American Plaice Hippoglossoides Platessoides Research Articles

Accounting for non-stationary stock–recruitment relationships in the development of MSY-based reference points

Asbtract Stock–recruitment relationships (SRRs) may vary over time due to ecological and anthropogenic impacts, challenging traditional approaches of calculating maximum sustainable yield (MSY)-based reference points that assume constant population traits. We compare seven methods to calculate MSY, FMSY and BMSY by modelling constant, stochastic (uncorrelated), and autocorrelated SRRs using simulations and two case studies [Atlantic cod (Gadus morhua) and American plaice (Hippoglossoides platessoides) on the Grand Bank off Newfoundland, Canada]. Results indicated that the method used to model SRRs strongly affected the temporal pattern of recruitment projection, and the variations generated by autocorrelated SRRs were more similar to observed patterns. When the population productivity had low-frequency and large-magnitude variations, stochastic SRRs generated greater MSY and FMSY estimates than constant or autocorrelated SRRs, while no consistent pattern of BMSY was detected. In the case studies, stochastic and autocorrelated SRRs produced asymmetric relationships between fishing mortality and yield, with higher risk of overfishing by going beyond FMSY. Overall, our results suggest that caution should be taken when calculating MSY-based reference points in highly dynamic ecosystems, and correctly accounting for non-stationary population dynamics could, therefore, lead to more sustainable fisheries.

Increasing temperatures, diversity loss and reorganization of deep-sea fish communities east of Greenland

In recent years, Arctic and sub-Arctic fish communities have shown extensive reorganization on shelves and in shallow waters, but little is known about the ecological impact of environmental changes in deeper waters. We examined temporal changes (1998-2016) in fish diversity and community structure based on research survey data from East Greenland, over a depth gradient spanning 400 to 1500 m. A northern and a southern continental slope region, 360 km apart, were analysed for temporal changes in water temperature and fish community structure. The bottom water temperature increased by up to 0.2 and 0.5°C, respectively. Contrary to expectations, there was a concomitant loss of species richness of up to 3 and 5 species, respectively, and a decrease in total abundance in both regions. Abundances of individual species displayed different trends between regions, with 3 species of wolf fishes (Anarhichas spp.) and American plaice Hippoglossoides platessoides decreasing in the north and blue antimora Antimora rostrata, Agassiz’ slickhead Alepocephalus agassizii and the roundnose grenadier Coryphaenoides rupestris decreasing in the south. The regional differences may reflect different oceanographic characteristics, as the northern region is more influenced by colder Arctic water, whereas the southern region is primarily influenced by the Subpolar Gyre (SPG). However, the observed temperature increase is expected to be due to an intensifying Atlantic Multidecadal Oscillation and/or anthropogenic climate change and not to SPG changes. The observed changes in biodiversity and community structure associated with warming are likely to affect community dynamics and alter ecosystem functioning.

Flatfish habitat use near North America's first offshore wind farm

Use of offshore wind power as a renewable energy source is underway in North America with the construction of the pilot, five wind turbine, Block Island Wind Farm, off Rhode Island, USA. Demersal trawl monitoring was conducted in two reference areas and near the wind farm that allowed an examination of whether flatfish abundances, size, and condition differed between baseline, construction, and operation time periods. Seven flatfish, (American plaice Hippoglossoides platessoides, fourspot flounder Paralichthys oblongus, Gulf stream flounder Citharichthys arctifrons, summer flounder Paralichthys dentatus, windowpane flounder Scophthalmus aquosus, winter flounder Pseudopleuronectes americanus, and yellowtail flounder Pleuronectes ferruginea) were collected in the study area. Winter flounder, windowpane and fourspot flounder accounted for 83% of all flatfish collected. Flatfish exhibited spatial and temporal variation in abundance, size, and condition, but this variation was not consistent with either positive or negative effects of wind farm construction or operation. Lower winter flounder abundances during the pile-driving time period and higher abundances during the cable-laying time period in the reference and wind farm areas suggest regionwide population fluctuations occurred. Although noise from pile driving may have been detectable in the reference areas, other flatfish abundances were not lower during this time period. Although no artificial reef effect was found for flatfish, negative impacts from construction activity and wind farm operation also were not evident.

