Nearshore Fish Assemblages Research Articles

The structure of a nearshore fish assemblage at an oceanic island: insight from small scale fisheries through bottom traps at Gran Canary Island (Canary Islands, eastern Atlantic)

Unsuitable management of fisheries may lead to overexploitation of marine resources. Oceanic islands with narrow continental shelves, in particular, are sensitive to unsustainable levels of fishing intensity. Fish traps are the modality of artisanal professional fishing more important in the coastal waters of the Canary Islands (eastern Atlantic) to capture demersal resources, which are deployed all year-round and allow a release of undersized captures. We aimed at studying the structure of nearshore fish assemblages through deployment of benthic bottom traps carried out at Gran Canary Island. A quantitative description of catches, in terms of abundance, biomass and sizes, of traps deployed from May to October 2009, between ca . 20 to 50 m depth, was carried out. We used this information to test whether the structure of nearshore fish assemblages at the island scale varied between three zones located at the NW, NE and E of the island with varying habitat structure. A total of 58 species (22 families) were collected for the overall study from a total of 2568 deployed traps. The species Sparisoma cretense (25% of the total biomass), the family Sparidae (16 species, 44%) and Mullus surmuletus (4%) accounted for more than 73% of the total catch in terms of biomass. The parrotfish, S. cretense , was the fish with the largest catches in terms of number of individuals, followed by Dentex gibbosus , Diplodus vulgaris , Stephanolepis hispidus , Chromis limbata and Mullus surmuletus . Differences in the structure of the fish assemblage at the island scale were not predicted by differences in the type of bottom. Fishing yields were similar between the NW (0.16 ± 0.02 kg trap -1 day -1 ) and NE side of the island (0.19 ± 0.01 kg trap -1 day -1 ), being lower at the E zone (0.15 ± 0.01 kg trap -1 day -1 ). The most abundant species, the parrotfish S. cretense , had a mean size close to its first maturity sizes (SFM 50 ), while both D. gibbosus and D. vulgaris were below SFM 50 . In general, the mean size of Sparids was well below SFM 50 , an indication of overexploitation, while M. surmuletus and S. hispidus reached a mean size beyond their first maturity sizes.

Franz Josef Land: extreme northern outpost for Arctic fishes.

The remote Franz Josef Land (FJL) Archipelago is the most northerly land in Eurasia and its fish fauna, particularly in nearshore habitats, has been poorly studied. An interdisciplinary expedition to FJL in summer 2013 used scuba, seines, and plankton nets to comprehensively study the nearshore fish fauna of the archipelago. We present some of the first underwater images for many of these species in their natural habitats. In addition, deep water drop cameras were deployed between 32 and 392 m to document the fish fauna and their associated habitats at deeper depths. Due to its high latitude (79°–82°N), extensive ice cover, and low water temperatures (<0 °C much of the year), the fish diversity at FJL is low compared to other areas of the Barents Sea. Sixteen species of fishes from seven families were documented on the expedition, including two species previously unknown to the region. One Greenland shark, Somniosus microcephalus (Somniosidae), ca. 2 m in length, was recorded by drop camera near Hayes Island at 211 m, and Esipov’s pout, Gymnelus esipovi (Zoarcidae), was collected at Wilton Island at 15 m in a kelp forest. Including the tape-body pout, Gymnelus taeniatus, described earlier from the sub-littoral zone of Kuhn Island, 17 fish species are now known from FJL’s nearshore waters. Species endemic to the Arctic accounted for 75% of the nearshore species observed, followed by species with wider ranges. A total of 43 species from 15 families are known from FJL with the majority of the records from offshore trawl surveys between 110 and 620 m. Resident species have mainly high Arctic distributions, while transient species visit the archipelago to feed (e.g., Greenland shark), and others are brought by currents as larvae and later migrate to spawn grounds in the south (e.g., Atlantic cod Gadus morhua, Capelin Mallotus villosus, Beaked redfish Sebastes mentella). Another species group includes warmer-water fishes that are rare waifs (e.g., Glacier lanternfish Benthosema glaciale, White barracudina Arctozenus rissoi). The rapid warming of the Arctic will likely result in significant changes to the entire ecosystem and this study therefore serves as an important baseline for the nearshore fish assemblages in this unique and fragile region.

