bluuebunny/crossref_metadata_2025 huggingface dataset:
Introduced and translocated fish species in the inland waters of Greece
Authors: Economidis P. S. , Dimitriou E. , Pagoni R. , Michaloudi E. , Natsis L.
Published: March 2003

Over the last 7 decades, 23 exotic fish species have been introduced into the inland waters of Greece. Some introductions were deliberately planned to take advantage of particular ecological or economic qualities of the species concerned. These include rainbow trout, Oncorhynchus mykiss (Walbaum), Pacific salmon, Oncorhynchus sp., vendace, Coregonus lavaretus (L.), grass carp, Ctenopharyngodon idella (Valenciennes), and silver carp, Hypophthalmichthys molitrix (Valenciennes). Other introductions, such as that of pumpkinseed, Lepomis gibbosus (L.), and false rasbora, Pseudorasbora parva (Temminck & Schlegel), were unintentional. Further transfers were made of species between various basins within the country, including common carp, Cyprinus carpio L., tench, Tinca tinca (L.), crucian carp, Carassius auratus gibelio (Bloch), bitterling, Rhodeus amarus (Bloch), and Aristotle's catfish, Silurus aristotelis Garman. Some species have become fully acclimatized and have built up important populations. In other cases, the transfers and introductions have had considerable negative impacts, particularly where introduced species have outcompeted native forms, as in the cases of the mosquito fish, Gambusia affinis (Baird & Girard), versus Greek toothcarp, Valencia letourneuxi (Sauvage), in the western Greek marshes, and of Aristotle's catfish versus the wels, Silurus glanis L., in Lake Volvi.
Threats imposed by water resource development schemes on the conservation of endangered fish species in the Guadiana River Basin in Portugal
Authors: Collares‐Pereira M. J. , Cowx I. G. , Ribeiro F. , Rodrigues J. A. , Rogado L.
Published: March 2003

The distribution and abundance of many of the 23 native fish species of the Guadiana River basin in Portugal have declined markedly in the past 20 years. This is because of increased pressure to exploit the water resources of the catchment for domestic supply, agriculture and recreation, but also as a result of general habitat degradation and the introduction of exotic species. Thirteen reservoirs have already been constructed in the region and a further 25 proposals have been put forward, mainly to supply the tourist sector in the south of the country. As a result of these activities, one species of fish, Anaecypris hispanica (Steindachner), is critically endangered. The present paper examines the status of the populations of A. hispanica in the Guadiana in Portugal, assesses the impact of water resource schemes on the stocks and general biodiversity, and suggests management options for conserving and enhancing the already degraded stocks.
Occurrence of canthaxanthin in Atlantic salmon, Salmo salar L., fry in Irish rivers as an indicator of escaped farmed salmon
Authors: Poole W. R. , Webb J. H. , Matthews M. A. , Youngson A. F.
Published: March 2003

The rapid growth of Atlantic salmon, Salmo salar L., culture in north‐western Europe has given rise to concerns regarding the biological consequences of fish farm escapes on wild salmonid populations. Canthaxanthin, a carotenoid pigment additive to farmed salmon feed which is passed from females to their progeny, may be used as an indicator of the numbers of escaped farmed salmon which spawn in the wild. In the present study, thin‐layer chromatography and high‐performance liquid chromatography (HPLC) were used to screen emergent Atlantic salmon fry sampled from seven river catchments in Ireland for canthaxanthin. The incidence of fry containing canthaxanthin at greater than trace levels (<5% of total carotenoid pigment) was 0–4%, with an average of 1.7%, among the seven rivers sampled, indicating that the progeny of farmed salmon were present at similarly low frequencies. Canthaxanthin was detected at trace levels in an unexpectedly high proportion (35%) of salmon fry. Canthaxanthin was present at levels exceeding trace amounts in 24% of 21 non‐anadromous brown trout, Salmo trutta L., sampled from six Irish rivers and present at trace levels in a further 57% of the fish, indicating that dietary canthaxanthin is freely available to salmonids in Irish rivers. The widespread presence of trace levels in salmon fry may be attributable, at least in part, to the increased sensitivity of the HPLC methods and to rapid dietary uptake during early post‐emergence feeding.
Eutrophication and Recreational Fishing on the Finnish Coast of the Gulf of Finland: A Mail Survey
Authors: Lappalainen A. , Pönni J.
Published: March 2003

The Gulf of Finland is one of the most eutrophic areas in the Baltic Sea and is also the main fishing area for more than 150 000 recreational fishermen in Finland. The findings of a mail survey showed that the most important species for the recreational fishery is perch, Perca fluviatilis L. There is no clear evidence that eutrophication has had a harmful effect on the stocks of perch and other species considered important. Heavy fouling of gear, particularly gill nets, is the most acute problem caused by eutrophication to the local recreational fishery. The rapid fouling of passive gear was experienced by 67–86% of all fishermen in the three study areas. A general deterioration in water quality was perceived because only 2–14% of fishermen rated the water quality as excellent. However, a minority of recreational fishermen seem to have adapted or grown accustomed to the deterioration in water quality. Even in the two most eutrophic study areas, 23–31% of recreational fishermen considered that an improvement in local water quality would not benefit their own fishing in any way.
Seasonal movements of silver kob, Argyrosomus inodorus, (Griffiths and Heemstra) in Namibian waters
Authors: Kirchner C. H. , Holtzhausen J. A.
Published: March 2003

