Evaluation of changes in macrobenthic standing stock and polychaete community structure along the south eastern Arabian Sea shelf during the monsoon trawl-ban
K.U. Abdul JaleelUsha V. ParameswaranAiswarya GopalChippy KhaderGanesh ThiruchitrambalamV. N. SanjeevanT. ShunmugarajAnil Kumar VijayanG.V.M. Gupta
34
Citation
75
Reference
10
Related Paper
Citation Trend
Keywords:
Benthos
Dominance (genetics)
Demersal fish
Bottom trawling
Within the last few decades, the main bottom fishery in the south-eastern North Sea has changed from otter to beam trawling with beam trawling effort increasing from 1960 onwards. During this period, the Zoological Station in Den Helder (The Netherlands) has collected and registered by-catch species caught by commercial fishermen. The annual numbers of registered specimens were used to estimate the species-specific catch efficiencies of otter and beam trawlers between 1945 and 1983. This analysis was restricted to 7 fishes (sharks, rays, skates) and 10 invertebrate species (whelks, urchins, squids, crabs) all of which have a demersal life style and were regularly delivered throughout the study period. For most species, the observed variations in annual numbers of fish and invertebrates delivered to the Zoological Station appeared to be related to the changes in type of gear and fishing effort. Results from the model suggest that otter trawlers caught relatively more fish than invertebrates, whilst beam trawlers caught proportionally more invertebrate species (i.e. velvet swimming crab, slender spindle shell) that were rarely delivered during periods of greatest otter trawling effort. On average, the catch efficiency of the beam trawl fleet appeared to be 10 times higher than that of the otter trawl fleet. Furthermore, the trends shown by the model in species delivered suggested that bottom fisheries had a considerable impact on several demersal fish and benthic invertebrates.
Demersal zone
Demersal fish
Bycatch
Bottom trawling
Cite
Citations (73)
Abstract Piet, G. J., van Hal, R., and Greenstreet, S. P. R. 2009. Modelling the direct impact of bottom trawling on the North Sea fish community to derive estimates of fishing mortality for non-target fish species. – ICES Journal of Marine Science, 66: 1985–1998. This study introduces a spatially explicit model that combines abundance data for all the main fish species in the demersal North Sea fish community with international effort data and estimates of gear-, species-, and size-dependent catch efficiency to determine the mortality of non-target fish species caused by bottom trawl fisheries and its spatial variation. Where necessary information was lacking, assumptions were made, and a sensitivity analysis performed to examine the impact of these issues on model results. Model outcomes were validated using international landings and discard data for five target species: cod, haddock, whiting, sole, and plaice. This showed that depending on its configuration, the model could reproduce recorded landings and discards of these species reasonably well. This suggests that the model could be used to simulate rates of fishing mortality for non-target fish species, for which few data are currently available. Sensitivity analyses revealed that model outcomes were most strongly influenced by the estimates of gear catch efficiency and the extent to which the distributions of fishing effort and each species overlapped. Better data for these processes would enhance the contribution that this type of model could make in supporting an ecosystem approach to fisheries management.
Discards
Whiting
Demersal fish
Demersal zone
Bottom trawling
Haddock
Bycatch
Marine ecosystem
Fish mortality
Cite
Citations (56)
Abstract Biodiversity assessment is an important part of conservation management that ideally can be accomplished with noninvasive methods without influencing the structure and functioning of ecosystems. Environmental DNA (eDNA) metabarcoding has provided a promising tool to enable fast and comprehensive monitoring of entire ecosystems, but widespread adoption of this technique requires performance evaluations that compare it with conventional surveys. We compared eDNA metabarcoding and trawling data to evaluate their efficiency to characterize demersal fish communities in the Estuary and Gulf of Saint‐Lawrence, Canada. Seawater and bottom trawling samples were collected in parallel at 84 stations. For a subset of 30 of these stations, water was also collected at three different depths (15, 50, and 250 m) across the water column. An eDNA metabarcoding assay based on the 12S mitochondrial gene using the MiFish‐U primers was applied to detect fish eDNA. We detected a total of 88 fish species with both methods combined, with 72 species being detected by eDNA, 64 species detected by trawl, and 47 species (53%) overlapped between both methods. eDNA was more efficient for quantifying species richness, mainly because it detected species known to be less vulnerable to trawling gear. Our results indicated that the relative abundance estimated by eDNA and trawl is significantly correlated for species detected by both methods, while the relationship was also influenced by environmental variables (temperature, depth, salinity, and oxygen). Integrating eDNA metabarcoding to bottom trawling surveys could provide additional information on vertical fish distribution in the water column. Environmental DNA metabarcoding thus appears to be a reliable and complementary approach to trawling surveys for documenting fish biodiversity, including for obtaining relative quantitative estimates in the marine environment.