Performance of the Nordmøre Grid in Shrimp Trawling and Potential Effects of Guiding Funnel Length and Light Stimulation

AbstractThe introduction of the Nordmøre grid to shrimp trawls has reduced the issue of bycatch to that of small‐sized species and juveniles that are able to pass through the grid and enter the small‐meshed cod end together with the targeted shrimp. This study estimated the size‐ and species‐selective performance of the Nordmøre grid in the configuration most often applied by fishermen and made a preliminary exploration of the effects of reducing the length of the guiding funnel in front of the grid and mounting light‐emitting diodes (LEDs) around the escape exit. Experimental fishing trials were conducted in the Barents Sea to assess the size‐selective properties of a 19‐mm bar spacing Nordmøre grid, mandatory in this Norwegian trawl fishery targeting deepwater shrimp Pandalus borealis (also known as northern shrimp), and its potential improvement. Results were obtained for the target species and four bycatch species: redfish Sebastes spp., Haddock Melanogrammus aeglefinus, Atlantic Cod Gadus morhua, and American Plaice Hippoglossoides platessoides. In general, very few deepwater shrimp were found to escape through the escape exit, although the quantity increased slightly at larger sizes. Between 80% and 100% of the bycatch species up to a species‐specific size passed through the grid and entered the cod end. A short guiding funnel decreased this for Haddock significantly by increasing the fraction of small Haddock seeking the escape exit. Further, adding LEDs around the escape exit significantly negated this effect. For the other bycatch species, the results indicated similar trends but were not statistically significant. However, considering that only a few fishing hauls were conducted using the short guiding funnel with or without mounting LEDs calls for some caution when attributing these changes to the configuration of the Nordmøre grid, and these preliminary results should be followed up by further testing before definitive conclusions are made.

A spatial approach to matching marine fish diversity and abundance with habitat features

Current issues in marine resource management have in common a geospatial component and a need to integrate both biotic and abiotic data from various sources. We propose a practical approach to address these issues looking at the American plaice (Hippoglossoides platessoides) and the demersal fish fauna in the Gulf of St. Lawrence (Canada). Central to our approach was the use of a common spatial grid and three different methods to match biotic and abiotic features at a broad regional scale, (1) matching plaice distribution with habitat categories determined a priori on the basis of abiotic features (cluster analysis), (2) habitat categories determined taking into consideration both plaice density and abiotic features (simple regression tree), and (3) habitat categories determined taking into consideration demersal fish species density (70 fish species) and abiotic features (multivariate regression tree, MRT). Hot spots and cold spots of plaice abundance in summer were described and matched with specific habitats. The spatial distribution of habitats was similar whether biotic variables were used in the classification or not. The MRT, however, identified 56 different fish species in the plaice habitat (median species richness by 100 km2 cell = 12), pointing to potential interactions with other fish species.

Bomb Radiocarbon Validates Age and Long‐Term Growth Declines in American Plaice in the Southern Gulf of St. Lawrence

AbstractThe growth rate and size composition of American Plaice Hippoglossoides platessoides in the southern Gulf of St. Lawrence has changed markedly over the past 40 years. The size at age recorded in commercial fisheries and research survey data has declined, particularly through the mid‐1980s. Females of the 1969 cohort grew to an estimated maximum length of 59 cm (males, 42 cm); the 1994 cohort grew to a much smaller maximum of 37 cm (29 cm for males). There is no indication of any reverse trend in growth or size at age in the 2000s, despite reduced harvests and warmer water temperatures. Incorrect aging methods are not the reason for the observed growth trends. Ages were determined by counting the growth increments visible on the surface of whole otoliths, and there is no bias in ages determined by this method (as opposed to those from thin‐sectioned otoliths). The accuracy of ages determined by reading whole otoliths was validated to at least 27 years (±2 years) by bomb radiocarbon assays of 39 otoliths collected between 1971 and 1986. While commercial fishing may have contributed to past declines in plaice growth, ongoing natural mortality may be keeping size at age and the growth rate low despite the recent increases expected from low fishing mortality and higher water temperatures.