A seasonal migration pattern for silver kob, Argyrosomus inodorus (Griffiths & Heemstra) is elucidated based on tag‐recapture data. Spawning adults start migrating southwards against the north‐westerly surface currents at the beginning of the austral summer from the northern end of their distributional range to their spawning grounds, Sandwich and Meob Bays, at the southern end of their distributional range. It is suggested that after spawning larvae drift north with the current to the nursery areas, the West coast Recreational area (WCR). When juveniles reach the age of approximately 2 years they will gradually move north towards the adult feeding ground, the Skeleton Coast Park (SCP) waters. At the end of the spawning season when the surf‐zone water temperature decreases to about 15 °C adult silver kob complete their spawning cycle by returning to the adult feeding ground, probably moving slightly offshore and with the current.
The onset of downstream movement of juvenile Atlantic salmon, Salmo salar L., in a chalk stream
Authors: RILEY W. D. , EAGLE M. O. , IVES S. J.
Published: March 2003

The downstream movements of wild Atlantic salmon, Salmo salar L., from their established feeding territories in the River Itchen, Hampshire, UK, were logged continuously over an 11‐month period using a passive integrated transponder (PIT) antenna system. The time of these movements was then related to a number of monitored and calculated environmental parameters. Initial downstream movement of smolts in April was correlated with the onset of darkness, at which time salmon moved from their established feeding territories alone. No relationship was found between the number of smolts migrating and river flow or maximum daily water temperature. The timing of downstream movement of parr between October and March was random with regard to sunset and time of maximum daily water temperature, suggesting the environmental cue that initiates movement may be different outside the spring smolt period.
Genetic diversity and translocation in the marron, Cherax tenuimanus (Smith): implications for management and conservation
Authors: NGUYEN T. T. T. , MEEWAN M. , RYAN S. , AUSTIN C. M.
Published: March 2003

Approximately 440 base pairs (bp) of the mitochondrial 16S ribosomal ribose nucleic acid (rRNA) coding region were sequenced from 13 marron, Cherax tenuimanus (Smith), samples from six locations and samples of two additional Cherax species from Western Australia. The results indicated that, with the exception of the Margaret River, no variation was found within or between marron populations. In contrast, marron from the Margaret River were found to be polymorphic for two divergent haplotypes (2.76% divergence). These findings were consistent with allozyme data that highlight the general lack of genetic variability within and between populations of this species apart from the Margaret River stocks. The genetic polymorphisms in the Margaret River stocks contrasted with earlier studies and indicated the recent translocation and mixing of genetically differentiated stocks within this river system. The implications of these findings for the conservation and management of genetic diversity within marron are discussed.
Juvenile growth and survival of heat‐shocked triploid hybrid saugeyes, Stizostedion vitreum × S. canadense
Authors: GARCIA‐ABIADO M. A. R. , LYNCH W. E. , DABROWSKI K. , CZESNY S. , RINCHARD J. , STAFFORD J.
Published: March 2003

Triploid hybrid saugeyes may be a desirable stocking alternative because diploid saugeyes are fertile and can compromise the genetic integrity of parental stocks. Four groups of saugeye eggs were heat‐shocked 5 min after fertilization for 15 min at 31 °C, which resulted in an 86.7 ± 9.4% triploidy rate and 57.8 ± 24.3% survival to the eyed‐stage. Heat shocked and control saugeyes were stocked in two ponds for 40 days at 395 000 ind. ha–1. Mean length and weight of triploid and heat‐shocked diploid saugeyes were greater (P < 0.01) than unshocked diploid saugeyes. Survival of heat‐shocked saugeyes (22.4%) was lower than unshocked saugeyes (94.7%). Heat‐shocked fish (n=25 851) harvested from ponds were stocked for 153 days in O'Shaughnessy Reservoir, Ohio, USA. Triploids were 34 mm shorter and weighed 41 g less than heat‐shocked diploids (P < 0.01). Mean length and weight of triploids were comparable with unshocked diploids elsewhere in Ohio.
An assessment of yellow perch, Perca flavescens, stocking contributions in eastern South Dakota lakes
Authors: BROWN M. L. , SAUVER T. St.
Published: March 2003