Spatial and Temporal Variation in Otolith Chemistry of Juvenile Atlantic Menhaden in the Chesapeake Bay

AbstractThe Atlantic Menhaden Brevoortia tyrannus is an important component of the estuarine and nearshore fish assemblages in the mid‐Atlantic region. It serves as a forage species for many piscivorous fish, birds, and marine mammals as well as being subject to an important commercial fishery. Currently there is concern over low standing stocks and recruitment, yet few studies have addressed those concerns. We evaluated the effectiveness of using an otolith chemistry approach to identify juvenile menhaden nursery areas throughout the Chesapeake Bay over 2 years. If successful, an otolith chemistry approach is capable of addressing a number of hypotheses regarding the source and fate of recruits in a stock. We found multiple unique otolith chemistry signatures in menhaden collected in the Chesapeake Bay. Overall correct classification was 85% for the 2005 cohort and 95% for the 2006 cohort. The ratios of most trace element: Ca and stable isotope ratios were different among areas. In addition to spatial differences, both seasonal and annual temporal variation was present in the otolith chemistry. However, a discriminant function that included temporal variation resulted in reduced prediction accuracy (overall errors increased 7–10%). We found that our classification function, which was developed for multiple cohorts, can successfully predict group membership. We recommend additional evaluation of this strategy because of its potential application to data‐poor stocks. Our data show that juvenile menhaden in the Chesapeake Bay can be reliably discriminated based on otolith chemistry signatures and that this approach can be used to critically evaluate the nursery contributions of the bay to the coastal adult stock of menhaden.Received July 11, 2013; accepted January 21, 2014

Nearshore fish assemblage structure and habitat relationships in protected and open habitats in the upper St. Lawrence River

Biological integrity of nearshore habitat in the Thousand Islands region of the upper St. Lawrence River is threatened by the cumulative effects of anthropogenic stressors such as water level regulation, habitat alteration, and invasion of non-native plant and animal species. To better understand how fish-habitat associations and fish assemblage structure differed based on existing environmental conditions, fish assemblages were compared from three protected and five open nearshore habitats within embayments. Two distinct and diverse fish assemblages were identified: a protected nearshore and an open nearshore assemblage. Protected nearshore areas contained a diverse fish assemblage that harbored predominantly phytophilic species dependent upon densely vegetated habitats whereas open nearshore areas contained a diverse assemblage of Notropis sp. minnows dependent on wind exposed habitats with firmer substrates. Increased macrophyte column density was associated with protected nearshore assemblages whereas firmer substrates and increased fetch were correlated with open nearshore assemblages. Nearshore areas within the Thousand Islands region support populations of sensitive and intolerant fish species. Management strategies should focus on protecting high-quality nearshore habitats and restoring connectivity between habitats.

Nearshore Fish Assemblages of the Northeastern Chukchi Sea, Alaska

The Arctic ecosystem is changing rapidly, yet information on nearshore fish assemblages for the northeastern Chukchi Sea is extremely limited. To address this information gap, we sampled nearshore fish assemblages with a beach seine and a small bottom trawl at six stations in the northeastern Chukchi Sea in August 2007, 2008, and 2009, and in September 2009. Catch and species composition differed by gear type and between sample periods, including the two in 2009. A total of 16 039 fish representing 18 species were captured in 24 beach seine hauls, and 3108 fish representing 24 species were captured in 48 trawl tows. Beach seine catch was dominated by capelin (83%), and trawl catch was dominated by Arctic cod (56%). Species that were good discriminators between gear types were capelin (seine) and slender eelblenny (trawl), and unidentified small sculpins were the most common taxa caught with both gear types. Capelin and Arctic cod captured by either gear type were mostly juveniles (judging by size). Variability among sampling periods in catch and species composition within gear types can likely be attributed to annual variations in environmental conditions, including differences in water temperature (range: 2˚–9˚C). The shallow nearshore environment of the northeastern Chukchi Sea provides important habitat for many fish species and is extremely vulnerable to disturbance. Loss of sea ice from global warming may open up formerly inaccessible areas to oil and gas exploration, vessel traffic, and commercial fishing. Thus, long-term monitoring of nearshore fish assemblages in the Alaskan Arctic is necessary for managers to make informed decisions in this fragile environment.

