This paper describes a method for assessing contaminant time-series when contaminant levels vary with some covariate and the contaminant-covariate relationship changes over time. At each time point, the contaminant data are split into two groups according to whether the corresponding values of the covariate are smaller or larger than some specified value, leading to two...
Dive-depth and swim-speed of a juvenile and an adult free-ranging, Yangtze finless porpoises (Neophocaena phocaenoides) were observed using velocity-time-depth recorders in an oxbow of the Yangtze River. In total, 8222 individual dives were recorded over 59 hours. Two dive types, deep-dive (≥2.7 m) and shallow-dive, were recognized. Horizontal travel distances of two finless...
This paper describes spatial, temporal and biotic patterns in the diet of Greenland halibut (Reinhardtius hippoglossoides, Walbaum) sampled from three different areas of the Barents Sea, namely the Hopen Deep (nursery area), the Bear Island Channel and the continental slope (spawning ground), during April 1996 to January 1998. Percentage of empty stomachs was based on 3294...
The biomass of fish assemblage inhabiting the Senigallia artificial reef (northern Adriatic Sea, Italy) was evaluated in the period July–November 1996. Density and biomass were assessed through a stationary hydroacoustic technique using an appropriately adapted SIMRAD EY500 system. Part of the system was placed inside the reef and it was linked by radio-modem to the Institute...
The otolith (lapillus) size–fish size relationship was examined for offspring of two Atlantic cod stocks, reared at different temperatures. Larvae and early juveniles reared at high temperatures (fast growing), had larger otoliths at a given length than fish reared at low temperatures (slow growing). Within a given temperature group, however, faster growing cod tended to have...
We present the first acoustic observations of predator–prey interactions between fin whales and herring. The school dynamics and predation events of Norwegian spring-spawning herring (Clupea harengus) in a cold front area (about 125 km2) in the Norwegian Sea in April were quantified. Data from high-resolution sonar tracking of herring schools combined with echosounder data were...
During spring 1994 and summer 1995 hydrographic transects across the Porcupine Bank, an elliptical topographic structure adjoining the shelf-edge west of Ireland, were carried out to investigate the thermohaline properties and flow field characteristics in the vicinity of the bank. The CTD observations show a dome-like deformation of the temperature and density field together...
During January 2000 a baited video camera system was deployed fifteen times at depths of 719–1518 m around the Subantarctic island of South Georgia. Four species of lithodid (Anomura: Lithodidae) crab (Paralomis formosa, P. spinosissima, Lithodes sp., and Neolithodes diomedeae) were attracted to the baits of which Paralomis formosa was the most abundant. Using arrival rate at...
Long-standing problems with acoustical terminology in fisheries applications such as echo-integration indicate the need for a more consistent approach. Based where possible on existing terms, a scheme of explicitly named quantities is proposed, backed by clearly stated definitions and preferred symbols. The emphasis is on scattering phenomena because the terminology in this area...
To facilitate intercalibration of the age readings of black scabbardfish, Aphanopus carbo, a collection of otoliths was exchanged among the participating laboratories in Portugal, Scotland, and Spain and a workshop was held to discuss the results. The age precision was significantly improved by the intercalibration exercises but remained relatively low. The indirect validation...
The objective of this study was to identify likely proximate cues to the seasonal migrations of cod, Gadus morhua L., in the southern Gulf of St Lawrence. We computed a migration timing index across several years using commercial fishery (1970–1992) and sentinel survey (1995–1999) catch rate data, and closely monitored the seasonal changes in temperature, dissolved oxygen, food...
Two methods of determining the age of herring (Clupea harengus L.) from the Bothnian Sea, in the northern Baltic Sea, were compared. Ages were estimated from whole otoliths, which is a routine method for herring age determination, and from neutral red stained otolith cross sections. There was disagreement between the methods, especially in specimens with more than five annual...