The success and value of yellow perch, Perca flavescens (Mitchill), stocking programmes are largely unknown because of the difficulties in differentiating between naturally recruited and translocated stocks. To determine stocking contributions of yellow perch, fingerlings and adults were collected from natural rearing ponds in south‐eastern South Dakota. Prior to stocking, all fish were marked for 6 h in transfer tanks containing 700 mg L−1 oxytetracycline hydrochloride. Six lakes containing yellow perch populations were supplemented at low, medium and high stocking densities of about 25, 135 or 200 fish ha−1, respectively. Yellow perch populations were subsequently sampled with experimental gill nets during late summer; two lakes were resampled with additional gears (electric fishing, trap nets and cloverleaf traps). Yellow perch were processed for routine measurements, and saggital otoliths were removed to determine the origin of the fish. Stock contribution estimates determined from gill‐net samples for Island (low), Oak (low), Twin (medium) and Wall (high) lakes were approximately 18, 5, 41, and 38%, respectively. Samples from other gears provided stock contributions of 15 and 10% for Cavour Lake and 41% for Diamond Lake (high density stockings). Although these results showed that supplemental stockings were successful, variability in stock contributions among populations indicates a need for further assessment of variables that may influence the stocking success of yellow perch.
The Irish sea trout enhancement programme: an assessment of the parr stocking programme into the Burrishoole catchment
Authors: BYRNE C. J. , POOLE W. R. , DILLANE M. G. , WHELAN K. F.
Published: March 2003

The success of the sea trout, Salmo trutta L., enhancement programme carried out in the Burrishoole catchment in the west of Ireland from 1993 until 1998 is reviewed in terms of the number of fish stocked, the number of fish which migrated to sea and the number which returned from sea during this period. The success of the programme is also evaluated in terms of the cost of producing parr for stocking and the subsequent value of returning post‐smolts (0+ sea age) and rod caught fish. A total of 49 235 tagged fish were released into Lough Feeagh, between 1993 and 1998. Of these fish, 14 788 were microtagged and the remainder, 34 447 had either elastomer or alphanumeric visible implant (VI) tags. Tag loss rates at release varied from 3 to 5.7%. Over the course of the programme a maximum of 7801 fish migrated through the traps towards sea, of which 581, or 7.4%, returned. In any 1 yr a maximum 13.1% of fish returned from sea. The average cost of producing a parr for stocking out was €1.15, which translated into average values of €8.16 per smolt and €169 per returning post‐smolt.
Predicting skipjack tuna forage distributions in the equatorial Pacific using a coupled dynamical bio‐geochemical model
Authors: LEHODEY PATRICK , ANDRE JEAN‐MICHEL , BERTIGNAC MICHEL , HAMPTON JOHN , STOENS ANNE , MENKES CHRISTOPHE , MEMERY LAURENT , GRIMA NICOLAS
Published: March 2003

Skipjack tuna (Katsuwonus pelamis) contributes ≈70% of the total tuna catch in the Pacific Ocean. This species occurs in the upper mixed‐layer throughout the equatorial region, but the largest catches are taken from the warmpool in the western equatorial Pacific. Analysis of catch and effort data for US purse seine fisheries in the western Pacific has demonstrated that one of the most successful fishing grounds is located in the vicinity of a convergence zone between the warm (>28–29°C) low‐salinity water of the warmpool and the cold saline water of equatorial upwelling in the central Pacific (Lehodey et al., 1997). This zone of convergence, identified by a well‐marked salinity front and approximated by the 28.5°C isotherm, oscillates zonally over several thousands of km in correlation with the El Niño–Southern Oscillation. The present study focuses on the prediction of skipjack tuna forage that is expected to be a major factor in explaining the basin‐scale distribution of the stock. It could also explain the close relation between displacements of skipjack tuna and the convergence zone on the eastern edge of the warmpool. A simple bio‐geochemical model was coupled with a general circulation model, allowing reasonable predictions of new primary production in the equatorial Pacific from mid‐1992 to mid‐1995. The biological transfer of this production toward tuna forage was simply parameterized according to the food chain length and redistributed by the currents using the circulation model. Tuna forage accumulated in the convergence zone of the horizontal currents, which corresponds to the warmpool/equatorial upwelling boundary. Predicted forage maxima corresponded well with high catch rates.
An adjoint data assimilation approach to diagnosis of physical and biological controls on Pseudocalanus spp. in the Gulf of Maine–Georges Bank region
Authors: MCGILLICUDDY D. J. , LYNCH D. R. , MOORE A. M. , GENTLEMAN W. C. , DAVIS C. S. , MEISE C. J.
Published: March 2003

The underlying scientific objective here is to determine the mechanisms that control seasonal variations in the abundance of Pseudocalanus spp. in the Georges Bank–Gulf of Maine region. It is postulated that the observed distributions result from the interaction of the population dynamics with the climatological circulation. The problem is posed mathematically as a 2‐D advection–diffusion–reaction equation for a scalar variable. Given an initial distribution of animals, we seek the population dynamics source term R(x,y) such that integration of the forward model will result in predictions3 that minimize the sum of squares of differences with observed concentrations at a later time. An adjoint data assimilation technique has been designed for these purposes.

