Adult Atlantic Cod Gadus Morhua Research Articles

High-frequency depth changes in Atlantic cod studied with implanted data storage tags

The main aim of this study was to investigate high-frequency depth changes in wild adult Atlantic cod Gadus morhua. The analysis was based on depth measurements collected with implanted data storage tags. The study was part of a ranching project carried out in an Icelandic fjord. In the project, net bags with frozen fish were regularly provided during the daytime at 4 stations where some cod formed distinct ‘herds’ (‘herd cod’) that did not mingle much with the rest of the unconditioned cod in the fjord (‘wild cod’). After tagging, some of the cod resumed life in the herds, whereas other cod left the herds immediately. On 20 subsequent Mondays, the electronic tags were programmed to measure at the highest frequency (every 30 s), and these results were used to study high-frequency depth changes in 4 wild cod and 4 herd cod, the latter as a control group. Several times, rapid cyclical depth changes were observed in both groups. This behaviour, which sometimes lasted for hours, was highest during dawn and dusk in wild cod but peaked during daytime in herd cod after deployment of the feed bags. The occurrence and properties of these vertical undulations varied greatly between fish, dates, and time of day. Most commonly, the periods of the cycles varied between 1 and 4 min and the heights between 2 and 4 m, but there were examples of much larger undulations. The results indicate that wild adult cod swim along vertically undulating paths when searching for prey, most likely to optimize foraging.

Acoustic scattering layers reveal a faunal connection across the Fram Strait

Acoustic scattering layers (SL) at various depths are common phenomena in most oceans, but the organisms that make up these layers vary and so does their density, and hence the backscattered energy. During two crossings of the deep Fram Strait between the shelves at Svalbard and Northeast Greenland at latitudes 77°N and 79°N, we registered epipelagic and mesopelagic SL across the entire Fram Strait and quantified their acoustic backscattered energy. In addition, one pelagic trawl haul was made at each crossing together with a CTD cast at the northern crossing. The epipelagic SL was present at 0–200 m depth, whereas the mesopelagic SL was located at 300–500 m depth during day and at shallower depths during night indicating diel vertical migrations. The epipelagic SL consisted of young-of-the-year fishes, mostly redfish Sebastes sp. No trawl hauls were made in the mesopelagic SL, and the identity of organisms is unknown. Few strong echoes from single targets at mesopelagic depths stood out from the rest of the targets and were interpreted as adult Atlantic cod Gadus morhua. This is the first report of scattering layers covering the whole distance of the deep parts of the Fram Strait, and strengthen the assumption about an east–west connection of organisms and young-of-the-year fishes originating from the spawning grounds along the Norwegian coast and the western Barents Sea towards Northeast Greenland.

Predator-borne acoustic transceivers and GPS tracking reveal spatiotemporal patterns of encounters with acoustically tagged fish in the open ocean

Pinnipeds are abundant upper trophic level predators in many marine ecosystems. Top-down effects of their consumption can play important roles in ecosystem structure and func- tioning. However, interactions between pinnipeds and their prey remain poorly understood due to their inaccessibility while foraging at sea. This uncertainty has fueled debate on the impact of seal predation on fish stocks of commercial or conservation interest. Here, we show that a novel com- bination of acoustic (Vemco Mobile Transceiver, VMT) and GPS technology can be used to deter- mine the spatial and temporal pattern of interactions between grey seals Halichoerus grypus and fish species in 2 large marine ecosystems, the Eastern Scotian Shelf and the southern Gulf of St. Lawrence, Canada. During 4 yr of study, the VMT on 9 of 64 adult grey seals recorded detections from 3 species of fish, namely 17 adult Atlantic cod Gadus morhua, 7 Atlantic salmon Salmo salar and 1 American eel Anguilla rostrata implanted with coded acoustic tags. An examination of the temporal and spatial pattern of these sealfish interactions suggested that 1 salmon and 2 cod might have been predated on. However, to have confidence in the occurrence of a predation event, more conclusive evidence is required, which may be gathered through validation experi- ments. These preliminary results provide proof-of-concept that large upper trophic level marine predators fitted with VMT and GPS tags can provide information on species locations in areas where fixed receiver arrays are not present and allow new insights into the nature of interspecies interactions in otherwise inaccessible environments.