Two Species of Commercial Flatfish, Winter Flounder, Pleuronectes americanus, and American Plaice, Hippoglossoides platessoides, as Sentinels of Environmental Pollution

Two species of marketable-size flatfish, winter flounder (Pleuronectes americanus) and American plaice (Hippoglossoides platessoides) from a fjord, were examined as sentinels for the effects of effluent discharged by a pulp and paper mill in Newfoundland, Canada. Reference samples for comparison were obtained from a pristine fjord. Condition factor, lymphocyte levels and the abundance of two intestinal parasites were significantly greater in flounder and plaice sampled at the reference site while macroscopic and microscopic lesions, and hepatic somatic indices were greater in flatfish taken from the contaminated site. These results suggest that both species of commercial flatfish are useful as sentinels for studying environmental pollution.

Relationships between maternal body size, condition and potential fecundity of four north‐west Atlantic demersal fishes

Fecundity data for four species (American plaice Hippoglossoides platessoides, yellowtail flounder Limanda ferruginea, witch flounder Glyptocephalus cynoglossus and Atlantic cod Gadus morhua) of north-west Atlantic demersal fishes, corresponding to nine populations, were examined in relation to fish size and condition in an attempt to explain the observed variability in potential fecundity. Both relative body (K(r)) and liver condition (H(r)) were poor single-factor predictors of fecundity, and in almost all cases fish body mass (M) was the best single-factor predictor. Annual variability in mean K(r) and H(r) existed for most populations. The inclusion of K(r) and H(r) in total length (L(T))-based predictive models improved model fit only slightly and not significantly in all cases. Multiple regression analyses to determine the best model for explaining the variability in fecundity often excluded K(r), H(r) and L(T) in favour of M. The amount of variability in fecundity that could be explained by the factors analysed here was species specific, with the highest proportion explained for H. platessoides and the lowest for L. ferruginea. The highly variable, and sometimes unpredictable, nature of north-west Atlantic groundfish fecundity suggests the need to continue collecting such reproductive data on an ongoing basis.

Optimal estimation of catch by the continuous underway fish egg sampler based on a model of the vertical distribution of American plaice (Hippoglossoides platessoides) eggs

Optimal estimation of catch by the continuous underway fish egg sampler based on a model of the vertical distribution of American plaice (Hippoglossoides platessoides) eggs

Ontogenetic variation in habitat associations for four flatfish species in the Gulf of Maine‐Georges Bank region

Multivariate ordination techniques were used to examine how size classes of four flatfish species, American plaice Hippoglossoides platessoides, winter flounder Pseudopleuronectes americanus, yellowtail flounder Limanda ferruginea and fourspot flounder Paralichthys oblongus, are related to bottom depth, bottom temperature, substratum grain size and temporal factors using a 35 year time series from autumn and spring in the Gulf of Maine‐Georges Bank region. Depth had the most explanatory value during both seasons in most cases, with fish size generally increasing with depth. One exception was yellowtail flounder in the spring for which a temporal factor explained the most variance, reflecting an increase in size over the time series due to changes in fishing pressure. Temperature was secondarily important for yellowtail flounder in the autumn and for fourspot flounder in both seasons. Substratum type was secondarily important for winter and yellowtail flounders in the spring with smaller fish associated with larger substratum types. Seasonal associations with depth, temperature and substratum are related to seasonal spawning migrations, thermal preferences and other ecological factors.

Major changes in fecundity and the effect on population egg production for three species of north‐west Atlantic flatfishes

Temporal and spatial variability in fecundity was investigated for three species of north‐west Atlantic flatfishes: American plaice Hippoglossoides platessoides, yellowtail flounder Limanda ferruginea and witch flounder Glyptocephalus cynoglossus. Significant log10 linear relationships existed between fecundity and total length (LT) for all three species and for all combinations of area (NAFO regulatory areas) and year. Fecundity differed between areas for yellowtail flounder and witch flounder and changed significantly for all three species since the last reported fecundity studies in the region 30–40 years ago. Three populations experienced decreases in fecundity (3LNO American plaice and yellowtail flounder, 3Ps witch flounder), one experienced an increase (3NO witch flounder) and one did not change (3L witch flounder). Significant yearly variability in fecundity at length and relative fecundity existed for all three species within the 6 year sampling period (1993–1998). Estimates of population egg production based on new and historic fecundity data revealed that using the old, invariant fecundity and LT relationship resulted in overestimation of total annual egg production by up to 24% for 3LNO American plaice and as high as 41% for 3LNO yellowtail flounder. These results clearly demonstrate the variable nature of fecundity for flatfishes in Newfoundland waters and suggest that the use of an invariant fecundity and LT relationship may result in inaccurate estimates of stock reproductive potential.

