Trawl Sets Research Articles

Hierarchical modelling of epibenthic communities on the Scotian Shelf and Gulf of Maine (Atlantic Canada) in support of conservation planning

Identification of ecologically significant units at different spatial scales is essential for management of biodiversity attributes. This case study illustrates a coupled methodological approach to delineate benthic habitats and associated assemblages at different spatial scales. Two complementary analyses were employed based on the occurrences of 99 epibenthic invertebrate species in Atlantic Canada, sampled during depth-stratified random trawl sets. To identify epibenthic assemblage types, isometric feature mapping and partitioning around medoids (ISOPAM) was used in combination with a joint species distribution model (JSDM), which also produced continuous distribution surfaces across the spatial domain. ISOPAM identified nine significantly spatially coherent assemblages (biotopes) at spatial scales of hundreds of meters to hundreds of kilometers, with associated diagnostic species. Those assemblages were closely matched by eight regions of common profile using the JSDM, indicating strong environmental influences on their distributions. These smaller-scale assemblages were grouped into three biophysical units. The results from the JSDM were validated with independent data showing good congruence. This indicates that the spatial units ascribed to identified assemblages are robust and suitable for marine spatial planning and monitoring.

Population ecology and juvenile density hotspots of thornback ray (Raja clavata) around the Shetland Islands, Scotland.

Elasmobranchs are facing global decline, and so there is a pressing need for research into their populations to inform effective conservation and management strategies. Little information exists on the population ecology of skate species around the British Isles, presenting an important knowledge gap that this study aimed to reduce. The population ecology of thornback ray (Raja clavata) around the Shetland Islands, Scotland, was investigated in two habitats: inshore (50-150 m deep) and shallow coastal (20-50 m deep), from 2011 to 2022, and 2017 to 2022, respectively. Using trawl survey data from the annual Shetland Inshore Fish Survey, the size composition of R. clavata catches was compared between shallow and inshore habitats across 157 trawl sets, and 885 individuals, over the years 2017-2022. Catch per unit effort (CPUE) of R. clavata was significantly higher in shallow than that in inshore areas (ANOVA, F = 72.52, df = 1, 5, p < 0.001). Size composition also significantly differed between the two habitats (analysis of similarities, R = 0.96, p = 0.002), with R. clavata being smaller in shallow areas and juveniles (<60 cm) occurring more frequently. Spatial distribution maps confirmed density hotspots of juveniles in shallow habitats, with repeated use of certain locations consistent over time. The results of this study provide the first evidence for R. clavata using shallow areas for potential nurseries in Shetland, which can inform the IUCN's Important Shark and Ray Area process. Furthermore, this study provides important new population ecology information for R. clavata around Shetland, which may have important conservation implications and be valuable for informing species and fisheries stock assessments in this region.

Cold-Water Soft Corals (Cnidaria: Nephtheidae) as Habitat for Juvenile Basket Stars (Echinodermata: Gorgonocephalidae)

Nephtheidae soft corals are a common component of benthic ecosystems in the Northwest (NW) Atlantic and in the Arctic, but little is known about their functional roles. Here we investigated their role as habitat for basket stars (Ophiuroidea). By examining over 4500 soft coral colonies of Drifa glomerata, Duva florida, Gersemia spp., and Pseudodrifa racemosa collected during trawl surveys in the regions of Newfoundland, Labrador and West Baffin Bay, we show that Nephtheidae soft corals are habitat for juvenile Gorgonocephalus sp. basket stars. Juvenile Gorgonocephalus sp. were found on all soft corals species, but Drifa glomerata was the soft coral species with the highest occurrence of associated juvenile basket stars (32%), with a maximum of 111 basket stars found on a single 4.8 cm tall (contracted state) colony. Individual basket star disc diameter did not change with colony height, but it varied with season for individuals found on D. glomerata. On the other hand, colony height was positively related with maximum disc diameter (D. glomerata), and presence and number of basket stars on a colony (D. glomerata and D. florida). One very young ophiuroid was found within one polyp of a D. florida colony collected in July. We also examined bottom trawl survey data from 2011-2017 from Newfoundland to Baffin Bay, and other locations in the Eastern Canadian Arctic and found that for our largest database, 45% of trawl sets that contained basket stars also contained corals, of which 67% were Nephtheidae soft corals. In this study we show that all four Nephtheidae soft coral taxa studied act as habitat for juvenile basket stars, which are conspicuous components of benthic communities in cold-water environments. Soft corals are commonly exposed and vulnerable to bottom fishing gear in the North Atlantic. We urge future studies evaluating the nature of this relationship, the potential role of soft corals as nurseries, and the potential degree of dependency/preference between basket stars and soft corals in relation to other organisms.