Fish Assemblage Shifts and Population Dynamics of Smallmouth Bass in the Beaver Archipelago, Northern Lake Michigan: A Comparison between Historical and Recent Time Periods amidst Ecosystem Changes

AbstractThe ecological and economic importance of Great Lakes nearshore areas and the paucity of information on nearshore Lake Michigan fish assemblages prompted us to document changes that occurred from a historical time period (1969–1972, 1975, 1977, and 1984) to a recent period (2005–2008) in a nearshore northern Lake Michigan (Beaver Archipelago) fish assemblage, with an emphasis on smallmouth bass Micropterus dolomieu. From historical to recent periods, the Beaver Archipelago fish assemblage shifted from predominantly brown bullheads Ameiurus nebulosus to predominantly smallmouth bass. Relative abundance of brown bullheads and white suckers Catostomus commersonii declined from historical to recent time periods, as did overall species richness. The relative abundance, recruitment variability, and mortality rates of smallmouth bass have not significantly changed since the historical time period, whereas both condition (ages 5–7) and growth (ages 2–7) of this species have significantly increased. Our results suggest that the smallmouth bass population in the Beaver Archipelago area has not been negatively affected by recent ecological changes (i.e., declining primary productivity, increasing benthic invertebrate densities, increasing numbers of double‐crested cormorants Phalacrocorax auritus, and increasing introductions of nonnative species). The smallmouth bass is currently the dominant nearshore species and remains a critical component of the nearshore fish assemblage in northern Lake Michigan.

Locating faunal breaks in the nearshore fish assemblage of Victoria, Australia

Marine communities are frequently biogeographically structured, despite the potential for dispersal. Previous research on a variety of marine taxa in south-eastern Australia has suggested that a biogeographic break occurs along the coastline of Victoria. However, little of this research has focussed on nearshore ichthyofauna and the location of the break remains debated. Using fish abundance measured by two methods: underwater visual census (UVC); and baited remote underwater video (BRUV) at six locations along the open coast of Victoria, we examined (1) whether there is sufficient concordance among species to indicate the presence of a faunal break; and if present (2) where any such breaks occur. Differences in assemblage composition between locations were tested with analyses of similarity and examination of residuals from regressions of pairwise dissimilarities against coastline distance. Data collected using UVC revealed two large faunal breaks co-located with a habitat discontinuity, the convergence of two currents and a thermal gradient. Data collected by BRUV revealed only a gradation of change across the study region. Greater understanding of the biogeographic structure of these communities will facilitate more effective management, especially in light of anticipated range shifts in response to global climate change.

