Juvenile Cod Gadus Morhua Research Articles

Substrate selection and use of protective cover by juvenile Atlantic cod Gadus morhua in inshore waters of Newfoundland

We investigated the habitat preferences and use of cover of 1 to 4 yr old juvenile cod Gadus morhua in the inshore waters (18 to 150 m depth) of Placentia Bay, Newfoundland, Canada, using deep sea submersibles (PISCES IV and SDL-1) in April 1995. We analysed a total of 32 h of 'on-bottom' videotape, audiotape, and written records from 9 daylight dives and 1 night dive. Habitat types were characterised by depth, substrate particle size, bathymetric relief, and the presence or absence of macroalgae. Juvenile cod found throughout the dive area were identified as either 'young' (age 1, 10 to 12 cm total length, and mottled in colour) or 'old' (age 2 to 4, > 15 cm total length, and relatively uniform in colour). Of old juveniles, 80% were found to be associated with areas of coarse substrate and high bathymetric relief (i.e. submarine cliffs). In contrast, 59% of young juveniles were found primarily in areas with a gravel substrate and low relief. Juvenile cod did not exhibit selection for substrates with macroalgae cover. We did not identify any difference between day and night observations. Old juveniles were often associated with individual substrate features (e.g. a single rock, boulder, or crevice), and exhibited a significant increase in activity (oriented swimming speed) with increasing distance from such features Young juveniles exhibited no such association with specific substrate features, although they exhibited greater variation in activity (non-oriented swimming speed). The observed patterns in activity between the age groups suggest a difference in predator avoidance behaviour. Young mottled individuals appeared to be relying on crypsis, whereas older uniform-coloured juvenile cod associated with a specific physical feature which represented cover. Our results corroborate the findings of previous laboratory and shallow water field studies on the behaviour of this species. In addition, these results demonstrated that substrate selection by juvenile cod is age specific.

Larval and small juvenile cod Gadus morhua concentrated in the highly productive areas of a shelf break front

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 125:21-30 (1995) - doi:10.3354/meps125021 Larval and small juvenile cod Gadus morhua concentrated in the highly productive areas of a shelf break front Munk P, Larsson PO, Danielsen D, Moksness E The early life of cod was studied during a survey programme covering the northeastern North Sea, the Skagerrak and the Kattegat in May 1992. Our aim was to asses the interrelated effects of physical and biological factors on distribution, growth and survival of larval cod. In the present paper we describe the identified nursery areas of larvae/juveniles and analyse the connection between the distribution of cod and hydrographical (frontal) characteristics of the areas. A total area of 67000 km2 was covered by stations in a 10 x 10 nautical mile grid. Salinity, temperature, NO3+NO2 and chlorophyll concentration were profiled through the water column. Zooplankton were sampled by a submersible pump and abundance of fish larvae/juveniles were estimated by depth-integrating tows of a 2 m ring net. The hydrographical measurements indicated a shelf break front positioned along the shelf slope in the southern part of the investigation area, and within the zone of the front we observed enhanced primary production and abundance of both phyto- and zooplankton. The distribution of larval and juvenile cod was also related to the hydrography, the abundance of cod peaked within a restricted zone and the aggregations extended as a continuous band along the front. We suggest that the observed concurrence between a hydrographic front and cod larvae/juveniles is a general and recurrent phenomenon based on the spawning habits of cod and aggregation due to flow convergence at the front. Gadus morhua . Larvae . Small juveniles . Nursery areas . Hydrographic fronts . Aggregation processes . North Sea and Skagerrak Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 125. Publication date: September 14, 1995 Print ISSN:0171-8630; Online ISSN:1616-1599 Copyright © 1995 Inter-Research.

