Mathematical models describing the components of predator-prey interactions are reviewed and evaluated, and new equations representing selected aspects of the relationship are proposed. A model of prey selection that distinguishes between predator performance and prey vulnerability is devised and shown to lead to conclusions that may be qualitatively different from those produced using previous methods. The feeding habits of staghorn sculpins (Leptocottus armatus), the extent to which they utilize estuarine habitats and their predatory response to chum salmon fry (Oncorhynchus keta) are examined for the purposes of (i) ascertaining the factors shaping sculpin foraging behaviour and (ii) assessing their potential for limiting survival of juvenile salmon. During periods of fry migration, sculpin populations in the estuaries of Big Qualicum River, Salmon Creek and Rosewall Creek (on Vancouver Island, B. C.) were composed predominantly of small juveniles less than 80 mm in length. Tolerance to waters of low salinity, which decreased with sculpin size, was found to be the major variable governing residence in these areas. There was little evidence that the migration of fry was important in attracting sculpins to estuaries. Sculpins preyed on a wide diversity of fauna concentrating on benthic crustaceans, particularly the amphipod Eogammarus confervicolus. Juveniles were active throughout the day, but feeding became progressively more restricted to periods of low light intensity as they grew. The smallest that captured fry were 40-45 mm in length. When chum fry were offered to starved sculpins in field enclosures, the response of those less than 80 mm in length was type 2 (Holling 1965) whereas that of 80-99 mm sculpins was type 3 (sigmoid). Predation on fry was inversely related to light intensity from dawn to dusk, and positively correlated with' light levels during the night. When benthic invertebrates were added, sculpins exhibited an overall preference for fry, which were 4-5 times more profitable in terms of net energy intake. However, preference for fry declined markedly as their abundance relative to other prey increased, indicating a divergence from the usual predictions of optimal foraging theory. Capture rates by sculpins initially naive to salmon fry increased up to three-fold over 3-5 two hour trials. It is suggested that the foraging strategy of sculpins given a choice between salmonid fry and benthic invertebrates represents a balance between the requirement of minimizing risk of starvation and the need to evade their own predators (particularly birds). The schooling behaviour of fry requires that sculpins, even when experienced, must devote considerable attention to the attack process and in so doing, run the risk of being eaten themselves. The combined effects of the schooling response, which reduces the incentive to attack fry, and a profusion of alternative prey, which decreases average hunger levels, were thought to be responsible for low fry consumption in natural situations. In Big Qualicum River, an estimated 240,000 and 40,500 chum were captured by sculpins in 1979 and 1980, respectively. This represents corresponding percentages of only 0.51% and 0.06% of the fry populations, and was calculated to be less than one-tenth of the potential that could have been realized. Predation rates on coho fry (0. kisutch) were considerably greater, despite a smaller population size. Estimated consumption was 817,700 (42.97%) and 144,000 (9.09%) in 1979 and 1980. Systems where sculpins could consume higher proportions of chum fry populations were identified as small, shallow, warm estuaries of intermediate to high salinity with relatively few suitable benthic invertebrates and small numbers of fry. Recommendations for reducing sculpin predation in such cases are proposed. Birds, particularly Bonaparte's gulls (Larus Philadelphia), were found to be even more avid predators than sculpins on juvenile salmon in Big Qualicum River. In contrast to sculpins, they exhibited pronounced numerical responses to the appearance of fry in the estuary. An estimated 10-25% of the hatchery-reared chinook salmon (O. tshawytscha) and 2-4% of the coho were removed by birds in the years 1979-81. / Science, Faculty of / Zoology, Department of / Graduate

Niche segregation among 4 species of sculpins (Myoxocephalus quadricornis, M. scorpius, M. scorpioides and Gymnocanthus tricuspis) inhabiting the east coast of James bay was studied along estuarine and depth gradients at different times of year between 1987 and 1990. A high degree of habitat overlap and absence of feeding segregation among sculpins was observed. M. quadricornis and M. scorpius dominated catch in the estuary and in the coastal zone, respectively. M. scorpioides and G. tricuspis were less abundant and generally avoided the estuary. G. tricuspis was the only cottid which seemed to migrate. Significant differences in the diets were observed at different sites, seasons and years, but not along depth gradients (2 a 20 m). The distribution and abundance of sculpins appeared to be regulated by physical (salinity and temperature) and biological (competition) factors.

