The Fisheries Research Board of Canada has sponsored several expeditions in Canadian waters since 1947. A large number of specimens of euphausids and pelagic amphipods have been collected from the various expeditions. [...]

Commercial harvest of fish stocks and their appropriate management requires an understanding of their population dynamics and of their ability to sustain exploitation. Here, some ecological and evolutionary consequences of excessive exploitation are examined. In Chapter 2 I evaluate the knowledge base and status of commercially exploited marine populations that undergo formal stock assessment. Despite a bias towards industrialised countries and stocks of commercial importance, I show the pervasiveness of overexploitation and, by using reference points of stock status, identify important regional differences in the effectiveness of fisheries management. In Chapter 3 I develop a data format suitable for ecological analyses to best disseminate the valuable information contained in scientific trawl surveys. This data format is suitable for inclusion into the public Ocean Biogeographic Information System (OBIS) and provides detailed observations that are suitable to the reconstruction of important fisheries-independent stock indices. In Chapter 4 I examine the spatiotemporal dynamics of groundfish populations. A positive abundance-occupancy relationship was estimated for the majority of groundfish populations examined suggesting that this well-described terrestrial pattern is also pervasive in the marine environment. Spatial hysteresis was exhibited by numerous populations, indicating that the spatial distribution of individuals failed to recover despite recoveries in abundance. In Chapter 5 I estimate the demographic consequences of changes in growth and maturation characteristics. The ability of a population to sustain harvest, and its ability to recover from previous depletions can be overestimated because of trends towards earlier maturation and slower growth. In Chapter 6 I conclude the thesis by discussing the implications of my research to fisheries science and management. I argue that trends in the spatial distribution and the overall productivity of populations must be accounted for when determining sustainable fishing levels and when predicting recovery trajectories under various catch abatement scenarios. While successful management measures have been implemented in a number of marine ecosystems, this thesis highlights the importance of improving our capacity to understand the dynamics of exploited populations and to fully use the wealth of available monitoring and assessment data.

No description available.

No description available.

The effects of salinity on the physiology and ecology of the mud-dwelling estuarine animal Corophium volutator (Pallas), a crustacean amphipod, have been investigated. A study of the effects ot salinity on the distribution and abundance of C. volutator on the estuary of the River Ythan, Aberdeenshire, indicates that 2‰ is a critical minimum salinity controlling its distribution. In areas with salinities between 2 and 5‰ C. volutator was present, but in reduced numbers. In areas with salinity greater than 5‰ , the distribution and abundance of C. volutator were controlled by the nature of the substrate; however, in areas with suitable substrates, but where the salinity was below 5‰ , the effects of salinity override the effects of the substrate. Experimental studies indicated that, if supplied with mud, it will survive the salinity range of 2 - 50‰, and without mud, the range 7.5 - 47.5‰. Moulting occurred in salinities of 2.6 - 46‰ , but most frequently in tho range 5 - 20‰ . Growth occurred at a maximum rate in 15.4 o/oo and only slightly slower at 4.4 and 30.6‰ ; but below 4.4‰ the growth rate was progressively reduced. The effects of salinity on the various stages in the life cycle are discussed. Freezing point studies show C. volutator to be a hyperosmotic regulator, having a tissue tolerance range of 13 - 50‰ . The effect of size, sex, feeding and moulting on the freezing point have been investigated. C. volutator was found to produce urine hypoosmotic to the blood when acclimated to low salinities, and isosmotic urine at salinities above 20‰ . Over a range of salinities from 1 - 35‰ , C. volutator was found to maintain Na+, K+,Ca ++,Cl-, more concentrated than the medium, and Mg++ less concentrated. The restricted permeable areas of the cuticle have been localised by silver staining. The oxygen consumption of animals of the same size, at the same level of activity, and at the same temperature, did not differ significantly between animals in different salinities. A salinity preference range of 10 - 30‰ has been demonstrated. Relevant literature on estuarine life, and osmoregulation of crustacea is reviewed. The adaptations of C. volutator to an environment with varying salinity are discussed.

Graduation date: 1999

No description available.

A free-fall oceanographic instrument has been used to measure vertical microstructure scale gradients of horizontal velocity, temperature and electrical conductivity. The velocity gradients, or shears, were measured at scales between 3 and 40 cm by an airfoil shear probe whose specifications and calibration procedure are discussed. Data collected in the equatorial Atlantic in July 1974 indicated a consistent pattern of turbulence near the velocity core of the Atlantic Equatorial Undercurrent. (The velocity core is the region of maximum speed. ) The most intense turbulence was found above the velocity core of the undercurrent. Turbulence in the velocity core was weak and intermittently spaced. Below the core, near the base of the thermocline, moderately intense turbulence was found. The rate of viscous dissipation of turbulent energy has been estimated from the shear measurements, and typical values were 3x10 ⁻³ cm² sec ⁻³ above the velocity core. Spectra of the shears have been computed. At small wavelengths the measured spectral coefficients fall below the universal Kolmogoroff spectrum. This discrepancy between the two spectra is attributed to spatial averaging of velocity fluctuations by the shear probe. The estimates of viscous dissipation include a correction for this spatial averaging. An energy balance has been determined for the turbulent velocity fluctuations. Above and below the core the basic balance is local production of turbulent energy equals local dissipation, and this balance gives a vertical eddy viscosity of order 10 cm² sec ⁻¹ above the core. The equation of the energy balance of the average motion has been vertically integrated at the equator where meridional terms are assumed small. In the South Equatorial Current the rate of energy gain from the average zonal wind stress is balanced by the rate of energy loss to the zonal pressure gradient plus the rate of dissipation. In the undercurrent, above the core, the rate of energy gain from the zonal pressure gradient equals the rate of dissipation within the uncertainty of the measurements, and the advection term is small but not negligible. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate

