scholarly journals Evolutionary response to size-selective mortality in an exploited fish population

2007 ◽  
Vol 274 (1613) ◽  
pp. 1015-1022 ◽  
Author(s):  
Douglas P Swain ◽  
Alan F Sinclair ◽  
J Mark Hanson
Keyword(s):  
Gadus Morhua ◽  
Atlantic Cod ◽  
Fish Population ◽  
Fish Populations ◽  
Selective Mortality ◽  
Genetic Changes ◽  
Evolutionary Response ◽  
In The Wild ◽  
Size At Age ◽  
Change In Mean

Many collapsed fish populations have failed to recover after a decade or more with little fishing. This may reflect evolutionary change in response to the highly selective mortality imposed by fisheries. Recent experimental work has demonstrated a rapid genetic change in growth rate in response to size-selective harvesting of laboratory fish populations. Here, we use a 30-year time-series of back-calculated lengths-at-age to test for a genetic response to size-selective mortality in the wild in a heavily exploited population of Atlantic cod ( Gadus morhua ). Controlling for the effects of density- and temperature-dependent growth, the change in mean length of 4-year-old cod between offspring and their parental cohorts was positively correlated with the estimated selection differential experienced by the parental cohorts between this age and spawning. This result supports the hypothesis that there have been genetic changes in growth in this population in response to size-selective fishing. Such changes may account for the continued small size-at-age in this population despite good conditions for growth and little fishing for over a decade. This study highlights the need for management regimes that take into account the evolutionary consequences of fishing.

Measuring changes in the direction and magnitude of size-selective mortality in a commercial fish population

2002 ◽  
Vol 59 (2) ◽  
pp. 361-371 ◽  
Author(s):  
A F Sinclair ◽  
D P Swain ◽  
J M Hanson
Keyword(s):  
Gadus Morhua ◽  
Slow Growth ◽  
Atlantic Cod ◽  
Fish Population ◽  
Disruptive Selection ◽  
Commercial Fishery ◽  
Fishing Mortality ◽  
Selective Mortality ◽  
Commercial Fish ◽  
Size Selection

A 28-year time series (1971–1998) of backcalculated length-at-age was used to investigate changes in the direction and magnitude of size-selective mortality of prerecruit and adult Atlantic cod (Gadus morhua) in the southern Gulf of St. Lawrence, Canada. Size selection changed from favouring fast growth in the 1970s to favouring slow growth in the late 1980s and 1990s. There was an intervening period of disruptive selection where fast and slow growth was favoured while intermediate growth rates were selected against. The intensity of size selection declined at the end of the study period following the closure of the commercial fishery. These different forms of selection (positive directional, negative directional, and disruptive selection) can all be accounted for by the sharply dome-shaped curve of fishing mortality against length observed in the fishery.

The influence of forage fish abundance on the aggregation of Gulf of Maine Atlantic cod (Gadus morhua) and their catchability in the fishery

2014 ◽  
Vol 71 (9) ◽  
pp. 1349-1362 ◽  
Author(s):  
David E. Richardson ◽  
Michael C. Palmer ◽  
Brian E. Smith
Keyword(s):  
Gadus Morhua ◽  
Gulf Of Maine ◽  
Atlantic Cod ◽  
Distribution Patterns ◽  
Fish Populations ◽  
Dependent Data ◽  
Forage Fish ◽  
Catch Per Unit Effort ◽  
Sand Lance ◽  
Unit Effort

Shifts in the distribution and aggregation patterns of exploited fish populations can affect the behavior and success of fishermen and can complicate the interpretation of fisheries-dependent data. Starting in 2006, coinciding with an increase in sand lance (Ammodytes spp.) abundance, Gulf of Maine Atlantic cod (Gadus morhua) concentrated on Stellwagen Bank, a small (405 km2) underwater plateau located in the southwestern portion of the larger (52 461 km2) stock area. The cod fishery in turn concentrated on Stellwagen Bank. Specifically, the proportion of Gulf of Maine cod landings caught in a single 10-minute square area (260 km2) encompassing the tip of Stellwagen Bank increased from 12% in 2005 to 45% in 2010. An increase in landings per unit effort in the fishery coincided with the concentration of the fleet on Stellwagen Bank. Overall, both fisheries-independent and fisheries-dependent data indicate that an increase in sand lance abundance resulted in cod aggregating in a small and predictable area where they were easily caught by the fishery. More broadly, this work illustrates how changes in the distribution patterns of fish and fisherman can decouple trends in abundance and fisheries catch per unit effort.

