Catch Density Research Articles

Forecasting the spread of an invasive forest‐defoliating insect

AbstractAimBiological invasions are an escalating environmental challenge due to their substantial ecological and socio‐economic consequences. Accurate near‐term forecasts of future areas occupied by an invasive species could enhance the efficiency and efficacy of invasion monitoring and management but spread forecasting models have been developed and tested for few invasive species thus far.LocationNortheastern USA.MethodsWe developed a quantitative model to forecast 1‐year‐ahead occupancy of Lymantria dispar dispar, an expanding invasive forest insect introduced into the eastern United States in 1869 that causes large‐scale defoliation of forests. We validated and tested the model using historical distribution and density data from a large‐scale network of pheromone‐baited traps. We first assessed how forecast accuracy depended on trap catch density thresholds for determining occupancy and on the spatial scale of local connectivity measures. Next, we tested how increasing the computational complexity and biological detail encoded in the models affected prediction accuracy.ResultsModels using lower occupancy thresholds and measuring connectivity over shorter distances tended to perform best. A simple model using only coarse and generic representations of habitat suitability and local diffusive spread potential performed at least as well as more complex models. Our best models achieved total accuracy and true‐positive rates exceeding 95%.ConclusionsOur baseline model illustrates the utility of a mechanistic model to forecast year‐to‐year occupancy dynamics of L. dispar. Near‐term spread forecasting can be a valuable tool for invasion management, even for species without detailed a priori ecological knowledge.

Individual-based model simulations indicate a non-linear catch equation of drifting Fish Aggregating Device-associated tuna

Abstract Catch per unit of fishing effort (CPUE) is often used as an indicator of tuna abundance, where it is assumed that the two are proportional to each other. Tuna catch is therefore typically simplified in tuna population dynamics models and depends linearly on their abundance. In this paper, we use an individual-based model of tuna and their interactions with drifting Fish Aggregating Devices (dFADs) to identify which behavioural, ocean flow, and fishing strategy scenarios lead to an emergent, non-linear dependency between catch, and both tuna and dFAD density at the ∼1○ grid scale. We apply a series of catch response equations to evaluate their ability to model associated catch rate, using tuna and dFAD density as terms. Our results indicate that, regardless of ocean flow, behavioural, or fisher strategy scenario, simulated catch is best modelled with a non-linear dependence on both tuna and dFAD abundance. We discuss how estimators of CPUE at the population scale are potentially biased when assuming a linear catch response.

Seasonal variability of nektonic community structure and phylogenetic diversity in Weizhou Island, the Beibu Gulf

The favorable natural conditions and variety of habitats in the Beibu Gulf provide a basis for harboring a high diversity of marine organisms. Sustainable coastal ecosystem management can be benefited from a comprehensive assessment of species diversity. In this study, we analyzed the seasonal changes in nektonic phylogenetic and community structures in the waters of Weizhou Island in the northern Beibu Gulf. The results showed that both the nektonic phylogenetic diversity and community structure in the northern Beibu Gulf exhibited strong seasonal differences between spring and autumn. The catch density was 291.9 kg per km2 in spring and 1081.1 kg per km2 in autumn. Phylogenetic diversity of nektonic communities obviously increased from spring to autumn, while phylogenetic patterns changed from clustering to overdispersion. The seasonal patterns of nektonic communities were mainly related to the different fishing intensities in spring and autumn. Summer fishing intensity in the Beibu Gulf was effectively controlled by a mid-summer fishing moratorium, during which nektonic diversity and fish stocks rapidly recovered from the larval pool. Our study revealed that fishing intensity had a greater impact on nektonic communities at smaller spatial scales, and even exceeded the effects of environmental factors.

