Juvenile Fish Species Research Articles

Spatial analysis of the trophic interactions between two juvenile fish species and their preys along a coastal–estuarine gradient

Coastal and estuarine systems provide nursery grounds for many marine fish species. Their productivity has been correlated with terrigeneous inputs entering the coastal–estuarine benthic food web, thereby favouring the establishment of fish juveniles. Studies in these ecosystems often describe the nursery as a single large habitat without verifying nor considering the presence of contiguous habitats. Our study aimed at identifying different habitats based on macrozoobenthic communities and morpho-sedimentary characteristics and assessing the trophic interactions between fish juveniles and their benthic preys within these habitats. It included 43 sampling sites covering 5 habitats in which we described taxonomically and quantitatively the invertebrates and fish communities with stable isotopes and gut contents. It suggested that the benthic common sole Solea solea displayed feeding plasticity at the population level, separating the juveniles (G0) from the older fish (G1) into different “feeding sub-populations”. Size-based feeding plasticity was also observable in the spatial occupancy of that species in the studied bay. The demersal pouting, Trisopterus luscus, equally used the different habitats but displayed low feeding plasticity across and inside each habitat. Stable isotopes proved to be powerful tools to study the spatial distribution of trophic interactions in complex ecosystems like the bay of Vilaine and to define optimal habitats for fish that use the coastal–estuarine ecosystem as nursery grounds.

Differential mercury transfer in the aquatic food web of a double basined lake associated with selenium and habitat

Food web trophodynamics of total mercury (THg) and selenium (Se) were assessed for the double-basined ultraoligotrophic system of Lake Moreno, Patagonia. Each basin has differing proportions of littoral and pelagic habitats, thereby providing an opportunity to assess the importance of habitat (e.g. food web structure or benthic MeHg production) in the transfer of Hg and Se to top trophic fish species. Pelagic plankton, analyzed in three size classes (10–53, 53–200, and >200μm), had very high [THg], exceeding 200μgg−1 dry weight (DW) in the smallest, and a low ratio of MeHg to THg (0.1 to 3%). In contrast, [THg] in littoral macroinvertebrates showed lower values (0.3 to 1.8μgg−1 DW). Juvenile and small fish species feeding upon plankton had higher [THg] (0.2 to 8μgg−1 muscle DW) compared to large piscivore fish species (0.1 to 1.6μgg−1 muscle DW). Selenium concentrations exhibited a much narrower variation range than THg in the food web, varying from 0.5 to 2.7μgg−1 DW. Molar Se:Hg ratios exceeded 1 for the majority of organisms in both basins, with most ratios exceeding 10.Using stable nitrogen isotopes as indicator of trophic level, no significant correlations were found with [THg], [Se] or Se:Hg. The apparent lack of biomagnification trends was attributed to elevated [THg] in plankton in the inorganic form mostly, as well as the possibility of consistent Se supply reducing the biomagnification in the food web of the organic portion of THg.

Competitive hierarchies among three species of juvenile coral reef fishes

Interspecific competition is often asymmetric, and it can limit the spatial distributions of competitively inferior species within a community. When asymmetric competition involves 2 or more component species, the ranking of species' competitive abilities may form competitive hier- archies (all species of higher rank out-compete all species of lower rank) or competitive networks (at least 1 species of lower rank out-competes ≥1 species of higher rank). Expectations of resource monopolization and patterns of distribution and abundance among species in competitive net- works are expected to differ from those in competitive hierarchies. We conducted a field experi- ment to evaluate the relative competitive abilities of juveniles of 3 closely related species of reef fish (bird wrasse Gomphosus varius, fivestripe wrasse Thalassoma quinquevittatum and the sixbar wrasse T. hardwicke) on Moorea, French Polynesia. We controlled for intrinsic variation in sur- vivorship among species and found that competition among these 3 species was highly asymmet- ric, resulting in a simple competitive hierarchy (sequence of competitive ability from superior to inferior competitors): fivestripe wrasse > bird wrasse > sixbar wrasse. We surveyed densities of the 3 reef fish species on 55 patch reefs and observed significant negative spatial covariation between superior and inferior competitors, consistent with competitive hierarchies that limit the spatial dis- tributions of the inferior species (sixbar wrasse). Our work demonstrates that intense asymmetric competition and the formation of competitive hierarchies may be an important determinant of resource monopolization and patterns of distribution and abundance in reef fishes.