This approach has been used to invert for the population dynamics associated with the transition between bimonthly (i.e. for 2 months) climatological Pseudocalanus spp. distributions derived from MARMAP data. Vertically averaged velocity and diffusivity fields diagnosed from hydrodynamical simulations of the climatological flow are specified. Solutions converge rapidly, and the procedure reduces the cost function by an order of magnitude within 50 iterations. The resulting population dynamics vary considerably in space and time, as does the balance between local tendency, physical transport and biological source terms. Generally speaking, the patterns in population dynamics are not inconsistent with current knowledge concerning potential controls such as predation and food limitation. Analysis of the solutions indicates that the Pseudocalanus spp. population centres located in the western Gulf of Maine and on Georges Bank may be self‐sustaining, in contrast to prior studies which characterize the former as a source region for the latter.
A Lagrangian ensemble model of Calanus finmarchicus coupled with a 1D ecosystem model
Authors: CARLOTTI FRANÇOIS , WOLF KARL‐ULRICH
Published: March 2003

A population dynamics model of Calanus finmarchicus based on Lagrangian particles has been coupled with a 1‐D ecosystem model. Each of the particles represents a variable number of copepods which experience the same fate. Therefore all copepods of a single particle represent a cohort and are characterized by a common set of individual properties such as age, development‐stage, depth, structural weight (length), lipid pool or food satiation. The physical environment is parameterized by a 1‐D‐water column with a vertical resolution of 1 m and a maximum depth of 800 m. Copepod food supply is provided by an interactive Eulerian NPZD model where Z represents microzooplankton. The model correctly reproduces both the dynamics of the ecosystem and the life history of the copepods in the Norwegian Sea. Simulated results of trajectories of particles in the water column, and of individual growth and stage development were analysed. Results on seasonal abundance, development time, number of generations, depth profiles, and patterns of diurnal and ontogenic migration are compared with field data from OWS India.
Continuous Plankton Recorder data and diel vertical migration in stage V and VI Calanus finmarchicus: a statistical analysis
Authors: Beare D. , McKenzie E.
Published: March 2003

Generalized linear models were used to assess the influence of diel vertical migration (DVM) on Continuous Plankton Recorder data for adult (stages V and VI) Calanus finmarchicus. To simplify interpretation, the data were first divided into individual months and modelled using a Generalized Linear Model incorporating factors for long‐term trend and daylight. The fitted models reveal that, at certain times of the year and particularly during the spring and autumn, the chances of catching a stage V or VI C. finmarchicus at 7 m depth are greater in darkness than during daylight. The magnitude of DVM was shown to be generally statistically independent of long‐term trend, which is a conclusion that fails to support other published results produced from the same data.
Calanus finmarchicus egg production and food availability in the Faroe–Shetland Channel and northern North Sea: October–March
Authors: Richardson K. , Jónasdóttir S.H. , Hay S.J. , Christoffersen A.
Published: March 2003

Physiological characteristics (egg production, lipid content and gonad development stage) of Calanus finmarchicus were examined on five cruises in the north‐east Atlantic carried out between the months of October to March in the years 1993–95 and related to phytoplankton food availability. Appreciable egg production rates were only recorded in October and March. Published values for maximum water volume filtered daily by individual females and the standing stock of phytoplankton (estimated from chlorophyll concentration) are used to argue that ingestion of phytoplankton carbon alone was not sufficient to support the egg production rates recorded in March. Data are presented that indicate C. finmarchicus is fuelling egg production through use of internal lipids. We argue that this species exhibits a life history strategy whereby females release a limited number of eggs to the water column upon returning to the surface waters following diapause, i.e. prior to the onset of the spring bloom. This pre‐spring bloom egg production will comprise only a small component of the annual Calanus egg production in shelf waters. Nevertheless, given that the recruitment of Calanus to their feeding grounds over the shelf is a function of transport of the copepods from off‐shelf to shelf regions via ocean currents, a burst of egg production in the period immediately following diapause and prior to the population's transport to shelf waters, would increase the chances of large numbers of the population reaching shelf regions. Thus, even a limited pre‐spring bloom burst of egg production may have important consequences for recruitment in this species.
Circulation and larval fish transport within a tidally dominated estuary
Authors: Churchill  , Forward  , Luettich  , Hench  , Hettler  , Crowder  , Blanton
Published: March 2003

In March 1996 two surveys of larval fish abundance and water flow were carried out within the estuarine region near Beaufort Inlet, NC. Each survey extended over two full semidiurnal tidal cycles and included measurements of larvae concentration and velocity distribution at several locations. There was a large across‐channel variation in the subtidal flow passing through Beaufort Inlet, with net inflow over the eastern and central portions of the inlet and net outflow on the western side of the inlet. This pattern was consistent with moored current meter measurements of a previous study, and was reproduced by a numerical model circu‐lation forced only by the M2 tide. A net ingress of larvae from the open ocean into the estuary was observ‐ed during both surveys. Most larvae entered the estuary over the eastern and central portions of the inlet, where the subtidal flow was up‐estuary. However, the mean circulation played a minor role in the net movement of larvae into the estuary. Rather, net up‐estuary transport of larvae was principally due to variation of larval abundance with tidal flow; with abundance during flood tide usually far exceeding ebb tide abundance. This mode of transport was likely driven by a behavioural response to tidal flow in which larvae tended to descend to the bottom on falling tides and reside throughout the water column on rising tides.
BAROTROPIC TIDAL AND WIND‐DRIVEN LARVAL TRANSPORT IN THE VICINITY OF A BARRIER ISLAND INLET
Authors: Luettich Jr  , Hench  , Fulcher  , Werner  , Blanton  , Churchill
Published: March 2003

Fish species such as Atlantic menhaden (Brevoortia tyrannus) must often transit relatively small barrier island inlets to move from their continental shelf spawning grounds to estuarine nurseries, where they spend their juvenile phase. Physical transport through these inlets is strongly influenced by tides, winds, local geometry and bathymetry, and can be very different from that occurring on the shelf. In March 1996, an extensive multidisciplinary field experiment was conducted to identify larval transport pathways in the vicinity of Beaufort Inlet, NC (
Blanton et al., 1999
;
Churchill et al., 1999
;
Forward et al., 1999
). One of the most interesting results from the field study was significant spatial inhomogeneity in the larval catches (
Forward et al., 1999
).

