ICES Journal of Marine Science: Journal du Conseil

Koueta,, N.;Castro, B., G.;Boucaud-Camou,, E.

doi: 10.1006/jmsc.1999.0503pmid: N/A

Abstract Aspartate transcarbamylase (ATCase) activity was used to estimate instantaneous growth in young cuttlefish (Sepia officinalis) reared under different diet conditions, and compared with estimation obtained by RNA concentration. During the first month of life, the changes in ATCase activity and RNA content of muscle are related to growth. ATCase appears to be a good index of growth during the first stage of intense cell multiplication. ATCase activity is correlated to food intake up to a maximum ration, but decreases when animals are more than 40 days old. The approach of using ATCase activity as a biochemical index for estimating short-term change in growth rates of young cuttlefish in experimental rearing could be extended to young cephalopods collected in the field, and used to predict the effect of biotic factors in recruitment. This content is only available as a PDF. © 2000 International council for the Exploration of the Sea

O'Dor, R. K.; Hoar, J. A.

doi: 10.1006/jmsc.1999.0502pmid: N/A

Pauly has argued for the generalization of von Bertalanffy growth models in fish, based on fundamental geometric relationships between surface area and volume. Recent evidence indicates growth curves of squids rise much more rapidly than those of fish, which appears to be in conflict with such geometric generalizations. Although the generalizations have recently been questioned even for fish, it remains important to establish that squid geometries differ greatly from those of fish. We measured key dimensions from a locomotory perspective in squid with masses from 100 μg paralarvae to 100 kg giants (nine orders of magnitude) and modelled their growth allometries. Elongation of the “hollow tubes” characterizing squid form, as well as increasing fin size contrasts with the relatively constant form of growing fish. When expressed as the dimensionless ratio of surface area1/2/volume1/3 (the “Vogel number”) cod show a small decrease, whereas the ratio for squid increases two-fold over the range for which data is available. The consequences for growth are potentially large because squid respire directly through these surfaces.

Balguerías, E.; Quintero, M. E.; Hernández-González, C. L.

doi: 10.1006/jmsc.1999.0572pmid: N/A

The Saharan Bank (West Africa, between 21°N and 26°N latitude) has been fished since the fifteenth century. Bottom trawls were introduced during the Second World War. Catches of cephalopods were very limited until the 1960s, when a spectacular increase was observed in their landings. The apparent replacement of finfish by cephalopods has been attributed to a change in the ecosystem due to overexploitation of Sparidae, but the hypothesis has never been quantitatively confirmed. The evolution of the profile of Spanish catches from the region from 1933 to 1996 shows a decreasing trend in the numbers of Sparidae, which virtually disappeared from landings at the beginning of the 1970s, with a simultaneous sharp increase in cephalopod catches. However, results from surveys carried out on the bank in 1942, 1962, 1974, and 1990 are not entirely consistent with the replacement hypothesis. The data suggest that there may have been some adjustment in the faunistic communities in response to fishing, but that the change has by no means been of the magnitude suggested by fishery statistics. We suggest that the changes observed are caused by a combination of factors, including economic incentives as well as oceanographic variations and competition for food, which have ultimately favoured benthic cephalopod populations at the cost of most finfish populations.

Sakurai, Y.; Kiyofuji, H.; Saitoh, S.; Goto, T.; Hiyama, Y.

doi: 10.1006/jmsc.2000.0667pmid: N/A

Annual catches of Todarodes pacificus in Japan have gradually increased since the late 1980s. Paralarval abundances have also been higher since the late 1980s compared to the late 1970s and mid-1980s. Here is proposed a possible scenario for the recent stock increase based on changing environmental conditions. Based on trends in annual variations in stock and in larval abundances, catches are reviewed and potential spawning areas inferred, assuming that egg masses and hatchlings occur over the continental shelf at temperatures between 15 and 23°C. Changes are then inferred in the spawning areas during 1984–1995, based on GIS data. Since the late 1980s, the autumn and winter spawning areas in the Tsushima Strait and near the Goto Islands appear to have overlapped, and winter spawning sites seem to have expanded over the continental shelf and slope in the East China Sea.