Fine-scale variability in catch and growth rates of western rock lobsters (

Context The western rock lobster fishery is recognised to be conservatively managed, with breeding stock levels estimated to be at record levels over the past decade. Despite this, anecdotal reports from commercial fishers identified an area of unexpectedly low catches in the centre of the fishery and lobsters’ biogeographic distribution. Aim To confirm the presence of this suspected ‘low-catch’ zone and examine the variability in catch and growth rates of lobsters if identified. Methods This study conducted an intensive mark–recapture survey over 8 months to explore catch rate, density, movement and growth rates across this ‘low-catch’ zone and three comparable locations. Key results In total, 9318 lobsters were caught and 7565 individuals were tagged during the study. Consistently low catch rates of under-sized lobsters were observed in the ‘low-catch’ zone, with catch rates increasing with distance from the zone. By contrast, similar catch rates of legal-sized lobsters were observed across all locations. Conclusions The study confirmed low catch rates, for under-sized lobsters, within an area of perceived low catch rates within the centre of the fishery. The lack of difference found in legal-sized catch rates among locations is likely to be due to the low fishing pressure in the ‘low-catch’ zone, resulting from hyperstability of fishers adapting to the historical perceived low catch rate. Modelled data demonstrated the ‘low-catch’ zone to be associated with faster growth rates and high fine-scale migration, indicating a potential release from density-dependent processes. Implications We anticipate that these results will be a useful starting point for future research into the mechanisms responsible for the unexpectedly low catch of sublegal lobsters within the ‘low-catch’ zone and the implications it may have on the wider population, both regionally and across the species distribution.

DISTRIBUSI SPASIAL DAN TEMPORAL IKAN TUNA (Thunnus sp) DI PERAIRAN BARAT SUMATERA BERBASIS SISTEM INFORMASI GEOGRAFIS

One tool that can be used to visualize and connect various types of spatial and temporal distribution is Geographic Information System. The purpose of this study is to analyze the pressure of longline fisheries, tuna catches and fishing effort and can model the spatial distribution and temporal (of tuna, during longline fishery activities in 2013. Experimental methods are used in determining the size pixels and kernel shape. The form of the kernel that displays the best results is quartic. The optimal radius produced from the equation 0.68n-0.2 is 0.25 degrees (27.78 km). The CPUE uses raster data on catch density (tail field) and fishing line density (field number of hooks). The calculation is done by multiplying the density of the raster catch (tail) by 1,000 then divided by the density of the raster fishing hooks. The results show that the range of CPUE values ranged from 0.833 - 416. The total area of the total fishing effort was 161,520 km2 with an ffort of catching of 57,502.017 per 1,000 hooks. The total number of CPUE top heatmap is 38,948.29 per 1,000 hooks in 38,080 km2, most are in the Mentawai Strait, other parts are also found in the south of Siberut Island, west of Enggano Island to the Indian Ocean. Seasonal patterns show that the East season is the season with the highest catching effort in the Mentawai Strait, the Siberut Strait to the southern part of Siberut Island and the Transition I season is the lowest catching effort.
 Keywords: Spatial and temporal distribution, tuna density, CPUE, heatmap, Indian Ocean

Long-Term Change of a Fish-Based Index of Biotic Integrity for a Semi-Enclosed Bay in the Beibu Gulf

The Beibu Gulf in the northwestern South China Sea is one of the world’s most productive fishing grounds, yet its biotic resources appear to be in rapid decline because of overexploitation. Assessments of the health status of the fisheries’ resources in the gulf provide a foundation for their conservation and management. As fish accounted for 84% to 97% of the total catch in the Beibu Gulf in the period 1962–2017, a Fish-based Index of Biotic Integrity (F-IBI) was developed for the Beibu Gulf, and data from otter trawl surveys during the period 1962–2017 were used to measure variations in the fish community. The assessment revealed a generally downward trend in total fish catch density (kg/km2), catch density of 12 traditional commercial demersal fish species, and percentage of nektonic-feeding species, but an upward trend for the percentage of fishes with a planktivorous or detritus diet, percentage of pelagic species, and percentage of the dominant species. The dominant species varied greatly over the 50 year period and showed a tendency towards small-sized species. The synthetic F-IBI variable showed a downward trend and has indicated a ‘fair’ state since 1998. The decline in the F-IBI over the last three decades suggests that anthropogenic disturbances, especially overfishing, have had a serious impact on the fish community of the Beibu Gulf. The F-IBI is currently at risk of becoming ‘poor.’ Consequently, we suggest that rigid and enforceable fishery management measures should be taken by both China and Vietnam to prevent further deterioration of the fisheries’ resources in the gulf.

