Movement Patterns and Migrations in Crabs: Telemetry of Juvenile and Adult Behaviour in Callinectes Sapidus and Maja Squinado

Abstract

Late stage juveniles and adults of Callinectes sapidus in Chesapeake Bay, USA, and Maja squinado off the Ria de Arousa, Spain, were compared for ontogenetic changes in movement patterns (speed, distance, orientation) and habitat selection (depth, substrate) using ultrasonic telemetry and published information. After settling in submerged grass beds in the lower Bay, 20-mm juvenile C. sapidus disperse long distances into low salinity sub-estuaries to feed and grow to maturity in two years. Within the Rhode River sub-estuary, juvenile C. sapidus moved with a mean speed of 12 m h 1 in nearshore shallows (1-1 m); whereas adults averaged 24 m h" 1 in the deeper (2-9 m) channel areas and moved freely in and out of the main estuary. Individuals of both life stages exhibited a pattern of slow meandering (juveniles, 2 m h 1 , adults 10 m h" 1 ) within a limited area, alternating with faster, directionally-oriented movement (both stages >50 m h' 1 ) between meandering sites. Juvenile and adult males over winter in deeper water nearby, while inseminated females migrate long distances into high salinity areas to incubate the eggs. Callinectes sapidus completes the migration cycle only once per 2-5-y generation. Maja squinado settles on rocks in shallow kelp forests in the coastal zone, where they grow to maturity in 2 y. Juveniles moved slowly (0-5 m h" 1 ) while meandering without directional orientation on shallow (4 m) small patch reefs during summer. After the pubertal moult in summer, adults also meandered slowly (1 m h" 1 ) mostly on rocks at slightly greater depth (7 m). In late summer and autumn, newly mature and older adults moved with directional orientation into deeper (10-40 m) water for the winter, until migrating back to the shallows for the summer; whereas juveniles remained inshore on rocks for the winter. Adult M. squinado live several years after puberty and complete the seasonal migratory cycle several times during their lives.Despite marked differences between the two species in life histories and habitats, their similarities in behaviour and shifts in habitat utilization during ontogeny reflect adaptation to similar selective pressures. For both species, juvenile movement and habitat selection primarily indicates adaptation to intense predation pressure and growth optimization; whereas adult behaviour and migration indicates relaxed predation pressure but optimization of energy needs and site of larval release.

Movements of Marine Fish and Decapod Crustaceans: Process, Theory and Application

“…Many of these broad-scale physical hydrodynamics are cyclical and animals have evolved behavioural interactions such as the scheduling of spawning to coincide with lunar phases, seasonal winds and tidal currents (Norcross and Shaw, 1984;Morgan and Christy, 1994;Botsford et al, 2001), or to place the juvenile 'growing season' in the warmer, more productive months of the year (Conover, 1992). For example, in Chesapeake Bay, USA, hatching of blue crab larvae (Callinectes sapidus) mainly coincides with night-time ebb tides, which distribute progeny offshore in spring and summer when planktonic food resources for larvae are most abundant (Hines et al, 1995). Clearly, this spatio-temporal scheduling of life histories is critical to the maintenance of populations.…”

“…However, some direct evidence has been provided through telemetric and tagging studies. For example, using ultrasonic telemetry, Hines et al (1995) showed an ontogenetic change in movement pattern of juvenile blue crabs (Callinectes sapidus) in Chesapeake Bay. After settlement to seagrasses, the crabs moved between 50-250 km into shallower, brackish water sub-estuaries in order to evade predators, feed and grow.…”

“…At other times of the year they are found in salt marshes, estuaries and embayments in the western Atlantic Ocean and are known to spawn on daytime high tides in saltmarshes (Middaugh and Takita, 1983). Blue crabs (Callinectes sapidus) in Chesapeake Bay, USA, and spider crabs (Maia squinado) in northwest Spain have also been observed to move in response to seasonal cycles in temperature and food availability (Hines et al, 1995).…”

“…higher temperature) of molting, mating and egg extrusion (Campbell, 1986). Blue crabs are also known to exhibit an over-wintering or hibernation phase in deeper water, which is thought to be associated with an ontogenetic transition from juvenile to sexually mature adults (Hines et al, 1995). Although they may have other functions, these seasonal movements may be better categorised as pre-spawning migrations, rather than seasonal migrations.…”

Efectos de la densidad de cultivo y de elementos de refugio en el crecimiento y supervivencia de juveniles de centollo,Maja brachydactyla (Balss, 1922)

“…Los juveniles de Maja sp. habitan aguas poco profundas, de no más de 15 metros de profundidad, con sustratos arenosos y/o rocosos (Hines et al 1995). La madurez sexual se produce tras la denominada muda terminal, que tiene lugar durante el verano en juveniles de unos dos años de edad .…”