Pacific ocean perch (Sebastes alutus) is a slow growing species of demersal rockfish, which inhabits the continental slope of the west coast of North America. This species represents a highly commercial fishery and an important part of the groundfish fishery of British Columbia. A variety of biological factors are known to influence the concentrations of trace metals in fish, including, age, body size and diet; all of which vary in this species. Little is known of the concentrations of total mercury and total arsenic in Sebastes alutus from British Columbia, a Canadian province where marine groundfish have previously been found with elevated concentrations of mercury. The spatial variability of trace elements across different fishing regions within British Columbia is also unknown. Substantial variability in concentrations of both mercury and arsenic has been reported in marine fish from around the globe. In the case of arsenic, associations between concentrations in muscle tissue and a variety of biological variables are not frequently reported. This contrasts with mercury, which is known to be intrinsically linked to the biology of fish. Consequently, biological variability in fish has the potential to confound studies of mercury and possibly arsenic in fish. This thesis examines the influence of biological variables and fishing region on total mercury and total arsenic in Sebastes alutus from British Columbia. It also assesses the concentrations found in muscle tissue from a food safety perspective. Samples were obtained from a commercial fish processing plant on Vancouver Island and had been caught by a commercial fishing vessel in Hecate Strait, Queen Charlotte Sound and the west coast of Vancouver Island. A multivariate outlier determination method was used to quantify the natural background variability across all three fishing regions. Significant differences in concentrations between regions were identified. This spatial variability of total arsenic did not appear to be related to age, body or body size. However, the spatial variability of mercury concentrations appear to be associated with the size and age of the fish sampled. The outlier determination procedure also identified the presence of elevated concentrations of both mercury and arsenic in specimens that were determined to be outliers. Outliers originated predominantly from the west coast of Vancouver Island and exceeded regulatory limits for both mercury and arsenic. In addition to the outliers, estimated quantities of MeHg frequently exceeded Provisional Tolerable Intakes for children and pregnant women. Generalized Additive Models were produced to examine the effect of age, body size (length and mass) and diet (δ13C and δ15N) on concentrations of total mercury and total arsenic in Sebastes alutus within each fishing region. These identified significant nonlinear, qualitative patterns between mercury and body size in two out of three fishing regions. A significant nonlinear effect of age on arsenic concentrations was found. Model results also suggest an effect on arsenic concentrations of organic carbon sources; i.e., fish with stronger links to continental slope or inshore food webs (with relatively enriched δ13C signatures) had greater arsenic concentrations. / Graduate

The Nile perch, Lates niloticus (Linnaeus, 1758), is a predacious freshwater fish widely distributed throughout the Afro-tropic eco-zone. The species was introduced to Lake Victoria in the early 1950s and by 1980 it had dominated the fisheries of Lake Victoria. This was followed by a dramatic decrease in the Nile perch fisheries production due to uncontrolled exploitation. The purpose of this thesis is to provide fundamental knowledge that can be applied in aquaculture and fisheries management through the study of the reproductive biology of L. niloticus. The research was aimed at the studying of the diverse aspects of the reproductive biology of L. niloticus in the Lake Victoria, Ugandan populations. This included reproductive patterns in relation to proximate environmental conditions, size at sexual maturity, gonad and gamete structure, gametogenesis and induced ovulation. The size at 50% sexual maturity for female Nile perch was 59.4 cm, which is lower than the earlier reported size of greater than 90 cm total length. Male L. niloticus matured at 57.8 cm total length in Lake Victoria. Microscopy revealed that L. niloticus from Lake Victoria had one spawning period that started in November and ended in March. Type I atresia occurred at high frequency from March to June, and type III atresia was present from July to September and between November and December. Spermatogenesis in L. niloticus is cystic and sperm development is the result of asynchronous activation of the germ cells. Type II spermatozoa are simple, uni-flagellate aquasperm with no acrosome. Oogenesis in L. niloticus differed from that of other fishes in that no cortical alveoli were present in any stage of oogenesis. Numerous oil globules were present in the primary yolk vesicle stage. This formed one centrally positioned, large oil globule in the tertiary yolk vesicle oocytes during final oocyte maturation. Clove oil was an effective sedative and an anaesthetic for the handling of L. niloticus. Induction time was more rapid at clove oil concentrations of 50 - 100 μl L⁻¹ than in fish exposed to clove oil concentrations less than 50 μl L⁻¹. Fish exposed to high concentrations exhibited significantly short induction times of less than 240 seconds. On average, fish recovered within 673 ± 58 seconds for all the concentrations used. Prolonged exposure of L. niloticus to low clove oil concentrations of 2.5 - 10 μl L⁻¹ did not change the blood plasma cortisol, glucose, and the lactate and chloride ion concentration, relative to the control treatment. Captive breeding was attempted by conducting induced spawning experiments. Only final oocyte maturation was achieved using a decapeptide Gonadotropin Releasing Hormone (Dargin, sGnRH-MET), combined with a water-soluble dopamine receptor antagonist metoclopramide. This thesis suggests a research approach that provides a basis for aquaculture of the new species by first studying reproductive biology patterns and then linking the information to gonad and gamete structure so that spawning times can be estimated. It further provides insights into aspects of the reproductive biology of the species and the effects of hormonal intervention on oocytes by showing at which stage of oocyte development hormones should be applied in L. niloticus. Clove oil can be used to sedate and anaesthetise L. niloticus broodfish to reduce the stress related to the handling of large specimens.

