Small Flatfish Research Articles

Shellfish aquaculture farms as foraging habitat for nearshore fishes and crabs

AbstractObjectiveOyster reefs across North America have declined precipitously over the past 140 years. In Washington State, Olympia oyster Ostrea lurida reefs historically provided water filtration and nearshore structural habitat for fishes and invertebrates, but this species is now functionally extinct across its historical range. In place of these naturally occurring reefs, shellfish farms consisting mainly of nonnative Pacific oysters Magallana gigas now occupy patches of nearshore habitat across Washington. These farms modify intertidal substrate by adding structural habitat via suspended oyster grow bags, predator exclusion nets, loose oyster beds, and other shellfish grow‐out gear. As interest and investment in shellfish aquaculture have expanded both locally and globally, so has interest in how these farms modify intertidal habitat and whether the complex structure created by the shellfish and shellfish growing gear provides ecosystem services that are comparable to those of unfarmed areas, such as mudflats and eelgrass meadows.MethodsIn this study, we sought to quantify how shellfish farms are used as foraging habitat for several common nearshore species of fish and crabs in Puget Sound, Washington. We used direct observations of species‐specific behaviors from underwater video to model how habitat type affected observed foraging rates.ResultWe obtained a total of 393 crab observations, 431 demersal fish observations, and 1856 pelagic fish observations across all seven farm sites. Several common species of pelagic fish (e.g., surfperch [Embiotocidae]) used aquaculture‐growing gear more frequently than unfarmed areas as foraging habitat, but Metacarcinus spp. crabs displayed higher foraging frequency in unfarmed mudflats. Species groups such as sculpins (Cottidae) and small flatfish (Pleuronectidae) clearly used specific aquaculture‐growing gear and mudflats in roughly equal proportion.ConclusionOur results indicate that shellfish farms within a larger nearshore habitat mosaic of eelgrass meadows, mudflats, bivalve aquaculture gear, and edge habitat can provide foraging habitat for several species of nearshore fish.

Unexpected dietary preferences of Eurasian Spoonbills in the Dutch Wadden Sea: spoonbills mainly feed on small fish not shrimp

After an historical absence, over the last decades Eurasian Spoonbills Platalea leucorodia leucorodia have returned to breed on the barrier islands of the Wadden Sea. The area offers an abundance of predator-free nesting habitat, low degrees of disturbance, and an extensive intertidal feeding area with increasing stocks of brown shrimp Crangon crangon, the assumed main prey of P. leucorodia leucorodia. Nevertheless, newly established and expanding colonies of spoonbills have surprisingly quickly reached plateau levels. Here we tested the often stated assertion that spoonbills mainly rely on brown shrimp as food, by quantifying the diet of chicks on the basis of regurgitates and by analysis of blood isotopes using stable isotope Bayesian mixing models. Both methods showed that, rather than brown shrimp being the staple food of spoonbill chicks, small flatfish (especially plaice Pleuronectes platessa) and gobies (Pomatoschistus spp.) were their main prey. Unlike shrimp, small flatfish have been reported to be rather scarce in the Wadden Sea in recent years, which may explain the rapid saturation of colony size due to food-related density-dependent recruitment declines of growing colonies. By way of their diet and colony growth characteristics, spoonbills may thus indicate the availability of small fish in the Wadden Sea. We predict that the recovery to former densities of young flatfish and other juvenile/small fish in the Wadden Sea will be tracked by changing diets (more fish) and an increase in the size of Eurasian Spoonbill colonies across the Wadden Sea.