Nearshore fish assemblages associated with introduced predatory fishes in lakes

Changes to native fish assemblages in lakes are commonly associated with introduced predatory fishes. How fish assemblages change as multiple predatory species are introduced is not well understood. This study investigated the relationship between the presence of introduced large-bodied predatory fishes (largemouth bass Micropterus salmoides, pike Esox lucius, rock bass Ambloplites rupestris, smallmouth bass Micropterus dolomieu, walleye Sander vitreus) and the composition of native fish assemblages in littoral areas of 40 lakes in Algonquin Provincial Park, Ontario, Canada. Fish assemblages were compared across lakes of different predator composition, and within lakes before and after recent predator invasions. The presence of an introduced predator was associated with significantly different native fish assemblages across lakes, after controlling for environmental and spatial variables. Native fish assemblages did not significantly vary across lakes with more than one predator species. Furthermore, while declines in native species richness over time were observed in a number of lakes, these were not associated with introductions of additional predators. Several small-bodied species (brook stickleback Culea inconstans, fathead minnow Pimephales promelas, finescale dace Chrosomus neogaeus, and northern redbelly dace Chrosomus eos) consistently showed strong negative correlations with predator presence. The results suggest that predatory fish introductions alter native fish assemblages and that this impact is consistent regardless of the number of predatory species introduced. Copyright © 2011 John Wiley & Sons, Ltd and Her Majesty the Queen in Right of Canada.

A comparison of two survey methods: differences between underwater visual census and baited remote underwater video

Essential to any model, conservation or management plan are measures of the distribution and abundance of a species. Countless methods for estimating these parameters exist, making it essential to assess the limitations and biases associated with a particular sampling protocol. Here, we compare between 2 methods commonly used to survey nearshore fish assemblages. Although most commonly employed, underwater visual census (UVC) may yield biased estimates of abundance depending on the strength of a fish's behavioural response (i.e. avoidance, attraction) to the presence of divers. Baited remote underwater video (BRUV) techniques have shown promise in overcoming some of the limitations of UVC, but are unable to provide an absolute measure of density in turbulent environments. We compare the abilities of these 2 methods to survey the nearshore rocky reef ichthyofauna of Southeast Australia. We found that relative to BRUV, UVC recorded more individuals (in terms of all species, herbivores, cryptic species, and most territorial species), higher richness at both the species and family level, and higher biodiversity as measured using the Shannon Index. These findings remain even when the data were adjusted for differences in sampling effort. In contrast, BRUV recorded proportionally more mobile predators, and a more taxonomically distinct population, though only when taxonomic evenness was not taken into account. Twenty species were unique to UVC and 17 species unique to BRUV. Considering this, studies aimed at cataloguing diversity should apply multiple methods. However, when logistical or financial constraints limit biodiversity studies to only 1 method, UVC will likely provide a more complete estimate of temperate reef fish diversity than BRUV. © Inter-Research 2010.

Complementary Sampling Methods to Inform Ecosystem-Based Management of Nearshore Fisheries

Area-based fishery management and ecosystem-based management strategies are considered beneficial marine resource management tools, but they require finite information about the structure and function of ecosystems to evaluate populations and describe the effects of fishing on ecosystems. The required information is not likely to be obtained from sporadic, fishery-dependent data collected from data-poor fisheries, and funding constraints preclude extensive fishery-independent surveys. This situation has led to an interest in relating or combining information from a variety of disparate sampling methods. From 2003 to 2006, we investigated the relationships between estimates of catch per unit effort (CPUE) and the abundance of fishes generated from typical nearshore commercial fishing operations and estimates of density and abundance derived from scuba surveys in the same locations. The relationships between CPUE and the density estimates derived from different sampling methods were found to be statistically significant in the case of many of the common species sampled across sites in Carmel Bay, California. The compounding effects of within-sample variance and the error associated with the regression equations, however, would result in poor confidence in the values translated from one sampling method to another. Different sampling methods may provide reasonable estimates of population trends, but they are sufficiently different and variable as to preclude the use of a scaling factor to standardize population estimates among sampling methods. Also, the differences in species composition (i.e., relative CPUE or density among species) produced by each sampling method were significant and were also affected by habitat relief and sample depth. Nonetheless, our results suggest the value of a cost-benefit analysis that would allow managers to design optimal sampling strategies for characterizing CPUE relationships within a region of interest. A sampling program that benefits from the complementary strengths of fishing gear and scuba sampling will probably result in the most comprehensive description of nearshore fish assemblages.

