Seasonal Bottom Trawl Surveys Research Articles

Spatio-temporal niche of major fish species in Pishan waters off Zhejiang Province, China.

Based on seasonal bottom trawl surveys in November 2015 (autumn), February (winter), May (spring) and August (summer) in 2016, the index of relative importance (IRI), Shannon index and Pianka index were used to analyze the breadth and overlap of spatio-temporal niche of major fish species in the Pishan waters off Zhejiang Province. Redundancy analysis and interspecific competition coefficient were used to examine the competition relationship and niche differentiation of those major fish species. The results showed that a total of 61 fish species were recorded throughout the year, which belonged to 13 orders, 29 families and 48 genera. A total of 19 species with IRI>100 were identified as major fish species. The temporal niche overlap value between Chelidonichthys kumu and Atule kalla was largest, indicating high temporal synchronization. Both the spatial niche overlap value and the spatio-temporal niche overlap value between Trpauchen vagina and Cynoglossus interruptus were largest, indicating that their spatial homology was high and that the use of spatial and temporal two-dimensional resource of both species were consistent. The percentage of species pairs with spatio-temporal niche overlap at the significant level (Qik>0.6) was only 5.8% in Pishan waters, indicating that the spatial and temporal distribution of those species were quite different. The overlap of spatio-temporal niche significantly varied across different seasons. The results of the interspecific competition coefficient were basically consistent with the niche overlap. Results of the redundancy analysis revealed the relationships between major fish species and environmental factors (temperature, salinity, dissolved oxygen), and further explained the niche diffe-rentiation among species.

Growth and maturity heterogeneity of three croaker species in the East China Sea

Big head croaker (BC) Collichthys lucidus, Large yellow croaker (LC) Larimichthys crocea, and Yellow croaker (YC) Larimichthys polyactis are important ecological and commercial species along the coastal seas of China. Based on samples collected from seasonal bottom trawl surveys in the southern East China Sea from 2015 to 2018, we analyzed the growth and maturity characteristics of these three croaker species. Simple linear model, mixed-effects model and hierarchical methods were conducted in this study to evaluate the variations in growth and maturity among sexes, seasons and years for each species. Our results showed that, mixed-effects model performed better than simple linear models, while hierarchical methods could reveal variations in different life stages. Female LC and YC tended to gain more weight at the same length and matured earlier than the male for LC and YC. The individuals tended to gain more weight in spring and fall, while all croakers had larger weight at the same length and matured earlier from 2015 to 2017 compared to those in 2018. Results from the hierarchical model indicated that for all captured croakers, individuals with bigger sizes were mostly females, especially for LC. Big head croaker and LC tend to gain more weight in spring, while YC tends to gain less weight in winter. Mixed-effects models and hierarchical methods can be incorporated to provide more information about the heterogeneity of fish life history traits. These results will help provide more insights related to the growth and maturity of these three important species in the East China Sea. Also, the methodology applied in this study may be used on the life history research for species with multiple data sources.

Population dynamics of threadfin porgy Evynnis cardinalis, an endangered species on the IUCN red list in the Beibu Gulf, South China Sea.

Threadfin porgy Evynnis cardinalis is both a dominant fish species and an important fishing target in bottom trawl fisheries in the Beibu Gulf, South China Sea. It was listed as endangered (EN) in a recent International Union for Conservation of Nature (IUCN) red list. Despite its economic importance and endangered status, limited research on its biological characteristics and spatial-temporal distribution has been undertaken this last decade, creating uncertainty in current conservation and management. We analyse this species' spatial distribution characteristics using data from four seasonal bottom trawl surveys in 2014-2015, and report average catch per unit effort to vary seasonally, from 49.1 to 594.5 ind h-1 . Growth, mortality and sexual maturity are reported for four time periods based on data from bottom trawl fishery surveys over 1961-1962, 1998-1999, 2006, and 2014-2015. Length frequency distributions changed from bimodal to unimodal, and the female-to-male ratio increased. Mean body length and length at first maturity decreased, whereas the growth coefficient increased, indicating miniaturization, early sexual maturity and accelerated growth, respectively. We report sparid catch to have first exceeded maximum sustainable yield in 2001, and to have remained overfished from 2010 to 2015. Since the 1980s, low-trophic-level fishes such as E. cardinalis have replaced high-trophic-level fishes such as Crimson snapper Lutjanus erythropterus to become dominant species. As catches have increased substantially, these species have been faced with overfishing, driving the ecosystem into an unstable state.

