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opencc-zeroNov 2021View details →

Allee effects and the allee-effect zone in northwest atlantic cod

According to the theory of compensatory dynamics, depleted populations should recover when the threat responsible for their decline is removed because per capita population growth is assumed to be highest when populations are at their smallest viable sizes. Yet, many seriously depleted fish populations have failed to recover despite threat mitigation. Atlantic cod (Gadus morhua) off Newfoundland despite thirty years of dramatically reduced fishing mortality and numerous fishery closures has not recovered suggesting that drivers other than fishing regulate the growth of collapsed fish populations, inhibiting or preventing their recovery. Here, using Bayesian inference, we show strong evidence of Allee effects in a south Newfoundland cod population, based on data on recruitment and spawning stock biomass. We infer the Allee-effect threshold, below which recovery is impaired. We demonstrate the necessity of data at low population sizes to make inferences about the nature of low-abundance dynamics. Our work indicates that Allee effects are not negligible in commercially exploited fish populations, as commonly projected, and that they represent an inhibitory force that can effectively prevent recovery from overfishing. Our findings contrast with prevailing fisheries management practices that assume compensatory dynamics at low abundances with potential to seriously overestimate the recovery potential of collapsed populations.

opencc-zeroJul 2022View details →

Otolith annual growth increments for cod populations in the Northeast Atlantic

Large-scale, climate-induced synchrony in the productivity of fish populations is becoming more pronounced in the world's oceans. As synchrony increases, a population's 'portfolio' of responses can be diminished, in turn reducing its resilience to strong perturbation. Here we argue that the costs and benefits of trait synchronization, such as the expression of growth rate are context dependent. Synchrony among individuals could actually be beneficial for populations if growth is optimized during favourable conditions and then declines under poor conditions when a broader portfolio of responses is needed. Importantly, growth synchrony among individuals within populations has seldom been measured, despite well-documented evidence of synchrony across populations. Here, we used century-scale time series of annual otolith growth to test for changes in growth synchronization among individuals within multiple populations of a marine keystone species (Atlantic cod, Gadus morhua). On the basis of 74,662 annual growth increments recorded in 13,749 otoliths, we detected a rising conformity in long-term growth rates within northeast Atlantic cod populations in response to both favorable growth conditions and a large-scale, multidecadal mode of climate variability similar to the East Atlantic Pattern. The within-population synchrony was distinct from the across-population synchrony commonly reported for large-scale environmental drivers. Climate-linked, among-individual growth synchrony was also identified in other Northeast Atlantic pelagic, deep-sea and bivalve species. We hypothesize that growth synchrony buffers marine populations to changing climate and growth conditions through its effect on the phenotypic expression of growth diversity, and thus provides an unexpected, but pervasive and stabilizing impact on marine population productivity.

opencc-by-4.0May 2015View details →

The Provincelands of Cape Cod National Seashore, Barnstable County, Massachusetts, USA. The reddish vegetation in the center of the photo is a cranberry (Vaccinium macrocarpon) bog, a wetland used for breeding by the Fowler's toad. The surrounding landscape is ideal for the Fowler's toad and supports one of the largest populations of this species in the United States. The landscape contains a patchwork of sand, pitch pine (Pinus rigida), scrub oak (Quercus ilicifolia), and dune grass (Ammophila breviligulata). Photo by Rebecca Flaherty. in Fowler's Toad (Anaxyrus fowleri) occupancy in the southern mid-Atlantic, USA

The Provincelands of Cape Cod National Seashore, Barnstable County, Massachusetts, USA. The reddish vegetation in the center of the photo is a cranberry (Vaccinium macrocarpon) bog, a wetland used for breeding by the Fowler's toad. The surrounding landscape is ideal for the Fowler's toad and supports one of the largest populations of this species in the United States. The landscape contains a patchwork of sand, pitch pine (Pinus rigida), scrub oak (Quercus ilicifolia), and dune grass (Ammophila breviligulata). Photo by Rebecca Flaherty.

Fig. 4 in Morphological and molecular identification of Cryptocotyle lingua metacercariae isolated from Atlantic cod (Gadus morhua) from Danish seas and whiting (Merlangius merlangus) from the English Channel

Fig. 4 Phylogenetic trees based on cox1 mtDNA (left tree) and ITS rDNA (right tree) sequences using the ML method with 1000 bootstraps

Fig. 3 in Morphological and molecular identification of Cryptocotyle lingua metacercariae isolated from Atlantic cod (Gadus morhua) from Danish seas and whiting (Merlangius merlangus) from the English Channel

Fig. 3 Excysted Cryptocotyle lingua metacercariae at different degrees of contraction a in whiting from the English Channel, b in cod from Danish waters

Fig. 2 in Morphological and molecular identification of Cryptocotyle lingua metacercariae isolated from Atlantic cod (Gadus morhua) from Danish seas and whiting (Merlangius merlangus) from the English Channel