Brandt's cormorant diet (1994–2012) indicates the importance of fall ocean conditions for northern anchovy in central California

AbstractEffective ecosystem‐based management requires a comprehensive understanding of the functional links in the system. In many marine systems, forage species constitute a critical link between primary production and upper trophic level marine predators. As top predators, seabirds can be indicators of the forage species they consume and the ocean processes that influence these populations. We analyzed the diet and breeding success for the years 1994, 2003, 2005, and 2007–2012 of the Brandt's cormorant (Phalacrocorax penicillatus), a piscivorous diving seabird, breeding in central California, to evaluate the extent to which cormorant diet composition relates to prey availability, and how diet composition relates to breeding success and ocean conditions. Cormorant diet was primarily composed of young‐of‐the‐year (YOY) northern anchovy (Engraulis mordax), YOY rockfish (Sebastes spp.), and several species of small flatfish (order Pleuronectiformes). YOY rockfish consumption was positively related to their abundance as measured in a late spring pelagic midwater trawl survey. Northern anchovy appeared to be the most important prey as its consumption was positively related to cormorant breeding success. More northern anchovy were consumed in years where warm‐water conditions prevailed in the fall season before cormorant breeding. Thus, warm ocean conditions in the fall appear to be an important contributing factor in producing a strong year‐class of northern anchovy in central California and consequently a strong‐year class of Brandt's cormorant on the Farallon Islands.

Diet of the harbour sealPhoca vitulina: implication for the flatfish nursery in the Bay of Somme (English Channel, France)

Changes in marine species abundance can impact ecosystems’ stability and sustainability of fisheries. In the eastern Atlantic Ocean, harbour seals (Phoca vitulina) are top predator occupying highest trophic level in coastal marine food webs. Although, the overall European population decline, harbour seals have increased dramatically since the 1990’s at the southern limit of their European distribution along the French coast of the English Channel. However, little is known about the feeding habits of the expanding peripheral populations limiting the assessment of the role and the impact of this predator in these coastal ecosystems. Here, we investigated the sex-specific diet of harbour seals during summer in the Bay of Somme, the largest colony in the English Channel. We collected 91 faecal samples from haul-out sites mainly used by harbour seal but also by few grey seals. Molecular methods have been used to discard grey seal samples and differentiate gender. Collectively, the 86 faecal samples of harbour seals contained the remains of 3327 prey belonging to at least 13 fish species, and represented ~109 kg of consumed fish (of which 85% were soles and plaices). Most of the fish consumed were juvenile and small flatfish (Buglossidium luteum, Microchirus variegatus, Solea vulgaris, Pegusa lascaris, Pleuronectes platessa and Platichthys flesus). Hard-part identification further showed a similar diet between the sexes in terms of primary prey consumed, but a greater diversity of preys in the male diet. The dependence of harbour seals on flatfish has not been reported elsewhere and has significant implications for the sustainability of the important flatfish nursery in the Bay of Somme. Consumption estimation and ecosystem modelling are now required to provide robust assessment of the effect of harbour seal predation on population dynamics of the flatfish nursery, on ecosystem of the Bay of Biscay at-large, and finally on interactions with fisheries.

The complete mitochondrial genome of Zebrias quagga (Pleuronectiformes: Soleidae)

Zebrias quagga (Soleoidei, Soleidae) is a sort of small and medium-sized commercial flatfish, characterized by both eyes on the right side of the body and with a dark brown short tentacle on each eye. In this paper, the complete mitogenome sequence of Z. quagga was first determined, which is 17,045 bp in length and contains 13 protein-coding genes, two rRNA genes, 22 tRNA genes, as well as a control region (CR) and a L-strand replication origin (OL). Gene contents, locations, and orders are identical to those of typical teleostean mtDNA. The nucleotide composition of the whole mitogenome is 28.8%, 29.3%, 15.8%, and 26.1% for A, C, G, and T, respectively, with a slight bias of A+T content (54.9%). This result is expected to contribute to a better understanding the phylogenetic study of Soleidae and Pleuronectiformes.

