Identification of skate nursery habitat in the eastern Bering Sea

Abstract

Identification of habitat used for skate egg deposition has been rarely studied or reported worldwide. Four nursery sites for the Alaska skate Bathyraja parmifera, 2 for the Aleutian skate B. aleutica and 2 for the Bering skate B. interrupta were identified along the upper continental slope in the eastern Bering Sea. All sites were located near undersea canyons from 145 to 380 m depth in relatively flat sandy to muddy bottom habitat. Bottom temperatures were relatively constant throughout the year, varying from 3.7 to 4.6°C. Egg case densities varied between nursery sites and were encountered at the Alaska skate nursery in Bering Canyon at densities greater than 800 000 eggs km -2 . Based on egg case composition, sites were predominantly used by a single skate species for egg deposition; however, up to 6 skate species used the habitat commonly. Seasonal sampling indicated that sites were continuously occupied throughout the year, and embryo length composition showed multiple cohorts developing simultaneously. Data from bottom trawl surveys suggest juvenile skates occupy habitats different than nursery sites. The movement of juvenile skates out of nursery habitat after hatching may lessen predation by common predators such as the Pacific cod Gadus macrocephalus and the Pacific halibut Hippoglossus stenolepis.KEY WORDS: Elasmobranch · Skate · Reproduction · Egg case · Undersea canyon · Nursery · Alaska Resale or republication not permitted without written consent of the publisherMar Ecol Prog Ser 403: [243][244][245][246][247][248][249][250][251][252][253][254] 2010 Lauth & Acuna 2009). Combined these 3 species constitute > 95% of the skate population and biomass in the entire EBS (20 to 1200 m depth) and are the major components of skate bycatch in non-target commercial bottom trawl and longline fisheries (Stevenson 2004). Other important slope-dwelling species in the EBS include the whiteblotched skate B. maculata, the mud skate B. taranetzi, the Commander skate B. lindbergi and the whitebrow skate B. minispinosa (Hoff & Britt 2009).This study focuses on identification of skate nursery habitat for 3 abundant skate species in the eastern Bering Sea. Four nursery sites for the Alaska skate, 2 nursery sites for the Aleutian skate, and 2 nursery sites for the Bering skate ( Fig. 1) are described. Some important biological aspects examined were skate and skate egg case composition, egg case densities and predation on juvenile skates. Nursery habitat parameters include location, temporal use, depth, temperature, bottom topography and associated sessile fauna EasternBering SeaGulf of Alaska P e rv e n e ts C a n y o n P r ib il o f C a n y o n B e r in g C a n y o n MATERIALS AND METHODSNursery habitat identification. Initial locations of nursery sites were identified based on fisheries data, and previous survey trawls in which large numbers of skate egg cases were reported in the catch. Identified sites were subsequently sampled using bottom trawls in an adaptive sampling approach to identify the egg...

Ecological Role of Submarine Canyons and Need for Canyon Conservation: A Review

“…An increasing amount of data provides evidence of how canyons act benefiting and supporting fisheries (Yoklavich et al, 2000;Company et al, 2012), and enhance carbon sequestration and storage (Epping et al, 2002;Canals et al, 2006;Masson et al, 2010). Canyon habitats also provide nursery (Sardà and Cartes, 1994;Hoff, 2010;Fernandez-Arcaya et al, 2013) and refuge sites for other marine life (Tyler et al, 2009;De Leo et al, 2010;Vetter et al, 2010;Morris et al, 2013), including vulnerable marine ecosystems and essential fish-habitats such as cold-water corals and sponge fields (Schlacher et al, 2007;Huvenne et al, 2011;Davies et al, 2014). Canyons have also been shown to provide habitat for spawning females of pelagic and benthic species of commercial interest (Farrugio, 2012).…”

Elasmobranch egg capsules associated with modern and ancient cold seeps: a nursery for marine deep-water predators

“…This genus is comprised of ~45 described species, which generally occur on continental slopes below 200 m (Compagno 1999). This area has possibly been a nursery for several generations of skates (Hoff 2010). Large (total length ca.…”

“…Carbonate deposits provide locations for capsule holdfasts, e.g. through tubeworms, gorgonians (Etnoyer & Warrenchuk 2007), and sponges (Hoff 2010); protection (between carbonate boulders or tubeworms), and/or enhanced current conditions (e.g. ventilation) for the egg capsules (Etnoyer & Warrenchuck 2007, Flammang et al 2007, Love et al 2008, Hoff 2010 on the otherwise nearly flat deepsea floor.…”

“…through tubeworms, gorgonians (Etnoyer & Warrenchuk 2007), and sponges (Hoff 2010); protection (between carbonate boulders or tubeworms), and/or enhanced current conditions (e.g. ventilation) for the egg capsules (Etnoyer & Warrenchuck 2007, Flammang et al 2007, Love et al 2008, Hoff 2010 on the otherwise nearly flat deepsea floor. We do not know if the seep biostrome is still of importance for the neonate and juvenile sharks and skates after hatching because we could not confirm their presence in the vicinity of the egg capsules.…”

“…Oviparous deepwater sharks are reported to preferentially deposit their eggs at well-ventilated and sheltered locations, such as elevated colonies of octocorals and gorgonians, to increase survivorship and decrease predation (Etnoyer & Warrenchuk 2007). Eggs of oviparous deep-water skates are found associated with canyon heads (Hoff 2010) or edges (Love et al 2008) that may provide optimum current conditions for egg ventilation. Here we demonstrate that cold-seep habitats with exposed carbonate landscapes and tubeworm colonies serve as nurseries for deep-water elasmobranchs, providing further evidence for the importance of these localized environments for the deepsea community.…”