This paper describes a computer modelling study of tidal and wind‐driven circulation and accompanying larval transport characteristics in the vicinity of Beaufort Inlet. Primary conclusions are as follows: (i) tidal currents are quite effective at creating net larval transport into the inlet; (ii) in the absence of wind forcing, to explain the spatial distribution of larval catches observed in the field experiment, the primary source of larvae must have been to the east of the inlet; (iii) the spring/neap cycle accounts for a variation of approximately 40% in larvae ingress; (iv) only a few wind directions enhance larvae ingress over the case of purely tidal forcing—wind blowing toward the north enhances ingress at the surface, and winds blowing toward the south and the east enhance ingress at the bottom; (v) if larvae are evenly distributed in space out‐side the inlet, then strong east wind (such as 10 m s−1) can cause larvae to move through the inlet in a way that is consistent with the larval catches in the field experiment. However, local wind records revealed that no significant eastward‐blowing winds occurred during or immediately preceding the field experiment.
Environmental conditions, satellite imagery, and clupeoid recruitment in the northern Benguela upwelling system
Authors: COLE JAMES
Published: March 2003

The relationship between oceanographic conditions and clupeoid (pilchard, Sardinops sagax, and anchovy, Engraulis capensis) recruitment in the northern Benguela upwelling system was investigated from 1981 to 1987 using a time‐series of mean weekly SST images. Two approaches were taken. The first involved correlating recruitment success with the number of weekly coastal `SST events' above various cut‐off temperatures during the main reproductive season. The second involved constructing a multiple regression model of recruitment success with two independent environmental variables: namely, the number of coastal `SST events' greater than 19°C, and an onshore retention index for the early life‐history stages. The retention index was derived from a spatial time‐series analysis of the SST images using principal components analysis. In general, pilchard recruitment showed a positive relationship with the `number of SST events' whilst anchovy recruitment had a negative relationship; 1987 was an outlier year, during which there were exceptionally high levels of both pilchard and anchovy recruitment. The multiple regression R2 values were high and significant for both species (pilchard R2 = 0.88, anchovy R2 = 0.96). The regression model also accounted for the 1987 outlier according to levels of onshore retention which, despite low inshore SSTs, were particularly high during the 1986/87 reproductive season. Although these results need to be validated with data from a longer time period, they show how satellite data might be used for predicting clupeoid recruitment success in the northern Benguela.
Environmental influences on the availability of smooth pink shrimp, Pandalus jordani, to commercial fishing gear off Vancouver Island, Canada
Authors: Perry R. Ian , Boutillier James A. , Foreman Michael G.G.
Published: March 2003

Short time scale (less than seasonal) variability in commercial catch rates of smooth pink shrimp, Pandalus jordani, off the west coast of Vancouver Island, Canada, was examined in relation to changes in environmental conditions. Catch per unit of effort (CPUE) data were used as a proxy for catchability to identify environmental conditions affecting the availability of shrimp to the two main gear types in this fishery: otter trawls and beam trawls. Correlogram analyses of the 1996 CPUE (log‐transformed) data from each gear type, and autocorrelation analyses of wind stress, tidal current speed, sea surface temperature and salinity, and hours of bright sunshine (the latter three as residuals from their seasonal trends) for 1996 indicated a mean decorrelation time scale of 7.7 days. This was used to construct smoothed time series of these CPUE and environmental data for 1996. Multiple regression analyses with CPUE as the dependent variable and the environmental data as independent variables were significant, explaining 44% of the variability in otter‐trawl data and 35% of the beam‐trawl variability. Three hypotheses are proposed to explain these results, involving interactions between the shrimp’s behaviour and environmental conditions. A significant proportion of the within‐season variability in CPUE (and therefore in the availability of shrimp to fishing gear) for P. jordani off Vancouver Island can result from variations in environmental conditions which, if included in stock analyses, should reduce the variability of population abundance estimates.
Predicting the temperature of the Barents Sea
Authors: Ottersen Geir , Ådlandsvik Bjørn , Loeng Harald
Published: March 2003

