Discrete spatial dynamics in a marine broadcast spawner: Re-evaluating scales of connectivity and habitat associations in Atlantic cod (Gadus morhua L.) in coastal Newfoundland

Atlantic cod ( Gadus morhua ) are being increasingly farmed in net pens adjacent to coastal populations that are currently at historic lows. One concern is that farmed escapees enter local spawning shoals and mate with wild cod. We tested for the potential of escaped farmed cod to interact and hybridize with wild fish by examining the spatial dynamics of, and associations between, fish tagged with ultrasonic transmitters. Based on these data, we also investigated the basic mating system of cod in the field. The spawning ground was best described as a lekking arena. Wild males aggregated near the seafloor and associations between individuals were frequent. Wild females had a pelagic and dispersed distribution and rarely associated with each other. Associations between individual wild males and females were also infrequent. Farmed males rarely associated with wild fish and had core usage areas above the wild males, suggesting that they were not admitted into the spawning arena. Farmed females were over the spawning arena more frequently than wild females and often associated with wild males at the depth of the spawning arena, indicating potential mating with wild males and the possibility of courtship interference. Hence, hybridization between escaped farmed and wild cod is likely.

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Seasonal variation in the habitat associations of Atlantic cod (Gadus morhua) and American plaice (Hippoglossoides platessoides) from the southern Gulf of St. Lawrence

Canadian Journal of Fisheries and Aquatic Sciences ◽

10.1139/f98-122 ◽

1998 ◽

Vol 55 (12) ◽

pp. 2548-2561 ◽

Cited By ~ 36

Author(s):

D P Swain ◽

G A Chouinard ◽

R Morin ◽

K F Drinkwater

Keyword(s):

Seasonal Variation ◽

Habitat Selection ◽

Gadus Morhua ◽

Atlantic Cod ◽

Statistical Significance ◽

Habitat Associations ◽

Practical Implications ◽

Hippoglossoides Platessoides ◽

Trawl Surveys ◽

Selection Of

We compared habitat associations of southern Gulf of St. Lawrence Atlantic cod (Gadus morhua) and American plaice (Hippoglossoides platessoides) between the summer feeding season on the Magdalen Shallows and the overwintering period in the Cabot Strait. Data were from bottom trawl surveys conducted in September 1993, 1994, and 1995 and January 1994, 1995, and 1996. Both species occupied much deeper, warmer water in winter than in summer. The effect of cod age on temperature distribution reversed between the two seasons, with younger cod occupying warmer water than older cod in summer and colder water in winter. Selection of both depth and temperature by cod tended to be more significant in September than in January. The reduced statistical significance of habitat selection by cod in winter was associated with a more aggregated distribution in this season. The contrast between seasons in habitat associations was particularly strong for plaice. The median habitats occupied by plaice were 58-67 m and -0.1 to 0.3°C in September and 374-426 m and 5.2-5.4°C in January. Habitat selection by plaice was significant in both seasons, but significance tended to be greater in January. Degree of aggregation in plaice distribution was similar between the two seasons. Female plaice occupied significantly warmer water than males in September but not in January. The ecological and practical implications of this striking seasonal variation in habitat associations are discussed.

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Home range and elevated egg densities within an inshore spawning ground of coastal cod

ICES Journal of Marine Science ◽

10.1093/icesjms/fsm028 ◽

2007 ◽

Vol 64 (5) ◽

pp. 920-928 ◽

Cited By ~ 40

Author(s):

Sigurd Heiberg Espeland ◽

Ailin Fernløf Gundersen ◽

Esben Moland Olsen ◽

Halvor Knutsen ◽

Jakob Gjøsæter ◽

...

Keyword(s):