Marine epibenthic functional diversity on Flemish Cap (north‐west Atlantic)—Identifying trait responses to the environment and mapping ecosystem functions

AbstractAimTo characterize the functional diversity and selected ecological functions of marine epibenthic invertebrate communities at the ecosystem scale and to evaluate the relative contributions of environmental filtering, including bottom‐contact fishing, and competitive interactions to benthic community assembly.LocationFlemish Cap, an ecosystem production unit and fishing bank in the high seas of the north‐west Atlantic Ocean.MethodsThrough the use of Hierarchical Modelling of Species Communities (HMSC), we have explored seven community response traits to the environment applied to 105 epibenthic species and evaluated the influence of such traits on the community assembly processes. Assumed bioturbation, nutrient cycling and habitat provision functions, linked to individual or a combination of biological traits, were mapped using random forest modelling.ResultsFunctional richness within benthic communities reached an asymptote for trawl sets with roughly more than 30 species. Assemblages on top of the Flemish Cap (&lt;500 m depth) were characterized by higher biomass of small‐ and medium‐sized species with short life spans, whereas large species with longer life spans and broadcast spawners were dominant in the deeper assemblages (500–1,500 m depth). The amount of variation explained by the species’ responses to the covariates mediated by the traits was relatively high (25%) indicating their relevance to community assembly. Community‐weighted mean trait values changed with depth and physical oceanographic variables, indicating that environmental filtering was occurring. Interspecific interactions, as inferred from the random effect at the sample level, accounted for 16.3% of the variance in the model, while fishing effort explained only 5.2% of the variance but conferred strong negative impacts for most species.Main conclusionsOur results suggest that while bottom‐contact fishing impacts have an effect on functional diversity, changes to the physical oceanography of the system are likely to have more profound impacts. The maps of benthic functioning can aid assessments of ecosystem impacts of fishing.

Elasmobranch bycatch in the demersal prawn trawl fishery in the Gulf of Papua, Papua New Guinea

The elasmobranch bycatch of the Gulf of Papua Prawn Fishery is investigated in detail for the first time. Fisheries observers collected data on the elasmobranch bycatch from a total of 403 trawl sets (1,273 hrs) in the Gulf of Papua. A total of 40 species of elasmobranchs were recorded ranging in size from a 12 cm disc width stingray to a 350 cm total length sawfish. High mortality rates were recorded (>80%), attributed to the long trawl durations (up to 4 hours). The future inclusion of bycatch reduction devices would likely reduce the number of larger elasmobranchs being caught, based on evidence from the prawn trawl fisheries of northern Australia, and is being investigated by the PNG National Fisheries Authority. Differences in catch compositions were detected across the management zones as well as between the two monsoonal seasons (SE Monsoon and NW Monsoon). Increased monitoring and additional research is required and management plans should address the elasmobranch bycatch and in particular their high mortality rate.