Optimal estimation of catch by the continuous underway fish egg sampler based on a model of the vertical distribution of American plaice (Hippoglossoides platessoides) eggs

Abstract Pepin, P., Curtis, K.A., Snelgrove, P.V.R., de Young, B., and Helbig, J.A. 2007. Optimal estimation of catch by the continous underway fish egg sampler based on a model of the vertical distribution of American plaice (Hippoglossoides platessoides) eggs – ICES Journal of Marine Science, 64, 18–30. We investigate how the vertical stratification of the water column (specifically density) affects predictions of the catch of American plaice eggs (Hipploglossoides platessoides) from a fixed-depth sampler [the continuous underway fish egg sampler (CUFES)] relative to the integrated abundance in the water column measured in bongo tows. A steady-state model of the vertical distribution of fish eggs coupled with a simple model of the vertical profile of eddy diffusivity (i.e. mixing) is applied. Key model parameters are estimated through optimization of a one-to-one relationship between predicted and observed catches fit, using a generalized linear model with a Poisson, negative binomial, or gamma error structure. The incorporation of data on the vertical structure of the water column significantly improved the ability to forecast CUFES catches when using Poisson or negative binomial error structure, but not using a gamma distribution. Optimal maximum likelihood parameter estimates for eddy diffusivity and egg buoyancy fell within the range of expected values. The degree of uncertainty in the parameterization of eddy diffusivity suggests, however, that greater understanding of the forces that determine the vertical profile of mixing is critical to achieving strong predictive capabilities. The inverse problem of predicting integrated abundance from CUFES catches did not benefit from the environmental-driven model because of the high uncertainty in the catches from the CUFES.

Associations between Surficial Sediments and Groundfish Distributions in the Gulf of Maine–Georges Bank Region

AbstractThe delineation of essential fish habitat is an important element of contemporary fisheries management. Although local‐scale species–habitat relationships have been established for some managed species, we lack an understanding of these associations at the synoptic spatial scales on which fish populations and their associated fisheries operate. Interest in habitat delineations has been elevated further by an increased awareness of ongoing habitat degradation caused by mobile fishing gears and by the advancement of spatial management tools. Here we examine the associations between surficial sediment grain size and groundfish distributions in the Gulf of Maine–Georges Bank region. The mean abundances for 58 demersal fish species were determined for a spatial cell grid (185.2 km2 per cell), which was subsequently joined to a spatially referenced sediment database in a geographical information systems environment. Multivariate statistical methods were then used to examine how fish distribution and abundance varied with substrate grain size. Of the 58 species examined, 12 were consistently associated with particular substrate types. Atlantic cod Gadus morhua, longhorn sculpin Myoxocephalus octodecemspinosus, sea raven Hemitripterus americanus, and winter flounder Pseudopleuronectes americanus were consistently abundant in large‐grained substrate types, whereas white hake Urophycis tenuis, goosefish Lophius americanus, red hake U. chuss, silver hake Merluccius bilinearis, witch flounder Glyptocephalus cynoglossus, and American plaice Hippoglossoides platessoides were consistently abundant in fine‐grained substrates. Little skate Leucoraja erinacea was most abundant in sediments of intermediate grain size. Although broadly distributed, spring dogfish Squalus acanthias consistently distinguished assemblages in fine‐grained sediments. Given that we were able to detect even weak associations and that these relationships were consistent with local‐scale studies, we recommend using these relationships to further refine essential fish habitat and that they be given more weight in this and similar temperate ecosystems.

Do environmental factors affect recruits per spawner anomalies of New England groundfish?