Arkhipkin, A.; Jereb, P.; Ragonese, S.

doi: 10.1006/jmsc.1999.0488pmid: N/A

Age and growth rates of the Mediterranean short-finned squid Illex coindetii (Ommastrephidae) were studied using statoliths from 704 specimens collected during trawl surveys within the Strait of Sicily in April and October–November 1995. In both samples, almost the whole ontogenetic spectrum was present, from juveniles to spent adults. Most of the squid captured in April had hatched between October and December 1994 (autumn–winter hatched group, AW), whereas most captured in October–November had hatched between May and July 1995 with a peak in June (spring–summer hatched group, SS). Age of the AW squid did not exceed 240 days (mainly 200–210 d), while that of the SS squid did not exceed 191 days (mainly 170–180 d). Growth in length and weight was best described by the logistic growth function. In both groups, daily growth rates (DGR) of males decreased at younger ages than in females, and sexual dimorphism in sizes (females larger than males) became evident in maturing and mature adults. The AW squids grew rather slowly during their juvenile and immature phases, which occurred in cool winter and spring seasons. They were characterized by a maximum DGR in mantle length (ML) and body weight (BW) at old ages, a prolonged period of maturation and old ages of mature specimens. AW squids attained large sizes and spawned at ages of 6–7 months in spring–summer. Their progeny (SS group) grew rapidly during the warm summer and autumn seasons and achieved their maximum DGR in ML and BW at younger ages than their AW predecessors. However, their younger age at maturation (5–6 months) reduced their somatic growth during the late ontogenetic stages, resulting in rather small sizes at maturity and early spawning. It is concluded that I. coindetii in the Strait of Sicily produce at least two alternating generations each year, which are adapted to live in different seasonal environmental conditions.

Yaragina, N. A; Marshall, C. T

doi: 10.1006/jmsc.1999.0493pmid: N/A

Temporal variation in the liver condition index (LCI) of five length classes of Northeast Arctic cod was described and compared to the abundance and availability of capelin and herring in the Barents Sea. On interannual time scales, large and rapid fluctuations in LCI occurred which were synchronous across length classes. For all length classes the annual mean LCI was non-linearly related to capelin stock biomass such that LCI decreased rapidly when capelin stock biomass was below one million tonnes. Liver condition index and the frequency of occurrence of capelin in cod stomachs were positively associated. Neither the abundance of juvenile herring in the Barents Sea nor the frequency of occurrence of herring in cod stomachs were positively correlated with LCI. However, a significant, inverse relationship between the frequency of occurrence of capelin in cod stomachs and total stock biomass of herring was observed suggesting that herring influence cod LCI via predation on capelin. On seasonal time scales, LCI values for February through July were significantly higher in years of high capelin biomass compared to years having low capelin biomass. In years of high capelin biomass the proportion of capelin in the stomach contents of cod showed a peak in March and (or) April.

Swain, D. P.; Poirier, G. A.; Sinclair, A. F.

doi: 10.1006/jmsc.1999.0516pmid: N/A

Correlations between catch rates in bottom-trawl surveys and indices of environmental conditions or fish distribution have been attributed to effects of the environmental conditions or fish distribution on catchability to the survey. We tested this hypothesis using data on cod in the southern Gulf of St Lawrence. Survey catch rates of cod were significantly correlated with indices of bottom temperature and of cod temperature and depth distributions. Correlations were in the directions expected on the basis of predicted effects on catchability or availability to the survey. However, tests involving calibrations of sequential population analysis (SPA) or residuals from multiplicative analyses of the survey catch rates (with terms for yearclass, age and cumulative mortality) did not support the hypothesis that these correlations resulted from effects on catchability to the survey. These tests provided no support for an effect of cod temperature or depth distribution on catchability. They provided some support for an effect of bottom temperature conditions on availability to the survey, but this effect on availability was not reflected by the correlations observed between bottom temperature indices and survey catch rates. We conclude that adjustments for effects on catchability should be based on relationships with inconsistencies in survey catch rates instead of relationships with the catch rates themselves. These adjustments could be incorporated in calibration of the SPA or calculated based on relationships with residuals from models relating survey catch rate to yearclass, age and fishing mortality. However, such adjustments were negligible in the case of southern Gulf of St Lawrence cod.