Distribution and environmental relationships of three species of wolffish (Anarhichas spp.) in the Gulf of St. Lawrence

AbstractThis study examines the spatial distribution of three species of wolffish in the Gulf of St. Lawrence on the basis of trawl surveys.A standardized method is proposed to assess species–habitat associations for the purpose of management and recovery of endangered marine species.Catch data (presence/absence in trawl sets) and landscape and environmental characteristics of the sea floor were aggregated using a common grid (100 km2 cells), and species–habitat relationships were explored using geospatial tools.Relative occurrence was lower and area of occupancy and concentration were much smaller for the northern wolffish (Anarhichas denticulatus) than for the spotted wolffish (Anarhichas minor), with the striped wolffish (Anarhichas lupus) being most widespread. Significant relationships were observed between values of the local spatial autocorrelation Gi* statistic and habitat descriptors for each of the three species.Hot spots for spotted and striped wolffish occurred in areas where a greater diversity of relief and habitats was found. They were associated with intermediate depths, coarse sediments and rock outcrops, and lower salinities and temperatures than for northern wolffish.Northern wolffish appeared to be associated mainly with the deep water sloped habitat bordering deep channels, whereas spotted and striped wolffish both concentrated most intensively into neighbouring deep water shelf habitats and relatively cold shallow to mid‐depth shelf habitats of the northern Gulf.The RDA analysis indicated a significant relationship between Gi* scores of the three species and environmental variables. The model explained 52% of the variability in the data; northern wolffish showed a distinct relationship compared with the two other species.The conservation of marine species and protection of their habitats pose a major challenge given the limited amount of information typically available on rare species and the scale and complexity of marine processes that affect those species. The broad‐scale approach presented here allows the provision of advice on important habitats on the basis of the best available knowledge. Copyright © 2013 Her Majesty the Queen in Right of Canada

Associations of demersal fish with sponge grounds on the continental slopes of the northwest Atlantic

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 477:217-230 (2013) - DOI: https://doi.org/10.3354/meps10127 Associations of demersal fish with sponge grounds on the continental slopes of the northwest Atlantic E. Kenchington1,*, D. Power2, M. Koen-Alonso2 1Fisheries and Oceans Canada, Bedford Institute of Oceanography, 1 Challenger Drive, Dartmouth, Nova Scotia B2Y 4A2, Canada 2Fisheries and Oceans Canada, Northwest Atlantic Fisheries Centre, PO Box 5667, St. John’s, Newfoundland A1C 5X1, Canada *Email: ellen.kenchington@dfo-mpo.gc.ca ABSTRACT: Association of demersal fish taxa with Geodia-dominated temperate sponge grounds was examined in 104 research vessel survey trawl sets from 500 to 1500 m depth along the continental slopes of the Grand Banks and Flemish Cap, northwest Atlantic. The total number of fish taxa and their total biomass were negatively correlated with sponge biomass and catch depth, and sponge biomass increased with depth. ANOSIM identified significantly different fish communities (biomass and abundance composition) associated with 3 sponge catch weight classes, and multidimensional scaling plots showed separation of trawl sets labelled by this factor to be strongest for abundance. SIMPER analysis identified the fish assemblage associated with the sponge grounds (≥250 kg km-1): roughhead grenadier Macrourus berglax, roundnose grenadier Coryphaenoides rupestris, blue hake Antimora rostrata, longnose eel Synaphobranchus kaupii, turbot Reinhardtius hippoglossoides, black dogfish Centroscyllium fabricii and deep-sea cat shark Apristurus profundorum. These contributed to 92 and 81% of the similarity (~50%) among trawl set catches using biomass and abundance data, respectively. Four additional taxa contributed to 92% similarity in abundance: common grenadier Nezumia bairdii, shortnose snipe eel Serrivomer beanii, lanternfish (Myctophidae) and goitre blacksmelts Bathylagus euryops. SIMPER dissimilarity identified 6 fish taxa with larger biomass in catches with high sponge catch weight: shortnose snipe eel, deep-sea cat shark, eelpout Lycodes spp., spinytail skate Bathyraja spinicauda, white skate Dipturus linteus and deepwater chimaeras Hydrolagus affinis. The first 3 species were also more abundant in those catches and are considered to be strongly associated with the sponge grounds. Future research focussing on these species identified as being associated with the sponge grounds may provide greater insight into the strength of the associations and the ecological linkages between these benthic and pelagic communities. KEY WORDS: Demersal fish assemblages · Sponge grounds · Trawl catch Full text in pdf format Supplementary material PreviousNextCite this article as: Kenchington E, Power D, Koen-Alonso M (2013) Associations of demersal fish with sponge grounds on the continental slopes of the northwest Atlantic. Mar Ecol Prog Ser 477:217-230. https://doi.org/10.3354/meps10127 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 477. Online publication date: March 12, 2013 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2013 Inter-Research.