Estimating Sampling Effort for Biomonitoring of Nearshore Fish Communities in Small Central Minnesota Lakes

AbstractI estimated the sampling effort required to sufficiently describe the species richness and composition of fish inhabiting the nearshore (wadeable) zone of lakes and compared 10 species richness estimators in 56 similarly sized (small) central Minnesota lakes. A systematic sampling design was employed wherein 10 stations were equally spaced around each lake and the first station was selected randomly. Sampling methods consisted of a combination of backpack electrofishing and shoreline seining. Using sample‐based rarefaction curves, eight sampling stations produced at least 90% of the sampled species in 96% of the study lakes. Less sampling effort (four to six stations) was needed to describe the composition of the nearshore fish assemblage, as measured by similarity of species composition or species relative abundances in cumulative samples. The effort needed to sufficiently describe nearshore species richness was not related to observed species richness but was negatively correlated with species evenness among sampling stations. Estimates of total nearshore species richness were made using an asymptotic accumulation function, a log‐linear model, two abundance‐based nonparametric estimators, and six incidence‐based nonparametric estimators. All estimates of total species richness were correlated with observed species richness. Estimated total species richness exceeded observed species richness; however, this difference was smallest when species evenness was high. Nonparametric methods produced unrealistically high richness estimates if many species were encountered infrequently. Observed richness varied among lakes and was positively related to measures of lake integrity. Observed richness, estimated total richness, and sufficient effort levels were similar for lakes sampled twice, suggesting that both the sampling method and estimated levels of sufficient effort were robust. The results of this study suggest that more intensive nearshore sampling with seines and backpack electrofishing will be of limited benefit unless the detection of rare species is the major goal of sampling; alternative sampling gears may be needed to detect new species.

Fish Distribution, Abundance, and Behavior along City Shoreline Types in Puget Sound

AbstractShoreline modifications, such as bulkheads, riprap, and overwater structures, have altered many of the natural habitats in nearshore urbanized areas surrounding coastal cities, including those in Puget Sound, Washington. The effects of such structures on ecological processes are poorly known, especially those impacting juvenile salmonids Oncorhynchus spp. The goal of our study was to compare the relative abundance and behavior of juvenile salmonids and other fishes along various modified and undeveloped shoreline types. We used enclosure nets and snorkel surveys to sample fishes during high tides in areas adjacent to shore at five main habitat types: cobble beach, sand beach, riprap extending into the upper intertidal zone, deep riprap extending into the subtidal zone, and the edge of overwater structures. Bottom‐dwelling fishes exhibited the only significant differences in density among cobble beach, sand beach, and riprap that extended into the upper intertidal zone. This suggests that substrate type and slope are important influences on fish densities when shoreline modifications only extend into the upper intertidal zone. Differences in pelagic fish density and behavior were more evident when shoreline modifications extended into shallow subtidal waters, truncating the shallow‐water zone and creating deep water at the shoreline. We typically found higher fish densities, larger schools of salmon, and fewer terrestrial riparian insects in salmon diets at these sites. Juvenile salmonids avoided swimming beneath overwater structures, whereas surfperch (family Embiotocidae), crabs (infraorder Brachyura), and sculpins (family Cottidae) were observed beneath or adjacent to pilings. Overall, our results indicate that shoreline modifications have the greatest effect on nearshore fish assemblages when the alterations extend from the supratidal zone into the subtidal zone. Our data suggest that the differences in fish behavior and usage between modified and unmodified shorelines were caused by physical and biological effects of the modifications, such as changes in water depth, slope, substrate, and shoreline vegetation.

Abundance, biomass and species composition of nearshore fish assemblages in Ghana, West Africa

Many of the world's fish populations are overexploited, including Ghana's fish resources. This study examines spatio-temporal trends in fish species composition in relation to biotic, abiotic and anthropogenic factors, towards achieving better-informed management of the beach-seine fisheries. Fishery-dependent data were collected between November 1999 and October 2001 from 94 beach-seine hauls fished at two stations along the Ghanaian coast. The catch consisted of fish, crustaceans, other invertebrates, and macroalgae. Generally, juveniles of species that are exploited by offshore fisheries were found in the catches. Species abundance and their occurrence generally peaked between November and January. Duration of solar radiation and tide level appeared to be important predictors of fish biomass. It is important to exploit the nearshore fish assemblage sustainably because of its nursery role. A co-managed (fishers and government) three-month ban on beach-seining (between May and July) is recommended as the most appropriate control measure towards the sustainability of Ghanaian fish stocks.