Susceptibility of Atlantic herring and plaice larvae to predation by juvenile cod and herring at two constant temperatures

Predation encounters were staged in the laboratory to compare prey responsiveness, predator error rate, and predator capture success for juvenile cod Gadus morhua (a suction feeder) and herring Clupea harengus (a biting predator) preying on herring and plaice Pleuronectes platessa larvae. Trials were conducted at near natural temperature extremes for the larvae (8 and 13°C) to assess the importance of water temperature to the interaction. Herring larvae were significantly more responsive to attacks by herring than were plaice larvae (5·7 vs 0′0%). The two prey species were equally responsive to attacks by cod (2–6 vs 10%). Cod caught 91% of herring larvae attacked and juvenile herring caught 87%. Cod were successful in 96% of attacks on plaice, but juvenile herring caught significantly fewer (83%) plaice larvae. For each predator species, capture success did not vary significantly with prey species. Overall capture success for herring was significantly lower than that for cod. Responsiveness of herring larvae to attacks by juvenile herring increased with temperature, but predator error rate and capture success were not altered by water temperature.

Migration pattern of juvenile cod (Gadus morhua) on the Swedish west coast

Migration pattern of juvenile cod (Gadus morhua) on the Swedish west coast

Toxic effect of the marine dinoflagellate Gymnodinium galatheanum on juvenile cod Gadus morhua

Juvenile cod Gadus morhua exposed to the dinoflagellate Gymnodinium galatheanum Braarud died within 2 d; before death the fish became lethargic and affected fish showed increased plasma osmolality. Severe histopathological changes were found in the gill tissue, with extensive separation of the respiratory epithelium from the underlying pillar cells. Though no recent blooms have been recorded, G. galatheanum should be considered as a potentially harmful bloom-forming alga in temperate waters.

Comparison of lipid, otolith and morphometric condition indices of pelagic juvenile cod Gadus morhua from the Canadian Atlantic

Comparison of lipid, otolith and morphometric condition indices of pelagic juvenile cod Gadus morhua from the Canadian Atlantic

A nocturnal inshore movement of juvenile cod Gadus morhua L. in eastern Newfoundland

Juvenile cod Gadus morhua L. (aged 1 + and 2 +) were counted, using an underwater scuba transect method, during the day and at night in shallow water at Newman Sound, Bonavista Bay, Newfoundland. They were 16 times more abundant during the night than during the day. Sampling at one site throughout a 24-h period showed that they arrive in shallow water at dusk, and leave again just before dawn. Much searching among algae and in crevices showed that the young cod are not simply hiding in cryptic habitats during the day. The hypothesis that they spend the day in deeper water is presented.

Ecology and distribution of juvenile cod and haddock in relation to sediment type and bottom currents on eastern Georges Bank

Recently-settled 0-group juvenile cod Gadus morhua and haddock Melanogrammus aeglefinus were observed by submersible dives and research bottom trawls to inhabit primarily a large pebble-gravel deposit located on the northeastern edge of Georges Bank at 70 to 100 m water depth. Pelagic juvenile gadids are widespread on the bank in late spring, but by late July, they have become demersal and are abundant only on the gravel bed. Coloration of the juveniles mimics the appearance of the pebble bottom, possibly making them less vulnerable to predation there than on the Light-colored sand bottom of most areas of the bank. On the basis of these observations, we hypothesize that the gravel habitat favors their survival through predator avoidance and, possibly to a lesser extent, through increased prey abundance. In particular, the pebble-gravel deposit on northeastern Georges Bank supports the largest aggregations of demersal juveniles, and it may be essential to the recruitment success of the Georges Bank gadid population. By September, the young fish are no longer present on the gravel bed because night-time feeding forays off the bottom result in their transport southeastward in the clockwise current gyre on the bank. The study area is characterized by strong, rotary tidal currents. During the day, demersal juveniles remain withn a few centimeters of the bottom in the boundary layer where currents are somewhat reduced and where they maintain their position by swimm~ng continually into the current. At night, regardless of the current, they rise off the bottom to feed on invertebrates in the near-bottom water column. Abundance estimates of demersal juvelules based on research bottom trawls show variability related to fish s u e and time of day. When compared with estimates of juvenile abundance based on submersible observations, the trawl data underestimate the numbers of juvenile fish present. We expect a knowledge of the die1 behavior, geographic location, and most favorable habitat of demersal 0-group juveniles wdl aid in the assessment and management of the Georges Bank gadid population.