胶州湾近岸浅水区鱼类群落结构及多样性

Jiaozhou Bay,which locates in the south of Shandong Peninsula,is a semi-closed natural bay extending from the Yellow Sea.It serves as an excellent spawning and feeding ground for fishes and other invertebrate animals,and is an important ecosystem with high productivity and biodiversity.However,due to the high fishing pressure,pollution,coastal development and the effect of global warming,major changes have taken place in the region.Based on the data collected monthly in the set net survey from March 2009 to February 2010 in Jiaozhou Bay,fish community structure and species diversity were examined by ecological diversity indices and multivariate statistical analysis.The results showed that there were 44 species of fishes(young of the year) in the survey,of which 27 species were marine fish,and the rest 17 species were estuarine fish.The fish species composition of Jiaozhou Bay was closely related with the bottom water temperature and salinity.The Margalef species richness index(R) of fish species composition in Jiaozhou Bay ranged between 0.33 and 3.50,and the Shannon-Wiener diversity index(H′) were from 0.42 to 2.25,with the Pielou evenness index(J′) varying from 0.23 to 0.93.According to the hierarchical cluster analysis(CLUSTER) and non-metric multi-dimensional scaling(MDS) analysis,fish samples were classified into three month-groups,which are group 1(G1,December—April) with the lowest bottom water temperature,Group 2(G2,May—June,October—November) with higher water temperature and Group 3(G3 July—September) with the highest water temperature.The typifying species in G1 were some resident cold temperate fish species such as great pipefish Syngnathus acus,blenny Enedrias fangi,sand eel Ammodytes personatus;Japanese anchovy Engraulis japonicus and great pipefish Syngnathus acus were main typifying species in G2,Pacific chub mackerel Scomber japonicus,cardinal fish Apogonichthys lineatus,Amoya pflaumi and other migrate fish species were typifying species in G3.The analysis of similarities(ANOSIM) indicated that there were significant differences in species compositions among the three month-groups.The biota-environment matching(BIOENV) analysis showed that bottom water temperature was the main environmental factor that determined the temporal pattern of fish assemblage in Jiaozhou Bay.About 40 larval and juvenile fish species were found in Jiaozhou Bay,but they are mainly low-valued fish species.The results indicated that the capacity as a spawning and nursery ground has declined in Jiaozhou Bay.Some measures should be taken to conserve and restore the ecological environment and fishery resources in the region.

Broad_scale, dense amphipod tube aggregations on the sea bed: implications for resource species that utilize benthic habitats

AbstractDuring a research cruise to Georges Bank in 1999 to study the areas closed to fishing, broad areas of the sea floor (3000_km2) were found to have a high percentage cover of emergent invertebrate tubes. Most of these tubes were attributable to the tubicolous epifaunal amphipod, Ericthonius rubricornis. Our data show the spatial extent that dense clumps of amphipod tubes could cover the sea floor on Georges Bank. When some of the same sites were sampled 1_yr later, in June 2000, the percent cover of the tube clumps on the sea floor was significantly reduced. Biogenic structures, such as invertebrate tubes, are important features of benthic habitats and may provide protection for juvenile fish and invertebrate resource species. Our observations reiterate that biogenic habitat characteristics are not spatially and temporally stable and this needs to be recognized by fisheries managers when managing the living marine resources that utilize these habitats.

