ICES Journal of Marine Science: Journal du Conseil

Hislop, J. R. G.; Robb, A. P.; Bell, M. A.; Armstrong, D. W.

doi: 10.1093/icesjms/48.2.139pmid: N/A

The stomachs of more than 19000 North Sea whiting were examined in 1981. Almost 50% were either empty or were judged to have lost all or part of their contents through regurgitation. The contents of the remaining stomachs (approximately 9800) were analysed. The average weight of the stomach contents (S, g) including fish with empty stomachs, was related to the ungutted weight of the fish (W, g) as follows: S=0.009 × W1.057. Fish and Crustacea comprised at least 85% by weight of the stomach contents of whiting of all sizes, the proportion offish increasing with predator size. Some geographical and seasonal differences in stomach contents were detected; annelids represented a significant proportion of the food of whiting in the southeastern North Sea, as did cephalopod molluscs in the north, during the first part of the year. Larger whiting eat larger prey. This is particularly noticeable in the case offish prey where: Prey length = 0.57 × predator length0.87. The bulk of the fish prey consisted of seven species (cod, haddock, whiting, Norway pout, sprat, herring, and sandeels), each of which is of considerable economic importance. Although whiting feed on fish representing the entire range of age classes of the smaller fish species (Norway pout, sprat, and sandeels) they eat mainly the youngest (0+ and 1+) age classes of herring, cod, haddock, and whiting. Quantifying the food requirements of fish species is notoriously difficult, but attempts have been made to estimate the annual food consumption by whiting in the North Sea. It is concluded that whiting may be one of the most important piscivorous fish in the North Sea.

Paul, A. J.; Coyle, K. O.; Haldorson, L.

doi: 10.1093/icesjms/48.2.157pmid: N/A

Depth specific abundance of copepod nauplii was monitored during the spring months of 1986 through 1989 in Auke Bay, southeast Alaska, to describe interannual fluctuations in prey concentration for larval walleye pollock (Theragra chalcogramma) and flathead sole (Hippoglossoides elassodon). The major cohorts of first-feeding pollock larvae were present in April and May, while flathead sole larvae were common from mid-May to early June. The larvae of both species feed on copepod nauplii and previous studies showed 10-20 nauplii 1−1 adequate for feeding. In April of all four years most larvae coexisted with nauplii concentrations ∼ 10 to 151−1. By early May in 1986, 1988, and 1989 nauplii were frequently over 201−1, while in 1987 corresponding values were 10 to 151−1. Nauplii concentrations were never low enough to cause mass starvation of competent walleye pollock larvae, and in all years food intake of some cohorts should not have been prey limited. In all years the average prey concentrations were high enough for successful feeding by flathead sole.

Jensen, A. L.

doi: 10.1093/icesjms/48.2.167pmid: N/A

The two-species Schaefer model for species that are captured with the same fishing gear, but which do not interact ecologically, was applied to examine the relation between the maximum sustainable yields for lake trout (Salvelinus namaycush) and lake whitefish (Coregonus clupeaformis) fished together and separately. Lake trout and lake whitefish are two important species in the Laurentian Great Lakes that historically have been Sshed with the same gear. Naturally reproducing lake trout populations have disappeared from most of the Great Lakes, but the lake whitefish supports a large fishery. Application of the logistic surplus production model to lake trout alone does not indicate serious over-exploitation, but applied to lake trout and lake whitefish together indicates that at the total maximum sustainable yield of the two species together, the lake trout is seriously over-exploited and abundance is low. A fishery can be optimized for only one species at a time, and, if several non-interacting species are exploited, some will be over-exploited and some will be under-utilized. One species among several in a multiple species fishery can, in theory, be fished to extinction at the total maximum sustainable yield of the combined species.

Nedreaas, Kjell; Nævdal, Gunnar

doi: 10.1093/icesjms/48.2.173pmid: N/A

In this study, three redfish species, Sebastes marinus, Sebastes mentella, and Sebastes niviparus, are investigated for inter- and intraspecies differences by the use of electrophoresis of haemoglobin and enzymes in white muscle, liver, and eye tissues. This study is a continuation of the work by Nedreaas and Nævdal (1989) on the analysis of protein polymorphism in redfish from Norwegian waters, the Barents Sea, and Svalbard. For the present study, specimens have been collected from the British Sector north of Shetland, putside the Faeroe Islands, from the Irminger Sea, and from East Greenland. The genetic species diagnostic criteria, which were also clear and unequivocal in this enlarged investigation of the Sebastes genus in the Northeast Atlantic, confirmed the less clear morphoogical, morphometric, and meristic criteria used to separate the species. The study urther revealed certain underlying genetic differences within species between areas that will help our understanding of the biological structure of redfish stocks in the Northeast Atlantic.