Hyperstability in Electrofishing Catch Rates of Common Carp and Bigmouth Buffalo

AbstractElectrofishing catch per unit effort (CPUE) can be an effective index of relative abundance when CPUE is proportional to population density. However, the relationship between fish catch rates and density can be variable and not proportional because catchability may not be constant under a range of environmental conditions. Hyperstability occurs when catch rates change faster than population density, whereas hyperdepletion occurs when catch rates change slower than population density. We used capture–mark–recapture methods to estimate density of Common Carp Cyprinus carpio and Bigmouth Buffalo Ictiobus cyprinellus across 24 lake‐years. Next, we developed log‐linear mixed‐effects models to assess the relationship between catch rates and density to predict electrofishing CPUE based on density and environmental covariates. Common Carp and Bigmouth Buffalo electrofishing CPUE exhibited hyperstability; CPUE initially increased faster at low density but reached an asymptote as density continued to increase. Common Carp catch rates increased with water temperature and were negatively associated with season; highest catch rates occurred in the warmest temperatures of spring, whereas the lowest catch rates occurred in the coldest temperatures of fall. Bigmouth Buffalo electrofishing CPUE was negatively related to water temperature but had a quadratic relationship with season; catch rates were highest in the spring and fall when water temperatures were coldest. Secchi depth, shoreline length, and maximum depth did not influence our model predictions in either species. Electrofishing had little power to detect simulated changes in Bigmouth Buffalo density regardless of sampling effort, whereas power to detect changes in Common Carp density increase with population changes and sampling effort. At low population densities for both species, electrofishing CPUE is expected to increase or decrease faster than density and can obscure conclusions about population trajectories but may still be useful for monitoring population fluctuations if hyperstability is accounted for by a correction factor.

Estimation of the Sustainable Potential of Scads Fish (Decapterus spp) landed at the Belawan Ocean Fishing Port North Sumatra

Scads fish (Decapterus spp.) is a fish that is widely consumed by the community so that consumer demand in the market is high for Scads Fish. Based on the Statistics book from the KKP, the catch of Scadsfish has decreased in catches from 2014 to 2016, this is due to continuous catching. The purpose of this study was to estimate the sustainable potential and to determine the level of utilization of Scads Fish in Belawan Ocean Fishing Port, North Sumatra. The research data was obtained from the Belawan Ocean Fishery Port in February 2021. The method used in this study is a survey method, using an equation model, namely Schaefer. The data analysis is a simple linear regression analysis using SPSS version 20. The sustainable potential of Scads Fish (Decapterus spp.) in the last 5 years is 16,526 tons/year with a utilization rate of 67.98% which is included in the catch density category and the number of fish catches allowed is 13,221 tons/year

Ocean warming alters the distributional range, migratory timing, and spatial protections of an apex predator, the tiger shark (Galeocerdo cuvier).

Given climate change threats to ecosystems, it is critical to understand the responses of species to warming. This is especially important in the case of apex predators since they exhibit relatively high extinction risk, and changes to their distribution could impact predator–prey interactions that can initiate trophic cascades. Here we used a combined analysis of animal tracking, remotely sensed environmental data, habitat modeling, and capture data to evaluate the effects of climate variability and change on the distributional range and migratory phenology of an ectothermic apex predator, the tiger shark (Galeocerdo cuvier). Tiger sharks satellite tracked in the western North Atlantic between 2010 and 2019 revealed significant annual variability in the geographic extent and timing of their migrations to northern latitudes from ocean warming. Specifically, tiger shark migrations have extended farther poleward and arrival times to northern latitudes have occurred earlier in the year during periods with anomalously high sea‐surface temperatures. A complementary analysis of nearly 40 years of tiger shark captures in the region revealed decadal‐scale changes in the distribution and timing of shark captures in parallel with long‐term ocean warming. Specifically, areas of highest catch densities have progressively increased poleward and catches have occurred earlier in the year off the North American shelf. During periods of anomalously high sea‐surface temperatures, movements of tracked sharks shifted beyond spatial management zones that had been affording them protection from commercial fishing and bycatch. Taken together, these study results have implications for fisheries management, human–wildlife conflict, and ecosystem functioning.

Catch Pattern for Antarctic krill (Euphausia superba) of Different Commercial Trawls in Similar Times and Overlapping Fishing Grounds

Antarctic krill (Euphausia superba) is harvested using different design midwater trawls. Knowing the selective properties between trawls is crucial information for the management of the krill resources. This study compared the catch patterns between different commercial krill trawls at similar times and overlapping fishing grounds based on scientific data collected by scientific observers onboard commercial trawlers Long Teng (LT) and Fu Rong Hai (FRH). The results showed significant differences in the length-dependent catch densities and cumulative catch densities of krill between the two trawls. The krill length range in catches from LT's trawl was wider than that of FRH's trawl. Furthermore, the catch would consist of a larger proportion of smaller krill in the LT's trawl. The LT's trawl caught significantly higher proportions of krill below 38 mm than FRH's trawl. Even, the LT's trawl caught substantial numbers of krill <30 mm, whereas the FRH's trawl caught very few of them. The main factors causing the difference between trawls in catch pattern were inferred to be related to gear design including differences in mesh sizes used. The results of this study enhance the quality of comparative analysis of scientific data from commercial trawls and the understanding of gear selectivity of different configuration trawls used for harvesting krill.