Home Range ◽

Site Fidelity ◽

Gadus Morhua ◽

Atlantic Cod ◽

Generalized Additive Models ◽

Spatial Dynamics ◽

Additive Models ◽

Spawning Season ◽

Spawning Ground ◽

Spawning Site

Abstract Espeland, S. H., Gundersen, A. F., Olsen, E. M., Knutsen, H., Gjøsæter, J., and Stenseth, N. C. 2007. Home range and elevated egg densities within an inshore spawning ground of coastal cod. – ICES Journal of Marine Science, 64: 920–928. Atlantic cod (Gadus morhua) along the Norwegian Skagerrak coast are structured into genetically distinct local populations. Mechanisms contributing to this genetic structure may include spawning site fidelity of adult cod as well as retention of pelagic early life stages close to the spawning grounds. Spawning in sheltered inshore localities is likely to favour retention of eggs and larvae, the opposite situation to offshore spawning. A combined study was made of area utilization by adult cod and the distribution of cod eggs within an inshore locality of the Norwegian Skagerrak coast. The behaviour of adult cod was studied using acoustic telemetry and kernel modelling, and eggs were sampled throughout the spawning season. Generalized additive models were applied to test hypotheses about the spatial dynamics of the eggs, and the best model described a central spawning area that retained its integrity through time. Adult cod were confined to small parts of the study area and remained there throughout the spawning season. The average home range of the adult cod was 27 ha. Overall, the study demonstrated two mechanisms by which coastal (i.e. inshore) cod maintain their population structure: spawning site fidelity and the spatial dynamics of their eggs.

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Historical spatiotemporal dynamics of eastern North Sea cod

Canadian Journal of Fisheries and Aquatic Sciences ◽

10.1139/f2012-028 ◽

2012 ◽

Vol 69 (5) ◽

pp. 833-841 ◽

Cited By ~ 17

Author(s):

Valerio Bartolino ◽

Massimiliano Cardinale ◽

Henrik Svedäng ◽

Hans W. Linderholm ◽

Michele Casini ◽

...

Keyword(s):

North Sea ◽

Gadus Morhua ◽

Historical Data ◽

Atlantic Cod ◽

Spatial Dynamics ◽

Current Status ◽

Temporal Perspective ◽

Data Set ◽

The North ◽

Early Century

Recent analyses of historical data of fish abundance and distribution have shown the importance of a long temporal perspective in the evaluation of the current status of fish populations, but pose numerous difficulties such as fragmentation and inhomogeneities in the amount of available information in space and time. Using mixed-effects models in a multiscale analysis, we identified an appropriate spatiotemporal scale of investigation of a high-quality, spatially explicit historical data set, and we reconstructed the long-term spatial dynamics of Atlantic cod ( Gadus morhua ) in the Kattegat–Skagerrak along the 20th century. We identified a northern and southern main aggregation of adult cod in the study area, corresponding to the Skagerrak portion of the North Sea and the Kattegat cod stocks, respectively. The stocks showed specificities in their spatial dynamics, but common extensive loss of coastal aggregations during the last decades when only 13% (Kattegat) and 35% (Skagerrak) of the estimated early century cod biomass was left. Our reconstruction showed that the collapse of the cod stocks in the area followed the peak in landings in the 1960s–1970s, suggesting that the postwar development of the industrial fisheries played a major role in the decrease of local abundances and disappearance of local adult cod aggregations.

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Density-independent and -dependent habitat selection of Atlantic cod (Gadus morhua) based on geostatistical aggregation curves in the northern Gulf of St Lawrence

ICES Journal of Marine Science ◽

10.1093/icesjms/fsq108 ◽

2010 ◽

Vol 67 (8) ◽

pp. 1676-1686 ◽

Cited By ~ 18

Author(s):

Hacène Tamdrari ◽

Martin Castonguay ◽

Jean-Claude Brêthes ◽

Daniel Duplisea

Keyword(s):

Habitat Selection ◽

Gadus Morhua ◽

Atlantic Cod ◽

Local Density ◽

Abiotic Factors ◽

Age Groups ◽

Spatial Dynamics ◽

Entire Area ◽

Dynamics Models ◽

Selection Of

Abstract Tamdrari, H., Castonguay, M., Brêthes, J-C., and Duplisea, D. 2010. Density-independent and -dependent habitat selection of Atlantic cod (Gadus morhua) based on geostatistical aggregation curves in the northern Gulf of St Lawrence. – ICES Journal of Marine Science, 67: 1676–1686. Relationships were sought between local density and population abundance of Atlantic cod (Gadus morhua) in the northern Gulf of St Lawrence (Canada) over its entire area (4RS) and also within a subarea (4R) where the stock has concentrated since it collapsed during the early 1990s. Relationships were analysed using geostatistical aggregation curves computed within the two areas between years of contrasting abundance levels. The curves were interpreted in terms of four conceptual models of spatial dynamics: models D1 and D2, forced mainly by environmental heterogeneity, and models D3 and D4, in which individual behaviour is influenced by local density. Over the entire area, the cod population follows the D2 model for all years and age groups, and it is influenced by abiotic factors. Within the subarea, all four models applied, and the density-dependent basin model (D4) dominated from 2006 to 2008. The year 2006 seems to be pivotal because it coincides with the expansion of the cod population into its former area in the western Gulf (4S).