Knowledge of the influence of the physical environment on commercially important fish stocks in the North Atlantic has increased during the last decade. To allow this information to be used in fisheries management, some forecast of the environment is important. Predictions of temperature in the Arcto‐boreal Barents Sea have been given for many years, both as subjective opinions of scientists and implicitly in stock assessment assumptions of, e.g., mortality rates. To evaluate an objective statistical forecasting system, we have analysed time series representing mechanisms previously proposed as influencing the temperature of the Barents Sea. These include components of suggested periodic nature, large‐scale advective effects, regional processes, and atmospheric teleconnections. The predictability of Barents Sea temperature based on the above mechanisms was evaluated through calculations of auto‐ and cross‐correlations, linear regression, spectral analysis and autoregressive modelling. Forecasts based on periodic fluctuations in temperature performed poorly. Advection alone did not explain a major part of the variability. The precision of predictions six months ahead varied with season; forecasts from spring to autumn had least uncertainty. A first‐order autoregressive model, including modelled atmospherically driven volume flux to the western Barents Sea during the preceding year and the position of the Gulf Stream off the eastern coast of the USA two years earlier, explained 50% of the total historical temperature variability.
A synthesis of biological and physical processes affecting the feeding environment of larval walleye pollock (Theragra chalcogramma) in the eastern Bering Sea
Authors: Napp  , Kendall  , Schumacher
Published: March 2003

Biological and physical phenomena that affect conditions for larval survival and eventual recruitment differ in the oceanic and shelf regions. In the oceanic region, eddies are a common feature. While their genesis is not well known, eddies have unique biophysical characteristics and occur with such regularity that they likely affect larval survival. High concentrations of larval pollock often are associated with eddies. Some eddies are transported onto the shelf, thereby providing larvae to the Outer Shelf Domain. Advection, rather than local production, dominated the observed springtime increase in chlorophyll (often a correlate of larval food) in the oceanic region. Over two‐thirds of the south‐eastern shelf, eddies are absent and other phenomena are important. Sea ice is a feature of the shelf region: its interannual variability (time of arrival, persistence, and areal extent) affects developmental rate of larvae, timing of the phytoplankton bloom (and potentially the match/mismatch of larvae and prey), and abundance and distribution of juvenile pollock. In the oceanic region, interannual variation in food for first‐feeding pollock larvae is determined by advection; in the shelf region, it is the coupled dynamics of the atmosphere–ice–ocean system.
Schooling and migration of large pelagic fishes relative to environmental cues
Authors: Humston Robert , Ault Jerald S. , Lutcavage Molly , Olson Donald B.
Published: March 2003

A kinesis model driven by high‐resolution sea surface temperature maps is used to simulate Atlantic bluefin tuna movements in the Gulf of Maine during summer months. Simulations showed that individuals concentrated in areas of thermal preference. Results are compared to empirical distribution maps of bluefin tuna schools determined from aerial overflights of the stock during the same time periods. Simulations and empirical observations showed similar bluefin tuna distributions along fronts, although interannual variations in temperature ranges occupied suggest that additional foraging factors are involved. Performance of the model is further tested by simulating the relatively large‐scale annual north–south migrations of bluefin tuna that followed a preferred thermal regime. Despite the model’s relatively simple structure, results suggest that kinesis is an effective mechanism for describing movements of large pelagic fish in the expansive ocean environment.
Alternating dominance of postlarval sardine and anchovy caught by coastal fishery in relation to the Kuroshio meander in the Enshu‐nada Sea
Authors: Nakata Hideaki , Funakoshi Shigeo , Nakamura Motohiko
Published: March 2003

In the mid 1970s, the fishery catch of postlarval Japanese anchovy (Engraulis japonica) in a shelf region of the Enshu‐nada Sea, off the central Pacific coast of Japan, started to decline corresponding to a rapid increase of postlarval sardine (Sardinops melanostictus). In late 1980s, sardine started to decline, and it was replaced by anchovy in the 1990s. This alternating dominance of postlarval sardine and anchovy corresponded to the alternation in egg abundance of these two species in the spawning habitat of this sea. It was also noteworthy that during the period of sardine decline, sardine spawning occurred in April–May, a delay of two months compared with spawning in the late 1970s.

The implication of oceanographic changes in the spawning habitat for the alternating dominance of sardine and anchovy eggs was explored using time‐series data obtained in 1975–1998, focusing on the effect of the Kuroshio meander. Large meanders of the Kuroshio may have enhanced the onshore intrusion of the warm water into the shelf region and contributed to an increase in temperature in the spawning habitat. This might favour sardine, because its egg abundance in the shelf region was more dependent on the temperature in early spring than was that of anchovy. In addition, enhanced onshore intrusion could contribute to transport of sardine larvae from upstream spawning grounds of the Kuroshio region. On the other hand, anchovy egg abundance was more closely related to lower transparency at the shelf edge, which may indicate the prevalence and prolonged residence of the coastal water, and therefore higher food availability, frequently accompanying non‐meandering Kuroshio.