The effects of dissolved oxygen levels on the metabolic interaction between digestion and locomotion in Cyprinid fishes with different locomotive and digestive performances

To test whether the effects of water oxygen concentration ([O(2)]) on the metabolic interaction between locomotion and digestion differ between fish species with different locomotive and digestive behaviours in normoxia, we investigated the swimming performance of fasted and fed fish at water [O(2)] of 1, 2 and 8 (normoxia) mg L(-1) (2.5, 5 and 20 kPa) at 25°C in three juvenile Cyprinidae fish species: goldfish (Carassius auratus), common carp (Cyprinus carpio) and qingbo (Spinibarbus sinensis). Digestion, taxon and water [O(2)] all had significant effects on the pre-exercise oxygen consumption rate [Formula: see text] and the swimming performance (P < 0.05). Among the three fishes, qingbo showed the highest swimming performance and the lowest feeding [Formula: see text] at the saturated water [O(2)], and its active oxygen consumption rate [Formula: see text] and critical swimming speed (U (crit)) decreased the most with decreases in water [O(2)]. Qingbo exhibited a locomotion-priority metabolic mode at all three water [O(2)]. Digestion was sacrificed to locomotion in a postprandial swimming situation, but fed qingbo could not maintain their U (crit) at water [O(2)] of 2 and 1 mg L(-1). Goldfish showed the lowest swimming performance and the highest feeding [Formula: see text] at the saturated water [O(2)]. They exhibited a digestion-priority metabolic mode at high water [O(2)]. However, with a decrease in water [O(2)], the feeding [Formula: see text] decreased more acutely than the respiratory capacity; thus, digestion and locomotion performed independently in a postprandial swimming situation (i.e., an additive metabolic mode) at a water [O(2)] of 1 mg L(-1). The common carp showed moderate and balanced swimming performance and feeding [Formula: see text] at the saturated water [O(2)], and exhibited an additive metabolic mode at all 3 water [O(2)], because digestion, swimming and respiratory capacities decreased in parallel with the decrease in water [O(2)].

Size and quantity of woody debris affects fish assemblages in a sediment-disturbed lowland river

Responses by fish assemblages to individual restoration actions among a suite of channel modifications are not well understood. We investigated whether increasing woody debris abundance, without significant change to channel morphology, would increase native fish abundance and species richness in a sediment-disturbed river channel (Glenelg River, Victoria, Australia). We conducted a Before–After, Control-Impact design experiment at twelve locations containing either a high (n=6) or low (n=6) quantity of large woody debris (LWD). We added small woody debris (SWD) to half (n=6: 3 high, 3 low LWD densities) of the locations to increase woody debris complexity without the impacts on channel morphology associated with LWD manipulations. Fish species richness and abundance was quantified using electrofishing surveys before (4 sampling trips) and after (3 sampling trips) SWD addition. Fish species richness was not associated with high or low quantities of LWD or with types of woody debris (LWD or SWD). Addition of SWD altered fish assemblage composition but the effect depended on LWD quantity. SWD additions to locations with low LWD quantities increased abundance of two, wood-affiliated species: Philypnodon grandiceps and Gadopsis marmoratus. SWD additions to locations with high LWD quantities increased abundance of P. grandiceps and Galaxias olidus. Fish body size was important in detecting a response to added SWD because for two species, only certain size classes responded: adults of P. grandiceps (>50mm TL) and juveniles of G. marmoratus (<123mm TL). Fish assemblages responded positively to increased density of SWD through local increases in abundance, despite channel sedimentation. Unlike LWD, SWD is relatively cheap to place in rivers because it does not require heavy machinery and can be obtained without tree mortality. The use of SWD to assist in habitat restoration, especially for small species of native fish and juvenile fish, should be considered as a strategy in river restoration.

Incorporating temporally dynamic baselines in isotopic mixing models

Stable isotopes (particularly C and N) are widely used to make inferences regarding food web structure and the phenology of consumer diet shifts, applications that require accurate isotopic characterization of trophic resources to avoid biased inferences of feeding relationships. For example, most isotope mixing models require that endmembers be adequately represented by a single probability distribution; yet, there is mounting evidence that the isotopic composition of aquatic organisms often used as mixing model endmembers can change over periods of weeks to months. A review of the literature indicated that the delta13C values of five aquatic primary consumer taxa, commonly used as proxies of carbon production sources (i.e., trophic baselines), express seasonally dynamic cycles characterized by an oscillation between summer maxima and winter minima. Based on these results, we built a dynamic baseline mixing model that allows a growing consumer to track temporal gradients in the isotopic baselines of a food web. Simulations showed that the ability of a consumer to maintain or approach isotopic equilibrium with its diet over a realistic growth season was strongly affected by both the rate of change of the isotopic baseline and equilibration rate of the consumer. In an empirical application, mixing models of varying complexity were used to estimate the relative contribution of benthic vs. pelagic carbon sources to nine species of juvenile fish in a fluvial lake of the St. Lawrence River system (Québec, Canada). Estimates of p (proportion of carbon derived from benthic sources) derived from a static mixing model indicated broad interspecific variation in trophic niche, ranging from complete benthivory to > 95% reliance on pelagic food webs. Output from the more realistic dynamic baseline mixing model increased estimated benthivory by an average of 36% among species. Taken together, our results demonstrate that failing to identify dynamic baselines when present, and (or) matching consumers with baseline taxa that possess substantially different equilibration rates can seriously bias interpretation of stable isotope data. Additionally, by providing a formalized framework that allows both resources and consumers to shift their isotopic value through time, our model demonstrates a feasible approach for incorporating temporally dynamic isotope conditions in trophic studies of higher consumers.

