Marine Wildlife - Assignment Example

The impact marine preys like fur seals have on their target prey and more especially their resultant interaction with other fisheries has been a subject of continuous study and research interest. The wide array of species and species groups within the marine ecosystem has further expounded this area of research (Wilke & Kenyon, 1954). Various researches have calculated the overall prey requirements of predators including the seabirds, seals as well as whales and such studies avail regional food assessment necessary for maintenance of the respective species population (Perez & Mooney, 1984).

In a world where many animals are faced with the possibility of extinction, such research are crucial and can go a long way in helping preserve the threatened population species. The studies have also facilitated and engaged in examination of food web interactions strengths. Additionally, such studies help in understanding the biogeochemical carbon cycling processes (Perez & Bigg, 1981; Townsend, 1899). According to Kajimura (1980, P. 46) fur seals are most commonly found in the areas lying within 74 to 130 km off the land and are frequently in large numbers along the continental shelf as well as slope in areas where pelagic schooling fishes and also squids are generally found in abundance.

The study also reported that the fur seals and most regularly found in waters whose temperatures range from 8°C to 14°C. At sea, the fur seals feed on a range of fish species. The relative proportion of individual prey species included in the fur seals' diet often varies by months (Kajimura 1982; Perez and Bigg 1984). This is as a result of the apparent changes in their scavenging locations, and also the seasonal movements, prey abundance, as well as availability (Lander & Kajimura, 1982). Generally, the fur seals' vary their diets during winter and spring to correspond to the prevailing conditions.

Previous researches estimate that the fur seals often consume preys whose respective lengths are 10 to 30 cm, although there are instances where much longer preys are consumed although such must be broken down before consumption (Townsend, 1899, p. 241). This study investigates the average length as well as biomass content of some of the species most fed on by the fur seals. Methods The first step involves measurement of otoliths and beaks of the seals. This is based on the fact that the otoliths are susceptible to degradation and size reduction as they move via the seal’s digestive tract as a result of prey size underestimation.

As a result, only the otoliths that reveal little erosion evidence are used to obtain the estimates of fish sizes. Each otolith is rated on scale of 1-5 as per their erosion levels whereby 1 is considered identifiable although substantially eroded while 5 is considered primeval. As an inclusion criterion, only otoliths whose ratings lie above 3 will be measured. Measurement of the otolith leg length is done between its anterior and posterior margins. The measurement is done in mmm with the help of a dissecting microscope and making use of eye-piece graticules.

In order to avoid obtaining of size estimates from the same fish, the measurements taken are only for the otoliths of the sides that possess the highest number of intact otoliths of each sample specie. Biasing the cephalopods estimate of sizes is also a key concern to this research. To avoid it, only the cephalopod beaks that are unbroken will be