McClelland, G.; Misra, R. K.; Martell, D. J.

doi: 10.1006/jmsc.1999.0518pmid: N/A

Larval sealworm (Pseudoterranova decipiens) infections were surveyed in the fillets and napes of 28 065 Canadian plaice (Hippoglossoides platessoides), 31–40 cm in length, collected throughout Atlantic Canada between February 1980 and August 1990. Samples were taken from 11 locations in a 1980–1982 survey, and from 38 to 55 locations in 1983–1984, 1985–1986, 1987–1988, and 1989–1990 surveys. Prevalence (P) and abundance (A) of P. decipiens were greatest (P=96–100%, A=12.47–22.32) in 1989–1990 samples from the central Scotian Shelf near Sable Island, while plaice from northeastern Newfoundland and the Grand Banks were seldom infected (P<1%). Temporal trend analyses revealed that between 1980 and 1990, sealworm infection levels increased significantly in plaice in 33 of 41 locations in the Gulf of St Lawrence, on the Breton and Scotian shelves, and in the Gulf of Maine. Spatial and temporal distributions of larval P. decipiens in plaice seemed to reflect the distribution and growing abundance of grey seals (Halichoerus grypus), important definitive hosts of the parasite, but increases in levels of infection over the course of the decade may also have been promoted by a period of relatively high near-bottom temperatures in Atlantic Canadian waters in the late 1970s and early 1980s. A more recent cooling trend in near-bottom temperature or other negative influences, such as sealworm density limiting mechanisms in fish and seal hosts, may have resulted in the stabilization or decline of sealworm levels in some plaice populations in the late 1980s and early 1990s.

Gates, J. M.

doi: 10.1006/jmsc.1999.0561pmid: N/A

This paper proposes a production function for a trap fishery and develops its implications for the economic management of associated inputs. The field observations and anecdotes from fishermen are drawn from the American lobster fishery, but the approach may also be used for other trap fisheries. The development includes a spatial aspect of fixed gear fisheries and an intuitive rationale for a congestion externality in such fisheries. This effect does not involve population dynamics per se. However, the production function developed below could eventually be imbedded within a population dynamics model, although this is not done here. This eventual imbedding is necessary not only because of the biological issues explained by population dynamics but also because of the dependence of price on the age-class structure of the population. A principal finding is that there are plausible reasons to expect market failure associated with a trap congestion externality and a soak time too short for cost effectiveness. The numerical analysis is consistent with the theory, and if this finding is supported by further research, then operating costs could be reduced with no change in catch by using more traps and longer soak times.

Dekker, Willem

doi: 10.1006/jmsc.1999.0562pmid: N/A

The European eel Anguilla anguilla L. is found in most European waters. This widespread species is usually exploited by small-scale companies fishing in localized areas. This implies a contrast of scales. This study analysed data on recruitment, stock, and fisheries to determine how they vary geographically. Coherence between 17 data series on glass eel recruitment is analysed by multivariate techniques. It is shown that the majority of these series exhibit a mutually correlated downward trend since 1980; two of the three stations in Ireland, one in the UK and one in Scandinavia show aberrant trends. The geographical distribution of the continental stock is exemplified by a variogram of the length of eel in the Netherlands. It is found that at a distance of only ∼10 km a large variance component is found, that can not be explained by mere distance. Apparently, the continental stock is fragmented by the fragmentation of the inland waters themselves. The geographical distribution of the continental fisheries is exemplified in an analysis of the dispersion of Dutch fishing licence holders over the country. It is shown that the licence holders are highly over-dispersed, except for the companies fishing on lake IJsselmeer. It is concluded that the distribution pattern of the European eel is characterized by great uniformity in the recruitment stage over the majority of the continent. In the growing stages, the stock (and fisheries) exist in extremely small, fragmented units. It is argued that this dual distribution characteristic necessitates large-scale, continent-wide management, while assessment of the fragmented continental stock and centralized management of the scattered fisheries is not practicable.