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The influence of complex structure on the spatial dynamics of Atlantic cod (Gadus morhua) in the Gulf of Maine

ICES Journal of Marine Science ◽

10.1093/icesjms/fsx064 ◽

2017 ◽

Vol 74 (9) ◽

pp. 2379-2388 ◽

Cited By ~ 4

Author(s):

Lisha Guan ◽

Yong Chen ◽

Kevin W Staples ◽

Jie Cao ◽

Bai Li

Keyword(s):

Gadus Morhua ◽

Mixed Model ◽

Linear Mixed Model ◽

Gulf Of Maine ◽

Atlantic Cod ◽

Complex Structure ◽

Spatial Dynamics ◽

Trawl Survey ◽

Marine Fishery ◽

Density Dependent Habitat Selection

Abstract Atlantic cod (Gadus morhua) in the Gulf of Maine (GOM) is an iconic marine fishery stock that has experienced a substantial distributional shift since the mid-1990s. A geostatistical delta-generalized linear mixed model was utilized to hindcast yearly season-specific distributions of GOM cod. These distributions were calculated using the spring and fall bottom trawl survey data for the stock, along with cell-based bathymetry and bottom temperature data for the study area for the years 1982–2013. The centre of stock distribution (the centre of gravity), spatial extent in latitude and longitude, area occupied and median habitat temperature were estimated annually to quantify changes in the spatial dynamics of GOM cod. Time series of these distributional metrics were then used to evaluate the influences of climate change and density-dependent habitat selection on GOM cod’s distribution. Results showed that the rapid southwestward shift in the stock distribution after the late 1990s could not simply be attributed to decreasing stock abundance or warming bottom temperatures. The observed shift in cod distribution requires further investigation on whether it is possibly a result of other factors, like fluctuating productivity among subpopulations.

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Linking tagging technology and molecular genetics to gain insight in the spatial dynamics of two stocks of cod in Northeast Atlantic waters

ICES Journal of Marine Science ◽

10.1093/icesjms/fsu083 ◽

2014 ◽

Vol 71 (6) ◽

pp. 1417-1432 ◽

Cited By ~ 15

Author(s):

Kathrine Michalsen ◽

Torild Johansen ◽

Sam Subbey ◽

Alexander Beck

Keyword(s):

Environmental Factors ◽

Molecular Genetics ◽

Data Storage ◽

Large Scale ◽

Gadus Morhua ◽

Atlantic Cod ◽

Spatial Dynamics ◽

Scientific Basis ◽

The North ◽

Shortest Distance

The Northeast Arctic cod (Gadus morhua L.: NEAC) remains the most abundant cod stock in the North Atlantic, while the catches of the partially co-occurring Norwegian coastal cod (NCC) stocks have dramatically decreased in recent years. To ensure effective management of the two stocks, it is necessary to know if the population genetic structure is associated with any pattern in the spatial dynamics or whether it is affected by any distinct environmental factors. By combining information from electronic data storage tags (DST) and molecular genetics methods with statistical tools, we have been able to associate spatial dynamics and distinct environmental factors to the two cod stocks. In general, adult NEAC migrate between deep, warm overwintering grounds and shallow summer feeding grounds where water temperatures maybe low. In contrast, NCC do not undertake large-scale seasonal migrations, show little seasonal variation in depth distribution, and experience the opposite seasonal change in temperature compared with NEAC. However, within the NCC group, some individuals did conduct longer horizontal movements than others. Even though the distances calculated in this study represent the shortest distance between release and recapture positions, they are far higher than previously reported by NCC. Distinctive depth profiles indicate that this migrant NCC have moved out of the area, passing the deep trenches outside Lofoten while more stationary NCC occupies shallower depths throughout the year. The temperature profiles also indicate that migrant and stationary NCC has occupied different areas during the year. We demonstrate that the combination of information from DSTs and molecular genetics offers a deeper understanding of individual cod behaviour, provides an insight in the spatial dynamics of the species, and ultimately, improves the scientific basis for management of a complex mixed fishery of Atlantic cod.

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