Environmental DNA
Demersal zone
Demersal fish
Bottom trawling
Whiting
Vulnerable species
Cite
Citations (82)
Demersal zone
Demersal fish
Bottom trawling
Cite
Citations (48)
Bottom trawling causes widespread disturbance to the sediments in shallow-shelf seas. The resultant mortality of benthic fauna is strongly size dependent. We empirically demonstrate that beam trawling frequency in the central North Sea had a greater effect on fauna size distribution in a soft sediment benthic community than variables such as sediment particle size and water depth. Accordingly, we simulated the impacts of trawling disturbance on benthos using a model consisting of 37 organism size classes between 1 μg and 140 g wet weight. The model produced a productionbiomass versus size relationship consistent with published studies and allowed us to predict the impacts of trawling frequency on benthos size distributions. Outputs were consistent with empirical data; however, at high yet realistic trawling frequencies, the model predicted an extirpation of most macrofauna. Empirical data show that macrofauna persist in many heavily trawled regions; therefore, we suggest that trawling by real fisheries is sufficiently heterogeneous to provide spatial refuges less impacted by trawling. If correct, our analyses suggest that fishery management measures that do not reduce total effort but do lead to effort displacement and spatial homogenization (e.g., temporarily closed areas) may have adverse effects on the systemic persistence of intermediate- and large-sized macrofauna.
Benthos
Bottom trawling
Cite
Citations (139)
Benthos
Bottom trawling
Netting
Cite
Citations (34)
Most experimental studies on the effects of trawling on the benthos use remote sampling techniques and are conducted in recently trawled areas. Thus it is difficult to determine the effects of trawling on previously unfished areas, and the fates of individual animals cannot be followed. In this study, I follow the fates of individuals of several sessile taxa when exposed to experimental trawling in areas that have not been trawled for some 1520 years. Although there was a significant trawling by location effect for all multivariate analyses and most individual taxa, I found that trawling had an overall negative effect on the benthos. Epifauna at trawled sites decreased in abundance by 28% within 2 weeks of trawling and by another 8% in the following 23 months (compared with control sites). Seasonal seagrasses were also less likely to colonise trawled sites than untrawled sites. The persistence of most taxa declined significantly in trawled areas compared with untrawled areas. In contrast to this, the recruitment rates of several taxa into visible size classes increased after trawling, presumably because of a reduction in competition.
Benthos
Bottom trawling
Cite
Citations (18)
Demersal finfishes are one of the major components in the marine fi sh landings along
the Indian coast. Demersal fish groups such as the sharks. groupers. snappers.
threadfins, porn frets and Indian halibut are commercially valuable and contribute
substantially to the economy of Indian marine fi sheries. Some of these groups,
especially of large-size, are targeted by the fishermen by using different craft and gear
combinations. However, several other demersal finfishes are not targeted, but are landed
as bycatch by shrimp trawlers. Compared with the pelagics, the demersal finfishes are
less affected by the changes in the environment. such as changes in temperature, speed
and direction of currents. Hence, the biological characteristics of the demersals are
relatively stable. Consequent upon the increase in the number and efficiency of trawlers,
the demersal landings have increased in the last 40 years. However, indiscriminate
trawling in the last one decade has affected the bottom habitat and the demersal
resources as well. ow there are evidences of decline in the stocks of few demersal
groups and shift in the composition of the landings.
Demersal zone
Demersal fish
Bottom trawling
Bycatch
Cite
Citations (1)
This paper studies the effect of the reduction in the trawling effort of large beam trawlers (>300 hp) in the coastal waters of the south-eastern North Sea following the establishment in 1989 of a protected area, the “plaice box”, using data from annual beam trawl surveys carried out since 1985. Two different aspects of the demersal fish assemblage were analysed: (1) the size distribution using multiple analysis of variance; and (2) the species composition using multivariate techniques such as principal component analysis, multidimensional scaling and multiple analysis of variance.
Demersal zone
Demersal fish
Bottom trawling
Assemblage (archaeology)
Cite
Citations (48)
The benthic and demersal communities in the Colombian Caribbean Sea (CCS) are heavily fished by the shrimp trawling fishery, which presents very high discard levels. Here, we conducted an analysis of the size structure of these benthic and demersal communities in the northern and southern zones of the CCS. Sampling was conducted onboard shrimp trawlers throughout an entire year. No significant differences were found in the size distributions of the two zones, among sites within southern ecoregions, or among the analyzed cruises. This homogeneity in size structure is remarkable since the zones analyzed possess very different species compositions and environmental conditions. The observed size structures were adequately described by non-linear distributions rather than the traditionally employed linear normalized biomass size spectra. It is hypothesized that the non-linearity is due to the effect of fishing and particularly, of discarding. This study emphasizes the need for a greater understanding of the impacts that trawl fishing has on community size structure and the applicability of this knowledge towards fishery resource management in ecosystems with high diversity.
Demersal zone
Bottom trawling
Demersal fish
Benthos
Marine protected area
Stock assessment
Cite
Citations (2)