Diet composition and resource partitioning in two small flatfish species in the German Bight

Since the late 1980s, the small-sized non-commercial flatfish species solenette ( Buglossidium luteum) and scaldfish ( Arnoglossus laterna) have increased in abundance in the southern North Sea. Because these species are considered as possible competitors for prey of commercial flatfish, this study aimed at advancing knowledge of their feeding ecology. Between January 2009 and January 2010 stomach contents of solenette and scaldfish and benthic infauna were sampled seasonally in a study area in the German Bight. The objectives were to investigate the seasonal variability of feeding activity and diet composition of both flatfish species related to benthic prey availability. For both flatfish, the highest feeding activity was found in summer, at the same time that the highest prey densities occurred in the study area. A reduced feeding activity was observed during the winter of 2010, but not in the winter of 2009, probably related to higher 2009 water temperatures. In all seasons, diet composition of solenette was dominated by meiofauna, mainly harpacticoid copepods. Macrofauna prey species, namely juveniles of bivalves and echinoderms became important in spring. An increase in amphipods and cumaceans was found in the stomach contents during summer and autumn, simultaneously with their increased abundance in the benthic infauna. In contrast, polychaetes were rarely found in the diet, but dominated the infauna during all seasons. Diet composition of scaldfish was dominated by larger and mobile prey, and, during all seasons, was mainly comprised of crustaceans. Amphipods characterised the diet in both winters, while decapods such as Crangon spp. and Liocarcinus spp. were the dominant prey from spring to autumn. Additionally, juveniles of flatfish (Pleuronectids) and bivalves were found in the scaldfish diet in spring, replaced by cumaceans in summer. No dietary overlap between both flatfish species was found across seasons, indicating partitioning of prey resources between solenette and scaldfish. Their different feeding strategies and prey preferences, in turn were influenced by the seasonal variability of available prey.

Trawl net modifications to reduce the bycatch of eulachon ( Thaleichthys pacificus) in the ocean shrimp ( Pandalus jordani) fishery

Two trawl gear modifications for reducing fish bycatch (weight) in ocean shrimp ( Pandalus jordani) trawls were tested in June and August–September 2010. The primary focus of the study was evaluating trawl system modifications for reducing bycatch of eulachon ( Thaleichthys pacificus) below levels already achieved via mandatory use of bycatch reduction devices (BRDs). An experimental footrope, modified by removing the central one third of the trawl groundline, reduced eulachon bycatch by 33.9%. It also reduced bycatch of slender sole ( Lyopsetta exilis), other small flatfishes and juvenile darkblotched rockfish ( Sebastes crameri) by 80% or more, but had no effect on bycatch of whitebait smelt ( Allosmerus elongatus) or Pacific herring ( Clupea pallasii). The experimental groundline also reduced the catch of ocean shrimp (weight) by 22.2% in hauls yielding commercial quantities of shrimp (>194 kg/haul) and by 23.2% in all hauls. Reducing bar spacing in a rigid-grate BRD from 25.4 mm to 19.1 mm reduced eulachon bycatch by 16.6%, with no reduction in ocean shrimp catch. It also reduced bycatch of slender sole, other small flatfish and juvenile darkblotched rockfish by 36.8%, 71.8% and 76.3%, respectively with no effect on bycatch of whitebait smelt or young-of-the-year (YOY) Pacific hake ( Merluccius productus). Although both trawl modifications reduced eulachon bycatch, the footrope modification tested, if developed further, has the potential to also avoid trawl entrainment for some demersal fishes, as well as reduce bottom impacts from trawling.

The role of flatfishes in the organization and structure of the eastern Bering Sea ecosystem

