ALBERT

Description: A pathogenic species of marine slime mold, Labyrinthula, has been identified as the etiological agent of the present recurrence of wasting disease of eelgrass, Zostera marina. It is also implicated as causing the previous epidemic eelgrass wasting disease that occurred in the 1930s. We propose Labyrinthula zosterae sp. nov. for this pathogen based on its host specificity, cytology, characteristic growth patterns in culture, cell size, color in mass, and aggregation structures.

Description: Starvation resulting from failure to feed successfully after absorption of the yolk reserves has been proposed to be a major source of pre-recruitment mortality in squids. To test this hypothesis, methods must be developed to determine whether paralarvae have fed successfully at sea. When paralarvae are stained with Alcian Blue and then cleared with trypsin, the entire digestive tract can be examined intact for the presence of food. This method was used for Abralia trigonura and Sthenoteuthis oualaniensis paralarvae from Hawaiian waters. Approximately 9% of the former and 16% of the latter contained recognizable food material, mostly crustacean fragments. Food was found in the stomach, caecum, and intestine. The smallest specimen of A. trigonura with recognizable food in its digestive tract was 2.2 mm dorsal mantle length (DML), while for S. oualaniensis the smallest was 5.2 mm DML. The method is also useful for visualizing the ontogeny of the digestive-tract organs, beaks and radula, and other organs such as statocysts and eyes.

Description: Inadequate identification of octopus age classes has severely limited field studies of their biology. Four predictions are made to differentiate males at the plateau of growth that precedes senescence, i.e., mature males, from immature males. Compared to immature males, mature males are predicted to be 1) more mobile because their reproductive fitness depends on the number of receptive females they encounter; 2) more often injured, due either to increased mobility or decreased regeneration capacity; 3) more attractive as mates due to their maturity; and 4) mature males, overall, are predicted to be larger due to their advanced age. An intertidal population of Octopus digueti, sampled for 1 year, provided data to test the hypothesis that males with a few conspicuously enlarged suckers represent a mature age class as characterized above. As a group, males of O. digueti with enlarged suckers met these expectations; therefore, the presence of enlarged suckers is concluded to accurately indicate male maturity. I suggest enlarged suckers act as chemoreceptors of chemical cues released by receptive females and thus may contribute directly to male fitness.

Description: Opportunistically collected information on sea temperature and wind was used in a preliminary investigation of physical factors affecting jigged catches of chokka squid Loligo vulgaris reynaudii. Results revealed sea temperature and wind to be correlated with catches during part of the summer upwelling season (October and December) in 1988. Multiple linear regression analysis confirmed that sea temperature was a highly significant explanatory variable (p = 0,0000) for catches from three boats, as well as for the overall catch. Wind direction also played a significant role (p = 0,0085) in the overall catch. A statistical linear multiple regression model is proposed for each boat and for the total catch. Upwelling events are suggested to play a major role in the availability of squid on the inshore spawning grounds (〈50 m) during summer. With further study, other independent physical variables, such as currents, swell height and turbidity, are likely to be introduced into the proposed model.

Description: The feeding patterns of fish caught on the inshore (〈50 m deep) spawning grounds of chokka squid Loligo vulgaris reynaudii were investigated between November 1988 and September 1990. Fish were sampled by demersal trawl, gillnet, handline and longline. SCUBA was used to observe interactions in situ. Potential predators consisted of 16 species each of teleost and elasmobranch. Of the teleosts, five species preyed on whole squid and one appeared to have scavenged squid fragments. Of the elasmobranchs, 12 species had squid in their stomachs, nine of these with a high incidence (〉33% frequency of occurrence). The squid were in spawning condition when taken and no spent squid were recovered from stomach contents. There was no evidence that squid had been moribund when ingested and no dead or moribund squid were encountered while diving during the two-year study. Cannibalism by squid was observed. Marine mammals and avian predators were rarely sighted on the spawning grounds.

