Density-Dependent Geographic Distribution of Atlantic Cod (<i>Gadus morhua</i>) in the Southern Gulf of St. Lawrence

Swain, Douglas P.; Wade, Elmer

doi:10.1139/f93-083

Cited by 120 publications

(99 citation statements)

References 25 publications

(13 reference statements)

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“…Gadus morhua expand their range during years of higher abundance (Rose & Leggett 1991, Swain & Wade 1993, Anderson & Gregory 2000. Although we did not measure range expansion directly, it is interesting to note that substantive catches of juvenile cod in sand habitat were restricted to high-abundance years.…”

Section: Discussionmentioning

confidence: 96%

Behavioural consequences of density-dependent habitat use in juvenile cod Gadus morhua and G. ogac: the role of movement and aggregation

Laurel¹,

Gregory²,

Brown³

et al. 2004

Mar. Ecol. Prog. Ser.

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Fish behaviour can change to accommodate a variable environment, but changes in behaviour have not been considered in the context of density-dependent habitat use. In Bonavista Bay, Newfoundland, we measured how fish density movement and schooling behaviour changed with habitat in 2 gadids, Atlantic cod Gadus morhua and Greenland cod Gadus ogac, using a combination of field-seines, mark-recapture and laboratory experiments. Density estimates from seines (n = 427) over 5 yr (1996, 1998 to 2001) indicated that these species associated with eelgrass but periodically were detected in high abundance over unvegetated habitat (i.e. sand). Within-site catch variation indicated both species aggregated more in sand than eelgrass habitat, and, in Atlantic cod, aggregations over sand increased as density in eelgrass increased. Although such patterns in catch data could be interpreted as due to the effects of differential mortality between habitats, a mark-recapture experiment indicated that both species of cod were not site-attached and moved between seine locations. Furthermore, video-analysis from laboratory experiments demonstrated that cod formed tighter aggregations over sand compared to eelgrass habitats. Our results suggest that juvenile cod modify their behaviour with changing density, possibly as a means of exploiting poor-quality habitats when high-quality habitats are saturated with conspecifics. Consequently, habitat suitability for Atlantic cod may be a dynamic rather than fixed variable in density-dependent habitat models.

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Section: Discussionmentioning

confidence: 96%

Behavioural consequences of density-dependent habitat use in juvenile cod Gadus morhua and G. ogac: the role of movement and aggregation

Laurel¹,

Gregory²,

Brown³

et al. 2004

Mar. Ecol. Prog. Ser.

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show abstract

“…This could be evidence of selection of AGP, with density-dependent dispersal to other substrata at higher population densities. This indicates that this substratum could be an important seabed type for juvenile G. morhua (Morris 1989, 2003, Swain & Wade 1993. Lough (2010) also indicated that limited gravel areas may inhibit the survival of juvenile G. morhua.…”

Section: Discussionmentioning

confidence: 99%

Juvenile gadoid habitat and ontogenetic shift observations using stereo-video baited cameras

Elliott¹,

Turrell²,

Heath³

et al. 2017

Mar. Ecol. Prog. Ser.

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The protection of species requires an understanding of their habitat requirements and how habitat characteristics affect their distribution, survival and growth. This need is especially important in areas where anthropogenic pressures can not only have a significant direct impact on the survival of the species but also damage their habitat. The Firth of Clyde in southwestern Scotland was an important commercial fishing area for a variety of demersal fish species up until 1973. However, stocks rapidly declined thereafter and the catch of targeted species ceased in 2005, despite fisheries measures put in place to aid recovery. Changes in the availability and quality of fish habitat are possible explanations for this lack of recovery. Here, we report on stereo baited remote underwater video surveys in the Firth of Clyde between June and September in 2013 and 2014 to determine the habitat of juvenile Atlantic cod Gadus morhua, haddock Melanogrammus aeglefinus and whiting Merlangius merlangus. Habitat predictor variables explored included substratum type, depth, wave fetch, and epibenthic and demersal fauna diversity. G. morhua were most abundant in shallow, sheltered areas composed of gravel−pebble containing maerl. M. aeglefinus and M. merlangus predominated over deeper sand and mud. Ontogenetic shifts in all 3 species were also observed. Relative abundances of G. morhua and M. merlangus were positively related to the diversity of epibenthic and demersal fauna. Our results indicate that spatial conservation measures to benefit demersal fish should be advised by patterns of epibenthic and demersal fauna diversity as well as physical substratum types.

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“…Fishing policies can be selective for both size and maturity stage of individuals in the stock: size selectivity results from mesh-size and gear regulation or from sizespecific incentives (Hart and Reynolds, 2002;Fromentin and Powers, 2005), while maturity selectivity may arise when a 12 stock's juveniles and adults are spatially segregated during spawning (Sinclair, 1992;Swain and Wade, 1993;Engelhard and Heino, 2004;Opdal, 2010). Harvest is readily adaptive, because fishers constantly tune their effort and selectivity for 14 maximum profit, targeting stock components that are most profitable to harvest.…”

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confidence: 99%

Fisheries-induced disruptive selection

Landi

Hui

Dieckmann

2015

Journal of Theoretical Biology

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Commercial harvesting is recognized to induce adaptive responses of life-history traits in fish populations, in particular by shifting the age and size at maturation through directional selection. In addition to such evolution of a target stock, the corresponding fishery itself may adapt, in terms of fishing policy, technological progress, fleet dynamics, and adaptive harvest. The aim of this study is to assess how the interplay between natural and artificial selection, in the simplest setting in which a fishery and a target stock coevolve, can lead to disruptive selection, which in turn may cause trait diversification. To this end, we build an eco-evolutionary model for a size-structured population, in which both the stock's maturation schedule and the fishery's harvest rate are adaptive, while fishing may be subject to a selective policy based on fish size and/or maturity stage. Using numerical bifurcation analysis, we study how the potential for disruptive selection changes with fishing policy, fishing mortality, harvest specialization, life-history tradeoffs associated with early maturation, and other demographic and environmental parameters. We report the following findings. First, fisheriesinduced disruptive selection is readily caused by commonly used fishing policies, and occurs even for policies that are not specific for fish size or maturity, provided that the harvest is sufficiently adaptive and large individuals are targeted intensively. Second, disruptive selection is more likely in stocks in which the selective pressure for early maturation is naturally strong, provided life-history tradeoffs are sufficiently consequential. Third, when a fish stock is overexploited, fisheries targeting only large individuals might slightly increase sustainable yield by causing trait diversification (even though the resultant yield always remains lower than the maximum sustainable yield that could be obtained under low fishing mortality, without causing disruptive selection). We discuss the broader implications of our results and highlight how these can be taken into account for designing evolutionarily informed fisheries-management regimes.

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Density-Dependent Geographic Distribution of Atlantic Cod (Gadus morhua) in the Southern Gulf of St. Lawrence

Cited by 120 publications

References 25 publications

Behavioural consequences of density-dependent habitat use in juvenile cod Gadus morhua and G. ogac: the role of movement and aggregation

Behavioural consequences of density-dependent habitat use in juvenile cod Gadus morhua and G. ogac: the role of movement and aggregation

Juvenile gadoid habitat and ontogenetic shift observations using stereo-video baited cameras

Fisheries-induced disruptive selection

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