Distribution of red king crabs and Tanner crabs in the summer by habitat and depth in an Alaskan fjord

Abstract

ABSTRACT.A manned submersible was used in a fjord in southeastern Alaska to study the distributional patterns of the red king crab (Paralithodes camtschaticus) and the Tanner crab (Chionoecetes bairdi) in summer. The cove was divided into three zones: inner, middle, and outer. Six types of habitats, including sand-mud, rock, shell, debris, rock wall, and algae, were identified from video tapes. A relatively flat sand-mud habitat located at the center of the cove occupied 60% of the sea bottom. This large habitat was bordered by steep rocky walls on both sides in most parts of the fjord except in the inner zone. The density of red king crab decreased from the inner zone to the outer zone, while the density of the Tanner crab was more uniform throughout the cove. Highest crab density was found in the sand-mud habitat with an overall density of 51 crabs ha -1 for the red king crab and 41 crabs ha -1 for the Tanner crab. No crabs were found in rock wall and algae habitats. Both crab species displayed a dome-shaped distribution with depth with maximum density at intermediate depths. Red king crabs had a maximum density (86 crabs ha Distribución de la centolla y del cangrejo Tanner en verano, de acuerdo al hábitat y a la profundidad, en un fiordo de Alaska RESUMEN. Se utiliza un sumergible tripulado para estudiar los patrones de distribución de la centolla (Paralithodes camtschaticus) y del cangrejo Tanner (Chionoecetes bairdi), en un fiordo del sureste de Alaska durante el período de verano. El área de estudio fue dividida en tres zonas: interior, media, y exterior. Seis tipos de habitat, incluyendo fangoarena, roca, conchas, cascajo, pared rocosa y algas, fueron identificadas a través de grabaciones realizadas en cintas de video. Un habitat fango-arenoso relativamente plano, ubicado en el centro de la ensenada, ocupa el 60% del fondo del mar. Este gran habitat estaba bordeado por paredes rocosas abruptas a ambos lados en la mayor parte del fiordo, excepto en la zona más al interior. La densidad de la centolla disminuye desde la zona interna hacia la zona exterior, en tanto que la densidad del cangrejo Tanner se presentó uniforme en toda la ensenada. La más alta densidad se encontró en el habitat fango-arenoso, con un total de 51 individuos ha -1 para la centolla y 41 individuos ha -1 para el cangrejo. Ni en las paredes rocosas ni en las algas se encontraron cangrejos. Ambas especies mostraron una distribución en forma de domo respecto a la profundidad, con densidades máximas en profundidades intermedias. La centolla presenta densidad máxima (86 individuos ha -1 ) en 70-80 m mientras que el cangrejo Tanner (105 individuos ha -1 ) a 140-150 m. Densas agregaciones de juveniles de centolla fueron observadas en la zona más interna de la ensenada, pero no se observaron allí agregaciones de individuos maduros de ninguna de estas especies.

Podding of juvenile king crabs Lithodes santolla (Molina, 1782) (Crustacea) in association with holdfasts of Macrocystis pyrifera (Linnaeus) C. Agardh, 1980

“…The podding behavior of L. santolla was similar to that reported for P. camtschatica (Zhou & Shirley, 1997) in that individuals > 80 mm in CL were not present in the pods. Crab podding in general was not previously reported as occurring in relation to algae, which makes the present report of particular interest regarding the potential harvesting of kelp, which is currently being contemplated in this region.…”

“…maturity stage, sex, intermoult stage) and possible changes in habitat conditions such as water temperature or the presence of predators (Sampedro & González-Gurriarán, 2004). Previous studies have cited podding in king, tanner, and spider crabs (Dew, 1990;Stevens et al, 1992a;Stone et al, 1993;Zhou & Shirley, 1997;Sampedro & González-Gurriarán, 2004). Nevertheless, this type of aggregational behavior has not been reported for southern king crabs.…”

“…This behavior has also been well documented for the Majidae, including Chionoecetes bairdi (Zhou & Shirley, 1997), Chionoecetes opilio (Comeau et al, 1998), Hyas lyratus (Stevens et al, 1992b), and Maja squinado (Sampedro & González-Gurriarán, 2004). Various reasons were proposed for the aggregation behaviour in the majids, including protection during moulting, location of mates, aid in food capture, and protection from predation (Powell & Nickerson, 1965;Stevens et al, 1994;Zhou & Shirley 1997;Gardner, 1999). Observations of M. squinado by Sampedro & González-Gurriarán (2004) suggested that this behaviour was based on protection from predation.…”

“…Nevertheless, this type of aggregational behavior has not been reported for southern king crabs. Previously, this type of behaviour has been studied by means of direct observations while diving, remotely operated vehicles (ROV) carrying video or still cameras, or submersible vehicles carrying observers (Zhou & Shirley, 1997). In Chile, little work has been done using underwater images, remote vehicles, and submersibles, except for the observations of megabenthic communities in the Strait of Magellan by Gutt et al (1999).…”

Temperature-Dependent Growth of Early Juvenile Southern Tanner CrabChionoecetes bairdi: Implications for Cold Pool Effects and Climate Change in the Southeastern Bering Sea

“…In the northeastern Pacific, Tanner crabs occur in coastal waters of Washington and British Columbia, in the Gulf of Alaska, westward along the Aleutian Islands, and northward across a broad swath of the Bering Sea shelf from the Alaska Peninsula northwestward to approximately 58°N (Zheng & Kruse 2006, Nielsen et al 2007, Zheng 2008. Adult and juvenile Tanner crabs are found at depths from 10 to more than 400 m (Nielsen et al 2007) and are generally associated with fine sediments (Zhou & Shirley 1997). In this depth range, across diverse oceanographic regions, Tanner crabs likely settle on seafloor characterized by a wide temperature range.…”