 ± 603 km; Niño: 1983 and1998;weak El Niño: 1987no El Niño: 1984to 1986, 1989to 1991to 1997 Mass 4.1 ± 0.9 0.65 ± 0.11 (n = 12) (n = 8) (n = 12) (n = 7) (n = 7) (n = 7) (n = 6) Weak El Niño 1.03 ± 0.25 70.1 ± 8.5 (n = 8) n/a (n = 8) n/a n/a n/a n/a…”

“…Marine predators may rely on oceanographic features, such as frontal systems, thermocline depth, and bathymetry to concentrate or aggregate prey (Hui 1979, 1985, Schneider 1982, Springer & Roseneau 1985, Haney 1986, 1991, Winn et al 1986, Ainley & DeMaster 1990, Reilly 1990, Boyd & Arnbom 1991, Hunt et al 1992, van Franeker 1992, Whitehead et al 1992, Elphick & Hunt 1993, Kenney et al 1995, Mehlum et al 1996, Hunt 1997. These aggregations may be essential to enable energy efficient foraging strategies in the oceanic environment.…”

“…Weak El Niño years included 1987. No El Niño years included 1984to 1986, 1989to 1991to 1997 Movement analysis. All Argos location qualities except class Z were included in the analysis.…”

“…The widespread biological impacts of El Niño events are not well understood. Dramatic impacts on reproductive parameters of seabirds and fisheries stocks have been described for previous ENSO events (Barber & Chavez 1983, 1986, Schreiber & Schreiber 1984, as well as dramatic large-scale changes in the distribution of some species (Arntz et al 1991, Raskoff 2001. Major changes in structure and productivity of the North Pacific sub-tropical gyre have been attributed to ENSO events (Karl et al 1995).…”