Acoustic data from fishing vessels: What can be obtained that research vessels cannot offer?

Use of fishing vessels and platforms of opportunity to collect acoustic‐based population distribution and abundance data has been considered since the 1990s. The idea was that low data quality was compensated by large sampling throughout the year, and in areas where research vessels did not sample. We present results and hypotheses on the use of such data from the anchovy and jack mackerel fishing industry in Peru, where many fishing vessels are equipped with SIMRAD ES60 echosounders. First, fishing vessels are selected according to a criteria set. Once “optimal” fishing vessels are selected, we show that exploiting acoustic data from these ships may provide new information. The first is a correlation of fishing activity with fish biomass. Ee analyzed echograms preceding trawl sets. Data on fish biomass and spatial distribution were correlated with catch and catch structure. Additionally, environmental information in an area of 1 nm2 centered on the trawl location was added to the acoustic and fishing data. The potential to obtain information on fish length within the exploited school before fishing was explored, using direct (TS measurements around the school) or indirect (environmental signature giving probabilistic information) methods.

Throwing in the towel: When do adverse conditions dictate a weather day during a bottom trawl survey?

Abstract Fishermen and field biologists routinely work under difficult conditions. It is natural in this setting to continue fishing during bad weather as long as safety is not compromised. However, as conditions deteriorate, the effectiveness of trawl survey gear may be reduced well before safety considerations force the cessation of sampling activity. Through comparison of 1754 hauls conducted on chartered vessels between 2003 and 2005 on the shelf and slope of the U.S. West Coast, we show a significant reduction in catch rates of bottom dwelling fish and invertebrates as a function of visually estimated wave height. Comparing randomly located trawl sets that occurred fortuitously close to one another, we conclude that to reduce the estimated effect of wave height on benthic species catch rates (and potentially relative biomass estimates) survey trawl activities on these vessels should be halted when wave heights reach six feet (1.83 m). Only 41 hauls from the 2003–2005 data were conducted when wave heights exceeded five feet (1.52 m), however their exclusion reduces the maximum expected bias in any single tow due to wave height by ∼31%. Further reductions in maximum wave height for routine sampling would begin to exclude geographic areas of the survey introducing a new bias to the randomized design. We further encourage the routine electronic measurement of vertical motion due to wave action during sampling so that future analyses can improve our understanding of its effect on trawl survey catch rates.

Bycatch and release of pelagic megafauna in industrial trawler fisheries off Northwest Africa

The accidental capture of large animals such as sharks, manta rays, sea turtles, and dolphins in pelagic trawler fisheries remains controversial because it threatens biological diversity in many biogeographical regions, including the subtropical eastern North Atlantic. Bycatch rates observed during more than 1400 trawl sets off Mauritania, Northwest Africa, are shown to have been considerable during the past 4 years, with high animal abundance in Summer when the Northwest African shelf is occupied by subtropical water. We demonstrate the urgency for bycatch reduction and evaluate the use of species-selective gear, a conservation method immediately available and immediately effective in waters fished through international access agreements. A modification tested in commercial trawls during the observer program guides pelagic megafauna deflected by a filter to an escape tunnel along the bottom of the trawl. This “excluder” reduces bycatch mortality of the most vulnerable megafauna species by at least 40–100%.