SCALES OF VARIABILITY IN FIN RAY COUNTS OF FLOUNDER, PLATICHTHYS FLESUS L. ON IRISH AND WELSH COASTS

Meristic variation within a fish species can arise due to environmental factors and can aid investigation between fish stocks and closely related juvenile fish species. The aim of this study was to investigate the spatial variation in meristic characteristics for juvenile flounder Platichthys flesus from Irish and Welsh coasts. Five meristic fin ray counts were taken from 120 fish from nursery grounds in three regions (west Irish coast, east Irish coast and Welsh coast). Statistical analysis revealed regional variability for two of the meristic counts (dorsal and anal fin rays). A discriminant function analysis revealed a weak separation of the three regions. This separation improved when samples from the east Irish region were eliminated, with 65% of the fish from the Irish west coast and 73% of the fish from Wales correctly classified.

Studi Kelimpahan Juvenil Ikan Pada Ekosistem Padang Lamun Di Perairan Karimunjawa, Kabupaten Jepara

Seagrass ecosystem of high organic productivity, with a high diversity of biota. On these ecosystems, diverse marine life such as fish juvenile, crustaceans, mollusks (Pinna sp, Lambis sp, Strombus sp), echinoderms (Holothuria sp, sp Synapta, Diadema sp, Arcbaster sp, Linckia sp) and worms (Polichaeta) (Bengen, 2001). The research was conducted at 10 stations. Sampling was conducted two times each observation station parallel to the shoreline and perpendicular to the shoreline using a small beam trawl. The results showed that the juvenile was found 27 species from 14 family. abundance average - average is 0.484 ind/m2 juvenile fish and the highest abundance at station 9 with the abundance of juvenile fish reaching ind/m2 1.40 and the lowest abundance found at station 3 and station 10 to the abundance of only 0.04 ind/m2 . The pattern of distribution of juvenile fish species tend to be random this is because in each station has similar characteristics.

Hierarchical and interactive habitat selection in response to abiotic and biotic factors: The effect of hypoxia on habitat selection of juvenile estuarine fishes

Habitat selection is a shared process among animals where individuals choose areas that differ in biotic and abiotic characteristics to maximize individual fitness. We used manipulative laboratory mesocosm choice experiments to examine hierarchical and interactive relationships influencing this habitat selection process of estuarine fishes. We assessed selection among substrate, dissolved oxygen (DO) concentration, food availability, and predation risk using two common juvenile estuarine fish species, pinfish (Lagodon rhomboides) and Atlantic croaker (Micropogonias undulatus). For both species oxygen concentration greatly influenced selection patterns; fishes strongly avoided low DO conditions, while in higher levels of DO factors such as substrate or food influenced selection patterns. However, both species strongly avoided predators even when alternative habitat was severely oxygen limited. These results suggest that predation risk may be the greatest determinant of habitat selection of the factors considered. Expansion of low DO areas in the world’s oceans is a major anthropogenic disturbance and is rapidly increasing. Assessing impacts of hypoxia on habitat usage of mobile organisms is critical as changes in environmental metrics including predator distribution and DO levels may alter habitat selection patterns disrupting critical ecosystem processes and trophic interactions. Our results indicate that juvenile fishes may forgo emigration from hypoxia due to predation risk. If similar patterns occur for juvenile fishes in estuaries they may potentially suffer from reduced growth, reproductive output, and survivorship.

