Distribution Of Demersal Fish Species Research Articles

Response of demersal fishes to low dissolved oxygen events in two eutrophic estuaries

Coastal ecosystems serve as important nursery areas, yet they are facing many challenges. For example, eutrophication-induced hypoxia is one of the major threats to the functioning of coastal ecosystems, particularly estuaries. The Sundays and Swartkops estuaries both experience persistent eutrophic conditions, with frequent phytoplankton blooms (>20 μg Chl-a l−1) that result in instances of bottom-water oxygen depletion (<4 mg/l). Bi-seasonal sampling of both physico-chemical parameters and demersal fishes between February 2018 and September 2019 in the Swartkops and Sundays estuaries allowed for the quantification of low dissolved oxygen (<4 mg/l) and hypoxic (<2 mg/l) events in both estuaries and the impact of low dissolved oxygen (DO) and hypoxic events on overall fish species abundance, richness and distribution. Low DO conditions were typically observed in the bottom waters of the vertically-stratified meso-to polyhaline middle and upper reaches of the Sundays and Swartkops estuaries, respectively. Hypoxic conditions ( DO = 0.5 mg/l) were recorded in the Sundays Estuary during the study, whereas in the Swartkops Estuary the lowest DO recorded was 2.4 mg/l. Low DO events resulted in a decrease in fish species richness and overall abundance in the Sundays Estuary, while in the Swartkops Estuary fish species richness declined during low DO events, with little effect on fish abundance. Fish only completely avoided areas where DO was <1 mg/l or >10 mg/l. As such, the low DO concentrations recorded in the Swartkops Estuary did not have a noticeable impact on fish distribution, although the abundance of Rhabdosargus holubi and Caffrogobius gilchristi declined in the upper reaches of the Swartkops Estuary when DO was <3 mg/l. The results from this study provide much-needed insights into the impact of low DO and hypoxic conditions on the spatial distribution of demersal fish species.

Numerical Simulations and Fish Diversity in Relation to Physico-chemical Parameters of Four Aquatic Stations in Badagry Division, Lagos, Nigeria

Aim: This study investigated common fish assemblages in four aquatic stations (Gbaji, Topo, Agboju and Ajegunle) in relation to physico-chemical parameters of its water and as well simulates numerical values of the physico-chemical parameters for year 2024.&#x0D; Methodology: Data were collected and computed using standard methods and algorithm machine learning model respectively. Statistical tools employed include ANOVA and Pearson correlation (r) test. All the parameters (except turbidity, chemical oxygen demand and biochemical oxygen demand) were within standard permissible limits.&#x0D; Results: The results of Pearson’s correlation analysis showed that increase in amount of fish species in the sampling stations was significantly and strongly linked to the decrease in value of biochemical oxygen demand (r = −0.571, P=.05), total dissolved solids (r= −0.696, P=.05) and conductivity (r=−0.882, P&lt;0.01) while increase in number of fish species was significantly and strongly linked to the increase in value of dissolved oxygen(r= 0.991, P=.05). However, salinity (r= 0.387), sulphate (r = 0.212) and turbidity (r= 0.282) had weak positive relationship with the number of fish species. The prediction by the machine learning algorithm modeling system revealed that at Agboju, total hardness would exceed permissible limit in February and September, carbondioxide (C02) in February, May and June, 2024.On the other hand, level of C02 at Ajegunle would exceed permissible limit in January, May, August and September, and total hardness in November, 2024. For both Agboju and Ajegunle, turbidity and chemical oxygen demand level would exceed limits throughout the months in year 2024.&#x0D; Conclusion: Hence, effects of higher parameters could results in declination of distribution of demersal fish species which often shuttle between the water bottom and surface.

Spatio-temporal distribution of demersal fish species in the northern Alboran sea and Gulf of Vera

Spatio-temporal distribution of demersal fish species in the northern Alboran sea and Gulf of Vera

Mouth gape determines the response of marine top predators to long-term fishery-induced changes in food web structure

Here, we analyse changes throughout time in the isotopic niche of the Franciscana dolphin (Pontoporia blainvillei), the South American fur seal (Arctocephalus australis) and the South American sea lion (Otaria flavescens) from the Río de la Plata estuary and adjacent Atlantic Ocean to test the hypothesis that fishing may modify the diet of small-gape predators by reducing the average size of prey. The overall evidence, from stable isotope and stomach contents analyses, reveals major changes in resource partitioning between the three predators considered, mainly because of an increased access of Franciscana dolphins to juvenile demersal fishes. These results are consistent with the changes in the length distribution of demersal fish species resulting from fishing and suggest that Franciscana dolphin has been the most benefited species of the three marine mammal species considered because of its intermediate mouth gape. In conclusion, the impact of fishing on marine mammals goes beyond the simple reduction in prey biomass and is highly dependent on the mouth gape of the species involved.

Ecological distribution of demersal fish species in space and time on the shelf of Antalya Gulf, Turkey

This study provides baseline data on demersal fish assemblages in a heterogeneous but little-studied portion of the shelf of Antalya Gulf. The distribution of fish abundances along three transects subject to different fishing regulations, at depths of 10, 25, 75, 125 and 200 m, was studied between May 2014 and February 2015 in the winter, spring, summer and autumn months. A total of 147 species belonging to 69 families were sampled. Lessepsian migrants from the Indo-Pacific region made up about a quarter of all species collected and some of them were found to greatly influence community structure. The spatial distribution of fish species was driven mainly by bathymetric gradient and two main assemblages were observed: shallow waters (10–25 m) and deep waters (75–125 m; 125–200 m). Significant differences in community structure were found with regard to all the main variables: depth, transect, season and their interactions. Environmental variables measured concurrently with trawling were tested for correlation with fish abundances by canonical correspondence analysis (CCA). The results showed that the distribution of all species depends first on water depth and second on bottom type. The possible effects of fishing restrictions in the eastern part of the study area on assemblages are also discussed. In general, the spatial distribution and ecological processes of the fish community seem to depend on small variations in local environmental characteristics.