We evaluated the role of flatfishes in the organization and structure of the eastern Bering Sea ecosystem using the Ecopath/Ecosim approach. As basic input data for the Ecopath/Ecosim model, we used estimates of biomass from bottom trawl surveys and age-structured population models, production/biomass (P/B) ratio, consumption/biomass (Q/B) ratio, diet composition (DC), and fisheries harvests for each component of species or species groups. We estimated the trophic level of each component, niche overlaps among flatfishes, and the impacts of competition and predation on flatfish species in the eastern Bering Sea ecosystem. Based on those estimates, we developed the tropho-dynamic structure of the ecosystem, and the model was used to simulate ecological effects of fishery exploitation patterns. No single flatfish species appeared to have a profound and uniquely important role in the organization and structure of the ecosystem. Instead, the most important component among the guild of flatfish species appeared to be yellowfin sole Pleuronectes asper, which had greater biomass than other flatfish and a relatively diverse diet among the small flatfish species. Pacific halibut Hippoglossus stenolepis, Greenland turbot Reinhardtius hippoglossoides, and arrowtooth flounder Atheresthes stomias were important keystone predators in the eastern Bering Sea ecosystem together with some groups of marine mammals and sea birds. Intra flatfish complex cannibalism was not observed, however, substantial diet overlaps were common in the flatfish guild system.

How climate warming impacts the distribution and abundance of two small flatfish species in the North Sea

Climate change, specifically temperature, affects the distribution and densities of species in marine and terrestrial ecosystems. Here, we looked at the effect of temperature during winter and spawning period on latitudinal range shifts and changes in abundance of two non-commercial North Sea fish species, solenette ( Buglossidium luteum) and scaldfish ( Arnoglossus laterna). Both species have increased in abundance and moved to the north since the late 1980s, coinciding with a series of mild winters. In 1996, following a very cold winter, the abundance of both species temporarily decreased as they retracted to the south. The shift in temperature affected adult habitat conditions, allowing them to immigrate into new areas where they subsequently reproduced successfully. We can conclude this because recruitment improved following the increase in abundance. The recruitment relates significantly to the higher adult stock and higher temperatures. The predictions of higher average temperatures and milder winters in the North Sea make it likely that these species will increase further in abundance and move northward. The observed increase in abundance of these small flatfish species will affect the North Sea food web and therefore commercial species, e.g. plaice, by predation on juveniles and competition for benthic food resources.

Fishing effects on energy use by North Sea fishes

Fishing affects patterns of energy use in fish populations, as demonstrated by changes in population energy consumption and the size and age when energy demands are greatest. We compare theoretical predictions and observed patterns of energy use (expressed as the primary production required to support fish production) by North Sea fish, based on simple and widely applicable theory that links life history parameters, fishing mortality ( F), trophic transfer efficiency and relationships between size and trophic level (as determined using nitrogen stable isotope analysis). For the demersal species that dominate total biomass, relationships between size and trophic level were quite consistent among years. There were large decreases in relative energy requirements of all exploited demersal populations except plaice Pleuronectes platessa during the last 3 to 4 decades. Relative energy requirements of plaice were more stable because smaller plaice, which now dominate the exploited population, feed at higher trophic levels than larger plaice. The sizes and ages when population energy demands were greatest fell with increasing fishing mortality and differences between the predicted ( F = 0) and observed ages at maximum energy demand were greater in larger species. Currently, the energy demands of most species peak early in life (1–3 years) and largely reflect patterns of recruitment, leading to a homogenisation of the trophodynamics of the fish community. The fate of energy that is no longer used by commercially exploited species is not clear, partly because of the infrequent and untargeted monitoring of species that are more resilient to fishing. However, we conducted a preliminary assessment of the energy demands of solenette Buglossidium luteum, a very abundant small flatfish in the central North Sea that has increased in abundance in recent years. The solenette's high abundance and resilience to fishing, suggests that it now requires 35% of primary production in part of the central North Sea, energy that may have supported larger species in a less heavily fished ecosystem.