Fish abundances in shoreline habitats and submerged aquatic vegetation in a tidal freshwater embayment of the Potomac River

Submerged aquatic vegetation (SAV) is considered an important habitat for juvenile and small forage fish species, but many long-term recruitment surveys do not effectively monitor fish communities in SAV. To better understand the impact of recent large increases of SAV on the fish community in tidal freshwater reaches of the Potomac River, we compared traditional seine sampling from shore with drop ring sampling of SAV beds (primarily Hydrilla) in a shallow water (depths, <1.5m) embayment, Gunston Cove. To accomplish this, we developed species-specific catch efficiency values for the seine gear and calculated area-based density in both shoreline and SAV habitats in late summer of three different years (2007, 2008, and 2009). For the dominant species (Fundulus diaphanus, Lepomis macrochirus, Etheostoma olmstedi, Morone americana, Lepomis gibbosus, and Fundulus heteroclitus), density was nearly always higher in SAV, but overall, species richness was highest in shoreline habitats sampled with seines. Although historical monitoring of fish in Gunston Cove (and throughout Chesapeake Bay) is based upon seine sampling (and trawl sampling in deeper areas), the high densities of fish and larger areal extent of SAV indicated that complementary sampling of SAV habitats would produce more accurate trends in abundances of common species. Because drop ring samples cover much less area than seines and may miss rare species, a combination of methods that includes seine sampling is needed for biodiversity assessment. The resurgence of SAV in tidal freshwater signifies improving water quality, and methods we evaluated here support improved inferences about population trends and fish community structure as indicators of ecosystem condition.

Catch Composition of a Set Bag Net used for Acetes Trapping in the Estuarine Waters of Kedah, Peninsular Malaysia

A study was conducted for a 12-month period, from June 2008 to May 2009 based on the catch data to determine the catch composition of Set Bag Net (SBN) that is a type of fishing net laid down to catch Acetes shrimps that move along the estuary of Merbok River in the state of Kedah, Peninsular Malaysia. Bag net is a static traditional gear with a cod end mesh size measuring 0.5 cm. The results showed that total catches of the bag net over a year period were constituted of three major catch groups viz. Acetes shrimps (89%), juvenile fishes (9%) and other non-Acetes shrimps (2%). The annual mean percentage composition of sergestid shrimps comprised of A. japonicus, A. vulgaris and A. indicus were found to be 89, 7 and 4%, respectively. The gear is very selective and besides Acetes there was also a small proportion of fish juvenile being caught. Seven species of juvenile fishes were recorded throughout the catch period however; their mean total abundance was very low (9%). Penaeid shrimp was the only group of non-Acetes shrimp been recorded. Based on the analyzed catch composition data, it could be concluded that SBN is Acetes-selective and not causing significant great damage to the juvenile fish population inhabiting the study area.

The effects of temperature on metabolic interaction between digestion and locomotion in juveniles of three cyprinid fish ( Carassius auratus, Cyprinus carpio and Spinibarbus sinensis)

To test whether the effects of temperature on the metabolic mode changed among different fish species, we investigated the specific dynamic action (SDA) and swimming performance of fasting and fed fish at 15 and 25 °C in three juvenile Cyprinidae fish species: goldfish ( Carassius auratus), common carp ( Cyprinus carpio) and qingbo ( Spinibarbus sinensis). Both taxon and temperature had significant effects on the resting oxygen consumption rate ( M ˙ O rest), SDA and swimming performance ( p < 0.05). In addition, the effect of temperature differed significantly among the different species (interaction effect, p < 0.05). Under the low temperature condition, digestion had no effect on either critical swimming speed ( U crit) or the active M ˙ O 2 ( M ˙ O active) for all fish species (additive metabolic mode). When the temperature was increased from 15 to 25 °C, the metabolic scope ( MS) for digestion increased approximately 182, 49 and 17%, and the MS for locomotion increased approximately 129, 58 and 138% in goldfish, common carp and qingbo, respectively. The total metabolic demands for both digestion and locomotion (i.e., the sum of digestive MS and locomotive MS) increased approximately 143, 56 and 112% in goldfish, common carp and qingbo, respectively. The total MS for both digestion and locomotion (the difference between M ˙ O active in fed fish and M ˙ O rest in fasting fish) increased approximately 106, 58 and 78% in goldfish, common carp and qingbo, respectively. Thus, the MS for locomotion in fed goldfish decreased due to the large increase in digestive function at the high temperature, and the U crit of fed goldfish decreased by 11% compared to that of fasting fish ( p < 0.05) (digestion-priory metabolic mode). The metabolic mode of qingbo changed to locomotion-priority mode, as illustrated by the large increase in locomotive MS in response to the increase in temperature. In the common carp, temperature had no effect on metabolic mode as illustrated by the parallel increases in cardio-respiratory capacity and metabolic capacity of digestive and locomotive organs. A discussion on the changes in metabolic mode in response to temperature and its possible relationship with the metabolic characteristics of a given fish species was also documented in this paper.

