ALBERT

Description: An investigation was carried out on larvae of the oceanic tropical squid Sthenoteuthis pteropus in the equatorial Atlantic (2°30′N–7°S;12°W –8°30′E) The age of the larvae was calculated from the statolith microstructure of 20 larvae; mortality was estimated from the size structure of 1128 larvae. The larval stage lasts 32–38 days. At ages ranging from 14 to 38 days. the daily relative growth rates of mantle length decrease from 7.5 to 2.8% day −1 and from 14–16 to 5.8% of body weight day −1 At age 12–24 days, mortality rates were estimated using both raw catch data and corrected data accounting for net avoidance. The mean value of raw mortality rates was 0.189, the corrected value was 0.158. During the proboscis division (transformation of the larva into juvenile) at age 25–35 days, a sharp decrease in larval growth rates and a simultaneous increase in mortality rates (raw 0.443, corrected 0.379) were observed.

Description: In 1988 and 1989 the occurrence of external diseases in fish from the German part of the Wadden Sea was quantified. Thirty-two stations, located along seven transects including four estuaries, were sampled monthly or at 3-month intervals with shrimp trawlers: more than 124 000 fish were studied. Six percent of the seven dominant fish species of 〉 12 cm length were diseased. In fish species which complete their life cycle in the Wadden Sea (gobies, hooknose, eelpout, sea scorpion) the total disease incidence was below 0.4%. In whiting, plaice and sole it was between 0.5 and 2.5%, while 6–8% of smelt, cod, eel, dab and flounder suffered from external lesions. The incidence of most diseases increased with increasing fish length. Similar geographical patterns in prevalence were observed for: (1) two types of skeletal deformities, (2) lymphocystis in dab and flounder, (3) papillomatosis in smelt and dab and (4) several infectious ulcerative diseases. Most of these ulcerative diseases of cod and flounder occurred on central estuarine stations, suggesting an impact of the relatively low, but greatly variable salinity on disease development. Buccal granulomatosis of smelt and papillomatosis of eels showed the highest incidence in the Elbe estuary as the most heavily polluted region of the Wadden Sea. A causal relationship between disease development and pollution, however, is not yet clear and requires experimental evidence. The disease types found are ranked into three priority groups regarding their indicator value for a pollution monitoring on the basis of fish diseases. There is evidence that the total disease load of fish in the Wadden Sea is higher than in other shallow coastal regions outside the North Sea. Little is known of the effects of these diseases on single fish and fish populations. “Yellow pest” of cod, which was recorded for the first time during this survey, and which occurred with an incidence of up to 14% in single estuarine samples, causes the most serious lesions and is supposed to be lethal. In total, however, the effects of a number of pathogenic parasites on fish survival is considered to be more serious than that of deformities and infectious diseases.

Description: 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.

Description: Artificial selection processes associated with harvesting may operate over relatively short time scales in short-lived semelparous species. The ommastrephid squid Illex argentinus on the Patagonian Shelf is the target of a major fishery. Recent work has provided new information on the biological characteristics of squid in this fishery. That information has been utilized in the development of a model of the cohort dynamics and some of the within-seasons selective effects considered. The model results are consistent with earlier data from the shelf fisheries, supporting suggestions that the males nature and migrate earlier towards the spawning grounds than the females. Earlier maturation results in a smaller mean size in the spawning stock, while later maturation results in greater exposure to the fishery and a reduced numbers of individuals surviving to spawn. Under the current fishing regime greater egg production and a larger spermatophoric complex mass for the whole cohort is achieved by relatively late maturation. In general, however, the earlier maturation occurs, the earlier is the peak in total egg production. The within-season pattern of effort expenditure in the fishery can affect not only yield from the fishery but also the reproductive potential of the spawning stock. The management policy adopted for this fishery is likely to be conservative in terms of maintenance of a spawning stock, however, the potential for selective effects is larger and this may affect both yield and reproductive potential. The results are discussed in relation to short- and long-term effects in the fishery and the implications for future research requirements.