How to predict biodiversity in space? An evaluation of modelling approaches in marine ecosystems

AbstractAimBiodiversity prediction becomes increasingly important in the face of global diversity loss, whereas substantial challenges still exist in both conceptual and technical aspects. There exist many predictive models, and an integrative evaluation can help understand their performance in handling the multifacets of biodiversity. This study aims to evaluate the performance of these modelling approaches to predict both α‐ and β‐diversity in diverse ecological contexts.LocationNorth Yellow Sea, China.MethodsThe biodiversity models follow three strategies, “assemble first, predict later”, “predict first, assemble later” and “assemble and predict together”. Hill diversity profile, Fisher's log‐series parameter and the distance decay of similarity are used to measure α‐ and β‐diversity. The evaluation study is conducted based on seasonal bottom trawl surveys from October 2016 to August 2017 in North Yellow Sea, China, allocated to coastal and offshore areas. We evaluate the predictive power of the models using cross‐validation.ResultsFollowing the “assemble first, predict later” approach, macroecological model (MEM) provided the most accurate prediction overall, whereas stacked species distribution model (SSDM) and joint species distribution model (JSDM), following the second and third modelling approaches, tended to overestimate α‐diversity and underestimate β‐diversity. The performances of SSDM and JSDM could be improved by moderately down‐weighting rare species. The relative performances of the three modelling approaches were consistent among seasons and spatial regions.Main conclusionsThe superior performances of MEM in a range of temporal and spatial contexts favour the “assemble first, predict later” approach and imply a tight community assembly in the studied area. The overall predictive powers of varying models suggest that the spatial pattern of marine biodiversity could be fairly well predicted with commonly accessible hydrologic data in a mesoscales. The approach of multi‐model evaluations is applicable to a variety of ecosystems for biodiversity prediction.

Spatio-temporal dynamics of summer flounder (Paralichthys dentatus) on the Northeast US shelf

Summer flounder (Paralichthys dentatus) are an economically and ecologically important fish on the Northeast U.S. shelf. There is evidence that their spatial distribution has shifted over time. However, there are conflicting reports on the importance of various potential drivers of the shift. Here, we investigate whether the stock has shifted and the extent to which this can be attributed to changes in abundance, size-structure, environmental variables, and fishing. We do so using a vector-autoregressive spatio-temporal model that incorporates data from two seasonal bottom trawl surveys that together span the nearshore and offshore Northeast US shelf over the past 41 years. We find that the summer flounder distribution has shifted north and east in both the spring and fall. The shift is observed in both recruits and spawners, with recruits shifting northward faster than spawners, suggesting that increased spawner abundance may not be driving the shift in recruits. We find that only a small portion of the variability in distribution can be attributed to changes in abundance, fishing, or environmental covariates. Instead, the shift is most strongly attributed to unidentified factors.

The breadth and overlap of ecological niche of major fish species in the Minjiang River Estuary, China.

Based on the seasonal bottom trawl surveys in the Minjiang River Estuary in 2015, the breadth and overlap of ecological niche of major fish species were analyzed. Those fish species were identified based on the index of relative importance (IRI). A total of 137 species belonging to 37 families and 16 orders were collected. Fifteen major fish species were determined by the IRI, including six dominant species Polydactylus sextarius, Harpadon nehereus, Pennahia argentata, Secutor ruconius, Cynoglossus abbreviates, Coilia mystus, and nine important species Collichthys lucidus, Amblychaeturichthys hexanema, Upeneus japonicas, Lagocephalus spadiceus, Pampus argenteus, Larimichthys crocea, Thryssa kammalensis, Takifugu oblongus, Lepturacanthus savala. Seven species whose spatio-temporal niche breadth was higher than 1 in a declining order were C. abbreviates, C. lucidus, S. ruconius, A. hexanema, T. kammalensis, C. mystus, H. nehereus. The ecological niche of major fish species in the Minjiang River Estuary showed obvious seasonal dynamics. The percentage of species pairs with spatio-temporal niche overlap at the meaningful level was as high as 81.9%. Six species pairs reached significant ecological niche overlap, indicating that major fish species had similar distribution at the spatial and temporal scales and the existence of resource utilization competition. The species pairs of U. japonicus-L. savalawas had the highest spatio-temporal niche overlap value, whereas U. japonicus-C. lucidus had the lowest niche overlap value. The spatio-temporal niche overlap of major fish species in the Minjiang River Estuary had substantial seasonal variation.