EVALUATION OF RIPARIAN HABITAT RESTORATION IN A LOWLAND RIVER

ABSTRACTFor many years, navigable lowland rivers have been embanked artificially or suffered from substantial shipping wave action, leading to habitat degradation. Recently, riparian habitats were restored by creating foreshores and spawning grounds in the river Yser, a lowland river in Flanders, Belgium. The aim of this paper was to evaluate the role of these restored habitats for spawning and nursery of juvenile fish. To cover a wide range of anthropogenic disruption, four riparian mesohabitat types were selected and compared, ranging from semi‐natural over artificial spawning grounds and foreshores to artificial embankments. Juvenile fish were subjected to sampling by using electrofishing between June and September 2009 at different microhabitats located in five sites of each riparian mesohabitat type. Juvenile fish strongly preferred natural riparian habitats, whereas artificial embankments showed the lowest species richness, abundance and functional organization of juvenile fish species. Restored riparian habitats appeared to be an appropriate alternative for artificial embankments in navigable lowland rivers but still score significantly less than natural habitats. Juvenile fish avoided bare microhabitats but did not prefer any other microhabitat type (reed, woody or grassy vegetation), emphasizing the importance of microhabitat diversity. This paper provides valuable insights into riparian habitat restoration to river managers and stakeholders. Copyright © 2011 John Wiley &amp; Sons, Ltd.

High species richness of early stages of fish in a locality of the Mesoamerican Barrier Reef System: a small-scale survey using different sampling gears

The Mesoamerican Barrier Reef System (MBRS) contains a diverse array of coastal habitats that are critical for the survival of the early stages of reef fish; however, the knowledge on the abundance and distribution of the early stages of coastal fishes is still limited in this region. This study investigated the species richness of larval and juvenile fishes using a combination of a sled net, standard plankton net, and a nightlight lift-net; these were deployed simultaneously at Bacalar Chico, a site on the MBRS within the protected “Parque Nacional Arrecifes de Xcalak” (PNAX). We collected 53 families and 118 species of larval and juvenile fishes in a small area of about 3 km2. This species diversity of early life-history stages is greater than previously found in surveys on the MBRS. Each gear caught a number of species exclusively, so combined sampling with the three methods provided a much fuller picture of the local larval and juvenile fish assemblage. A species-accumulation model estimated that the samples likely represented 84% of the total assemblage. Many species caught were represented predominantly by newly settled juveniles, underscoring the importance of this coastal habitat for settlement of many ecologically and economically important fish species. This information is expected to improve the conservation and management strategies in the fragile PNAX coastal zones by providing additional information based on original field data to raise awareness among managers about the ecological relevance of these coastal habitats. This study provides encouraging evidence that the PNAX is a well-suited natural protected area to preserve a critical fish habitat in a hotspot of marine biodiversity.