Retelling the History of the Red Sea Urchin Fishery in Mexico

The red sea urchin fishery has a long harvest and management history along the Northeastern Pacific coast. In Mexico, it has been commercially harvested since 1972, and although it is one of the most important fisheries in Baja California, efforts to assess the condition and dynamics of harvestable stocks have been focused on certain harvested areas with scarce fisheries independent data. Additionally, the analysis of yearly information for small geographic areas has obscured the actual status of harvested populations. This study aims to re-assess population trends, fishing effort, and catches, incorporating all available information from the last 19 years. Information was grouped based on 14 landing sites along Baja California’s Pacific coast. Length based virtual population analysis (LVPA) was implemented to estimate site-specific catch rates and densities. Red sea urchin catches / landings varied widely within and between areas. Average population density for the region reflects higher recruit values (≈2.5 urchin m-2); density of reproductive juveniles/adults averaged 0.79 (SE ± 0.04) urchins m-2; while estimated density of adults was lowest, with only 0.26 (SE ± 0.01). LVPA produced biomass estimations that double previous estimates. We suggest that the model parameters used in previous estimations might not reflect key biological traits of the red sea urchin, failing to reproduce population trends accurately. Based on current estimations, there is no apparent stock decline in areas where catches/landings are high; there, consistent settlement/recruitment may partially mitigate for fishery removals. New management measures must be adopted: maximum legal size of 110 mm, continuous fishery independent surveys, improvement on fishery logs and analysis, and tracking red sea urchin density, as means to track changes in the population that might not be so apparent when observing only catch/biomass data. Reinforce the under legal size urchins since results suggest that sites with high abundances of small urchins can support higher catches.

Komposisi Jenis Tumbuhan dan Analisis Sebaran Langkap (Arenga obtusifolia Mart.) di Taman Nasional Ujung Kulon

Langkap (Arenga obtusifolia) is one of the species of the Arenga clan, which has a wide distribution in Ujung Kulon National Park (UKNP). The aim of study was to determine the pattern of spreading langkap in order to support the management of Javan Rhino habitat. The vegetation analysis method used is a combination method between the line method and the path method. Langkap is the dominant species in UKNP at the sapling growth rate, with a density of 480-624 individuals/ha and INP value of 61.47% -78.30%, while the catch density at seedling growth rate is 900- 2,200 individuals/ha with INP value of 21.31% -49.41%. The standard Morisita coefficient value of langkap in each research block and growth rate is obtained in the range of values (-0.32) - 0.51, the spreading pattern shows a clustered spread pattern (Ip> 0) and uniform (Ip <0). The tendency of langkap domination in the research block can be seen from the ratio of catch density compared to the total density or its relative density at various growth rates. This shows that in the dominant catchment area there is a reduction in the density of plants other than langkap, especially the Javan Rhino feed plants.

A field-based investigation of behavioural interactions between invasive green crab (Carcinus maenas), rock crab (Cancer irroratus), and American lobster (Homarus americanus) in southern Newfoundland.

Marine species invasions pose a global threat to native biodiversity and commercial fisheries. The European green crab (Carcinus maenas) is one of the most successful marine invaders worldwide and has, in the last decade, invaded the southern and western coastal waters of the island of Newfoundland, Newfoundland and Labrador (NL), Canada. Impacts of green crab on the American lobster (Homarus americanus), which are native to Newfoundland, are not well understood, particularly for interactions around deployed fishing gear. Declines in lobster catch rates in invaded systems (i.e., Placentia Bay, NL), have prompted concerns among lobster fishers that green crab are interfering with lobster catch. Here, we conducted a field experiment in a recently-invaded bay (2013) in which we deployed lobster traps pre-stocked with green crab, native rock crab (Cancer irroratus) (a procedural control), or empty (control). We compared catch per unit effort across each category, and used underwater cameras to directly observe trap performance in situ. In addition, we used SCUBA surveys to determine the correlation between ambient density of lobster and green crab in the ecosystem and the catch processes of lobster in traps. We found: (1) Regardless of the species of crab stocked, crab presence reduced the total number of lobster that attempted to enter the trap, and also reduced entry success rate, (2) lobster consumed green crab, rock crab and other lobster inside traps and (3) there was a positive association between lobster catch and ambient lobster density. Our results suggest that while there was a relationship between in-trap crab density and trap catch rates, it was not linked to the non-native/native status of the crab species.