The trend of lessepsian fish populations with an emphasis on temperature variations in Iskenderun Bay, the Northeastern Mediterranean

AbstractThe fish assemblages of the Eastern Mediterranean are highly variable owing to the Lessepsian migration. So far, there has been limited discussion about the temporal variation of Lessepsian populations, which may be a key to better understanding the establishment, persistence and spreading dynamics of these species. The objective of this study was, therefore, to develop an understanding of inter‐annual variations of Lessepsian fish populations through investigating the effects of climate conditions. For this purpose, we evaluated the data obtained from the seasonal bottom trawl surveys conducted over the course of 12 years, from 2004 to 2015, at the infra‐littoral zone of Iskenderun Bay. Our results indicated that Lessepsians constituted 27%, 62% and 85% of total teleost fishes in the number of species (LS‐%), biomass (LW‐%) and abundance (LN‐%), respectively. The linear trends showed that the dominance of Lessepsian fishes increased with annual rates of 1.9 (p < .01, LS‐%), 2.77 (p < .01, LW‐%) and 1.43% (p < .05, LN‐%) per year during the study period. In contrast, seasonal trend decomposition based on GAMMs revealed that the true shape of trends was non‐linear. The majority of the new Lessepsians entered the study area after 2009 when warmer conditions prevailed. Those new invaders such as Nemipterus randalli, Pomadasys stridens and Apogon smithi successfully settled in a short time and remarkably altered the composition of fish assemblages after 2010. We found that variations of lessepsian fish assemblages were correlated with the increase of annual minima and average values of sea surface temperature.

Spatial and seasonal variations in the trophic spectrum of demersal fish assemblages in Jiaozhou Bay, China

Trophic structure of fish communities is fundamental for ecosystem-based fisheries management, and trophic spectrum classifies fishes by their positions in food web, which provides a simple summary on the trophic structure and ecosystem function. In this study, both fish biomass and abundance trophic spectra were constructed to study the spatial and seasonal variations in the trophic structure of demersal fish assemblages in Jiaozhou Bay, China. Data were collected from four seasonal bottom trawl surveys in Jiaozhou Bay from February to November in 2011. Trophic levels (TLs) of fishes were determined by nitrogen stable isotope analysis. This study indicated that most of these trophic spectra had a single peak at trophic level (TL) of 3.4–3.7, suggesting that demersal fish assemblages of Jiaozhou Bay were dominated by secondary consumers (eg. Pholis fangi and Amblychaeturichthys hexanema). The spatial and seasonal variations of trophic spectra of Jiaozhou Bay reflected the influence of fish reproduction, fishing pressure and migration of fishes. Two-way analysis of variance (ANOVA) showed that seasonal variations in trophic spectra in Jiaozhou Bay were significant (P 0.05). The trophic spectrum has been proved to be a useful tool to monitor the trophic structure of fish assemblages. This study highlighted the comprehensive application of fish biomass and abundance trophic spectra in the study on trophic structure of fish assemblages.

Length-weight and length-length relationships of 11 fish species from Zhimai River estuary, China

The present work provides the length–weight relationships (LWRs) and total length – standard length relationships (LLRs) of 11 fish species belonging to six families. The fishes were collected from seasonal bottom trawl surveys in the Zhimai River estuary, March 2011 to May 2013. This is the first record of LWRs and LLRs for several of the fish species in this area.

Reproductive biology of Benthosema pterotum (Teleostei: Myctophidae) in the shelf region of the East China Sea