Detection of deep water benthic macroalgae using image-based classification techniques on multibeam backscatter at Cashes Ledge, Gulf of Maine, USA

Benthic macroalgae form an important part of temperate marine ecosystems, exhibiting a complex three-dimensional character which represents a vital foraging and spawning ground for many juvenile fish species. In this research, image-based techniques for classification of multibeam backscatter are explored for the detection of benthic macroalgae at Cashes Ledge in the Gulf of Maine, USA. Two classifications were performed using QTC-Multiview, differentiated by application of a threshold filter, and macroalgal signatures were independently extracted from the raw sonar datagrams in Matlab. All classifications were validated by comparison with video ground-truth data. The unfiltered classification shows a high degree of complexity in the shallowest areas within the study site; the filtered demonstrates markedly less variation by depth. The unfiltered classification shows a positive agreement with the video ground-truth data; 82.6% of observations recording Laminaria sp., 39.1% of Agarum cribrosum and 100.0% ( n = 3) of mixed macroalgae occur within the same acoustically distinct group of classes. These are discrete from the 8.1% recorded agreement with absences and nulls (>40 m) of macrophytes ( n = 32) from a total of 86 ground-truth locations. The results of the water column data extraction ( WCDE) show similar success, accurately predicting 78.3% of Laminaria sp. and 30.4% of A. cribrosum observations. The unfiltered classes which showed agreement with the ground-truth data were then compared to the WCDE results. Comparison of surface areas reveals the overall percentage agreement is relatively constant with depth (67.0–70.0%), with Kappa coefficient increasing from k = 0.17–0.35 as depth (and surface area) increases. The results have demonstrated that both methods were more effective at detecting the presence of Laminaria sp. (82.6–77.3%) than Agarum cribrosum, (66.6–30.4%), and that the efficiency of prediction decreased with depth. Canopy volume derived from the WCDE analysis was between 1.21 × 10 6 m 3 at <24 m water depth, 1.82 × 10 6 m 3 at <30 m and 2.45 × 10 6 m 3 at <40 m. These results suggest that the presence of benthic macrophytes has a significant capacity to affect image-based classification of acoustic data, and highlights the fact that multibeam backscatter and image-based classification have significant potential for benthic macroalgal research. This is beneficial to help refine segmentations of substrates, adding valuable contextual information about biological characteristics of infaunal and epifaunal benthic communities.

Species composition and distributions of mesopelagic fishes over the slope of the north-central Gulf of Mexico

Midwater fish faunas over three cold seep habitats >1000m (AC601, GC852, AT340) and over a cold-water coral bank (VK826, <1000m) in the north-central Gulf of Mexico (GOM) are described and compared. Day and night discrete-depth sampling was accomplished at each study site, 9–29 August 2007, using an opening–closing Tucker trawl towed at depth for 30min. The 159 Tucker trawl stations yielded 9802 individuals and at least 126 species (30 families) of juvenile and adult midwater fishes. Myctophidae (38 species, 28% of the total catch), Stomiidae (17 species, 1.4%), Gonostomatidae (12 species, 56%), Sternoptychidae (10 species, 6%), and Phosichthyidae (5 species, 6%) dominated catches at all sites. Thirty-one species (8 families) comprised about 90% of the overall abundance of fishes across the four sites. Despite the wide separation of study sites and some differences in physical oceanography, geographic and temporal patterns in mesopelagic fish assemblages were not evident (ANOSIM, Global R=0.20, p=0.1%, pairwise R values <0.3). However, station groupings were related mostly to similarities in sampled depths (SIMPROF, p<1.5%). Upper water-column station groups (<400m) were typified by Lepidophanes guentheri, Diaphus dumerilii, Vinciguerria nimbaria, Vinciguerria poweriae, Valenciennellus tripunctulatus, Argyropelecus aculeatus, Notolychnus valdiviae, Benthosema suborbitale, Gonostoma elongatum, and Hygophum taaningi. Deeper station groups (mean depth=609m) were typified by Cyclothone alba, Cyclothone acclinidens, Cyclothone braueri, Cyclothone obscura, Cyclothone pallida, Cyclothone pseudopallida, V. tripunctulatus, and Hygophum benoiti. Depth, diel, and size distributions were also analyzed for abundant species. For example, Cyclothone spp., abundant at all sites except VK826, usually occurred in deeper waters (>130m), especially during daylight hours (>335m). Most Cyclothone individuals were captured at night at GC852, whereas catches were more evenly distributed across times at AT340 and VK826. Cyclothone spp. individuals occurred in the deeper parts of the sampled depth range at AT340 and VK826 at all times compared with GC852, where they appeared to undergo a diel migration. The two most abundant Cyclothone spp., C. pallida and C. pseudopallida, had the broadest depth ranges (150–1377m) and exhibited a trend for larger specimens to occur deeper at GC852. Most V. tripunctulatus were captured at night and tended to have larger mean sizes in deeper waters. This species did not exhibit strong diel patterns of vertical distribution. Shallower depths were occupied at night by some individuals at all sites, but most individuals remained somewhat deeper at night at VK826 (350–450m at night and 200–350m by day) and AT340 (200–600m at night and 300–500m by day) compared with GC852 (150–450m at night and 750 and 1000m by day). Nearly all Vinciguerria poweriae were caught at night, and no clear trend of size with depth was apparent. This species occupied a wider depth range at night, with most in the upper 200m. Most myctophids, the strongest diel migrators, were captured at night at the offshore stations. The dominant myctophid, N. valdiviae, was most abundant at GC852 (550–1050m by day and 50–750m at night), but diel movement was more distinct at AT340 (<200m at night and 350–500m by day). No size-related trends with depth were apparent at any site for N. valdiviae, and size distributions were similar among sites.This study and others support the hypothesis that there is a geographically similar mesopelagic fish fauna throughout the GOM. However, the fauna does vary by depth, with some species remaining in deep waters at all times (e.g., Cyclothone spp.) and others occurring at mid-depths and exhibiting varying degrees of diel migration (e.g., many myctophids). Even though faunal composition is similar across the GOM, some species exhibit different movement behaviors at different locations. Such variances could be related to differences in physical or chemical factors, food resources, lunar phase, or bottom depth.