Climate change and human land use leads to browning of waters with decreased visual conditions. This impacts the fish community via changes in foraging ability and food chain efficiency. There are indications that brownification leads to decreased body size of the Eurasian perch (Perca fluviatilis) and that roach (Rutilus rutilus) are favoured over perch in brown lakes since roach is less dependent on its eyesight when foraging. The aim with this project is to examine how browning impacts the fish community in lakes in the south of Sweden and if browning reduces the size of perch in relation to their age. Data on water colour and length-at-age for 1+ and 5+ perch as well as the number of perch and roach captured was collected from 20 lakes. The data was examined using linear regression and paired samples T-test in SPSS. The results show that browning does reduce the body size of perch. Perch is smaller in relation to their age in brown lakes. There was however no evidence indicating that roach is favoured over perch in brown lakes, but there was a difference between the number of 1+ and 5+ perch caught in relation to roach. The perch: roach ration decreased for older fish (from 1+ to 5+) indicating that there is a difference in survival rate. Survival rate of perch was however not dependent on water colour or TOC. This shows that climate change and increased browning could result in changes of the fish community and size structure of fish.

No description available.

No description available.

With a population estimate of 99 pairs, the Madagascar fish-eagle (Haliaeetus vociferoides) is one of the rarest birds of prey in the world. I investigated the ecological requirements of the Madagascar fish-eagle in 1994 and 1995 to help determine management action to prevent its extinction. I investigated fish-eagle foraging ecology in 1996 to determine its prey preference and whether fish abundance and availability affect fish-eagle foraging rates and foraging success. Madagascar fish-eagle nest and perch trees were taller, broader, had more unobstructed branches, and had a greater arc of accessibility than unused trees. Perch trees also were deciduous more often and had a narrower growth form than unused trees. Nest sites had more shoreline perch trees than unused sites. Lakes occupied by fish-eagles were deeper and clearer, and had more shoreline perch trees, more fish, a greater total fish weight, and more fish species than unoccupied lakes. I developed logistic regression models to predict the probability of Madagascar fish-eagle use based on the measured habitat variables. Nest and perch tree models included tree height. The nest site model included number of shoreline perches. Lake models included number of shoreline perches and either number of fish, total fish weight, or number of fish species. These models can be used to predict fish-eagle habitat use with > 70% accuracy. Introduced tilapia, Oreochromis spp. and Tilapia spp., made up the majority of both the gill net (66.3%) and fish-eagle catch (64.7%) in similar proportion, which suggests that the fish-eagle is an opportunistic predator. Replacement of native fish species by exotics, thus, probably has not been detrimental to the island's fish-eagle population. Male fish-eagle foraging success was positively correlated with number of fish, total fish weight, and number of fish species, which suggests that declines in the fish population could adversely affect the fish-eagle population. The results of this study indicate that Madagascar fish-eagles require bodies of water with large shoreline trees and an ample fish population. I recommend greater protection of aquatic habitats, monitoring and management of freshwater fish populations, and education of local people in sustainable tree harvesting practices. / Ph. D.