No description available.

Thesis (M.S.)--Georgia Southern University, 2007. / "A thesis submitted to the Graduate Faculty of Georgia Southern University in partial fulfillment of the requirements for the degree Master of Science." In Biology, under the direction of James B. Claiborne. ETD. Electronic version approved: December 2007. Includes bibliographical references (p. 77-85)

Thesis (Ph. D.)--University of Washington, 1993. / Vita. Includes bibliographical references (leaves [145]-169).

The predatory functional response is one of the important components of the interaction between predator and prey populations. This response has not been measured for fish predators and fish prey, in spite of the demonstrated importance of predation in regulating numbers in populations such as the juvenile salmon system used in this thesis. Laboratory exeriments were conducted to determine the form of the functional response of the prickly sculpin (Cottus asper), a common freshwater predator, to density of sockeye salmon fry, Oncorhynchus nerka. An alternative prey, chum salmon eggs (Oncorhynchus keta), were presented to the predator with the salmon fry, in order to facilitate switching at low fry densities and possibly lead to a sigmoid (type III) response. Initial experiments showed that sculpin feeding rate did not substantially differ from day to night; that in the absence of food, hunger increased to a maximum after about seven days' starvation; and that a density of 400 chum salmon eggs in a 2000 1 tank produced maximum consumption level by sculpins of 160 mm total length. The functional response experiments did not indicate a sigmoid rise in consumption over low fry densities. However, the initial decelerated rise in consumption was followed by an anomalous drop in response and a subsequent rise in response. It is suggested that this may result from the summation of separate responses through different sensory modalities, or from interference with predation by fry at intermediate densities. This shape of functional response may imply a stable local equilibrium at intermediate densities of salmon. Sculpins probably have a significant impact on fry numbers only at very localized points in space and time, such as at the outlets of tidal creeks on a falling tide. / Science, Faculty of / Zoology, Department of / Graduate

Etheostoma spectabile, E. punctulatum, and Cottus carolinae were sampled Mar., 1983, - Feb., 1984, in Flint Creek, Oklahoma. Immature E. spectabile ate primarily microcrustaceans, while mature fishes relied more on mayflies and amphipods. Juvenile E. punctulatum fed upon mayflies, amphipods, and Asellus. Mature E. punctulatum ate primarily mayflies, and other relatively larger prey. Cottus carolinae consumed chironomids almost exclusively in Jan. - Feb., 1984, while mayflies were predominant the remainder of the year. No significant habitat partitioning between the two darters, and seasonal habitat segregation between C. carolinae and the two darters was found. Dietary overlap between the darters was significantly correlated (p<0.0005) to differences in x prey sizes.

In the Pacific Northwest ecoregion of North America, sculpins represent a major constituent of freshwater assemblages in coastal rivers. Based on their prevalence and abundance, sculpins are likely important ecologically, yet little is known of their interactions with co-occurring species, such as widely studied salmon and trout (salmonines). In this study, I evaluated inter- and intraspecific interactions involving cottids (Cottus sp.) and coastal cutthroat trout (Oncorhynchus clarkii clarkii). I used a response surface experimental design to independently evaluate effects of cutthroat trout and sculpin biomass on growth and behavior. There was evidence of both intra- and interspecific interactions between cutthroat trout and sculpins, but the interactions were asymmetrical with biomass of cutthroat trout driving both intra- and interspecific interactions, whereas sculpins had little influence overall. Cutthroat trout biomass was positively related to conspecific aggressive interactions and negatively related to growth. Sculpin exhibited increased use of cover during the day in response to greater biomass of cutthroat trout, but not sculpin biomass. Nocturnal use of cover by sculpins was unaffected by biomass of either species. This experiment provides insights into the species interactions and the mechanisms that may allow sculpins and salmonines to coexist in nature. As cutthroat trout appear to be superior competitors, coexistence between sculpins and cutthroat trout may depend on some form of refuge, either in the form of in-stream cover or crypsis coupled with diel resource segregation. Cutthroat trout are usually active during the day, indicating that nocturnal foraging by sculpins may in part represent a behavior that minimizes interspecific competition with cutthroat trout. / Graduation date: 2012