Fish Depth Research Articles

Measurements and modeling of low-frequency scattering from fish on the New Jersey shelf

Low-frequency (400–2000 Hz) scattering strength measurements were obtained from aggregations of fish on the New Jersey shelf using a co-located transducer and vertical line array receiver. Concurrent measurements with a fisheries echosounder revealed the presence of nighttime layer(s) and daytime schools. The day–night behavior is consistent with several species of fish found on the New Jersey shelf, as are the observed resonance frequencies near 800 Hz. Data-model comparisons are used to characterize both the strength and bandwidth of the frequency response, as well as its dependence on fish type and behavior. From these data, parameters such as fish depth, density and size can be estimated, and, in turn, the scattering strength as a function of frequency and grazing angle can be predicted and then compared with those of other potential scattering mechanisms. The implications of the fish scattering to reverberation and clutter are discussed. [Work supported by ONR.]

Development and assessment of habitat suitability criteria for adult brown trout in southern New England rivers

Abstract – Habitat suitability criteria (HSC) for depth, mean velocity, nose velocity, substrate, embeddedness, and cover were developed for brown trout ≥170 mm (Salmo trutta Linnaeus) on the West Branch Farmington River, CT, USA. Microhabitat data was collected by underwater observation using an equal effort habitat sampling design; HSC were constructed using nonparametric tolerance limits. Transferability of previously published HSC to the West Branch Farmington River was poor; only 1 of 13 HSC tested was considered transferable. The HSC developed for the West Branch Farmington River were tested for transferability to the East Branch Westfield River, Massachusetts. First, a composite suitability index (SI) score was calculated using the source HSC for each occupied and unoccupied location in the Westfield River. Then, χ2‐tests were used to determine if optimal or suitable locations were occupied in greater proportion than usable or unsuitable locations. Composite SI scores based on total depth, mean velocity, and cover were not transferable, but composite SI scores based only on total depth and mean velocity were. A multivariate profile analysis was also used to test for transferability. In each test, only total depth, fish depth, and mean velocity HSC were successfully transferred. Transferability of depth and velocity HSC between rivers shows promise for applications to similar systems where brown trout occur.

Influence of thermal conditions on biomass of fish in the Polish EEZ

Systematic acoustic surveys of fish resources in the Polish EEZ, carried out during the autumn as a part of international ICES programme, begun in 1989. A noticeable increase in fluctuations of fish biomass and water temperature has been observed since 1996. Methods elaborated in Sea Fisheries Institute were applied to correlate acoustic data on fish distribution with relevant environmental factors, and to develop models of trends observed. Relationships between mean temperature at fish depth and total fish biomass in each year were estimated separately for day- and night-time. High positive correlation ( r=0.910 for day-time, r=0.885 for night-time) was found for data from the 1989 to 2000 period. It was shown that fish reaction to temperature was stronger during the night (exponential model), at which time a 3 °C increase of temperature at fish depth could result in a 1.7 multiplier of total biomass in the area. During the day, a 6 °C increase of temperature was necessary to produce a comparable effect. Research was implemented by application of macrosounding methods to confirm direct correlation between temperature and fish distribution along most representative transects in the area. Analysis of all results indicates the role of the surface waters, where temperature seems to be one of the most important factors influencing final geographic fish distributions. Lower temperatures in the Polish EEZ accelerate northeast migration of fish from the zone, reducing a feeding season. It can be concluded also that climate instability can strongly affect temporal distribution of fish. In a longer period such a negative phenomenon can produce a systematic degradation of fish stocks, what could be observed on the basis of our results.