Seasonal Variation in Fish Assemblages Within the Estuarine Portions of the Myakka and Peace Rivers, Southwest Florida

Juvenile and small adult fish were sampled monthly from 1996 to 2002 in the estuarine portions of the Myakka and Peace rivers, at the northern end of Charlotte Harbor (a relatively pristine estuarine system in southwest Florida). We provide a detailed description of the fish faunas in these areas, including seasonal assemblage structure. Seasonal cycles in assemblage structure were evident. Nearshore (to ~5 m) fish assemblages sampled by seine were separated into three main seasonal groups by cluster analysis (January-April, May-September, September-January). The ichthyofauna collected from deeper (≥1.8 m) areas by otter trawl formed two seasonal groups (June-October and November-March). Small schooling taxa such as Anchoa mitchilli, Menidia spp. and Eucinostomus spp. dominated seine catches, and variations in their abundances contributed greatly to dissimilarities between seasons, as did seasonal recruitment of young-of-the-year (YOY) estuary-dependent species such as Mugil cephalus, Lagodon rhomboides, Leiostomus xanthurus, and Bairdiella chrysoura. Estuarine residents (e.g., A. mitchilli and Trinectes maculatus) and YOY estuary-dependent species (e.g., Cynoscion arenarius and Menticirrhus americanus) were important in defining seasonal dissimilarities in fish assemblages from the trawled areas. Correlations between biotic patterns and environmental factors (water temperature, salinity, dissolved oxygen, precipitation, and river discharge) were relatively low, perhaps reflecting the euryhaline nature of the fish present and their intrinsic spawning periods. The present study provides a detailed description of temporal ichthyofaunal patterns in the estuarine portions of two tidal rivers in southwest Florida and provides a baseline with which future fish populations in this area can be compared.

Spatial and temporal variation in nearshore fish and macroinvertebrate assemblages from a temperate Australian estuary over a decade

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 182:253-268 (1999) - doi:10.3354/meps182253 Spatial and temporal variation in nearshore fish and macroinvertebrate assemblages from a temperate Australian estuary over a decade G. Jackson1,*, G. K. Jones2 1Western Australian Marine Research Laboratories, PO Box 20, North Beach, Western Australia 6020, Australia 2South Australian Research and Development Institute (Aquatic Sciences), PO Box 120, Henley Beach, South Australia 5022, Australia *E-mail: gjackson@fish.wa.gov.au ABSTRACT: Nearshore fish and macroinvertebrate assemblages of the Port River-Barker Inlet estuary, South Australia, were sampled by beach seine at monthly intervals between January 1985 and December 1994. Multivariate analyses were used to determine patterns in species distribution and abundance, to determine the influence of site, month and year on assemblage structure, and to identify trends in species composition over the decade. A total of 403626 individuals representing 56 species were recorded, with Aldrichetta forsteri, Hyporhamphus melanochir, Sillaginodes punctata and Pelates octolineatus responsible for 76% of the total abundance. Estuarine-opportunistic species were consistently dominant over the decade with marine stragglers and estuarine-dependents important in some years only. Abundances of the 19 species determined to be dominant varied between years, with some species, e.g. Spratelloides robustus, Hyporhamphus regularis, Arenigobius bifrenatus, Nesogobius sp. 3 and Cristiceps australis, demonstrating considerably greater inter-annual variability compared with others, e.g. S. punctata, A. forsteri, H. melanochir, P. octolineatus, Haletta semifasciata and Sillago schomburgkii. The importance of temporal scale in any assessment of community stability is re-stated; although individual species varied in abundance between months and years, assemblage structure was shown to be reasonably stable over the decade. Water temperature and salinity were weakly correlated with patterns in species composition and abundance. Further experimental studies are required to improve ecological understanding of the system's fish fauna and on-going monitoring is necessary to assess future changes to fish populations in relation to adjacent wetland developments. KEY WORDS: Estuarine fish · Assemblage structure · Spatial and temporal variability · Community stability · Environmental influences · Southern Australia Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 182. Publication date: June 11, 1999 Print ISSN:0171-8630; Online ISSN:1616-1599 Copyright © 1999 Inter-Research.