Presence of larger flatfish modifies habitat preference by Age-0 northern rock sole Lepidopsetta polyxystra

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 342:227-238 (2007) - doi:10.3354/meps342227 Presence of larger flatfish modifies habitat preference by Age-0 northern rock sole Lepidopsetta polyxystra Clifford H. Ryer1,*, Allan W. Stoner1, Mara L. Spencer1, Alisa A. Abookire2 1Fisheries Behavioral Ecology Program, Alaska Fisheries Science Center, NOAA Fisheries, Hatfield Marine Science Center, Newport, Oregon 97365, USA 2Alaska Fisheries Science Center, NOAA Fisheries, Kodiak Laboratory, 301 Research Court, Kodiak, Alaska 99615, USA *Email: cliff.ryer@noaa.gov ABSTRACT: Essential fish habitat (EFH) is poorly defined for the early stages of most commercially important species. Age-0 flatfish making summer use of shallow coastal embayments around Kodiak Alaska distribute themselves according to a variety of bottom features. Both field and laboratory studies indicate that the numerically dominant species, northern rock sole Lepidopsetta polyxystra and Pacific halibut Hippoglossus stenolepis, demonstrate an affinity for seafloor with emergent structure: algae, shell, worm-tubes, etc. We conducted field manipulations, in which bivalve shell was scattered on the seafloor along 100 m transects, with the goal of examining movements of juvenile flatfish in response to these habitat alterations. In the first manipulation, contrary to expectations, Age-0 flatfish emigrated from the shell-enhanced seafloor, producing fish densities that were lower than on adjacent un-enhanced bottom. In comparison, larger flatfish, predominantly Age-1+ rock sole Lepidopsetta spp., increased in abundance on shell-enhanced bottom. Small flatfish may have moved to avoid larger flatfish. The manipulation was repeated at another site with similar physical features, but where large flatfish abundances are generally lower. This time, Age-0 flatfish densities were greater on the shell-enhanced bottom than on adjacent un-enhanced bottom. Again, large flatfish were more abundant on the shell bottom, but they were nearly an order of magnitude less abundant than in the first manipulation. In a subsequent laboratory experiment, Age-1 northern rock sole demonstrated stronger affinity for shell bottom than did Age-0 northern rock sole. In another experiment, Age-0 northern rock sole moved to avoid aggregations of larger conspecifics as well as other species of large flatfish. We conclude that these Age-0 flatfish, predominantly northern rock sole, perceive larger fish as predators and/or competitors, with habitat quality degraded by their presence. These results demonstrate that habitat quality for juvenile fish is influenced by biotic factors as well as by physical characteristics of habitat. KEY WORDS: Habitat complexity · Habitat quality · Rock sole · Pacific halibut · Predator-prey interactions · Competitive interactions · Essential fish habitat · Indirect predation effects Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 342. Online publication date: July 24, 2007 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2007 Inter-Research.

Top-down modeling and bottom-up dynamics: Linking a fisheries-based ecosystem model with climate hypotheses in the Northern California Current

In this paper we present results from dynamic simulations of the Northern California Current ecosystem, based on historical estimates of fishing mortality, relative fishing effort, and climate forcing. Climate can affect ecosystem productivity and dynamics both from the bottom-up (through short- and long-term variability in primary and secondary production) as well as from the top-down (through variability in the abundance and spatial distribution of key predators). We have explored how the simplistic application of climate forcing through both bottom-up and top-down mechanisms improves the fit of the model dynamics to observed population trends and reported catches for exploited components of the ecosystem. We find that using climate as either a bottom-up or a top-down forcing mechanism results in substantial improvements in model performance, such that much of the variability observed in single species models and dynamics can be replicated in a multi-species approach. Using multiple climate variables (both bottom-up and top-down) simultaneously did not provide significant improvement over a model with only one forcing. In general, results suggest that there do not appear to be strong trophic interactions among many of the longer-lived, slower-growing rockfish, roundfish and flatfish in this ecosystem, although strong interactions were observed in shrimp, salmon and small flatfish populations where high turnover and predation rates have been coupled with substantial changes in many predator populations over the last 40 years.