Quantifying habitat associations in marine fisheries: a generalization of the Kolmogorov–Smirnov statistic using commercial logbook records linked to archived environmental data

Understanding species–habitat associations is critical for designing marine reserves, defining essential fish habitat, and predicting the impacts of climate change on fisheries. For many species, however, there is a paucity of fisheries-independent data that simultaneously track abundance and environmental variables, as is the case for widow rockfish (Sebastes entomelas), a commercially important fishery off the west coast of the United States. In this paper, I generalize a previous approach to identifying habitat associations so that fisheries-dependent data can be used. In analyzing Oregon commercial logbook records and archived environmental data from the National Oceanographic Data Center, I found three environmental variables (bottom depth, vertical depth of fish in the water column, and temperature) to be statistically adequate. Using a generalized Kolmogorov–Smirnov test statistic, I compared an empirically derived cumulative distribution function (CDF) of the habitat sampled to a CDF weighted by widow rockfish catch. Results suggest that the significant habitat association for widow rockfish includes bottom depths between 136 and 298 m, vertical depths between 101 and 197 m, and temperatures between 7.1 and 8.1°C. This novel use of commercial logbook data, which links disparate data sources and explicitly accounts for unequal spatial sampling, is a methodological advance that also provides initial insights into widow rockfish habitat preferences.

Environmental Factors Controlling the Distributions of Benthic Invertebrates on Rocky Shores of Lake Malawi, Africa

An airlift was used to collect 170 quantitative samples of benthic macroinvertebrates from the rocky nearshore zone of islands in southern Lake Malawi from August 1998 to Febuary 1999. Total invertebrate densities were very low (< 6,000 ind/m 2), and were dominated by Ostracoda, Hydracarina, and Chironomidae. Most of the insects were lotic forms, including hydropsychid caddisflies, heptageneid mayflies, and dryopoid beetles. Sampling sites differed in degree of exposure to wave-action, substratum texture, depth (1.5 to 5 m), and abundance of fish, and the density and diversity of the benthic fauna varied significantly with each of these factors. Both numbers of taxa and densities of invertebrates were greater at exposed than sheltered sites, and decreased with increasing depth. Gravel substratum harbored more taxa and higher densities of macroinvertebrates than did cobble or bedrock. The only seasonal change observed was a decrease in the abundance of animals during the rainy season at a sheltered site where sediment was deposited from a large river. There was a weak inverse relationship between the densities of fish and larger invertebrates on cobble and bedrock substrata. Bedrock surfaces covered by fish-exclusion cages supported five-fold more invertebrates than open surfaces after 2 months. Overall, the benthic fauna of rocky shores in southern Lake Malawi is a taxonomically rich community similar in composition and diversity to those reported from other Great Lakes worldwide. Continuous, intense fish predation appears to be responsible for low invertebrate densities and probably influences invertebrate species diversity.

Horizontal and vertical distribution of organic contaminants in deep-sea fish species.

Polychlorobiphenyls (PCBs) and pesticides are persistent, semivolatile contaminants whose global circulation is now well established. One of their ultimate sink is the bio- and geo-phases in the deep-sea. We have investigated the distribution of selected PCBs and pesticides with depth and longitude in various deep-sea fish, namely black scabbardfish (Aphanopus carbo), orange roughy (Hoplostethus atlanticus), roundnose grenadier (Coryphaenoides rupestris) and Bathysaurus ferox from Madeira, Sesimbra, the Meriadzec Terrace and Rockall Trough in the North Eastern Atlantic at 1000 m depth, and at 2000 m depth where available. In most species, males presented higher levels of contamination than females. This pattern was probably due to the females eliminating contaminants through egg production. Roundnose grenadier presented higher levels of contamination (mainly p,p'-DDE, CB 153, 138, 180, sigmaCB(24) and p,p'-DDT) in fish caught at 2000 m than at 1000 m depth. Similarly, B. ferox, which is found deeper than the other species studied, showed much higher levels of most CBs and pesticides (lipid normalised) than the other species. Concentrations were up to 10 times higher, and showed differences between water masses.