Data collected from a three-year continuing sampling program were used to study the persistence of the macrofaunal communities living in the Valli di Comacchio (44°41′N, 12°10′E), a complex of shallow-water brackish lagoons located in the southernmost part of the Po River deltaic area (Italy). Univariate and multivariate analyses were used to assess the variability and...
Calibrated and digitized data from two or more discrete echosounder frequencies can be combined for the purpose of separating and extracting the acoustic scattering from zooplankton and fish in mixed recordings. This method is also useful for quantifying the relative contribution of each frequency to the total acoustic-backscattering when scrutinizing records in large-scale...
Previous studies indicate that predation by Northeast Arctic cod is an important cause of natural mortality of juvenile Norwegian spring-spawning herring in the Barents Sea. In this paper broad scale temporal and spatial variation in the predator–prey interaction between these two species in the Barents Sea was analysed. The analysis was based on cod stomach data from this area...
The lesser sandeel, Ammodytes marinus, is a key food for many seabirds and seals, and is also the target of the largest single-species fishery in the North Sea. Despite claims that sandeel fishing has harmed dependent predator populations, census data show that most seabirds and grey seals increased in numbers as the fishery grew and reached peak harvest. Generally high breeding...
Assessing the spawning abundance of marine fishes is difficult if spawning periods exceed the residency of individual fish on the spawning grounds. For Atlantic cod (Gadus morhua), which has a protracted spawning period, we use biotelemetric surveys to estimate the rate at which individual fish vacate the spawning ground and develop a method to adjust multiple acoustic-survey...
This paper describes spatial relationships between whiting, Merlangius merlangus (Linnaeus, 1758), abundance in the northern North Sea and contemporaneous measures of environmental conditions: sea surface temperature (SST), sea bottom temperature (SBT), and depth, with particular reference to the processes underlying patterns in SST. Generalised additive models (GAMs) were used...
General Additive Model (GAM) fitting techniques have been employed to understand and predict cephalopod abundance variations in the north-east Atlantic using data on commercial fisheries and geographic and climatic variables. Spatial patterns were studied for general average, seasonal average and monthly recruitment abundance. The capability of this method to model abundance in...
External information and Generalized Additive Models (GAMs) are used to improve the indices provided by the BTS survey for the stock assessment of plaice and sole. These ancillary data consist of the following variables: Depth, Sediment grain-size, Surface temperature, Latitude, Longitude, Time of day and Day of year. Three approaches that predict the catches of four age-groups...
The scope of this study is to identify temporal dynamics in fishing power, by deriving three different indices (IFP1, IFP2, IFP3) based on three independent methods. IFP1 is derived from the GLM analysis of the relationship between fishing mortality and fishing effort, assuming that total fishing mortality estimates from XSA (eXtended Survivors Analysis) are accurate. IFP2 is...
Effort in trawl surveys is standardized by using a common gear and fixing haul duration and vessel speed. Such standardization should result in a fairly constant distance trawled and area or volume swept. Protocols for the North Sea International Bottom Trawl Survey (IBTS) establish hauls of 30 min at a target speed of 4 knots over ground with a standard GOV (Grande Ouverture...
Microincrements in the lapilli otoliths of Lophius piscatorius L. were used to validate the age of fish <27 cm TL collected in spring and autumn. Contrary to published estimates of size at age based on illicia by Dupouy et al. (1986) and Duarte et al. (1997), these small specimens were found to be either 0- or 1-group. Comparison between the macrostructures of illicia and...
Over the past thirty years catches of skates have increased in the western Atlantic as a result of targeted fisheries and as by-catch. Presently, sustainable harvest levels for skates in the western Atlantic are unknown. Available life history information was used to model three western Atlantic skate species, little skate Leucoraja erinacea, winter skate Leucoraja ocellata, and...
Reaction norms for age and size at maturation describe the probability of immature fish maturing at a certain age and size. Knowledge of such reaction norms is increasingly important, both for observing and understanding changes in maturation and for calibrating size- and age-structured population models. Estimating the reaction norms for age and size at maturation by logistic...