scholarly journals Detecting regime shifts in fish stock dynamics

2015 ◽  
Vol 72 (11) ◽  
pp. 1619-1628 ◽  
Author(s):  
Tommi Perälä ◽  
Anna Kuparinen
Keyword(s):  
Gadus Morhua ◽  
Atlantic Cod ◽  
Stock Assessment ◽  
Detection Algorithm ◽  
Regime Shifts ◽  
Change Point Detection ◽  
Fish Stock ◽  
Fish Stocks ◽  
Data Generating Process ◽  
Change In Mean

Environmental factors such as water temperature, salinity, and the abundance of zooplankton can have major effects on certain fish stocks’ ability to produce juveniles and, thus, stock renewal ability. This variability in stock productivity manifests itself as different productivity regimes. Here, we detect productivity regime shifts by analyzing recruit-per-spawner time series with Bayesian online change point detection algorithm. The algorithm infers the time since the last regime shift (change in mean or variance or both) as well as the parameters of the data-generating process for the current regime sequentially. We demonstrate the algorithm’s performance using simulated recruitment data from an individual-based model and further apply the algorithm to stock assessment estimates for four Atlantic cod (Gadus morhua) stocks obtained from RAM legacy database. Our analysis shows that the algorithm performs well when the variability between the regimes is high enough compared with the variability within the regimes. The algorithm found several productivity regimes for all four cod stocks, and the findings suggest that the stocks are currently in low productivity regimes, which have started during the 1990s and 2000s.

Depth-dependent vertebral number of Atlantic cod (Gadus morhua) on the Magdalen Shallows and Scotian Shelf: stock mixing or microgeographic trends within populations?

2000 ◽  
Vol 57 (12) ◽  
pp. 2393-2401 ◽  
Author(s):  
D P Swain ◽  
K T Frank
Keyword(s):  
Gadus Morhua ◽  
Atlantic Cod ◽  
Spatial Scales ◽  
Relative Length ◽  
Scotian Shelf ◽  
Age Classes ◽  
Vertebral Number ◽  
Size At Age ◽  
Stock Mixing ◽  
Summer Feeding

We examined spatial variation in the vertebral number of Atlantic cod (Gadus morhua) during the summer feeding season in the southern Gulf of St. Lawrence and on the Scotian Shelf. Mean vertebral number increased significantly with depth in the southern Gulf and on the northeastern Scotian Shelf but not on the southwestern Scotian Shelf. In the southern Gulf, where sampling was most extensive, mean vertebral number increased steadily as depth increased from 25 m to over 175 m. Mean vertebral number was also strongly related to relative length within age-classes, with the larger fish at age having more vertebrae. However, the association between vertebral number and depth could not be attributed to confounding between depth and size at age. These results indicate either unexpected mixing between neighbouring cod populations or unexpected structure at fine spatial scales within cod populations.

scholarly journals Trade-offs between growth and reproduction in wild Atlantic cod

2014 ◽  
Vol 71 (7) ◽  
pp. 1106-1112 ◽  
Author(s):  
Arild Folkvord ◽  
Christian Jørgensen ◽  
Knut Korsbrekke ◽  
Richard D.M. Nash ◽  
Trygve Nilsen ◽  
...  
Keyword(s):  
Gadus Morhua ◽  
Atlantic Cod ◽  
Life History Strategy ◽  
Skipped Spawning ◽  
Growth Increments ◽  
Trade Offs ◽  
Survival And Reproduction ◽  
Size At Age ◽  
Allocation Strategies ◽  
Growth And Reproduction