Diel and Seasonal Patterns of Horizontal and Vertical Movements of Telemetered Cutthroat Trout in Lake Washington, Washington

Abstract Salmonid fishes are often the top predators in cool lakes, and their movements may reflect the distribution of available prey as well as physical factors such as light and temperature. We used ultrasonic telemetry to examine the vertical and horizontal movement patterns of cutthroat trout Oncorhynchus clarki in Lake Washington, a monomictic lake in Washington State. We hypothesized that the trout would show seasonal shifts in vertical distribution, balancing avoidance of warm surface waters with the need to forage on vertically migrating limnetic planktivores. During the lake's annual stratification period, the trout avoided the near-surface waters (mean fish depth = 15.7 m); however, the trout were nearer to the surface when the lake was mixed (mean fish depth = 7.5 m), consistent with a thermal constraint. The trout did not show notable diel changes in behavior, either in depth or swimming speed. Rather, they swam about 0.5 body lengths per second in open water during the day and were only some...

Application of a habitat‐based model to estimate effective longline fishing effort and relative abundance of Pacific bigeye tuna (Thunnus obesus)

A new habitat‐based model is developed to improve estimates of relative abundance of Pacific bigeye tuna (Thunnus obesus). The model provides estimates of `effective' longline effort and therefore better estimates of catch‐per‐unit‐of‐effort (CPUE) by incorporating information on the variation in longline fishing depth and depth of bigeye tuna preferred habitat. The essential elements in the model are: (1) estimation of the depth distribution of the longline gear, using information on gear configuration and ocean currents; (2) estimation of the depth distribution of bigeye tuna, based on habitat preference and oceanographic data; (3) estimation of effective longline effort, using fine‐scale Japanese longline fishery data; and (4) aggregation of catch and effective effort over appropriate spatial zones to produce revised time series of CPUE. Model results indicate that effective effort has increased in both the western and central Pacific Ocean (WCPO) and eastern Pacific Ocean (EPO). In the WCPO, effective effort increased by 43% from the late 1960s to the late 1980s due primarily to the increased effectiveness of effort (deeper longline sets) rather than to increased nominal effort. Over the same period, effective effort increased 250% in the EPO due primarily to increased nominal effort. Nominal and standardized CPUE indices in the EPO show similar trends – a decline during the 1960s, a period of stability in the 1970s, high values during 1985–1986 and a decline thereafter. In the WCPO, nominal CPUE is stable over the time‐series; however, standardized CPUE has declined by ∼50%. If estimates of standardized CPUE accurately reflect relative abundance, then we have documented substantial reductions of bigeye tuna abundance for some regions in the Pacific Ocean. A decline in standardized CPUE in the subtropical gyres concurrent with stability in equatorial areas may represent a contraction in the range of the population resulting from a decline in population abundance. The sensitivity of the results to the habitat (temperature and oxygen) assumptions was tested using Monte Carlo simulations.

Roach habitat shifts and foraging modified by alarm substance 2. Reasons for different responses of fish in field and laboratory studies

The Schreckstoff-induced fright reaction (shift in fish depth distribution) was studied in roach from a European lowland lake in two twin vertical tubes of 0.85 m diameter and 11.5 m depth (Plon Plankton Towers) in an attempt to find possible reasons for the weakness of roach responses to the alarm substance in the field, as compared to those in laboratory conditions. Roach (fork length 15.4 ± 1.6 cm), fed Daphnia and chironomids under diel 9/15 h light/dark periodicity, displayed a transitory but firm response to the alarm-substance treatment in one of the towers, while no change was seen in the reference one. The mean depth of fish within 1 h of dusk following Daphnia supply to the towers' epilimnia (0-2.5 m depth), as well as 3 h later in the dark, was significantly greater in the treatment than in the reference tower. The response was more pronounced in prey (Daphnia) density than in the depth distribution of roach. The indirect effects on Daphnia were extremely strong (Daphnia many-fold more abundant in the tower with alarm substance than in the reference one), but shortlasting. Frightened fish were more reluctant to feed than the reference fish in the daylight, but the initial evening difference in Daphnia abundance vanished overnight due to feeding in the dark.

