Silver hake (Merluccius bilinearis) larvae preserved in either formalin or ethanol decreased in length over time, most shrinkage being achieved in the first 15 d. The magnitude and variability of the length reduction was greater for smaller larvae. Rate and magnitude of shrinkage for ethanol-preserved larvae exceeded those of formalin-preserved larvae. Frozen specimens were extremely variable in length change response, and we noted a transition from shrinkage to expansion with increasing larval length.
The abundance of P. decipiens sampled from the stomachs of 553 grey seals (aged 0-48 years) collected during 14 field trips to Sable Island in 1983 and 1989 did not change significantly between years, even though the seal population has been increasing at over 12% annually and there has been a substantial decline in the fish biomass upon which they depend. The proportion of mature worms in the seals’ stomachs has decreased, however. Seal growth, expressed in terms of either age orlength, showed the strongest correlation with total worm abundance. These infections were not completely eliminated at any time during the year, but a seasonal pattern in worm abundance was apparent. Among the youngest seals an inverse relationship was demonstrated between the abundance of P. decipiens and another parasitic nematode, Contracaecum osculatum. Sexually mature P. decipiens were found in pups within 3 to 4 months of the commencement of independent feeding, and the abundance of P. decipiens progressively increased throughout the first year of life. Male pups contracted more worms than female pups of the same age. P. decipiens abundances in juvenile seals were primarily associated with seasonal pattern and age, with C. osculatum abundance still influencing the abundance of P. decipiens, but to a much lesser extent than seen with pups. Length of seals was the main predictor of total worm abundance in adult seals, with a seasonal pattern being next in order of importance. Age was also significant, possibly representing a component of growth not accounted for by length alone. No relationship between the abundances of P. decipiens and C. osculatum was apparent for adult seals. The seasonal pattern in total worm abundance of juvenile and adult seals was characterized by declines during the winter and mid-summer. We suggest these declines are due, respectively, to the breeding season fast and one or both of 1) a change in seal diet from primarily highly infected fish species to less infected ones, and 2) a partial fast during the annual moult. The proportion of mature worms increased during reductions in worm abundance throughout most of the year, but during the breeding fast both total abundance and the proportionmature declined.
A compilation of groundfish mark-recapture studies conducted in the Northwest Atlantic from 1953 to 1985 was examined by analysis of deviance to determine the effects of release parameters on subsequent recoveries of Atlantic cod (Gadus morhua), haddock (Melanogrammus aeglefinus), pollock (Pollachius virens), and American plaice (Hippoglossoides platessoides). Fish length was a major determinant of recoveries for all four species, with recovery rates generally increasing with increasing fish length. Depth of capture was a significant determinant of recoveries for cod and haddock, with recovery rates decreasing as depth increased. Year of release was a significant determinant for all four species, with recovery rates declining in recent years. Declines in recovery rates of cod, haddock, and pollock occurred during certain months or seasons. Recovery rates decreased where fish were tagged in areas most distant from inhabited coastal regions, but the interpretation of this effect is complicated by changes in the fisheries over time between areas. Recovery rates also decreased with increasing catch size and varied between different tag types and capture methods. The results should prove useful in the design of tagging protocols and analysis of recovery data.
Three species of anisakine nematodes (Pseudoterranova decipiens, Contracaecum osculatum, Anisakis simplex) co-occur in the stomachs of Sable Island harbour seals (Phoca vitulina). The sealworm, P. decipiens, was the commonest nematode in these seals. Anisakis simplex was found in much smaller numbers, none mature, indicating that the harbour seal is not a true final host to this parasite. Contracaecum osculatum was rare but half were mature. Pseudoterranova decipiens increased in abundance with size of the seal. An inverse relationship was observed between P. decipiens abundance and the age of seals of similar size, probably owing to changes in diet. Numbers of P. decipiens may have declined over the summer, coincident with an increase in the proportion of mature worms in the stomach. From similarities between the worm infections of grey seals (Halichoerus grypus) and harbour seals, we infer that A. simplex abundance may also exhibit a decline in abundance. Contracaecum osculatum was only encountered during the latter half of the year, suggesting an association with prey species of corresponding periodicity in their distribution. We estimate that the abundance of sealworm in harbour seals is about 2.5% of that carried by the grey seal population. This could imply that harbour seals represent an insignificant vector of the sealworm infecting commercial fish species in the Northwest Atlantic, provided density-dependent relationships exist between worm abundances in different host species.Résumé : On trouve trois espèces de nématodes anisakinés (Pseudoterranova decipiens, Contracaecum osculatum et Anisakis simplex) dans l'estomac des phoques communs (Phoca vitulina) de l'île de Sable. L'anisakidé P. decipiens est le nématode le plus commun chez ces phoques. Seulement de petits nombres d'A. simplex ont été rencontrés, aucun à maturité, ce qui indique que le phoque commun n'est pas l'hôte terminal réel de ce parasite. Les C. osculatum étaient rares, mais la moitié étaient parvenus à maturité. Chez P. decipiens, l'abondance augmentait avec la taille de l'hôte. Il y avait une corrélation négative entre l'abondance de P. decipiens et l'âge de phoques de même taille, probablement à cause de changements dans le régime alimentaire. Le nombre de P. decipiens a peut-être diminué au cours de l'été, alors que la proportion de vers à maturité dans l'estomac augmentait. Étant donné les similitudes entre les infections des phoques gris (Halichoerus grypus) et des phoques communs, nous supposons que l'abondance d'A. simplex subit probablement aussi un déclin. Le C. osculatum n'a pas été vu avant la deuxième moitié de l'année, ce qui semble indiquer qu'il est associé à des espèces de proies qui possèdent des périodicités semblables dans leur répartition. L'abondance des anisakidés chez les phoques communs équivaut à environ 2,5 % de celle qui prévaut chez les phoques gris. Il se pourrait bien que le phoque commun soit un vecteur peu important des anisakidés parasites des poissons d'intérêt commercial dans l'Atlantique du nord-ouest,...
Hot branding has been used for many years by researchers to identify seals from a long distance. In livestock, cold branding has been proposed as an alternative because it is thought to be less painful. The purpose of this study was to compare the healing process of hot and cold brands applied to harbour seal pups (Phoca vitulina). A total of 306 animals was branded with a unique set of four characters: three applied for 3–5 s with an iron heated to 500°C, and one applied for either 10 or 20 s with an iron frozen to –175°C. At three subsequent times over 10 weeks, 43, 41 and 51 animals, respectively, were recaptured, the macroscopic appearance of their brands recorded, and biopsies taken for microscopic examination. Cold brands had a faster healing rate than hot brands. However, they resulted in less destruction of hair follicles, and cold brands applied for 20 s caused more depigmentation. Regrowth of hair follicles could subsequently obscure brands, while depigmentation reduces the contrast between the brand and the surrounding fur. Cold brands applied for 20 s also caused more extensive deep vascular damage, which subsequently may have resulted in deeper wounds in some of these brands. Yet, macroscopically, other cold brands, or portions thereof, were almost invisible. On the basis of this short-term study, the technique of cold branding that we used in harbour seals does not appear to be as reliable as that of hot branding to provide permanent legible brands.
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