The influence of habitat structure on nearshore fish assemblages in a southern Australian embayment: Comparison of shallow seagrass, reef-algal and unvegetated sand habitats, with emphasis on their importance to recruitment

Assemblage structure and juvenile recruitment of fishes was compared amongst three habitats: seagrass, Heterozostera tasmanica (Martens ex Aschers.) den Hartog; reef-algal; and unvegetated sand. Sampling was conducted monthly from October 1993 to March 1994 at three locations in Port Phillip Bay, southern Australia. A fine-mesh seine net was used to sample subtidally at a depth of approximately 0.5 m. Fish assemblages differed primarily between structured habitats and unvegetated sand, and a number of species previously reported to occur in seagrass habitat were also found to utilise reef-algal habitat. Species richness was highest in seagrass and lowest in unvegetated sand with significant differences amongst all habitats. Total abundance varied between habitats depending on location and month examined, but the most common pattern was highest abundance in seagrass and lowest in unvegetated sand, with a significant difference only between seagrass and unvegetated sand. At the level of individual taxa, pipefishes of the genus Stigmatopora showed a strong preference for seagrass habitat from an early juvenile stage. The King George whiting, Sillaginodes punctata (Cuvier and Valenciennes), showed a complex relationship with habitat, occurring on both seagrass and reef-algae immediately after settlement, but, with growth, showing an increasing preference for reef-algae before finally shifting to unvegetated sand approximately 4 months after settlement. Other species previously found as juveniles on seagrass beds also recruited to reef-algal habitats. Strong locality effects were also found, particularly for King George whiting. This variation was unlikely to be related to habitat structure, because macrophyte biomass showed much greater variation within locations than amongst locations. We conclude that while the presence of structure per se is sufficient for the recruitment of many species, some taxa will discriminate amongst habitats based on structural characteristics.

The influence of habitat structure on nearshore fish assemblages in a southern Australian embayment: colonisation and turnover rate of fishes associated with artificial macrophyte beds of varying physical structure

Experiments were undertaken to investigate (1) whether nearshore fish assemblages were mainly influenced by the presence or absence of macrophyte beds, irrespective of their structure, or whether the particular structural characteristics of the macrophyte beds were important, and (2) whether fishes associated with macrophytes can be considered to `settle and stay' or whether assemblages are relatively mobile. In the first experiment, replicate artificial macrophyte beds of equal leaf area to bottom ratio, but with narrow and wide leaf morphologies, were placed at two sites in Port Phillip Bay, Australia. Artificial macrophyte beds were sampled with a small seine net on two occasions. Species richness was not significantly different between the two macrophyte treatments, but these treatments were significantly higher in species richness than unvegetated sand. Abundances were much higher in the narrow-leaf treatment compared with the wide-leaf treatment, that was in turn higher than unvegetated sand. Thus, the physical structure of the habitat did influence fish assemblages beyond the simple presence or absence of structure. In the second experiment, artificial beds of the two leaf morphologies were sampled either frequently (1–2 days), or only at the end of the sampling period of 9 days, with the small seine net. Most fishes were juveniles rather than recently settled post-larvae, and abundances were again higher in the narrow-leaf treatment. The cumulative abundance of fishes in the frequently sampled treatment was much higher than in the once sampled treatment, suggesting high turnover of post-settlement fishes in the macrophyte beds. Physical data suggested that wave action may have been an important factor in the high turnover of fishes in the beds.