Considerations on the biology of &lt;i&gt;Plesionika edwardsi&lt;/i&gt; (Brandt, 1851) (Decapoda, Caridea, Pandalidae) from experimental trap catches in the Spanish western Mediterranean Sea

In this study, the results obtained from three experimental trap shrimp (Plesionika edwardsi) fishing cruises in three different seasons are presented. They were carried out during a total of 50 days, of which 43 days were of effective fishing, covering the whole Spanish Mediterranean coast including the island of Alboran. On the whole, the fishing depth varied between 220 and 384 m, with a mean depth of 318 m. The target species appeared in 81% of the total samples carried out, with a mean yield (cpue) of 108.6 g/trap/day. The largest yields (cpue) of this species were from the Balearic islands, followed by Levant region, whereas the Alboran sea gave the lowest yields. The largest mean length was observed on the Levant zone, but on the contrary the smallest mean lengths were found towards the south, more specifically at Alboran island. Significant differences were found in both the relative and absolute growth, between males and females, with equilibrium in the ratio of the sexes (0.49). A total of 15 crustacean and 12 fish species were identified as accompanying fauna, with Conger conger, Plesionika narval and Scyliorhinus canicula being the most important, based on their mean cpue, although differences in the appearance and yields of the species were found in the different zones and depths. However, the mean yields of these species were very low, due to the high selectivity of the fishing gear used. The appearance of Heterocarpus ensifer, deserves a special mention, since it is the second documented record of the species in the Mediterranean.

Near-body flow dynamics in swimming fish

We consider the motions and associated flow patterns of a swimming giant danio (Danio malabaricus). Experimental flow-visualization techniques have been employed to obtain the unsteady two-dimensional velocity fields around the straight-line swimming motions and a 60 degrees turn of the fish in the centerline plane of the fish depth. A three-dimensional numerical method is also employed to predict the total velocity field through simulation. Comparison of the experimental and numerical velocity and vorticity fields shows good agreement. The fish morphology, with its narrow peduncle region, allows for smooth flow into the articulated tail, which is able to sustain a large load for thrust generation. Streamlines of the flow detail complex processes that enhance the efficiency of flow actuation by the tail. The fish benefits from smooth near-body flow patterns and the generation of controlled body-bound vorticity, which is propagated towards the tail, shed prior to the peduncle region and then manipulated by the caudal fin to form large-scale vortical structures with minimum wasted energy. This manipulation of body-generated vorticity and its interaction with the vorticity generated by the oscillating caudal fin are fundamental to the propulsion and maneuvering capabilities of fish.

Survival of young gadoids excluded from a shrimp trawl by a rigid deflecting grid

The survival of one-year-old cod (Gadus morhua), haddock (Melanogrammus aeglefinus) and whiting (Merlangius merlangus), excluded from a shrimp trawl by a diagonal metal grid placed in front of the codend (the Nordmore grid), was studied during June 1993 and 1994. Fish leaving the gear in front of this grid during trawling were retained by a net covering the fish outlet, and led into a collecting cage. The collecting cages were released from the trawl at the fishing depth and anchored for 5 to 12 days. The fish in the cages were then observed daily by underwater television, and in the second season also by divers. The escapees from separate trawl hauls were analysed for body damage. No mortality was found among the young gadoids during the observation period, except for one haddock in the control group. There were almost no visible skin injuries or scale loss in cod, while in whiting and haddock there was a significantly larger incidence of these factors. No correlation was observed between fish size and the amount of scale loss. ? 1997 International Council for the Exploration of the Sea

Effects of hanging ratio and fishing depth on the catch rates of drifting tuna gillnets in Sri Lankan waters