The relationship between pheromone trap catch and local population density of the oak processionary moth Thaumetopoea processionea (Lepidoptera: Thaumetopoeidae)

AbstractOak processionary moth (OPM) was introduced into the U.K. in 2004–2005 and pheromone traps have been used to monitor its spread and provide an early warning of the colonization of new areas. The traps capture adult male OPM, although catches are highly variable and it has proved difficult to establish a relationship between the numbers of males caught and local population densities. Surveys carried out around 260 pheromone traps as part of the U.K. OPM control programme, however, reveal a consistent linear relationship between square‐root transformed adult males per trap and cube‐root (or log10) transformed numbers of larval nests (r2 = 0.47; P < 0.001) In 91% of cases where traps captured no adult males, there were no OPM nests within 250 m and, where nests were present, the numbers of nests were low. Traps that captured more than 10–20 males were associated with counts of ≥ 50 larval nests. Defoliation and risks to human health from OPM are more closely related to nest density (i.e. the numbers of nests per tree). Consequently, identifying trap catches that might initiate a management response also requires information on the number of oak trees in the surrounding area.

Effects of sticky trap colour, UV illumination and within-trap variation on tomato potato psyllid captures in glasshouses

ABSTRACTThe tomato potato psyllid (TPP) is a serious pest of New Zealand glasshouse crops. This study examined the use of sticky traps in a glasshouse tomato crop to identify factors that influence TPP catches, with a view to developing a more consistent TPP monitoring system for use in IPM decision models. TPP catches were highest on yellow traps compared with black traps and white traps, and were greatest when traps were set near the glasshouse roof (2.1 m). Ultraviolet (UV) illumination substantially increased TPP catches on traps of all colours. There was considerable variation in TPP catch density within traps, especially near the edges. The results suggest that yellow sticky traps have good potential as TPP monitoring tools in glasshouse tomato crops. Consistency in TPP counts could be enhanced if traps were placed at constant height, were illuminated by UV, and assessments were limited to the trap centres.

Spatial and temporal dynamics of the Antarctic krill fishery in fishing hotspots in the Bransfield Strait and South Shetland Islands

Antarctic krill is a vital part of the food web and supports a significant fishery in the Southern Ocean. Shifts in historical fishing grounds and spatial distribution of catches have occurred as a result of recent changes in fishery practices. To understand these shifts, fishery spatial dynamics and fishing fleet behavior evaluated on different spatial and temporal scales are critical. We examine the catch distribution on three spatial-temporal scales. At the Western Antarctic Peninsula (WAP) scale, we assessed the fleet’s southward expansion, identifying the Bransfield Strait (BS) as the main current fishing ground, replacing the historical Drake sector. At the BS scale, we identified fishing hotspots (FHs) that concentrated 48%–57% of the total catch over a period of 2–6 months and had high catch densities (2.2–30.3 ton km−2). At the FH scale, we tracked the spatial distribution of the fleet within FHs, demonstrating a shift of fishing vessels to contiguous zones as a result of a decrease in daily catch rates (CPUE). Such shifts (allowing the fleet to increase CPUE) occurred every 4–17 days. Previously exploited fishing grounds were revisited based on FH persistence and sea ice conditions. This paper concludes with a discussion of the potential impact of fishing fleet behavior and catch concentration, considering the recent spatial shift towards less-exploited areas, the overlap with critical zones for predator feeding, and several implications for fisheries management.

Aggregations and associations in deep-sea chondrichthyans

Abstract Group living has been recorded across a diverse range of chondrichthyans, but due to a variety of factors, any inferences of social associations in deep-sea cartilaginous fishes have yet to be described. Using a companion preference analysis, aggregating behaviour and associations in deep-sea chondrichthyans (four holocephalans, ten elasmobranchs) were evaluated across class and group size from long-term archived fisheries independent research trawl survey datasets. Results indicated that not all selected species engaged in aggregative behaviour, but those that did suggested patterns of sex- and size-specific associations, which varied with catch density. Adult females were caught most frequently in low densities, and were highly associated with other adult females. Adult males were consistently associated with each other. The nature of associations has important implications for selective mortality by spatial or temporally stratified, or aggregation-targeting, fisheries.