Diel seasonality in fish biodiversity in a sandy beach in south-eastern Brazil

Diel fluctuations in nearshore fish communities were studied at a sandy beach in south-eastern Brazil. A total of 192 samples were performed by beach seines, during 3-hour intervals throughout 48-hour periods, between spring 2005 and winter 2006. Mean biomass and number of species were significantly higher at night, while number of individuals did not differ between day and night. Major disruptions in the fish community occurred during the winter when the assemblages underwent restructuring. Harengula clupeola, Sardinella janeiro, Anchoa lyoleps and Umbrina coroides were the predominant species at night, while Atherinella brasiliensis, Pomatomus saltatrix and Trachinotus carolinus peaked during the day, although significant diel changes in community structure were recorded only in the summer. Biological interactions, behavioural variations and local constraints might explain diel differences in the fish distribution. This study confirms that changes in diel activity in juvenile fish species can differ in similar areas, even for a given species, and the causes of these changes needs to be investigated.

Fractal measures of habitat structure: maximum densities of juvenile cod occur at intermediate eelgrass complexity

Habitat patchiness is known to alter the relation of a population to both its predators and its prey. We developed a biologically interpretable measure of habitat complexity to test whether juvenile fish density depends on degree of patchiness. In Newfoundland coastal waters, juvenile fish species, including Atlantic cod Gadus morhua, are associated with eelgrass Zostera marina. How- ever, the association of density with eelgrass cover is dependent upon site and the scale of analysis. We tested for non-monotonic relationships (with an intermediate optimum) between 5 spatial charac- teristics of eelgrass and density of 3 juvenile (Age-0) fish species: Atlantic cod, Greenland cod G. ogac, and white hake Urophycis tenuis. We used aerial photography to determine eelgrass perimeter and area measurements at multiple scales, fractal dimensions of perimeter (DP) and area (DA), and a measure that combines perimeter and area complexity at these scales (βP/A). Fish densities were esti- mated at each site using a seine net. We found parabolic relationships between βP/A and density for all 3 species, indicating highest fish densities at sites of intermediate patchiness and edge regularity. Furthermore, we determined that βP/A provided a less ambiguous estimate of spatial configuration than other measures. This intermediate maximum may reflect a trade-off, whereby eelgrass sites of intermediate spatial complexity provide juvenile fish with both optimal protective cover and oppor- tunity to feed. This pattern may apply to any species requiring open areas in which to forage as well as shelter to offset predation risk.