The expansion/shrinkage of the spawning habitat of sardine and anchovy in the shelf region, apparently responding to the change in the Kuroshio, possibly makes the alternation in dominance of postlarval sardine and anchovy most prominent in the Enshu‐nada Sea, in combination with changes in the abundance of spawning adults, which occurred almost simultaneously in the overall Kuroshio region. The implication of this rather regional feature for the alternating dominance of sardine and anchovy populations on a larger spatial scale is also discussed.
Ecological variations and El Niño effects off the southern coast of the Korean Peninsula during the last three decades
Authors: Kim Suam , Kang Sukyung
Published: March 2003

To explore ecosystem response to environmental changes, we investigated interannual and decadal changes in the marine ecosystem using data collected from the southern coast of the Korean Peninsula during the 1960s–1990s. Water properties such as sea surface temperature (SST) and salinity in April did not show large variation during the 1970s, but a relatively cool water mass appeared from the early to mid 1980s and a warm water mass replaced it after 1989. Chl a concentration in April, which was converted from Secchi disc information, was low (mean=1.18 mg m−3) during the period 1968–1980 excluding 1974, but there was a period of greater biomass for 7 years from 1981 (mean=2.78 mg m−3). A negative correlation (r=−0.387, P < 0.05) between SST and chl a in April matched high chl a during the low‐SST period in the early and mid 1980s. Annual zooplankton biomass ranged from 37 to 132 mg m−3, but abundance was frequently high after 1984 and low during 1972–1982. The most representative pelagic fishes in the South Sea seemed to respond to the increase in planktonic organisms. Anchovy, mackerel and sardine increased in abundance since the mid 1970s. High catches of anchovy and mackerel lasted until the 1990s, whereas sardine decreased after the early 1990s. From the matrix of simple correlation coefficient, the Southern Oscillation Index (SOI) exhibited a high correlation with SST in December in the study area (P < 0.05). Catches of anchovy and mackerel were positively correlated with chl a and zooplankton during their early life periods, as well as with SST in December.
Modelling changes in the length–frequency distributions of fish larvae using field estimates of predator abundance and size distributions
Authors: Paradis A. R. , Pepin P.
Published: March 2003

The goal of this study is to determine if an individual‐based size‐dependent model can realistically simulate changes in the length–frequency distributions of several species of fish larvae collected in Conception Bay in 1993 and 1994, using field estimations of growth and predator abundance. We first model the length–frequency distribution of field samples with the best possible estimates of mean growth rate. Then, we add predation mortality given the characteristics of the predator community observed during our surveys, which was composed of macrozooplankton and adult capelin. The larval fish community is generally not affected by predation by macrozooplankton, as the average instantaneous mortality rate predicted by the model was 0.004 day–1. Fish larvae appear to be more vulnerable to predation by the population of adult capelin. We estimate that an abundance of adult capelin ranging between 0.2 and 1.0 individuals per 1000 m–3 may have a substantial impact on the larval fish community. The predictions of an individual‐based model are directly related to the accuracy of estimates of the mean growth rates of the larval fish cohorts. We find that it is difficult to differentiate size‐selective removal of individuals from random selection by analysing changes of the length–frequency distributions of the larval fish community.
Springtime ichthyoplankton of the slope region off the north‐eastern United States of America: larval assemblages, relation to hydrography and implications for larval transport
Authors: Hare Jonathan A. , Fahay Michael P. , Cowen Robert K.
Published: March 2003

Larval transport in the slope region off north‐eastern North America influences recruitment to juvenile habitats for a variety of fishes that inhabit the continental shelf. In this study, collections of larval fishes were made during springtime over the continental slope to provide insights into larval distributions and transport. Ichthyoplankton composition and distribution mirrored the physical complexity of the region. Three larval fish assemblages were defined, each with different water mass distributions. A Gulf Stream assemblage was found predominantly in the Gulf Stream and associated with filaments of discharged Gulf Stream water in the Slope Sea. Larvae of this assemblage originated from oceanic and shelf regions south of Cape Hatteras. Several members of this assemblage utilize habitats in the Middle Atlantic Bight (MAB) as juveniles (Pomatomus saltatrix, Peprilus triacanthus) and other members of the assemblage may share this life cycle (Mugil curema, Sphyraena borealis, Urophycis regia). A Slope Sea assemblage was found in all water masses, and was composed of epi‐ and mesopelagic fish larvae, as well as larvae of benthic shelf/slope residents. Larvae of one member of this assemblage (U. tenuis) are spawned in the Slope Sea but cross the shelf‐slope front and use nearshore habitats for juvenile nurseries. A MAB shelf assemblage was found in MAB shelf water and was composed of larvae that were spawned on the shelf. Some of these species may cross into the Slope Sea before returning to MAB shelf habitats (e.g. Enchelyopus cimbrius, Glyptocephalus cynoglossus). Previous studies have examined the effect of warm‐core rings on larval distributions, but this study identifies the importance of smaller‐scale features of the MAB shelf/slope front and of filaments associated with Gulf Stream meanders. In combination with these advective processes, the dynamic nature of larval distributions in the Slope Sea appears to be influenced, to varying degrees, by both vertical and horizontal behaviour of larvae and pelagic juveniles themselves.
Environmental factors and recruitment of mackerel, Scomber scombrus L. 1758, along the north‐east Atlantic coasts of Europe
Authors: Borja A. , Uriarte A. , Egaña J.
Published: March 2003