Impact of environmental temperature on Atlantic cod Gadus morhua energy allocation to growth, condition and reproduction

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 404:185-195 (2010) - DOI: https://doi.org/10.3354/meps08502 Impact of environmental temperature on Atlantic cod Gadus morhua energy allocation to growth, condition and reproduction M. J. Morgan*, R. M. Rideout, E. B. Colbourne Fisheries and Oceans Canada, St. John’s, Newfoundland A1C 5X1, Canada *Email: joanne.morgan@dfo-mpo.gc.ca ABSTRACT: The effect of temperature on the allocation of energy to growth, condition and reproduction was examined in juvenile and adult Atlantic cod Gadus morhua inhabiting the southern Grand Bank off Newfoundland, Canada. The study period included both the warmest and coldest environmental conditions in the area over the past 60 yr. Temperature did not influence growth in length or weight, perhaps because growth at higher temperatures was limited by prey availability. Temperature significantly influenced both gutted body condition and liver condition (observed weight divided by predicted weight at length), but the effect was not consistent between the 2 measures of condition. Gutted body condition was highest at warm temperatures, whereas liver condition was highest at low temperatures. Measures of reproductive investment showed clear temperature effects. Fish matured earlier at both low and high temperatures than at intermediate temperatures. Fecundity of southern Grand Bank cod was highest at low temperatures, while the gonadosomatic index (GSI) was highest at warm temperatures. The lack of correlation with fecundity indicates that GSI may not be a good metric of reproductive investment but may be an indicator of how close fish are to spawning. The lower maturity and fecundity at intermediate temperatures could indicate a decrease in reproductive potential under these environmental conditions. Temperature throughout the entire year influenced fish condition, but only temperature during October to May affected reproductive investment. Most of the metrics were highly correlated between males and females, suggesting that both sexes make similar decisions about energy allocation over the observed temperature range. KEY WORDS: Cod · Growth · Reproduction · Temperature Full text in pdf format PreviousNextCite this article as: Morgan MJ, Rideout RM, Colbourne EB (2010) Impact of environmental temperature on Atlantic cod Gadus morhua energy allocation to growth, condition and reproduction. Mar Ecol Prog Ser 404:185-195. https://doi.org/10.3354/meps08502 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 404. Online publication date: April 08, 2010 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2010 Inter-Research.

Site fidelity and movement of adult Atlantic cod Gadus morhua at deep boulder reefs in the western Gulf of Maine, USA

Little is known about the role that patterns of habitat selection play in mediating move- ment of Atlantic cod Gadus morhua, particularly in off-shore environments. We used acoustic teleme- try to study the movement of adult cod tagged at deep boulder reefs (DBRs) in the western Gulf of Maine. The movement of 65 cod tagged with acoustic transmitters was monitored by acoustic receivers deployed on the seafloor at 4 DBRs from May to September 2002 and September 2004 to February 2005. Each receiver encompassed an area of the seafloor of approximately 0.5 km 2 , and data on each fish were recorded for up to 95 d post-release. Twenty-three cod (35.4% of tagged fish) exhibited high site fidelity to the DBR where they were caught and released (recorded in >82% of the 1 h time bins), while 33 cod (50.8% of tagged fish) appeared to depart the area rapidly following release (recorded in <20% of the 1 h time bins). Cod with high site fidelity exhibited no pattern of diel activity. Cod movement among DBRs was recorded in both sampling periods (maximum linear dis- tance of at least 24 km). Patterns of site fidelity and movement did not differ significantly with fish total length, among individual DBRs, or between sampling periods. Understanding the spatial dynamics of fish populations with both resident and transient components that are linked to particu- lar habitats can aid in development of unique management strategies for both sustainable fisheries and conservation of biological diversity.