Comparative fishing trials for tuna with drifting gillnets in Sri Lankan waters tested whether a reduction of the hanging ratio ( E) from the currently used 0.6 to 0.5 would increase catch rates. The effect of varying fishing depth was also studied, using three different pendent line lengths (1, 6 and 8 m). Tuna (frigate, skipjack and yellowfin) and sharks made up approximately 95% by number and 80% by weight of the catches. Nets with E = 0.5 resulted in 40% higher overall catch by weight per unit netting area than nets with E = 0.6. The higher catch rates were mainly due to more large skipjack and yellowfin tunas being caught by tangling. Even when catches per net were compared, the E = 0.5 nets gave 25% higher catches by weight, despite the net area being 10% less due to the reduced hanging ratio. The fishing trials further indicated that pendent lines exceeding 6 m will lower catch rates compared with shorter pendent lines. This is caused by declining skipjack catches as fishing depth increases.

Morphological Constraints on Intracohort Cannibalism in Age-0 Largemouth Bass

Abstract Intracohort cannibalism can be an important process shaping the growth and survival of age-0 largemouth bass Micropterus salmoides. To assess the morphological constraints on Intracohort cannibalism in largemouth bass, we evaluated the relationship of mouth width, body depth, and total length in age-0 fish. Morphological measurements predicted a threshold predator-prey relationship of: prey length = 0.309·predator length1.109, whereas experimental results suggested the relationship of: prey length = 0.5·predator length. Our results indicated that Intracohort cannibalism may begin as early as 9 d after swim-up in southern lakes and reservoirs and 12 d in northern lakes. However, because of the length of the spawning season, slower growth, and male guarding, Intracohort cannibalism may be more important in southern systems than in northern lakes.

An evaluation of light-mediated vertical migration of fish based on hydroacoustic analysis of the diel vertical movements of rainbow smelt (Osmerus mordax)

We used hydroacoustics to examine diel changes in the vertical distributions of rainbow smelt, Osmerus mordax, in Lake Memphremagog, Quebec/Vermont. Our objective was to evaluate hypotheses linking diel vertical movements of fish with light levels. Smelt distributions were also monitored from June through October (1988 and 1990) to evaluate seasonal changes in their behavior. A strong relationship (r2 = 0.83) between ambient light intensities and the upper fish layer in the water column was observed. Fish depth was also related to the depth of the thermocline during the night and when surface water temperatures were &gt; 18 °C. The most characteristic feature was the strong avoidance of light levels &gt; 0.1 μW/cm2. However, we found considerable variation in lower light levels experienced by the whole fish population. The results suggest that existing models of anti-predation behavior relating light and fish depth are consistent, with some limitations, with patterns of diel vertical migration in rainbow smelt.

A Preliminary Assessment of Increases in Fishing Power On Stock Assessment and Fishing Effort Expended in the Western Rock Lobster (Pajvulirus Cygnus) Fishery

This study looks at the changes in nominal fishing effort and fishing power that occurred between 1971-72 and 1991-92. It examined the trends in the use of various components of fishing power (e.g., radar, colour echo sounder, global positioning system, pot type) and their effect on catch rates, using a two stage ANOVA/regression approach. This information is then used to standardise the time series of nominal fishing effort to reflect changes in fishing power. The changes in fishing power with respect to months and depth of fishing, and fishing regions, are discussed. The standardised fishing effort is then used in modeling the effect of exploitation on the breeding stock.

Vertical segregation and seasonal changes in fish depth distributions between lakes of contrasting trophic status

High frequency (200kHz) echosounding was used to determine vertical structuring and seasonal changes in the depth distributions of limnetic fish in three New Zealand lakes. Juvenile (f.l. 30–50 mm) and large‐sized (f.l. 50–80 mm) smelt Retropinna retropinna were segregated into discrete layers by depth in all three lakes throughout the year. Larval and post‐larval bullies Gobiomorphus cotidianus (f.l. 8–20 mm) formed a further layer between the layers of small and iarge‐sized smelt. Although the depths of the large‐sized smelt and bully layers changed on a seasonal basis, vertical segregation between the three layers of fish persisted throughout the year, even when the lakes were homothermal. Seasonal movements of fish were disrupted by the autumnal deoxygenation of the hypolimnion in Lake Rotoiti. The schools of large‐sized smelt were forced to ascend towards the layer of bullies, but segregation between these smelt and the bullies was maintained as the smelt occupied a much reduced depth range above the hypolimnion, and just below the bullies. The winter descent of bullies, which precedes their transition to a benthic existence failed to occur in Lake Rotoiti, even though the lake was fully mixed at this time.