The role of heterotrophic bacteria in the carbon and nitrogen flux of the pelagic food web was investigated during laboratory and field-based studies of the temporal development of the planktonic community after upwelling. Bacterial community structure, activity and production were closely coupled to the upwelling cycle and to the dynamics of the phytoplankton community. The initial bacterial population (<l x 10⁶ cells ml⁻¹, 20 to 40 μg C l⁻¹) was metabolically dormant. Increased availability of phytosynthetically produced dissolved organic carbon (PDOC) stimulated bacterial growth (0.016 h⁻¹) and abundance (8 to 10 x 10⁶ cells ml⁻¹, 140 to 200 μg C l⁻¹). Rapid successions in the dominant plateable strains were attributed to substrate preferences and substrate availability. Significant correlations of bacterial biomass with total standing stocks of phytoplankton and particulate carbon provided evidence of close coupling between bacteria and PDOC, and between bacteria and recalcitrant substrates available during phytoplankton decay. These relationships were best described by power functions, suggesting that bacterial biomass was relatively reduced at high levels by predation. A microcosm study indicated that zooflagellate predation could control bacterial biomass. Low net growth yields (34 to 36%) of flagellates suggested inefficient transfer of carbon to higher trophic levels, but considerable nitrogen regeneration (ca 6 to 7 μg N mg dry weight⁻¹ h⁻¹). Thymidine-measured bacterial production (TTI, <0.1 to 1.25 mg C m⁻³ h⁻¹) was linearly related to phytoplankton growth. Non-uniform response of bacteria to added tracer substrates may result in underestimates of bacterial production by 2 to 34 times by TTI, particularly in deep or oligotrophic waters, or during phytoplankton decay. Close coupling of copepod (Calanoides carinatus) production to the upwelling cycle suggested co-existence of the microbial food web and the classical diatom-copepod food chain. Recently upwelled water was dominated by phytoplankton. Assuming that all phytoplankton carbon was available for utilisation, copepods and bacteria were calculated to consume approximately 12 and 22% of primary production respectively. As the bloom declined the planktonic community was increasingly dominated by bacteria, detritus and mesozooplankton. On average, copepods consumed 60% of primary production, while bacteria consumed 49%. Carbon consumption requirements of both bacteria and copepods were satisfied by resource partitioning and carbon cycling. Under food-limiting conditions herbivorous copepods may switch to omnivory, ingesting microzooplankton of the microbial food web, and stimulating enhanced remineralisation to further sustain primary production. A generic size-based simulation model of the dynamics of the plankton community indicated that bacteria and the microbial food web increase the overall productivity of the planktonic food web, and that heterotroph predation in the smaller size classes (<200 μm) is an important mechanism in nutrient recycling.

Bibliography: pages 147-155. / 92 cytheracean species, representing 44 genera are recorded from the Palaeogene Agulhas Bank and west coast margin of South Africa. 11 genera and 3 species are common with the Upper Cretaceous faunas. 12 genera (18 species) are left in open nomenclature. The following genera are represented:- Bythoceratina, Incongruellina, Ruggieria, Eucythere, Krithe, Parakrithe, Eucytherura, Cytheropteron, Ambostracon, Urocythereis, Muellerina, Leguminocythereis, Loxoconcha, Schlerochilus, Poseidonamicus, Bradleya, Agrenocythere, Australileberis, Chrysocythere, Costa, Echinocythereis, Haughtonileberis, Henryhowella, Parvacythereis, Phacorhabdotus, Soudanella, Stigmatocythere, Togoina, Trachyleberis, Veenia, Atlanticythere, Xestoleberis. Data on South African Cretaceous and Palaeogene ostracod faunas are discussed in terms of: faunal associations for the South African Palaeogene JC-1, Agulhas Bank and west coast provinces; characteristic species of Upper Eocene and Upper Eocene to Oligocene strata; generic variations across the Cretaceous/Tertiary boundary. Palaeo-environmental trends from a Cytheracea, Cypridacea + Bairdiacea, Cytherellidae (CCBC) plot indicate a sea level change from <100m (Palaeocene- Eocene), to shallower water with restricted circulation (Upper Eocene) to moderate depth, 100 - 200m (Lower Oligocene). South African faunas are compared with those from adjacent Palaeogene ostracod faunal provinces. Strong generic links occur with West Africa (8 genera in common) and Pakistan (9 genera in common) with only 3 genera in common with Australia and 3 with Argentina.