Fig. 2 Morphology of excysted Cryptocotyle lingua metacercariae (ventral view) from Gadus morhua and Merlangius merlangius. Abbreviations: bi.i, bifurcation of intestine; e, oesophagus; ex.c, excretory canal; ex.p, excretory pore; ic, intestinal caecum; pp, prepharynx; ph, pharynx; ov, ovary; os, oral sucker; s.r, seminal receptacle; t, testis; vg.c, ventrogenital complex; vi, vitellaria; ① distance from oral sucker to end of pharynx; ② distance from oral sucker to intestinal branches; ③ width 1; ④ width 2; ⑤ oral sucker diameter; ⑥ ventrogenital complex diameter; ⑦ total length

Fig. 1 in Morphological and molecular identification of Cryptocotyle lingua metacercariae isolated from Atlantic cod (Gadus morhua) from Danish seas and whiting (Merlangius merlangus) from the English Channel

Fig. 1 Infected Atlantic cod (Gadus morhua) (a) and microscope observation of encysted metacercariae in caudal fin (b)

Fig. 3 in The effects of Contracaecum osculatum larvae on the growth of Atlantic cod (Gadus morhua)

Fig. 3. End condition as Fulton's K by cod age; with abundance (i.e. number of C. osculatum) in a) and C. osculatum density (number of C. osculatum per gram liver) in b). Darker and larger circles means higher abundance or density.

Fig. 2 in The effects of Contracaecum osculatum larvae on the growth of Atlantic cod (Gadus morhua)

Fig. 2. Plotted change (end-start) in cod length, weight, and condition as Fulton's K against C. osculatum abundance (the number of C. osculatum in a liver) to the left and C. osculatum density (the number of C. osculatum per liver weight (gram)) to the right, separated by season. Data represents the cod that survived the trials.

Fig. 5 in The effects of Contracaecum osculatum larvae on the growth of Atlantic cod (Gadus morhua)

Fig. 5. Prediction of growth in weight per day depending on the number of parasites per liver weight (gram) with confidence intervals for a model cod with a GSI of 5 and a starting weight of 0.5 kg at different levels of start condition (medium condition is represented by Fulton's K 0.8, below 0.8 is considered low condition and>1 is considered high (Marteinsdottir and Begg 2002)). Below zero on the y-axis represents no growth. Dots represents observations.

Fig. 1 in The effects of Contracaecum osculatum larvae on the growth of Atlantic cod (Gadus morhua)

Fig. 1. Map of the study area. The circle marks the position for the sea pen trial and the larger dashed area is where the fish were caught for the trial. The numbers in the map refers to ICES subdivisions (SD).

Fig. 4 in The effects of Contracaecum osculatum larvae on the growth of Atlantic cod (Gadus morhua)

Fig. 4. Prediction of growth in length per day depending on C. osculatum density (the number of C. osculatum per liver weight (gram)) with confidence intervals. Below zero on the y-axis represents no growth. Dots represents observations.

opencc-zeroSep 2023View details →

Atlantic cod individual spatial behaviour and stable isotope associations in a no-take marine reserve

<ol> <li>Foraging is a behavioural process and, therefore, individual behaviour and diet are theorized to covary. However, few comparisons of individual behaviour type and diet exist in the wild.</li> <li>We tested whether behaviour type and diet covary in a protected population of Atlantic cod, Gadus morhua. </li> <li>Working in a no-take marine reserve, we could collect data on natural behavioural variation and diet choice with minimal anthropogenic disturbance. We inferred behaviour using acoustic telemetry and diet from stable isotope compositions (expressed as δ13C and δ15N values). We further investigated whether behaviour and diet could have survival costs.</li> <li>We found cod with shorter diel vertical migration distances fed at higher trophic levels. Cod δ13C and δ15N values scaled positively with body size. Neither behaviour nor diet predicted survival, indicating phenotypic diversity is maintained without survival costs for cod in a protected ecosystem.</li> <li>The links between diet and diel vertical migration highlight that future work is needed to understand whether the shifts in this behaviour during environmental change (e.g. fishing or climate), could lead to trophic cascades. </li> </ol>

opencc-zeroOct 2023View details →

Large females connect Atlantic cod spawning sites

In this study, we used acoustic telemetry to monitor the movements of mature Atlantic cod (Gadus morhua) during the winter spawining season. The fish were captured in traps with the help of a local fisher, and released near their point of capture after tagging and body size measurements. Fish detection data were downloaded from the moored receivers twice per year, before and after the spawning season. The acoustic receivers were distributed among several known inshore spawning grounds, and we used network analyses to quantify how individual cod moved at a finer and broader scale among these sites. Movement traits representing connectivity were used as response variables in the statistical analyses, while body size measurements, residency (time spent within the array), tagging location and year, were tried as predictors.