Benthosema pterotum is a dominant myctophid in the shelf region of the East China Sea (ECS). They are a key species linking secondary producers and upper trophic levels. We examined the reproductive biology of B. pterotum in the ECS, based on 3065 specimens (10.7–54.8 mm standard length (SL)) sampled during cruises in 1999 and 2004–2009 to enable data over a 12 month cycle to be assessed. Between 14 and 30 mm SL, the ratio of females to males was ~1:1; it increased with SL, and all individuals ≥46 mm SL were females. The gonadosomatic index (GSI) at 50% sexual maturity of females and males was 3.91 and 0.24, respectively. Based on this criterion, females and males can mature at sizes larger than 28 mm and 24 mm SL, respectively. Although mature females having GSI ≥3.91 occurred over nine months (May–January), mean GSI of females peaked sharply during August–September, i.e. the primary spawning period. The hepatosomatic index peaked during April–July, and declined during August–September, indicating storage of materials and energy for reproduction. Based on data from seasonal bottom trawl surveys, small individuals of B. pterotum began to occur abundantly in autumn, and modal body lengths increased progressively during spring–summer, corresponding to the above reproductive seasonality. Oocytes at various sizes were found in mature ovaries, indicating that they are multiple spawners. Egg size at hydration ranged from 0.5 to 0.85 mm. Batch fecundity was positively correlated with SL, and ranged from 253 to 1942 eggs in fish from 30.1–54.8 mm SL.

Length-weight relationships of 43 fish species from Haizhou Bay, central Yellow Sea

Specimens of 43 fish species belonging to 25 families were collected from seasonal bottom trawl surveys in Haizhou Bay from March to December 2011. The length–weight relationships (LWRs) of these fish species were estimated, with 22 species presented for the first time. Maximum total length records of ten species exceeded those in FishBase. The effects of sex, season and growth phase on the relationships for some of these species were taken into account whereby one species had significantly (P < 0.05) different LWRs by sex, and eight species exhibited significantly different LWRs by season. Two different growth stanzas were detected for two species using the double-logarithmic plot of body weight versus total length.

Migrations and structure of the species range in ridge-scaled rattail Macrourus carinatus (Southwest Atlantic) and their application to fisheries management

AbstractLaptikhovsky, V. 2011. Migrations and structure of the species range in ridge-scaled rattail Macrourus carinatus (Southwest Atlantic) and their application to fisheries management. – ICES Journal of Marine Science, 68: 309–318. The biology, distribution and abundance of the ridge-scaled rattail (Macrourus carinatus) was studied in four seasonal bottom-trawl surveys in 2006–2009 using biological material collected on board different research and commercial fishing vessels. The species was found to exhibit ontogenetic and seasonal migrations. Upon switching to the demersal lifestyle, juveniles gradually move north with the Falkland Current. Adults return to the spawning areas (50–54°S) and remain there. They move seasonally along the slope from 54°S to 50°S between 500 m and 900 m, with males and females moving separately. The northernmost aggregations (at 50–51°S) occur in autumn, during the major spawning event. In winter, fish migrate south. During spring and summer the entire population gradually shifts north with ongoing minor off-season spawning. Females, which are the larger sex, tend to stay shallower than males. Such a sex-related migratory behaviour should be taken into account when the existence or absence of Heincke's law is considered for a particular species. A complicated migratory pattern should also be accounted for in fishery management.

Spatio-temporal distribution and biomass of Benthosema pterotum (Pisces: Myctophidae) in the shelf region of the East China Sea

We examined the spatio-temporal distribution and biomass of Benthosema pterotum, a dominant mesopelagic-boundary myctophid in the shelf region of the East China Sea, based on data from seasonal bottom-trawl surveys. They are a major prey item for commercially important demer- sal fishes in this area. A total of 980 000 individuals with a wet weight of 554 kg were collected from 694 bottom-trawl net samples. Dense distributions (>10 5 ind. km -2 ) of B. pterotum were observed mainly in the area south of Cheju Island in all seasons, where a persistent cyclonic eddy occurs. The distribution pattern indicated the presence of an independent population completing their life cycle in the area south of Cheju Island. Daytime habitat depth of B. pterotum (mainly 40 to 90 m depth) was a markedly shallower depth than previous reports for adult fishes for the family Myctophidae. The mechanism of population maintenance of this mesopelagic species in such a shallow area was hypothesized to be related to the presence of highly turbid waters in the benthopelagic layer, which produces dim light conditions during the daytime. The biomass of B. pterotum in the area south of Cheju Island was estimated to range from 3900 to 38 400 t.