Temporal and Spatial Patterns in Abundance and Diversity of Fish Assemblages in Elkhorn Slough, California

Assemblages of ichthyofauna of shallow inshore habitats along California’s central coast are described in terms of species composition, abundance, and life-style categories. A total of 22,334 fishes from 65 species and 27 families was collected with otter trawls at six sites in the main channel and tidal creeks of Elkhorn Slough, a tidal embayment and seasonal estuary, and two nearshore ocean stations in Monterey Bay during 44 months between August 1974 and June 1980. Greater than 90% of the catch comprised 10 species. The four dominant species,Cymatogaster aggregata, Leptocottus armatus, Phanerodon furcatus, andEmbiotoca jacksoni, occurred during most or all seasons and were classified as residents or partial residents. Several abundant species were marine immigrants that seasonally use the slough as spawning and nursery grounds; this resulted in higher abundance and species richness during summer. Species collected during winter largely were slough residents. Species compsosition and richness varied with distance from the slough entrance. The ocean assemblage was most different, and its similarity to other stations decreased progressively with distance inland and into the tidal creeks. During our study, 5,074 fishes were collected by beach seine in Bennett Slough, a remote shallow marsh basin adjacent to the entrance of Elkhorn Slough. Species richness was relatively low and three euryhaline species accounted for >80% of the total catch. The species assemblage was most similar to those at the tidal creek and most shallow stations of Elkhorn Slough. Resident species numerically dominated assemblages in Bennett Slough and the most inland areas of Elkhorn Slough. The high relative abundance of marine-related fishes (classified as marine, marine immigrant, and partial resident), entering Elkhorn Slough early in life or as spawning adults indicates the importance of this habitat to nearshore fish assemblages.

Species composition and dietary relationships in a brackish shallow water fish assemblage in the Bothnian Sea, Sweden

A nearshore fish assemblage inhabiting a shallow bay in the southern Bothnian Sea, Sweden, with demanding environmental conditions (c. 5‰; >15°C during 4 months 1980 and 1 month 1981) was studied during a two-year period, in 1980 and 1981. Seasonal distribution patterns, dietary relationships, and growth rates were studied in Pungitius pungitius (L.), Pomatoschistus minutus (Pallas.), Gasterosteus aculeatus (L.), Phoxinus phoxinus (L.), Pomatoschistus microps (Krøyer) and Gobius niger L. The structure of the juvenile populations changed both over seasons and years but the adult populations remained constant. Lower water temperature, fewer individuals, lower and delayed fish growth, and lower interspecific food overlaps were found in 1981 compared to 1980. Few significant correlations were found in both years between the following community parameters: diversity, niche width, food overlap, and the proportion of each species in the fish assemblage.According to these results it is suggested that food competition and resource partitioning were of minor importance for the structuring of the fish community in the present area. Rather, the extreme salinity and the fluctuations in temperature regulated the fish populations. One may conclude that the populations of juveniles were more influenced by short-term changes in the environment than those of the adults.

Diversity as a Measure of Alewife (Alosa Pseudoharengus) Dominance in Southeastern Lake Ontario

Nearshore fish assemblages at Nine Mile Point, Lake Ontario, were sampled with gill nets twice a month from April to December in 1974 and 1975. Seasonal fluctuations in diversity (H’) were compared with and without the presence of alewife ( Alosa pseudoharengus), which comprised about 75% of the total number of individuals. Because H’ was highly correlated with the proportional contribution (p i log p i) of alewife abundance, fairly large temporal changes in composition of the remainder of the fish community were masked. This effect was explained by certain properties of the H’ index; i.e., once a species has a dominance greater than about 70%, it influences H’, not only through its own contribution, but also by restricting p i values for all other species below 0.30, the region where the index is most sensitive to change.