Description: The methodology for analysis of marine mammal diets may be thought of as a series of choices; about the sampling regime, the type of sample, the processing of samples, the identification of prey remains, the quantification of prey importances, and the estimation of population food consumption. In addition to directed sampling, samples may be obtained directly or opportunisitically and the most frequently used types of sample are gut contents of dead animals, and faeces. Direct observation of feeding may be possible for species living inshore, and humane approaches to sampling (e.g. lavaging) have been succesfully applied to seals, but all methods are subject to bias. Identification of fish prey usually relies on recognition of otoliths, but additional information may be obtained from other hard remains or serological analysis of proteins. Remains of invertebrate prey may also be identified from hard parts. A variety of methods exists for quantifying the importance of prey in marine mammal diets. The most useful currency is probably prey biomass but, for fish, natural variation in otolith size-fish weight relationships makes it difficult to estimate fish weights from otolith size. Also, otoliths are reduced in size or lost during digestion. Notwithstanding these problems, otoliths are widely used. If the diet of a population has been adequately characterised, the amounts of each prey type consumed may be derived from direct or indirect estimates of energy requirements. Ideally the measurements should be taken in the field. Possible improvements in methodology include improved calibrations for otolith measurements, the development of keys and guides to fish bones, and of serological methods for identifying fish proteins. Feeding is normally inferred rather than directly monitored and a means for remote detection of prey ingestion and defaecation would greatly enhance the interpretation of foraging activity. To predict diet choice it is necessary to undertand the underlying behavioural mechanisms. Measurement of the energetic costs of prey capture would be an important step in this direction.

Description: The enoploteuthid cephalopod Abraliopsis lineata is re-described and its generic position discussed. Specimens for the present study were captured during the Indian Ocean Expedition of RV Meteor in 1987, where the species occurred in considerable numbers. The geographical distribution of A. lineata is described and discussed. The detailed analysis of the photophore pattern of the present specimens differs from the original description. The diagnostic features in the male, especially the structure of the hectocotylus which separates A. lineata easily from the members of the subgenus Pfefferiteuthis, are outlined. The morphological differences which separate A. lineata from A. gilchristi, the only other member of the subgenus Micrabralia, are summarized.

Description: Samples of Loligo gahi (D'Orbigny) were collected from commercial fishing vessels in the Falkland Islands Interim Conservation and Management Zone (FICZ) between March and October 1987, and from the R/V Wieczno during a survey in August 1988. Samples were divided according to the two fishing seasons (February to July; August to October) and the samples from the scientific survey were pooled with those of the second commercial fishing season. L. gahi were aged using putative daily growth increments within the statoliths. There was indirect evidence that growth increments in the statolith were laid down at the rate of one per day. The maximum life span of the males was a little over 1 year and was approximately 1 year in females. Back-calculation ofthe month of hatching reveals the presence of two spawning groups within the FICZ population which give rise to the two fishing seasons. Growth rates were calculated for both sexes from both seasons. There was considerable individual variation in growth rate in squid from both seasons and there was more scatter in the data from first season samples taken from the commercial fishery alone. Log-linear growth models give the best fit to the data combining the fishery and scientific survey samples from the second season. Very low or apparent negative growth exhibited by squid sampled during the first season may be due to bias because the commercial fishery samples a narrow depth range. Migration of schools of squid of similar size through the narrow depth range in which the fishery operates probably yields samples that are size selected. Care should be taken in modelling squid growth where migratory effects may bias the data.

Description: Cephalopods, including octopus, cuttlefish, and squid, are a major component in the marine biomass. Due to high behavioral diversity among species, uncertainty exists concerning the general applicability of sampling and capture techniques. This factor impacts on understanding of the overall abundance and status of stocks. In addition to accelerated exploitation of cephalopods by international fisheries countries, cephalopods represent a major prey component in the diets of other marine species. In the Southern Ocean alone, it is estimated that the consumption of cephalopods by seabirds, whales and seals may reach 34 million tons annually. On a worldwide basis, the total natural predation on cephalopods probably exceeds 100 million tons, more than the total annual harvest of aquatic species by humans. Scientists and fisheries managers are not able to accurately measure cephalopod stocks under direct exploitation. Yet the relatively few species being exploited comprise only a fraction of available worldwide resources. Some of the traditional capture techniques are discussed with an indication of their effectiveness; possible options and access to new or latent methods also are noted.

Description: Professor Gilbert L. Voss served the leading role in American cephalopod research for nearly 40 years. He drew attention to the importance of cephalopods in marine ecosystems and as fisheries resources. Through his research and that of his students he significantly advanced the knowledge of cephalopod systematics, distribution and biology. An insight into Gil Voss' ideas and attitudes concerning cephalopod research and teaching is given. Voss's broad interests are indicated in his bibliography of over 210 diverse published items, including 73 book reviews, 16 editorials, and 124 research papers on cephalopods, fishes, crustaceans, botany, zoogeography, history of oceanography, anthropology, fisheries, and marine and deepsea biology. He authored or co-authored descriptions of two new families or subfamilies, 6 new genera and more than 65 new species or subspecies.