Description: Gray whales (Eschrichtius robustus) feeding in the northern Bering Sea produce prey-rich mud plumes that provide ephemeral foraging opportunities for seabirds. Approximately 67% of all gray whales were attended by birds. In four whale-associating bird species (Northern Fulmar, Fulmarus glacialis; Red Phalarope, Phalaropus fulicaria; Black-legged Kitti-wake, Rissa tridactyla; and Thick-billed Murre, Uria lomvia), from 17 to 87% of all individuals that we observed on the water or foraging were in the whales' mud plumes. The combined density of these same four species was strongly correlated with whale density over a broad range of spatial scales. The whale-associating seabirds exhibited species-specific patterns of foraging behavior at plumes, including differences in mean group size, mean residence time, and patterns of movement between plumes. Birds tended to form larger groups and to form more mixed-species flocks in association with whales. The association of marine birds with gray whales in the Bering Sea provides a model system for examining seabird interactions at fine-scale oceanographic patches and demonstrates the importance of these patches in shaping patterns of seabird distribution and behavior.

Description: Mortality of two dogs, after exposure to water of a brackish lake on the German North Sea coast in 1990, is considered to be caused by a toxic Nodularia spumigena Mertens bloom.

Description: The Rhynchoteuthion larvae of Illex argentinus resulting from summer spawning in North Patagonic shelf waters, its distribution and abundance, are described in this paper. The material was collected in the Argentine Sea (35–55°S) by means of plankton nets. The research cruises were made by the R/V Shinkai Maru and the R/V Walther Herwig during the period April 1978 to April 1979. The most important spawning ground of the summer spawning subpopulation is found in continental-shelf waters (between 43 and 46°S) during the period December-February. This area was established on the basis of both ripe (December) and spent females (February). The larvae which were caught during the same period, especially in March, confirmed the spawning area of this demographic unit. The larvae showed the length of the mantle (ML) to be from 1.2 to 6.5 mm. Tentacles were splitting in specimens from 5.0 to 6.5 mm ML (transition stage). When 7.0 mm ML or more, all specimens were juveniles and had their tentacles completely separated. Larvae were characterized as type C, following the proposal of Sato (1973) and Sato and Sawada (1974) in the Bulletin of the Shizuoka Prefectural Fisheries Experimental Station.

Description: A joint research cruise (Japan-Argentina-Uruguay) was carried out in the South-western Atlantic during August-September 1989 in order to study the winter-spawning and hatchery areas of Illex argentinus, and also the migration pattern of the juveniles towards the continental shelf. A few Rhynchoteuthion larvae were found in subtropical waters of the Brazil Current, next to the Brazil-Malvinas confluence, and in the frontal zone with shelf water, but never at temperatures below 14°C. Large numbers of juveniles found in subantarctic waters (6–10°C) on the shelf were probably migrating southward from their hatchery grounds following the zooplankton concentrations on which they were feeding.

Description: Ripe egg dimensions in the squid genus Illex are close to the minimum for cephalopods. The average diameter varies significantly depending on species (0.77–0.82 mm in I. coindeti , 0.75–0.88 mm in I. illecebrosus , and 0.96–1.04 mm in I. argentinus ), on geographical distribution intraspecifically, e.g. I. argentinus (0.96–0.97 mm in the shelf groups and 1.04 mm in the slope oceanic group), and between pre-spawning and spawning females of the summer-spawning shelf group of I. argentinus (0.97 and 0.92 mm, respectively). The potential fecundity (PF), defined as total oocyte stock both in the ovary and oviducts, depends on mantle length (ML in each species. It varies from 90 000 (ML = 150–160 mm) to 800 000 (ML = 230–250 mm) in I. coindeti , from 200 000 to 630 000 (ML = 220–280 mm) in I. illecebrosus , and from 75 000 (ML = 150–170 mm) to 1 200 000 (ML = 360–380 mm) in I. argentinus . It is possible to estimate the actual value of PF shortly before vitellogenesis begins and up to a start of spawning, when the diameter of the smallest oocytes exceeds 0.05 mm. The summer-spawning shelf females of I. argentinus release about of 70% of PF. Their spawning is intermittent and ripe egg production decreases over time with only a 50% replacement of the initial stock of vitelline oocytes and a decreasing volume of eggs at each release. Feeding activity decreases and the mantle wall and internal organs shrink once spawning commences. In spent animals, a degeneration of both vitelline and protoplasmic oocytes occurs. The squids genus Illex is one of typical r-strategists among the cephalopods.