Abstract We evaluated the influence of environmental factors on recruits per spawner (RS) anomalies of 12 New England groundfish stocks. Nonparametric methods were used to analyse time-series of RS anomalies derived from stock-recruitment data in recent assessments. The 12 stocks occur in three geographic regions: the Gulf of Maine (cod Gadus morhua, redfish Sebastes fasciatus, winter flounder Pseudopleuronectes americanus, American plaice Hippoglossoides platessoides, witch flounder Glyptocephalus cynoglossus, and yellowtail flounder Limanda ferruginea), Georges Bank (cod, haddock Melanogrammus aeglefinus, and yellowtail flounder), and Southern New England (summer flounder Paralichthys dentatus, yellowtail flounder, and winter flounder). Randomization tests were applied to detect years when RS anomalies were unusually high or low for comparison with oceanographic conditions such as the 1998 intrusion of Labrador Subarctic Slope water into the Gulf of Maine region. Randomization methods were also used to evaluate the central tendency and dispersion of all RS anomalies across stocks. Average RS anomalies were significantly positive in 1987 across stocks and regions, indicating that environmental forcing was coherent and exceptional in that year. Responses of RS values of individual stocks to lagged and contemporaneous environmental variables such as the North Atlantic Oscillation (NAO) index, water temperature, windstress, and shelf water volume anomalies were evaluated using generalized additive models. Overall, the NAO forward-lagged by 2 years had the largest impact on RS anomalies. This apparent effect is notable because it could provide a leading indicator of RS anomalies for some commercially exploited stocks. In particular, the three primary groundfish stocks on Georges Bank (cod, haddock, and yellowtail flounder) all exhibited positive RS anomalies when the NAO2 variable was positive.

Variation with age in the timing and duration of spawning in American plaice

Spawning time of female American plaice Hippoglossoides platessoides varied significantly with age. This effect, however, was not consistent across years. Generally, younger fish spawned earlier than older fish, but in the 1990s they spawned later than older fish. Spawning duration also varied with age, with younger fish generally having a longer spawning period than older fish. Changes in depth distribution were related to changes in both spawning time and duration. As depth increased, spawning time became later and duration became shorter. Fish <11 years old showed the largest change in both spawning time and depth distribution.

The effect of smaller mesh sizes on catching larger fish with trawls

Selection curves of small mesh trawls were assessed with one alternate haul and two trouser trawl experiments. The effect of fish length on the ratio ( p i ) of the number of fish of length i caught in the large mesh cod-end to the number of fish of length i caught in both cod-ends was estimated with generalized linear modeling. The alternate haul experiment was conducted with beam trawls equipped with 2 and 18 mm stretched mesh cod-ends to assess size selectivity for perch Perca fluviatilis. None of the perch that entered the cod-end could escape through the mesh of the small mesh cod-end. For small perch (<ca. 10 cm total length), p i reflected the ratio in areas swept by the large and small mesh nets, but for larger perch, p i increased. Water flow through the small mesh net must have been lower than through the large mesh net, enabling relatively more larger perch (>ca. 10 cm total length) to out-swim the small mesh net. The trouser trawl experiments were conducted to study selectivity for smelt Osmerus eperlanus, using 12 and 22 mm stretched mesh cod-ends, and for American plaice Hippoglossoides platessoides, using 39 and 155 mm stretched mesh cod-ends (published data). During both trouser trawl experiments, smaller fish that entered the cod-end could escape through the large mesh cod-ends, so p i increased with increasing fish size. However, also beyond the size where fish could escape through the large mesh cod-end, p i continued to increase. This implied that the small mesh cod-end was less selective to larger fish. We demonstrated that the lower selectivity to larger fish in the cod-end with the smaller mesh could result in 20–50% overestimation of the length ( L 50) at which 50% of the fish entering the cod-end escape through the mesh.

Sex-specific temperature distribution in four populations of American plaice Hippoglossoides platessoides