Reproductive evaluation of triploid yellowtail flounder, Limanda ferruginea (Storer)

The reproductive effects of induced triploidy were assessed in 3-year-old yellowtail flounder. Diploids of this small flatfish show a propensity for early sexual maturation in culture. Triploidy was effective in reducing gonadal development in yellowtail flounder, but permitted physiological maturation in both sexes. Triploid males sampled during the regular spawning period in captivity had small testes and variable plasma androgen levels ( n=7; age, 34 months). A limited production of spermatozoa and evidence of spermatogenetic dysfunction were noted histologically. Spermatozoa from triploids exhibited poor or no motility and further demonstrated reduced fertility in fertilization trials with eggs from diploid females. Most larvae resulting from fertilization trials were abnormal and nonviable; however, some triploid males produced a few larvae of normal appearance which may indicate long-term viability. Females sampled at 37 and 40 months of age had small ovaries with varying numbers of oocytes, previtellogenic to vitellogenic, that were developing amid oogonial tissue (oog). Evidence of prior summer ovulatory activity was found in 2 of the 17 females. A high proportion of the remaining 3-year-old females had vitellogenic oocytes and was likely to become fully mature by 4 years of age. Plasma estradiol-17β (E 2) levels were low in triploid females despite the fact that ovarian tissue from pubertal triploids can demonstrate a strong steroidogenic response to gonadotropic stimulation in vitro. The production of triploids will help to reduce the energetic costs of reproduction in the yellowtail flounder.

Diet of the harbour seals Phoca vitulina of Dundrum Bay, north-east Ireland

This study has shown that the main constituents of the diet of the harbour seals (Phoca vitulina) of Dundrum Bay, County Down, north-east Ireland, during the past few years (1995–2000) have been small flatfish and gadid fish, with the emphasis shifting from the beginning to the end of the study period from flatfish to gadids, principally whiting and haddock/pollack/saithe. During both 1995 and 1996 the diet of post-weaning pups consisted almost entirely of small gadid fish. The implications of this relatively poor diet, apparently deficient in oily fish, are considered—together with information on fish stocks in the north-west Irish Sea in recent years—in the context of an apparent decline both in the breeding population of harbour seals along the County Down coast and in the play behaviour of juvenile seals.

Etropus crossotus, an annual flatfish species; age and growth of the fringed flounder in South Carolina

Fringed flounder, Etropus crossotus, a small flatfish common along the southeastern coast of the US, were collected along the South Carolina coast in the fall of 1992, and in the North Inlet estuary from August 1992 until July 1994. Standard length was 82% of total length and the relationship between standard length and wet weight showed near-isometric growth with no significant differences between males and females. Dry weight was 21% of wet weight and ash-free dry weight 14% of wet weight with no significant differences between sexes. Daily increments in the sagittal otoliths were used for age determination. No annual structures could be identified. The maximum age was about 14.5 months. Age-at-length was not different between the sexes. The relationship between age and length was exponential, with age (in days) equalling an e power of 4.242 + 0.135 × standard length (in cm). Back-calculated hatch dates and catches of early juveniles indicated a spawning season that lasted from March to October. Females started to be sexually mature at 7 to 7.5 cm standard length, but 50% maturity was reached at 8 to 8.5 cm. Females could grow to that size within one spawning season. Individuals hatched early in the spawning season could produce eggs in the latter portion of that season's spawning period.

Prey selection by the hogchoker, Trinectes maculatus (Pisces: Soleidae), along summer salinity gradients in Chesapeake Bay, USA