Animals partition and trade off their resources between competing needs such as growth, maintenance, and reproduction. Over a lifetime, allocation strategies should result in distinct trajectories for growth, survival, and reproduction, but such longitudinal individual data are difficult to reconstruct for wild animals and especially marine fish. We were able to reconstruct two of these trajectories in wild-caught Northeast Arctic cod (Gadus morhua) females: size-at-age was back-calculated from otolith growth increments, and recent spawning history was reconstructed from postovulatory follicles and present oocyte development. Our findings indicate distinct trade-offs between length growth and reproduction. Fish that sexually matured early had attained a larger size at age 3 than immatures, but onset of reproduction caused slower growth compared with immatures. We found that 6- and 7-year-old females skipping spawning grew significantly more in the year of missed spawning than females spawning for the second consecutive year. The latter tentatively supports the hypothesis that skipped spawning may occur as an adaptive life-history strategy, given the potential future fecundity gain with increased size.

Diel foraging cycles and interactions among juvenile Atlantic cod (Gadus morhua) at a nearshore site in Newfoundland

1998 ◽  
Vol 55 (6) ◽  
pp. 1307-1316 ◽  
Author(s):  
Scott M Grant ◽  
Joseph A Brown
Keyword(s):  
Resource Use ◽  
Zostera Marina ◽  
Gadus Morhua ◽  
Atlantic Cod ◽  
Prey Size ◽  
Foraging Activity ◽  
Daily Ration ◽  
Behavioural Responses ◽  
In The Wild ◽  
Activity Cycles

In coastal Newfoundland, age 0 Atlantic cod (Gadus morhua) settle in shallow, nearshore regions occupied by older conspecifics. Although intercohort cannibalism is common, little is known of the behavioural responses that limit interactions among juvenile cohorts in the wild. We examined the day-night differences in catch and diet of age 0 and age 1 cod to delineate peak foraging activity and resource use in eelgrass (Zostera marina) habitat. Cod exhibited a size-related shift (age 0 to age 1) from feeding predominantly on zooplankton by day to benthos at night. Intercohort cannibalism occurred when age 1 cod were approximately three times larger than their prey. Concentrations of age 0 cod foraged in the water column during the day, ceased feeding at night, and appeared to disperse to the bottom. Seasonally decreasing daylength and prey size contributed to a decline in daily ration, yet age 0 cod still maintained a strict diurnal foraging cycle. The nocturnal decrease in feeding coincided with an increase in the catch of older conspecifics (age 2 and age 3) and increased foraging activity of age 1 cod, suggesting that avoidance of older conspecifics is an important factor influencing the diel foraging and activity cycles of age 0 cod.

scholarly journals Catch-and-release of Atlantic cod (Gadus morhua): post-release behaviour of acoustically pretagged fish in a natural marine environment

2015 ◽  
Vol 72 (2) ◽  
pp. 252-261 ◽  
Author(s):  
Keno Ferter ◽  
Klaas Hartmann ◽  
Alf Ring Kleiven ◽  
Even Moland ◽  
Esben Moland Olsen
Keyword(s):  
Large Scale ◽  
Gadus Morhua ◽  
Sublethal Effects ◽  
Atlantic Cod ◽  
Small Scale ◽  
Marine Environments ◽  
Vertical Movements ◽  
Catch And Release ◽  
Diel Vertical Migrations ◽  
In The Wild

Studying the sublethal effects of catch-and-release (C&R) is challenging, as there are several potential sources of bias. For example, if behavioural alterations immediately after the release event are to be studied, separation of tagging effects from actual C&R effects is required, which is a challenge in the wild, particularly in marine environments. To investigate the effects of C&R on Atlantic cod (Gadus morhua) in their natural environment, 80 cod were caught in fyke nets, fitted with acoustic transmitters, and released. After recovery from tagging and handling for at least 14 days, nine individuals were recaptured and released at least once during experimental angling, following best release practice. All cod survived the C&R event and did not show any large-scale behavioural changes (i.e., changes in diel vertical migrations). However, analysis of small-scale vertical movements showed that three individuals underwent short-term alterations (e.g., reduced or increased swimming activity). This study showed that pretagging fish with acoustic transmitters before experimental angling is an option when investigating fish behaviour immediately after the release event in marine environments. Moreover, release guidelines for cod should be developed, as cod can recover quickly if caught in shallow waters (<20 m) and properly handled and released.

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