Distribution and migration of age‐0 jack mackerel (Trachurus japonicus) in the East China and Yellow Seas, based on seasonal bottom trawl surveys

AbstractWe examined the distribution and migration of age‐0 jack mackerel in the East China Sea (ECS) and Yellow Sea, based on data from seasonal bottom trawl surveys. Sampling was conducted at 79–161 stations during five cruises in spring (April–June), early summer (May–July), late summer (August–October), autumn (October–December), and winter (January–February). During early summer, jack mackerel (mean 92 mm fork length), which were estimated to have hatched in the southern East China Sea (SECS) during winter, began to occur abundantly, especially along the shelf‐break region of the central East China Sea (CECS). In late summer, the distribution center of young fish (mean 126 mm) shifted northward into the shelf region of northern East China Sea (NECS), corresponding with the rise of bottom water temperature and high prey abundance. In winter when the bottom water temperature declined in the shelf region, the distribution center of jack mackerel (mean 144 mm) shifted southward, with high densities occurring in the SECS and CECS. In spring, overwintering jack mackerel that had become age‐1 (mean 175 mm) were distributed abundantly along the shelf‐break region of the ECS. On the other hand, jack mackerel were only sporadically found, generally at low densities, in the Yellow Sea during all seasons. High densities of jack mackerel were largely restricted to areas of &gt;15°C bottom water temperature during all seasons. Our results indicate that the seasonal shifts of the 15°C isotherm of the bottom layer and the food conditions are significant environmental factors determining the migration of jack mackerel within the ECS.

Seasonal, diel and ontogenetic variation in feeding patterns of small yellow croaker in the central Yellow Sea

Stomach contents of 1603 small yellow croaker Pseudosciaena polyactis, sampled from seasonal bottom trawl surveys in the central Yellow Sea between March 2001 and January 2002, were examined. The results showed that small yellow croaker was a carnivorous predator and &gt;30 prey species were identified from stomach contents analysis. Crustaceans (mainly euphausiids and decapods) were the most important prey, occurring in 93·1% of the stomachs containing food, and accounting for 77·6% of the total food by mass. Feeding activity was highest in autumn and lowest in spring and winter. Decapods were more important in summer, whereas euphausiids were more important during other seasons. Ontogenetic differences were found in the diet composition and feeding activity within the range of size (standard length, LS) studied. The importance of fishes and decapods increased with LS, whereas euphausiids, copepods and amphipods decreased in importance with LS. Dietary breadth increased markedly for adults. A positive relationship was found between LS and prey size. In each season the maximum diel feeding activity occurred at 0800 and 2400 hours, indicating that there was crepuscular and nocturnal feeding by small yellow croaker.

Demersal bony fish of the outer shelf and upper slope of the southern Brazil Subtropical Convergence Ecosystem

Ninety-three species of bony fishes were caught in 4 seasonal bottom-trawl surveys carried out between July 1986 and May 1987 on the outer shelf and upper slope (124 to 587 m depth) along the southern Brazilian coast (30°40' to 3430' S). On the outer shelf (< 179 m), the demersalpelagic species Trichiurus lepturus, Trachurus lathami, Cynoscion guatucupa, Scomber japonicus, and Thyrsitops lepidopoides predominated and also to a lesser degree the demersal benthonic Umbrina canosai and Mullus argentinae. Antiyonia capros and Priacanthus arenatus were found associated with the relic coral hard bottoms of the shelf break (180 to 249 m). Further offshore, the demersal-pelagic species Ariomma bondi and Zenopsis conchifera and the demersal benthonic species Polyprion americanus and Helicolenus lahillei were abundant, both associated with rocky bottoms. The macrourids Coelorinchus marinii and Malacocephalus occidentalis characterized deep-water hauls p 4 5 0 m). Frequent and widespread, but less abundant in the catch, were Polymixia lowei, Urophycis mystacea and Merluccius hubbsi. Mean total catch (kg h-') decreased 6-fold and the number of species by more than half along the depth range, with a sharp step at 350 m. Both catch and number of species were slightly higher in the winter cruises. Most species occurred in both winter and summer-autumn cruises, but, with increasing depth, the relative abundance of species that occur year-round decreased, whereas fishes that occur mostly in winter increased. The catch of demersal-pelagic fish decreased sharply below 350 m and differed little among seasons; catches of demersal-benthonic fish were more evenly distributed across the depth range and were larger in winter and spring. The high number of species on the shelf break may be attributable to the higher variety of soft and consolidated substrates and the overlapping of different water masses along the water column. The north-south shift of the western boundary of the Subtropical Convergence appears to be mainly responsible for the seasonal changes in abundance of the species.