The Tail of Grand Bank, southeast of Newfoundland, as a geographical boundary for continental slope fishes

Fish catches in about 4300 bottom trawl sets made in 1949 – 1991 on the continental slope (365 – 1700 m) between Labrador and the Scotian Shelf in the northwest Atlantic were examined for geographical discontinuities in species distribution and density. Eighteen of 24 taxa that were reliably identified to species showed discontinuities in the vicinity of the Tail of Grand Bank, the remaining 6 having ubiquitous distributions. Bottom temperatures, collected in conjunction with trawl sets, also showed a discontinuity associated with this location, lower temperatures occurring to the east and north than to the south and west at all depths sampled. The species with geographical limits of distribution near the Tail of Grand Bank were those with depth ranges centred on the upper slope (200 – 750 m) and some of those with shelf – upper-slope ranges (the remainder of the latter having ubiquitous geographical distributions). Species with middle- and lower-slope ranges (750 – 2250 m) did not have geographical limits of distribution at this location; nonetheless, they apparently had substantially different levels of density on either side of it.

Improving the Precision of Abundance Estimates of Eastern Scotian Shelf Atlantic Cod from Bottom Trawl Surveys

Abstract Abundance estimates from bottom trawl surveys are important elements in the evaluation of stock status. The reliability of stock assessment results are greatly influenced by the precision of the survey abundance estimates. In this study, a new stratified random design, based upon historical spatial distribution, for estimating the abundance of ages 5–12 Atlantic cod Gadus morhua on the eastern Scotian Shelf off Nova Scotia was evaluated. Gains in precision from the new design, relative to simple random sampling, were mainly due to the improved allocation of trawl sets to strata, whereas the gains solely due to the new stratification scheme were minimal. We conclude that any reasonable stratification scheme that is flexible enough to allow for the optimization of the allocation of sets to strata should perform well. In our study, the allocation scheme was based upon the historical spatial distribution of abundances. Although annual changes in spatial distribution would require revision of the allo...

Demersal Fish Assemblages on the Scotian Shelf, Northwest Atlantic: Spatial Distribution and Persistence

This study is based on 18 surveys, 12 in summer, and three each in spring and fall, with bottom trawls over the Scotian Shelf and Bay of Fundy. The data analysis sequence was: temporal and spatial aggregation of trawl sets; estimation of interspecies and intersite distance indices; clustering and ordination of sites and species, and discrimination of site groups using environmental variables. Nine species-groups, and 10 site-groups were defined, and displayed in a two-way table. Depth and temperature were the environmental variables most strongly associated with differences in assemblage structure among site-groups. Changes in assemblage structure from one area to another were distinct but apparently gradual, with no sharp assemblage boundaries. This pattern is expected if species are distributed independently on environmental gradients, rather than if assemblages consist of highly co-evolved, interdependent species. The observed spatial patterns were highly persistent through time. There are regions which are relatively homogeneous with regard to species composition and which can therefore be useful in dealing with bycatch problems. However, this study does not indicate the existence of discrete assemblages which might be appropriate as ecologically based fishery management units.

Survival of Atlantic Halibut (Hippoglossus hippoglossus) Caught by Longline and Otter Trawl Gear

To assess the effectiveness of a proposed minimum size limit (81 cm) for Atlantic halibut (Hippoglossus hippoglossus) in Canadian waters, the survival of small fish caught in longline and bottom trawl gear was examined using live holding facilities onboard a research vessel and subsequently, in a land-based laboratory. Commercial practices were simulated during fishing operations. Of halibut less than the proposed size limit, 35% of the otter trawl catch and 77% of the longline catch survived more than 48 h. Factors potentially influencing halibut survival (handling time, total catch, fish length, maximum depth fished, and trawl duration) were examined using proportional hazard models. On the basis of those analyses, it was concluded that in bottom trawl sets of duration used in the commercial fishery (≥ 2 h), higher survival times were associated with shorter handling time, larger fish size, and comparatively small total catch weight. Supplemental information on the condition of trawl-caught halibut was also obtained from observers stationed onboard commercial trawlers.