Growth and feeding habits of grey seals (Halichoerus grypus) in the northwestern Gulf of St. Lawrence, Canada

Growth and feeding habits were determined for 82 grey seals (Halichoerus grypus) collected in the northwestern Gulf of St. Lawrence, Canada, between 3 July and 6 December 1983. Male grey seals reached an asymptotic standard length of 242 cm, whereas females attained a length of 201 cm. Most (96%) females 175 cm or longer and 5 years of age or older were pregnant. A larger proportion of grey seal stomachs contained food items in July than in the other months sampled, regardless of sex or maturity status. The diet consisted primarily of cod (Gadus morhua), herring (Clupea harengus harengus), and capelin (Mallotus villosus), which together contributed 72% of the wet mass and 76% of the gross energy of all the prey consumed. Invertebrates contributed negligible mass or gross energy to the diet. Grey seals primarily consumed fish ≤30 cm in length and ate only one or two different fish species during any one feeding bout. Based on our stomach content analyses, the food consumed daily by adult male and female grey seals provided an average gross energy of 3628 and 2925 kcal (1 kcal = 4.18 kJ), respectively, which is consistent with daily energy requirements estimated using bioenergetic models. However, the large percentage of empty stomachs (50%), together with differential digestion of fish species, suggests that grey seals may not feed every day.

Isolation and characterization of antifreeze proteins from smelt (Osmerus mordax) and Atlantic herring (Clupea harengus harengus)

Antifreeze proteins (AFPs) from smelt (Osmerus mordax) and Atlantic herring (Clupea harengus harengus) were isolated using gel filtration, ion exchange chromatography, and high performance liquid chromatography. The AFPs of smelt appeared to consist of at least six components and those of Atlantic herring, of at least two components. The relative molecular masses of these antifreezes were 24 000 and 14 600, respectively. Amino acid analysis showed both proteins to be cystine-rich, type II AFPs like those of the sea raven (Hemitripterus americanus). In addition, smelt AFPs were found to be immunologically similar to those of the sea raven. The smelt AFPs differed from those of Atlantic herring and sea raven in that they contained a small amount of glucosamine (~3%). The activity levels of the smelt and herring AFPs were reduced in the presence of dithiothreitol, indicating the functional importance of intact disulfide bonds.

Plasma Antifreeze Levels Reflect the Migratory Behaviour of Atlantic Herring (Clupea harengus harengus) in the Southern Gulf of St. Lawrence

This study compared freeze protection conferred by blood antifreeze proteins to juvenile and adult Atlantic herring (Clupea harengus harengus) in the southern Gulf of St. Lawrence in December 1988. Juvenile herring had significantly lower plasma freezing points and significantly higher antifreeze activity than adults. Differences in antifreeze activity and in late autumn distribution suggest that juvenile herring are more capable of wintering in the Gulf of St. Lawrence than adults. This conclusion is consistent with our observation that during December, juveniles were present in shallow waters of Chaleur Bay, which is ice-covered during winter, while adults were found only in the deeper waters of Sydney Bight, which do not freeze during winter.

Reappearance of Spawning Atlantic Herring (Clupea harengus harengus) on Georges Bank: Population Resurgence not Recolonization

Spawning Atlantic herring (Clupea harengus harengus L.) have been recorded on Georges Bank for the first time since the collapse in 1977 of what had once been the largest herring fishery in the Northwest Atlantic. The reappearance after almost a decade could have resulted from resurgence of a residual extant Georges Bank population or from recolonization by fish from neighboring spawning groups. Three independent lines of evidence are consistent with the resurgence hypothesis: the Georges bank fish differed in age composition and isozyme characteristics from neighboring populations, and the reappearance was later than expected for recolonization. The degree of isozyme variability and of mitochondrial DNA lineage diversity gave no indication that stochastic events influenced the genetic structure of the herring population at Georges Bank after the collapse. The persistence of this population, in spite of considerable potential for recolonization, supports the discrete population concept in herring.

Direct and Indirect Estimation of Gillnet Selection Curves of Atlantic Herring (Clupea harengus harengus)

Length-specific selection curves for Atlantic herring (Clupea harengus) were calculated for a series of gillnets ranging in mesh size from 50.8 to 76.2 mm (stretched measure) using Holt's (1963) model (ICNAF Spec. Publ. 5: 106–115). These curves were than compared with direct estimates of length-specific selectivity obtained from a comparison of gillnet catch length frequencies with population length composition data as determined from acoustic surveys. Selection curves calculated indirectly using the Holt model were unimodal and congruent. The empirical selection curves however were multimodal and fishing power varied with mesh size. These differences in selectivities were due to the fact that herring were caught not only by wedging at the maximum girth but also at other body positions such as the gills and snout. Each of these modes of capture have different length-specific selectivity characteristics and, since the relative contributions of the different modes of capture varied both between nets and annually, the selection curve of herring for a particular mesh size is not unique. It can however be reasonably approximated when girth is used as the selection criterion. Direct empirical selectivities are therefore recommended when interpreting population parameters from herring gillnet catch data.

Identification of Spring- and Autumn-Spawning Herring (Clupea harengus harengus) using Maturity Stages Assigned from a Gonadosomatic Index Model

A model is developed to identify the spawning type of individual herring (Clupea harengus harengus) from the sympatric spring and autumn spawning stocks in the southern Gulf of St. Lawrence (NAFO Division 4T). The maturity stage is assigned from a gonadosomatic index model using discriminant analysis and the spawning type is determined from the maturity stage and the month of capture according to a detailed description of the annual maturity cycle of each type. The model is shown to be objective, quantitative, and precise. Greater than 97% overall agreement was achieved between the spawning type classification of individuals by histological means and by the model, significantly improving the identification accuracy compared with a macroscopic maturity stage key. The model also has the advantages of (1) identifying the spawning type directly by determining the "season of spawning" rather than the "season spawned" as is inferred from indirect evidence such as otolith characteristics or meristic data, (2) requiring easily obtained, quantifiable data, and (3) enabling the rapid treatment of a large number of specimens.