The yellow perch, (Perca flavescens), is an important commercial and sport fish in Indiana waters of Lake Michigan. The population is currently managed by temporary restrictions of commercial harvest. A computer simulation model was developed to examine the effects of various constant harvest quotas and alewife densities on yellow perch relative numbers.Model design is based on the SLAM II simulation language incorporating a FORTRAN biological subroutine. The age-structured population model includes measured or predicted biological characteristics of the dynamic pool model. Recruitment is based on a preestablished three-dimensional Ricker stock-recruitment function including alewife (Alosa pseudoharengus) species interaction as a constant or stochastic factor. Sex-specific natural mortality rates were established through life history parameter analysis and the von Bertalanffy growth factors. Density-dependent growth is incorporated into each year of a model run and fluctuates with the simultaneous density of fish. Constant levels of commercial harvest ranging from 0 to 700,000 kg were used in 20-year forecasts. Initial conditions for model runs were 1984 and 1994 trawl CPUE levels when yellow perch were at high and low levels, respectively according to standardized sampling. Response variables were examined as mean catches over each forecast length and included: age 2 fish, spawning stock (z 190 mm), and total catch > age 1.Alewife densities had a tremendous impact on mean catches of the response variables. Highest catches under any forecast period occurred when alewife was considered absent from the system. Catches declined as alewife density was increased as a 20-year constant under each harvest regimen.Catches of spawning size fish were maintained at highest levels for all forecast periods when harvest was set to zero. Catches of young fish were moderate with this harvest regimen if initial catch conditions were high such as in 1984. Catches of young fish were always higher in the absence of a commercial fishery if initial catch conditions were low such as in 1994. Low to moderate harvest quotas could maintain moderate levels of young fish for the forecast length if initial model conditions were high. However, these quota levels for the 1984-2004 forecast length resulted in lower mean catches of spawning size fish as compared to the no commercial fishery regimen. The best case scenario for all response variables when initial catch conditions were low was under a no commercial harvest regimen. / Department of Biology

I determined differences in yellow perch gill-net catch-per-unit-effort (CPUE) at two depths (10 and 15 m) in the Indiana waters of Lake Michigan during June, July, and August from 1989 to 2006. I evaluated the abiotic factors of water temperature, water clarity, wave height, and wind direction to determine whether they influence the differences in yellow perch CPUE. This study suggests that yellow perch in southern Lake Michigan may select habitat based on water temperature during the summer, moving in response to thermocline changes. We also evaluated mortality rates for two distinct periods (1984-1994 and 2000-2007) in order to identify the response of the population to changes in exploitation. Yellow perch during 1984-1994 (high exploitation) and 2000-2007 (low exploitation) displayed an increase in mortality for fish of harvestable size. In addition, during 2000-2007 (low exploitation) we identified that female yellow perch reached exploitable size earlier in life than males. / Department of Biology

A computer simulation model was developed to examine the effects of various levels of alewife densities, harvest, and bycatch rates on yellow perch Perca flavescens relative densities in Indiana waters of Lake Michigan. The model utilized STELLA® Research software to develop the age-structured population model to include measured or predicted biological characteristics of density-dependent growth, recruitment, and mortality.The model was validated by simulating historically documented yellow perch catch per unit effort (CPUE) from 1984 - 1998. A strong linear relationship (R2= 0.70) between the model predicted CPUE values and the actual CPUE values was found. Twenty year model projections were performed using 1998 yellow perch trawl CPUE as starting values. Alewife abundance was established as either constantly high, constantly low, or allowed to fluctuate randomly and forecasts made used the average of 100 runs. Harvest was imposed on the yellow perch population at 20, 40, and 60% rate levels for fish >_ 200 mm coupled with bycatch at20, 40 and 60% rate levels for fish ranging from 165 - 200 mm.Alewife abundance was the major factor determining the relative abundance of the yellow perch population. On average, constantly high alewife abundance with no harvest or bycatch resulted in projected continuing suppression of yellow perch abundance from 1998 levels. The model predicted the population to rebound using constant low and random alewife abundance with no harvest or bycatch to approximately 1,100 fish/h and 700 fish/h, respectively.The model revealed harvest to have a generally negative impact on the yellow perch population. Increasing harvest and bycatch rate levels resulted in the suppression of projected increases in yellow perch relative abundance. Additionally, increasing harvest and bycatch rates resulted in greater predicted declines in yellow perch abundance. / Department of Biology

Metal-contamination of lakes simplifies food webs and reduces the efficiency of energy transfer to top trophic organisms, such as yellow perch (Perca flavescens). Benthic invertebrate community composition and yellow perch diet, growth and activity levels from lakes along a metal-contamination gradient were used to assess the importance of a naturally diverse prey base for maintaining energy transfer to growing fish, and how this is disrupted by metal-contamination. As perch grow larger, they shift their diet to larger prey; otherwise, the activity costs of foraging for many, small prey, instead of a few large prey, become too high and the fish stop growing. Metal contaminated lakes have less diverse zoobenthic communities, particularly the lack of large bodied invertebrate taxa, forcing perch to rely on smaller benthic prey. Perch from metal-contaminated lakes display slow growth and poor condition during benthivory. Estimates of fish activity, using the activity of the glycolytic enzyme Lactate dehydrogenase in perch white muscle tissue as a proxy, suggest that diet shifts to larger prey lower activity costs and may explain how diet shifts maintain growth efficiency as perch grow larger. Perch from metal-contaminated lakes cannot benefit from the energetic advantages of switching to larger prey and thus exhibit poor growth.