Methven, David A.; Piatt, John F.

doi: 10.1093/icesjms/48.2.187pmid: N/A

The seasonal abundance and vertical distribution of capelin in relation to water temperature have been investigated by conducting repeated hydroacoustic surveys at a coastal site off eastern Newfoundland. Water temperatures were warmer in 1983 than in 1984 as indicated by the earlier appearance and greater depth of the seasonal thermocline. Correspondingly, schools of capelin appeared earlier, were more abundant, and extended deeper in the water column in 1983 than in 1984. Most capelin were found between the surface and the 5°C isotherm. In both years, initial peaks of capelin abundance occurred when nearshore water temperatures increased from about 0-1°C to above 6°C and, at or near, periods of maximum tidal oscillation. Short-term variations in the depth of the 5°C isotherm were related to nearshore wind-induced upwelling events. Annual variations corresponded to the volume of cold (>0°C) water and sea-ice transported south by the Labrador Current.

Jarre, A.; Clarke, M. R.; Pauly, D.

doi: 10.1093/icesjms/48.2.195pmid: N/A

Earlier work by the second author on the growth of oceanic squids, based on sizefrequency distributions of beaks sampled from sperm whale stomachs and on structural marks on those beaks, showed that these squids apparently had growth rates far in excess of those reported for the fastest-growing fishes, e.g. bluefin tuna. The application of recently developed methods for analysis of length-frequency distributions to some of these earlier data, and new approaches for assessing and comparing the growth performance offish and aquatic invertebrates, suggest the need for a downward revision of these high growth estimates. This is illustrated here with data on Kondakovia longimana (Cephalopoda, Onychoteuthidae) sampled off Durban and Donkergat, South Africa, in the early to mid-1960s.

Andrew, N. L.; Graham, K. J.; Kennelly, S. J.; Broadhurst, M. K.

doi: 10.1093/icesjms/48.2.201pmid: N/A

The catch per swept area and size selectivities of several configurations of prawn trawls were assessed during night-time trials. Catches using triple rigged prawn trawls were compared to single trawls with and without sweeps of 40 and 140 m length in a nested sampling design. Sweeps were found to herd Australian red spot whiting and sand flathead but not prawns and shovelnose lobsters. Single trawls with long sweeps caught significantly larger red spot whiting and sand flathead than any other trawl configuration. Triple gear caught more smaller red spot whiting than other configurations but this effect was not evident for sand flathead. The results are discussed in terms of the likely behaviour of the herded species and implications for the management of fisheries for prawns and herded species of finfish.

Foote, Kenneth G.

doi: 10.1093/icesjms/48.2.211pmid: N/A

Methods for determining fish target strength or backscattering cross section at ultrasonic frequencies are intercompared. Tabulated results derived by the methods at 38 kHz show a general consistency.

Lapointe, Michael F.; Peterman, Randall M.

doi: 10.1093/icesjms/48.2.219pmid: N/A

Researchers have frequently correlated estimates of abundance of recruits with oceanographic variables. Our simulation analysis shows that when such correlations are based on estimates of recruits from virtual population analysis (VPA), and when there are time trends in the fishing mortality rate and the oceanographic factor (as is almost always the case, to some degree), the magnitude and statistical significance of correlations depend on the natural mortality rate (M) used in VPA. Our simulation model of an agestructured fish population assumed some correlation between the “true” abundance of recruits and an oceanographic factor, and generated catch data and terminal fishing mortality rates for input to VPA. VPA was then given a set of deliberately mis-specified M values to represent inaccurate knowledge of M; correlations were calculated between the VPA estimates of recruits and the oceanographic factor. When the model's true recruitment was significantly correlated with the oceanographic variable, certain ranges of incorrect M used in VPA resulted in estimated correlations that were not significantly different from zero. When the true correlation was zero, other ranges of incorrect M created spurious correlations between recruitment and the oceanographic factor. First differencing the data used in calculating correlations solved some of the problems but created others. In practice, sensitivity analyses can be used to determine how the choice of M used in VPA influences conclusions about links between the environment and recruitment in fish populations.

Richardson, C. A.; Walker, P.

doi: 10.1093/icesjms/48.2.229pmid: N/A

Annual lines in the internal shell structure of Mercenaria mercenaria were used to age clams from North Wales (cultivated stock) and Southampton Water (wild stock). A comparison was made between the number of lines visible under low-power ( × 6 magnification) in shell sections and the number observed microscopically (× 10 to × 25 magnification) in acetate peel replicas of sections. The number of lines in peels from the shells of nine cultivated clams from North Wales coincided exactly with the known number of years (22) since deposit; the estimated age of the other four shells from the same sample differed by only one year from expectation. In contrast, counting lines under × 6 magnification could underestimate age by up to 7 years. The ages of one-hundred-and-thirtyfour wild clams from Southampton Water were determined using acetate peel replicas. The age frequency distribution in the samples collected in 1983 and 1988 revealed certain prominent year classes in the population. The years 1969, 1976, 1977, and 1984 were occasions when there was above average settlement and/or subsequent survival. With the exception of 1977, successful settlement was found to correspond with above average water temperatures. The reasons why some years are more successful than others for larval settlement and recruitment of the clams are discussed. It is suggested that a combination of below average freshwater flow into Southampton Water as well as above average water temperatures may have been the important factors influencing larval settlement and survival of clams during 1976 and 1984.