Vertical segregation and seasonal changes in fish depth distributions between lakes of contrasting trophic status

High frequency (200kHz) echosounding was used to determine vertical structuring and seasonal changes in the depth distributions of limnetic fish in three New Zealand lakes. Juvenile (f.l. 30–50 mm) and large-sized (f.l. 50–80 mm) smelt Retropinna retropinna were segregated into discrete layers by depth in all three lakes throughout the year. Larval and post-larval bullies Gobiomorphus cotidianus (f.l. 8–20 mm) formed a further layer between the layers of small and iarge-sized smelt. Although the depths of the large-sized smelt and bully layers changed on a seasonal basis, vertical segregation between the three layers of fish persisted throughout the year, even when the lakes were homothermal. Seasonal movements of fish were disrupted by the autumnal deoxygenation of the hypolimnion in Lake Rotoiti. The schools of large-sized smelt were forced to ascend towards the layer of bullies, but segregation between these smelt and the bullies was maintained as the smelt occupied a much reduced depth range above the hypolimnion, and just below the bullies. The winter descent of bullies, which precedes their transition to a benthic existence failed to occur in Lake Rotoiti, even though the lake was fully mixed at this time.

Bathymetric Demography and Management of Dover Sole

Bathymetry is a key element in the demography of Dover sole Microstomus pacificus. Juvenile Dover soles begin life in relatively shallow water on the continental shelf but move gradually down the continental slope into deeper water as they grow and reach sexual maturity. Large and old individuals may eventually reach depths greater than 1,500 m. The ontogenetic migration of Dover soles into deeper water gives rise to a general pattern of increasing fish size with water depth, but there are differences between sexes and locations. To describe these patterns in greater detail, we computed probability distributions for depth, length, and sex using research trawl data for Dover sole taken off central California and Oregon. Our results indicate that females live at greater depths than do males and that abundance of large Dover soles may be lower at depths where lowest oxygen concentrations occur. In addition, major differences in bathymetric demography exist between study sites due, we suggest, to differences in bottom topography. We used one group of probability distributions and logbook data for Oregon and central California in a simple model to demonstrate how depth of fishing and bathymetric demography complicate interpretation of length composition and other data from a commercial fishery. Results from the model indicate that depth-stratified assessment models may be required to interpret fisheries data for Dover sole and other species, like shortspine thornyhead Sebastolobus alascanus and sablefish Anoplopoma fimbria that undergo ontogenetic migration from shallow into deep water.

Photoregulatory behavior of bluegill,Lepomis macrochira, in a virtual light gradient

Vertical movements of bluegill were monitored in gradients of light intensity to assess this fish's photoregulatory ability and mechanisms. A computerized monitoring and control system created virtual gradients of light intensity by adjusting an overhead lamp's output in response to fish movements, in a vertical tube, to produce a programmed intensity at the fish's depth position. This approach separated the process of gradient formation from normal clues for photoregulation and allowed formation of light gradients incompatible with natural taxic responses to intensity. Hourly shifts in gradient position minimized the possibility of confounding photoregulation with position regulation. Observed patterns of movement reduced the extremes of light intensity to which bluegill were exposed, compared to no movement or random movement. Seven fish were tested, producing 10 experiments. In 4 of 10 experiments, the fish effectively photoregulated in gradients in which light intensity decreased with depth, as in natural habitats. In 1 of 10 experiments, the fish photoregulated in an inverse gradient, with intensity increasing with depth. Evidence of regulation in an inverse gradient suggests that normal taxic responses are not essential for photoregulation in bluegill.