Increasingly, scientific publications refer to some of the environmental factors affecting the recruitment in fish species. However, presently, there is little information available concerning the influence of the environment on the recruitment of Scomber scombrus, the North‐east Atlantic mackerel (NEAM). In this contribution, North Atlantic Oscillation (NAO), upwelling and turbulent mixing (or `turbulence') series were compared with recruitment estimates, at age‐0. The results show that the southern prespawning migration pattern of the Atlantic mackerel is directed towards areas with low turbulent mixing at spawning time, providing a `stable environment' for egg and larval survival. In the southern areas, where the spawning starts, the turbulence conditions of prespawning and spawning periods have the largest influence on the success of recruitment; this is related, possibly, to the more `stable' weather in the subsequent months and for the remainder of the year. In contrast, in the northern areas, the role of turbulence over the entire year becomes increasingly more relevant; this is related, possibly, to the high levels of turbulence during autumn and winter, which may become limiting to the survival of juveniles. About 50% of the variability in the Atlantic mackerel recruitment may be explained by means of environmental variables, such as turbulence. Other variables, such as upwelling and NAO, are only slightly, or not, statistically significant.
The effects of short space and time scale current variability on the predictability of passive ichthyoplankton distributions: an analysis based on HF radar observations
Authors: Helbig J. A. , Pepin P.
Published: March 2003

The importance of small scale variations in currents on the predictability of spatial distributions of fish eggs is investigated using dense observations of surface currents. The currents were measured with HF radar and used to drive an advection–diffusion model of ichthyoplankton concentration. We first demonstrate that the model produces acceptable agreement with observed egg fields. We then use the predicted egg fields as a basis for comparison with model runs made with currents subsampled in space and filtered in time. Significant error was found for spatial sampling intervals as small as 3 km, even though most of the variance in the currents occurred at much longer length scales. This was primarily due to the loss of the rich small scale variability in horizontal divergence. Nevertheless, most of the error is due to the misfit in the egg fields at larger length scales; that is, small scale forcing is necessary in this system for the larger scale features to be reproduced. This study thus suggests that considerable caution should be exercised before assuming that circulation models, even very sophisticated and detailed ones, capture enough of the variability of marine systems to make accurate forecasts of plankton distributions.
Fish larvae distribution off Mejillones Peninsula (northern Chile) during a coastal upwelling event in Spring 1999: interactions with the cold upwelling plume
Authors: Rojas Pablo M. , Escribano Ruben , Marín Victor H.
Published: March 2003

We examined the interaction between vertical and horizontal distribution of fish larvae off Mejillones Peninsula (23°S), northern Chile, under conditions of active coastal upwelling. An oceanographic survey covered spatial variability in temperature, chlorophyll‐a (chl a), dissolved oxygen, salinity and water density. Fish larvae were sampled during daytime and nighttime periods through two consecutive days in four stations: two inside and two outside of a well‐developed upwelling plume, and at three depth strata: 0–20, 20–80 and 80–200 m. Eighteen taxa were analysed, of which the Myctophidae Diogenychthys atlanticus, Diogenichthys laternatus, and the anchovy Engraulis ringens, were most abundant. Our data showed little evidence for diel vertical migration and larvae were more abundant at depth (>80 m) under low temperature (∼12°C) and low chl a (∼2 mg m–3), below the highly advective upper layer. The exploratory K‐means analysis allowed the separation of data into two distinct habitats: upwelling and nonupwelling types. Most taxa were allocated in nonupwelling waters, i.e. outside the cold plume. However, short‐term variations (<24 h) in the position of the upwelling plume influenced both horizontal and vertical occurrence as well as abundance of taxa, and caused variability in temperature, oxygen and chl a. These changes in oceanographic conditions, caused by upwelling circulation and the dynamics of the cold plume, may sharply modify the habitat of fish larvae and have an important role in survivorship and recruitment success.
Importance of the Shatsky Rise Area in the Kuroshio Extension as an offshore nursery ground for Japanese anchovy (Engraulis japonicus) and sardine (Sardinops melanostictus)
Authors: Komatsu Teruhisa , Sugimoto Takashige , Ishida Ken‐Ichi , Itaya Kazuhiko , Mishra Pravakar , Miura Teisuke
Published: March 2003

Recent findings suggest that recruitment of Japanese anchovy (Engraulis japonicus) and sardine (Sardinops melanostictus) depends on survival during not only the first feeding larval stage in the Japanese coastal waters and the Kuroshio front but also during the post‐larval and juvenile stages in the Kuroshio Extension. Spatial distributions of juvenile anchovy and sardine around the Shatsky Rise area in the Kuroshio Extension region and the Kuroshio–Oyashio transition region are described, based on a field survey in the late spring using a newly developed mid‐water trawl for sampling juveniles. All stages of anchovy from post‐larvae to juveniles were obtained in the northern Shatsky Rise area. The Kuroshio Extension bifurcates west of the Shatsky Rise area and eddies are generated, leading to higher chlorophyll concentrations than in the surrounding regions in April and May. When Japanese anchovy and sardine spawn near the Kuroshio front or the coastal waters south‐east of Japan, their larvae are transported by the Kuroshio Extension and are retained in the Shatsky Rise area, which forms an important offshore nursery ground, especially during periods of high stock abundance.