In the American plaice Hippoglossoides platessoides, the sexes differ in size at age in most populations, with females being larger. Because of the links between growth, ration and tem- perature, differences in temperature selection might be expected between the sexes in species with dimorphic growth, with the sex with the higher growth rate selecting higher temperatures. Temper- ature selection has also been predicted to be density-dependent in fishes, with fish occupying colder temperatures at higher levels of abundance. We examined these aspects of temperature selection in 4 populations of American plaice: the southern Gulf of St. Lawrence population and 3 populations off Newfoundland (Labrador and NE Newfoundland, Grand Bank and St. Pierre Bank). Throughout the 1970s and most of the 1980s plaice occupied cold water relative to that available in all of the areas surveyed. In all 4 populations, females tended to occupy warmer water than males. Differences between the sexes in temperature selection and in length at age both tended to be greatest in the southern Gulf population during this period. However, there was no correspondence among popula- tions in these differences in the early 1990s, when distribution of the Grand Bank and St. Pierre Bank populations shifted sharply into warm water and the difference in temperature distribution between the sexes increased dramatically in these populations. These shifts to warmer water may be related to density-dependent effects on temperature preference. There was a strong negative relationship between the temperatures occupied by plaice and their relative abundance in the 3 Newfoundland populations but not in the southern Gulf population. Densities appear to have remained higher in the southern Gulf population than in the Newfoundland populations, suggesting that density-dependent effects on temperature preference only occur when densities fall below some threshold level.

Evaluation of Atlantic Cod Predation on American Lobster in the Southern Gulf of St. Lawrence, with Comments on Other Potential Fish Predators

Abstract Demersal fishes are widely thought to be an important source of natural mortality for juvenile American lobster Homarus americanus. There were no significant relationships between abundance indices of American lobster and the dominant demersal fish species, Atlantic cod Gadus morhua, in the southern Gulf of St. Lawrence. American lobster was found in only one of 22,625 Atlantic cod stomachs collected between 1955 and 1980—a period of low American lobster abundance. Only six of 12,008 Atlantic cod collected between July 1990 and October 1996 (a period of high American lobster abundance) had eaten American lobster. Most size-classes of the two species were spatially separate from early July to early September and November to May. American plaice Hippoglossoides platessoides, the second most abundant demersal fish species, did not eat American lobster (n = 1,800 stomachs). Again, the two species were spatially isolated for most of the year. More limited studies (in terms of spatial or seasonal cover...

Effects of release parameters on recovery rates of tagged groundfish species

A compilation of groundfish mark-recapture studies conducted in the Northwest Atlantic from 1953 to 1985 was examined by analysis of deviance to determine the effects of release parameters on subsequent recoveries of Atlantic cod (Gadus morhua), haddock (Melanogrammus aeglefinus), pollock (Pollachius virens), and American plaice (Hippoglossoides platessoides). Fish length was a major determinant of recoveries for all four species, with recovery rates generally increasing with increasing fish length. Depth of capture was a significant determinant of recoveries for cod and haddock, with recovery rates decreasing as depth increased. Year of release was a significant determinant for all four species, with recovery rates declining in recent years. Declines in recovery rates of cod, haddock, and pollock occurred during certain months or seasons. Recovery rates decreased where fish were tagged in areas most distant from inhabited coastal regions, but the interpretation of this effect is complicated by changes in the fisheries over time between areas. Recovery rates also decreased with increasing catch size and varied between different tag types and capture methods. The results should prove useful in the design of tagging protocols and analysis of recovery data.

Egg Production, Fertility, and Hatch Success of American Plaice Held in Captivity

The reproductive performance of individual female American plaice Hippoglossoides platessoides was monitored during a spawning season under laboratory conditions. The majority (74%) of females produced eggs at some point in a 2-month period (May–July) during which they were checked every 2 d for ovulated eggs. Most females produced several batches of eggs during an average production period of 26 d. Approximately 12% of the total number of eggs produced by each female were obtained in the first egg batch. There were periodic peaks of egg production for the group in increasing intervals at about 8, 20, and 34 d after the first eggs were collected. The mean relative fecundity was 1.5 × 105 eggs/ kg body weight, but there was no relationship between actual fecundity and either length or weight. The mean percentages of viable and fertile eggs were 44.7% and 13.7%, respectively. A significant decline in the percentage of fertile eggs was observed with time, such that percent of fertile eggs by the sixth batch was significantly (P < 0.05) lower than in the first batch. There was no significant decline in viable eggs with time, although there was a positive correlation (r = 0.72, P < 0.001) between viability and fertility. The number of larvae hatched from viable eggs varied widely during the spawning period with a mean hatch success rate of 23%. A significant positive correlation was observed between the number of larvae hatched and the percentage of fertile eggs (r = 0.82, P < 0.001).