A Covered Cod-End and Tow-Path Evaluation of Midwater Trawl Gear Efficiency for Catching Delta Smelt (Hypomesus transpacificus)

Author(s): Mitchell, Lara; Newman, Ken; Baxter, Randall | Abstract: For nearly 50 years, the California Department of Fish and Wildlife has used a midwater trawl to intensively monitor fish populations in the San Francisco Estuary during the fall, sampling over 100 locations each month. The data collected have been useful for calculating indices of fish abundance and for detecting and documenting the decline of the endangered fish species delta smelt (Hypomesus transpacificus). However, efforts to calculate estimates of absolute abundance have been hampered by the lack of information on gear efficiency, in particular questions about contact selectivity and the effect of tow method on catches. To answer these questions we conducted a study that used a covered cod end on a net towed either near the surface, referred to as a surface tow, or throughout the water column, referred to as an oblique tow. A contact selectivity model was fit to estimate the probability that a delta smelt that has come into contact with the net is retained in the cod end of the net conditional on its body length. Full retention of delta smelt was found to occur around 60 mm fork length. Delta smelt catch densities for the surface tows were an order of magnitude greater than densities in the oblique tows, suggesting a surface orientation at the sub-adult life stage. These results represent an important step in being able to calculate absolute abundance estimates of the delta smelt population size using decades’ worth of monitoring data.

Quantifying risk of overharvest when implementation is uncertain

Abstract Sustainable harvest management implies an ability to control harvest rates. This is challenging in systems that have limited control of resources and resource users, which is often the case in small game harvest management. The difference between management strategies and actual harvest bag size (i.e. implementation uncertainty) may be substantial, but few studies have explored this. We investigated how different management strategies and ecosystem variables affected realised harvest of willow ptarmigan (Lagopus lagopus L.) among nine independently managed, state‐owned hunting areas in Central and South Norway during 2008–2015. First, we focused our empirical analysis around three response variables of interest: hunting bag (scaled by area), hunting effort (number of hunting days scaled by area) and hunter efficiency (shot birds per hunting day). Akaike information criteria (AIC) guided model selection among candidate GLMMs. Then, we used model‐averaged parameter estimating from the statistical models in numerical simulations to explore risk of overharvest due to implementation uncertainty. The most parsimonious model explaining hunting bag included total allowable catch (TAC) and willow ptarmigan density. Hunting effort was explained by number of permits sold and type of quota (daily vs. weekly quota). The most parsimonious model describing hunter efficiency only included the effect of willow ptarmigan density. Our results show that managers have only partial control over harvest rates in this system, and that hunters were relatively more efficient and harvest rates higher at low densities. This effect was present for all management strategy scenarios, including when managers adjusted TAC according to population estimates from monitoring programmes. Synthesis and applications. Quantifying risk of unsustainable harvest rates under different scenarios enables managers to make informed decisions, when dealing with competing objectives of harvest opportunities and sustainability. The substantial risk of high harvest rates at low densities reported here should encourage frequent use of threshold strategies. This study is one of the first approaches for quantifying implementation uncertainty in small game harvest, and shows how estimates from empirical analyses could be used to quantify risk of overharvest.

Multispecies acoustic dead-zone correction and bias ratio estimates between acoustic and bottom-trawl data

Abstract In this study, we extended the original work of Kotwicki et al. (2013. Combining bottom trawl and acoustic data to model acoustic dead zone correction and bottom trawl efficiency parameters for semipelagic species. Canadian Journal of Fisheries and Aquatic Sciences 70: 208–219) to jointly estimate the acoustic dead-zone correction, the bias ratio, and the gear efficiency for multiple species by using simultaneously collected acoustic and bottom-trawl data. The model was applied to cod (Gadus morhua) and haddock (Melanogrammus aeglefinus) in the Barents Sea and demonstrated a better or similar performance compared with a single species approach. The vertical distribution of cod and haddock was highly variable and was influenced by light level, water temperature, salinity, and depth. Temperature and sunlight were the most influential factors in this study. Increase in temperature resulted in decreasing catch and fish density in the acoustic dead zone (ADZ), while increasing sun altitude (surrogate for light level) increased the catch and fish density in the ADZ. The catch and density of haddock in the ADZ also increased at the lowest sun altitude level (shortly after midnight). Generally, the density of cod and haddock changed more rapidly in the ADZ than in the catch (from bottom to the effective fishing height) indicating the importance of modelling fish density in the ADZ. Finally, the uncorrelated variability in the annual residual variance of cod and haddock further strengthen the conclusion that species vertical distribution changes frequently and that there are probably many other unobserved environmental variables that affect them independently.