Exploring diversity and distribution of demersal fish species from the Northern Alboran Sea and Gulf of Vera (Western Mediterranean Sea)

Exploring diversity and distribution of demersal fish species from the Northern Alboran Sea and Gulf of Vera (Western Mediterranean Sea)

Exploring diversity and distribution of demersal fish species from the Northern Alboran Sea and Gulf of Vera (Western Mediterranean Sea)

Exploring diversity and distribution of demersal fish species from the Northern Alboran Sea and Gulf of Vera (Western Mediterranean Sea)

Seasonal dynamics in the distribution of demersal fish species in the pacific ocean coast of the northern Kuril Islands and southeastern Kamchatka regarding the near-bottom water temperature

Based on the analysis of multiyear data on the distribution of demersal fish species regarding the near-bottom temperature in the Pacific Ocean coast of the northern Kuril Islands and southeastern Kamchatka, seasonal changes in the habitat temperature for 16 fish species were revealed (preference and weighted average values are given). Functional relationships between the fish catch value and near-bottom water temperature were determined. All the species under study were divided into three groups regarding the near-bottom temperature of habitat: cold water, eurythermal, and warm water.

Multi-scale fish–habitat associations and the use of habitat surrogates to predict the organisation and abundance of deep-water fish assemblages

Deep-water demersal fishes are an important component of continental shelf and slope ecosystems and play an important role in the economies of many countries. Strong and predictable relationships of fishes with seabed habitats, in conjunction with rapid advances in acoustic seabed mapping capabilities, indicate there is great potential for using habitats as proxies or ‘surrogates’ to predict species distribution and abundance patterns at broad regional scales. However, few studies have evaluated this potential in complex seabed environments. In this study, we examined the spatial distributions, assemblage composition, and benthic habitat associations of deep-water demersal fish species over three spatial scales across Cordell Bank, a deep-water bank in central California. Demersal fishes were counted and habitats quantified from 60 strip-transects allocated over the extent of the bank using in situ observer and video-recorded data from the two-person Delta submersible. Both abundance and distribution of demersal fish species on Cordell Bank were strongly correlated with spatial location and habitat composition on the bank. Habitat structure was heterogeneous at several spatial scales. At broad scales, the rocky bank itself contained the highest diversity of both habitats and fishes. At intermediate scales, transition zones (10–100s of m wide) between the bank and continental slope and shelf sediments supported a diverse and characteristic suite of fish species. Habitats were also heterogeneous at finer-scales (1–10s of m) within these broad-scale zones, and fish responses to these habitat characteristics were taxon-specific, and often contingent on the spatial configuration of fine scale habitats within the broader-scale landscape. The results of this study indicate that for many species it is not sufficient to just know the fine-scale habitat association to predict fish assemblages. The landscape setting is also an important predictor if habitat is to be used as a surrogate for fish distributions in the management and conservation of these demersal fish assemblages.

Geographic, seasonal and bathymetric distribution of demersal fish species in the eastern Mediterranean

Summary The distributional abundance of three demersal fish species, Merluccius merluccius, Mullus barbatus and Lophius budegassa, was studied as a function of sampling season, bathymetry and geographic area. Data were collected during research trawl surveys in the Aegean and Ionian seas under the same sampling scheme, thereby allowing comparisons to be made on the mean regional densities in numbers and biomass of these three commercially important species in Greek waters. Results indicated that European hake, M. merluccius, demonstrated a wide bathymetric and geographic distribution, with specimens encountered in all regions between 20 and 500 m depth, although density was found to be highest usually between 101 and 200 m. The mean regional density of hake was observed to vary seasonally, being higher mainly in winter. Red mullet, M. barbatus, was distributed in shallow water depths (<100 m) throughout the Greek seas, particularly in the northern part of the Aegean Sea. Abundance of this species steadily decreased with increasing depth. The geographic distribution of anglerfish, L. budegassa, was found to be restricted to the central and northern part of the Aegean Sea, with the highest mean densities encountered in the Thermaikos Gulf and in intermediate water depths between 101 and 200 m. Spatial patterns of observed density are assumed to be attributed mainly to prevailing topographic and hydrographic conditions and related biological productivity levels.

Trends in cpue and related changes in spatial distribution of demersal fish species in the Kattegat and Skagerrak, eastern North Sea, between 1981 and 2003

Abstract We explored the trends in ln-transformed catch per unit effort, defined as average weight (kg) per 1 h trawling, and the spatial distribution of 32 demersal fish species in the Kattegat and Skagerrak using International Bottom Trawl Survey data collected between 1981 and 2003. As in other areas, the biomass of roundfish species such as cod, pollack, hake, and ling drastically decreased during this period most likely owing to fishing pressure. However, other commercially important fish species, e.g. haddock, whiting, and some flatfish, showed a constant or increasing trend during the same period. Non-commercial species showed no or an increasing trend in ln-cpue, by as much as 40 times in hagfish. Furthermore, analyses of the spatial distribution of 14 selected fish species by means of distribution maps of ln-cpue suggested that fish stocks contracted and expanded in response to decrease and increase of the stock biomass, respectively, with some flatfish species (i.e. plaice and flounder) and hagfish representing the exceptions to this general pattern.