We investigated feeding by the hogchoker, Trinectes maculatus (Bloch and Schneider), in freshwater, oligohaline, mesohaline, and polyhaline regions of Chesapeake Bay, USA, and examined prey selection in relation to food availability. Otter trawling for fish and Van Veen grab sampling for benthic macrofauna occurred in July and August 1992 and August and September 1993. Hogchokers exhibited both opportunistic and selective feeding patterns along the estuarine salinity gradient in four tributaries (Potomac, Rappahannock, York, and James Rivers) and in the mainstem Chesapeake Bay. Major prey taxa included annelids, arthropods, and tellinid siphons. In polyhaline habitat, polychaetes dominated both the benthos and gut contents numerically and gravimetrically. On the other hand, oligochaetes were numerically dominant in freshwater/oligohaline areas but were rarely eaten, perhaps because of their burial depth. Arthropods (mostly amphipods) occurred at most salinities, were common in gut contents in low-salinity areas, and were replaced as prey by larger proportions of polychaetes in polyhaline regimes. Although hogchokers ate tellinid siphons, they rarely consumed whole bivalves or gastropods. These diet patterns (and especially the importance of siphon nipping) are similar to those of juvenile or small flatfish elsewhere in Europe, Africa, and North America. A size–salinity relationship for hogchokers occurred along the summer salinity gradient, with smaller fish predominating upstream and larger fish downstream. It was not clear from our data if variation in diet composition reflected changes in prey composition along the salinity gradient rather than changes in fish size.

The summer food of turbotPsetta maxima(L.) off the Coast of Galicia, N.W. Spain

Abstract The diet of the turbot (Psetta maxima (L.)), offthe Galician coast was deduced from the stomach contents of specimens caught by fishing boats. The frequency of occurrence, numbers and weight of each prey were determined, and overall prey im portance was measured by the index of relative importance (IRI), a function of all three. Young turbot were found to feed on mysids, decapods and small fish such as ammodytids, callionymids and small flatfish. Larger individuals preferred other kinds offish, especially the gadoids Micromesistius poutassou, Trisopterus luscus and T. minutus and clupeoids such as Sardina pilchardus, while continuing to eat decapods, mainly brachyurans. The difference between the diets of males and females appears to be related to the latter's greater mean length.

Community Structure of the Demersal Fish Species of Laguna Joyuda, Puerto Rico

A year-long trawl survey of the mangrove-fringed Laguna Joyuda, Puerto Rico yielded 41 species of juvenile and adult fishes. Twelve percent of the species and 55% of the individuals were residents in the lagoon; 56% of the species and 44% of the individuals were cyclic visitors, mostly juveniles of species which spawn offshore. The lagoon yielded fewer species than tropical estuaries in continental regions of the Caribbean and temperate estuaries of North America. However, paralleling other estuarine habitats, Laguna Joyuda supported three primary types of fishes, a resident small flatfish (Achirus lineatus), a complex of transient juveniles (Gerreidae, paralleling the Sciaenidae of higher latitudes), and small planktivores (Anchoa spp.). Seasonal patterns in the abundance of individual species were not strong, but overall abundance showed a wet season maximum, particularly because of recruitment of anchovies and cyclic visitors in April, May, and June. Wet season abundance corresponded with highest water column productivity and detrital input to the benthos. Fishes associated with the water column appeared to show greater variation in abundance than those associated with more stable benthic food webs.

Production, Predation and Food Niche Segregation in a Marine Shallow Soft-Bottom Community

A shallow soft bottom in Gullmar Fjord (Sweden) was investigated in order to determine the impact by epibenthic predators and possible competition for food between CO-occurring shrimp and fish species. Large numbers of the shrimp Crangon crangon, juvenile plaice Pleuronectesplatessa and sand goby Pornatoschistus rninutus aggregated during summer in shallow areas and fed on benthic macroand meiofauna. Predation impact was calculated using estimates of gross production efficiencies and productlon rates. In 1976 and 1977, yearly predation amounted to 12 and 17 %, respectively, of the total macroand meiofauna productlon. The low exploitation rate of the benthic community contradicts the hypothesis that predation should be the major extrinsic determinant keeping population levels below the carrying capacity of the environment. Shallow soft bottoms provide an abundant food supply that will neither limit growth nor produce severe competition between the epibenthic predators, although their diets are almost identical. It IS suggested that larger predators will control the abundance of epibenthic feeders such as shrimp, gobies and small flatfish inhabiting shallow water.